Flame brazing

Flame Brazing differs from welding in that when soldering solder melts only while welding melts the mating edges of the metal. In this case, the melting point of the solder is much less than the connecting metal.
It should be noted that when soldering is fairly high consumption of metal, and some types of solders are very expensive. In addition, often involves the use of solder joints overlap. Due to these reasons, the soldering is not as widespread as welding. However, for some types of work it is indispensable (soldering electrical and radio equipment, printed circuits for precision instruments, the joints of food and medical equipment, etc.).
In soldering used and soldering and brazing. Soldering is performed using solder with a melting point
below 550 ° C, and high temperature provides the use of solders with a melting point above 550 ° C. Soldering can be done with electric soldering or gazovodushnymi burners and high temperature - burners that work on the oxygen-acetylene or propane-butane mixture. When soldering large items can be used burner.
The choice of the type of solder will depend on the type of base metal and, of course, on the type of soldering. Used for soldering tin-zinc and tin-lead solder, and the latter have been widely disseminated. Used for brazing silver, copper, zinc and copper-phosphorous alloys. The widest range of applications have silver solders that are high quality soldering almost all ferrous and non-ferrous metals (except zinc and aluminum). Copper-zinc alloys are used for brazing nickel, steel and iron, although they can be used for soldering copper metal band. Copper-phosphorous alloys are used only for soldering copper and copper alloys (brass, bronze). These alloys are characterized by the fact that when soldering copper does not require flux, but they are quite fragile and so they can not be used in structures that are subject to mechanical stress.
Application of flux when soldering is almost always necessary, as they dissolve oxides formed during soldering, improve the wetting of the solder metal, and prevent oxidation of the metal and solder.
When soldering is most often used such flux, as rosin. Zinc chloride, ammonium chloride, sodium fluoride are used less frequently.
Brazing ferrous and nonferrous metals involves the use of flux often based drills. In the case of increasing the operating temperature of the soldering (when used in more refractory alloys) are sometimes added boric acid. Complex salts composed of chlorides of alkali and alkaline earth metals, used in soldering of magnesium and aluminum alloys. In flux introduced zinc chloride, fluoride, potassium and other alkali metal compounds when necessary to perform the work low-melting solder.
It should be noted that the flame soldering fluxes are best applied in the form of powder or paste.
Features brazed joints. When soldering, as mentioned above, there are basically lap joints, the bond strength which is closely associated with the magnitude of overlap. However, when soldering is used butt, sleeve, special seams and flanged joints (Fig. 136).

Типы паяных швов

Fig. 136. Types of solder joints: 1 - Butt, 2 - lap 3 - Flare 4 - bush, 5 - special.

It is necessary to remember that in order to improve the reliability of its butt joint area can be increased by performing an oblique or synchronous interface. Of course, such a design would require special solder joint and precise machining, but it is well justified, for example, when soldering blade circular and band saws.
Pike various tubular structures used widely. Features tubular connections are shown in Fig. 137.

Варианты трубчатых соединений

Fig. 137. Variants of tubular connections.

Tubular connection types 1 and 2 are available in the event that may be increased when the outer diameter of the pipe, and the compounds of types 3 and 4 - when you need to preserve the exact diameter of the pipe. When soldering the gap between parts to do the least. This is to improve solder filling the gap under the influence of capillary forces.
T-connection is used for soldering is relatively rare.
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