Applied aeronautics; the airplane - Beeldbibliotheek

:80 APPLIED AERONAUTICSJoininf/ of metals hi/ soldering and related jyrocesses.—There are severalmethods of joining metals together by allovs which melt at a lowertemperature thau the metals to be joined. These processes differ in tliealloys used and in tlieir melting temperatures. They are divided intofour classes, as follows(1) Soft soldering.—This method is the one used in tin-smithinggenerally, where the solder is melted by means of a hot soldering copperover the surfaces to be joined. The solder used in this process has a lowmelting point.(2) Hard soldering.—This method is usually used in jewelry workand in the arts, where a higher temperature must be withstood. Thejoining metal in this case has a much higher melting point than softsolder, and must be heated with a blow-torch to make it flow.(3) Brazing.—This process differs from hard soldering onh- in thefact that the joining metal has a still higher melting point. It is usedprincipally in motorcycle, bicycle and automobile construction, wheregreater strength isrequired.(4) Sweating.—This is a process used where the pieces to be joinedcan first be fitted together, then individually coated with solder, thenclamped together and heated until the solder flows, and cements themsolidly together. This method allows for a more perfect joint beingmade. The more accurately the parts are fitted together the strongerthe union will be. Also, the thinner the coat of soldering material, withinreasonable limits, the stronger the joint.All of the above methods are used more or less in airplane constructionand maintenance, but the one that is most generally used isthe first, or soft-soldering method.Cleanliness is of prime importance in making joints or fasteningby any of these methods. In soldering, the first step is to see that thesoldering copper is clean and well tinned, for this may determine the successor failure of the job.There are several ways of cleaning and tinningthe soldering copper, but the one recommended is to heat the copper toabout 600 deg. F., then dip the point quickly into a cup or jar containingammonium chloride (NH4 CI) and granular tin or small pieces of solder.If any considerable amount of work is to be done, an earthen jar or ateacup can be used, and kept partly filled with this mixture.Tinning Soldering CoppersAnother way of tinning the soldering copper is to make a depressionin a piece of sheet tin and place in ita small quantity of soldering fluxtogether with a piece of solder. File the copper until bright, heat it toabout 600 deg. F., and then move it around, while hot, in the depressionin the tin until it becomes coated with molten solder. It will now beready to use.The next step is to clean thoroughly the parts to be joined, usingfine emery cloth, sandpaper or a scraper. If the parts are of raw material,sandpaper will do, but if they are old parts which previously have