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TRANSCRIPT
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Fastening
Manufacturing
Processes
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Outline
Brazing
Filler Metals and Fluxes
Brazing Methods
Soldering
Adhesive Bonding
AdhesivesDesign Consideration
Threaded Fasteners
Standard Screw ThreadsThread Classes
Rivets
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Brazing
Brazing
A joining process in which filler
metal is melted between thesurfaces to be joined; the base
metal is not melted
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Brazing
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Filler Metals and Fluxes
Filler metals
Melted between the surfaces to
form the join
Brazing fluxes
Used to dissolve, combinewith, or inhibit formation of
oxides or other by-products; it
is displaced by the filler metaland removed after the
operation
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Filler Metals
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Brazing Methods
Torch brazing
A flame is used to heat the joint, thenfiller is added
Furnace brazing
The parts and filler are heated in afurnace; flux may not be needed
Induction brazing
Uses heat from electrical resistance to aninduced current in the work
Resistance brazing
A current is supplied directly to the part tocause resistance heating
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Brazing Methods
Dip brazing
Parts are immersed in a molten saltor metal bath to heat them
Infrared brazing
Uses heat from a high-intensity
infrared lamp
Braze welding
Applies filler metal to a
conventional weld joint; the basemetal does not melt
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Soldering
Soldering
A filler metal is melted and
distributed between thesurfaces to be joined; the base
metal does not melt, but the
filler metal combines with it toform a metallurgical bond
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Soldering
Soldering a wire: soldering iron (heat source), left,solder rod, right
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Examples of Soldered
Parts
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Examples of Soldered
Parts
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Soldering Materials
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Soldering Fluxes
Soldering fluxes should:
- be molten at soldering
temperatures
- remove oxide films and tarnish
- prevent oxidization
- promote wetting of thesurfaces
- be displaced readily by the
filler metal- leave residue that is not
corrosive or conductive
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Adhesive Bonding
Courtesy of Air Products and Chemicals, Inc
http://www.airproducts.com/pressroom/photogallery/Adhesive.jpg -
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Adhesive Bonding
Types of Adhesives
1. Natural adhesives
starch
animal products
2. Inorganic adhesives
sodium silicatemagnesium oxychloride
3. Synthetic organic adhesives
thermoplastics (soften when heated,harden when cooled)
thermosetting (harden permanentlywhen heated)
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Adhesive Bonding
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Primers
Primers used as metal surface
conditioners perform these
functions:
1. protect corrosion sensitive
surfaces2. modify the properties of the
bond
3. tacky resins help hold orposition bonded parts
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Theories of Adhesion
Chemical bond theory
Adhesion between adhesive
and adherend is related to theforces holding atoms andmolecules together
The predicted strength of theattractive force is far higherthan in reality; however, the
theory is valid becausechemically active primersimprove adhesion
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Theories of Adhesion
Weak boundary layer theory
Poor adhesion or adhesive
failure is caused by aninclusion of low-molecular
weight liquid or an
unpolymerized liquid; the liquidforms a weak boundary layer
that prevents the proper
bonding
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Theories of Adhesion
Surface energy theory
A liquid should have a lower
surface tension than the criticalsurface tension of a solid in order to
spread on the solid surface
Surface contamination of the solidcould lower the critical surface
tension below the surface tension
of the liquid, causing the bond to be
ineffective
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Theories of Adhesion
Inherent roughness theory
Once the adhesive has wet and
spread over the adherend surface,the mechanical strength of the resin
coupled to the rough surface is the
basic reason for the strength of the
bond
Roughness would increase the
surface area in which electrostatic
forces could operate
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Theories of Adhesion
Polar theory
Polar adhesives bond to polar
adherends and nonpolaradhesives bond to nonpolar
adherends
Liquids wet and spread more
effectively on solid surfaces
with similar properties
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Common Adhesives
1. Epoxies
thermosetting
metal, glass, ceramic, woodtwo-component epoxies
resin
curing agentapplication time: 8-12 hours
2. Cyanoacrylatesliquid monomers
application time: 2 seconds
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Common Adhesives
3. Anaerobics
thermosetting polyesteracrylics
almost any material
application time:6-24 hours; 5min. with proper additives andheat
4. Acrylics
thermoplastic
plastics, metals, ceramics,composites, even with dirtysurfaces
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Common Adhesives
5. Urethanes
one-part thermoplastic or
two-part thermosettingapplication time: solidifies in2 min, cures fully in 24hours
6. Silicones
silicone thermosets
metal, glass, paper,plastics, rubber
cures slowly
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Common Adhesives
7. High-temperature adhesives
epoxy phenolics, modified
silicones or phenolics,polyamides, ceramics
cures slowly
8. Hot melts
thermoplastic resins
not true structural
adhesives; applied asheated liquids and bond asthey solidify
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Application Methods
Brushing
Performed manually; coating is oftenuneven
Manual rollers
Similar to paint rollers
Silk screeningBrushing through open areas of a screento coat selected areas
Flowing
Using manually operated flow guns; moreconsistent control than brushing
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Application Methods
Spraying
Using a spray gun for fast applicationover large areas
Automatic applicators
Automatic dispensers and nozzles formedium and high production rates
Roll coatingA roller is partially immersed in theadhesive and transfers it to the part
Pull-tab sheets
The adhesive sheet comes preparedcovered by a protective layer which isremoved before use
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Design Consideration
Material
porosity, hardness, surface
propertiesthermal expansion
Assembly
bond areastresses
Temperature
during use of parts
temperature extremes, rate oftemperature change
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Design Consideration
Exposure
to solvents, water, fuels, light,
ultraviolet, acid, weathering
Flexibility/stiffness
Stability
required length of time
load
Appearance
Adhesive application
Cost
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Design Consideration
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Limitations
1. Proper selection is required
2. Most are unstable above
350F (180C)
3. High-strength adhesives are
often brittle
4. Long term durability and lifeexpectancy are difficult to
predict
5. Surface condition, adhesivepreparation, and curing can
be critical
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Limitations
6. Assembly times may be
greater than other methods
7. Joint quality is difficult toevaluate
8. Some adhesives contain or
produce unfavorablechemicals
9. Many adhesives deteriorate
under certain conditions10.Joints cannot be easily
disassembled
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Threaded Fasteners
Screw
An externally threaded fastener,generally assembled into a blindthreaded hole
Bolt
An externally threaded fastenerinserted through holes in parts andscrewed into a nut on the oppositeside
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Types of Screw Heads
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Types of Screws
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Threaded Fastener
UnitsU.S. Standard
measured in inches and fractions of
inches: , 5/8,1-1/8 etc.
Metric (SI)
measured in millimeters
A fastener specified to one
measurement system may have
similar sizes to a fastener of theother system, but they will not fit
together properly
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Types of Screw
Threads1. Coarse-thread series
general use where not
subjected to vibration2. Fine-thread series
automotive and aircraft
3. Extra-fine thread series
thin-walled material
4. Eight-thread series
pipe flanges, cylinder-head
studs5. Twelve-thread series
not used extensively
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Types of Screw
Threads6. Sixteen-thread series
where fine threads are required
7. American Acme threadtransmitting power and motion
8. Buttress thread
9. Square thread
10. 29 Worm thread
11. American standard pipe
threadpipe joints
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Standard Screw
Threads
Where p = thread pitch, d = thread depth,and r = fillet radius,
d = .54127p
r = .14434p
This applies to U.S. Standard and Metricbolts, but does not necessarily apply toscrews
r
p
d
60
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Standard Screw
Threads
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Standard Screw
Threads
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Standard Screw
Threads
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Thread Classes
Unified system
Class 1
special applications
Class 2 normal production
grade
Class 3
minimum tolerances,tight fit required
A external thread
B
internal thread
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Rivets
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Rivets
Rivet
An unthreaded, headed pin used to
join parts by passing the pinthrough holes in the parts and then
forming a second head on the
opposite side
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Rivets
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Summary
Brazing and soldering melt only
filler material to form a join
Adhesive bonding uses a viriety
of chemicals that are applied
as a liquid and solidify to forma bond
Screws, bolts, nuts, and rivetsare applied and hold material
together by physical means
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