General - Congress of Liege - M. Jottrand, La Societe l'Oxhydrique - MM. Jottrand and Lulli Process - Installation for Cutting Metals - Speed of Cutting - Metropolitan Railway, Paris - Hydrogen Process for Breaking up Ships - Cutting of Ornamental Iron - Consumption of Oxygen - Consumption of Gas and Cost per Metre of Cutting.

One of the most important applications of compressed gases, and more particularly that of oxygen, refers to cutting of metals.

The process is the reverse to that of welding: by welding a reducing gas mixture, by cutting an oxidising one by surplus of oxygen.

It is a well-known fact that there are many metals which when brought to a white heat burn in an atmosphere of pure oxygen. The experiment is familiar in every course in physics and chemistry. The same phenomenon occurs when a jet of oxygen is directed upon iron heated to a bright red ; that is to say, the metal burns, and the heat evolved fuses the oxide. The process for cutting metals by oxygen is based on these phenomena. It can readily be seen that it is possible to divide a piece of metal by means of an oxygen jet, but it is not easy in practice to obtain a regular and clean cut.

At the congress of Liege, 1901, M. Jottrand, of La Societe l'Oxhydrique, exhibited for the first time a blowpipe for cutting iron and steel, which created a great deal of attention by reason of the important part its development probably would play in metallurgy.

The apparatus consisted of an oxyhydrogen blowpipe by means of which the part of the metal to be cut was brought to a bright red heat. Then the flow of hydrogen was cut off, and the pure oxygen was increased. A good combustion was produced, but it did not proceed very long. The resultant iron oxide, not being hot enough, lacked fluidity. It was with difficulty removed, became mixed with the partially melted iron, and thus obstructed the close contact of the metal with the oxygen. The combustion stopped, and it was necessary to bring the blowpipe into play again. The manipulation, even after long practice, could produce only an irregular cut, dirty and with edges incrusted with closely adhering oxide.

The process prepared in 1904 by Jottrand and Lulli is different, and remedies all the previously appearing difficulties. This process consists of two blowpipes in one piece, which travel along the section to be cut. The first is an ordinary oxyhydrogen blowpipe, which heats the metal to a bright red; the second one directs a fine jet of pure oxygen upon the heated spot under a pressure varying with the thickness of the metal.

The action of the two blowpipes is continuous. The first prepares the way for the second, furnishing a volume of heat sufficient to permit instantaneous combination of the oxygen with the metal in the heated zone. The metal is not melted, and the adjoining parts remain unaltered, as the action proceeds too rapidly for the heat to spread into the mass, and the oxidised portion is removed by the pressure of the oxygen; the section is cleaner than the raw cut, and its width never exceeds 4 m.m.

The speed of travel of the double blowpipe is about 20 cm. a minute; in other words, the operation is quite rapid and comparable to hot sawing. The consumption of gas is relatively small, depending upon the thickness of the metal to be cut; and as the work is rapidly done, the labour cost is not important.

The double blowpipe, which is easily handled, and furthermore may be guided by any sort of mechanical device, is available for cutting not only thick plates, but also, and with equal ease, tubes, beams, shafts, and all sorts of rolled sections.

The cutting may be made to follow any line, executing all sorts of curves and profiles, the smoothness of the surface depending a great deal upon the skilful handling of the blowpipe. The reaction takes place almost immediately; therefore even a shaking of the hand or raising or lowering of the blowpipe will cause an uneven surface. In all cases where a special appearance is desirable - for instance, the cutting of manholes, locomotive frames - it is advisable to use a mechanical appliance to guide the blowpipe.

An installation for cutting of metals is extremely simple, and consists of: -

1. The cutting blowpipe with various exchangeable burners to suit the different thicknesses of metal.

2. A high pressure regulator up to thirty atmospheres.

3. A high pressure rubber tube.

Besides the hydrogen-cutting blowpipe before mentioned, there are various other constructions, especially for the use of acetylene instead of hydrogen. One may be equally as good as the other known under various names, but this is of little importance, as the blowpipes are generally obtainable on trial, so as to enable the choice of the best construction for the special work in view.

As the pressure of the gases in the receptacles, the ordinary steel cylinders, is high, being about 150 atmospheres when filled, the gas passes through a pressure-reducing valve before being used. The pressure of the oxygen, when used for cutting, varies from about one and a half to five atmospheres, for the hydrogen or any other combustible gas used a water pressure of 20 cm. being sufficient.

The process of cutting metals is in no way limited by the mechanical properties of the material, whether it be hard or soft, tempered or annealed, chrome or nickel, the steel burning just as fast.

The problem of cutting armour plates is thus fully solved.

It might be assumed that the metal would be severely attacked on the surface by the influence of the oxygen, but this, however, is claimed not to be the case. With the exception of a layer of 0.01 in., at the most, next to the cutting edge, the metal keeps its original chemical composition, and the physical properties remain the same.

The essential qualities of the process may be thus summarised: extreme simplicity of the installation and appliances; complete mobility; independence of any need of motive power; absence of any reaction upon the tool; extraordinary speed of operation; and, so to speak, unlimited adaptability.