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13 Cards in this Set
- Front
- Back
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Define soldering and classify
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Joining of a number of metal elements of the same composition usually by fusing another alloy that has a lower MP than the elements to be joined.
Soft - Pb & Sn Hard - silver solder (austenitic stainless steel) - gold solder (bridgework) |
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Define welding and give two examples
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The metal to be fused are melted and joined. Spot welding and laswer welding
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Benefits of laser welding?
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10. weld is the same metal as the substrate
11. little mechanical distorion of the elements 12. quick 13. energy input is low so the heat affected zone is minimal 14. welds can be small and precise 15. a large variety of alloys can be joined this way |
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Silver solder is used for?
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Austenitic stainless steel (ortho wires)
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What are the flux properties?
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20 has MP lower than that of the alloy
21 should not effloresce 22. will dissolve oxide 23 must easily separate and be removed from the final solid solder surface after cooling |
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Should acetylene be used for soldering flame? Why or why not?
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No becasue the flame is unstable. Carbon by product is picked up by solder and reduces mechanical properties.
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When soldering one must be cautious of putting minimal heat. Why?
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Possibility of unintentional annealing of a cold worked structure
Possibility of oxidizing surfaces of parent metal Possibility of undoing or softening of intended age hardened structure within gold castings Possibility of producing weld decay in stainless steel |
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What is weld decay?
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In austenitic stainless teels, during welding or soldering, heat can caus formation of complex chrome carbide particles along the grain boundaries. This causes local depletion of chrome in the grains and when less than 12%, the areas will be subject to corrosion since it cannot form passivating layers.
Also the parent material shifts from beining ductile to being more brittle |
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How can you achieve good wetting of solder?
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Clean surface
Flux or mechanical cleaning |
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Describe silver solder
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Used to join stainless teel
contains AgCuZn Requires the use of Fluoride flux |
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For gold solder what type of flux to use?
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BORAX
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2 – When we are soldering a join on an orthodontic appliance which is effectively constructed of Austenitic stainless steel wire, what things should we remain aware of so as not to affect the performance and integrity of the appliance. [5]
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The source of heating can affect the soldering process
Duration of heating The gap size between the elements to be soldered will determine the strength of the bond Surface integrity: use of flux or sand blasting |
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3 - What are the differences between soldering and welding? [6]
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Soldering does not involve melting of metals while welding does
Soldering uses filling material that is different from parent metal while soldering uses the same filling material as the parent metal. Soldering applies large areas of heat (subject to annealing) while welding is more localised. Welding is quicker than soldering Soldering more user friendly and versatile Soldering is not as strong as welding |
