TYPES AND FORMS OF SOLDER a Types of solder.

(1) The most common material used as a soft solder bond is an alloy

composed of 50 percent tin and 50 percent lead. This is known as "half and half" or 50/50 solder, the tin content being represented by the first figure. Solders having various other proportions of tin to lead, such as 60/40, 40/60, and 30/70, may be obtained for use on certain jobs.

(2) It is essential that the solder "set" or alloy with the metal surface on which it is applied. Tin is the principal "wetting" or alloying element of soft solders; lead is added to decrease the cost of the mixture and because it has a low melting point (like tin). Solders with a high lead content cool slower than

solders containing mostly tin; therefore, they leave a smoother joint.

(3) The 50/50 solder, which reaches the plastic stage at approximately 300ºF and turns liquid at 415ºF, is suitable for soldering automobile radiators, electrical connections, copper tubing, copper. sheet, brass, cast iron, galvanized iron, and sheet steel. An alloy of 60 percent tin and 40 percent lead is generally used where the temperature of the work requirement is critical. This alloy has a very narrow plastic range; it becomes plastic at approximately 360ºF and liquid at approximately 370ºF. Solders containing 30 percent tin and 70 percent lead are specially used for filling dents and welding joints on automobile bodies; they have a wide plastic range and are most suitable to this type of work. This solder

becomes plastic at approximately 360ºF and remains mostly in that state until approximately 495ºF, when it turns to a near liquid form.

b. Forms of solder. Soft solders are manufactured commercially in solid 1 pound bars and wire forms (fig 20). Solder is also obtainable in special forms such as pellets, rings, washers, and other unusual forms for special applications. Wire solder is wound on a spool and may be solid or contain a core of compressed powdered rosin (rosin core solder) or acid (acid core solder). Cross sectional views of a solid and several acid and rosin core solders are shown in figure 21. To prevent the liquid acid from leaking from the acid core solder, the solder is crimped at short intervals. Wire solder is designated by number, and the core size determines the ratio of solder to flux, regardless of strand size, type of flux, or alloy use,

Figure 20. Forms of soft solder.

Figure 21. Forms of wire solder.

30. FLUXES.

a. Types of flux.

(1) General. There are two classes of flux: corrosive and noncorrosive. A corrosive flux, such as borax, sal ammoniac, or zinc chloride, is used when

soldering galvanized iron, zinc, iron, and steel. A corrosive flux should seldom be used on electrical work as it eats away the metal being soldered. When a corrosive flux has been used, the joint must be thoroughly cleaned to remove any trace of flux that may be left on it, thus preventing the flux from eating away any of the material. Noncorrosive fluxes, such as stearine, rosin, and tallow, are used when soldering tin, copper, lead, etc. The noncorrosive flux prevents the forming of oxide and cleans the metal surfaces without eating away any of the surface material. Rosin is the most common noncorrosive-type flux.

(2) Process. In order to have a cleansing effect on a metal surface, the flux used must melt at or below the fusing point of the solder, and it must prevent any oxidation by excluding the air during the soldering process. Different metals solder better with different fluxes: therefore, the manufacturer's recommendations should be followed whenever possible.

(3) Liquid flux. Liquid fluxes are usually salts of acids in solution; for example: zinc chloride dissolved in water. All liquid fluxes, with the exception of rosin dissolved in alcohol, are corrosive. The residue of the salt solution left on the work after soldering must be thoroughly removed to prevent

deterioration of the soldered joint. Liquid rosin flux is noncorrosive, and its residue need not be removed.

(4) Paste flux. Soldering pastes may be acid- or nonacid-type fluxes. They consist of grease or wax containing an acid or nonacid flux. Acid pastes are

corrosive, and their residue must be removed. Nonacid pastes, such as petrolatum (e.g., vaseline) mixed with rosin, are noncorrosive but should also have their residue removed to prevent dust and dirt from collecting on the finished work. This is particularly important in soldering electrical connections, because the dust and paste mixture may form a short circuit. In all work in which pastes are used as fluxes, the joints should be thoroughly cleaned to remove any excess grease.

b. Preparation of zinc chloride. Zinc chloride flux is made from hydrochloric (muriatic) acid by placing the acid in an earthenware container and adding a few pieces of zinc to "cut" it. This causes a vigorous chemical reaction. Enough zinc should be added to "kill" the acid; that is, until all reactions have stopped. The reaction produces explosive hydrogen gas; therefore, the preparation of the

solution should be done outdoors. After the solution has been strained through several thicknesses of cloth, it is ready for use. Hydrochloric acid may be used, without adding zinc, as a cleaning agent on heavily oxidized surfaces. When using hydrochloric acid on zinc and galvanized iron, the zinc metal or the zinc in the galvanized coating combines with the acid to form zinc chloride flux.

31. SOLDERING IRONS. Soldering irons are heated by one of two methods -externally or internally. The externally heated iron may be heated by a

blowtorch, bunsen burner, portable fire pot, etc. The internally heated iron is heated by an electrical heating element.

a. Flame-heated iron (nonelectric). The ordinary flame-heated soldering iron consists of a tip made of solid copper 3 or 4 inches long, usually octagonal in cross section with a tapered point on one end and a steel rod to which a suitable wooden handle is fastened (fig 22). Soldering irons are rated according to weight. Selecting the proper size or weight iron is important. A heavy iron will hold heat longer than a light one; however, a medium or lightweight iron is easier to handle and is more suitable for small jobs. Beginners should start by using a medium weight iron. The lightweight flame-heated iron is generally used by radiator repairmen, electricians, etc, who require only a little solder at a time and an easily manipulated tool that retains sufficient heat for a short period. This type of soldering tool, however, requires repeated heating over an open flame.

Figure 22. Soldering irons.

b. Electric iron. The electric soldering iron is a more convenient tool to use if a 110-volt alternating or direct current is available (fig 22). This iron is obtainable In different sizes (100-, 200-, 300-, and 500-watt). The 100- and 200-watt sizes are used for light work, the 300-watt for medium work, and the 500- watt for heavier work. A variety of tips are also available for use on special jobs. The electric iron heats quickly and remains uniformly hot until the current is turned off, thereby permitting faster work than with externally heated irons. If the electric iron becomes too hot for a given job, the current can be turned off for a few minutes to allow the iron to cool to a suitable soldering temperature. Automatic electric soldering irons also have been developed that have a

thermostatic unit, similar to that found in electric flatirons, to limit and control the temperature.