fastening

FasteningFastening

Manufacturing Manufacturing ProcessesProcesses

OutlineOutline

BrazingBrazingFiller Metals and FluxesFiller Metals and FluxesBrazing MethodsBrazing Methods

SolderingSolderingAdhesive BondingAdhesive Bonding

AdhesivesAdhesivesDesign ConsiderationDesign Consideration

Threaded FastenersThreaded FastenersStandard Screw ThreadsStandard Screw ThreadsThread ClassesThread Classes

RivetsRivets

BrazingBrazing

BrazingBrazingA joining process in which filler A joining process in which filler metal is melted between the metal is melted between the surfaces to be joined; the base surfaces to be joined; the base metal is not meltedmetal is not melted

BrazingBrazing

Filler Metals and FluxesFiller Metals and Fluxes

Filler metalsFiller metalsMelted between the surfaces to Melted between the surfaces to form the joinform the join

Brazing fluxesBrazing fluxesUsed to dissolve, combine Used to dissolve, combine with, or inhibit formation of with, or inhibit formation of oxides or other by-products; it oxides or other by-products; it is displaced by the filler metal is displaced by the filler metal and removed after the and removed after the operationoperation

Filler MetalsFiller Metals

Brazing MethodsBrazing Methods

Torch brazingTorch brazing A flame is used to heat the joint, then A flame is used to heat the joint, then filler is addedfiller is added

Furnace brazingFurnace brazingThe parts and filler are heated in a The parts and filler are heated in a furnace; flux may not be neededfurnace; flux may not be needed

Induction brazingInduction brazingUses heat from electrical resistance to an Uses heat from electrical resistance to an induced current in the workinduced current in the work

Resistance brazingResistance brazingA current is supplied directly to the part to A current is supplied directly to the part to cause resistance heatingcause resistance heating

Brazing MethodsBrazing Methods

Dip brazingDip brazingParts are immersed in a molten salt Parts are immersed in a molten salt or metal bath to heat themor metal bath to heat them

Infrared brazingInfrared brazingUses heat from a high-intensity Uses heat from a high-intensity infrared lampinfrared lamp

Braze weldingBraze weldingApplies filler metal to a Applies filler metal to a conventional weld joint; the base conventional weld joint; the base metal does not meltmetal does not melt

SolderingSoldering

SolderingSolderingA filler metal is melted and A filler metal is melted and distributed between the distributed between the surfaces to be joined; the base surfaces to be joined; the base metal does not melt, but the metal does not melt, but the filler metal combines with it to filler metal combines with it to form a metallurgical bondform a metallurgical bond

SolderingSoldering

Soldering a wire: soldering iron (heat source), left, solder rod, right

Examples of Soldered Examples of Soldered PartsParts

Soldering MaterialsSoldering Materials

Soldering FluxesSoldering Fluxes

Soldering fluxes should:Soldering fluxes should:- be molten at soldering be molten at soldering

temperaturestemperatures- remove oxide films and tarnishremove oxide films and tarnish- prevent oxidizationprevent oxidization- promote wetting of the surfacespromote wetting of the surfaces- be displaced readily by the filler be displaced readily by the filler

metalmetal- leave residue that is not leave residue that is not

corrosive or conductivecorrosive or conductive

Adhesive BondingAdhesive Bonding

Courtesy of Air Products and Chemicals, Inc

http://www.airproducts.com/pressroom/photogallery/Adhesive.jpg


Types of AdhesivesTypes of Adhesives

1. Natural adhesives1. Natural adhesivesstarchstarchanimal productsanimal products

2. Inorganic adhesives2. Inorganic adhesivessodium silicatesodium silicatemagnesium oxychloridemagnesium oxychloride

3. Synthetic organic adhesives3. Synthetic organic adhesivesthermoplastics (soften when thermoplastics (soften when

heated, heated, harden when cooled)harden when cooled)thermosetting (harden thermosetting (harden

permanently permanently when heated)when heated)

PrimersPrimers

Primers used as metal surface Primers used as metal surface conditioners perform these conditioners perform these functions:functions:

1.1. protect corrosion sensitive protect corrosion sensitive surfacessurfaces

2.2. modify the properties of the modify the properties of the bondbond

3.3. tacky resins help hold or tacky resins help hold or position bonded partsposition bonded parts

Theories of AdhesionTheories of Adhesion

Chemical bond theoryChemical bond theoryAdhesion between adhesive Adhesion between adhesive and adherend is related to the and adherend is related to the forces holding atoms and forces holding atoms and molecules togethermolecules together

The predicted strength of the The predicted strength of the attractive force is far higher attractive force is far higher than in reality; however, the than in reality; however, the theory is valid because theory is valid because chemically active primers chemically active primers improve adhesionimprove adhesion


Weak boundary layer theoryWeak boundary layer theoryPoor adhesion or adhesive Poor adhesion or adhesive failure is caused by an failure is caused by an inclusion of low-molecular inclusion of low-molecular weight liquid or an weight liquid or an unpolymerized liquid; the liquid unpolymerized liquid; the liquid forms a weak boundary layer forms a weak boundary layer that prevents the proper that prevents the proper bondingbonding


Surface energy theorySurface energy theoryA liquid should have a lower A liquid should have a lower surface tension than the critical surface tension than the critical surface tension of a solid in order to surface tension of a solid in order to spread on the solid surfacespread on the solid surface

Surface contamination of the solid Surface contamination of the solid could lower the critical surface could lower the critical surface tension below the surface tension tension below the surface tension of the liquid, causing the bond to be of the liquid, causing the bond to be ineffectiveineffective


Inherent roughness theoryInherent roughness theoryOnce the adhesive has wet and Once the adhesive has wet and spread over the adherend surface, spread over the adherend surface, the mechanical strength of the resin the mechanical strength of the resin coupled to the rough surface is the coupled to the rough surface is the basic reason for the strength of the basic reason for the strength of the bondbond

Roughness would increase the Roughness would increase the surface area in which electrostatic surface area in which electrostatic forces could operateforces could operate


Polar theoryPolar theoryPolar adhesives bond to polar Polar adhesives bond to polar adherends and nonpolar adherends and nonpolar adhesives bond to nonpolar adhesives bond to nonpolar adherendsadherends

Liquids wet and spread more Liquids wet and spread more effectively on solid surfaces effectively on solid surfaces with similar propertieswith similar properties

Common AdhesivesCommon Adhesives

1. Epoxies1. Epoxiesthermosettingthermosettingmetal, glass, ceramic, woodmetal, glass, ceramic, woodtwo-component epoxiestwo-component epoxiesresinresincuring agentcuring agentapplication time: 8-12 hoursapplication time: 8-12 hours

2. Cyanoacrylates2. Cyanoacrylatesliquid monomersliquid monomersapplication time: 2 secondsapplication time: 2 seconds


3. Anaerobics3. Anaerobicsthermosetting polyester thermosetting polyester

acrylicsacrylicsalmost any materialalmost any materialapplication time:6-24 hours; application time:6-24 hours;

5 5 min. with proper additives and min. with proper additives and heatheat

4. Acrylics4. Acrylicsthermoplasticthermoplasticplastics, metals, ceramics, plastics, metals, ceramics,

composites, even with dirty composites, even with dirty surfacessurfaces


5. Urethanes5. Urethanesone-part thermoplastic or one-part thermoplastic or two-part thermosettingtwo-part thermosettingapplication time: solidifies in application time: solidifies in 2 min, cures fully in 24 2 min, cures fully in 24 hourshours

6. Silicones6. Siliconessilicone thermosetssilicone thermosetsmetal, glass, paper, metal, glass, paper, plastics, rubberplastics, rubbercures slowlycures slowly


7. High-temperature adhesives7. High-temperature adhesivesepoxy phenolics, modified epoxy phenolics, modified silicones or phenolics, silicones or phenolics,

polyamides, ceramicspolyamides, ceramicscures slowlycures slowly

8. Hot melts8. Hot meltsthermoplastic resinsthermoplastic resinsnot true structural not true structural

adhesives; applied as adhesives; applied as heated liquids and bond as heated liquids and bond as they solidifythey solidify

Application MethodsApplication Methods

BrushingBrushingPerformed manually; coating is often Performed manually; coating is often unevenuneven

Manual rollersManual rollersSimilar to paint rollersSimilar to paint rollers

Silk screeningSilk screeningBrushing through open areas of a screen Brushing through open areas of a screen to coat selected areasto coat selected areas

FlowingFlowingUsing manually operated flow guns; more Using manually operated flow guns; more consistent control than brushingconsistent control than brushing

Application MethodsApplication Methods

SprayingSprayingUsing a spray gun for fast application Using a spray gun for fast application over large areasover large areas

Automatic applicatorsAutomatic applicatorsAutomatic dispensers and nozzles for Automatic dispensers and nozzles for medium and high production ratesmedium and high production rates

Roll coatingRoll coatingA roller is partially immersed in the A roller is partially immersed in the adhesive and transfers it to the partadhesive and transfers it to the part

Pull-tab sheetsPull-tab sheetsThe adhesive sheet comes prepared The adhesive sheet comes prepared covered by a protective layer which is covered by a protective layer which is removed before useremoved before use

Design ConsiderationDesign Consideration

MaterialMaterialporosity, hardness, surface porosity, hardness, surface propertiespropertiesthermal expansionthermal expansion

AssemblyAssemblybond areabond areastressesstresses

TemperatureTemperatureduring use of partsduring use of partstemperature extremes, rate of temperature extremes, rate of temperature changetemperature change


ExposureExposureto solvents, water, fuels, light, to solvents, water, fuels, light, ultraviolet, acid, weatheringultraviolet, acid, weathering

Flexibility/stiffnessFlexibility/stiffnessStabilityStability

required length of timerequired length of timeloadload

AppearanceAppearanceAdhesive applicationAdhesive applicationCostCost

LimitationsLimitations

1.1. Proper selection is requiredProper selection is required2.2. Most are unstable above Most are unstable above

350°F (180°C)350°F (180°C)3.3. High-strength adhesives are High-strength adhesives are

often brittleoften brittle4.4. Long term durability and life Long term durability and life

expectancy are difficult to expectancy are difficult to predictpredict

5.5. Surface condition, adhesive Surface condition, adhesive preparation, and curing can preparation, and curing can be criticalbe critical

LimitationsLimitations

6.6. Assembly times may be Assembly times may be greater than other methodsgreater than other methods

7.7. Joint quality is difficult to Joint quality is difficult to evaluateevaluate

8.8. Some adhesives contain or Some adhesives contain or produce unfavorable produce unfavorable chemicalschemicals

9.9. Many adhesives deteriorate Many adhesives deteriorate under certain conditionsunder certain conditions

10.10. Joints cannot be easily Joints cannot be easily disassembleddisassembled

Threaded FastenersThreaded Fasteners

ScrewScrewAn externally threaded fastener, An externally threaded fastener, generally assembled into a blind generally assembled into a blind threaded holethreaded hole

BoltBoltAn externally threaded fastener An externally threaded fastener inserted through holes in parts and inserted through holes in parts and screwed into a nut on the opposite screwed into a nut on the opposite sideside

Types of Screw HeadsTypes of Screw Heads

Types of ScrewsTypes of Screws

Threaded Fastener Threaded Fastener UnitsUnits

U.S. StandardU.S. Standardmeasured in inches and fractions of measured in inches and fractions of inches: ¼, 5/8,1-1/8 etc.inches: ¼, 5/8,1-1/8 etc.

Metric (SI)Metric (SI)measured in millimetersmeasured in millimeters

A fastener specified to one A fastener specified to one measurement system may have measurement system may have similar sizes to a fastener of the similar sizes to a fastener of the other system, but they will not fit other system, but they will not fit together properlytogether properly

Types of Screw Types of Screw ThreadsThreads

1.1. Coarse-thread seriesCoarse-thread seriesgeneral use where not general use where not subjected to vibrationsubjected to vibration

2.2. Fine-thread seriesFine-thread seriesautomotive and aircraftautomotive and aircraft

3.3. Extra-fine thread seriesExtra-fine thread seriesthin-walled materialthin-walled material

4.4. Eight-thread seriesEight-thread seriespipe flanges, cylinder-head pipe flanges, cylinder-head studsstuds

5.5. Twelve-thread seriesTwelve-thread seriesnot used extensivelynot used extensively

Types of Screw Types of Screw ThreadsThreads

6.6. Sixteen-thread seriesSixteen-thread serieswhere fine threads are requiredwhere fine threads are required

7.7. American Acme threadAmerican Acme threadtransmitting power and motiontransmitting power and motion

8.8. Buttress threadButtress thread9.9. Square threadSquare thread10.10. 29° Worm thread29° Worm thread11.11. American standard pipe American standard pipe

threadthreadpipe jointspipe joints

Standard Screw Standard Screw ThreadsThreads

Where p = thread pitch, d = thread depth, Where p = thread pitch, d = thread depth, and r = fillet radius,and r = fillet radius,

d = .54127pd = .54127pr = .14434pr = .14434p

This applies to U.S. Standard and Metric This applies to U.S. Standard and Metric bolts, but does not necessarily apply to bolts, but does not necessarily apply to screwsscrews

r

p

d

60°

Standard Screw Standard Screw ThreadsThreads

Thread ClassesThread Classes

Unified systemUnified system

Class 1 – special applicationsClass 1 – special applicationsClass 2 – normal production Class 2 – normal production

gradegradeClass 3 – minimum tolerances, Class 3 – minimum tolerances,

tight fit requiredtight fit requiredA – external threadA – external threadB – internal threadB – internal thread

Thread ClassesThread Classes

ISO systemISO system

e – large tolerancee – large toleranceg – small toleranceg – small toleranceH – no allowanceH – no allowance

3-9 – tolerance grade3-9 – tolerance gradeLower = fine quality; higher = Lower = fine quality; higher =

coarse qualitycoarse qualityGrade 6 is roughly equivalent to Grade 6 is roughly equivalent to

U.S. class 2A and BU.S. class 2A and B

RivetsRivets

RivetsRivets

RivetRivetAn unthreaded, headed pin used to An unthreaded, headed pin used to join parts by passing the pin join parts by passing the pin through holes in the parts and then through holes in the parts and then forming a second head on the forming a second head on the opposite sideopposite side

RivetsRivets

SummarySummary

Brazing and soldering melt only Brazing and soldering melt only filler material to form a joinfiller material to form a join

Adhesive bonding uses a viriety Adhesive bonding uses a viriety of chemicals that are applied of chemicals that are applied as a liquid and solidify to form as a liquid and solidify to form a bonda bond

Screws, bolts, nuts, and rivets Screws, bolts, nuts, and rivets are applied and hold material are applied and hold material together by physical meanstogether by physical means

fastening

Documents

base metal

filler metal combines

metal bath

metal surface conditioners

critical surface tension

lower surface tension

filler metalleave residue

unpolymerized liquid