The particulars and instructions on pp. 136 to 139 are due to the Acetylene Corporation, Ltd. Fig. 72 presents a diagrammatic illustration of a complete oxy-acetylene blowpipe equipment with the exception of the acetylene generator and holder, which apparatus may be placed in any suitable position (preferably outside) at any reasonable distance from the blowpipe. A is an ordinary gas tap connecting the hydraulic back pressure valve B with the acetylene supply pipe from the acetylene holder. The blowpipe is connected at valve C by means of a flexible tube with the outlet tap D of the hydraulic back-pressure valve. This forms the acetylene supply pipe to the blowpipe. The blowpipe is connected at valve E by means of a special canvas-covered strong rubber pipe with the outlet tap F of the oxygen pressure regulator, which is fixed, as shown, on the oxygen cylinder. G is a pressure gauge. This pipe conveys the oxygen supply to the blowpipe, and should be securely attached, as it is subject to pressures varying from 5 lb. to 40 lb. per sq. in. The hydraulic back-pressure valve should have been previously charged with water, and the gas regulator screwed into the oxygen cylinder. The blowpipe apparatus is now ready for use, with the taps A and D closed and the taps C, E and F open.

First, slowly open the oxygen cylinder valve (not shown) with the key supplied for that purpose. By means of the thumb-screw H, adjust the gas pressure to the correct working pressure for the blowpipe used. The approximate pressure of oxygen required for each blowpipe is as follows: No. 2, 8 lb. per sq. in.; No. 3, 10 lb.; No. 4, 11 lb.; No. 5, 12 lb.; No. 6, 14 lb.; No. 7, 16 lb.; No. 8, 19 lb.; No. 10, 20 lb.; No. 12, 25 lb.; No. 15, 30 lb. Then open the acetylene taps A and D, and when acetylene is unmistakably smelt at the nozzle of the blowpipe, ignite the gases by means of a gas jet, candle, or taper. Then by means of the tap C slowly throttle down the acetylene until the small white cone of flame at the nozzle of the blowpipe shows a clearly defined outline. As some indication of the correct size of the cone, it may be mentioned that when working with the No. 10 blowpipe this should be about ¹/₄ in. diameter by ⁵/₈ in. long. This cone in the other blowpipes is greater or less according to the relative size.

The tap A must never be used to regulate the supply of acetylene; in fact, after the hydraulic back-pressure valve has been charged with water, it is best to leave this tap always on.

The working pressure for oxygen previously given should not be too rigidly adhered to. Even in the same sizes of blowpipes the conditions must vary slightly, and a little practical experience with each blowpipe will soon indicate the best working conditions. If the flame is not properly regulated it may fire back and go out. If so, the taps C and E should be shut off at once, and a few seconds allowed to elapse before relighting. When work is carried on for a long time at a stretch and the burner becomes warm, it will be found necessary to slightly open the acetylene tap C from time to time. If work is being done which involves the nozzle of the blowpipe being held in a confined space, it is advantageous to cool this end of the blowpipe by immersing it from time to time in a bucket of water. While this is done the gases must be turned off at C and E.

Welding should be done at the apex or outer extremity of the small white cone.

If the hole in the nozzle of the blowpipe gets obstructed at any time through beads of iron being splashed into it, or from any other cause, it may be cleared with a piece of copper wire and cleaned with a wire brush. No steel reamer or other sharp instrument should be used in the hole, which otherwise will be altered in size.

On stopping work the acetylene tap C should be closed first and then the oxygen tap E. When work is completely stopped, the oxygen cylinder should be shut off. The oxygen cylinder valve should never be opened until taps F and E are open, and it should then be opened slowly. In this way sudden impact of oxygen in the regulator is obviated.

The following instructions on the methods of welding copper, cast-iron and aluminium are contributed by a foreman welder.

Welding Copper.

—Copper to be welded should have its edges bevelled to enable the welding to penetrate the entire thickness of the metal. Bevelling is not generally practised below a thickness of ³/₃₂ in. From ³/₃₂ in. to ³/₁₆ in., a slight open bevel is sufficient; ³/₁₆ in. thick and over, the angle of the bevel should be about 90°. It is not necessary to go beyond this even with great thickness. The bevelling should be regular, especially at the bottom, so as not to produce holes or excess of thickness at the bottom of the bevel.

The edges to be welded and their immediate neighbourhood should be thoroughly cleaned. This can be done with a file, scraper, or sheets of emery. Chemical agents such as spirits of salt or nitric acid are sometimes employed; but it is preferable to precede their use by a mechanical cleaning.

Before beginning the welding the parts should be carefully arranged so that during the welding operation they remain perfectly in position. Owing to the high conductivity of copper, a relatively larger blowpipe tip must be used than when welding either iron or mild steel of the same thickness. The power of a blowpipe of 225 litres with an approximate consumption of 7·75 cub. ft. of acetylene per hour would be suitable, with economical results, for iron or mild steel ¹/₈ in. thick, whereas for copper of the same thickness the power of the blowpipe should be of 300 litres, having an approximate consumption of 10·5 cub. ft. of acetylene per hour. Also, a blowpipe which is too strong tends to melt the metal too rapidly. This should be as carefully avoided as that of melting too slowly.

A pure copper welding rod may be employed for filling in, but it is not so effective as a welding rod made of phosphor copper. The phosphorus is incorporated in a very small quantity, so that none remains in the weld after its execution. A filler rod which contains too much phosphorus lacks fluidity, and melts at a temperature much lower than that of the copper to be welded, thus facilitating adhesion. Moreover, the welds in which the phosphorus remains lack elongation, and therefore do not possess the same mechanical properties as pure copper. The welding rod after ¹/₁₆ in. of its diameter should be about equal to the thickness of the weld, although in practice feeders about ¹/₄ in. in diameter are not generally employed. Welds made on copper without a deoxidising welding rod properly prepared have a tendency to oxidise, and therefore do not possess the required qualities. In addition, the surface of the metal must be covered with a carefully prepared mixture of potassium phosphate and potassium carbonate to a depth of about ¹/₁₆ in. Upon the application of the flame, the mixture will melt and form a glaze over the surface of the copper, thus preventing oxidation and assuring good work.

A flux consisting of chloride of sodium, sodium borate, and boracic acid is also recommended. The flux should be sparingly applied by dipping the end of the welding rod into the vessel containing the flux. The end of the rod should be warmed in order that the flux adheres.

Before beginning the actual operation of welding, it is essential to raise the edges of the weld and the parts in the vicinity to a high temperature. The high conductivity of the metal necessitates this, as any supply of molten welding rod before the edges are in a molten state inevitably produces adhesion. The flame of the blowpipe should be perfectly regulated and maintained without excess of either acetylene or oxygen. In executing the weld, care must be taken to avoid contact of the white jet of the blowpipe flame with the metal just about to be melted. The distance of the white jet should vary according to the power of the blowpipe, say from ³/₁₆ in. to ³/₈ in. If this distance is increased, the gases resulting from the second phase of combustion, carbonic acid and water vapour, influence the weld. Care must be taken that the fusion of the metal should not be undertaken until the edges of the weld and the parts near have been raised to a high temperature. At this moment the welding rod and the parts to be joined should be melted simultaneously. It is essential that the welding rod should be regularly incorporated in the line of welding, and must not be allowed to fall in drops. The operation should be continuous, taking care to attack regularly the two edges of the metal. The welding is thus executed rapidly.

It is well known that internal strains are always set up in every process of welding, due to the expansion and contraction when a metal is heated and cooled. Copper lacks tenacity when heated; hence contraction of the metal, whose coefficient of expansion is also fairly high; fractures thereby are often produced, especially in the welded part. However, pre-heating the article to a high temperature, maintaining the heating after the operation of welding and slow cooling, enables one in many cases to avoid fractures due to contraction. It is also necessary to hammer the line of welding and its vicinity. After the hammering operation it is essential to reheat the copper, raising it to redness (500° C. to 600° C.). Then plunge into cold water, or cool as rapidly as possible. The structure of the weld is not quite as homogeneous as other parts of the piece welded. This is, however, controlled largely by the skill and workmanship of the operator, who can, at will, make the weld more or less homogeneous.

It is impossible to enumerate in anything like detail all the work in copper which may be executed by oxy-acetylene autogenous welding. However, copper-smiths are advantageously making great use of the system, thereby replacing their old methods of brazing and riveting.

Welding Aluminium.

—In preparing aluminium to be welded, the edges must first be thoroughly cleaned and the welding rod very pure, so as to avoid the incorporation of impurities, which is apt to bring about rapid disintegration in the line of welding. Bevelling the edges to be joined is not necessary below a thickness of ¹/₈ in. From ¹/₈ in. to ³/₁₆ in. a slight open bevel is sufficient, ³/₁₆ in. thick and above angle of bevel should be about 90°. For thin sheets up to a maximum of ³/₃₂ in., welding is facilitated by flanging the edges at right angles. The depth of the flange should be slightly deeper than the thickness of the metal. By this method no welding rod is required, the edges being simply fused. The weld should afterwards be hammered level.

Aluminium should never be welded without a flux. If welding is attempted without a flux, globules consisting of aluminium within and a coating of alumina (oxide of aluminium) will appear. In order to eliminate these by the blowpipe flame it would be necessary to raise the temperature to the melting point of the oxide of aluminium, which is nearly 3,000° C., whilst the melting point of metallic aluminium is only 657° C. To produce a flux which will dissolve the oxide at the low melting point of the metal and at the same time protect the hot metal from contact with the air has obviously not been a simple problem to the chemist and engineer. However, several good fluxes are now obtainable which enable any experienced welder to effect satisfactory welds in aluminium.

A flux consisting of the following ingredients can be recommended: sodium chloride 30 parts, potassium chloride 45 parts, lithium chloride 15 parts, potassium fluoride 7 parts, and bisulphate of potassium 3 parts.

When making fluxes for the welding of aluminium, great care is necessary in order to completely dry the ingredients, thus avoiding their combination with each other. On aluminium above ³/₃₂ in. thick, the flux is best applied by dipping the end of the welding rod into the vessel containing the flux. The end of the rod should be first warmed in order that the flux adheres. The welding rod after ¹/₁₆ in., its diameter should be just about equal to the thickness of the weld, although in practice feeders above ¹/₄ in. diameter are not advisable.

In executing the weld, care must be taken to avoid contact of the white jet of the blowpipe flame with the metal just about to be melted, because the high temperature of this part tends to produce holes which are difficult to fill in. The distance of the white jet should vary according to the power of the blowpipe, say from ¹/₄ in. to ³/₄ in. The flame should be so adjusted as to furnish an excess of acetylene. There need be but little fear of carbonising the metal, for the reason that the temperature of the work is comparatively low. For thin welds, up to ¹/₈ in. thick, it is preferable to hold the welding rod in front of the blowpipe in the direction of the edges to be welded. As soon as the latter begins to melt it is heated rapidly, and should be lowered to form one molten bath with the metal of the piece. The welding is thus done very rapidly. For great thicknesses it is preferable to obtain fusion of the welding rod, previously heated in the molten bath of the bevel. Directly after welding, the weld should be thoroughly washed in clean warm water in order to remove all remaining traces of the flux, which would otherwise continue to have a chemical action on the metal, thereby setting up corrosion.

Welding Cast-Iron.

—The edges of the weld should be bevelled when the thickness exceeds ¹/₈ in.; this enables the welding to penetrate the entire thickness of the metal. Both edges must be bevelled to an angle of 45°, so as to form a right angle at the weld. The bevelling should be regular, especially at the bottom, so as not to produce holes or excess thickness at the bottom of the bevel. Workers who attempt to effect welds on cast-iron above, say, ¹/₄ in. in thickness, without bevelling, invariably obtain poor results, as it is impossible to get regular and thorough penetration. The bevelling of the edges may be done by chipping or grinding, etc. Grinding wheels made from a carbide of silicon abrasive are very effective for cast-iron. The edges to be welded and their immediate neighbourhood must be free from sand, dirt, and rust.

It is known that internal strains are always set up in every process of welding, due to the expansion and contraction when a metal body is heated and cooled. These strains are not unavoidable, but their effect may be minimised or nullified. In the case of cast-iron, the tendency to crack will be greatly increased if the cooling of the metal after fusion is rapid or irregular. Consequently, the article to be welded should be pre-heated slowly to about 700° F. to 1,000° F. Generally speaking, the higher the temperature of pre-heating, the less the danger of cracking. Preferably, pre-heating and subsequent slow cooling should be carried out in a muffle, particularly where light and intricate castings have to be dealt with.

In all cases care should be taken in the selection of the proper size of blowpipe tip to be used on any particular job. Therefore, the size of tip recommended by the manufacturers should be employed. The total heat of fusion of cast-iron being high, it is necessary to use a blowpipe with a greater power than for the same thickness of welds on mild-steel or wrought-iron. In the actual operation of welding, the blowpipe flame should be played on the edges to be welded until the melting of the iron just takes place. It is essential to avoid contact of the white cone of the blowpipe flame with the metal just about to be melted; the point should be kept at a distance varying from ³/₁₆ in. to ³/₄ in., according to the thickness of the work. The two edges to be joined should melt simultaneously. As soon as the first fusion is obtained, a little flux or scaling powder must be added; this is usually applied by dipping the extremity of the welding rod into the vessel containing the flux, the rod having been previously heated. Avoid throwing the powder into the molten metal whilst executing the weld, as the supply from the welding rod is always sufficient.

Many kinds of fluxes for cast-iron are furnished by the manufacturers of welding apparatus, which vary considerably in composition. The principle of all of them is to provide some chemical which, at the high temperature involved, will break up the oxide into its component parts. The following combinations will perform these functions, and can be recommended: (1) Boracic acid 80 parts, powdered chlorate of potash 20 parts, ferric carbide 15 parts. (2) Equal parts of carbonate and bicarbonate of soda, to which is added from 10 to 15 per cent. of borax and 5 per cent. of precipitated silica. (3) Carbonate of soda 50 per cent. and bicarbonate of soda 50 per cent. The necessity for using a flux may not be thoroughly appreciated; but if it is attempted to weld cast-iron without it difficulty will at once be experienced.

Do not add any metal from the welding rod until the bottom of the V is filled from the sides. It is found that by employing silicon in the welding rod, in the form of ferro-silicon, the iron combines with the silicon in preference to the carbon, allowing the carbon to take the form of graphite, and thus facilitate the formation of grey iron. The welding rod should contain about 4 per cent. of silicon and as low as possible in manganese. The purchase of such a welding rod is not at all difficult, and may be obtained from the same manufacturers as the flux, from ¹/₈ in. to ¹/₂ in. in diameter.

One criticism of cast-iron welding has been directed against the hardness of the weld. This hardness may be due to a number of causes, such as inefficiency of the operator, unsatisfactory fluxes and welding apparatus, rapid cooling, etc. Therefore, as stated previously, in order to get good workable welds, there must be slow cooling after the welding is complete; and there is no reason why the worker who carefully follows the instructions given, and applies himself diligently to the task, should not be able to weld cast-iron of any thickness in an efficient and workmanlike manner.

This method of welding cast-iron successfully solves an unlimited variety of manufacturing and repair problems in the engineering industry, and can be relied on to make homogeneous welds on cast-iron. It is impossible to enumerate in anything like detail all the work in cast-iron which may be executed by oxy-acetylene welding; but the following are some of the applications for which it has already been advantageously employed: For repairing broken machine parts, gear boxes, motor cylinders, crank cases, tanks, manifolds, flywheels, etc., filling blowholes and defects in castings. Castings impossible or difficult to mould can be made in parts and united. Teeth broken from gear wheels can be renewed, and adding metal in any desired quantity to worn parts of cast-iron articles. As a concrete example of its economical and positive aid to the engineering industry, the following may be of interest. A cast-iron belt-wheel would have gone on the scrap heap, a total loss, with four of the six spokes broken, three entirely out. It was 5 ft. in diameter, and weighed about 500 lb., but was not worth much as scrap metal. Scrapping it meant the purchase of a new wheel, and perhaps a long delay in getting one cast. But with the oxy-acetylene process the three spokes that were fractured were welded into place; the fourth spoke broken near the hub was also welded. There were seven welds, each about 1¹/₂ in. by 4 in.; the job was done profitably at a cost of £5, ready for delivery in two days, and was considerably better than buying a new wheel, and waiting two weeks or two months for delivery. The process is particularly suitable for this class of work, and cannot fail to give satisfaction if performed by an experienced welder. The cost of welding a given job depends not only on its thickness, but on the skill of the workman. For example, the same class of job may vary as much as 50 per cent. if executed by different operators.