aluminium voor constructeurs
DESCRIPTION
design rules for aluminium profilesTRANSCRIPT
2. Aluminium – the properties
After iron, aluminium is now the second most widely used metal in the world. This is because aluminium has a unique combination of attractive properties. Low weight, high strength, superior malleability, easy machining, excellent corrosion resistance and good thermal and electrical conductivity are amongst aluminium’s most important properties.Aluminium is also very easy to recycle.
Weight
With a density of 2.7 g/cm3, aluminium is approximately one third as dense as steel.
Strength
Aluminium alloys commonly have tensile strengths of between 70 and 700 MPa. The range for alloys used in extrusion is 150 – 300 MPa.Unlike most steel grades, aluminium does not become brittle at low temperatures. Instead, its strength increases. At high temperatures, aluminium’s strength decreases. At temperatures continuously above 100°C, strength is affected to the extent that the weakening must be taken into account.
Linear expansion
Compared with other metals, aluminium has a relatively large coeffi cient of linear expansion. This has to be taken into account in some designs.
Malleability
Aluminium’s superior malleability is essential for extrusion. With the metal either hot or cold, this property is also exploited in the rolling of strips and foils, as well as in bending and other forming operations.
Machining
Aluminium is easily worked using most machining methods – milling, drilling, cutting, punching, bending, etc. Furthermore, the energy input during machining is low.
Jointing
Features facilitating easy jointing are often incorporated into profi le design. Fusion welding, Friction Stir Welding, bonding and taping are also used for jointing.
Aluminium combines low density and high strength. These properties are here being used in the decking of a bridge.
These heat sinks exploit aluminium’s high thermal conductivity.
Aluminium has superior malleability.
Conductivity
Aluminium is an excellent conductor of heat and electricity. An aluminium conductor weighs approximately half as much as a copper conductor having the same conductivity.
Reflectivity
Aluminium is a good reflector of both visible light and radiated heat.
Screening . EMC
Tight aluminium boxes can effectively exclude or screen off electromagnetic radiation. The better the conductivity of a material, the better the shielding qualities.
Corrosion resistance
Aluminium reacts with the oxygen in the air to form an extremely thin layer of oxide. Though it is only some hundredths of a (my)m thick (1 (my)m is one thousandth of a millimetre), this layer is dense and provides excellent corrosion protection. The layer is self-repairing if damaged.
Anodising increases the thickness of the oxide layer and thus improves the strength of the natural corrosion protection. Where aluminium is used outdoors, thicknesses of between 15 and 25 ¥ìm (depending on wear and risk of corrosion) are common.
Aluminium is extremely durable in neutral and slightly acid environments. In environments characterised by high acidity or high basicity, corrosion is rapid.
Further details are given in chapter 16, "Corrosion".
Non-magnetic material
Aluminium is a non-magnetic (actually paramagnetic) material. To avoid interference of magnetic fields aluminium is often used in magnet X-ray devices.
Zero toxicity
After oxygen and silicon, aluminium is the most common element in the Earth¡¯s crust. Aluminium compounds also occur naturally in our food. For further details, see chapter 4, "Environmental impact".
Physical properties of some of the most commonly used metals1) and plastics
Al Fe Cu Zn Nylon® Delrin®
(Polyamide 6-6) (Polyacetal)
Density, g/cm3 2.7 7.9 8.9 7.1 1.1 1.4
Melting point, °C 658 1540 1083 419 255 175
Thermal capacity, J/kg, °C 900 450 390 390 1680 1470
Thermal conductivity, W/m,°C 230 75 390 110 0.23 0.23
Coeff. of linear expansion, x 10 -6 /°C 24 12 16 26 70-100 80-90
El. conductivity, % I.A.C.S. 2) 60 16 100 30 - -
El. resistance, x 10 -9 Ωm 29 105 17 58 - -
Modulus of elasticity, GPa 70 220 120 93 3 3
Aluminium is easy to work using most machining methods.
Aluminium has excellent resistance in neutral and slightly acid environments.
Weight and strength – aluminium is approximately one third as dense as steel. Aluminium alloys have tensile strengths of between 70 and 700 MPa.
3. From bauxite to recycled metal
There is plenty of raw material for the production of aluminium. In a variety of forms, aluminium compounds make up a full 8% of the Earth's crust.
Bauxite
Bauxite is the main starting point in the production of aluminium. It has been estimated that, given the present rate of aluminium production, there is enough bauxite to last another 200 to 400 years. This assumes no increase in the use of recycled aluminium and no further discoveries of bauxite. Bauxite forms when certain aluminium bearing rocks decompose. Its main constituents are aluminium oxides, iron and silicon. The largest and most lucrative bauxite deposits are located around the Equator. Major producers include Australia, Brazil, Jamaica and Surinam.
Alumina (Al2 O3 )
Normally in close proximity to the mine, bauxite is refi ned into alumina. The next stage, production of aluminium by molten electrolysis of the alumina, is concentrated in countries with good supplies of electricity. The production of 1 kg of aluminium requires around 2 kg of alumina. The production of 2 kg of alumina requires about 4 kg of bauxite.
The metal
Due to aluminium's chemistry, relatively large amounts of energy (primarily electricity) are required to reduce alumina to aluminium. Around 47 MJ (approx. 13 kWh) goes into the molten electrolysis of 1 kg of the metal. However, this investment gives excellent dividends. The energy expended in aluminium production is often recouped several times over. By reducing the weight of vehicles, the use of aluminium reduces fuel consumption (see also chapter 4). Similarly, energy losses in aluminium power lines are comparatively small.
Recycling
Scrap aluminium is a valuable resource that is set to become even more important. In principle, all scrapped aluminium can be recycled into a new generation of products.With appropriate sorting, scrap aluminium can advantageously be recycled to produce the same sorts of products over and over again. Furthermore, recycling requires only 5% of the original energy input.
In today's environmental-conscious society, the recycling of used aluminium products is becoming ever more important and ever more common.
The aluminium cycle
So easy to recycle: Aluminium is th eperfect "eco-metal". Very little aluminium is lost in the remelting process. Increased recovery, dismantling and sorting of spent products has led to even greater recycling of aluminium.
4. Environmental impact
All industrial activity consumes natural resources and has an impact on the environment. The aluminium industry is no exception to this. However, using aluminium in preference to other products often has a positive impact.
Thus, to gain a true assessment of an aluminium product from the environmental point of view, a life cycle analysis is essential. Several examples are given later in this chapter.
Absolute recycling
Absolute recycling - repeatable recycling with maintained quality and high yield. Aluminium collected for recycling enters an almost never-ending “eco-circle”. This is because very little metal is lost in remelting. On average, losses through oxidation during remelting amount to a few per cent only. Furthermore, the quality of the remelted material is so high that it can be used for the same product over and over again. Hence our use of the term “absolute recycling” – repeatability with maintained quality and high yield.
Extrusion
As mentioned in chapter 3, producing aluminium from bauxite requires comparatively large amounts of energy. The manufacture of aluminium profi les, on the other hand, requires relatively little energy. At the web site of EAA (the European Aluminium Association) you can obtain further information on profi le manufacturing and a number of other subjects connected with the use of aluminium and profi les. The address: www.aluminium.org
The remelting works in Sjunnen, Sweden
4.1 The environmental impact of extrusion, surface treatmentand machining
Cutting to length is the main source of noise in factories producing aluminium profiles. This noise has been reduced by screening. Changing the lubricants used on billet end faces has not only improved the quality of air in workshops, but also given cleaner profi les that require less post-extrusion cleaning.
A further measure to reduce potentially negative environmental impact is the increased use of gas nitriding for the hardening of dies. Dies are now stored with residue aluminium on them, thus minimising the need for cleaning. Similarly, the mineral oil based cooling and cutting fl uids previously used in the machining of semi-fi nished goods have been replaced by water-based products. This has reduced the need to use organic degreasing agents.
Sapa no longer uses trichloroethylene for degreasing. The alkaline water solutions used today produce a semi-stable emulsion containing droplets of grease and oil. Drawing off this emulsion extends the life of the degreasing bath and gives a product that can be recycled as, for example, a lubricant for machining operations.
The etching process in anodising has been improved by the use of “neverdump” baths. These consume minimum quantities of chemicals and produce less waste. Used etching baths are neutralised. This precipitates the aluminium content as a hydroxide, which is then refi ned into chloride. To an increasing extent, the chloride is being used as a fl ocking agent in water treatment plants.
Copper and cobalt salts were previously used for dyeing profiles during anodising. Again to lessen any potentially negative impact on the environment, these have been replaced by tin salts.
Die cleaning - a closed process producing no waste water.
4.2 Product examples
4.2.1 Cars
More and more car manufacturers are using aluminium in preference to steel. It is perfectly possible to replace 182 kg of steel components with 82 kg of aluminium – 100 kg less strain on the engine.
If no recycled metals are used, aluminium components require 2,740 MJ more energy to produce than the steel parts they replace. However, with a typical lifetime of use, the lighter car will require 640 litres less fuel. This is the equivalent of 23,000 MJ.
Furthermore, when the content of recycled metal reaches 90%, an aluminium component actually consumes less production energy than its steel counterpart.
Environmental benefits
Assuming no recycled steel or aluminium is used: – During the car’s lifetime, the extra energy used in producing aluminium is recouped a good eight times over. – Production of the aluminium components emits 100 kg more CO than is the case for steel. This higher impact on the environment is made good many times over during the car’s lifetime – the reduced petrol consumption reduces CO emissions by 1,500 kg.
Total life cycle analysis
The production of a steel bonnet presents a 60% greater total load on the environmetn than the production of an aluminium bonnet. Total life cycle analyses underline the energy and environmental benefits resulting from the use of aluminium. Car manufacturers make extensive use of such analyses. In this sector of industry, the Swedish EPS method1) is the most widely used analytical tool. An example is given below.
A steel car bonnet is replaced by an aluminium one. This reduces the weight from 18 to 10 kg. Applying the EPS method, the total load on the environment presented by the steel bonnet is around 60% greater than the load presented by the aluminium bonnet.
1) EPS = Environmental Priority Strategies in product design is a practical method for calculating “environmental load”. The method takes into account what happens throughout the manufacture, use and eventual disposal of a product. Calculations are based on the following formula:
Environmental load index x Quantity = ELU (Environmental Load Unit)
An environmental load index is a numerical value corresponding to the load on the environment considered to be presented by a defi ned quantity/amount of a substance, product or activity.
Space frame
One of the modern technologies used in the manufacture of car bodies is the Space Frame, a skeleton of aluminium profi les. Covering the frame with aluminium sheets gives weight reductions of up to 200 kg per car. This is double the saving cited on the previous page.
As in other applications, replacing steel with aluminium reduces weight. Here, this leads to reductions in petrol consumption and emissions. Other plus points are improved crash-safety, reduced risk of corrosion and decreased environmental load.
4.2.2 Underground railway carriages
Nearly all modern underground railways use carriages with bodies constructed of longitudinally welded aluminium profiles.
In Japan, analyses of real energy consumption have been carried out on the Chiyoda line. The analyses compared the line’s steel-carriaged trains with those having aluminium-bodied carriages. In the latter, 9,450 kg of steel is replaced by 4,000 kg of aluminium.
Energy consumption in the production process 1) Aluminium 4,000 x 37.2 2) = 148,800 kWh 3)
Steel 9,450 x 9.5 2) = 89,775 kWh
Difference 59,025 kWh
Energy consumption during two years of operation Steel carriages
561,200 kWh
Aluminiumcarriages 489,900 kWh
Difference 71,300 kWh1) No recycledmetal used
2) Consumption as estimated by Sapa Technology.3) 1 kWh = 3.6 MJ.
Energy savings in less than two years.
Assuming no use of recycled aluminium or steel, the Chiyoda example shows that, in less than two years, aluminium carriages represent an "energy saving". Similar rela-life analyses in Atlanta (USA) and Germany have given figures of 3 and 1.6 years respectively as the times in which the extra energy used in production is recouped.
When the use of recycled metals is taken into consideration, aluminium carriages are clearly more "energy-efficient" even than the recycling of steel.
4.2.3 Window frames
In Austria, there has been a study in 1991 of the environmental aspects of the use of various materials (aluminium, PVC coated steel, wood and aluminium clad wood) in window frames. The results obtained using the EPS method are summarised below.
– Calculated over the entire life cycle of the product, aluminium clad wooden frames present the lowest load on the environment. – In the production phase, wooden frames present unquestionably the lowest environmental load. However, this is more than nullifi ed by the need for regular maintenance/replacement. – Aluminium frames are far superior to plastic coated steel frames. – Frames of plastic coated steel present the largest load on the environment. – The possibility of recycling aluminium with very little energy consumption is a significant factor in aluminium’s good performance.
Conclusion
The use of aluminium in products such as window frames has clearly demonstrable benefits for the environment.
4.3 Health
All normal forming and cutting of aluminium has no consequences for human health. However, if worksite ventilation is inadequate, lengthy periods of gas welding can have an effect on the respiratory organs. Before undertaking gas welding, current recommendations and regulations should be studied. Local health and safety bodies are usually able to provide help here.
Friction Stir Welding (see pages 68 – 73 of this manual) does not use filler metals or shielding gases. This avoids the problem outlined above.
Aluminium is non-toxic
Aluminium in the diet: 97% from foodstuffs , 3% from foodpreparation. All life on Earth is adapted to its presence – aluminium has always been a natural part of the environment. The soil contains, on average, 7% aluminium (by weight). The use of aluminium products, whether untreated or anodised, presents no health hazards. As an illustration of this, aluminium has been used for decades in kitchen pots and pans. At one time, aluminium was cited as a possible cause of Alzheimer’s disease. However, the leading medical scientists of today consider that there is no such link.
It is also worth mentioning that our normal diet includes aluminium. Food and food additives account for roughly 97% of our daily intake of approximately 12 mg. The remaining 3% comes from aluminium products such as kitchen foil and cooking vessels.
5. Aluminium profiles- the applications
The purpose of this manual is to give its readers an insight into optimum design using aluminium profi les. Further details and concrete advice are readily available from Sapa.
Whatever the field
Whatever the field of operation, it seems that aluminium profiles have something to offer. The transport industry makes extensive use of aluminium profi les in lorries, buses, cars, trains, ships, etc. With increasing demand for lighter vehicles that consume less fuel and place less strain on the environment, the use of profiles is constantly rising. The benefits are clear.
Other sectors of industry have also seen the advantages. Profi les are being used in all types of design solutions. Examples include machine parts, a wide range of products for everyday home and offi ce use and equipment used in free time activities. In the electronics industry, aluminium profi les are used in heat sinks, casings, front plates and so on. The building industry uses aluminium profi les in, amongst other things, doors, windows, fascias and glass roofs. The list of sectors and applications is long.
In all sectors, the demand for recyclability is growing ever stronger. No structural material can be more profi tably recycled than aluminium. This factor is sure to acquire increasing significance.
Aluminium profiles will become more common in all industries. In some respects, the use of aluminium and extrusion has really only just begun.
The advantages of aluminium and extrusion
Profile use is increasing in line with the demand for reduced energy consumption and minimum stress on the environment. More and more constructors and designers are realising the advantages of extrusion – the freedom it gives them to create precisely the shape that solves the problem, low tooling costs, easy machining, purpose-tailored surface treatment, etc. Furthermore, extrusion technology continues to develop and new production methods such as Friction Stir Welding and hydroforming are adding still further to the possibilities opened up by aluminium profiles.
On top of all this, aluminium has a host of unique structural properties.
Simply put, aluminium profiles facilitate the creation of effi cient designs at competitive prices – exactly the right conditions for new products on new markets.
Young metal, young industry
The electrolysis of alumina to produce aluminium was first achieved in 1886. This was the major breakthrough that eventually led to the commercial production of aluminium products.
By the turn of the century, world production of primary aluminium had reached around 5,700 tons. In 2001, highlighting the importance of aluminium in modern industrial production, the fi gure was approximately 24.5 million tons. To give some idea of scale, 24.5 million tons is the combined weight of something over 18 million Volvo S40s.
In Sweden, the fi rst attempts to extrude aluminium were made in the middle of the 1920’s. Still in Sweden, it was in 1937 that Metallverken, a company in Finspång, started regular production of profi les. At the same time, Saab began production of aeroplanes in Linköping. Over the next few years, and reaching a peak at the end of the Second World War, Saab made extensive use of aluminium. Since the late 1940’s, the consumption of aluminium and aluminium profiles has risen steadily as shown in the graph below.
6. Extrusion principles
Extrusion starts with aluminium alloy logs. These are cut into billets, which then go into an induction furnace for heating to the right extrusion temperature of 450 – 500°C. Next, applying considerable pressure, each heated billet is forced through a die, the profile emerging rather like toothpaste from a tube.
The profile emerges at a speed of 5 – 50 metres per minute and length is normally between 25 and 45 metres. Cooling in air or water commences immediately the profi le leaves the die.
After cooling, the profile is stretched. This is both to relieve any stress and to give the profile the desired straightness. At the same time, all functionally important dimensions and surface quality are checked. The profi le is then cut to a suitable length or to the exact length requested by the customer.
The final strength of the material is controlled through natural or artificial ageing.
Dies
Dies are made of tool steel (normally SIS 2242). The die aperture, which corresponds to the desired cross section of the profi le, is produced by spark erosion. Sapa both makes its own dies and buys in from independent manufacturers.
Billets are heated to the right temperature in an induction furnace.
Two main classes
There are two main classes of profile – solid and hollow: Solid profiles are produced using a flat, disc-shaped die. Hollow profiles are produced using a two-part die.
In hollow dies, the mandrel (the part that shapes the cavity in the profi le), is supported on a bridge. During extrusion, the metal separates around the bridge. The other part of the die shapes the outer contour of the profile.
Large and medium-sized profi les are pressed through a die with only one aperture. Smaller profi les can be advantageously pressed through multi-apertured dies – there may be as many as 16 apertures.
Die lifetime depends on the shape and desired surface quality of the profile. The cost of replacement dies is covered in the price of the profile.
Dies for solid profiles . A hollow die.
A profile emerging onto the cooling table. Stretching relieves profiles of any stress
or twisting.
7. Choosing the right alloy
The 6000 series is by far the most widely used in extrusion. Pure aluminium is relatively soft. To overcome this, the metal can be alloyed and/or cold worked. Most of the aluminium reaching the marketplace has been alloyed with at least one other element. Sapa uses a long-established international system for identifying aluminium alloys (see the table below). The first digit in the four-digit alloy code identifies the major alloying element. The European standard uses the same codes.
The table below gives the broad outline of the systems.
Alloying element Alloy code Alloy type
None (pure aluminium) 1000 series Not hardenable
Copper 2000 series Hardenable
Manganese 3000 series Not hardenable
Silicon 4000 series Not hardenable
Magnesium 5000 series Not hardenable
Magnesium + silicon 6000 series Hardenable
Zinc 7000 series Hardenable
Other 8000 series
As cold working is the only way to increase the strength of the alloys that cannot be hardened, most of these go for rolling. In extrusion, on the other hand, hardenable alloys are the most commonly used.
The 6000 series, which has silicon and magnesium as the alloying elements, is by far the most widely used in extrusion. In Sapa¡¯s 7021 alloy, zinc and magnesium are responsible for the hardening effect.
Some alloys use manganese, zirconium or chrome to increase toughness. Iron, which is found in all commercial aluminium, can have a negative effect on toughness and fi nish (amongst other things) if present in high quantities.
Heat treatment
Apart from 1050A, all Sapa alloys are hardenable. Their final strength is thus determined by solution heat treatment and ageing (precipitation hardening). Solution heat treatment is normally carried out during extrusion by carefully controlling the temperature of the emerging profile. Precipitation hardening, which takes a few hours, occurs afterwards in special furnaces. In some circumstances, it may be necessary for the customer to carry out heat treatment. Sapa¡¯s recommendations in these cases are given in the table on page 25. Natural ageing is the spontaneous hardening of solution treated aluminium at room temperature (refer to the table on page 25).
Choosing the right alloy
In cases of doubt, contact Sapa for advice. Amongst the factors affecting the choice of the right alloy for an extruded product are:
¨C Strength, finish, suitability for decorative anodising, corrosion resistance, suitability for machining and forming, weldability and production costs.
The at-a-glance table on the next page should only be used as a rough guide. In cases of doubt, contact Sapa for advice and guidance. For example, optimum cost-effi ciency may sometimes be gained by choosing a comparatively lower strength alloy with higher extrudability.
Logs being prepared for extrusion.
At-a-glance alloy selection Relative grading: 3 = top mark
Property
Commonconstruction alloys
Special alloys for
High-strenghtconstructions
Electricalconductors
Brightanodising
Sapa6060
Sapa6063
Sapa6063A
Sapa6005
Sapa6005A
Sapa6082
Sapa7021
Sapa1050A
Sapa6101
Sapa6463
Tensile Strenght
1 1 1 2 2 2 3 0 1 1
Impact strenght
3 3 3 1 2 2 2 3 3 3
Surface finish 3 3 3 2 2 2 1 3 3 3
Suitable fordecorative anodising
3 3 3 2 2 1 1 2 3 3
Corrosion resistance
3 3 3 2 2 2 1 3 3 3
Machinability:
cutting 1 2 2 2 2 2 3 0 2 2
forming 3 3 2 2 2 2 2 3 3 3
Weldability 3 3 3 3 3 3 3 3 3 3
Price 3 3 3 2 2 2 2 3 3 3
Suitable allyoys for anodising
Refer to 15.3, "Anodising".
Sapa6060
Sapa6063
Sapa6063A
Sapa6005
Sapa6005A
Sapa6082
Sapa7021
Sapa1050A
Sapa6101
Sapa6463
Soft annealing: Rapid full through heating, followed by approx. 30 min. at stated temper-ature. Cooling should be slow and, down to 250¡ãC, preferably in afurnace. After that, free cooling.
380-420
380-420
380-420
380-420
380-420
380-420
400-420a)
380-450b)
380-420
(380-420)c)
Solution heat treatment: Rapid full through heating, follo-wed by 15-30 min. (depending on wall thinckness) at stated temperature. Forced air-cooling (fan) if wall
510¡À10
510¡À10
530¡À10
530¡À10
530¡À10
535¡À10
460¡À10
--
530¡À10
(510¡À10)
d) e) c)
thickness under 6 mm. Water cooling where
Natural ageing: Occurs spontaneously at room temperature. Temper T4 achieved in stated number of days.
2 2 2 2 2 2 30 - 2 2
Artificial ageing: Heat to the stated age hardening temperature (¡ãC). Hold there for approx. 8 hours.After that, free cooling
175¡À5
175¡À5
175¡À5
175¡À5
175¡À5
175¡À5
f) g) - 175¡À5
175¡À5
a) Cool to 220-230 ¡ãC in a furnace. Hold at this temperature for 4-6 hours. After that, free cooling.
b) Coarse grain structure may form (a coarse-grained structure decreases strenght and gives a poorer finish after anodising).
c) Sapa 6463 should not be soft annealed and subjected to solution heat treatment. This lessens the material's suitability for bright anodising.
d) To be cooled quickly (usually in water). When cooling, the material must be moved quickly from furnace to water (approx. 10 sec.).
e) The cooling rate in the critical range, 400-200¡ãC, should be at least 1¡ãC per sec. It must not exceed 5¡ãC per sec. Rates above this may cause stress corrosion.
f) Artificial ageing can be 100¡ãC (¡À5¡ãC) for 4 hours + 150¡ãC (¡À5¡ãC) for 8 hours.
g) For maximum strenght, a break of at least 72 hours between solution heat treatment and artificial ageing is required.
Heat treatment alters alloy properties. The picture above shows temperature controlduring solution heat treatment.
Common Construction Alloysalloy data as per EN-755-2
Alloy designations
Sapa 6060 Sapa 6063 Sapa 6063A Sapa 6005 Sapa 6005A
European standards:numerical notationchemical notation 1)
EN-AW-6060
AlMgSi
EN-AW-6063AlMg0.7Si
EN-AW-6063A
AlMg0.7Si(A)
EN-AW-6005AlSiMg
EN-AW-6005A
AlSiMg(A)
USA: Aluminium Association
AA 6060 AA 6063 AA 6063A AA 6005 AA 6005A
Swedish standards:
SS-EN-AW-6060
SS-EN-AW-6063
SS-EN-AW-6063A
SS-EN-AW-6005
SS-EN-AW-6005A
Alloy dataTemper T42) T6 T42) T6 T66
F25 T42) T6 T6 T6 T6 T6
Solidprofil
e
Hollow
profile
Solidprofil
e
Hollow
profile
Tensile strenght 3)
t = wall thickness, mm
Yield strenght Rp0.2 ,MPa, min.
t ¡Ü 2560
t ¡Ü 3
150
t ¡Ü 2565
t ¡Ü 10170
t ¡Ü 10200
t ¡Ü 2590
t ¡Ü 10190
t ¡Ü 5225
t ¡Ü 5215
t ¡Ü 5225
t ¡Ü 5215
3 < t¡Ü 25140
10 < t
¡Ü 25160
10 < t
¡Ü 25180
10 < t¡Ü 25180
5 < t¡Ü 10215
5 < t¡Ü 15200
5 < t¡Ü 10215
5 < t¡Ü 15200
10 < t¡Ü 25200
10 < t¡Ü 25200
Ultimate tensile strenght Rm ,MPa, min.
t ¡Ü 25120
t ¡Ü 3
190
t ¡Ü 25130
t ¡Ü 10215
t ¡Ü 10245
t ¡Ü 25150
t ¡Ü 10230
t ¡Ü 5270
t ¡Ü 5255
t ¡Ü 5270
t ¡Ü 5255
3 < t¡Ü 25170
10 < t
¡Ü 25195
10 < t
¡Ü 25225
10 < t¡Ü 25220
5 < t¡Ü 10260
5 < t¡Ü 15250
5 < t¡Ü 10260
5 < t¡Ü 15250
10 < t¡Ü 25250
10 < t¡Ü 25250
Elongation A, % min.
t ¡Ü 2516
t ¡Ü 258
t ¡Ü 2514
t ¡Ü 258
t ¡Ü 258
t ¡Ü 2512
t ¡Ü 107
t ¡Ü 258
t ¡Ü 158
t ¡Ü 258
t ¡Ü 158
10 < t¡Ü 25
5
Hardness (for guidence)
Webster B, approx.
5 10 5 12 13 7 13 14 14 14 14
Vickers, approx.
40 60 45 70 80 50 80 85 85 85 85
Thermal conductivity
at 20¡ã, W/m,¡ãC
190 190 190 190 190 190 190 170 170 170 170
Density, kg/dm3
2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7
Alloys suitable for decorative anodising
All applicationsrequring thehighest qualityfinish andwhere strenghtis no thecrucial factor,e.g. pictureframes,exclusivefurniture.
All applications- furniture,decorativetrims, etc. This alloyhas good propertiesin most areas.
Certainload-bearingstructures,e.g. sailing-boat masts,ladders, etc.
Where highstrengt isessential,e.g. balconies,doorways,ladders, sailing-boat masts.
High-strenghtbuilding andstructuralcomponents,e.g. profilesfor lorry bedsand trains.Can beanodised.
Temper codes:
F As extruded
T4 Hardened and naturally aged
O Annealed
T6 Hardened and artificially aged
T66 Hardened and artificially aged
1) The designations must start with EN-AW, e.g. EN-AW-AlMgSi.
2) Stated tensile strenght is attained with a minimum of 72 hours natural ageing after extrusion.
3) Stated tensile strenght applies to sections with a wall thickness of up to 25 mm. For further information, contact Sapa.
4) Sapa 1050A is a non-hardenable alloy - its mechanical properties cannot be improved by heat treatment.
Special AlloysAlloy data as per EN-755-2
Alloy designations
Sapa 7021 Sapa 1050A Sapa 6101 Sapa 6463 Sapa 6082
European standards:numerical notation
EN-AW-7021AlZn5.5Mg1.
5
EN-AW-1050A
Al99.5(A)
EN-AW-6101
AlMgSi
EN-AW-6463AlMg0.7Si(B
)
EN-AW-6082AlSi1MgMn
chemical notation 1)
USA: Aluminium Association
AA 1050A AA 6101 AA 6463 AA 6082
Swedish standards:
SS-EN-AW-7021
SS-EN-AW-
1050A
SS-EN-AW-6101
SS-EN-AW-6463
SS-EN-AW-6082
Alloy dataTemper T6 F4) T6 T4 T6 T42) T6 T6
Solidprofile
Hollowprofile
Tensile strenght 3) t = wall thickness, mm
Yield strenght Rp0.2
,MPa, min.
310 20t ≤ 50170
t ≤ 5075
t ≤ 50160
t ≤ 25110
t ≤ 5250
t ≤ 5250
t < 5≤ 25260
t < 5≤ 25260
Ultimate tensile strenght Rm ,MPa, min.
350 60 t ≤ 50200
t ≤ 50125
t ≤ 50195
t ≤ 25205
t ≤ 5290
t ≤ 5290
5 < t≤ 25310
5 < t≤ 15310
Elongation A, % min. 10 25
t ≤ 508
t ≤ 5014
t ≤ 5010
t ≤ 2514
t ≤ 58
t ≤ 58
5 < t≤ 2510
5 < t≤ 1510
Hardness (for guidence)
Webster B, approx.
16 10 7 10 11 15 15
Vickers, approx.
110 60 50 60 65 95 95
Thermal conductivit
y
at 20°, W/m,°C
145 235 190 190 190 170 170 170
Density, kg/dm3
2.8 2.7 2.7 2.7 2.7 2.7 2.7 2.7
All alloys:Coefficient of linearexpansion:23 x 10-6 /°CModulus of elasticity:70,000MPaModulus of rigidity:27,000MPaPoisson's ratio: 0.33
When choosingthis high-strenght alloy,Sapa should becontacted forfurther details.Applicationsinclude carbumpers andmotorwaysafety barriers.
Goodconductivity(approx. 60%I.A.C.S. at20°C) and lowmechanicalstrenght.Applications- conductorrails, etc.
Goodconductivity(approx. 55-60%I.A.C.S. at 20°C)and goodmechanicalstrenght.Applications- Tubes fortransformerstations, etc.
Specificallyintended forchemicalbrightanodising,e.g.decorativetrims,reflectors,etc.
High-strenghtbuildingand structuralcomponents,e.g. trailer profilesfor lorries and floorprofiles.unsuitable fordecorativeanodising.
Temper codes:
F As extruded
T4 Hardened and naturally aged
O Annealed
T6 Hardened and artificially aged
T66 Hardened and artificially aged
1) The designations must start with EN-AW, e.g. EN-AW-AlMgSi.
2) Stated tensile strenght is attained with a minimum of 72 hours natural ageing after extrusion.
3) Stated tensile strenght applies to sections with a wall thickness of up to 25 mm. For further information, contact Sapa.
4) Sapa 1050A is a non-hardenable alloy - its mechanical properties cannot be improved by heat treatment.
8. Wide profiles with tight tolerances
The illustration shows max. profile dimensions for the largest Swedish press.The entire cross section of the desired profile must fit within the bold line .
WeightSapa can extrude profiles weighing from as little as 0.1 kg/m to as much as 20 kg/m .
ImportantWe continously develop techniques and processes and invest in new production equipment. It is therefore important to contact Sapa before finally deciding measurements and exact shape of your profile.
9. General design advice
Wall thickness
When deciding how thick the walls of a profi le should be, strength and optimum cost-efficiency are two of the main considerations.
Profiles with a uniform wall thickness are the simplest to produce. However, where necessary, wall thickness within a profile can easily be varied. For example, a profi le’s bending strength can be increased by concentrating weight/thickness away from the centre of gravity.
Cost-efficient production
To optimise cost-efficiency, a profile's design should always be as production-friendly as possible. To achieve this, the profile should: – have a uniform wall thickness – have simple, soft lines and radiused corners – be symmetrical – have a small circumscribing circle – not have deep, narrow channels.
Recommended wall thickness - guidelines
Amongst the factors having an effect on wall thickness are extrusion force and speed, the choice of alloy, the shape of the profi le, desired surface finish and tolerance specifications.
Circumscribing circle, mm
9.1 Uniform wall thickness
It is often acceptable to have a large range of wall thicknesses within a single profile.
However, a profile with uniform wall thickness is easier to extrude .
Here, the profile's internal and external walls have different dimensions.
It is advantage if internal and external walls are of the same thickness. This decreases die stress and improves productivity .
9.1.1 Exceptions
It is of course perfectly acceptable for a profile to have walls of defferent thicknesses. For example, for strength reasons, it may be best to concentrate weight/thickness away from the centre of gravity.
9.2 Soft lines
Extrusion cannot achieve razor-sharp corners.
Corners should be rounded. A radius of 0.5-1 mm is often sufficient.
A design may sometimes demand sharp internal angles, e.g. a profile to enclose a box shape.
This is easily solved by incorporating a hollow moulding .
AS far as possible, sharp tips should be avoided. The tip can easily become wavy and uneven.
Tips should, therefore, also be rounded.
Following extrusion, a profile with large variations in wall thickness cools unevenly. This gives rise to a visible structural unevenness that is particularly marked after anodising.
Always use soft lines!
9.3 Solid profiles if possible
Solid profiles reduce die costs and are often easier to produce .
9.4 Fewer cavities in hollow profiles
This hollow profile is extremely complex to produce.
By replacing the hollow profile on the left with two telescoping profiles, the product is considerably easier to produce .
Is it essential for this profile to have two cavities?
In many cases, reducing the number of cavities in a hollow profile makes it easier to extrude. This increases die stability.
9.5 Profiles with deep channels
For profiles with pockets or channels, there is a basic rule that the width to height ratio should be approximately 1:3 .
By using large radii at the opening of the channel, and a full radius at the bottom, the ratio can be increased to 1:4 .
NB! Where channels width is under 2 mm, or where a profile's design is complex, permissible channel depth must be determined on a case-by-case basis.
A profile can be extruded "open" ...
... and then rolled to its final shape.
It may be possible to increase radii and opening dimensions without compromising functionality.
Here, a holder has to enclose a slide. Redesigning the holder on the left gives a more extrusion-friendly profile and improved functionality.
The solution above gives a narrow, deep channel and an extrusion-friendly profile.
Reduced channel depth using a step. The step is removed during rolling.
9.6 Heat sinks
The use of cooling fins on profiles greatly increases the heat dissipating area. This can be further increased by giving the fins a wavy surface.
Where there is forced air-cooling longitudnally along the profile, it is better leave the fins smooth. This helps to avoid the poroblem of eddy formation
Waviness here increases the area by 10-15 %
An undulation surface increases the heat dissipation area of fins.
This profile exemplifies technical development at Sapa:
A large profile with deep channels - yet tight tolerances are respected and there is a
high quality surface finish.
9.7 Decorate!
Decoration has several advantages:
Design Masking of imperfections Protection against damage during handling and machining
Designfördelar
A decorative pattern can make a plain aluminium surface more attractive. The consistent use of a pattern on all a product's component profiles can help make it uniquely identifiable. There are endless possibilities for creating unique designs.
A joint can be elegantly hidden by making it a part of a fluted design.
Masking of imperfections Protection against damage
Where a profile has, for example, arms and screw ports, there may be process induced shadowing (heat zones) opposite such features.
Using decoration, the heat zones can be completely masked .
Well designed decoration can also protect profiles fromhandling and machining damage
9.1 Uniform wall thickness
It is often acceptable to have a large range of wall thicknesses within a single profile.
However, a profile with uniform wall thickness is easier to extrude .
Here, the profile's internal and external walls have different dimensions.
It is advantage if internal and external walls are of the same thickness. This decreases die stress and improves productivity .
9.1.1 Exceptions
It is of course perfectly acceptable for a profile to have walls of defferent thicknesses. For example, for strength reasons, it may be best to concentrate weight/thickness away from the centre of gravity.
9.2 Soft lines
Extrusion cannot achieve razor-sharp corners.
Corners should be rounded. A radius of 0.5-1 mm is often sufficient.
A design may sometimes demand sharp internal angles, e.g. a profile to enclose a box shape.
This is easily solved by incorporating a hollow moulding .
AS far as possible, sharp tips should be avoided. The tip can easily become wavy and uneven.
Tips should, therefore, also be rounded.
Following extrusion, a profile with large variations in wall thickness cools unevenly. This gives rise to a visible structural unevenness that is particularly marked after anodising.
Always use soft lines!
9.3 Solid profiles if possible
Solid profiles reduce die costs and are often easier to produce .
9.4 Fewer cavities in hollow profiles
This hollow profile is extremely complex to produce.
By replacing the hollow profile on the left with two telescoping profiles, the product is considerably easier to produce .
Is it essential for this profile to have two cavities?
In many cases, reducing the number of cavities in a hollow profile makes it easier to extrude. This increases die stability.
9.5 Profiles with deep channels
For profiles with pockets or channels, there is a basic rule that the width to height ratio should be approximately 1:3 .
By using large radii at the opening of the channel, and a full radius at the bottom, the ratio can be increased to 1:4 .
NB! Where channels width is under 2 mm, or where a profile's design is complex, permissible channel depth must be determined on a case-by-case basis.
A profile can be extruded "open" ...
... and then rolled to its final shape.
It may be possible to increase radii and opening dimensions without compromising functionality.
Here, a holder has to enclose a slide. Redesigning the holder on the left gives a more extrusion-friendly profile and improved functionality.
The solution above gives a narrow, deep channel and an extrusion-friendly profile.
Reduced channel depth using a step. The step is removed during rolling.
9.6 Heat sinks
The use of cooling fins on profiles greatly increases the heat dissipating area. This can be further increased by giving the fins a wavy surface.
Where there is forced air-cooling longitudnally along the profile, it is better leave the fins smooth. This helps to avoid the poroblem of eddy formation
An undulation surface increases the heat dissipation area of fins.
Waviness here increases the area by 10-15 %
This profile exemplifies technical development at Sapa:
A large profile with deep channels - yet tight tolerances are respected and there is a
high quality surface finish.
9.7 Decorate!
Decoration has several advantages:
Design Masking of imperfections Protection against damage during handling and machining
Design advantages
A decorative pattern can make a plain aluminium surface more attractive. The consistent use of a pattern on all a product's component profiles can help make it uniquely identifiable. There are endless possibilities for creating unique designs.
A joint can be elegantly hidden by making it a part of a fluted design.
Masking of imperfections Protection against damage
Where a profile has, for example, arms and screw ports, there may be process induced shadowing (heat zones) opposite such features.
Using decoration, the heat zones can be completely masked .
Well designed decoration can also protect profiles fromhandling and machining damage
10. Jointing
10.1 Screw ports
Skruvfickan kan gängas på vanligt sätt för maskinskruv .
Vanligast är att skruvfickan används direkt för gängpressade skruv . Skruvfickan förses då med knaster som centrerar skruven.
Håldiameter för gängpressade skruv
Skruvnr.
Hål-diam. D
Väggtjocklekt, min 1)
Frigående hål
ST 3,5 (B6)ST 4,2 (B8)ST 4,8 (B10)ST 5,5 (B12)ST 6,3 (B14)
3,1 ± 0,153,8± 0,154,2 ± 0,24,9 ± 0,25,6 ± 0,2
1,51,51,52,02,0
4,25,05,86,67,4
Någon gång vill man skruva genom skruvfickan vinkelrätt mot profilriktningen . Fickan förses då med en anliggningsyta enligt figuren.
Sluten skruvficka : När konstruktionen kräver grövre skruv (exempelvis M8) kan skruvfickan slutas. Hålet dimensioneras för gängning eller för gängpressade metrisk skruv.
Genom att placera skruvfickan i ett hörn reduceras godsökningen . Vid ytterhörn bör man beakta skruvskallens diameter, så att skallen inte går utanför profilens ytterkanter.
10.2 Tracks for nuts or bolt heads
10.3 Snap-fit joints
10.4 Jointing - profile to profile
10.4.1 Longitudinal jointing
10.4.2 Telescoping
10.4.3 Latitudal jointing
[saknar bild 270 graders öppning...]
10.4.5 T-joints
10.4.6 Corner joints
10.5 Jointing with other materials
10.6 Riveting
10.7 End caps
10.8 Adhesive bonding
After steel, aluminium is the metal that is most frequently bonded. Though, for example, far more cars are produced than aeroplanes, the adhesive bonding of aluminium in the aero-industry has attracted the most detailed research.
Aeroplanes have used bonded joints since the mid 40’s. Nowadays, the bonding of aluminium is even used for load-bearing components in aircraft.
Of course, there are many more down-to-earth examples of the use of bonded aluminium joints. Volvo’s roof rack rail is just one of these.
Many different adhesives, pretreatments and bonding methods have been developed. Selecting the right one is not always easy. Nor is it risk-free to simply start bonding without adequate information.
Essential knowledge
The intermolecular forces that determine whether bonding is possible exert their pull over a maximum range of 0.5 nm (one half of a millionth of a millimetre). If the surface is contaminated or is made up of low strength oxides exceeding this critical “thickness”, there will be no attraction between the adhesive and the aluminium profile.
For good and consistent bonds, the joint surface must be known, reproducible and clean.
The adhesive must wet the entire surface that is to be bonded. To do this, it has to have a lower surface tension than the material being bonded. Otherwise, the adhesive will form droplets rather than spread evenly over the surface.
All adhesives wet aluminium. To bond aluminium profiles to another material, the adhesive must be able to wet this material too. If the other material is a plastic, it can sometimes be diffi cult to fi nd an adhesive with a lower surface tension.
[bild 58.1] Traditional tongue and groove. [bild 58.1] Tongue and groove with a channel into which the “locking hook” can be hammered or rolled. [bild 58.1] A variant of the “adhesive trap” and “locking hook” method.
Joint design
Adhesive bonding involves the formation of a plastic or rubber load-carrying element. The material in the cured adhesive bond is not as strong as the aluminium. This can be compensated for by designing profi le solutions that provide large contact surfaces.
Aluminium profiles can be easily worked into a wide range of shapes. Where tongue and groove type bonded joints are a possibility, they may be the best solution. The illustrations above give some ideas and guidance on joint design.
Adhesives cope best with shearing forces. Joints subjected to tensional forces are often unsuitable for high loads. Peeling and cleaving forces concentrate stress on a small part of the joint and should be avoided whenever possible.
Choice of adhesive
Bonded joints distribute stress relatively well. However, very rarely is stress evenly distributed across the entire surface area of a bonded joint. As a rule, stress is greatest at the edges of the joint.
The stiffer the chosen adhesive, the greater the concentration of any subsequent stress. This leads to (sometimes unnecessarily) high stress on the adhesive and the surface that has been bonded to.
Thus, never choose an adhesive that is stiffer than necessary. Thicker bonded joints also reduce the concentration of stress at the edges of the joint. The choice of adhesive is determined by the way in which the adhesive works and what is required of the bonded joint (filling/sealing, heat resistance, toughness, etc.).
To be able to mould itself to the surface structure of the profi le, the adhesive must have good liquid properties. It must also harden into a material that can transfer stress in the environment where it is used. Furthermore, it is important that the adhesive has time to mould itself to the surface’s micro-profi le. Fast setting, high-viscosity adhesives rarely permit this. In such cases, it may be advisable to first apply a low-viscosity primer.
The change from liquid to solid is effected in three different ways.
Drying Cooling Curing by
Solventor watervaporisation
The adhesiveis liquid whenit is hot.
- Mixing- Heating- Exposure to moisture- Illumination (UV or blue light)- In the abscence of oxygen- Contact between adhesiveand hardener (withoutpreliminary mixing).
Drying
Solvents and water vaporise. Thus, adhesives containing solvents or water are unsuitable where: – gap filling is required – both the materials are unable to let the solvent escape.
Double-sided PSA tape should be regarded as a drying adhesive that never dries.
The material forming the joint is the same as that in the roll. However, if the stress is low, double-sided structural PSA tape may prove suitable for joining aluminium profiles together.
Double-sided PSA structural tapes formed entirely of the adhesive substance itself are available in thicknesses from 0.1 to 6 mm. There are also double-sided PSA tapes that can be heat cured. The tape holds the components even during curing – other forms of clamping are unnecessary. Testing of a simple overlap joint has shown a strength after curing of around 10 N/mm2.
Cooling
Some thermoplastic adhesives have good plasticity when hot. Hot-melt adhesives are the most widely used. However, the thermoplastic hot-melt adhesives usually set too quickly on aluminium. This results in poor contact with the aluminium surface. Hot-melt adhesives also have very low creep and heat strengths. Many thermoplastic hot-melt adhesives become brittle in cold environments.
Moisture-curing hot-melts are applied at lower temperatures and, compared to thermoplastic hot-melts, have excellent properties after curing. They are used for, amongst other things, applying foil coatings to aluminium profiles.
Heat-reactivated adhesive is also used when coating aluminium profiles with foil. An adhesive solution or a water-based adhesive is applied to the material and left to dry completely. In the bonding process, so that it wets the opposite surface, the adhesive is heated.
Moisture-curing hot melts and heat-reactivated adhesives can both give strong, durable bonds.
Curing
Curing adhesives make up the large group of structural adhesives. They cure (often with negligible contraction) in one of the following ways:
Curing by mixing of the components Typical of this group are the epoxy and polyurethane adhesives. They have very good gap fi lling properties. In principle, they can be cast. Modifi ed acrylic adhesives are now also becoming more common.
There are both stiff and elastic, 2-component, epoxy and polyurethane based adhesives. Epoxy adhesives with an elongation at fracture of up to 120% are now available. Elastic epoxy adhesives normally give a bond that is relatively heat-sensitive.
Using epoxy adhesives, higher strength bonds and improved durability are achieved by curing at elevated temperatures. The curing times are also considerably reduced – the curing time halves for each 10°C rise in temperature.
Two-component polyurethane elastomers give “rubber-like” joints that remain elastic even at low minus temperatures (°C).
There are also 2-component silicon adhesives that cure relatively quickly at room temperature.
Curing by contact between hardener and adhesive (adhesive on one surface – hardener on the other)These types of adhesives are usually referred to as SGA adhesives. They have excellent peel and impact strengths, but are not particularly suitable where a gap fi lling adhesive is required. These adhesives have been largely replaced by modifi ed acrylic adhesives, which are mixed direct from their packaging and can be used to form thick joints.
Acrylic adhesives of this type that adhere to untreated polyolefi nes (e.g. PE and PP) are now also available.
Curing by heating Here, the most common adhesives are the 1-component epoxies. These require heat curing at
a minimum of 100°C. With induction heating of aluminium profiles, curing times of approx. 60 seconds are possible.
The aero-industry makes extensive use of heat-hardening adhesive films. These require at least 30 minutes to harden at a minimum of 125°C.
One-component polyurethane elastomers can be heat cured at 70°C – 90°C (in 10 – 30 minutes).
Curing by contact with moisture Cyanoacrylate adhesives harden very quickly in contact with moisture. A bond between two aluminium surfaces takes longer to harden than a bond between aluminium and plastic or rubber materials.
Cyanoacrylate adhesives are best suited for small joint surfaces and thin bonds. Normally, they have low peel and impact strengths. However, there are “rubber-filled” (black) cyanoacrylate adhesives with good peel and impact properties. Colourless, elastic cyanoacrylates are also available, but these are not particularly suitable as structural adhesives for metal.
Cyanoacrylate adhesives may be suitable where, for example, a plastic is to be bonded to an aluminium profile.
One-component polyurethane elastomers can also be cured by the humidity of the air. This type of adhesive is used in, for example, the bonding of car windows and, on a large scale, for aluminium profi les in container and vehicle body manufacturing. Curing is comparatively slow (hours) and dependant on relative air humidity and joint geometry.
Heat-curing polyurethane elastomers have been mentioned above. There are also polyurethane elastomers that harden both with moisture and heat. Two-component type polyurethane elastomer adhesives are also available. As an alternative to polyurethane elastomers, there are the so-called MS polymers. These also harden with moisture. Two-component MS polymers are primarily chosen for work environment considerations.
Curing in UV light There have long been 1-component acrylate adhesives that cure in tenths of a second when exposed to UV light (wavelength approx. 350 nm) or blue light (wavelength > 400 nm). Acrylate adhesives are often limpid and very suitable for bonds between aluminium profi les and glass (most of them perform less well with transparent plastics).
Epoxy adhesives that harden in UV light have also been developed. There are many types of these - limpid, fi lled, low-viscosity, hard, elastic, etc. Some of these adhesives can be irradiated prior to bonding and will then cure relatively quickly.
Curing in the absence of oxygen Such adhesives cure on contact with active metal ions. They are normally referred to as anaerobic adhesives (or “locking fl uids”). They are not particularly suitable for aluminium. Aluminium surfaces should be regarded as passive. An activator has to be used in such cases. This gives a lower strength bond.
Variants of these adhesives that do harden without an activator on aluminium surfaces are now available.
Temperature limits
With many adhesives, the practical maximum temperature at which stressed bonded joints can be used is between 60 and 80°C. The highest heat-resistance (approx. 150 – 250°C) is achieved with heat-curing adhesives and heat-curing adhesive films. However, silicon adhesives can give heat-resistance of around 250°C without heat curing.
Long-term strength
Aluminium surface at x 25,000 magnification
(the red bar is 1 µm).
Bonds to aluminium are as strong and durable as the aluminium oxides with which the bond is formed. Aluminium that has had no surface treatment has a
large percentage of magnesium in its surface. Aluminium surfaces should normally always be treated in some way.
Used in a dry environment, an untreated aluminium profi le can give an excellent bond. The same bond outdoors in a coastal climate may have a far shorter life. Bond lifetime depends on the synergistic effects of stress, temperature and environment.
Normally, the problem is not the degradation of the adhesive or the failure of adhesion, but the effects of changes in the underlying aluminium. Any good microscope will show that there are no completely fl at or even surfaces. Highly viscous (slow fl owing) and fast setting adhesives will, therefore, most probably only come into limited contact with the surface. This results in a bond with in-built weak points (air pockets) where the adhesive’s properties are not being exploited. In humid environments, this air will eventually be replaced by water. Where the water is salty, the need for surface treatment is even greater.Aluminium’s durability can be improved by, for example, anodising.
Basic principles for long-lasting bonds
The basic principles for long-lasting bonds are well fi lled joints and resistant oxides. A large number of pretreatment processes have been developed for aluminium. Some of the most common (and some of the more unusual) are presented here. Choice is determined by the environment where the aluminium is to be used, likely stresses and costs.
Full details of the processes and any risks to the work environment should, of course, be obtained before starting any form of treatment.The main purpose of priming prior to the bonding of aluminium is to fill (seal) the surface when high-viscosity and/or fast setting adhesives are to be used.Priming becomes more important where the aluminium is to be used in a corrosive environment and no surface treatment that improves corrosion resistance (e.g. anodising) is
contemplated. Primer also “impregnates” and strengthens porous oxides, e.g. after chromating.
Requirement specification
It is advisable to draw up a requirement specifi cation for the properties of the final bond and the use-related aspects of the adhesive. This helps crystallise the demands really being placed on the adhesive. It also makes it easier to specify exactly what is required to the adhesive manufacturer.
Pretreatment operations in bonding
Process Result Use (max.)
Cleaning/ degreasing
Minimum requirement forensuring a clean and defi nedbonding surface.
For moderately stressed jointsin dry surroundings.
Fine grinding/blast cleaning
Removes weak surface layers e.g. oxides. Safer than degreasing.
Highly stressed joints in dryenvironments. Unstressedjoints in fresh water.
Alkalinepickling
Removes weak surface layers e.g. oxides. Safer than degreasing.
Highly stressed joints in dryenvironments. Unstressedjoints in fresh water.
Boiling water for5 – 10 min.after pickling
Gives resistant, but moderately strong oxides.
Lightly stressed joints usingflexible adhesives in humid,corrosive environments.
Phosphating/chromating
Corrosion resistant, but weak, porous oxides.
Lightly stressed joints using elasticor very low-viscosity adhesives incorrosive environments.
Hydrochloric acidat 20°C for30 seconds
Quick, can impart a dark-colouring
to the aluminium surface.
Moderately stressed joints, evenin corrosive surroundings. Relativelyuncommon process.
Etching inchrome/sulphuric acid
Thin, strong oxides. Long used in the American aero-industry.
Highly stressed joints outdoors.However, cannot withstand stronglycorrosive environments.
Anodising insulphuric acid
Thick very resistant oxide. Lightly stressed joints in corrosiveenvironments. Best with elasticadhesives.
Anodising inchromic acid
Medium-thick, strong oxide. Used in the European aero-industrysince the 40’s.
Highly stressed joints, even incorrosive environments.
Anodising inphosphoric acid
Porous, very resistant oxide. Is used together with low-viscosity primer.
Optimum pretreatment for highlystressed joints in corrosiveenvironments.
Literature Limning av aluminium, Sapa Technology Ð 2001. Readily available publication on aluminium bonding. Includes examples of adhesives and bonded joints (28 pages). In Swedish.
Limhandboken, Casco Nobel, Helsingborg Ð 1991, ISBN 91-630 0608-1. Easy-to-read introduction to bonding (108 pages). In Swedish.
Industrial Adhesives Handbook, Casco Nobel, Helsingborg Ð 1992, ISBN 91-630 1007-0. Easy-to-read introduc-tion to bonding (108 pages).
Adhesion in Bonded Aluminium Joints for Aircraft Construction, W. Brockman, O-D Henneman, H. Kollek and C. Matz, International Journal of Adhesion and Adhesives, volume 6, no. 3, July 1986. Discusses the phenomena associated with stressed bonds to aluminium in corrosive environments (28 pages).
Handbook of Aluminium Technology and Data, J. Dean Minford, Marcel Dekker Inc, New York, Basel, Hong Kong, ISBN 0-8247 8817-6. Collated findings and data on aluminium bonding. Contents include 4,686 references (744 pages).
Härdplaster, AFS 1996: 4, Arbetarskyddsstyrelsens Författningssamling, Publication service, Solna. Regulates the use of hardening plastics and adhesives in Sweden (78 pages). In Swedish.
10.9 Fusion welding
Aluminium is eminently suitable for welding. Although many welding methods are possible with aluminium, only a few are used in practice. Refinements in welding machines, equipment and materials have resulted in welding acquiring increasing importance as a jointing method.
Oxide formation
When welding aluminium, the metal’s reaction with oxygen, and the oxide rapidly generated therein, have to be taken into account. The oxide is strong, has a high melting point (approx. 2,050°C) and can easily cause welding defects. The oxide is heavier than the weld pool and may form inclusions. Thus, before all welding of aluminium, it is important to remove oxides from the joint surfaces. This may suitably be done using a stainless steel wire brush. Thoroughly cleaned, oxide-free joint surfaces are a basic requirement for faultless welded joints.
Weld porosity formation
The risk of void formation must also be taken into account. The hydrogen contained in moisture and contaminants on or in the welding materials, work piece or air is highly soluble in molten aluminium. It loses this solubility almost completely when the metal solidifi es. As the weld pool sets, the hydrogen forms bubbles that may become trapped and form voids.
Most aluminium alloys can be welded
Highlyweldablealloys
Sapa Chemicaldesignation
EN-AW
Swedishstandard
SS-EN-AW
All types of unalloyedaluminium, e.g. 1050A Al99.5(A) 1050A
Most of the non-hardenablealloys, e.g
- AlMn1 3103
AlMg2.5 5052
AlMg4.5Mn0.7 5083
Certain hardenablealloys, e.g.
6063 AlMg0.7Si 6063
6063A AlMg0.7Si(A) 6063A
6005 AlSiMg 6005
6005A AlSiMg(A) 6005A
6082 AlSi1MgMn 6082
7021 AlZn5.5Mg1.5 7021
6101 AlMgSi 6101
Methods
Nowadays, gas arc welding methods, MIG and TIG in particular, dominate. Argon (Ar) and helium (He) are used as the shielding gases in the MIG and TIG welding of aluminium. Argon and helium are inert gases and do not, therefore, form chemical compounds with other substances. Where there is a high penetration requirement, e.g. in a fi llet weld or when welding very thick work pieces, an argon-helium mixture can be used in MIG welding. The economic threshold for using mixed gases is a material thickness of 10 – 12 mm. As welds in aluminium are prone to the formation of oxide inclusions and voids, the shielding gas must also meet certain purity requirements. The minimum requirement is 99.5% argon or helium. Besides playing a part in the electrical processes in the arc, the gas also has the jobs of protecting the electrode and the weld pool from oxidation and of cooling the electrode.
MIG welding
As a rule, MIG welding is used for material thicknesses from 1 mm upwards. In special cases, thicknesses under 1 mm can be welded using a pulsed MIG arc. Filler metal is added in the form of a wire fed through the welding torch. MIG welding can be performed in any position and for all joint types. A higher current density than in TIG welding gives higher welding speeds. The high welding speed has a positive effect on distortion and shrinkage (narrower heat-affected zone).
TIG welding
TIG welding is suitable for material thicknesses down to under 1 mm. In practice, there is an upper limit of around 10 mm, but edge preparation is then necessary. Filler metal is normally used and is introduced from the side. TIG welding can be performed in any position and, when performed correctly, gives the most fault-free welds. The welding speed is relatively high, and even higher in mechanical TIG welding. TIG welding can be recommended where the gap width varies.
Robot welding
Robotised MIG welding can be used with advantage in long production runs. This method noticeably increases productivity and is also advantageous from a work environment point of view. The position of the work piece is easy to control. This facilitates welding from the optimum position and gives good results. Certain problems may arise with very thin materials and uneven gap widths.
Welding economy
Measured on cost per length, MIG welding is normally cheaper than TIG welding. Equipment costs are identical.
Filler metals
The table below gives recommendations for appropriate fi ller metals. AIMg5 generally gives the greatest strength. AISi5 is more stable as regards cracking and easier to use when welding hardenable alloys. If the welded assembly is to be anodised, Si alloyed fi ller metals cannot be used. When anodising, the silicon is precipitated and imparts a dark grey, almost black, colour. In order not to compromise weld quality, filler metals should be stored so that the risk of oxidation and the formation of other coatings is avoided.
Parent metal A
Sapa
Swedish
standardSS-EN-AW
Chemicaldesignatio
nEN-AW
10901080
A1070
Al99.90Al99.8(A)Al99.7(A)
Al99.8
A
1050A
1050A
1200
Al99.5(A)Al99.0
Al99.5Al99.5
Ti
Al99.5Al99.5
Ti
3103 AlMn1 Al99.5Ti
AlMn1
Al99.5Ti
AlMn1
AlMn1
AlSi5
5005525150525754
AlMg1(B)AlMg2
AlMg2.5AlMg3
AlMg52)
AlMg52)
AlMg52)
AlMg3AlMg5
5083 AlMg4.5Mn0.7
AlMg52)
AlMg52)
AlMg52)
AlMg5AlMg4.
5Mn
AlMg5AlMg4.5
Mn
606060636063
A60056005
A6082
606060636063
A60056005
A6082
AlMgSiAlMg0.7S
iAlMg0.7S
i(A)AlSiMg
AlSiMg(A)
AlSi1MgMn
AlSi5 AlSi5 AlSi5 AlMg3AlMg51)
AlMg5AlMg4.5
Mn
AlSi51) AlMg3AlMg5
7021 7021 AlZn5.5Mg1.5
AlSi5 AlSi5 AlSi5 AlMg4.5Mn
AlMg5
AlMg4.5Mn
AlMg5
AlMg4.5Mn
AlSi5AlMg5
AlMg4.5Mn
AlMg5
Parentmetal B
ChemicaldesignationEN-AW
Al99.90
Al99.8(A)
Al99.7(A)
Al99.5(A)
Al99.0
AlMn1
AlMg1(B)
AlMg2AlMg2.
5AlMg3
AlMg4.5Mn0.7
AlMgSiAlMg0.7
SAlMg0.7
Si(A)AlSiMgAlSiMg(
A)AlSi1Mg(
A)AlSi1Mg
Mn
AlZn5.5Mg1.5
Swedish standardSS-EN-AW
10901080A1070A
1050A1200
3103 5005525150525754
5083 60606063
6063A6005
6005A
7021
6082
Sapa
1050A 60606063
6063A6005
6005A6082
7021
1) Unsuitable where there is to be subsequent anodising.
2)Less suitable material combinations. However TIG welding with stated filler metal is possible.
Strength
In welding, the heat treatment to which the material is subjected affects the structure locally around the weld. The illustration is a schematic representation of how strength and hardness vary with distance from a weld in a hardenable alloy. With aluminium profiles, it is easy to compensate for decreased joint strength by increasing the wall thickness locally. Furthermore, edge preparation can be directly incorporated into the profile’s design.
Profile design with regard to fusion welding
Appropriately designed profiles can greatly simplify welding. Edge preparation, material compensation, in-built fastening, integral root backing and the minimisation of the number of welds required are all examples of proactive aluminium profile design.
In many cases, aluminium profi les can be designed in a way that reduces the required number of welds. Sometimes, welds can also be located in a low stress section of the cross-sectional area. This will mean fewer welds and improved strength.
Edge preparation integrated into the profile design - the illustration also features material compensation
for strength reduction in the weld zone.
Permanent root backing.
In-built fastener - used in dry environments.
Placing welds in lower stress sections of the cross sectional area. This results in fewer welds, and butt rather than fillet welds.
Number of welds reduced from 12 to 4 - butt welds rather than the weaker fillet welds (which are also harder to x-ray). Fewer components, reduced welding (consequently fewer heat-affected zones) and straightening minimsed.
10.10 Friction Stir Welding (FSW)
Friction Stir Welding (FSW) exploits aluminium’s ability to withstand extreme plastic deformation at temperatures that are high, but not above the melting point. In FSW, the clean metal surfaces of the profi les that are to be joined are heated by friction generated by a rotating tool and pressed together at very high pressures. This forms a new, homogeneous structure.
Compared with fusion welding, FSW gives:
Increased strength.
Increased leakproofness – entirely void-free, impermeable joints of a higher strength than fusion welded joints.
Joints that are, in principle, fl ush with the surface.
Reduced thermal deformation – only low thermal stress in the material, hence the flat surfaces.
Increased repeatability – production has few variables and these are easily controlled; the result is tight tolerances.
A heat sink panel – using FSW, profiles have been joined to form a flat, 530 x
1,290 mm panel.
An established technology
FSW is an established technology. It was developed by The Welding Institute (TWI) in Cambridge, England. Sapa has actively participated in the process of converting theory and laboratory experimentation into full-scale production.Sapa started series production using FSW in 1996. We are now the world leaders in the use of FSW and can supply FSW joined panels up to 3 metres wide and 14.3 metres long. Several leading classification societies have, after extensive testing, approved FSW as a jointing method for demanding uses in railway and marine applications.
A cross-section of a joint – x 13 magnification.
The homogeneous crystal structure in the centre section of an FSW joint – x 220 magnification.
Using FSW rather than traditional fusion welding to join panels together gives, amongst much else, increased flatness and straightness. Strength is also increased (see the Royal Institue of Technology's tests, pages 72-73).
The Sapa panel below is 3 x 14.3 metres.
A rotating tool is pressed into the metal and moved along the line of the joint. No filler metals or shielding gases are used. FSW takes place at a temperature below the metal's melting point. The results include very little thermal deformation, hence the flat surface.
The joint is in principle, flush with the surface and the FSW weld is, to all intents and purposes, completely void-free. The strength
properties are also very good.
The FSW weld – homogenous and void-free with no oxide inclusions
To paint a clearer picture of FSW, we have chosen to compare it with the most commonly used method of welding – fusion welding. At the same time, we must stress that, in our production of added-value aluminium profi les, we often use fusion welding (MIG). The old does have its place alongside the new. Fusion welding, MIG for example, uses fi ller metals and shielding gases.
The filler metal and the parent metal are melted and produce a weld bead that has a solidification structure different from that of the rest of the metal. In MIG and TIG welding, attention has to be paid to the metal’s reaction with oxygen. The oxide rapidly formed in this reaction can cause weld failure. The oxide is heavier than the weld pool and may form inclusions. There is also a risk of void formation.
FSW uses no fi ller metals or shielding gases. The joint is formed under the influences of friction generated heat and extreme plastic deformation. The material being joined never reaches its melting point, but the profiles weld together in a way entirely analogous to the extrusion of hollow profiles. The result is a homogenous and void-free weld with no inclusions.
FSW stands out in having only a few variables. These can be easily controlled to ensure the same results from one weld to the next. Fusion welding is a more complicated process. Consequently, results often vary.
MIG FSW
To give a fair comparison, the adjacent pictures are of very high quality fusion welds.
Precipitation in a MIG-weld. Precipitation in an FSW weld.
The MIG weld rises above the surface. Furthermore, its chemical composition differs from that of the welded material.
The FSW weld is, in principle, flush with the welded material. No filler metals are used.
A MIG weld viewed from above. An FSW weld viewed from above.
Strength
Experience and extensive testing have shown that an FSW weld is usually stronger than a fusion weld. The table below shows the standardised values for arc welded butt joints as per SS-EN 288-4 (see also the tests carried out by the Royal Institute of Technology, pages 72 – 73). The values given for FSW joints are based on a large number of measurements and should be regarded as guideline values. Since there are, as yet, no standards for FSW joints, the values for fusion welded joints are used in calculating the strength of standardised designs.
Condition of parent
metal before welding
Ageing afterwelding
T =
Rm (W)
Rm (pm)
T4 Natural ageing
Arcwelding 1)
FSW 2)
0.9 0.9
T4 Artificial ageing 0.7 0.9
T5-T6 Natural ageing 0.6 0.7
T5-T6 Artificial ageing 0.7 0.8
Ultimate tensile strength, R (w), of the welded test rod normally has to satisfy the following:
Rm (W) = Rm (pm) x T
where Rm (pm) is the prescribed minimum ultimate tensile strength of the parent metal and T is the joint’s weld factor.
1. For example MIG or TIG. 2. Guideline values only.
All 25,000 units passed helium testing for leakproofness.
Leakproofness
The pictures on the right are of heat sink units based on solid profiles that are then CNC machined by Sapa. The machined interior is closed with a cover, welded in place by FSW. Helium leak testing was used to assess leakproofness. The result was no loss of impermeability owing to weld failures. FSW joints have also been tested using the water pressure test. The results are unambiguous – FSW gives a joint that can be used in components with the severest demands for leakproofness.
Repeatability
The experience Sapa has gained in series production since 1996 shows: – Very small variations from joint to joint throughout a production cycle. – Very small variations from joint to joint in repeat customer orders. This is true of all variables – the joint’s structure, its strength, leakproofness and flatness.
Corrosion resistance
The chemical composition of the material in the joint is identical to that of the original material. Thus, in principle, corrosion resistance is unaltered.
Limitations
FSW requires the work piece to be held securely in place. This means, amongst other things, that repair welding of finished constructions is rarely possible with FSW. Repairs can, of course, be carried out using traditional methods.
Strength of FSW jointsComparison with MIG and TIG - Reference:The Royal Institute of Technology, Sweden
FSW welds have higher fatigue strength than MIG and TIG welds. This is the finding documented by Mats Ericsson, graduate engineer, and Rolf Sandström, professor, (both of the Institution for Materials Science at Sweden's Royal Institute of Technology) in the December
2001 research report, Influence of Welding Speed on the Fatigue of Friction Stir Welds and Comparison with MIG and TIG. Test material and test methods
Test mateial and test methods
This extract from the report gives values for extruded profiles in alloy SS-EN AW 6082 (AlSi1MgMn) Ð temper T6, material thickness 4 mm. The dimensions of the test pieces were as per SS-EN 284-4. FSW was carried out by Sapa in a plant used for series production. Test materials welded at two different speeds were included in testing. To the same high quality standards as those applying in the aero-industry, fusion welding was carried out by CSM Material Technology. TIG and pulse MIG welding were used. Vickers hardness was measured with a load of 10 kg. Fatigue testing was carried out with a stress ratio ( min/ max) of 0.5, the main direction of stress being across the weld.
The graph shows the variations in Vickers hardness across a cross section of an FSW joint (green) welded at a speed of 1, 400 mm/ min. and across a MIG weld (grey).
Comments: In both welds, hardness in the heat-affected zone decreases. This is clearly more marked in the MIG weld. Hardness is lowest (just under
60 HV) around the centre of the MIG weld. This is because fusion welding involves higher working temperatures, "foreign" filler metals and a less favourable structure in the weld. More heat is supplied in TIG welding than MIG welding. Consequently, the HAZ is a little wider. No significant difference was observed between the HAZs of the two FSW welds carried out at different speeds.
Mechanical properties Fractures under the microscope
SS-EN-AW6082
Yieldstrenght
Rp0,2
(MPa)
Tensilestrenght
Rm
(MPa)
ElongationA50 mm (%)
Reference
T6, parent metal
291 317 11.3 ME, RS 1)
Min. valuesfor profilest < 5 mm
250 295 6 SS-EN755-2
Pulsed MIG
147 221 5.2 ME, RS 1)
TIG 145 219 5.4 ME, RS 1)
FSW,speed A 2)
150 245 5.7 ME, RS 1)
FSW,speed B 2)
150 245 5.1 ME, RS 1)
1) Mats Ericsson and Rolf Sandström, averages of the results in the report in question.
2) Speed A, 700 mm/min. Speed B, 1,400 mm/min.
Fatigue strength
The graph above shows the results of fatigue tests on MIG welds (grey), TIG welds (blue) and FSW welds (green).
Comments: The FSW weld shows the best values throughout. In the study, TIG welds gave considerably better results than MIG welds. For failure at 500,000 cycles, the stress ranges were: MIG approx. 60 MPa, TIG approx. 70 MPa, FSW approx. 90 MPa at 700 and 1, 400 mm/ min (a shade higher at 1, 400 mm/ min).
MIG-weld: This SEM micrograph (x 25 magnification) shows the fracture surface. Fatigue fracture developed at several points in the root (to the right).
MIG-weld: as above (2.500 magnification) Fatigue striation in the area close to the root edge.
FSW: Fracture surface through the
fine-grained section of an FSW weld (root to the right). Fracture probably developed close the root.
Literature
A. Kluken, M. Ranes, Aluminium bridge constructions Ð welding technology and fatigue properties, Svetsaren, vol 50, no. 3, pages 13 Ð 15, 1995.
P. J. Haagensen, O. T. Midling, M. Ranes, Fatigue performance of friction stir butt welds in a 6000 series aluminium alloy, Computional Mechanics Publications (USA), pages 225 Ð 237, 1995.
12. Surface classes
Surface quality
The surface quality of an extruded aluminium profi le depends on, amongst other things, the condition of the die, production conditions and choice of alloy. Sapa has a well proven classifi cation system for evaluating surface quality (fi nish). The six classes have been devised to satisfy the standard requirements of different product groups. Always contact Sapa for advice on which class is best suited to a product. Various types of surface defects are recognised. Stripes, for example, are formed by the extrusion process itself (when the profile emerges from the die) and are always to be expected. They occur, to greater or lesser extents, in all surface classes. Sapa’s production standards minutely detail the requirements applying to each surface class.
Visible surfaces – important information
Information on a profile’s visible surfaces is important. Besides being used in surface evaluation, surface specifications are also vital in the construction of dies and when preparing profiles for anodising or painting. Incorrect or incomplete information may increase production costs. Profile drawings must obligatorily indicate visible, less visible and invisible surfaces.
[legend ]Visible surface: - - - - -Less visible surface: ========Invisible surface:(no marking)
Less visible surfaces are those which are not normally exposed in the fi nal product. Examples include the rabbets of door and window frames, the underneaths of table surfaces and the backs of cabinets. A profile’s surface class relates to its visible surfaces. Less visible surfaces are classed one step lower and invisible surfaces two steps lower (though never higher than surface class 5). Profiles with no visible surfaces at all are classified as surface class 6. Any changes in surface class requirement must be clearly stated when ordering. In some cases, it is impossible to achieve a higher surface class using the specified die. Always contact Sapa for advice.
Review profile design carefully
Even at the design stage, it is possible to reduce the risk of surface defects. Sharp transitions between thick and thin areas of material may give rise to heat zones. These, in turn, can affect surface fi nish in a way that is particularly visible after anodising. A large radius also reduces the risk of surface defects. Consult Sapa for advice on profile design. Specimen profiles are not representative as regards surfaces and material properties. They should only be used for checking dimensions, etc. If possible, the profile’s area of application should be stated. This information is important not only when evaluating surface class, but also in all other production phases.
The effects of surface treatment
Anodising results in a general improvement of surface quality. With chemical or mechanical treatment (grinding, brushing and/or polishing) before anodising, material supplied as surface class 2 can be brought up to surface class 1. Bright anodising emphasises any surface defects. Consequently, it lowers surface class one step compared to the untreated material as extruded.
Handling and stocking
Where it is important to maintain the decorative finish of products in surface classes 1 – 5, the following should be borne in mind: – When handling aluminium that has not been surface treated, special attention should be paid to the metal’s poor scratch resistance. To protect the profile against sweat-initiated corrosion, gloves should always be worn. – Aluminium which has not been surface treated is to be stocked dry, preferably indoors, so that it is not exposed to corrosive forces.
[saknar bild vit handske...]
Surfaceclass
(at delivery)
Area of application, etc.Suitable
Sapa alloys
Viewingdistance Normal eyesight
in normal lighting
1 Profiles with extremely high surface quality requirements Radios/TVs, lighting fi xtures, decorative trims, ornaments.Max. delivery length, 2.4 m unless otherwise agreed.This surface class can only be achieved with material extruded assurface class 2 and then treated chemically or mechanically (grinding,brushing and/or polishing) before finally being anodised.Production requires individual handling and inspection as well asa large labour input in all phases.Profiles that have visible surfaces on all sides cannot be produced inthis surface class (except where the profile is also to be ground on all sides).Individual packaging/protection required during transport.
6060, 6063,6463
approx. 0.6 m
2 Profiles with very high surface quality requirements Furniture, fittings, radios/TVs, picture frames, ornamentation andprofiles that are to be brought up to surface class 1.Max. delivery length, 2.4 m unless otherwise agreed.Production requires individual handling and inspection as well asa large labour input in all phases.Highest surface class for bright anodising.Profiles that have visible surfaces on all sides cannot be producedin this surface class.Profiles in this class must, as a rule, be anodised.Individual packaging/protection required during transport.
6060, 6063,6463
approx. 1 m
3 Profiles with high surface quality requirements Furniture, light fittings, fridge-freezers, bathroom fittings and equipment,shower cubicles and decorative trims.As a rule, profiles that have visible surfaces on all sides cannot beproduced in this surface class.Profiles in this class are usually anodised.
6060, 6063,6463
approx. 2 m
4 Profiles with ordinary surface quality requirements Structural systems, facades, windows, doors, balustrades. Also productsfor use in public facilities: Furniture, shop fittings, showcases, showercubicles, machine casings, heat sinks.Profiles in this surface class are usually anodised/painted.
6060, 6063,6463
approx. 3 m
5 Profiles with low surface quality requirements Structural systems, balconies, roofs, doorways, awnings, railing posts,sailing boat masts, ladders, goalposts, etc.Standard sections in Sapa 6063 alloy, body sections.
6060, 6063,6063A, 6005,6005A, 6082,6101, 6463
approx. 5 m
6 Profiles with no surface quality requirements Load-bearing structures, guide rails, conducting rails, scaffolding,components in mechanical systems, brackets, industrial railings,fencing posts.Standard profiles in Sapa 6082 alloy, trailer profiles for lorries and
All approx. 8 m
floor profiles.Profiles with no visible surfaces.Profiles in Sapa 7021 and Sapa 1050A alloys can only be extrudedto this surface class.
13. Thermal break profiles
Why insulated profiles? Because aluminium’s good thermal conductivity leads heat out and lets cold in. This can be a problem in, for example, facades, windows and doors designed with uninsulated profiles. Sapa’s solution is to connect the internal and the external sections of a profile via plastic insulation strips.
Sapa’s methodGlass fibre reinforced polyamide (nylon) strips
In Sapa’s solution, rolling is used to join two aluminium profiles via glass fibre reinforced polyamide strips. – Insulating strip width is normally 14 – 30 mm. Sapa keeps the most common widths in stock (check with Sapa). – Rolling can be used on lengths from 4.5 – 7.5 m. – Degree of insulation depends on strip width and profi le design.
Produced in three steps
The production equipment is purpose-designed. The three steps are: 1. Machining (knurling) of the track to ensure durability. 2. Joining of the aluminium profi les by sliding in the polyamide strips. 3. Rolling – the aluminium channels are closed around the polyamide strips. During production, random sampling is used to check the strength of the rolling.
1. Knurling of the profi le. 2. Joining of the profiles. 3. Rolling.
Single or double insulation
Two insulation strips are always recommended where lack of space does not leave single insulation as the only possibility. Strength properties and tolerances are considerably better with two strips.
Insulated profile design
Besides normal design rules, the following also apply: – To provide the necessary support during rolling, the sides have to be minimum 5 mm and perpendicular to the plastic strips. – Regarding the handling of aluminium profiles in the rolling equipment, Z profiles must be modified so that they do not tilt. The rolling surfaces should be centred and at 90° to the insulation strips. A certain degree of imbalance can be handled by special supports (contact Sapa for advice). – The minimum distance between insulation strips is 16 mm. – Both insulation strips should normally be of the same width.
Examples of insulated door profiles.
14. Machining
At the design stage, it is possible to create a profile that needs a minimum amount of post-extrusion machining. However, some form of further processing is often necessary after extrusion. Machining aluminium profiles is, comparatively speaking, inexpensive. The metal’s
malleability means that die costs are, as a rule, highly competitive. The cutting speeds attainable with aluminium are far higher than those with steel. Machining can take place both before or after anodising. The choice is determined by the demands made on the product. "Protective anodising" is a good way of preventing damage to profiles during machining.
High-speed machining
In recent years, machines and equipment for machining aluminium have seen relatively rapid development. High machining speeds have made it possible to achieve reduced wall thicknesses and tighter tolerances. This has further increased aluminium’s competitiveness. As regards the high-speed machining of aluminium, it is cutting speeds of 3,500 m per minute and over that are most interesting. At this point, the cutting forces diminish and, with increased cutting speed, fall to a very low level. This allows feed speeds to be increased. As a result, machining times are reduced. Lower cutting forces also reduce burr formation and increase tool service life. Machines capable of exploiting these higher feed speeds require signifi cantly improved dynamics, and considerably more efficient control systems, than conventional machines.
Shorter lead times
In today’s market, there is a constant demand for ever shorter lead times. Amongst other things, this has led to the development of the “product workshop” concept of production. The demand for shorter lead times makes it highly desirable to avoid transfers of materials between independent machining centres and areas of responsibility. The solution is a concept in which operations are integrated – there is a single centre of responsibility and, very often, a single supplier.
Series sizes
The size of a product series is often a crucial factor in deciding which production methods are to be used. Thus, as early as possible, it is vital that an assessment is made of the series sizes of all the necessary parts.
Scrap – a valuable raw material
For Sapa, production scrap is a valuable raw material that can be immediately exploited for transformation into new profiles. This is an important consideration.
Machining methods
Machining methods are classifi ed by the way in which they give shape to the work piece – plastic deformation, stock cutting and stock removal . The following pages examine some of the methods that are suitable for machining aluminium.
14.1 Stock cutting
14.1.1 Punching/cutting
Cutting using a punch and a die is commonly referred to as punching. The bottom part of the punch and the upper edges of the die present a cutting profile corresponding to the contours and cavities of the part to be cut. Usually, the punch is mobile and the die is fixed.
The punch penetrates the material. Deformation is at first elastic and then plastic. This is followed by fracture initiation, first at the punch edges and then at the die edges. Cutting is completed by these fractures propagating through the material and then joining.
14.2 Stock removal
Extruded aluminium is easy to cut. Thanks to high cutting speeds, and the high feed speeds this makes possible, machining costs are low and production rates are high. If care is not taken, problems such as build-up on the cutting tools, chip blockages, burr formation and difficulty in meeting tolerances can arise. The right cutting settings and tool geometry are important. Broadly speaking, cutting tools for extruded aluminium are characterised by positive cutting angles and ample space for chips. PKD tools (tools with diamond inserts) very often give good results. Sapa has, on occasions, drilled up to 500,000 holes using the same tool. Titanium coated, hard metal blades are a further example of a class of cutting tool with a long service life. In long production runs, machining can often be streamlined by, for example, having automated transport between machines and using a line system.
14.2.1 Turning
Turning in automatic lathes is only possible with alloys that produce short chips. As a rule, an alloy should be worked at its highest possible temper. Furthermore, if possible, a hardenable alloy should be chosen. With the metal in a soft condition, problems such as build-up on the blade, long chips, chip blockages, extreme burr formation and diffi culty in meeting tolerances may arise.
It is important to choose the correct cutting settings (e.g. cutting speed and feed) so that, amongst other things, the chips fall away from the point of cutting. Cutting fluid (mineral oil or, in some cases, a water-based emulsion) is used to cool the cutting tool and wash chips away. Cutting tools are most usually made of hard metals or high-quality high-speed steel. To give good turning results and surface quality, the cutting tool should have high surface fineness and a good edge. In CNC lathes with several tool arms, drilling, tapping and milling can be carried out at the same time as turning.
14.2.2 Drilling
Drill bits suitable for extruded aluminium have a tip angle of around 130°, a spiral angle of approx. 40° and provide ample room for chips.
Recommended settings for cutting
Cutting speed, vFeed, s
High-speed steel
70-150 m/min.0.1 - 0.4 mm/rotation
Hard metal
150 - 1,000 m/min.0.1 - 0.7 mm/rotation
The cutting speed depends on the drill’s speed (rpm) and the speed at which the bit is fed into the material. With the right equipment and settings, a 10 mm wide, 30 mm deep hole can be drilled in 0.3 seconds.
14.2.3 Milling
Extruded aluminium can be milled in everything from simple milling machines to high-speed machines. High-speed machining makes it possible to achieve very good tolerances, surface finishes and processing speeds. Sapa has high-speed machines that operate from 20,000 to 40,000 rpm.
Milling. Cutting to length.
14.2.2 Drilling
Drill bits suitable for extruded aluminium have a tip angle of around 130°, a spiral angle of approx. 40° and provide ample room for chips.
Recommended settings for cutting
Cutting speed, vFeed, s
High-speed steel
70-150 m/min.0.1 - 0.4 mm/rotation
Hard metal
150 - 1,000 m/min.0.1 - 0.7 mm/rotation
The cutting speed depends on the drill’s speed (rpm) and the speed at which the bit is fed into the material. With the right equipment and settings, a 10 mm wide, 30 mm deep hole can be drilled in 0.3 seconds.
14.3 Plastic forming
14.3.1 Draw bending
Draw bending is the most commonly used bending method. It is suitable for tight radii and has a high degree of repeatability. Using an adjustable clamping jaw, the work piece is fixed against a rotating die. The clamping jaw and the tool are shaped to reproduce the profile’s cross section. The work piece rotates with the die. This stretches the material on the outside of the profile and compresses that on the inside. To prevent scratches and clamping marks on the profile, the tools are usually made of plastic. Anodised profiles: Being hard and brittle, the oxide layer forms many fine cracks during bending. If a high quality surface is required, it is recommended that anodising is left until after bending.
Draw bending. Roller bending.
14.3.2 Roller bending
Roller bending is used for forming large radii in the work piece. The work piece is rolled between two drive rollers and a pressure roller. The shape presented by the rollers corresponds to the profile’s cross section. Vertical adjustment of the upper roller (the pressure roller) alters the radius of the bend. Thus, in CNC machines, a number of different radii can easily be pressed into a single work piece. As rollers are most usually made of steel, lubrication is often required to prevent cutting and scratching of the profile.
14.3.3 Stretch bending
Stretch bending gives very high three-dimensional shape accuracy. The work piece is fixed between two clamping jaws and then gradually stretched over a shaping block. The shape presented by the block corresponds to the profile’s cross-section. The metal is stretched to its upper elastic limit and spring-back is thus negligible. As the tooling investment is relatively high, stretch bending is best suited to large series production.
Stretch bending.
14.3.4 Press bending
Press bending (point bending) is suitable for simple bending of large series. The work piece is formed using compressive force. An upper and a lower die are contoured to give the work piece the desired shape. Pressure is applied by some form of excentric or hydraulic press. Depending on the exterior of the part to be pressed, dies can be steel or plastic.
Press bending.
14.4 Threading
Cutting and forming methods can both be used to make threads. When cutting using taps, a chipping angle of 35 – 40º is recommended. Cutting speed should be 30 – 40 m/min. When producing a thread by rolling, the so-called oil groove method is recommended. Speed should be 40 – 70 m/min. The milling of threads gives good results all the way down to, in some cases, M3.
14.5 Tolerances
Machining is normally to ISO 2768-1 (middle), but tighter tolerances normally present no problem. In high-speed machining, channels and holes can be milled to, for example, H7. This does away with the need for subsequent reaming.
14.6 Hydroforming
Our starting point is an extruded aluminium pipe. Hydroforming allows us to shape it three-dimensionally in a single operation. The process offers as yet unexplored possibilities. All, or parts, of a profile’s cross section can be tailored using hydroforming. In a single operation, complex parts can be created with very good dimensional accuracy. In a single hydroforming operation, it is also possible to make local changes such as domes or holes. By eliminating several machining operations, lead times can be shortened. Hydroforming of aluminium profiles is a competitive choice at yearly volumes of around 20,000 units upwards.
The principle
The profile is placed in a die that has an inner geometry exactly replicating the shape of the finished component. The die is locked securely in position and hydrostatic pressure is then set up in the pipe (profi le). As the profile is pressed against the die, it takes up the shape of the die.
The automotive industry – Research and series deliveries
Since the end of the 90’s, along with Volvo and Ford, Sapa has been involved in research projects on, and prototype production of, vehicle side beams hydroformed from extruded aluminium profiles. Today, Sapa has world-leading and unique expertise and experience in the hydroforming of long aluminium beams. In the autumn of 2001, Sapa began series deliveries to Volvo.
Simulation, using the FE method,
to study the critical points in the forming process.
The shaped component.Note the cross-sectional changes throughout its length
Example product: Side beam for a Space Frame
Cross-sectional change so that the profile can fit into a narrow
passage.
In order to make a hole during the hydroforming process, a punch is included in the tooling. Punching extends process time by a few seconds only. The hole is precisely positioned and no further machining is required..
1. Production starts from an extruded aluminium pipe2. The pipe then goes through draw bending. 3. The finished component.
The result – very good dimensional accuracy and exactly the geometry required by the product and production.
Compared with traditional steel/plate bodies, hydroforming gives weight savings of around 50%.
Profile design, dimensions and tolerances
In discussions, Sapa has contributed advice in respect of a wide range of designs for, amongst others, the automotive, furniture, electronics and engineering industries. In design discussions, it has become clear that hydroforming opens the way to unique solutions for a wide range of design problems. Thus, it would not be easy to here give simple rules for profile design, dimensions and tolerances. Contact Sapa’s hydroforming department in Vetlanda, Sweden, for further details.
14.5 Tolerances
Machining is normally to ISO 2768-1 (middle), but tighter tolerances normally present no problem.
In high-speed machining, channels and holes can be milled to, for example, H7. This does away with the need for subsequent reaming.
Cutting to length, CNC machining (milling, drilling, threading), anodising, bending, assembly.
Cutting to length, CNC machining (contour milling, drilling, threading), anodising, bending, assembly.
Cutting to length, CNC machining (milling, drilling, threading), anodising, bending, assembly.
Cutting, CNC machining (milling, drilling, threading), end brushing, deburring (blasting), alkaline washing, assembly.
Cutting to length, draw bending, punching, end brushing.
Cutting to length, stamping, threading (ten threads), end brushing, anodising.
Cutting to length, deburring, CNC machining (fl at face milling), anodising, CNC machining (lathe boring), alkaline washing.
Cutting to length, end brushing, CNC machining (milling), punching.
Cutting to length, CNC machining (lathe boring, flat face milling, drilling), alkaline washing.
Cutting to length, CNC machining (milling, drilling, threading), end brushing, deburring (blasting), alkaline washing.
Cutting to length and stamping in a special machine, end brushing, alkaline washing.
Cutting to length, stamping, end deburring, press bending.
Cutting to length, CNC machining (drilling, milling, threading), end brushing, deburring (blasting), alkaline washing.
Cutting to length, CNC machining (milling, threading), end brushing, deburring (blasting), alkaline washing, white chromating.
Cutting to length, CNC machining (milling, hole cutting), alkaline washing.
Cutting to length, CNC machining (drilling, milling, lathe boring, reaming, threading, centring), anodising in long lengths.
Turning. Cutting to length, CNC machning (milling, special latheboring), anodising.
Kapning, CNC-bearbetning (planfräsning), slipning, anodisering, CNC-bearbetning (fräsning, borrning).
Cutting to length, deburring, CNC machining (milling), punching, anodising, assembly.
Anodising (long lengths), cutting to length, turning, punching.
Cutting to length, CNC machining (fl at face milling) grinding, anodising, CNC machining (milling, drilling).
Cutting to length, CNC machining, deburring, alkaline washing.
Anodisning (long lengths), cutting to length, punching, threading, countersinking, alkaline washing.
15. Surface treatment
Even before surface treatment, the appearance and surface quality of extruded aluminium profiles is perfectly satisfactory for many applications.
Thanks to good corrosion resistance, surface treatment is rarely necessary simply to provide corrosion protection. However, there are many other reasons for treating the surfaces of profiles.
Examples of attributes that can be changed by surface treatment include:
surface structure colour corrosion resistance hardness wear resistance reflectivity electrical insulation.
The untreated surface
Surfaces do no always need treatment after extrusion. Load-bearing structures and machine parts are examples of products where the surface quality is satisfactory without any treatment.
15.1 Profile design
Lines and extrusion stripes that would be noticeable on visible surfaces can easily be hidden using decoration. Such patterns or optical effects are an integral part of the profile solution created at the design stage. Refer also to "Decorate", page 32.
Sailing boat mast - Sapa delivers profiles in 12.4 metre lengths. Seldén Mast joins these to form 20 Ð 25 metre high masts.
15.2 Mechanical surface treatment
Grinding
Grinding is one of the methods used for improving surface quality. The process leaves a fi ne striation in the direction of grinding. The resultant surface can be "very fi ne", "medium" or "coarse". Grinding is most commonly used for furnishing and interior design products. Ground surfaces are often anodised. Grinding before painting can further improve the surface finish.
Polishing
Polishing smoothes the surface. Quality and gloss are determined by customer specifications. Polished surfaces normally go on to be anodised. To achieve a high-gloss finish, polishing is followed by bright anodising.
Tumbling (barrel polishing)
Tumbling is mainly used for deburring. Determined by the polishing medium used in the drum, surfaces range all the way from matt to gloss.
Bottle openers - deburred by tumbling, anodised in short lengths and screen printed.
Deburring by tumbling.
Ground surfaces - A: "very fine", B: "medium", C: "coarse".
15.3 Anodising
The reasons for anodising
Anodising, one of the most common surface treatments, is used to (amongst other things):
maintain a product's "as-new" appearance. enhance corrosion resistance. create a dirt repellent surface that satisfies stringent hygiene requirements. create a decorative surface with durable colour and gloss. create a "touch-friendly" surface. create function-specifi c surfaces, for example, slip surfaces, abrasion-resistant
surfaces for use in machine parts, etc. give surfaces an electrically insulating coating. provide a base for the application of adhesives or printing inks.
Recommended layer thicknesses when anodising
Layer thickness
Area of application
25 µm Where surfaces are exposed to severe stress in the form of corrosion or abrasion.
20 µm Great or normal stress outdoors (e.g. transport and construction industries).Indoors – great stress arising from the use of chemicals (e.g. the foodstuffs industry).
15 µm Severe abrasion, indoors and outdoors in dry and clean atmospheres.
10 µm Normal stress indoors.
3-5 µm Protective anodising before machining, short period of etching.
Choice of alloy when anodising
Sapa alloy 6060 6063 6063A 6005 6005A 6082 7021 1050A 6101 64633
Decorative anodising(natural coloured, Hx,2-stage Hx)1) x x x x x
Protective anodising(natural) x x x x x x 2) x x (x)
1)Using the same anodising process, gloss and shade vary between different alloys.
2) Anodising should be avoided as it contaminates the process bath.
3) Specifi cally intended for bright anodising (prior protective anodising
should be avoided).
The anodising process
There are normally four stages in the process: pretreatment, anodising, colouring (where required) and sealing. The most frequent type of anodising is natural anodising. The electrolytic process takes place once the metal surface has received the appropriate mechanical or chemical pretreatment and has been thoroughly cleaned.
The profile is connected to a direct current source and becomes the anode (hence anodising). An electrolytic cell is formed. Dilute sulphuric acid at room temperature is normally used as the electrolyte. During electrolysis, the surface of the metal is oxidised. The process continues until the desired layer thickness (usually 5 - 25 µm) is reached.
Sealing
The oxide layer contains a large number of pores, approx. 10 11 /cm 2 (i. e. around a hundred billion). The diameter of the pores is between 120 and 330 Å. To obtain an impermeable surface, the pores have to be sealed. Sealing is achieved by treating the surface in de-ionised water at 95 - 98° C. This changes the aluminium oxide into bohemite, the attendant increase in volume closing the pores. The oxide layer formed in natural anodising is transparent. Coloured oxide layers are also possible (see pages 104 and 105). Natural anodised profiles are delivered with matt or semi-matt surfaces.
Maintenance - cleaning
The anodic oxide layer has good corrosion resistance in most environments. With the proviso that the surface is cleaned, anodised profiles are virtually maintenance-free. The surface cleans easily in both water with a little neutral detergent and in white spirits. Although solvents do not affect aluminium, strong alkaline solutions should be avoided. Resistance to corrosion, discoloration and abrasion increases with layer thickness. Recommendations for suitable thicknesses are given in the table on the previous page. As the anodic oxide layer has poor cold formability, forming should take place before anodising. Cutting and drilling can be carried out after anodising but the exposed surfaces will, of course, be untreated. Welding is to be carried out before anodising.
Properties of anodised aluminium
Corrosion resistance is very good, especially where pH is between 4 and 9. In contact with strongly alkaline substances, surfaces can stain and be damaged. Thus, it has to be borne in mind that aluminium should be protected against lime, cement and gypsum (e. g. on building sites). Visible surfaces can be protected using tape. The hardness of the oxide layer depends on the anodising process used. Generally, the layer is harder than glass and as hard as corundum. The oxide layer is transparent. Whether natural or coloured, its appearance depends on the viewing angle. At temperatures above 100° C, fi ne cracks form in the oxide layer. From an aesthetic point of view, this may be an undesirable effect.
The reflectivity of bright etched aluminium is high. The gloss value is 90 units (ISO 7599, 60° viewing angle). This decreases slightly with anodising. The oxide layer is an electrical insulator. A sealed, 15 µm oxide layer has a breakdown voltage of 500 Ð 600 V. An anodised
profile can be recycled with no pretreatment. Before remelting, painted profiles must fi rst have the paint removed.
Coloured oxide layers
Dyeing Natural anodised, unsealed aluminium can be coloured using organic or inorganic pigments (dyes). Profiles are sealed after dyeing.
Electrolytic Hx colouring
Like the dyeing process, electrolytic colouring is also a separate stage after anodising. Under the infl uence of an alternating current, pigment is precipitated at the bottom of the oxide layer's pores. The pigmenting agent is tin salt and the colour scale ranges from champagne to black. The colours, designated from Hx 10 to Hx 50, are highly resistant to fading. After colouring, profiles are sealed.
Outdoor colourfastness
The colourfastness of an anodised layer depends on the pigments and colouring technique used. Dyeing: Some coloured layers have limited outdoor colourfastness. Electrolytic Hx colouring: Limited choice of colours, very good lightfastness, suitable for outdoor use.
Sapa's colour designations
See the colour guide on page 118. All colours are delivered with a matt or semi-matt finish.
Refl ector panels emerging from the anodising bath. This profile, produced for Infrarödteknik AB, is GD-20-l, semi-matt anodised.
Combined casings-heat sinks for compact modules using hybrid technology from Ericsson Components. Protective anodising before treatment, then BL-20-I, semi-matt anodising in short lengths.
15.4 Painting
Painting offers a limitless choice of colours and very good colour matching (repeatability). Powder coating is now easily the most widespread method of painting aluminium profiles.
GSB certification
Since 1994, Sapa Lackering has been certifi ed to the German GSB standards. It is the only company in Sweden to have this certifi cation. To qualify for certifi cation, our products and processes must meet stringent requirements. Continued compliance is monitored by inspectors who make a number of unannounced visits every year. Besides continous checks during production, we have also undertaken to, amongst other things, carry out some 15 tests a day in shielded rooms. To ensure traceability, the tests are archived for 5 years.
Pretreatment
To ensure the right adhesion for the paint, it is important that pretreatment, paint application and subsequent curing are all carried out correctly. As maximum adhesion and durability are prime goals, pretreatment is of crucial importance. Pretreatment normally comprises degreasing and pickling of the surface, followed by a chemical treatment. The chemical treatment (chrome-free or chrome-based) gives good adhesion and effective corrosion resistance. The chrome-free titanium based process is GSB approved and is now our standard method. It has undergone extensive testing. Rinse water from the chromating process is treated in effi cient cleaning plants. The sludge is drawn off and sent away for appropriate disposal. Pretreatment is the same for both powder coating and wet painting.
15.4.1 Powder coating
Broadly speaking, there are absolutely no limits to the choice of colour. Besides the RAL and NCS S colour systems, we also work to customers' own colour definitions. Standard gloss is 77 units (ISO 2813, 60° viewing angle). Powder coatings are applied and cured without solvents. This gives a good work environment and has no negative impact on the external environment. In a wet coating plant, half the paint is lost through evaporation and the waste involved in over-spraying. In Sapa's powder coating plant, up to 98% of the powder is used. Powder that does not adhere to the product is recirculated via a reclamation system.
Powder coating qualities
The prime qualities of powder coating and powder coats are:
No risk of running or blistering. High repeatability. Powder coatings withstand knocks and abrasion far better than wet paint coatings. Good formability (e. g. can be formed after coating). Suitable for outdoor use good resistance to UV and corrosion.
Coating thickness is normally 60 - 140 µm. In some designs, the thickness of the coating has to be taken into consideration when determining profile dimensions and tolerances.
Structural, metallic, clear and Decoral coatings
Sapa works with all the kinds of coatings requested by customers. In addition to the traditional powder coatings, this includes structural, metallic and clear coatings. Decoral, a development of powder coating, gives patterned surfaces (see also 15.4.2).
Sapa has a number of powder coating plants, each of them specialising in different products. We also have a Decoral production unit and one for wet painting. The picture shows a vertical powder coating line - profiles up to 7 metres long are suspended vertically rather than horizontally, thereby giving a manifold increase in capacity.
Left: Powder coatings are applied via triboelectric (friction) or electrostatic
Right: Profiles on their way to the curing oven (temperature is approx. 180° C). Curing
charging. Profiles emerging from the powder box.
takes about 15 minutes, the time depending on the design of the profile. Both these pictures are taken from one of our horizontal coating lines.
15.4.2 Decoral
A development of powder coating that gives patterned surfaces
The technique: A special composition powder coating is fi rst applied. The pattern is then transferred to the profile. The original pattern, most usually a photographic image of wood or stone, is copied onto a film that holds the pigments forming the decorative design.
The depth of penetration is crucial for the results Ð a shallow pattern is subject to comparatively large stresses. The Decoral technique ensures deep penetration. The result is a surface with all the properties of a traditional powder coating (see "Powder coating qualities", page 106).
Key properties
Test Method Result
Thickness ISO 2360 Min. 60µm on visible surfaces
Adhesion ISO 2409 Cross-cut 0 1)
Buchholz hardness ISO 2815 Min. 80
Erichsen ISO 1520 Min. 3 mm
Bending 2) ISO 1519 Ø 8 mm
Kesternich (SO2 ) ISO 3231 24 cycles < 1 mm
Boiling water Pressure cooker, 1 hour No defects or blisters
Mortar resistance ASTM D 3260 Meets base requirements
Damp resistance DIN 50017, 1,000 hours < 1 mm
Salt spray ISO 9227 < 1 mm
Impact 2) ASTM D 2794 < 22 inch-pounds
All tests carried out on decorated plates and profiles
1) Evaluation is on a scale of 0 - 5 where 0 is best.
2) Test carried out on 1 mm thick, AA 5005 H 24 aluminium alloy plates
The Decoral system has been used in series production since 1996. This has given us a wealth of experience regarding how Decoral surfaces work in practice in, amongst other countries, Italy and Germany. Extensive testing in laboratories has also provided comprehensive documentation.
Example patterns - choose from a wide range, or create your own.
Design and construction advantages of Decoral
Without being any thicker than normal powder coatings, Decoral can add the look of solid wood to a profile's durability, "create" marble with the same density as aluminium... When it comes to patterns and colours, there are no limitations.
15.4.3 Wet painting
Sapa uses many different types of paint and can, of course, offer water-based paints. Alkyd paints are often used in wet painting. However, they have low formability and cannot be used for products that are to be formed after painting. Resistance to solvents and oils is poor.
15.5 Sapa HM-white
The perfect complement to both anodising and powder coating Sapa HM-white is produced by electrophoresis (Honnystone Method). An anodised and unsealed profile is dipped into a tank where, using direct current, the paint is applied Ð electrophoretic deposition. The paint (an acrylic based melamine) is then hardened in an oven at around 180° C. Total coating thickness is approximately 30 µm.
This method offers a range of advantages:
A UV-resistant white. Very good gloss retention and resistance to chemicals. Very good corrosion resistance. The coating penetrates into the pores of the anodised surface and sticks there. This
gives very good adhesion. The surface is impermeable and dirt-repellent. The values for hardness, impact and abrasion resistance are almost identical to those
for powder coatings. However, as regards abrasive wear, it must be borne in mind that HM-white has a surface thickness of 30 µm compared to powder coating's 60 - 140 µm.
Surface thickness is the same for the entire surface. There is no build-up of coating at the edges. This is perfect for structural profiles that
have to be mated with each other and for snap-fit and telescopic designs.
HM-white coating at approx. x 20,000 A hinge Ð HM-white has a great advantage
magnifi cation. One third of the coating is the anodic oxide layer, 2/ 3 is the paint itself. This picture was taken by a scanning electron microscope (SEM).
here as the coating thickness is even on all profile surfaces and there is thus no build-up at the edges.
Pictures above and left: HM-white in use. Right: Coloured profiles emerging from the process bath.
Test Method Result
Thickness ISO 2360 30µm
Gloss ISO 1813 (60° viewing) 85 ± 5
Adhesion ISO 2409 Cross-cut 0 1)
Buchholz hardness ISO 2815 < 100
Pencil harness - destructive/abrasive INTA 160 30 5H - 3H
Kesternich (SO2 ) ISO 3231 24 cycles
Salt spray test ISO 3768 1,000 hours
Machu < 0.5 mm
Boiling water BS 4842 5 hours
Mortar resistance ASTM C 207 C, 24 hours No adhesion
1) Evaluation is on a scale of 0 - 5 where 0 is best.
15.6 Screen printing
Screen printing (formerly silk-screen printing) is an ancient printing method. The original design is reproduced on a transparent fi lm that is then placed on a fine-meshed screen (usually nylon nowadays). This is then exposed and developed photographically. The screen is next fitted into a frame. Either manually or automatically, a squeegee is dragged along the screen to transfer the design onto the printing surface. Initial costs (production of the nylon screen, etc.) are low - often less than EUR 100.
Tampon printing
Tampon printing is a technique that makes it possible to use screen printing on both concave and convex surfaces.
Natural and coloured anodising on the same profile
Using screen printing, a profile's surfaces can combine natural anodising and colouring. Anodising is interrupted when the oxide layer has formed. The profile areas that are not to be printed are then coated with a special masking ink. After printing, the profile is sealed in the normal way.
Unanodised surfaces on anodised profiles
A masking technique is also used when parts of a profile are to emerge unanodised from the anodising process. This preserves the surface's electrical and thermal conductivity (the anodic oxide layer is insulating).
Screen printing can also be used on painted and HM-white surfaces .
15.7 Function-specific surfaces
We define a function-specific surface as one where certain function-related properties are of critical importance. Whatever you require of your function-specifi c surfaces, have a word with Sapa!
Slip, friction and sealing surfaces
Here, the surface roughness (i. e. the R a values, axially and radially) is of the utmost importance. Sapa can meet even the most severe demands. Cylinder tubes are an example. Direct from the press, we can deliver tubes where the insides have R a values as low as 0.6 axially and 1. 2 radially. The R a values can, of course, be further improved by machining.
Abrasion-resistant surfaces
These surfaces have to be anodised.
Four height adjustable legs made from telescoping aluminium profiles - slip surfaces direct from the press (no machining). The product: Control cabinet lift columns from MPI.
15.8 At-a-glance guide for choice of surface treatment
Process Result Use
Profile Design Patterning. Design purposes. Covering lines andextrusion stripes. Increasing friction(grip).
MECHANICALSURFACETREATMENT
Embossing Patterning. Design purposes. Marking.
Grinding Improved surface quality. Superior appearance.
Wherever an exclusive appearanceat a reasonable price is the goal.
Polishing Improved surface finish. Superior appearance.
Furnishing and interior design products.Finish and gloss as specified by thecustomer.
Tumbling Smoothing of cut edges. Deburring. Matt to glosssurfaces depending on tumbling medium.
Primarily deburring.
ANODISING
General Very good corrosion protection. The surface retains its “as-new” appearance, is dirt-repellent and resistant to mechanical abrasion. Colour and gloss resist fading. An electrically insulating coating.
Both indoors and outdoors.A base for application of adhesivesor printing inks.
Bright anodising Intense gloss, high reflectivity. Where there are high demands asregards surface finish.
Colour anodisingColouring
Huge choice of colours, some of them with very high lightfastness.
Primarily indoors – some outdoorapplications.
Hx Limited choice of colours – champagne to black. Very high lightfastness.
Primarily outdoors.
PAINTING Unlimited choice of colours. A range of painting
Both indoors and outdoors.
systems to meet different requirements. Very goodcorrosion resistance.
ELECTROPHORESISSapa HM-white
UV-resistant colour with a more durable gloss than traditional paints. Very good corrosion resistance.Coating thickness the same over the entire surface.
Both indoors and outdoors.
SCREEN PRINTING
Printing in theoxide coating
Wear-resistant print. Limited choice of colours.
Design purposes. Logos.
Printing on the surface Wide choice of colours. Limited abrasion resistance.
Design purposes. Logos.
15.9 Color guide for anodising
Sapa's standard colours
Designation
Maxlenght(mm)
Designation
Maxlenght(mm)
Natural 5-25µm
NA-5 - NA-25
12,400
Violet LI-25-I 2,400
Hardoxal LI - 30-I 2,400
Champagne
Hx-10 7,500 Brown olive
BO-20-! 2,400
Light amber
Hx-20 7,500(x)
BO-35-I 2,400(x)
Amber Hx-30 7,500
Dark amber
Hx-40 7,500(x)
Black SV-50-U 2,400
Black Hx-50 7,500
Gold GD-20-I 7,800 Bright anodising (alloy Sapa 6463)
GD-30-I 7,800 Nature NA-5-GI 2,400
GD-30-U 7,800 Gold GD-20-GI 2,400
GD-40-I 7,800 Yellow
YW-20-GI 2,400
Yellow YW-40-U 2,400 Orang OR-35-GI 2,400
e
Orange OR-35-I 2,400 Red RD-25-GI 2,400
Red RD-15-I 2,400 Red cerice
RC-30-GI 2,400(x)
RD-25-U 2,400 Green GN-40-GI 2,400
Red cerice RC-30-I 2,400 Blue BL-20-GI 2,400
Green GN-40-I 2,400 Blue grey
BG-30-GI 2,400
Blue BL-20-I 2,400 Violet LI-30-GI 2,400
BL-30-U 2,400(x)
Brown olive
BO-20-GI 2,400(x)
Blue-grey BG-10-I 2,400 BO-35-GI 2,400(x)
BG-30-I 2,400 Black SV-50-GI 2,400
(x) Certain restrictions apply to coloursmarked (x) - see below
Explanation of RD-25-U, GD-30-I, etc
Sapa's colour designations have three parts:
Colour - intensity - properties.
RD = red 25 = intensity U = outdorr use
GD = gold 30 = intensity
I = primarily indoor use
The intensity scale runs from 0 to 50.
Amongst the many factors infl uencing the perceived appearance of anodised surfaces are:
Profile shape Viewing light and
angle Surface structure Thickness of the
anodising layer Choice of alloy.
Taken all together, this means that aluminium is truly a "living" material. All colours can be delivered with a matt or semi-matt finish. Gloss finishes are also available. The table above lists the colours that can be delivered with a gloss finish.
16. Corrosion
16.1 Aluminium'scorrosion resistance
Untreated aluminium has very good corrosion resistance in most environments. This is primarily because aluminium spontaneously forms a thin but effective oxide layer that prevents further oxidation. Aluminium oxide is impermeable and, unlike the oxide layers on many other metals, it adheres strongly to the parent metal. If damaged mechanically, aluminium's oxide layer repairs itself immediately. This oxide layer is one of the main reasons for aluminium's good corrosion properties. The layer is stable in the general pH range 4 – 9. In strongly acid or alkaline environments, aluminium normally corrodes relatively rapidly.
Corrosion resistance in common profile alloys
Between Sapa's most widely used alloys, there is little variation in corrosion resistance. However, alloys containing more than 0.5% copper generally have poorer resistance. Therefore, they should not be used unprotected in environments with a high chloride content (e. g. where there is road salt or near sea water).
16.2 The most common kinds of corrosion
The most common types of corrosion are:
galvanic corrosion pitting crevice corrosion
Stress corrosion, which leads to crack formation, is a more special type of corrosion. It occurs primarily in high-strength alloys (e. g. AlZnMg alloys) where these are subjected to prolonged tensile stress in the presence of a corrosive medium. This type of corrosion does not normally occur in common AlMgSi alloys.
16.2.1 Galvanic corrosion
Galvanic corrosion may occur where there is both metallic contact and an electrolytic bridge between different metals. The least noble metal in the combination becomes the anode and corrodes. The most noble of the metals becomes the cathode and is protected against corrosion. In most combinations with other metals, aluminium is the least noble metal. Thus, aluminium presents a greater risk of galvanic corrosion than most other structural materials. However, the risk is less than is generally supposed.
A small cathode surface and a large anode surface results in negligible corrosion.
In the reverse situation (large cathode, small anode), attack can be serious in diffi cult environments.
Galvanic corrosion and aluminium
Galvanic corrosion of aluminium occurs:
Only where there is contact with a more noble metal (or other electron conductor with a higher chemical potential than aluminium, e. g. graphite).
While , at the same time, there is an electrolyte (with good conductivity) between the metals.
Galvanic corrosion is often attributable to unsuitable structural design. Galvanic corrosion does not occur in dry, indoor atmospheres. Nor is the risk great in rural atmospheres. However, the risk of galvanic corrosion must always be taken into account in environments with high chloride levels, e. g. areas bordering the sea. Copper, carbon steel and even stainless steel can here initiate galvanic corrosion. Problems can also occur where the metallic combination is galvanised steel and aluminium. The zinc coating of the galvanised steel will, at fi rst, prevent the aluminium being attacked. However, this protection disappears when the steel surface is exposed after the consumption of the zinc. As it has a thicker zinc coating than electroplated material, hot dip galvanised material gives longer protection. Thus, in combination with aluminium in aggressive environments, hot dip galvanised material should be used.
Close-up of galvanic corrosion in an aluminium rail post (25 year's use). The rectangular hollow profile was held in place by a carbon steel bolt. The contact surfaces between the steel and the aluminium were often wet and attack was aggravated by wintertime salting.
16.2.2 Preventing galvanic corrosion
The risk of galvanic corrosion should not be exaggerated Ð corrosion does not occur in dry, indoor atmospheres and the risk is not great in rural atmospheres.
Electrical insulation Where different metals are used in combination, galvanic corrosion can be prevented by electrically insulating them from each other. The insulation has to break all contact between the metals. The illustration shows a solution for bolt joints.
Breaking the electrolytic bridge
In large constructions, where insulation is diffi cult, an alternative solution is to prevent an electrolytic bridge forming between the metals. Painting is one way of doing this. Here, it is often best to coat the cathode surface (i. e. the most noble metal). A further solution is to use an insulating layer between the metals.
Cathodic protection
Cathodic protection can be gained in two ways. The most common is to mount an anode of a less noble material in direct metallic contact with the aluminium object to be protected. The less noble material "sacrifi ces" itself (i. e. corrodes) for the aluminium. It is thus referred to as a sacrifi cial anode. For the above to work, there also has to be liquid contact between the surface to be protected and the sacrifi cial anode. Zinc or magnesium anodes are often used for aluminium. Another way of obtaining cathodic protection is to connect the aluminium object to the negative pole of an exterior DC voltage source. The illustration below shows the cathodic protection of an outboard motor.
16.2.3 Pitting
For aluminium, pitting is by far the most common type of corrosion. It occurs only in the presence of an electrolyte (either water or moisture) containing dissolved salts, usually chlorides. The corrosion generally shows itself as extremely small pits that, in the open air, reach a maximum penetration of a minor fraction of the metal's thickness. Penetration may be greater in water and soil. As the products of corrosion often cover the points of attack, visible pits are rarely evident on aluminium surfaces.
16.2.4 Preventing pitting
Pitting is primarily an aesthetic problem that, practically speaking, never affects strength. Attack is, of course, more severe on untreated aluminium. Surface treatment (anodising, painting and coating with HM-white) counteracts pitting. Cleaning is necessary to maintain the treated surface's attractive appearance and its corrosion protection. Rinsing with water is often suffi cient. Alkaline detergents should be used with care. Mild alkaline detergents are now available. These are used in, amongst other areas, the industrial cleaning of aluminium. Pitting can be prevented by cathodic protection (see previous page). It is also important to design profiles so that they dry easily.
Avoid angles and pockets in which water can collect.
Instead, use a shape that promotes draining.
The risk of dirt build-up is reduced with radiused corners.
Stagnant water is avoided by suitably inclining the profile and/ or providing drain holes (min. Ø 8 mm, or 6 x 20 mm, so that capillary forces do not prevent the water running off). The ventilation of "closed" constructions reduces the risk of condensation.
16.2.5 Crevice corrosion
Crevice corrosion can occur in narrow, liquid-filled crevices. The likelihood of this type of corrosion occurring in extruded profiles is small.
However, significant crevice corrosion can occur in marine atmospheres, or on the exteriors of vehicles. During transport and storage, water sometimes collects in the crevices between superjacent aluminium surfaces and leads to superfi cial corrosion (" water staining"). The source of this water is rain or condensation that, through capillary action, is sucked
in between the metal surfaces. Condensation can form when cold material is taken into warm premises. The difference between night and day temperatures can also create condensation where aluminium is stored outdoors under tarpaulins that provide a tight seal.
16.2.6 Preventing crevice corrosion
Preventing crevice corrosion Using sealing compounds or double-sided tapes before joining two components prevents water from penetrating into the gaps.
In some cases, rivets or screws can be replaced by, or combined with, adhesive bonding. This counteracts the formation of crevices.
16.3 Aluminium in open air
The corrosion of metals in the open air depends on the so-called time of wetness and the composition of the surface electrolytes. The time of wetness refers to the period during which a metal's surface is suffi ciently wet for corrosion to occur. The time of wetness is normally considered to be when relative humidity exceeds 80% and, at the same time, the temperature is above 0° C (e. g. when condensation forms). In normal rural atmospheres, and in moderately sulphurous atmospheres, aluminium's durability is excellent. In highly sulphurous atmospheres, minor pitting may occur. However, generally speaking, the durability of aluminium is superior to that of carbon steel or galvanised steel.
The presence of salts (particularly chlorides) in the air reduces aluminium's durability, but less than is the case for most other construction materials. Maximum pit depth is generally only a fraction of the thickness of the material. Thus, in marked contrast to carbon steel, strength properties remain practically unchanged.
Field exposure tests by the Swedish Corrosion Institute
In a range of outdoor atmospheres, the Swedish Corrosion Institute has carried out field exposure tests on untreated metals. For plates that had received no surface treatment, the weight losses after eight year's exposure are given here. After the eight years, the average pit depth in the aluminium plates was 70 µm (0.07 mm). The bar chart shows that aluminium's weight loss near the sea was: Ð approx. 1/ 100 th that of carbon steel (Fe). Ð approx. 1/ 10 th that of galvanised steel (see Zn in the bar chart). The rate of corrosion decreases rapidly with distance from the sea. Approximately 1 km from the sea, aluminium behaves more or less the same as it does in a rural atmosphere. The corrosion rate of the pits decreases with time.
The picture shows an untreated sample after 20 years off the south-west coast of Sweden. UV radiation, sulphuric acid and nitric acid in combination with chlorides have not left any deep marks. After 22 years in a marine atmosphere, examination of an untreated aluminium sample (alloy AA 6063) showed that corrosion attack was so limited (max. depth approx.
0.15 mm) that strength was not affected.
16.4 Aluminium in soil
Soil is not a uniform material. Mineral composition, moisture content, pH, presence of organic materials and electrical conductivity can all vary widely from site to site. These differences make it difficult to predict a metal's durability in soil. Furthermore, other factors (e. g. stray currents from DC voltage sources) can also affect durability. Aluminium's corrosion properties in soil very much depend on the soil's moisture, resistivity and pH value. Unfortunately, present knowledge about the corrosiveness of different types of soils is not comprehensive. When using aluminium in soil, some form of protective treatment, e. g. a bitumen coating, is recommended. Corrosion can also be prevented by cathodic protection.
Bitumen coating (here of a fence post and a telephone pole) prevents corrosion. Aluminium in soil protection is recommended.
16.5 Aluminium in water
A metal's corrosion in water is largely dependent on the composition of the water. For aluminium, it is the presence of chlorides and heavy metals that has the greatest effect on durability. In natural fresh water and drinking water, aluminium may be subject to pitting. However, with regular drying and cleaning, the risk of harmful attack is small. Pots, pans and other household equipment can be used for decades without there being any pitting. The likelihood of harmful attack increases where water is stagnant and the material is wet for long periods.
Pitting can however be prevented by:
design solutions that reduce the risk of water being trapped cathodic protection corrosion inhibitors, e. g. used in car radiators.
The rate of pitting in fresh water decreases strongly with time and has been proven to obey the above formula, where d is maximum pit depth, k a constant determined by the alloy and water composition and t is time. The formula indicates, for example, that a doubling of the pit depth that has developed by the end of the fi rst three years can only be expected after a total of 24 years. In sea water, AlMg alloys with over 2.5% Mg (and AlMgSi alloys) show particularly good durability. Copper containing alloys should be avoided. Where they are used, they must be given effective corrosion protection. When correct attention has been paid to design, especially as regards use with other materials (and the risk of galvanic corrosion), aluminium is an excellent material in a marine context. One example of this is the extensive use of aluminium in many types of ships and boats. Cathodic protection against corrosion is widely used here.
Corrosion at the water line
Aluminium that is only partly submerged in water can corrode directly under the water line (so-called waterline corrosion). This type of corrosion, which only occurs in stagnant water, can be prevented by coating the area around the water line.
16.6 Aluminium and alkaline building materials
Splashes of damp alkaline building materials, e. g. mortar and concrete, leave superfi cial but visible stains on aluminium surfaces. As these stains are diffi cult to remove, visible aluminium surfaces should be protected on, for example, building sites. Other materials also require the same sort of protection. Aluminium cast into concrete is similarly attacked. This increases the adhesion between the materials. Once the concrete has set (dried), there is normally no corrosion. However, where moisture persists, corrosion may develop. The volume of the products generated by corrosion can give rise to cracks in the concrete. This type of corrosion can be effectively prevented by coating the aluminium with bitumen or a paint that tolerates alkaline environments. As the oxide layer is not stable in strongly alkaline environments, anodising does not improve durability here. Provided that the concrete has set, aluminium does not need to be protected in dry, indoor atmospheres.
16.7 Aluminium and chemicals
Aluminium and chemicals Thanks to the protective properties of the natural oxide layer, aluminium shows good resistance to many chemicals. However, low or high pH values (less
than 4 and more than 9) lead to the oxide layer dissolving and, consequently, rapid corrosion of the aluminium. Inorganic acids and strong alkaline solutions are thus very corrosive for aluminium. Exceptions to the above are concentrated nitric acid and solutions of ammonia. These do not attack aluminium. In moderately alkaline water solutions, corrosion can be hindered by using silicates as inhibitors. Such kinds of inhibitors are normally included in dishwasher detergents. Most inorganic salts are not markedly corrosive for aluminium. Heavy metal salts form an exception here. These can give rise to serious galvanic corrosion due to the reduction of heavy metals (e. g. copper and mercury) on aluminium surfaces. Aluminium has very good resistance to many organic compounds. Aluminium equipment is used in the production and storage of many chemicals.
16.8 Aluminium and dirt
Coatings or build-ups of dirt on the metal's surface can reduce durability to a certain extent. Very often, this is attributable to the surface now being exposed to moisture for considerable periods. Thus, depending on the degree of contamination, dirty surfaces should be cleaned once or twice a year.
16.9 Aluminium and fasteners
When choosing fasteners for use with aluminium, special attention should be paid to avoiding galvanic corrosion and crevice corrosion (see sections 16.2.1, 16. 2.2 and 16.2.5).
Galvanic corrosion of aluminium occurs where there is metallic contact with a more noble metal. It should be pointed out that, indoors and in other dry atmospheres, aluminium can be in permanent contact with brass and carbon steel with no risk of galvanic corrosion.
The table on page 129 shows some of the most common surface coatings for fasteners. The evaluation of the surface coatings is based on the findings of fastener and coating suppliers, as well as the experience of Sapa and its customers (primarily in the building and automotive industries).
In deciding which fasteners to use, the table should be regarded as an introductory guideline. As development is rapid, Sapa also recommends that fastener and coating suppliers be contacted.
The pictures below show the results of an accelerated corrosion test, the Volvo Indoor Corrosion Test (VICT). The test cycle is 12 weeks. This corresponds to fi ve year's use of a car in a moderately large town (Gothenburg).
Zinc/ iron-coated steel nut and bolt. The fastener is completely rusted. In the aluminium, 0.43 mm deep pits have formed.
Dacrolit-coated steel nut and bolt. The fastener has not been attacked. No pits have formed in the aluminium.
At-a-glance guide for choosing fasteners
The table below lists some of the most common materials and coatings for fasteners used with aluminium. It also gives an evaluation of corrosion resistance in different environments.
16.10 Corrosion checklist
Environments
Rural atmosphere Aluminium has excellent durability.
Moderately sulphurousatmosphere
Aluminium has excellent durability.
Highly sulphurousand marine atmospheres
Superficial pitting can occur. Nonetheless, durability isgenerally superior to that of carbon steel and galvanised steel.
Corrosion problemscan be overcome
Profile design The design should promote drying, e.g. good drainage.
Avoid having unprotected aluminium in protracted contactwith stagnant water.
Avoid pockets where dirt can collect and keep the materialwet for protracted periods.
pH values Low (under 4) and high (over 9) values should, in principle,be avoided.
Galvanic corrosion In severe environments, especially those with a high chloride
content, attention must be paid to the risk of galvaniccorrosion. Some form of insulation between aluminium andmore noble metals (e.g. carbon steel, stainless steel, copper)is recommended.
Closed systems (liquid) In closed, liquid containing systems, inhibitors can oftenbe used to provide corrosion protection.
Severe, wet environments In difficult, wet environments, the use of cathodic protectionshould be considered.
17. Cost efficiency
When compared with other design solutions, aluminium profiles are almost always competitive. Though the price per kg is higher than that of, for example, steel, this is counterbalanced by advantages such as:
very great freedom in creating exactly the shape that solves the design problem and contributes to the high quality of the end product
aesthetically pleasing surfaces low die costs Ð low machining costs low weight combined with high strength long lifetime, minimum maintenance high recycling value.
The balance sheet comes out in favour of products based on aluminium profiles!
17.1 How you, the designer can influence cost-efficiency
Through carefully considered design, designers can infl uence the following cost-affecting factors: alloy, shape, weight per meter, surface class, tolerances, surface treatment, machining, recycling.
Alloy
A number of factors have to be taken into consideration when choosing the right alloy for an extruded product. These include strength requirements, surface quality, suitability for decorative anodising, corrosion resistance, machining (cutting or plastic), weldability and costefficiency. High-alloy aluminiums are relatively more expensive and more difficult to extrude. Thus, alloys with higher than necessary strength should not be chosen. It is sometimes more cost-efficient to increase dimensions and extrude the profile in a slightly softer, but more easily extruded, alloy. See also chapter 7, "Choosing the right alloy".
Shape
Exploit the potential to create a shape that reduces the need for further machining and simplifi es the assembly of the final product. Simplify the cross section as much as possible. Refer back to chapters 9 and 10, "General design advice" and "Jointing".
Weight per meter
Carefully considered design can reduce weight per meter. This often lowers costs. See also chapter 9, "General design advice".
Surface class
The choice of surface class affects price. The fi ner the surface, the higher the production cost (greater monitoring of dies, lower extrusion speed, increased handling costs). Surface classes 5 and 6 are the most economical to produce. Think carefully about which surfaces really need to be classed and marked as visible (refer to chapter 12, "Surface classes").
Tolerances
Tight tolerances decrease productivity and, consequently, increase production costs. Thus, special tolerances should be restricted to the dimensions that are most important for the profile's functionality. See also chapter 11, "Profile tolerances".
Surface treatment
Choosing the right surface treatment has a positive impact on appearance, function and durability. See also chapter 15, "Surface treatment".
Machining
At the design stage, it is important to create a shape that requires a minimum amount of subsequent machining. Extrusion provides many possibilities for including a number of functional features (screw ports, tracks, snap-fi t joints, etc.) in the profile solution. Refer to chapters 9 and 10, "General design advice" and "Jointing". Carefully considered machining (tolerances, deburring, machining before or after surface treatment, etc.) can also have a positive impact on the product's final price. See also chapter 14, "Machining".
Recycling
The recycling of aluminium consumes relatively little power. It must be borne in mind that bolt joints, and other solutions involving the use of materials other than aluminium, can complicate recycling. See also chapter 4, "Environmental impact".
17.2 How you, the purchaser can influence cost-efficiency
Order volumes
Unit price for small volumes is always higher than it is for large volumes. The larger the ordered volume, the less the unit price is affected by fi xed costs such as tooling-up, machine adjustments, etc.
Precise budgeting
Where you yourself take charge of machining, a lot of work is involved in inviting and evaluating tenders. Besides material and machining costs, calculations should also make provision for:
inspection of incoming profile material warm storage production preparation tool inspection tool storage tool installation rejects production waste transport to and from subcontractors loading, packing, unpacking, etc. dealing with offers and orders dealing with invoices.
On top of all that, the cost of tied-up capital also has to be taken into consideration.
Rejects and production waste
With Sapa in charge of machining, you do not have the bother of taking care of rejects and production waste. You receive a fi xed price for the finished component. Production is tailored to minimising production waste. Sapa's long experience ensures that there is minimal rejection.
All the scrap stays at Sapa
For Sapa, rejects and production waste are a high-grade raw material that can be directly exploited and put back into production without expensive intermediaries.
Shorter lead times
Our planning is made easier by the fact that we have control of the entire production chain. Should anything unexpected occur, e. g. during machining, we can rapidly bring in extra profiles. Along with reduced transport, this contributes to shorter lead times.
Less tied-up capital
When you choose Sapa as your partner, you only pay: Ð when the finished components are delivered Ð for the exact number of components supplied. When you yourself take charge of machining, you have to bear the full capital cost of materials all the way through production. This includes the costs associated with what becomes scrap and waste.
Reduced administration
For you, having Sapa as the single centre of responsibility, means (amongst other things):
reduced work in connection with tenders reduced ordering and organising of transport
simplifi ed monitoring of deliveries simplified quality assurance fewer invoices minimal work in connection with claims.
Simplicity itself
You have a single supplier, a single point of contact, one order, one delivery, one invoice and one telephone number to ring. It really is that simple!
Having Sapa as your partner reduces the burden of administration. It also offers every possibility for increased profi tability, higher productivity and improved quality.
It is all about coordination - general and specific, large and small, chalk and cheese, strategic and tactical. Business development, research and development, quality assurance, logistics, market analyses, materials science, mechanical engineering, assembly, production planning,
product development, profile optimisation, project management, technical development, technical calculation, monitoring and inspection, training, surface treatment and much, much
more.
17.3 Sapa's vision
"Sapa shall be the most sought after partner in our industry and shall be the market leader in the Nordic countries. Our focus is customer service, technical expertise, quality and delivery dependability."
Are we in a position to help you with expertise, quality and resources? Can we free resources for your company's core business? There is a reason for contacting Sapa for open discussions. Many companies have found that the closer the partnership with Sapa, the sharper the resultant competitive edge.
18.2.3 Colleges, industry organisations, etc
Colleges, industry organisations, etc. Outside Sapa, a number of institutions are involved in aluminium-related research, development and knowledge sharing. Many technical and regional colleges, high schools and private sector training companies run projects that have the goal of raising understanding of aluminium technology.
Industry organisations such as Skanaluminium, Svenskt Aluminium and Aluminiumriket support, at many different levels, researchers and lecturers in their aluminium-related activities.
In all these initiatives, Sapa plays an active role as an institutor and implementor.
