The procedure and materials necessary to efficient soldering vary according to the type of work, but there are general principles which should be observed at all times. The surfaces to be united must be chemically clean, free from grease and dirt and sufficient heat must be applied not only to melt and flow the solder, but to warm the parts of the joint. The soldering bit must be clean and free from oxide. A flux is used to seal off the surfaces from the air and prevent oxidation, and to assist the flow of melted solder. On electrical work a non-acid flux should be used, to avoid corrosion and damage to the adjacent parts of the object; but (and this is an important consideration with the novice) in general it is easier to solder with an acid flux such as killed spirits. For ordinary work in which functional safety is not involved acid flux may be used providing the residue is removed when the work is finished.
One more point, solder, an alloy of tin and lead, can be used with resin flux applied directly on tin-plated objects, but for other materials the jointing surfaces must first be coated with a thin film of solder. The beginner should, for practice, test out the use of resin as a flux because it possesses certain characteristics which require some understanding before it can be used efficiently. Tubular solder, with an internal core of resin, is very handy in use, but it will be found that soldering will be improved by a touch of acid flux. Paste fluxes are much used and are excellent, but the liquid acid is preferable until the handyman is proficient. Acid flux incidentally, cleans the surfaces, besides preventing oxidation.
Joints can be ‘sweated’ together in the following manner:—The method is to hold the surface of one joint over a flame, and meanwhile apply a little solder to make a thin film over the whole area of the joint face. Both surfaces are similarly treated. Next the surfaces are clamped tightly together and heat is applied, by holding the clamped joint over a flame, or by directing a blowpipe jet systematically over the whole joint. Two electric wires twisted together can be soldered by a tiny flame, properly applied and directed. Other minute jobs can be served in the same way.
Source of Heat
An atmospheric gas burner, Bunsen type, is the best for heating the soldering bit, or for applying heat to work to be sweated. Unfortunately a certain amount of oxide is deposited on the bit, so that it requires frequent cleaning by wiping with a rag. Occasionally, after heating, it will need to be filed clean with an old coarse file (while still hot). A small block of sal ammoniac should be obtained, and the hot soldering bit rubbed on this occasionally to clean it (unpleasant fumes are given off).
The old-fashioned method of heating the bit in a clear fire has much to recommend it, but the worker must guard against too prolonged heating, which will burn away the working faces of the copper. When using a gas ring, choose one with a small ring of jets close together; cover the bit with a bent piece of sheet iron put on top, to conserve the heat.
Electric soldering bits are very satisfactory, but there is a time-lag in heating up, and the tool should be given ample time to attain the correct temperature. This may be determined by the simple expedient of applying a stick of solder to the working surface.
Patch on a Tinplate Kettle
A typical job, which is described in detail hereunder. Scrape clean the surface around the hole; emery cloth may be used, but wipe off all emery dust afterwards. Cut a piece of tinplate to a polygonal shape (octagon, etc.) at least A in. larger in cross dimension than the hole. Brighten the tin on top and under sides, with emery cloth. Sheet copper may be used with very good results but as sheet tin is more easily procurable this material is recommended here.
Procure- a clean canister lid of tinplate for use as a solder tray; rest it on a piece of board or asbestos to prevent heat going through to the kitchen table, etc. Pour a little acid flux into the tray. Have a stick of solder (50/50 grade) handy, or a’ length of blowpipe solder. Get the parts of the job handy too, since the soldering bit must not be allowed to cool. Apply flux to the kettle around the hole, and also to the underside of the patch, using a spill of wood as a ‘brush’.
Heating the soldering bit
Light the gas ring, and put the bit across so that the middle of the copper as well as the pointed end gets the flame. Presently the flame will turn a vivid green, and when the colour is very pronounced remove the tool. Avoid overheating the bit, otherwise the solder may not adhere. Wipe the working faces of the bit on a thick, clean (non-greasy) cloth, and immediately put the bit in the tray, on the end of the stick of solder. The solder will run, and flow over the working faces of the copper bit, which is then ready for use.
A little pool of solder will form in the tray. The cleaning and tinning may take so much of the heat away that the bit has at once to be returned to the gas ring for a warm up; do not let it stay longer over the flame than necessary, and wipe it again on the rag when you take it off.
Hold the kettle firmly, bottom up, by some means. Put the soldering bit on the little heap of solder in the tray; it will pick up solder in a molten state. Now rub the bit around the fluxed margin of the joint area, and the solder should flow over the parts. All this is done in less time than it takes to tell; probably, after a little experience, the worker will be able at once to proceed to the next stage, which is that of tinning the patch. This consists of laying the patch on a wood block, holding it down with the tang of an old file and applying the soldering bit to the margins all round to give them a thin coat of solder. After heating the bit again, put the patch over the hole in the kettle, tinned side downwards, hold the patch firm with the file, and run the soldering bit around to melt the solder underneath and so attach the patch firmly to the kettle.
However, assuming that the slower method has to be followed, return the bit to the flame after tinning the part around the hole. Possibly the patch also can be tinned in the same heating, but be on the safe side, and never work with a cool bit, which makes for messy and slovenly results. In case of difficulty, merely stick the patch down at about two places at first, and complete the job after re-heating the bit. The edges of a tinplate patch must be well tinned in order to prevent eventual rusting.
Assuming that a ccppcr patch is to be used, tin it rather more thoroughly on the underside, and in other respects proceed as before described. In dealing with a large area of copper it will be found that the heat will be drawn out of the soldering bit rather quickly, as copper is such a good conductor; this means heating the bit more often. Brass, tinplate and zinc can be soldered easily; zinc melts at a low temperature, so use a hot bit and get it on and off the work in the quickest possible time. On zinc, the flux should be neat spirits of salts, not the usual killed spirits.
Clean all surfaces thoroughly; throw away the tray when the solder in it begins to get dirty, and get a new tray. This solder, after frequent heating, loses some of its more volatile characteristics by evaporation. Keep the soldering bit clean and bright at the working surfaces. If it gets corroded, file it after heating up, as explained above. Keep the flux well corked up. Always test the bit on solder to ensure that the correct heat has been attained. Re-heat immediately the solder ceases to flow readily. Acid flux is corrosive to human skin and it will damage most material and should be used with caution.
On a fairly large job, after the joint or seam has been stuck at intermediate points by applying solder picked up on the end of the bit, as explained earlier, the work has to be continued by slowly running the soldering bit along the seam, meanwhile holding a stick of solder close to and in front of the point. The joint or seam should be held firmly by thin iron wire twisted around the object, or by some other means. Often a joint is first secured by rivets or mechanically shaped seams, etc. and the solder used merely to seal the joint.