Soldering, brazing and welding, ed.

Front matter

Soldering, Brazi and Welding

Iazing,

WITH MANY ILLUSTRATIONS J i

Contents

CHAPTER PAGE

1. Vaeious Processes of Joining Metals . 1

2. Soft Solders .....

Index

12 17

129 134 150 155

CHAPTEE I The Various Processes of Joining Metals

Apakt from the use of rivets, screws, etc., metal is commonly joined by soldering, ' brazing, or welding, three groups of processes that have one thing in common — the use of heat to fuse either the metals themselves or an alloy which is interposed to consolidate the joint. The word " solder " is derived through the French from a Latin word meaning " solid."

Soldering may be "soft " or "hard." Soft-soldering uses lead-tin alloys which are easily melted in a bunsen gas flame or with a hot iron or bit ; while hard-soldering employs a silver-copper alloy, to melt which a mouth blowpipe at least is necessary. Brazing is hard-soldering with spelter (brass), and a forge or a heavy blowlamp or a powerful blowpipe must be employed to provide the heat.

Welding is a fusion process which in the past was almost entirely confined to wrought-iron and steel, these metals possessing the property of weldability to an extent unknown in the case of any other metals.

The blacksmith's process of welding is to heat the iron or steel until the surface of the metal becomes pasty, and then to bring the two pieces into intimate contact by hammering on the anvil. Of late years the welding of iron, steel, copper and some other metals has been rendered possible by the use of certain electrical and chemical methods and — most important of all — by the- use of the oxy-acetylene blowpipe, the process being known as "fusion welding " or "autogenous soldering," the word autogenous implying that the process is complete in itself and independent of the use of any extraneous ' substance such as solder. The thermit process, of which so much has been heard, and which is briefly dealt with later, is the fusion welding of iron and steel by means of the intense heat produced by the combustion of a special chemical compound. Perhaps the oldest of the autogenous soldering processes is "lead-burning," in which the flame of an airohydrogen blowpipe is brought to bear upon the lead, the joint being fed with a strip of the same metal.

Soft-soldering is an operation that the beginner will not find nearly so difficult as hard-soldering or brazing, and although the strength of joints made by it is not nearly equal to that produced by the methods named, it fills a useful place within its scope. It is purely a surface union — that is, the solder adheres to the faces in contact in much the same manner as an adhesive sticks to metal ; but with the assistance of fluxes, the contact is made so intimate that some force is necessary to break the joint. Soft-soldering is also of use where

PROCESSES OF JOINING METALS 3 brazing would- simply mean the ruin or destruction of the metals, as in the cases of lead, poor-quality brass, pewter, tin, zinc, and in tinplate and galvanised iron.

In silver-soldering and brazing, the silver or spelter that fuses to form the joint alloys itself so intimately with the copper or brass that it actually becomes part of the piece itself, and for all practical purposes cannot be distinguished from it. But soft-solderinois not always inferior to hard-soldering. Indeed, the surface nature of the soldering often constitutes its value.

The strongest joints of all are produced by fusion welding, as will be duly understood from later chapters.

CHAPTER II Soft Solders

A solder should melt at a slightly lower temperature than the metals which it unites, and Should possess the quality of alloying with the two surfaces, thus effecting a sound and true metallic joint. Ordinary soft solders are lead-tin alloys , and the larger the proportion of lead the commoner is the solder said to be. At an extreme is plumber's solder, consisting of 2 parts of lead to 1 part of tin, and, at the other, the best blowpipe soft solder, which contains 2 parts of tin to only 1 part of lead. In the ordinary way, a "coarse " or "common" solder is 2 parts of lead to 1 part of tin; a "fine " or "medium " solder, 1 part of lead to 1 part of tin ; and a "very fine " or "best " solder, 1 part of lead to 2 parts of tin.

Eutectic Alloys. — Lead - tin solders are eutectic alloys — that is, they are examples of the phenomenon of a combination of two metals melting at a temperature lower than one of them would if melted separately. Thus, lead melts at about 328° C, and tin at about 232° C, yet reference to the following table, given by Mr. A. H. Hiorns, will show that the "commonest " solder mentioned fuses at 303° C, and the "best " at 175° C.

SOFT SOLDERS

Tin%

Lead%

Melting points of lead-tin alloys

Melting point (C)

Hardness of Solders. — According to the before-mentioned authority, Saposhniko, in 1908, determined the hardness of various lead-tin alloys by Brineli's method, by which a steel cone is forced into the metal. The results he obtained are as follow :

These results, says Mr. Hiorns, show that the hardest alloy is the one with 00° (about 2 parts) of tin and 34° (about 1 part) of lead, which also is the one having the lowest melting point of all the lead-tin alloys. The resufts also show that tin is slightly harder than lead.

Compositions of Soft Solders. — As already shown, solders vary in fusibility according to their composition, and the choice should be determined by the nature of the work and the properties of the metal to be soldered. Should a solder be used of too high a melting-point, the metal will itself be fused before the solder begins to flow.

A point to be particularly observed is that the introduction of a foreign substance into the solder— for example, the addition of a little zinc to a pot of "very fine " solder — will utterly spoil it and render it unworkable. To remove zinc from solder, melt the solder in a pot, take it off the fire and stir in powdered sulphur or brimstone until the whole is of the consistency of wet sand. Replace the pot on the fire and melt, but do not stir the contents. The sulphur and zinc will rise to the surface and form into a cake. Now take the pot off the fire and carefully remove the cake without breaking by employing two pieces of hoop iron with bent ends.

It is false economy to use a rough solder for fine work on the score of cheapness, since more solder is required for a given job on account of the rough particles of solder clinging to the work ; moreover, the rough appearance of the soldering may completely spoil the job.

The table on the opposite page gives the fluxes and the compositions of soft solders suited to a number of different metals.

Making Solder Strips, Wire, Tears, etc.— Only clean, pure tin and pure lead should be employed. The lead is first melted and then the tin added. When all is melted, place a piece of resin on the molten

SOFT SOLDERS

Soft Solders for Various Metals

Soft

Solder

Metal to be

Flux soldered

Tin

Lead

Other constituents

Aluminium stearin see table on p, 59

Brass . . r Gunmetal .

Copper . I

* zinc chloride, resin < or ammoniuinJ chloride . . . 1

Lead tallow or resin

Block tin zinc chloride .

Tinplate zinc chloride or resin

Galvanised steel .

hydrochloric acid .

Zinc hydrochloric acid .

Pewter.

gallipoli oil

Iron and steel .

ammonium chloride

Britannia metal tallow or resin

Gold .

zinc chloride .

Silver .

zinc chloride .

zinc chloride .

* Zinc chloride is the ordinary "killed spirits."

metal to act as a flux, and after well stirring, the solder is made into strips by pouring from a ladle. Solder should not be poured into sand. It may be poured into strips on an oiled sheet of black iron, preferably corrugated to accommodate the strips. In the absence of a corrugated iron sheet, some workers use a ladle resembling a large spoon with a hole about ^ in. in diameter near the end. To form the strips, get a ladle full of solder, place it on a flat iron sheet; then, tilting the ladle to allow the solder to flow over the hoe, quickly draw the ladle across the sheet. A thin strip of solder should thus be formed, and the thickness of the strip may be varied by increasing or decreasing the diameter of the hole in the ladle. A button of solder usually forms at one or both ends of the strip, and this excess should be melted off the strips by just dipping the ends into the molten solder in the pot.

Solder wire is very handy for small work, and can be made in the following way : Roll a sheet of stiff writing or drawing paper into a conical form, rather broad in comparison with its length ; make a ring of stiff wire to hold it in, attaching a suitable handle to the ring. The point of the cone should first of all be cut off to leave an orifice of the size required. It should then be filled with molten solder, and held above a pail of cold water, and the stream of solder flowing from the cone will solidify as it runs and form the wire. If held a little higher, so that the stream of solder breaks into drops before striking the water, it will form handy elongated "tears" of metal; when it is held still higher, each drop forms a thin concave cup or shell, and each of these forms will be found to have its own peculiar uses in blowpipe work.

The method adopted for granulating tinman's solder, which is very rarely called for, is as follows : Place a piece of wood, well greased, over a tub containing water, and by gently pouring the molten alloy from a distance in a small stream on to the greased board, the metal is broken up into a large number of very fine shots, which run off the board into the water

SOFT SOLDERS and are immediately cooled. The fine shots are then taken from the water and gently dried.

Making Solder from Pewter. — This alloy is composed of variable proportions of tin and lead, the average composition being about 4 parts of lead to 1 part of tin. If old pewter is to be utilised for making solder, tin will have to be added to the molten pewter. Thus, to convert 5 lb. of average pewter to " coarse " or "common " solder, add 1 lb. of tin; to "fine " or "medium," add 3 lb. of tin; and to "very fine " or "best," add 7 lb. of tin. The respective proportions of lead and tin will then be '2 and 1 ; 1 and 1 ; and 1 and *2. After the proper quantity of tin has been added, mix some powdered sal-ammoniac with the molten metals, and well stir the alloy; it is then ready for pouring into the moulds.

Making Coarse Solder from Composition Piping. — Good composition piping is made of nearly all tin, or an alloy of tin and lead, in which the former metal is in excess, and formerly was much used by plumbers in the making of coarse solder, as the material consisted of odd pieces of small value. As, however, a great deal of composition tubing is made out of old metals of which lead, tin, antimony, arsenic, and zinc form the alloy, it is not advisable to introduce it into solder. Should it be done, the melting point of the solder would be raised, and in applying it to the lead to be joined together, would probably partly melt it. Neither do the metals named alloy in a thorough manner, but partake more of the nature of a mixture in which the constituents partly separate when making the joints, and some, especially zinc, show as small bright lumps on the surface. Joints wiped with what is usually called ''poisoned metal "are difficult to make, almost invariably leak when on water service pipes, and are dirty grey, instead of bright and clean. The zinc could be removed from the mixture by the method already given.

Combined Solder and Flux.— This consisted of equal parts of lead and tin made into fine tubing and afterwards filled with flux having resin as a base. "Thiol" is a paste made of finely powdered solder and a special flux, and there is also "Thiol wire " having a core of flux.

A "magic " solder, sold by hawkers, consists of the above tubular flux-filled solder of such low melting point that it can be fused in the flame of a lighted match.

Soft Solders that Melt in Boiling Water.— The following soft solders melt at a temperature lower than that of boiling water: 1 part tin, 1 part lead, and 2 parts bismuth, melting point about 200° F. ; 8 parts lead, 4 parts tin, 15 parts bismuth, and 3 parts cadmium, melting point 140° to 150° F. ; 6 parts lead, 7 parts bismuth, and 1 part cadmium, melting point about 180° F. To ensure the alloys melting at the temperatures stated, the metals of which they are formed should be free from impurities, and care should be taken to prevent oxidation while making the alloys. When melting the metals, that having the highest

SOFT SOLDERS n

melting point should be melted first, with a layer of resin over it, the other metals being added in the order of their melting points. The alloy should then be well stirred with a wooden stick, and poured quickly into moulds.

Re-melting and Overheating Solder. — After solder has been re-melted a number of times or has been overheated, its content of tin will be reduced, and the solder will become poorer and coarser. The tin melts earlier than the lead and, being the lighter of the two, floats over it, and is thus fully exposed to the air, the oxidising effect of which on heated, molten metal is extremely active. The oxidised tin forms a dross, from which most of the tin may, however, be recovered by melting it with powdered charcoal, which combines with the oxygen and frees the tin. The addition of a little fresh tin is desirable.