Part 8 (1/2)

Other gases have been and are now being used in the torch. None of them, however, produce the heat that acetylene does, and therefore the oxy-acetylene process has proved the most useful of all. Hydrogen was used for many years before acetylene was introduced in this field. The oxy-hydrogen flame develops a heat far below that of oxy-acetylene, namely 4500 Fahrenheit. Coal gas, benzine gas, blaugas and others have also been used in successful applications, but for the present we will deal exclusively with the acetylene fuel.

It was only with great difficulty that the obstacles in the way of successfully using acetylene were overcome by the development of practicable controlling devices and torches, as well as generators. At present the oxy-acetylene process is the most universally adaptable, and probably finds the most widely extended field of usefulness of any welding process.

The theoretical proportion of the gases for perfect combustion is two and one-half volumes of oxygen to one of acetylene. In practice this proportion is one and one-eighth or one and one-quarter volumes of oxygen to one volume of acetylene, so that the cost is considerably reduced below what it would be if the theoretical quant.i.ty were really necessary, as oxygen costs much more than acetylene in all cases.

While the heat is so intense as to fuse anything brought into the path of the flame, it is localized in the small ”welding cone” at the torch tip so that the torch is not at all difficult to handle without special protection except for the eyes, as already noted. The art of successful welding may be acquired by any operator of average intelligence within a reasonable time and with some practice. One trouble met with in the adoption of this process has been that the operation looks so simple and so easy of performance that unskilled and unprepared persons have been tempted to try welding, with results that often caused condemnation of the process, when the real fault lay entirely with the operator.

The form of torch usually employed is from twelve to twenty-four inches long and is composed of a handle at one end with tubes leading from this handle to the ”welding head” or torch proper. At or near one end of the handle are adjustable c.o.c.ks or valves for allowing the gases to flow into the torch or to prevent them from doing so. These c.o.c.ks are often used for regulating the pressure and amount of gas flowing to the welding head, but are not always constructed for this purpose and should not be so used when it is possible to secure pressure adjustment at the regulators (Figure 16).

Figure 16 shows three different sizes of torches. The number 5 torch is designed especially for jewelers' work and thin sheet steel welding. It is eleven inches in length and weighs nineteen ounces. The tips for the number 10 torch are interchangeable with the number 5. The number 10 torch is adapted for general use on light and medium heavy work. It has six tips and its length is sixteen inches, with a weight of twenty-three ounces.

The number 15 torch is designed for heavy work, being twenty-five inches in length, permitting the operator to stand away from the heat of the metal being worked. These heavy tips are in two parts, the oxygen check being renewable.

[Ill.u.s.tration: Figure 16.--Three Sizes of Torches, with Tips]

Figures 17 and 18 show two sizes of another welding torch. Still another type is shown in Figure 19 with four interchangeable tips, the function of each being as follows:

No. 1. For heavy castings.

No. 2. Light castings and heavy sheet metal.

No. 3. Light sheet metal.

No. 4. Very light sheet metal and wire.

[Ill.u.s.tration: Figure 17.--c.o.x Welding Torch (No. 1)]

[Ill.u.s.tration: Figure 18.--c.o.x Welding Torch (No. 2)]

[Ill.u.s.tration: Figure 19.--Monarch Welding Torch]

At the side of the shut off c.o.c.k away from the torch handle the gas tubes end in standard forms of hose nozzles, to which the rubber hose from the gas supply tanks or generators can be attached. The tubes from the handle to the head may be entirely separate from each other, or one may be contained within the other. As a general rule the upper one of two separate tubes carries the oxygen, while this gas is carried in the inside tube when they are concentric with each other.

In the welding head is the mixing chamber designed to produce an intimate mixture of the two gases before they issue from the nozzle to the flame.

The nozzle, or welding tip, of a suitable size are design for the work to be handled and the pressure of gases being used, is attached to the welding head and consists essentially of the pa.s.sage at the outer end of which the flame appears.

The torch body and tubes are usually made of bra.s.s, although copper is sometimes used. The joint must be very strong, and are usually threaded and soldered with silver solder. The nozzle proper is made from copper, because it withstands the heat of the flame better than other less suitable metals.

The torch must be built in such a way that it is not at all liable to come apart under the influence of high temperatures.

All torches are constructed in such a way that it is impossible for the gases to mix by any possible chance before they reach the head, and the amount of gas contained in the head and tip after being mixed is made as small as possible. In order to prevent the return of the flame through the acetylene tube under the influence of the high pressure oxygen some form of back flash preventer is usually incorporated in the torch at or near the point at which the acetylene enters. This preventer takes the form of some porous and heat absorbing material, such as aluminum shavings, contained in a small cavity through which the gas pa.s.ses on its way to the head.

_High Pressure Torches._--Torches are divided into the same cla.s.ses as are the generators; that is, high pressure, medium pressure and low pressure. As mentioned before, the medium pressure is usually called the high pressure, because there are very few true high pressure systems in use, and comparatively speaking the medium pressure type is one of high pressure.

[Ill.u.s.tration: Figure 20.--High Pressure Torch Head]

With a true high pressure torch (Figure 20) the gases are used at very nearly equal heads so that the mixing before ignition is a simple matter.

This type admits the oxygen at the inner end of a straight pa.s.sage leading to the tip of the nozzle. The acetylene comes into this same pa.s.sage from openings at one side and near the inner end. The difference in direction of the two gases as they enter the pa.s.sage a.s.sists in making a h.o.m.ogeneous mixture. The construction of this nozzle is perfectly simple and is easily understood. The true high pressure torch nozzle is only suited for use with compressed and dissolved acetylene, no other gas being at a sufficient pressure to make the action necessary in mixing the gases.

_Medium Pressure Torches._--The medium pressure (usually called high pressure) torch (Figure 21) uses acetylene from a medium pressure generator or from tanks of compressed gas, but will not take the acetylene from low pressure generators.

[Ill.u.s.tration: Figure 21.--Medium Pressure Torch Head]