英语翻译Soldering and BrazingSoldering and brazing processes are

英语翻译
Soldering and Brazing
Soldering and brazing processes are similar in principle in that the filler material melts at a comparatively low temperature and this liquid filler is drawn by capillary action into the small gap between the parts being joined .One major advantage of soldering and brazing operations is that the joint is made at fairly low temperatures so that there is little heat distortion of parts and little change to the microstructure of the parent metal.Soft solders are comparatively weak but hard solders (brazes) may have tensile strengths in the range 400~500MN/㎡.
Soft soldering
Soft solders are alloys of tin and lead or tin/lead with antimony,cadmium or bismuth and have melting temperatures in the range 70~300℃.For soldering to be effective the liquid solder must ‘wet’the surface of the metal to be soldered.This means that some alloying must take place between a constituent of the solder and the metal to be joined.The type of alloying that occurs may cause formation of a solid solution or the formation of an intermetallic compound.In soft solders tin will form intermetallic compounds with both copper and iron.A liquid solder will only wet a metal surface that is clean and grease free so all surfaces to be soldered must be perfectly clean.A thin oxide film will quickly form on a fresh metal surface and so a soldering flux is necessary to dissolve this oxide layer.The flux used is either zinc chloride solution or of the resin type.
The most commonly used heat source for soft soldering is a soldering iron with an electrically heated copper bit.
Hard soldering
Hard soldering ,or brazing makes use of copper-base alloys with melting tempertures ranging from 620℃ to 900℃ for making the joint.Again,the materials to be joined must be clean and a flux must be used.The most commonly used flux is borax .Borax melts at 750℃ and is a good solvent for many metal oxides.For brazing at lower temperatures than this alkali metal fluorides are used as fluxes.
As with soft soldering the parts to be joined are prepared and fitted together.During brazing the molten filler metal is drawn by capillary action into the joint.The most commonly used heat source for brazing is the oxy-gas torch.The gas used is propane or acetylene.Generelly,a neutral or slightly reducing flame is used ,but when brazing copper a slightly oxidizing flame should be used to reduce the possibility of hydrogen embrittlement.
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