CHAPTER V

Soft-soldering with Blowpipe or Bunsen Burner

=The Mouth Blowpipe.=--Although soft-soldering is usually associated with the use of a copper bit, quite a number of jobs can be done without one, using instead a bunsen burner or, more generally, a mouth blowpipe, which is an inexpensive appliance, useful for both hard and soft soldering, and with either gas, candle, or a methylated-spirit flame. Three shapes of mouth blowpipe are shown in Figs. 23 to 25. In a blowpipe flame there are three cones, X, Y, Z (Fig. 26). X is a non-luminous cone, consisting of a mixture of atmospheric air and unburnt combustible gases (each with a low temperature); Y is a luminous cone, composed of burning gases (carbon and carbonic acid being in excess); and Z is a cone the oxygen in which renders it less luminous and free from combustible materials, its temperature being exceptionally high, especially where the cone comes in contact with the point of the cone Y. Because of its properties, Z is termed the oxidising or outer flame, whilst Y is known as the inner or reducing flame, because when it is applied to some easily reducible substance--say, lead oxide--the oxygen in the substance heated mingles with the unburnt carbon in the cone of the flame and produces carbonic oxide, the lead being thus separated or reduced. The blowpipe flame is one of intense heat, even that produced by blowing a common candle being capable of melting metallic fragments when they are supported on a bed of charcoal. The pointed flame gives the greatest heat, and this can be produced simply by increasing or decreasing the space between the flame and the article to be soldered or the metal to be melted.

The particular advantage of a blowpipe is that it gives a fierce heat at a very localised area, beyond which the solder does not run, and it enables spots to be soldered, or parts to be unsoldered, adjusted and re-soldered without allowing heat to stray and cause trouble at other places. A useful little addition to the ordinary blowpipe is a small washer soldered on near the mouth end (see Fig. 23), the object of this being to raise this part off the bench and so keep it from contamination with dirt, filings, etc., which are unpleasant to the lips. Sometimes the washer is made elliptical and slightly concave to fit the lips, so that it forms a convenient stop or steady when the blowpipe is held between the teeth without help from either hand.

=Bunsen Burner, Spirit Lamps, etc.=--The bunsen burner is, of course, the most convenient device for heating (when the bit is not in question); but failing a gas supply, a spirit-lamp must be employed. This is a small glass bottle with wick, methylated spirit being used. Plumbers and gasfitters make use of metal tubular lamps fed with spirit poured on cotton-wool, and having a blowpipe tube attached and coupled up to the lips with a rubber tube; they also use wax tapers.

A methylated wick lamp may be easily made out of a small “self-opening” canister, as shown in Fig. 27. The holes near the top increase the efficiency of the flame. Another spirit soldering-lamp is shown by Fig. 28. The container for the spirit can be made about 3 in. in diameter by about 1-1/2 in. deep, with a handle soldered on. A glance at the illustration will explain the burner. An outer wick surrounds a piece of tube, which itself contains another wick. The spirit in the inner tube is vaporised by the heat from the burner when the outside wick is lit. The spirit vapour issues from a 1/32-in. hole at A. At B a ring is slipped over the outer wick, holding it to the central tube. By lifting the central tube the height of the vaporising flame can be adjusted. The vaporising tube is a piece of 3/8-in. brass tube with a 3/8-in. gas cap screwed on the end, or a brass disc can be brazed in. The total cost should not exceed sixpence.

=Bench Blowpipes.=--The best form of gas bracket for bench use is one having a horizontal swivelling arm, and screwed to the bench by a flange, as shown in Fig. 29. The swivelling head is also a cock, which shuts off the gas when the jet arm is pushed over at right angles to the edge of the bench, as indicated, and the gas is connected by an iron or compo pipe under the bench. A second gas tap should be arranged in the supply to regulate the amount of gas, and for reasons of safety. A simple device (see Fig. 30) may be made by anyone, and connected to a rubber-pipe connecting head on the gas bracket supplying light to the bench and workshop.

A design of gas blowpipe which leaves one hand free is shown by Fig. 31. This enables the worker to apply the solder to the work (holding the end of a strip against it), after it has been brought to the melting heat of the solder. The blowpipe is arranged so that it can be held in the hand or dropped into a hole in the bench.

=Tapers.=--Tapers for a blowpipe flame are made by untwisting cotton rope until the threads of the individual strands are straight. These are then dipped in melted wax made by melting two wax candles over a gas stove in a jam jar. They are repeatedly dipped until sufficient thickness of wax is obtained. The wax should be just sufficiently hot to keep melted.

=Catching-tray for Bunsen Burner.=--The blowpipe is not essential for some kinds of work, such as when the job can be held wholly in the flame without causing any damage. When solder is being melted to drop on to a surface, the plain bunsen or atmospheric flame is also sufficient, though in this case it is well to tilt the burner over so as to prevent the solder dropping down the tube. An elbow fitted on the top of the tube is handy in this connection, to deflect the flame at an angle, and Figs. 32 and 33 show this, with the addition of a tray to catch the dripping solder which otherwise would splash on the bench and cause untidiness. The tray is riveted to a strip of brass bent round to slip over the outside of the elbow, and a small pin riveted into the tube prevents the tray from falling down.

=Blow Lamps.=--A soldering lamp is used sometimes in the place of a blowpipe, and it should combine perfect security with compactness and portability. Tool merchants’ catalogues show a number of styles. In the lamp shown by Fig. 34, benzoline is burnt. When the lamp is in use and the body of it is very hot, the inside pressure does not exceed three-fifths of an atmosphere, whether the regulator R is open or almost closed. Thus the danger of explosion, which is such a drawback to some of the lamps that use ordinary paraffin, is avoided. The upper parts of the lamp are subjected to great heat and therefore are packed with asbestos, which serves as a filter and stops any impurity in the benzoline from getting to the burner. The flame can be lowered to a glimmer when not actually in use, thus saving the trouble of relighting. When the lamp is to be used, the regulator R is screwed up tight; and care must be taken to ascertain, from time to time, that the burner or nipple C is open and perfectly clean. If this becomes obstructed, it can be cleaned by unscrewing the tube T and passing a fine steel wire through the hole. The lamp should be completely filled with benzoline every time it is to be used. A little methylated spirits is poured into the basin A, and set alight. When the apparatus has become slightly warm, the regulator is opened gradually. To extinguish the flame, the regulator must be screwed up tight. If any escape is observed round the screw of the regulator, the square P should be screwed up with the key supplied by the makers, so as to tighten the asbestos packing. The lamp above described is only one of a great number of such appliances, but it is fairly typical of them all. The difference between a solderer’s and a brazer’s blowlamp is merely one of size and power.

=How to Operate a Mouth Blowpipe.=--The operation of using the mouth blowpipe does not consist in blowing intermittent and strong blasts with the lungs, as this would soon exhaust the wind power. For very light jobs, however, this method is sometimes adopted; but once the proper way is discovered, the user naturally falls into the use of this method.

The proper way to keep a continuous blast is to breathe naturally through the nose, and at the same time keep the cheeks distended by forcing the air at sufficient pressure from the lungs. The cheeks naturally resist the pressure, and force the air through the blowpipe. The operation requires some practice and a clear nose passage. There is practically no limit to the time a continuous blast can be kept up.

The blowpipe flame is produced by holding the blast end of the blowpipe just above the wick of the taper and touching the flame; the blast then causes a long blue flame to project. This flame is hottest at the tip, which is slightly brown.

=Typical Blowpipe Jobs.=--Some of the photographic reproductions in this chapter show the methods of soldering comparatively light and heavy articles. Fig. 35 shows a lading-can handle being resoldered. As it had broken away, the old solder remained, and the joint did not need cleaning. It is dabbed with the killed-spirit brush, and a small piece of solder put near the joint. The flame is first played on the parts away from the solder to get them to the requisite heat, and as the heat reaches the solder it melts, and flows where required. Where the solder should be the thickest, that part of the joint is inclined downwards.

A job needing very much heat, and therefore a continuous blast for some time, is shown by Fig. 36. A lug is shown being soldered to a heavy brass lamp bottom. Before putting the lug in position the parts of the joints have to be tinned. This consists of applying a film of solder. In this case the heat is applied to the lamp bottom for several minutes, and without loss of time the part where the lug fits is cleaned with a fine file, the spirit brush dabbed on a piece of solder, put in position, and the flame again applied. The solder almost immediately flows over the cleaned portion; if it does not flow as required, the flame is played on the solder and lamp bottom, a dab with the spirit brush helping matters. The lug, which should have been previously tinned, is placed in position on the lamp bottom, and with a slight application of the flame, the solder flows and unites the parts firmly together. It should be particularly noted that, when uniting light articles to heavy ones, the light ones should be tinned first, and secured to the heavier article whilst the latter is still hot.

Fig. 37 shows the wires of a vegetable masher being soldered. There is nothing special about the job, except that the solder cannot be placed on the joint. To effect this a piece of tin (Fig. 38) is indented at one end, and a small hole made in the centre of the depression. The bead of solder is placed in this depression, and held over the joint to be soldered; the flame is then played on the joint and on the solder which flows through the hole.

Figs. 39 and 40 show the method of tinning a brass dial ring. The ring is filed clean and placed on a piece of asbestos board, the flame being applied until the ring is sufficiently hot all round. A bead or two of solder is placed on, and, as they melt, the solder is brushed round as shown in Fig. 39 with the spirit brush, the flame being applied at intervals to aid the flow.

=Re-soldering Kettle Spout.=--Refixing a spout in a “tinned” wrought-iron or copper kettle. The spout and that part of the kettle which comes in contact with it should first of all be filed bright and clean. Next place the spout in position, apply killed spirits, and hold it over a bunsen flame, as in Fig. 41, until sufficient of the strip solder is melted to flow around and sweat through to make a strong sound joint. Should any difficulty be experienced in getting the solder to flow readily, apply a little more flux.

=Soldering Corroded Metal.=--When the surface of metal to be soldered is badly corroded, and it is difficult to obtain a clean, bright surface preparatory to soldering, it should be treated to a liberal application of raw spirits of salts (hydrochloric acid), which will soon remove the cause of the trouble, but all traces of the acid should be washed away with clean water before attempting the soldering. It is also a good plan in these cases to tin the surface by repeatedly rubbing it with a hot bit and solder, together with plenty of killed spirits, before proceeding with the actual soldering process.

=Soldering Small Work.=--When soldering two small awkward-shaped pieces together, they can be held in position by pressing slightly into a piece of damp clay. When the work has several soldered joints it can be buried in sand or covered with clay to confine the heat to the part being operated on.

Although care should be taken to limit the solder to the area of the joint, there are circumstances in many cases where it is difficult to prevent some of it from straying. To clean this off, resort may be had to the blowpipe, applying the blast and quickly wiping the surface while the solder is in a molten state. Or it may be filed off while cold and finished with a scraper or a knife and emery-cloth. Or if there is only a thin film the knife or emery-cloth alone will suffice.

=Soldering Pipe Joints.=--Most joints in lead, tin and compo. pipe are now preferably made by means of a blowlamp, or with a mouth blowpipe, strip-solder being used. When making the joint, heat the pipe in the immediate vicinity, and, dipping the solder in the flux, stroke it around the pipe to form the joint.

In soldering block tin or compo. pipe with a bit, if this is too hot it will promptly melt the pipe. This is also liable to happen with very thin zinc. The only way to prevent this is to have the bit just hot enough to melt the solder, and not to let it rest any length of time on the soft metal.

In making connections with soft pipe it is better to make use of brass couplings, and these can be soldered more easily and safely by means of the blowpipe than with a bit. First clean and tin both ends of the coupling, and with the bit put a little ring of solder round about 1/8 in. from the end, as shown at D in Fig. 42. Next with a penknife cut a hole in the pipe B where the connection is wanted, a neat fit for the end of the coupling tail A, scraping the surface of the pipe all round the hole. Insert the coupling in the hole in a vertical position. Sprinkle a little powdered resin round the joint, or smear it with fluxite. Using the flame of a spirit lamp or a candle and a mouth blowpipe, heat the upper part of the coupling, being careful not to allow the flame to come too near the soft pipe. The solder will soon melt, and run down into the joint (see D in Fig. 43), when the flame must be instantly withdrawn. The same proceeding can be adopted in soldering the other portion of the coupling into the connecting pipe. If a vertical position is inconvenient for the coupling it can still be soldered in that position, and afterwards twisted carefully into the desired position. In Figs. 42 and 43, C represents a wood plug for steadying the coupling tail.

=Soldering Birdcage Wires.=--For this job, it is better to flatten out the solder to the thinness of brown paper and with a pair of scissors or shears to cut it into very narrow strips. Take little pieces about 1/4 in. long, and with the fingers pinch them round the wires just above the joints to be soldered. Touch each joint with a small quantity of killed spirit, and apply the flame of a small blowlamp just underneath the joint; this will cause the solder to run in the joint in an instant (see Fig. 44). The flame is quite free from smoke, and does not discolour the wire in the least, as the solder will run long before the wire is red hot. Every joint may thus be neatly made. With a thin piece of copper wire secured in a handle as illustrated, the solder may be drawn any way desired to make special joints in awkward places, where the point of an ordinary soldering bit could not be used.

=Sweating.=--In the preceding chapter it was shown how useful sweating is, when accomplished with the help of the bit. In blowpipe work, also, this method is of much utility, particularly in delicate work where portions have to be joined up in very precise relations. After tinning the joint faces the pieces are secured in accurate relationship with binding wire, or by bolts or screws or other means, or a soldering clamp is employed, having jaws which clamp the pieces and enable them to be adjusted to the exact locations desired, and the flame then brought to bear until the work is hot enough to cause the solder to run.

An example of the usefulness of sweating occurs in the making or repairing of metal name plates having superimposed brass, copper, or other metallic letters. The plate having been flattened and polished and the letters cut out, filed and finished, the backs of the letters must be rendered chemically clean by careful scraping, and are next “tinned” with soft solder. The tinning may be done in several ways, but the easiest is by the blowpipe, using resin oil as flux.

Each letter may be placed in succession on a lump of charcoal, using plenty of the resin oil, and applying the flame of the blowpipe to the surface while one hand holds the charcoal and the other the strip of solder. To prepare the solder, which is sold in sheets by the pound, cut some strips 1/3 in. wide. Take hold of one end 1 in. from the end, and with a sharp knife scrape the surface, drawing the knife edge downwards. Do not use the last 2 in. of the strip, as the handling of this part makes it chemically unclean. The greater part of the solder should be about the edges of the letters. The next operation is to solder the letters to the brass plate. As the brass plate also must be chemically clean, the parts where the letters are to go should be lightly scraped. Having ruled parallel lines in order to get the letters in line, lay each down in its proper place, and draw a pencil line round it; then with a scraper just remove the surface of the brass where the letters are to be soldered. A thin piece of solder is now placed underneath each letter, and each in turn is fixed in its place and secured with a loop of binding wire screwed up tight. Nothing now remains to be done but to apply the blowpipe flame and resin oil, when the solder will run underneath the letters. It is better to set the plate on some small lumps of charcoal. When the letters appear to be set fast, remove the plate and boil it in a solution of potash, about 1/2 lb. to 1-1/2 gal. of water, and clean in dry sawdust. The resin oil may be made by dissolving resin in sweet oil by gentle heat, until the oil will cause the solder to run.