INDUSTRIAL TRAINING REPORT

IN

PORWAL AUTO COMPONENTS LTD. PITHMPUR M.P.

IN

MAY-JUNE 2014

AMAN SHRIMAL111101108MATERIAL SCIENCE AND METALLURGICAL ENGINEERINGMAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY, BHOPAL (MP)

ACKNOWLEDGEMENT  

I have taken efforts in this project. However, it would not have been possible without the kind support and help of many individuals and organizations. I would like to extend my sincere thanks to all of them.

I am highly indebted to Mr. Atin Jain, Mr. RK Sahu (HR), Mr. Sunil (Production in-charge) and rest of the members of PORWAL AUTO COMPONENTS LTD. for their guidance and constant supervision as well as for providing necessary information regarding the project & also for their support in completing the project.I would like to express my gratitude towards my parents and sister for their kind co-operation and encouragement which help me in completion of this project.I would like to express my special gratitude and thanks to industry persons for giving me such attention and time.My thanks and appreciations also go to my colleague in developing the project and people who have willingly helped me out with their abilities.

CONTENTS

1. Company profile 2. Product manufactured3. Facilities4. Founding and casting5. Foundry industry

5.1. Employment 5.2. Production5.3. Investment5.4. Raw material 5.5. Technology

6. Flow chart of process7. Process

7.1. Mold making7.2. Pattern making7.3. Design 7.4. Material used7.5. Sand casting

8. Melting 9. Cold box method10. Sand 11. CO2 process12. No bake 13. Mold material14. Sand reclamation 15. Cast iron

15.1 Grey iron15.2 Ductile iron

16. Leeb test17. Brinell test18. Vicker test19. Sand test

Company Profile

Porwal Auto Components Ltd. (PACL) is involved in the manufacture of a variety of Ductile Iron, Grey Cast Iron Steel and Steel Alloy Casting Components and Subassemblies. PACL caters to the various sectors including Automobile, Engineering, Pumps and Valves, Agriculture and Tractor Equipments, Construction Equipments, Machine Tools, Railways etc. 

Porwal Auto Components Ltd. was incorporated in the year 1992 as an ancillary to M/s. Eicher Motors Limited now VE Commercial Vehicles Ltd. (A Volvo Group and Eicher Motors joint venture). PACL has registered impressive growth and has established itself as a trusted supplier of Quality Castings and gained recognition from its customers for Outstanding Contribution to Parts Development and Supply Chain Management. 

Products being manufactured

1) Automotive partsa) AXLE PARTS

i) DRUM BRAKE (FG-30)ii) REAR WHEEL HUB (SG-500/7)iii) BRAKE SHOE MACHINING (SG-400/12)iv) FRONT WHEEL FLANGE (SG-500/7)

b) ENGINE PARTSi) EXHAUST MANIFOLD (SG-400/12)ii) EXHAUST BEND 4 Cyl.(SG-400/12)iii) EXHAUST MANIFOLD 6 Cyl. (SG-400/12)

c) CHASSIS PARTSi) BRACKET FOR AXEL ROD (SG-400/12)ii) LEVER FOR ENGINE CONTROL( SG-400/12)iii) FRONT SPRING REAR BKT( SG-400/12)iv) LEVER ANCHOR (SG-500/7)v) REAR SPRING BKT REAR ( SG-400/12)vi) BRACKET ( SG-400/12)vii) BELL CRANK LEVER ( SG-400/12)viii) FRONT SPRING BKT FRONT( SG-400/12)ix) BRACKET ( SG-400/12)x) BRACKET FOR AXEL ROD ( SG-400/12)xi) REAR SPRING MTG BKT FRONT ( SG-400/12)xii) H SHACKLE FRONT( SG-400/12)

d) Transmission partsi) HOUSING SPINDLE (SG450/10)ii) COVER REAR (FC-25)iii) NPUT COVER (FC-25)iv) CASE TIMING GEAR (FC-25)v) HOUSING G-1 (FC-25)vi) CASE TRANSMISSION (FC-25)

e) Differential partsi) DIFF CARRIER G ( SG-400/12 )ii) THROUGH DRIVE HOUSING ( SG-400/12 )iii) DIFF CASE . STRD. MTD.( SG-400/12 )iv) FRONT WHEEL FLANGE ( SG-400/12 )v) BEARING RETAINER (SG-500/7)vi) DIFF CARRIER STRD. MTD. ( SG-400/12 )

2) Earthmovinga) LINK LOADER (SG-500/7)b) HOUSING (FC - 25)c) BACK PLATE LUB. OIL PUMP (FC-25)d) HOUSING 550 (FC - 25)

3) Locomotive4) Heavy Engg. M/c parts

a) CASTING GEAR (FC-25)b) HOUSING-450-(-FC-25-)

Facilities: Manufacturing

Casting

MELTING & CUPOLA 1500 KW / 300 Hz VIP Dual track coreless Induction Furnace with 2 nos. 2000 Kg

Crucibles of Inductotherm Make. 650 KW /500 Hz dual track core-less induction furnace with 1000 kg crucibles of

Inductotherm make.

POURING SYSTEM Pouring lines with bi-rail handling system. Pusher & pullers on track for handling mould box make Fonundarc.

MACHINE MOULDING  Air Impulse High Pressure Molding Machine – FONDARC (French Design).

Rated Production Capacity 90 moulds per hour Box Size 700 X 700 X 300 / 300 mm 2 Pairs DARPA -450 Molding Machines. Molding Box Size 500 X 500 X 175 / 250 mm,

650 X 600 X 175 / 250 mm

HEAVY MOULDING

Dimension Maximum (In mm): 2000 x 2000 x 1000, Weight: 100 kg to 2000 kg

COLD BOX Fully automatic cold box sand preparation & distribution system. Capacity: 2 Ton/ Hrs.

Fully automatic residual gas scrubber for cold box Process. Capacity : 10000 CFM Fully Automatic Amine cold box machine with complete Hydraulic operation – 2 nos.

Parting: VerticalShot Capacity: 3 kgTooling Size: 400 X 250 X 250Tooling Size: 500 X 250 X 300

Fully Automatic Universal Amine cold box machine & operation Hydraulic.Shot Capacity: 7.5 KgParting: VerticalTooling Size: 500 X 250 X 300

Fully Automatic Universal Amine cold box machine & operation Hydraulic.Shot Capacity: 60KgParting: Vertical: 700 X 400 X 500Parting Horizontal: 700 X 500 X 500

SAND PLANT

SAND PLANT OF FONDARC MAKE (French Design) Capacity: 80 MT/ Hr with online sand testing, online sand cooling & with fully automated, PLC controlled operations.

KNOCKOUT & DECORING Decoring cutter Tumbling barrel, make - jadav industry. Knock out 2000, make - sunny precision, Chipping hammer, make- Chicago pneumatic

FETTLING - FINISHING & PAINTING Cutter grinder, make- Chicago Pneumatic. Swing frame grinder. Pedestal grinder. Pneumatic hand grinder, Chicago Pneumatic. Pneumatic cutter, Chicago Pneumatic Heat treatment, make Dhan Prakash. Shot blasting m/c make Meera. Conveyorised hanger type shot blasting machines - 2Nos Conveyorized, forced air drying painting booth.

MATERIAL HANDLING E.O.T. crane f/c tapping 3 ton, make- Meeka Industries.  Pouring hoist & ladle (1000kg & 500kg) make- Dhanprakash, Electric  & power stacker, make- Godrej. Bundling machine, make-Sona Industries. Fork lift trucks make Godrej.

CORE SHOP Shell core shooter. Electric oven. Sand drier, make - Rhino Machinery. Core sand mixer make- J K Foundry.

PATTERN SHOP Methoding and simulation Through SOFTCAST. Pattern and Core Boxes are made on

CNC. Maintenance of the tooling of the Tooling done in-house.

Lathe machine, make-Kirlosker. Milling machine, make- Looper Engg. Drilling Machine.

TESTING

METALLURGICAL TESTING  Microscope with Image Analyzer with magnification of 100 times Brinell hardness Tester Vickers hardness Tester Portable Leeb Hardness Tester Universal Testing Machine. Impact Testing machine ASTM.

CHEMICAL TESTING Spectrometer F20 Foundry Analyzer Metal Lab of GNR Italy for chemical composition C.E. apparatus with recorder Carbon Sulphur analyzer Other relevant wet analysis facilities

SAND TESTING Sieve Shaker Universal Sand Testing Machine Mould Hardness Tester Permeability Meter Moisture Tester.

METROLOGICAL TESTING Surface Finish Tester Slip Gauge Surface plate Conventional facilities for measurement. Inspection through CMM

 NON DESTRUCTIVE TESTING Ultrasonic Flow Detector Dye Penetrant Magnetic flaw detector

Founding and Casting

The process of pouring molten metal into a cavity that has been molded according to a pattern of the desired shape. When the metal solidifies, the result is a casting—a metal object conforming to that shape. A great variety of metal objects are so molded at some point during their manufacture.

The most common type of mold is made of sand and clay; ceramics, sand with cement, metals, and other materials are also used for molds. These materials are packed over the face of the pattern (usually made of wood, metal, or resin) that forms the cavity into which the molten metal is to be poured. The pattern is removed from the mold when its shape is able to be retained by the mold material. Molds are usually constructed in two halves, and the two halves are joined together once the pattern has been removed from them. Pins and bushings permit precise joining of the two halves, which together are enclosed in a mold box. The metal is then poured into the mold through special gates and is distributed by runners to different areas of the casting. The mold must be strong enough to resist the pressure of the molten metal and sufficiently permeable to permit the escape of air and other gases from the mold cavity; otherwise, they would remain as holes in the casting. The mold material must also resist fusion with the molten metal, and the sand at the mold surface must be closely packed to give a smooth casting surface.

The making of patterns for foundries requires care and skill. Patterns are uniformly larger than the desired casting in order to compensate for shrinkage during drops of temperature and the liquid-to-solid phase change. Polystyrene foam patterns remain in the mold and evaporate upon contact with the poured metal; wax patterns are melted out of the mold prior to the pouring of the molten metal. Metal molds are used in that type of founding known as die-casting. Often a hollow space is desired within the casting; in this case a core of fine sand is placed in one of the mold halves. Core boxes made of wood, metal, or resin are also used in this regard.

Modern foundries capable of large-scale production are characterized by a high degree of mechanization, automation, and robotics, and microprocessors allow for the accurate control of automated systems. Advances in chemical binders have resulted in stronger molds and cores and more accurate castings. Accuracy and purity are increased in vacuum conditions, and further advances are expected from zero-gravity casting in space.

Foundry Industry

A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal in a mold, and removing the mold material or casting after the metal has solidified as it cools. The most common metals processed are aluminium and cast iron. However, other metals, such as bronze, brass, steel, magnesium, and zinc, are also used to produce castings in foundries. In this process, parts of desired shapes and sizes can be formed.

According to the recent World Census of Castings by Modern Castings, USA India Ranks as 2nd largest casting producer producing estimated 7.44 Million MT of various grades of Castings as per international standards.

The various types of castings which are produced are ferrous, non ferrous, Aluminium Alloy, graded cast iron, ductile iron, Steel etc. for application in Automobiles, Railways, Pumps Compressors & Valves, Diesel Engines, Cement/Electrical/Textile Machinery, Aero & Sanitary pipes & Fittings etc & Castings for special applications. However, Grey iron castings are the major share approx 70 % of total castings produced.

There are approx 4500 units out of which 80% can be classified as Small Scale units & 10% each as Medium & Large Scale units Approx 500 units are having International Quality Accreditation. The large foundries are modern & globally competitive & are working at nearly full capacity. Most foundries use cupolas using LAM Coke. There is growing awareness about environment & many foundries are switching over to induction furnaces & some units in Agra are changing over to coke less cupolas.

Employment The industry directly employs about 5, 00,000 people & indirectly about 1, 50,000 people & is labor intensive. The small units are mainly dependant on manual labor However, the medium & large units are semi/ largely mechanized & some of the large units are world class. 

Product-MixGrey iron is the major component of production followed by steel, ductile iron & non ferrous as shown below.

 

Investments India would need approx. $ 3 Billion in investment to meet the demand of growing domestic industry and strong export drive. Following the economic reforms the Govt. of India has reduced tariffs on imported capital goods as a result the annual average amount of FDI is reported to have increased but is still one tenth of the annual FDI in China. The reforms also encourage the privatization of industry enabling foreign companies to invest or enter into joint ventures with Indian Foundries. FDI projects are permitted an automatic approval process. Several International corporate from USA, EU and East Asian Countries have increased overseas foundry operations in India. i.e. VOLVO foundries in Chennai and Suzuki in Haryana. Sundaram Clayton has joined hands with Cummins. Hyundai Motors, Delphi. Ford India, Tata-Cummins, GM and Ford have contracts of foundry products for export with a value of $ 40 Million. 

Raw material & Energy 

Since 2003 the steep increase in cost of raw materials and energy have resulted in the closure of approx. 500 units, Overall India is exporter of Pig Iron but must import Scrap metals and Coke etc. Cost recovery for material and energy is very difficult as most contracts are long term contracts without any clause for price adjustment. India has to import coke & scrap.Moulding sand is locally available & India has an advantage on this account.

Energy cost typically vary between 12-15% 

Labor 

India has major competitive advantage over the foundry industries in the developed countries. The total labor cost account for 12-15% 

Technology

Govt. of India (GOI) has encouraged technology transfer through JV with foreign Companies and GOI has cooperated with UNIDO with many foundry clusters. Indian foundry industry has an edge over China for producing complex machined and precision castings as per international quality standards. The GOI also helps upgrade foundry clusters. The clusters in Belgaum, Coimbatore and Howrah are undergoing modernization under the industrial infrastructure up gradation scheme. More of such clusters are likely to follow The Institute of Indian Foundry men has plans to strengthen and develop various foundry clusters.

Flow chart of the foundry processes:

Process

In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods.

Mold making

In the casting process a pattern is made in the shape of the desired part. Simple designs can be made in a single piece or solid pattern. More complex designs are made in two parts, called split patterns. A split pattern has a top or upper section, called a cope, and a bottom or lower section called a drag. Both solid and split patterns can have cores inserted to complete the final part shape. Cores are used to create hollow areas in the mold that would otherwise be impossible to achieve. Where the cope and drag separates is called the parting line.

When making a pattern it is best to taper the edges so that the pattern can be removed without breaking the mold. This is called draft. The opposite of draft is an undercut where there is part of the pattern under the mold material, making it impossible to remove the pattern without damaging the mold.

The pattern is made out of wax, wood, plastic or metal. The molds are constructed by several different processes dependent upon the type of foundry, metal to be poured, quantity of parts to be produced, size of the casting and complexity of the casting. These mold processes include:

Sand casting — Green or resin bonded sand mold. Lost-foam casting — Polystyrene pattern with a mixture of ceramic and sand mold. Investment casting — Wax or similar sacrificial pattern with a ceramic mold. Ceramic mold casting — Plaster mold. V-process casting — Vacuum is used in conjunction with thermoformed plastic to form sand

molds. No moisture, clay or resin is needed for sand to retain shape. Die casting — metal mold. Billet (ingot) casting — Simple mold for producing ingots of metal normally for use in other

foundries.

Patternmaking

The making of patterns, is a skilled trade that is related to the trades of tool and die making and mold making, but also often incorporates elements of fine woodworking. Patternmakers learn their skills through apprenticeships and trade schools over many years of experience. Although an engineer may help to design the pattern, it is usually a patternmaker who executes the design.

DesignSprues, gates, risers, cores, and chills

The patternmaker or foundry engineer decides where the sprues, gating systems, and risers are placed with respect to the pattern. Where a hole is desired in a casting, a core may be used which defines a volume or location in a casting where metal will not flow into. Sometimes chills may be placed on a pattern surface prior to molding, which are then formed into the sand mould. Chills are heat sinks which enable localized rapid cooling. The rapid cooling may be desired to refine the grain structure or determine the freezing sequence of the molten metal which is poured into the mould. Because they are at a much cooler temperature, and often a different metal than what is being poured, they do not attach to the casting when the casting cools. The chills can then be reclaimed and reused.

The design of the feeding and gating system is usually referred to as methoding or methods design. It can be carried out manually, or interactively using general-purpose CAD software, or semi-automatically using special-purpose software (such as Auto CAST).

Types of Patterns

Single piece pattern Multi-piece pattern Gated pattern Sweep pattern Skeleton pattern Shell pattern Loose piece pattern

Allowances

To compensate for any dimensional and structural changes which will happen during the casting or patterning process, allowances are usually made in the pattern.

Contraction allowances / Shrinkage allowance

The pattern needs to incorporate suitable allowances for shrinkage; these are called contraction allowances, and their exact values depend on the alloy being cast and the exact sand casting method being used. Some alloys will have overall linear shrinkage of up to 2.5%, whereas other alloys may actually experience no shrinkage or a slight "positive" shrinkage or increase in size in the casting process (notably type metal and certain cast irons). The shrinkage amount is also dependent on the sand casting process employed, for example clay-bonded sand, chemical bonded sands, or other bonding materials used within the sand. This was traditionally accounted for using a shrink rule, which is an oversized rule.

Shrinkage can again be classified into Liquid shrinkage and solid shrinkage. Liquid shrinkage is the reduction in volume during the process of solidification, and Solid shrinkage is the reduction in volume during the cooling of the cast metal.

Generally during shrinkage, all dimensions are going to be altered uniformly, unless there is a restriction.

Draft allowance

When the pattern is to be removed from the sand mold, there is a possibility that any leading edges may break off, or get damaged in the process. To avoid this, a taper is provided on the pattern, so as to facilitate easy removal of the pattern from the mold, and hence reduce damage to edges. The taper angle provided is called the Draft angle. The value of the draft angle depends upon the complexity of the pattern, the type of molding (hand molding or machine molding), height of the surface, etc. Draft provided on the casting 1 to 3 degrees on external surface (5 to 8 internal castings).

Finishing or machining allowance

The surface finish obtained in sand castings is generally poor (dimensionally inaccurate), and hence in many cases, the cast product is subjected to machining processes like turning or grinding in order to improve the surface finish. During machining processes, some metal is removed from the piece. To compensate for this, a machining allowance (additional material) should be given in the casting. 

Shake allowance

Usually during removal of the pattern from the mold cavity, the pattern is rapped all around the faces, in order to facilitate easy removal. In this process, the final cavity is enlarged. To compensate for this, the pattern dimensions need to be reduced. There are no standard values for this allowance, as it is heavily dependent on the personnel. This allowance is a negative allowance, and a common way of going around this allowance is to increase the draft allowance. Shaking of pattern causes enlargement of mould cavity and results in a bigger casting.

Distortion allowance

During cooling of the mold, stresses developed in the solid metal may induce distortions in the cast. This is more evident when the mold is thinner in width as compared to its length. This can be eliminated by initially distorting the pattern in the opposite direction.

Demand

Patterns continue to be needed for sand casting of metals. For the production of gray iron, ductile iron and steel castings, sand casting remains the most widely used process. For aluminum castings, sand casting represents about 12% of the total tonnage by weight (surpassed only by die casting at 57%, and semi-permanent and permanent mold at 19%; based on 2006 shipments). The exact process and pattern equipment is always determined by the order quantities and the casting design. Sand casting can produce as little as one part, or as many as a million copies.

Materials used

Typically, materials used for pattern making are wood, metal or plastics. 

Wax and Plaster of Paris are also used, but only for specialized applications.

Mahogany is the most commonly used material for patterns, primarily because it is soft, light, and easy to work. The downside is that it wears out fast, and is prone to moisture attack.

Metal patterns are more long lasting, and do not succumb to moisture, but they are heavier and difficult to repair once damaged.

Wax patterns are used in a casting process called investment casting. A combination of paraffin wax, bees wax and carnauba wax is used for this purpose.

Plaster of Paris is usually used in making master dies and molds, as it gains hardness quickly, with a lot of flexibility when in the setting stage.

Sand casting

Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 70% of all metal castings are produced via a sand casting process.

Sand casting is relatively cheap and sufficiently refractory even for steel foundry use. In addition to the sand, a suitable bonding agent (usually clay) is mixed or occurs with the sand. The mixture is moistened, typically with water, but sometimes with other substances, to develop strength and plasticity of the clay and to make the aggregate suitable for molding. The sand is typically contained in a system of frames or mold boxes known as a flask. The mold

cavities and gate system are created by compacting the sand around models, or patterns, or carved directly into the sand.

Basic process

There are six steps in this process:

1. Place a pattern in sand to create a mold.2. Incorporate the pattern and sand in a gating system.3. Remove the pattern.4. Fill the mold cavity with molten metal.5. Allow the metal to cool.6. Break away the sand mold and remove the casting.

Molding box and materials

A multi-part molding box (known as a casting flask, the top and bottom halves of which are known respectively as the cope and drag) is prepared to receive the pattern. Molding boxes are made in segments that may be latched to each other and to end closures. For a simple object—flat on one side—the lower portion of the box, closed at the bottom, will be filled with molding sand. The sand is packed in through a vibratory process called ramming, and in this case, periodically screened level. The surface of the sand may then be stabilized with a sizing compound. The pattern is placed on the sand and another molding box segment is added. Additional sand is rammed over and around the pattern. Finally a cover is placed on the box and it is turned and unlatched, so that the halves of the mold may be parted and the pattern with its sprue and vent patterns removed. Additional sizing may be added and any defects introduced by the removal of the pattern are corrected. The box is closed again. This forms a "green" mold which must be dried to receive the hot metal. If the mold is not sufficiently dried a steam explosion can occur that can throw molten metal about. In some cases, the sand may be oiled instead of moistened, which makes possible casting without waiting for the sand to dry. Sand may also be bonded by chemical binders, such as furane resins or amine-hardened resins.

Chills

To control the solidification structure of the metal, it is possible to place metal plates, chills, in the mold. The associated rapid local cooling will form a finer-grained structure and may form a somewhat harder metal at these locations. In ferrous castings, the effect is similar to quenching metals in forge work. The inner diameter of an engine cylinder is made hard by a chilling core. In other metals, chills may be used to promote directional solidification of the casting. In controlling the way a casting freezes, it is possible to prevent internal voids or porosity inside castings.

Cores

To produce cavities within the casting—such as for liquid cooling in engine blocks and cylinder heads—negative forms are used to produce cores. Usually sand-molded, cores are inserted into the casting box after removal of the pattern. Whenever possible, designs are made that avoid the use of cores, due to the additional set-up time and thus greater cost.

With a completed mold at the appropriate moisture content, the box containing the sand mold is then positioned for filling with molten metal—typically iron, steel, bronze, brass, aluminium, magnesium alloys, or various pot metal alloys, which often include lead, tin, and zinc. After filling with liquid metal the box is set aside until the metal is sufficiently cool to be strong. The sand is then removed revealing a rough casting that, in the case of iron or steel, may still be glowing red. When casting with metals like iron or lead, which are significantly heavier than the casting sand, the casting flask is often covered with a heavy plate to prevent a problem known as floating the mold. Floating the mold occurs when the pressure of the metal pushes the sand above the mold cavity out of shape, causing the casting to fail.

After casting, the cores are broken up by rods or shot and removed from the casting. The metal from the sprue and risers is cut from the rough casting. Various heat treatments may be applied to relieve stresses from the initial cooling and to add hardness—in the case of steel or iron, by quenching in water or oil. The casting may be further strengthened by surface compression treatment—like shot peening—that adds resistance to tensile cracking and smoothes the rough surface.

Design requirements

The part to be made and its pattern must be designed to accommodate each stage of the process, as it must be possible to remove the pattern without disturbing the molding sand and to have proper locations to receive and position the cores. A slight taper, known as draft, must be used on surfaces perpendicular to the parting line, in order to be able to remove the pattern from the mold. This requirement also applies to cores, as they must be removed from the core box in which they are formed. The sprue and risers must be arranged to allow a proper flow of metal and gasses within the mold in order to avoid an incomplete casting. Should a piece of core or mold become dislodged it may be embedded in the final casting, forming sand pit, which may render the casting unusable. Gas pockets can cause internal voids. These may be immediately visible or may only be revealed after extensive machining has been performed. For critical applications, or where the cost of wasted effort is a factor, non-destructive testing methods may be applied before further work is performed.

Mechanized sand molding

The mechanized molding lines consisted of sand slingers and/or jolt-squeeze devices that compacted the sand in the flasks. Subsequent mold handling was mechanical using cranes, hoists and straps. After core setting the copes and drags were coupled using guide pins and clamped for closer accuracy. The molds were manually pushed off on a roller conveyor for casting and cooling.

Automatic high pressure sand molding lines

Increasing quality requirements made it necessary to increase the mold stability by applying steadily higher squeeze pressure and modern compaction methods for the sand in the flasks. In early fifties the high pressure molding was developed and applied in mechanical and later automatic flask lines. The first lines were using jolting and vibrations to pre-compact the sand in the flasks and compressed air powered pistons to compact the molds.

Horizontal sand flask molding

In the first automatic horizontal flask lines the sand was shot or slung down on the pattern in a flask and squeezed with hydraulic pressure of up to 140 bars. The subsequent mold handling including turn-over, assembling, pushing-out on a conveyor was accomplished either manually or automatically. In the late fifties hydraulically powered pistons or multi-piston systems were used for the sand compaction in the flasks. This method produced much more stable and accurate molds than it was possible manually or pneumatically. In the late sixties mold compaction by fast air pressure or gas pressure drop over the pre-compacted sand mold was developed (sand-impulse and gas-impact).

The major disadvantages of these systems is high spare parts consumption due to multitude of movable parts, need of storing, transporting and maintaining the flasks and productivity limited to approximately 90–120 molds per hour.

Vertical sand flask-less molding

A flask-less molding process by using vertically parted and poured molds. The first line could produce up to 240 complete sand molds per hour. Molding lines can achieve a molding rate of 550 sand molds per hour and requires only one monitoring operator. Maximum mismatch of two mold halves is 0.1 mm (0.0039 in). Although very fast, vertically parted molds are not typically used by jobbing foundries due to the specialized tooling needed to run on these machines. Cores need to be set with a core mask as opposed to by hand and must hang in the mold as opposed to being set on parting surface.

Match-plate sand molding

The principle of the matchplate, meaning pattern plates with two patterns on each side of the same plate, was developed and patented in 1910, fostering the perspectives for future sand molding improvements. However, first in the early sixties the American company Hunter Automated Machinery Corporation launched its first automatic flaskless, horizontal molding line applying the matchplate technology.

The matchplate molding technology is today used widely. Its great advantage is inexpensive pattern tooling, easiness of changing the molding tooling, thus suitability for manufacturing castings in short series so typical for the jobbing foundries. Modern matchplate molding machine is capable of high molding quality, less casting shift due to machine-mold mismatch (in some cases less than 0.15 mm (0.0059 in)), consistently stable molds for less grinding and improved parting line definition. In addition, the machines are enclosed for a cleaner, quieter working environment with reduced operator exposure to safety risks or service-related problems.

Melting

Melting metal in a crucible for casting

Melting is performed in a furnace. Virgin material, external scrap, internal scrap, and alloying elements are used to charge the furnace. Virgin material refers to commercially pure forms of the primary metal used to form a particular alloy. Alloying elements are either pure forms of an alloying element, like electrolytic nickel, or alloys of limited composition, such as ferroalloys or master alloys. External scrap is material from other forming processes such as punching, forging, or machining. Internal scrap consists of gates, risers, defective castings, and other extraneous metal oddments produced within the facility.

The process includes melting the charge, refining the melt, adjusting the melt chemistry and tapping into a transport vessel. Refining is done to remove deleterious gases and elements from the molten metal to avoid casting defects. Material is added during the melting process to bring the final chemistry within a specific range specified by industry and/or internal standards. Certain fluxes may be used to separate the metal from slag and/or dross and degassers are used to remove dissolved gas from metals that readily dissolve certain gasses. During the tap, final chemistry adjustments are made.

Furnace

Furnaces are refractory lined vessels that contain the material to be melted and provide the energy to melt it. Modern furnace types include electric arc furnaces (EAF), induction furnaces, cupolas, reverberatory, and crucible furnaces. Furnace choice is dependent on the alloy system quantities produced. For ferrous materials EAFs, cupolas, and induction furnaces are commonly used. Reverberatory and crucible furnaces are common for producing aluminium, bronze, and brass castings.

The design can be optimized based on multiple factors. Furnaces in foundries can be any size, ranging from small ones used to melt precious metals to furnaces weighing several tons, designed to melt hundreds of pounds of scrap at one time. They are designed according to the type of metals that are to be melted. Furnaces must also be designed based on the fuel being used to produce the desired temperature. For low temperature melting point alloys, such as zinc or tin, melting furnaces may reach around 500° C. Electricity, propane, or natural gas is usually used to achieve these temperatures. For high melting point alloys such as steel or nickel based alloys, the furnace must be designed for temperatures over 1600° C. The fuel used to reach these high temperatures can be electricity (as employed in electric arc furnaces) or coke.

The majority of foundries specializes in a particular metal and has furnaces dedicated to these metals. For example, an iron foundry (for cast iron) may use a cupola, induction furnace, or EAF, while a steel foundry will use an EAF or induction furnace. Bronze or brass foundries use crucible furnaces or induction furnaces. Most aluminium foundries use either electric resistance or gas heated crucible furnaces or reverberatory furnaces.

Melting furnaces used in the foundry industry are of diverse configurations. The selection of the melting unit is one of the most important decisions foundries must make with due consideration to several important factors including:

1. The temperature required to melt the alloy2. The melting rate and quantity of molten metal required3. The economy of installation and operation4. Environmental and waste disposal requirements

Induction Furnaces

The principle of induction melting is that a high voltage electrical source from a primary coil induces a low voltage, high current in the metal or secondary coil. Induction heating is simply a method of transferring heat energy.

Induction furnaces are ideal for melting and alloying a wide variety of metals with minimum melt losses, however, little refining of the metal is possible. There are two main types of induction furnace: coreless and channel.

The heart of the coreless induction furnace is the coil, which consists of a hollow section of heavy duty, high conductivity copper tubing which is wound into a helical coil. Coil shape is contained within a steel shell and magnetic shielding is used to prevent heating of the supporting shell. To protect it from overheating, the coil is water-cooled, the water being re-circulated and cooled in a cooling tower. The shell is supported on trunnions on which the furnace tills to facilitate pouring.

The crucible is formed by ramming a granular refractory between the coil and a hollow internal former which is melted away with the first heat leaving a sintered lining.

The power cubicle converts the voltage and frequency of main supply, to that required for electrical melting. Frequencies used in induction melting vary from 50 cycles per second (mains frequency) to 10,000 cycles per second (high frequency). The higher the operating frequency, the greater the maximum amount of power that can be applied to a furnace of given capacity and the lower the amount of turbulence induced.

When the charge material is molten, the interaction of the magnetic field and the electrical currents flowing in the induction coil produce a stirring action within the molten metal. This stirring action forces the molten metal to rise upwards in the centre causing the characteristic meniscus on the surface of the metal. The degree of stirring action is influenced by the power and frequency applied as well as the size and shape of the coil and the density and viscosity of the molten metal. The stirring action within the bath is important as it helps with mixing of alloys and melting of turnings as well as homogenizing of temperature throughout the furnace. Excessive stirring can increase gas pick up, lining wear and oxidation of alloys.

In all coreless induction furnaces, there is an “ideal” refractory wall thickness, carefully calculated by the manufacturers to offer the optimum melting performance. Designed into this calculation are

1. Safety considerations2. Electrical characteristics of the coil3. Metallic charge electrical conductivity4. Structural and refractory considerations5. Operational constraints 6. Production needs.

When the furnace melt diameter is reduced by buildup, the melting process becomes compromised. Traditionally, to remove the buildup, furnace operators must mechanically scrape the lining that may also damage the refractory face. During this process, the power is generally reduced for safety reasons. The result is a reduction in the percent power utilization that causes the energy consumption to increase, which is graphically shown below:

.

Furnace operators often scrape slag buildup from the lining, which may damage the refractory face. During this process, power is generally reduced for safety considerations. The result is a reduction in the percent power utilization that causes the energy consumption to increase.

Slag formation is inevitable during melting. In a coreless induction furnace, slag residuals normally deposit along the refractory walls and within the active power coil. The composition of slag varies with the type of metal being melted in a coreless furnace. The cleanliness of the metallic charge, (consisting of sand-encrusted gates and risers, or rust- and dirt-encrusted scrap) significantly affects the type of slag formed during the melting operation. Because these oxides and non-metallic’s are not soluble in the molten metal, they float in the liquid metal as an emulsion. This emulsion of slag particles remains stable if the molten metal is continuously agitated, the result of the magnetic stirring inherent in coreless induction melting. Until the particle size of the nonmetallic increases to the point where buoyancy effects countervail the stirring action, the particle will remain suspended. When flotation effects become great enough, non-metallic’s rise to the surface of the molten metal and agglomerate as slag. Once the nonmetallics coalesce into a floating mass on the liquid metal they can be removed. The use of fluxes accelerates these processes.

Fluxes will help to maintain slags at a melting point below the coldest temperature in the system; to prevent slags and other insolubles from freezing on cooler refractory surfaces; to encourage flotation of the emulsified oxides; and to reduce the melting point of the slag below the lowest temperature in the furnace and liquid metal handling system.

When slag makes contact with the hot face of the refractory wall that is colder than the melting point of the slag, the cooling slag will adhere to the lining. This adhering material is called buildup. High-melting point slags are especially prone to promoting buildup. If not prevented from forming or not removed as it forms, buildup will reduce the overall efficiency.

Controlling buildup allows for continuous furnace operation. Buildup can be controlled or eliminated with the addition of fluxes. It should be noted that in the past ferrous foundries have been discouraged from using fluxes by refractory companies. However, new developments in flux chemistry (Redux U.S. Patent 7, 68,473) allow fluxes to be used in furnaces lined with even silica refractory, without refractory attack. Generally, adding fluxes ensures that slags have a melting point below the coldest temperature in the system. Fluxes can help prevent slags and other insolubles from freezing on the cooler refractory surfaces. Using a flux allows for the flotation of the emulsified oxides; it also reduces the melting point of the slag to below the lowest temperature encountered in the melting furnace and associated liquid metal handling system.

Improper use of fluxes can rapidly erode refractory furnace linings, especially if potent fluorspar-based fluxes are used. However, if a flux is carefully engineered for specific applications and used properly, refractory life may actually increase. Some foundries using specialty fluxes have reported increased refractory life. One large foundry significantly increased lining life from 11 months to 26 months just by incorporating Redux in their operation. Refractory life also can be extended by reduced damage due to mechanical chipping required to remove tenacious slag deposits. Elimination of buildup optimizes power utilization, thereby reducing energy consumption.

Foundry G is a medium-sized manufacturer of gray iron castings. It has historically experienced extensive slag buildup on the upper sidewalls of its four 3-ton medium-frequency coreless induction furnaces in a semi-batch melting operation. Foundry G’s charge consists of 100% metallic fines. Each coreless furnace is lined with a silica dry vibratable refractory. During melting, slag generation and accompanying buildup immediately reduced furnace capacity and contributed to increased power consumption. After 48 hours of operation, three inches of buildup occurred along the entire sidewall. Foundry G initially incorporated 2 lb of Redux EF40L flux per ton of charge, added to each back-charge to determine its effect on buildup. EF40L was placed in the furnace before back charging on top of existing molten metal to ensure excellent mixing (a minimum 50% molten metal bath). Immediate improvements were observed and buildup along the sidewalls was essentially eliminated. Foundry G observed the following benefits by using Redux on a continuous basis:

1. Using Redux EF40 reduced “bridging” tendencies due to cleaner refractory walls2. Reduced power consumption during each melt3. Hourly maintenance from scraping was greatly reduced4. Consistent furnace capacities, with less interruption for charging delays5. Improved “electrical coupling” was observed with improved temperature control6. No adverse effects on the dry vibratable silica refractory linings.

Foundry D operates two, 12-metric ton, 9,000-kW, 180-Hz medium frequency coreless furnaces batch melting ductile-base iron. Each 12-metric ton charge consists of 15% ductile pig iron, followed by the addition of 35% carbon steel clips and 50% ductile returns. Tap temperatures average 2,775°F. Current batch melt time (from charging to completely molten) is typically 40-50 minutes per heat. The furnace is lined with a dry-vibratable silica lining. Without fluxing, buildup would occur along the sidewalls of the furnace, including in the active power coil. This caused delays in charging, reduced furnace capacity, and longer downtime for scraping the lining, adding an additional 5 to 15 minutes per heat. Buildup above the molten metal line (top cap area) caused additional production delays. By adding 6 lbs of Redux EF40 flux with each charge, slag buildup is eliminated. Refractory lining life increased from 4,500 tons throughput to 7,500 tons per lining installation. Foundry D continues to realize the following benefits from fluxing:

1. Furnace volume remains constant at 12 metric tons2. Consistent melting cycles of 40-50 minutes for each charge3. Less frequent top cap cleaning4. Delays at the mold line for molten iron was reduced by 50%5. Reduced mechanical damage to the refractory by eliminating scraping.

Insoluble buildup and slag related problems have become serious issues for foundries. These problems will likely increase as the quality of scrap continues to deteriorate. Using fluxes properly can alleviate these challenges while increasing melting efficiency and saving foundries time and electricity, and most important, improving profitability.

Heat recovery can provide significant energy and cost savings as well as environmental benefits. Today, as energy costs escalate, heat recovery efforts may lead to an attractive payback and help many foundries reduce their carbon footprints, as well as contribute to a more sustainable society.

To remove the heat generated by the induction coil, as well as the thermal loss from the refractory system in the induction furnace, water cooling is commonly used. This heated fluid is typically pumped to an exterior mounted cooling tower. In the induction melt shop, the high efficiency power supply powering the furnace typically has a low water temperature rise on the electrical/ electronic components. Thus, heat recovery for the power supply system is typically not economical. However, in some cases, this temperature rise is fed to a water-to-water heat exchanger feeding the furnace and raising the inlet temperature, thus enhancing overall recovery. While almost all the heat is produced in the melting furnace and, in most cases under full power, an expected 40°F+ temperature rise is common. This temperature level is lower than the drain temperature sensor range/furnace safety cutout. Typical furnace drain water runs in the 140°F temperature range. Some applications may be in the 150°F range or higher, based on the application and type of system.

While today’s furnaces offer high electrical efficiency, a sizable amount (20-30%) of the rated power can be recovered from the furnace coil water temperature generated by the I2R losses (current on the coil), as well as thermal refractory loss in the furnace. To recover the heat in the cooling water based on geographical location, a number of options exist. Each location, as well as the cooling system type, must be considered for a cost-effective air handler and cooling system selection.

A heat recovery system should always be considered as a secondary selection after choosing the highest efficiency melt system that offers the lowest energy consumption per ton of melted metal.

As noted, today’s melt shops need to look at the long term and always keep in mind the “life cycle cost,” supplementing cost reductions with secondary selections, such as heat recovery, zero discharge water cooling systems, charging systems or, the most recent addition, the Automated Robotic Melt Shop System. All secondary selections carry a relatively small cost added up front with sizable benefits realized during the years of operation.

Metal and pouring sections of the foundry should be provided with hard hats, tinted eye protection and face shields, aluminized clothing such as aprons, gaiters or spats (lower-leg and foot coverings) and boots. Use of protective equipment should be mandatory, and there should be adequate instruction in its use and maintenance. High standards of housekeeping and exclusion of water to the highest degree possible are needed in all areas where molten metal is being manipulated.

Where large ladles are slung from cranes or overhead conveyors, positive ladle-control devices should be employed to ensure that spillage of metal cannot occur if the operator releases his or her hold. Hooks holding molten metal ladles must be periodically tested for metal fatigue to prevent failure.

The pouring station is provided with a compensating hood with a direct air supply. The poured mould proceeds along the conveyor through an exhausted cooling tunnel until shakeout. In case moulds may be poured on a foundry floor and allowed to burn off there. In this situation, the ladle should be equipped with a mobile exhaust hood.

Tapping and transport of molten iron and charging of electric furnaces creates exposure to iron oxide and other metal oxide fumes. Pouring into the mould ignites and pyrolyses organic materials, generating large amounts of carbon monoxide, smoke, carcinogenic polynuclear aromatic hydrocarbons (PAHs) and pyrolysis products from core materials which may be carcinogenic and also respiratory sensitizers. Moulds containing large polyurethane bound cold box cores release a dense, irritating smoke containing isocyanates and amines. The primary hazard control for mould burn off is a locally exhausted pouring station and cooling tunnel.

In foundries with roof fans for exhausting pouring operations, high metal fume concentrations may be found in the upper regions where crane cabs are located. If the cabs have an operator, the cabs should be enclosed and provided with filtered, conditioned air.

Cold box

Use organic and inorganic binders that strengthen the mold by chemically adhering to the sand. This type of mold gets its name from not being baked in an oven like other sand mold types. This type of mold is more accurate dimensionally than green-sand molds but is more expensive. Thus it is used only in applications that necessitate it.

Cold Box Process As the name already indicates, the cold box process is based on the reaction of two components with polyurethane. A poly addition of the part 1 component, the phenol-formaldehyde resin, and the part 2 components, the isocyanate, is initiated through basic catalysis, usually by means of gassing with a tertiary amine.

The hardening reaction is very fast, which makes the cold box process attractive for the highly productive production of series components in particular. The high strength level enables fast and automated core production with process reliability. The cores can be cast just a short time after production and feature high thermal stability, which also allows the dimensionally accurate production of water jackets or oil duct cores. Due to their almost pH-neutral properties, high proportions of mechanically or thermally treated used sands from cold box production can be reused.

Properties and advantages

Rapid model change possible (cold core boxes) Excellent thermal stability Short cycle times and high productivity thanks to rapid hardening Secure core extraction, low core fracture thanks to high initial strength High dimensional accuracy Smooth core surfaces Low tooling and energy costs

The main reason why the cold box process is so successful is that it makes it possible to achieve complicated core geometries with high dimensional accuracy and high productivity. When looking at the overall process of core production, the cold box process is distinguished by the fact that the cores that were shot can be mounted to core packages and coated directly after production, i.e. short cycle times are possible from the shot to the core that is ready to use. Excellent disintegration after casting and various possibilities of regeneration with very high reuse rates round off the picture.

Fundamentals of the process, the components, phenol-formaldehyde resin and isocyanate, are mixed with the mold material, compressed in a core box and hardened with a catalyst. The

addition rates can vary depending on the application and mold material; in relation to the mold material, they are usually between 0.4% and 1.2% per part. The binder bridges that develop during the reaction (see SEM photo) ensure that the molding material compound is stable. After casting, the casting heat has weakened the binder bridges to the extent that the sand can be removed from the cast part by means of mechanical input.

SEM photo of binder bridges

Advantage: Economic and automatic core production and excellent possibilities for “online production.” The cores are inserted into the ingot or green sand mold as soon as possible after production and then cast.

Requirements for cold boxThe most important prerequisite for standing one’s ground in the international competition is to produce high quality cast parts with intricate geometry at a reasonable price. The most important market requirements for the cold box resin are:

High reactivity Reduced emission and odor pollution or a low concentration of monomers (free phenol

and free formaldehyde) Reduction of amine consumption Long processing time (bench life) of the sand mixture High core box cleanliness High strength level High thermal resistance (thermal stability) High stability with respect to water-based coatings (hydro-stability)

In general, we can distinguish between two methods of sand casting; the first one using green sand and the second being the air set method.

Green sand

These expendable molds are made of wet sands that are used to make the mold's shape. The name comes from the fact that wet sands are used in the molding process. Green sand is not green in color, but "green" in the sense that it is used in a wet state (akin to green wood). Unlike the name suggests, "Green sand" is not a type of sand on its own, but is rather a mixture of:

Silica sand (SiO2), or chromite sand (FeCr2O), or zircon sand (ZrSiO4), 75 to 85%, or olivine, or staurolite, or graphite.

bentonite (clay), 5 to 11% water, 2 to 4% inert sludge 3 to 5% Anthracite (0 to 1%)

There are many recipes for the proportion of clay, but they all strike different balances between mold ability, surface finish, and ability of the hot molten metal to degas. The coal typically referred to in foundries as sea-coal, which is present at a ratio of less than 5%, partially combusts in the presence of the molten metal leading to off gassing of organic vapors. Green Sand for non-ferrous metals do not use coal additives since the CO created is not effective to prevent oxidation. Green Sand for aluminum typically uses olivine sand (a mixture of the minerals forsterite and fayalite which are made by crushing dunite rock). The choice of sand has a lot to do with the temperature that the metal is poured. At the temperatures that copper and iron are poured, the clay gets inactivated by the heat in that the montmorillonite is converted to illite, which is non-expanding clay. Most foundries do not have the very expensive equipment to remove the burned out clay and substitute new clay; so instead, those that pour iron typically work with silica sand that is inexpensive compared to the other sands. As the clay is burned out, newly mixed sand is added and some of the old sand is discarded or recycled into other uses. Silica is the least desirable of the sands since metamorphic grains of silica sand have a tendency to explode to form sub-micron sized particles when thermally shocked during pouring of the molds. These particles enter the air of the work area and can lead to silicosis in the workers. Iron foundries spend a considerable effort on aggressive dust collection to capture this fine silica. The sand also has the dimensional instability associated with the conversion of quartz from alpha quartz to beta quartz at 1250 degrees F. Often additives such as wood flour are added to create a space for the grains to expand without deforming the mold. Olivine, Chromites, etc. are used because they do not have a phase conversion that causes rapid expansion of the grains, as well as offering greater density, which cools the metal faster and produces finer grain structures in the metal. Since they are not metamorphic, they do not have the polycrystals found in silica, and subsequently do not form hazardous sub-micron sized particles.

The "air set" method

The air set method uses dry sand bonded with materials other than clay, using a fast curing adhesive. The latter may also be referred to as no bake mold casting. When these are used, they are collectively called "air set" sand castings to distinguish them from "green sand" castings. Two types of molding sand are natural bonded (bank sand) and synthetic (lake sand); the latter is generally preferred due to its more consistent composition.

With both methods, the sand mixture is packed around a pattern, forming a mold cavity. If necessary, a temporary plug is placed in the sand and touching the pattern in order to later form a channel into which the casting fluid can be poured. Air-set molds are often formed with the help

of a casting flask having a top and bottom part, termed the cope and drag. The sand mixture is tamped down as it is added around the pattern, and the final mold assembly is sometimes vibrated to compact the sand and fill any unwanted voids in the mold. Then the pattern is removed along with the channel plug, leaving the mold cavity. The casting liquid (typically molten metal) is then poured into the mold cavity. After the metal has solidified and cooled, the casting is separated from the sand mold. There is typically no mold release agent, and the mold is generally destroyed in the removal process.

The accuracy of the casting is limited by the type of sand and the molding process. Sand castings made from coarse green sand impart a rough texture to the surface, and this makes them easy to identify. Castings made from fine green sand can shine as cast but are limited by the depth to width ratio of pockets in the pattern. Air-set molds can produce castings with smoother surfaces than coarse green sand but this method is primarily chosen when deep narrow pockets in the pattern are necessary, due to the expense of the plastic used in the process. Air-set castings can typically be easily identified by the burnt color on the surface. The castings are typically shot blasted to remove that burnt color. Surfaces can also be later ground and polished, for example when making a large bell. After molding, the casting is covered with a residue of oxides, silicates and other compounds. This residue can be removed by various means, such as grinding, or shot blasting.

During casting, some of the components of the sand mixture are lost in the thermal casting process. Green sand can be reused after adjusting its composition to replenish the lost moisture and additives. The pattern itself can be reused indefinitely to produce new sand molds. The sand molding process has been used for many centuries to produce castings manually. Since 1950, partially automated casting processes have been developed for production lines.

Sodium Silicate/CO2Coremaking

One of the easiest modern core making processes for instructional and small foundries to use is the sodium silicate/ CO2process. In this process, liquid sodium silicate is mixed with the sand. The sand is rammed into a core box and cured by passing CO2 through the core. Sodium silicate cores are very strong. The bond is so strong that hot tearing and collapsibility can be an issue. Cores made from this process produce less gas than other processes. Cleanup is also easy since water can dissolve the sodium silicate. The environmental friendliness, ease of cleanup, and simplicity makes the process very simple to conduct in the teaching foundry.

The sodium silicate/CO2process hardens through the following reaction: Na2Si2O5.H2O (l) +CO2 (g) = SiO2 (gel) +Na2CO3.H2O (glass)The silica gel that is formed binds individual sand grains together. Sand temperature is critical in this process. The core should be between 25ºC to 30ºC (75ºF to 85ºF). Below 15ºC (60ºF) the reaction proceeds very slowly, and more CO2 or gassing time is required to fully cure the core. Above 30ºC, excessive amounts of moisture evaporate during the curing process, resulting in a very weak and brittle bond. It should also be noted that the gel tends to hydrate, which causes a reduction in binder strength. This limits core shelf life to about one month. Experience at SVSU has found shelf life can be as long as two months during winter. There are several things to keep in mind when developing a recipe for cores. Most liquid sodium silicate has a ratio of 3.22 parts silica to one part sodium oxide. This material is not suitable for

foundry core making. A ratio of 2.4 to 2.6 is appropriate for cores. Schools should contact one of the many foundry industry suppliers or a local foundry to get the correct material. If you cannot obtain this, you can dilute the liquid sodium silicate with water to reach the desired ratio. Typical binder levels are between 2-5% by weight of sand. Collapsibility can be improved by adding 0.25-0.5% by weight of sand of wheat flour, starch, molasses, or oat meal. Carbon dioxide gas pressure should be between 5-15 psi. Typical gassing times are 5-20 seconds. Thick cores may require a series of small holes be created in the sand to distribute the CO2.

Mixing Equipment Sodium silicate can be mixed using a variety of equipment. Small amounts of core sand can be prepared using heavy duty kitchen stand mixers. These are very suitable for small teaching foundries. Mullers, high intensity mixers, and continuous mixers are normally used by industry.Mixing equipment and core boxes should be cleaned immediately with water. If not cleaned, then a hard, rock-like deposit forms. The deposit can be removed by soaking it with water.

Gassing Equipment Gassing equipment is relatively simple. A cylinder of CO2 with a regulator and some type of diffusing system are all that are needed. A simple diffuser system made from an air gun, PVC end cap, and rubber pipe reducer. Large core boxes should have a cover with a hole for the CO2to enter and an open cavity above the core sand.

Procedure 1) Measure out sand, sodium silicate binder, and wheat flour. 2) Place the sand in a mixing bowl and mix for 2 minutes. Use setting 2 on the mixer. 3) Add the sodium silicate binder to the sand and mix for 4 minutes. 4) Add your wheat flour and mix for 2 minutes 5) Remove the sand and ram it into the core box. 6) Using the cake tester place several small holes into the sand. The depth of each hole should be about three quarters of the core thickness 7) Rap the core box prior to gassing. 8) Making sure the CO2gas pressure is 10psi, gas the core for the specified time. 9) Remove the core and any loose sand in the core box.

No bake molds

No bake molds are expendable sand molds, similar to typical sand molds, except they also contain a quick-setting liquid resin and catalyst. Rather than being rammed, the molding sand is poured into the flask and held until the resin solidifies, which occurs at room temperature. This type of molding also produces a better surface finish than other types of sand molds. Because no heat is involved it is called a cold-setting process. Common flask materials that are used are wood, metal, and plastic. Common metals cast into no bake molds are brass, iron ferrous, and aluminum alloys.

No-bake Casting

As the metal casting industry’s second favorite method for producing cast components (green sand molding is the first), no-bake molding has proven its worth as an efficient means to produce medium and low volumes of complex castings in both ferrous and nonferrous metals.In the no-bake process, sand is mixed with a chemical binder/catalyst system and then molded around the cope and drag halves of the tooling. After a specified period of time (from as little as 10 sec to as long as the foundry requires depending upon mold size), the sand mixture hardens (resembling a brick in strength) to form the mold halves and the tooling is drawn. Then, a refractory coating may be applied to both mold halves before they are brought together to form one complete mold for pouring. (No-bake molded cores also can be produced using a similar method and assembled into the mold to form more complex shapes.)No-bake molding, like green sand molding, is known for its versatility. Virtually all metals can be cast via no-bake molding with component weights ranging from less than a pound to several hundred thousand pounds. For casting designers, no-bake molding offers:

1. good dimensional tolerances (±0.005-0.015) because the rigidity of the mold withstands the pressures exerted by the molten metal during casting;

2. Compatibility with most pattern materials, including wood, plastic, metal, fiberglass and Styrofoam, allowing for inexpensive tooling options for casting runs as low as one. In addition, no-bake molding imparts minimal tooling wear;

3. Design flexibility for intricate casting shapes. The rigidity and tensile strength of no-bake molds allows for thin sections of 0.1-in. to be routinely produced. In addition, mold strength allows for minimal draft and radii requirements in casting design.

4. reduced opportunity for gas-related defects as the nitrogen content of most binder systems used for no-bake molding minimize susceptibility to gas porosity;

5. Fine surface finishes that can be upgraded further with the mold and core coatings to support special finishing on the cast components such as paint or dressing. In addition, no-bake casters can alter their molding media make-up from basic silica sand to higher-end media such as chromite or zircon sand for applications requiring X-ray quality and extreme pressure tightness;

6. Ability to work well with unique metal casting quality enhancement tools such as metal filters, ceramic runner systems and exothermic risers to improve casting properties.

7. Low to medium volume production capability with runs from 1-5000 parts/yr.The key, as with any casting process, is to ensure the casting design is optimized to take advantage of the benefits afforded by no-bake molding.

No-bake molding typically is an option for production runs from 1-5000 castings/yr . Due to the curing time required for the chemicals to harden the mold as well as the methods to distribute the molding media on the pattern, the high productions achievable with green sand, permanent mold or die-casting aren’t possible with nobake. No-bake molding prefers cast components with higher complexities in low to medium volume runs.Anything that can be cast in a green sand mold can be cast in a nobake mold, but the reverse isn’t true. Besides the number of castings that need to be produced, the decision between green sand

and nobake comes down to the complexity of the casting design. Since unfinished nobake molded castings (without machining) typically cost 20-30% higher than green sand, designers and purchasers sourcing to nobake molding must offset this price difference by taking advantage of what the process offers. Significant reductions in machining costs can be achieved through the process’ tight tolerances and minimal dimensional variability and by designing in complex shapes and geometries, thin walls, and reduced draft, radii and machine stock.Tooling cost also plays a factor in this comparison. Green sand molds require compaction force during the molding process, which means that the tooling must be able to withstand this force. No-bake tooling doesn’t have to withstand a strong compaction force (often only light vibrations), allowing wood and plastic to be viable tooling materials. In addition, the lack of compaction force in molding also allows nobake molders to use loose pattern pieces and other innovative tooling options to increase casting complexity and add design features to the components.Pattern materials for nobake molding include wood, plastic, fiberglass, metal and Styrofoam. This allows the tooling cost to be minimized as much as if not more than any other production casting process. In addition, with the Styrofoam option for the Full Mold process hard tooling doesn’t even have to be created for small production runs.Designing castings for traditional nobake molding follows many of the same principles used in all other casting processes. Draft is required so patterns can be drawn, sharp corners and angles should be minimized and uniform section thicknesses (especially in the same plane) should be employed as much as possible. However, the process does allow for more daring designs.

Mold materials

There are four main components for making a sand casting mold: 

1) Base sand 2) A binder 3) Additives 4) A parting compound.

Molding sands

Molding sands, also known as foundry sands, are defined by eight characteristics: 1) refractoriness 2) chemical inertness 3) permeability, 3) surface finish, 4) cohesiveness, 5) flowability, 6) collapsibility, 7) availability/cost.

Refractoriness — this refers to the sand's ability to withstand the temperature of the liquid metal being cast without breaking down. For example some sands only need to withstand 650 °C (1,202 °F) if casting aluminum alloys, whereas steel needs sand that will withstand 1,500 °C (2,730 °F). Sand with too low a refractoriness will melt and fuse to the casting.

Chemical inertness — the sand must not react with the metal being cast. This is especially important with highly reactive metals, such as magnesium and titanium.

Permeability — this refers to the sand's ability to exhaust gases. This is important because during the pouring process many gases are produced, such as hydrogen, nitrogen, carbon, and steam, which must leave the mold otherwise casting defects, such as blow holes and gas holes, occur in the casting. Note that for each cubic centimeter (cc) of water added to the mold 16,000 cc of steam is produced.

Surface finish — the size and shape of the sand particles defines the best surface finish achievable, with finer particles producing a better finish. However, as the particles become finer (and surface finish improves) the permeability becomes worse.

Cohesiveness (or bond) — this is the ability of the sand to retain a given shape after the pattern is removed.

Flowability – The ability for the sand to flow into intricate details and tight corners without special processes or equipment.

Collapsibility — this is the ability of the sand to be easily stripped off the casting after it has solidified. Sands with poor collapsibility will adhere strongly to the casting. When casting metals that contract a lot during cooling or with long freezing temperature ranges sand with poor collapsibility will cause cracking and hot tears in the casting. Special additives can be used to improve collapsibility.

Availability/cost — the availability and cost of the sand is very important because for every ton of metal poured, three to six tons of sand is required. Although sand can be screened and reused, the particles eventually become too fine and require periodic replacement with fresh sand.

In large castings it is economical to use two different sands, because the majority of the sand will not be in contact with the casting, so it does not need any special properties. The sand that is in contact with the casting is called facing sand, and is designed for the casting on hand. This sand will be built up around the pattern to a thickness of 30 to 100 mm (1.2 to 3.9 in). The sand that fills in around the facing sand is called backing sand. This sand is simply silica sand with only a small amount of binder and no special additives.

Types of base sands

Base sand is the type used to make the mold or core without any binder. Because it does not have a binder it will not bond together and is not usable in this state.

Silica sand

Silica (SiO2) sand is the sand found on a beach and is also the most commonly used sand. It is made by either crushing sandstone or taken from natural occurring locations, such as beaches and river beds. The fusion point of pure silica is 1,760 °C (3,200 °F), however the sands used have a lower melting point due to impurities. For high melting point casting, such as steels, a minimum of 98% pure silica sand must be used; however for lower melting point metals, such as cast iron and non-ferrous metals, a lower purity sand can be used (between 94 and 98% pure).

Silica sand is the most commonly used sand because of its great abundance, and, thus, low cost (therein being its greatest advantage). Its disadvantages are high thermal expansion, which can cause casting defects with high melting point metals, and low thermal conductivity, which can lead to unsound casting. It also cannot be used with certain basic metal because it will chemically interact with the metal forming surface defect. Finally, it causes silicosis in foundry workers.

Olivine sand

Olivine is a mixture of orthosilicates of iron and magnesium from the mineral dunite. Its main advantage is that it is free from silica; therefore it can be used with basic metals, such as manganese steels. Other advantages include a low thermal expansion, high thermal conductivity, and high fusion point. Finally, it is safer to use than silica; therefore it is popular in Europe.

Chromite sand

Chromite sand is a solid solution of spinels. Its advantages are a low percentage of silica, a very high fusion point (1,850 °C (3,360 °F)), and a very high thermal conductivity. Its disadvantage is its costliness; therefore it’s only used with expensive alloy steel casting and to make cores.

Zircon sand

Zircon sand is a compound of approximately two-thirds zircon oxide (Zr2O) and one-third silica. It has the highest fusion point of all the base sands at 2,600 °C (4,710 °F), a very low thermal expansion, and a high thermal conductivity. Because of these good properties it is commonly used when casting alloy steels and other expensive alloys. It is also used as a  mold wash (a coating applied to the molding cavity) to improve surface finish. However, it is expensive and not readily available.

Chamotte sand

Chamotte is made by calcining fire clay (Al2O3-SiO2) above 1,100 °C (2,010 °F). Its fusion point is 1,750 °C (3,180 °F) and has low thermal expansion. It is the second cheapest sand; however it is still twice as expensive as silica. Its disadvantages are very coarse grains, which result in a poor surface finish, and it is limited to dry sand molding. Mold washes are used to overcome the surface finish problem. This sand is usually used when casting large steel work pieces.

Other materials

Modern casting production methods can manufacture thin and accurate molds—of a material superficially resembling papier-mâché, such as is used in egg cartons, but that is refractory in nature—that are then supported by some means, such as dry sand surrounded by a box, during the casting process. Due to the higher accuracy it is possible to make thinner and hence lighter castings, because extra metal need not be present to allow for variations in the molds. These thin-mold casting methods have been used since the 1960s in the manufacture of cast-iron engine blocks and cylinder heads for automotive applications.

Binders

Binders are added to base sand to bond the sand particles together (i.e. it is the glue that holds the mold together).

Clay and water

A mixture of clay and water is the most commonly used binder. There are two types of clay commonly used: bentonite and kaolinite, with the former being the most common.

Oil

Oils, such as linseed oil, other vegetable oils and marine oils, used to be used as a binder, however due to their increasing cost; they have been mostly phased out. The oil also required careful baking at 100 to 200 °C (212 to 392 °F) to cure (if overheated the oil becomes brittle, wasting the mold).

Resin

Resin binders are natural or synthetic high melting point gums. The two common types used are urea formaldehyde (UF) and phenol formaldehyde (PF) resins. PF resins have a higher heat resistance than UF resins and cost less. There are also cold-set resins, which use a catalyst instead of a heat to cure the binder. Resin binders are quite popular because different properties can be achieved by mixing with various additives. Other advantages include good collapsibility, low gassing, and they leave a good surface finish on the casting.

MDI (methylene diphenyl diisocyanate) is also a commonly used binder resin in the foundry core process.

Sodium silicate

Sodium silicate [Na2SiO3 or (Na2O)(SiO2)] is a high strength binder used with silica molding sand. To cure the binder carbon dioxide gas is used, which creates the following reaction:

The advantage to this binder is that it can be used at room temperature and it's fast. The disadvantage is that its high strength leads to shakeout difficulties and possibly hot tears in the casting.

Additives

Additives are added to the molding components to improve: surface finish, dry strength, refractoriness, and "cushioning properties".

Up to 5% of reducing agents, such as coal powder, pitch, creosote, and fuel oil, may be added to the molding material to prevent wetting (prevention of liquid metal sticking to sand particles, thus leaving them on the casting surface), improve surface finish, decrease metal penetration, and burn-on defects. These additives achieve this by creating gases at the surface of the mold cavity, which prevent the liquid metal from adhering to the sand. Reducing agents are not used with steel casting, because they can carburize the metal during casting.

Up to 3% of "cushioning material", such as wood flour, saw dust, powdered husks, peat, and straw, can be added to reduce scabbing, hot tear, and hot crack casting defects when casting high temperature metals. These materials are beneficial because burn-off when the metal is

poured creating voids in the mold, which allow it to expand. They also increase collapsibility and reduce shakeout time.

Up to 2% of cereal binders, such as dextrin, starch, sulphite lye , and molasses, can be used to increase dry strength (the strength of the mold after curing) and improve surface finish. Cereal binders also improve collapsibility and reduce shakeout time because they burn-off when the metal is poured. The disadvantage to cereal binders is that they are expensive.

Up to 2% of iron oxide powder can be used to prevent mold cracking and metal penetration, essentially improving refractoriness. Silica flour (fine silica) and zircon flour also improve refractoriness, especially in ferrous castings. The disadvantages to these additives are that they greatly reduce permeability.

Parting compounds

To get the pattern out of the mold, prior to casting, a parting compound is applied to the pattern to ease removal. They can be a liquid or a fine powder (particle diameters between 75 and 150 micrometers (0.0030 and 0.0059 in)). Common powders include talc, graphite, and dry silica; common liquids include mineral oil and water-based silicon solutions. The latter are more commonly used with metal and large wooden patterns.

Sand Reclamation

Sand Reclamation can be termed as the process of reconditioning of used sand in a foundry without lowering its original properties, which are particularly required for foundry application. Reclamation process for foundry sand is broadly of two types – Mechanical (Attrition) and Thermal.

Thermal Reclamation is the process in which the sand is heated to a temperature of about 800 deg. C, in a specially designed fluidized bed Combustor which is the main equipment of the thermal reclamation system. Thermal reclamation is, in many ways, better than attrition (mechanical) reclamation process, for the following reasons:

1. New sand has higher thermal expansion. During pouring, the mould expands excessively and causes distortion, instability and dimensional inaccuracy. When sand is heated above 600 Deg. C, the same undergoes phase change which is permanent in nature. This phase-changed sand has lower thermal expansion and, therefore, all the problems mentioned above are less.

2. Unlike mechanical reclamation, 100% sand, except those reduced to dust, is reclaimed to better-than-new condition.

In the Thermal Reclaimer, the sand grains obtained after breaking the lumps are pre-heated in a heat exchanger and fed into the Combustor at a pre-determined rate. Here it is fluidized by precisely controlled air. The fluidized bed of sand receives controlled stream of flame and hot products of combustion from a specially designed LPG / Natural gas combustion system. The binder in the sand is totally burnt and hot reclaimed sand is obtained at the outlet of the Combustor. The hot sand from the Combustor is transported to a bunker and then made to pass through a Fluidized Bed Cooler having a water cooling system. The cooler is also connected with a dust extraction system for classification of sand. The reclaimed sand, cooled down to usable temperature and classified, is then pneumatically transported to the sand bunker for re-use. 

Thermal Sand Reclaimer is field tested and has been found to consume only 7 to 9 Kg of LPG per MT of sand. Though it is better to use Natural gas or LPG, the reclaimer can be fired with Light oil where the gaseous fuel is not available. Thermal Sand Reclaimer can be used for reclaiming Shell sand, Phenolic 2-part/3-part sand, Furan sand etc. Even Green sand may be reclaimed with additional downstream equipment.

PouringIn a foundry, molten metal is poured into molds. Pouring can be accomplished with gravity, or it may be assisted with a vacuum or pressurized gas. Many modern foundries use robots or automatic pouring machines for pouring molten metal. Traditionally, molds were poured by hand using ladles.

Shakeout

The solidified metal component is then removed from its mold. Where the mold is sand based, this can be done by shaking or tumbling. This frees the casting from the sand, which is still attached to the metal runners and gates - which are the channels through which the molten metal traveled to reach the component itself.

Degating

Degating is the removal of the heads, runners, gates, and risers from the casting. Runners, gates, and risers may be removed using cutting torches, band saws or ceramic cutoff blades. For some metal types, and with some gating system designs, the sprue, runners and gates can be removed by breaking them away from the casting with a sledge hammer or specially designed knockout machinery. Risers must usually be removed using a cutting method but some newer methods of riser removal use knockoff machinery with special designs incorporated into the riser neck geometry that allow the riser to break off at the right place.

The gating system required to produce castings in a mold yields leftover metal, including heads, risers and sprue, sometimes collectively called sprue that can exceed 50% of the metal required to pour a full mold. Since this metal must be remelted as salvage, the yield of a particular gating configuration becomes an important economic consideration when designing various gating schemes, to minimize the cost of excess sprue, and thus melting costs.

Heat treating

Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. Heat treatment techniques include

annealing, case hardening, precipitation strengthening, tempering and quenching. It is noteworthy that while the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.

Surface cleaning

After degating and heat treating, sand or other molding media may adhere to the casting. To remove this surface is cleaned using a blasting process. This means a granular media will be propelled against the surface of the casting to mechanically knock away the adhering sand. The media may be blown with compressed air, or may be hurled using a shot wheel. The media strikes the casting surface at high velocity to dislodge the molding media (for example, sand, slag) from the casting surface. Numerous materials may be used as media, including steel, iron, other metal alloys, aluminium oxides, glass beads, walnut shells, baking powder among others. The blasting media is selected to develop the color and reflectance of the cast surface. Terms used to describe this process include cleaning, bead blasting, and sand blasting. Shot peening may be used to further work-harden and finish the surface.

FinishingThe final step in the process usually involves grinding, sanding, or machining the component in order to achieve the desired dimensional accuracies, physical shape and surface finish.

Removing the remaining gate material, called a gate stub, is usually done using a grinder or sanding. These processes are used because their material removal rates are slow enough to control the amount of material. These steps are done prior to any final machining.

After grinding, any surfaces that require tight dimensional control are machined. Many castings are machined in CNC milling centers. The reason for this is that these processes have better dimensional capability and repeatability than many casting processes. However, it is not uncommon today for many components to be used without machining.

A few foundries provide other services before shipping components to their customers. Painting components to prevent corrosion and improve visual appeal is common. Some foundries will assemble their castings into complete machines or sub-assemblies. Other foundries weld multiple castings or wrought metals together to form a finished product.

More and more the process of finishing a casting is being achieved using robotic machines which eliminate the need for a human to physically grind or break parting lines, gating material or feeders. The introduction of these machines has reduced injury to workers, costs of consumables whilst also reducing the time necessary to finish a casting. It also eliminates the problem of human error so as to increase repeatability in the quality of grinding. With a change of tooling these machines can finish a wide variety of materials including iron, bronze and aluminium.

CAST IRON

Cast iron is iron or a ferrous alloy which has been heated until it liquefies, and is then poured into a mould to solidify. It is usually made from pig iron. The alloy constituents affect its color when fractured: white cast iron has carbide impurities which allow cracks to pass straight through. Grey cast iron has graphite flakes which deflect a passing crack and initiate countless new cracks as the material breaks.

Carbon (C) and silicon (Si) are the main alloying elements, with the amount ranging from 2.1–4 wt% and 1–3 wt%, respectively. Iron alloys with less carbon content are known as steel. While this technically makes these base alloys ternary Fe–C–Si alloys, the principle of cast iron solidification is understood from the binary iron–carbon phase diagram. Since the compositions of most cast irons are around the eutectic point of the iron–carbon system, the melting temperatures closely correlate, usually ranging from 1,150 to 1,200 °C (2,100 to 2,190 °F), which is about 300 °C (572 °F) lower than the melting point of pure iron.

Cast iron tends to be brittle, except for malleable cast irons. With its relatively low melting point, good fluidity, cast-ability, excellent machinability, resistance to deformation and wear resistance, cast irons have become an engineering material with a wide range of applications and are used in pipes, machines and automotive industry parts, such as cylinder heads (declining usage), cylinder blocks and gearbox cases (declining usage). It is resistant to destruction and weakening by oxidation (rust).

The earliest cast iron artifacts date to the 5th century BC, and were discovered by archaeologists in what is now modern Luhe County, Jiangsu in China. Cast iron was used in ancient China for warfare, agriculture, and architecture. During the 15th century, cast iron became utilized for artillery in Burgundy, France, and in England during the Reformation. The first cast iron bridge was built during the 1770s by Abraham Darby III, and is known as The Iron Bridge. Cast iron is also used in the construction of buildings.

Grey cast iron is characterized by its graphitic microstructure, which causes fractures of the material to have a grey appearance. It is the most commonly used cast iron and the most widely used cast material based on weight. Most cast irons have a chemical composition of 2.5–4.0% carbon, 1–3% silicon, and the remainder is iron. Grey cast iron has less tensile strength and shock resistance than steel, but its compressive strength is comparable to low and medium carbon steel. Its melting point is 1093 degree C-1315 degree C.

Ductile cast iron

A more recent development is nodular or ductile cast iron. Tiny amounts of magnesium or cerium added to these alloys slow down the growth of graphite precipitates by bonding to the edges of the graphite planes. Along with careful control of other elements and timing, this allows the carbon to separate as spheroidal particles as the material solidifies. The

properties are similar to malleable iron, but parts can be cast with larger sections. 1120 degree Celsius-1176 degree C melting point. Gray iron, or grey iron, is a type of cast iron that has a graphitic microstructure. It is named after the gray color of the fracture it forms, which is due to the presence of graphite. It is the most common cast iron and the most widely used cast material based on weight. It is used for housings where tensile strength is non-critical, such as internal combustion engine cylinder blocks, pump housings, valve bodies, electrical boxes, and decorative castings. Grey cast iron's high thermal conductivity and specific heat capacity are often exploited to make cast iron cookware and disc brake rotors.

Structure

A typical chemical composition to obtain a graphitic microstructure is 2.5 to 4.0% carbon and 1 to 3% silicon. Silicon is important to making grey iron as opposed to white cast iron, because silicon is a graphite stabilizing element in cast iron, which means it helps the alloy produce graphite instead of iron carbides. Another factor affecting graphitization is the solidification rate; the slower the rate, the greater the tendency for graphite to form. A moderate cooling rate forms a more pearlitic matrix, while a fast cooling rate forms a more ferritic matrix. To achieve a fully ferritic matrix the alloy must be annealed. Rapid cooling partly or completely suppresses graphitization and leads to formation of cementite, which is called white iron.

The graphite takes on the shape of a three-dimensional flake. In two dimensions, as a polished surface will appear under a microscope, the graphite flakes appear as fine lines. The graphite has no appreciable strength, so they can be treated as voids. The tips of the flakes act as preexisting notches; therefore, it is brittle. The presence of graphite flakes makes the Grey Iron easily machinable as they tend to crack easily across the graphite flakes. Grey iron also has very good damping capacity and hence it is mostly used as the base for machine tool mountings.

Classifications

In the United States, the most commonly used classification for gray iron is ASTM International standard A48. This classifies gray iron into classes which corresponds with its minimum tensile strength in thousands of pounds per square inch (ksi); e.g. class 20 gray iron has a minimum tensile strength of 20,000 psi (140 MPa). Class 20 has a high carbon equivalent and a ferrite matrix. Higher strength gray irons, up to class 40, have lower carbon equivalents and a pearlite matrix. Gray iron above class 40 requires alloying to provide solid solution strengthening, and heat treating is used to modify the matrix. Class 80 is the highest class available, but it is extremely brittle. ASTM A247 is also commonly used to describe the graphite structure. Other ASTM standards that deal with gray iron include ASTM A126, ASTM A278, and ASTM A319.

In the automotive industry the SAE International (SAE) standard SAE J431 is used to designate grades instead of classes. These grades are a measure of the tensile strength-to-Brinell hardness ratio.

Advantages and disadvantages

Gray iron is a common engineering alloy because of its relatively low cost and good machinability, which results from the graphite lubricating the cut and breaking up the chips. It also has good galling and wears resistance because the graphite flakes self lubricate. The graphite also gives gray iron an excellent damping capacity because it absorbs the energy.

Gray iron also experiences less solidification shrinkage than other cast irons that do not form a graphite microstructure. The silicon promotes good corrosion resistance and increase fluidity when casting. Gray iron is generally considered easy to weld. Compared to the more modern iron alloys, gray iron has a low tensile strength and ductility; therefore, its impact and shock resistance is almost non-existent.

Ductile iron, also known as ductile cast iron, nodular cast iron, spheroidal graphite iron, spherulitic graphite cast iron and SG iron, is a type of cast iron invented in 1943 by Keith Millis. While most varieties of cast iron are brittle, ductile iron has much more impact and fatigue resistance, due to its nodular graphite inclusions.

Properties of ASTM A48 classes of gray iron

ClassTensilestrength [ksi]

Compressivestrength [ksi]

Tensile modulus(E) [106 psi]

20 22 33 10

30 31 109 14

40 57 140 18

60 62.5 187.5 21

Properties of SAE J431 grades of gray iron

GradeBrinell hardness

t/h† Description

G1800 120–187 135 Ferritic-pearlitic

G2500 170–229 135 Pearlitic-ferritic

G3000 187–241 150 Pearlitic

G3500 207–255 165 Pearlitic

G4000 217–269 175 Pearlitic†t/h = tensile strength/hardness

Ductile iron microstructure at 100×. Note carbon islanding effect around

nodules.

Ductile iron is not a single material but is part of a group of materials which can be produced to have a wide range of properties through control of the microstructure. The common defining characteristic of this group of materials is the shape of the graphite. In ductile irons, the graphite is in the form of nodules rather than flakes as it is in grey iron. The sharp shape of the flakes of graphite create stress concentration points within the metal matrix and the rounded shape of the nodules less so, thus inhibiting the creation of cracks and providing the enhanced ductility that gives the alloy its name. The formation of nodules is achieved by the addition of nodulizing elements, most commonly magnesium (note magnesium boils at 1100°C and iron melts at 1500°C) and, less often now, cerium (usually in the form of Mischmetal). Tellurium has also been used. Yttrium, often a component of Misch metal, has also been studied as a possible nodulizer.

"Austempered Ductile Iron" (ADI) was invented in the 1950s but was commercialized and achieved success only some years later. In ADI, the metallurgical structure is manipulated through a sophisticated heat treating process. The "aus" portion of the name refers to austenite.

Composition

A typical chemical analysis of this material:

Carbon 3.3 to 3.4% Silicon 2.2 to 2.8% Manganese 0.1 to 0.5% Magnesium 0.03 to 0.05% Phosphorus 0.005 to 0.04% Sulfur 0.005 to 0.02% Iron balance

Other elements such as copper or tin may be added to increase tensile and yield strength while simultaneously reducing ductility. Improved corrosion resistance can be achieved by replacing 15% to 30% of the iron in the alloy with varying amounts of nickel, copper, or chromium.

Applications

Much of the annual production of ductile iron is in the form of ductile iron pipe, used for water and sewer lines. It competes with polymeric materials such as PVC, HDPE, LDPE and polypropylene, which are all much lighter than steel or ductile iron, but which, being flexible, require more careful installation and protection from physical damage.

Ductile iron is specifically useful in many automotive components, where strength needs surpass that of aluminum but do not necessarily require steel. Other major industrial applications include off-highway diesel trucks, Class 8 trucks, agricultural tractors, and oil well pumps.

Gray Iron

Cast irons are alloys of iron, carbon, and silicon in which more carbon is present than can be retained in solid solution in austenite at the eutectic temperature. In gray cast iron, the carbon that exceeds the solubility in austenite precipitates as flake graphite. Gray irons usually contain 2.5 to 4% C, 1 to 3% Si, and additions of manganese, depending on the desired microstructure (as low as 0.1% Mn in ferritic gray irons and as high as 1.2% in pearlitics). Sulphur and phosphorus are also present in small amounts as residual impurities.Cast irons are alloys of iron, carbon, and silicon in which more carbon is present than can be retained in solid solution in austenite at the eutectic temperature. In gray cast iron, the carbon that exceeds the solubility in austenite precipitates as flake graphite.Gray irons usually contain 2.5 to 4% C, 1 to 3% Si, and additions of manganese, depending on the desired microstructure (as low as 0.1% Mn in ferritic gray irons and as high as 1.2% in pearlitics). Sulphur and phosphorus are also present in small amounts as residual impurities.The composition of gray iron must be selected in such a way to satisfy three basic structural requirements:

The required graphite shape and distribution The carbide-free (chill-free) structure The required matrixFor common cast iron, the main elements of the chemical composition are carbon and silicon. High carbon content increases the amount of graphite or Fe3C. High carbon and silicon contents increase the graphitization potential of the iron as well as its castability.

The combined influence of carbon and silicon on the structure is usually taken into account by the carbon equivalent (CE):CE = %C + 0.3 x (%Si) + 0.33 x (%P) - 0.027 x (%Mn) + 0.4 x (%S)Although increasing the carbon and silicon contents improves the graphitization potential and therefore decreases the chilling tendency, the strength is adversely affected. This is due to ferrite promotion and the coarsening of pearlite.The manganese content varies as a function of the desired matrix. Typically, it can be as low as 0.1% for ferritic irons and as high as 1.2% for pearlitic irons, because manganese is a strong pearlite promoter.The effect of sulfur must be balanced by the effect of manganese. Without manganese in the iron, undesired iron sulfide (FeS) will form at grain boundaries. If the sulfur content is balanced by manganese, manganese sulfide (MnS) will form, which is harmless because it is distributed

within the grains. The optimum ratio between manganese and sulfur for a FeS-free structure and maximum amount of ferrite is:%Mn = 1.7 x (%S) + 0.15Other minor elements, such as aluminum, antimony, arsenic, bismuth, lead, magnesium, cerium, and calcium, can significantly alter both the graphite morphology and the microstructure of the matrix.In general, alloying elements can be classified into three categories. Silicon and aluminum increase the graphitization potential for both the eutectic and eutectoid transformations and increase the number of graphite particles. They form colloid solutions in the matrix. Because they increase the ferrite/pearlite ratio, they lower strength and hardness.Nickel, copper, and tin increase the graphitization potential during the eutectic transformation, but decrease it during the eutectoid transformation, thus raising the pearlite/ferrite ratio. This second effect is due to the retardation of carbon diffusion. These elements form solid solution in the matrix. Since they increase the amount of pearlite, they raise strength and hardness.Chromium, molybdenum, tungsten, and vanadium decrease the graphitization potential at both stages. Thus, they increase the amount of carbides and pearlite. They concentrate in principal in the carbides, forming (FeX)nC-type carbides, but also alloy the a Fe solid solution. As long as carbide formation does not occur, these elements increase strength and hardness. Above a certain level, any of these elements will determine the solidification of a structure with Fe3C (mottled structure), which will have lower strength but higher hardness.Generally, it can be assumed that the following properties of gray cast irons increase with increasing tensile strength from class 20 to class 60:

All strengths, including strength at elevated temperature Ability to be machined to a fine finish Modulus of elasticity Wear resistance.On the other hand, the following properties decrease with increasing tensile strength, so that low-strength irons often perform better than high-strength irons when these properties are important:

Machinability Resistance to thermal shock Damping capacity Ability to be cast in thin sections.Successful production of a gray iron casting depends on the fluidity of the molten metal and on the cooling rate, which is influenced by the minimum section thickness and on section thickness variations.

Casting design is often described in terms of section sensitivity. This is an attempt to correlate properties in critical sections of the casting with the combined effects of composition and cooling rate. All these factors are interrelated and may be condensed into a single term, castability, which for gray iron may be defined as the minimum section thickness that can be produced in a mold, cavity with given volume/area ratio and mechanical properties consistent with the type of iron being poured.Scrap losses resulting from miss-runs, cold shuts, and round corners are often attributed to the lack of fluidity of the metal being poured.Mold conditions, pouring rate, and other process variables being equal, the fluidity of commercial gray irons depends primarily on the amount of superheat above the freezing

temperature (liquidus). As the total carbon content decreases, the liquidus temperature increases, and the fluidity at a given pouring temperature therefore decreases. Fluidity is commonly measured as the length of flow into a spiral-type fluidity test mold.The significance of the relationships between fluidity, carbon content, and pouring temperature becomes apparent when it is realized that the gradation in strength in the ASTM classification of gray iron is due in large part to differences in carbon content (~3.60 to 3.80% for class 20; ~2.70 to 2.95% for class 60). The fluidity of these irons thus resolves into a measure of the practical limits of maximum pouring temperature as opposed to the liquidus of the iron being poured.The usual microstructure of gray iron is a matrix of pearlite with graphite flakes dispersed throughout. Foundry practice can be varied so that nucleation and growth of graphite flakes occur in a pattern that enhances the desired properties. The amount, size, and distribution of graphite are important. Cooling that is too rapid may produce so-called chilled iron, in which the excess carbon is found in the form of massive carbides. Cooling at intermediate rates can produce mottled iron, in which carbon is present in the form of both primary cementite (iron carbide) and graphite.Flake graphite is one of seven types (shapes or forms) of graphite established in ASTM A 247. Flake graphite is subdivided into five types (patterns), which are designated by the letters A through E. Graphite size is established by comparison with an ASTM size chart, which shows the typical appearances of flakes of eight different sizes at l00x magnification.Type A flake graphite (random orientation) is preferred for most applications. In the intermediate flake sizes, type A flake graphite is superior to other types in certain wear applications such as the cylinders of internal combustion engines.Type B flake graphite (rosette pattern) is typical of fairly rapid cooling, such as is common with moderately thin sections (about 10 mm) and along the surfaces of thicker sections, and sometimes results from poor inoculation.The large flakes of type C flake graphite are formed in hypereutectic irons. These large flakes enhance resistance to thermal shock by increasing thermal conductivity and decreasing elastic modulus. On the other hand, large flakes are not conducive to good surface finishes on machined parts or to high strength or good impact resistance.The small, randomly oriented interdendritic flakes in type D flake graphite promote a fine machined finish by minimizing surface pitting, but it is difficult to obtain a pearlitic matrix with this type of graphite. Type D flake graphite may be formed near rapidly cooled surfaces or in thin sections. Frequently, such graphite is surrounded by a ferrite matrix, resulting m soft spots in the casting.Type E flake graphite is an interdendritic form, which has a preferred rather than a random orientation. Unlike type D graphite, type E graphite can be associated with a pearlitic matrix and thus can produce a casting whose wear properties are as good as those of a casting containing only type A graphite in a pearlitic matrix. There are, of course, many applications in which flake type has no significance as long as the mechanical property requirements are met.

Leeb rebound hardness test 

One of the four most used methods for testing metal hardness. This portable method is mainly used for testing sufficiently large work pieces (mainly above 1 kg).

The Leeb rebound hardness test method was developed in 1975 by Leeb and Brandestini at Proceq SA to provide a portable hardness test for metals. It was developed as an alternative to

the unwieldy and sometimes intricate traditional hardness measuring equipment. The first Leeb rebound product on the market was named “Equotip”, a phrase which still is used synonymously to “Leeb rebound” due to the wide circulation of the “Equotip” product.

Traditional hardness measurements, e.g. according to Rockwell, Vickers and Brinell, are stationary, i.e. fixed workstations are set up in segregated testing areas or laboratories of plants. Most of the times, these methods are used selectively in destructive tests. Samples are cut off from selected parts and measured in the laboratory. From the individual results, statistical conclusions are drawn for the entire batch. The portability of Leeb testers can sometimes help to achieve higher testing rates without destruction of samples (test is considered as non-destructive), which in turn simplifies processes and saves costs.

When using the dynamic Leeb principle, the hardness value is derived from the energy loss of a defined impact body after impacting on a metal sample, similarly to the Shore scleroscope. The Leeb quotient (vi,vr) is taken as measure of the energy loss by plastic deformation: the impact body rebounds faster from harder test samples than it does from softer ones, resulting in a greater value 1000×vr/vi. When using a magnetic impact body, the velocities can be deduced from the voltage induced by the body as it moves through the measuring coil. The quotient 1000×v r/vi is quoted in the Leeb rebound hardness unit HL. While in the traditional static tests the test force is applied uniformly with increasing magnitude, dynamic testing methods apply an instantaneous load. A test takes a mere 2 seconds and, using the standard probe D, leaves an indentation of just ~0.5 mm in diameter on steel / steel casting with a Leeb hardness of 600 HLD. By comparison, a Brinell indentation on the same material is ~3 mm (hardness value ~400 HBW 10/3000), with a standard-compliant measuring time of ~15 seconds plus the time for measuring the indentation.

Brinell hardness Test

The Brinell scale characterizes the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece. It is one of several definitions of hardness in materials science.

It was the first widely used and standardized hardness test in engineering and metallurgy. The large size of indentation and possible damage to test-piece limits its usefulness.

The typical test uses a 10 millimeters (0.39 in) diameter steel ball as an indenter with a 3,000 kgf (29 kN; 6,600 lbf) force. For softer materials, a smaller force is used; for harder materials, a tungsten carbide ball is substituted for the steel ball. The indentation is measured and hardness calculated as:

Where:

P = applied force (kgf)D = diameter of indenter (mm)d = diameter of indentation (mm)

The BHN can be converted into the ultimate tensile strength (UTS), although the relationship is dependent on the material, and therefore determined empirically. The relationship is based on Meyer's index (n) from Meyer's law. If Meyer's index is less than 2.2 then the ratio of UTS to BHN is 0.36. If Meyer's index is greater than 2.2, then the ratio increases.

BHN is designated by the most commonly used test standards (ASTM E10-12  and ISO 6506–1:2005) as HBW (H from hardness, B from brinell and W from the material of the indenter, tungsten (wolfram) carbide). In former standards HB or HBS were used to refer to measurements made with steel indenters.

HBW is calculated in both standards using the SI units as

Where:

F = applied force (N)D = diameter of indenter (mm)d = diameter of indentation (mm)

Vickers hardness test 

Alternative to the Brinell method to measure the hardness of materials. The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, and the indenter can be used for all materials irrespective of hardness. The basic principle, as with all common measures of hardness, is to observe the questioned material's ability to resist plastic deformation from a standard source. The Vickers test can be used for all metals and has one of the widest scales among hardness tests. The unit of hardness given by the test is known as the Vickers Pyramid Number (HV) or Diamond Pyramid Hardness (DPH). The hardness number can be converted into units of Pascal, but should not be confused with a pressure, which also has units of Pascal. The hardness number is determined by the load over the surface area of the indentation and not the area normal to the force, and is therefore not a pressure.

An indentation left in case-hardened steel after a Vickers hardness test. The difference in length of both diagonals and the illumination gradient, are both classic indications of an out-of-level sample. This is not a good indentation.

It was decided that the indenter shape should be capable of producing geometrically similar impressions, irrespective of size; the impression should have well-defined points of measurement; and the indenter should have high resistance to self-deformation. A diamond in the form of a square-based pyramid satisfied these conditions. It had been established that the ideal size of a Brinell impression was 3/8 of the ball diameter. As two tangents to the circle at the ends of a chord 3d/8 long intersect at 136°, it was decided to use this as the included angle of the indenter, giving an angle to the horizontal plane of 22° on each side. The angle was varied experimentally and it was found that the hardness value obtained on a homogeneous piece of material remained constant, irrespective of load. Accordingly, loads of various magnitudes are applied to a flat surface, depending on the hardness of the material to be measured. The HV number is then determined by the ratio F/A, where F is the force applied to the diamond in

kilograms-force and A is the surface area of the resulting indentation in square millimeters. A can be determined by the formula.

This can be approximated by evaluating the sine term to give

Where d is the average length of the diagonal left by the indenter in millimeters. Hence,

,

Where F is in kgf and d is in millimeters.

The corresponding units of HV are then kilograms-force per square millimeter (kgf/mm²). To calculate Vickers hardness number using SI units one needs to convert the force applied from kilogram-force to Newton by multiplying by 9.806 65 (standard gravity) and dividing by a factor of 1000 to get the answer in GPa. To do the calculation directly, the following equation can be used:

Where F is in N and d is in millimeters. Here, HV is in GPa and should be roughly between 0-15 GPa.

Bulking of sand

When mixes are specified by volume, the sand is assumed to be dry. The volume of a given weight of sand, however, varies according to its moisture content. Equal weights of dry and inundated sand have practically the same volume but the same weight of sand in a damp condition can occupy a volume as much as 40% greater. This phenomenon is known as 'bulking'.

It may be demonstrated by filling a gauge box with dry sand. If the sand is flooded with water the level will sink a little, but not to any great extent. When the box is similarly filled with damp sand and the surface is flooded the drop in level will be very much greater.

Unless allowance is made for bulking when batching by volume, the mortar may contain too little sand. This is one of the reasons why measurement by weight is preferable. Bulking occurs far more with fine sands.

Testing for impurities

Sands are usually washed by the suppliers to remove clay, silt, and other impurities which, if present in excessive amounts, result in poor quality mortar. A guide to the amount of clay and silt in sand can be obtained from the field settling test. An excessive amount recorded in this test will indicate that other more sensitive tests should be made.

The test involves placing about 50 ml of a 1% solution of common salt in water (roughly one teaspoon per pint/0.57 litre) in a 250 ml measuring cylinder. Sand as received is then added gradually until the level of the top of the sand is at the 100 ml mark and more solution is added to bring the liquid level to the 150 ml mark. The cylinder is shaken vigorously and the contents allowed to settle for about three hours. The thickness of the silt layer is measured and expressed as a percentage of the height of the sand below the silt layer.

The amount of clay and silt in the sand may be considered acceptable if it does not exceed 10%.

If a measuring cylinder is not available, a jam jar filled to a depth of 50 mm with sand and to a depth of 75 mm with the solution, will give a comparable result if the contents are allowed to settle for three hours. The thickness of the silt layout in this case should not be more than 3 mm.

A simple check for organic impurities is to fill a medicine bottle with sand as delivered, to the 115 ml mark, and then add a 3% solution of sodium hydroxide (caustic soda) in water, until the level of the liquid after shaking is 200 ml. A solution of this strength may be purchased from local chemists. The bottle is then stoppered, shaken vigorously, and allowed to stand for 24 hours. If at the end of that time the colour of the solution above the sand is darker than the standard colour shown in BS 812, or similar local standard, laboratory tests should be undertaken to determine whether the sand is acceptable.

Sand sieve analysis

The sand sieve analysis is carried out as often as is required to maintain the correct grading of sand that is to be used. The grading of a sand aggregate for ferro-cement is found by passing a representative sample of dry sand through a series of BS sieves Nos. 7, 14, 25, 52, 100 (or local equivalent standard), starting with the largest sieve. A record should be maintained of the result and be compared to the required acceptable envelope. Figure 8. Example of sand sieve test form

If the sieving is done manually, each sieve is shaken separately over a clean tray for not less than two minutes. If machine sieving is applied, a nest of sieves should be shaken for at least 15 minutes. The material retained on each sieve, together with any material cleaned from the mesh is weighed and recorded. The percentage by weight passing each sieve is then calculated. Sieving will not be accurate if there is too much material left on any mesh after shaking.