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54 Cards in this Set
- Front
- Back
How are brazing and soldering similar? |
They both sue filler metals to permanently join metal parts, but there is no melting of base metals. |
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When are brazing and soldering used? |
- Metals have poor weldability - Dissimilar metals are to be joined - Intense heat of welding - Geometry of joint is not suitable for welding - High strength is not required |
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How does adhesive bonding work? |
It uses forces of attachment between a filler material and two closely-spaced surfaces to bond the parts |
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What is brazing? |
A joining process in which a filler metal is melted and distributed by capillary action between faying surfaces of metal parts being joined. |
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Describe the strength of a brazed joint under ideal conditions? Why? |
If the joint is properly designed, and the brazing op is properly performed, the joint will be stronger than the filler metal out of which is was formed, beacause metallurgical bonding occurs between base and filler. |
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How does brazing compare to welding? |
- Any metals can be joined, including dissimilar ones - Can be done quickly and consistently, permitting high prod rates - Multiple joints can be brazed at once - Less heat and power required than for FW - Joint areas that are inaccesible by many welding processes can be brazed - Cappilary action daws molten metal filled into the joint |
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What are four disadvantages and limitations of brazing? |
- Joint strength is generally less than a welded joint - Join strength is likely to be less than the strength of the base metals - High service temperatures may weaken a brazed joint - Colour of brazing metals may not match the colour of the base metal parts |
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What are the most common joints in brazing? |
Butt and lap joints, specially lap ones since they provide larger interface area between parts. |
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What are 5 filler metals in brazing? |
Aluminum and silicon Copper Copper and phosphorous Copper and zinc Stainless steel |
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What are the desirable characteristics of filler metal? |
- Low surface tension in liquid phase - High fluidity for penetration - Capable of being brazed into a joint of adequate strength for app - Avoid chemical and physical interactions with base metal (like a galvanic reaction) |
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What are the six heating methods in brazing? |
- Torch brazing - Furnace brazing - Induction brazing - Resistance brazing - Dip brazing - Infrared brazing |
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Describe torch brazing: |
A torch directs flame against work in vicinity of joint |
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Describe induction brazing |
Heating by electrical resistance to high frequency current in work |
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What is resistance brazing? |
Heating is done by electrical resistance in parts |
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What is dip brazing? |
Molten salt or molten salt bath |
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What is Infrared brazing? |
Uses high-intensity infrared lamp |
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What is soldering? |
A Joining process in which a filler metal is melted and distributed by capillary action between faying surfaces. Tm < 450 C |
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What are the advantages of soldering? |
- Lower energy than brazing or FW - Variety of heating methods available - Good electrical and thermal conductivity in joint - Easy repair and rework
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What are the disadvantages of soldering? |
- Low joint strength unless reinforced mechanically - Joint weakens or melts at elevated temperatures |
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What are the two traditional solders? |
Tin and lead. |
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Why is lead less used as a solder? |
Because it is poisoned. |
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Why is tin good with copper? |
Because tin is chemically active at the soldering temperature and forms intermetallic compounds with it that strengthen the bonds. |
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What are two less used solders? |
Silver and antimony |
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What are some functions of soldering fluxes? |
- Prevent oxidation during heating - Promote wetting of faying surfaces - Be readily displaced my molten solder during process - Leave non-corrosive, nonconductive residue |
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What are some methods unique to soldering? (most are the same as for brazing) |
Hand soldering - Wave soldering - Reflow soldering |
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What is wave soldering? |
Soldering of multiple lead wires in printed circuit cards |
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What is reflow soldering? |
It is used for surface mouny components on printed circuit cards |
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What is adhesive bonding? |
A joining process in which a filler material is used to hold two or more closely-spaced parts together by surface attachment |
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When is adhesive bonding used?> |
A wide range of bonding and sealing apps for joining similar and dissimilar materials such as metals, plastics, ceramics, wood, paper, and cardboard. |
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What is an adhesive? |
A filler material, nonmetallic, and usually a polymer. |
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What are the adherends? |
The parts being joined? |
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What are structure adhesives? |
Adhesives capable of forming strong, permanent joints between strong, rigid adherends. |
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What is curing in adhesive bonding? |
A process by which physical properties of the adhesive are changed from liquid to solid, usually by chemical reaction, to accomplish surface attachment of parts. |
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Curing is often aided by ____ and/or ______. |
1) Heat 2) Catalyst |
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What is one disadvantage of curing? |
It takes time. |
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Pressure is sometimes applied between parts to ___________________. |
Activate bonding process. |
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Joint strength in adhesive bonding depends on _________________ and _________________ between adhesive and adherends. |
1) strength of adhesive 2) Attachment |
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What are three attachment mechanisms? |
1) Chemical bonding 2) Physical interactions 3) Mechanical interlocking |
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What is chemical bonding? |
Adhesive and adherend form primary bond on curing. |
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What are physical interactions? |
Secondary bonding forces between surface atoms
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What is mechanical interlocking? |
Roughness of adherend causes adhesive to become entangled in surface asperities. |
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Adhesive joints are stronger in _______ and _______. |
Shear and tension loads |
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Adhesive joints are weakest in _____ or _____. |
Cleavage or peeling. |
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What are the three types of adhesives? |
- Natural adhesives - Inorganic adhesives - Synthetic adhesives |
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Define natural adhesives. Where are they used? |
Derived from natural sources, including gums, starch, dextrin, soya flour, collagen. Low stress applications: Cardboard cartons, furnituyre, bookbinding, etc. |
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Define inorganic adhesives. Where are they used? |
They are based primarily on sodium silicate and magnesium oxychloride. They are low cost, but low strength. |
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What are synthetic adhesives? |
Various thermoplastic and thermosetting polymers. |
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What are the most important adhesive in manufacturing? |
Synthetic adhesives. |
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By which mechanisms are synthetic adhesives cured? |
- Mixing catalyst or reactive ingredient with polymer prior to applying - Heating to initiate chemical reaction - Radiation curing, as with UV light - Curing by evaporation of water - Films or pressure-sensitive coatings |
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For metals, ____________ is often used for cleaning and ____________ improves surface adhesion. |
1) Solvent wiping 2) Surface adhesion |
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For nonmetallic parts, surfaces can be ____________ or __________________ to increase roughness. |
1) Mechanically abraded 2) Chemically etched |
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What are 6 app methods for adhesives? |
1) Manual brushing and rolling 2) Silk screening 3) Flowing, using manually operated dispensers 4) Spraying 5) Automatic applicators 6) Roll coating |
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What are the advantages (5) of adhesive bonding? |
- Applicable to a wide variety of materials - Bonding occurs over entire surface area of joint - Low temperature curing avoids damages to parts being joined - Can be used for sealing as well as bonding - The joint design is often simplified
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What are the limitations of adhesive bonding? |
- Joints are generally not as strong as other joining methods - Adhesive must be compatible with materials being joined - Service temperatures are limited - Cleanliness and surface prep prior to application adhesive are important - Curing times can limit production rates - Inspection of joint is difficult |