Solder

SOLDER, an alloy easily melted and used as a cement to unite two metallic surfaces. The derivation is through the French from Lat. soldare, to make firm.

The soft solders are mainly compounds of tin and lead, and vary widely in composition. Common tinner's solder is composed of equal parts of tin and lead, and melts at ; plumber's solder has 2 of lead to 1 of tin. Excess of lead in plumber's solder ren ders the solder difficult to work ; excess of tin allows it to melt too easily. Pewterers add bismuth to render the solder more fusible, e.g., lead 4, tin 3, bismuth 2 ; or lead 1, tin 2, bismuth 1. Unless these are cooled quickly the bismuth separates out. The hard solders are the spelter and the silver solders. Soft spelter solder is composed of equal parts of copper and zinc, melted and granu lated and passed through a sieve. As some of the zinc volatilizes the ultimate proportions are not quite equal. The proportion of zinc is increased if the solder is required to be softer or more f us ible. A valuable property of the zinc is that its volatilization indi cates the fusing of the solder. Silver solder is used for jewellery and other fine metal work, and has the advantage of high fusing points. The hardest contains from 4 parts of silver to 1 of copper; the softest 2 of silver to i of brass. Borax is the flux used with silver solder as with spelter.

The specifications of the American Society for Testing Materials (1921) are of two classes, of which class A is made from new or virgin metal and class B has at least one-half virgin metal. For galvanized iron and zinc, only class A solders should be used. In general, that solder should be selected which has the least amount of tin required to give suitable flowing and adhesive qual ities. The specified compositions are given in the following table as well as the temperature at which melting begins, and the temperature of complete liquation.

The permissible variation in the tin is not over

1 %. Copper should not exceed 0.08% in class A, or 0.55 in class B grades.

Other impurities not to exceed 0.10%. Grades /A, /B, 2A, 2B, 3A and 3B practically conform with the similarly numbered speci fications of the Society of Automotive Engineers (1922). In addi tion, S.A.E. specification No. 4 (1922) is a solder with lead 75%, tin 25, antimony 2.00 max., copper 0.08 max. in the A grade; tin, 23%, antimony 2.00 max. and copper 0.15 max. in the B grade. This solder is for work that is to be coated with enamel and then baked, as it withstands higher temperatures than the others listed. The complete liquation points are for grade A and for grade B.

Brazing Solder,

or brazing spelter, consists of 5o% to 55% of zinc, the remainder being copper. This is cast into ingots and granulated under a drop hammer into grades known as "long grain," "short grain," "fine grain," etc. The Society of Automo tive Engineers specification No. 45 (1922) calls for copper 50-52%, lead 0.50 max., iron o.io max., zinc remainder. This starts to melt at 1,56o° and is completely melted at The material to be brazed may be dipped in molten brazing solder, or the solder in powdered form mixed with boric acid as a flux may be melted on the material in a furnace or by a torch. The alloy mainly used as brazing metal consists of 8o% copper and 2o% zinc. Brazing solder and metal are used to unite brass, copper, iron and steel in strong joints. Silver solder is used by jewellers and for other fine metal work. The hardest consists of 4 parts silver to 1 of copper ; the softest, 2 parts silver to 1 of copper.

Fluxes for soft solders consist of powdered rosin, hydrochloric acid "killed" by the addition of zinc scraps, and tallow—when used by plumbers; for brazing and with silver solder, powdered borax. Sal ammoniac is sometimes used in brazing copper. Fluxes used to prevent the oxidization of the metals are borax, cream of tartar, sal ammoniac, resin, chloride of zinc and hydrochloric acid. There are many soldering pastes and solutions on the market.