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New Progress Made in Commercial-motor Metallurgy

13th January 1940
Page 27
Page 27, 13th January 1940 — New Progress Made in Commercial-motor Metallurgy
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Developments in Scientific Treatment of Metals, of Value to Our Industry

A SURVEY of what is happening in 1-1 the laboratories and workshops of the world reveals a large number of developments of interest and importance to the commercial-motor industry. In Russia, for example, a small, compact apparatus for surface hardening of metals has been invented. This employs a gas pressure of 10 cm. of water, and it is possible to carbonize, nitride, cyanide, and bright anneal, at different temperatures, various steels and nonferrous metals. The apparatus includes equipment needed to produce the different gas. mixtures.

In Germany, a new electric-welding machine has been introduced, in which the voltage inertia is eliminated by the excitation of additional leakage fields, thereby producing a higher efficiency. From America comes a successful procedure for welding 18-8 stainless steel to 66-34 brass. These two metals can now be united with a fair degree of weld strength. The weld itself, and its efficiency, are to some extent governed by the constitution and form of the welding-electrode tips.

New Bearing Metal

Great Britain records a new metal for main bearings and big-ends. The alloy in question contains 5.5 per cent. tin, 1.5-1.8 per cent, nickel, 0.6-0.9 per cent. copper, 0.7-1.0 per cent. magnesium, 0.15-0.3 per cent. silicon, and 0.2-0.45 per cent, iron, the balance being aluminium, This alloy improves fatigue .resistance, anti-friction properties, corrosion resistance, and mechanical strength.

Another interesting advance is the manufacture of fabricated bearings with duplex structures, such as chromium-bronze bearings, which are claimed to be extremely tough and ductile, so that wherever toughness is required their employment is advantageous. The chromium bronze contains approximately 2-10 per cent, tin, with 1 per cent, and upwards of iron and chromium For piston rings, a new silicaaluminium alloy has been produced in the United States. This includes in its analysis certain age-hardening constituents.

This metal has enabled a great improvement in piston performance to be achieved, since the previous defect of these alloys was a lack of elastic

modulus, This lack has now been overcome, and the silico-aluminiurn alloy has an elastic modulus about twothirds that of cast iron, with a force of inertia, due to mass, of only onethird. Again, the to-efficient of thermal expansion of the alloy is lower, it is claimed, than that of any other commercial alloy of aluminium type.

A non-magnetic alloy iron has proved of great value in improving the design of magnetic clutch-brake combinations. This is a nickel-copper-chromium cast iron, non-magnetic, and possessing a high degree of electrical resistance, Used in the contacting elements, it permits smooth and rapid acceleration and deceleration.

Crankcase forgings are being made from an alloy containing 1,5-2.5 per cent. copper, 0.5-1.5 per cent. nickel, 0.6-1.2 per cent. magnesium, 0.8-1.5 per cent. iron, 0,12 per cent, titanium, and 1 per cent, silicon, the balance being aluminium. For gears of lorries, high-tensile nickel-chromium steel is being used, with a copper-silicon-nickelaluminium alloy for the casing.

Cylinder liners are being made from a cast iron to which has been given a nitrogen-hardening treatment. This iron contains small percentages of aluminium and chromium. The liner is heated up in an atmosphere of dissociated ammonia and maintained at 500 degrees C. for from 40 to 90 hours. Another interesting discovery is that silicon carbide, added to cast. iron, raises the tensile strength and hardness without in any way making the iron more difficult' to machine. • On the production side, the invention of a new hard-cutting metal must be mentioned. The hardness of this is obtained from crystalline chromium borides, together with an " unknown " crystal "X." This metal is claimed

• to be considerably lighter than tungsten carbide. It has been used for the hard-facing of various parts, when it is applied in the form of a paste and sweated on. The boride crystals alloy with the base metal, whilst "X " crystals permeate the mass as if held in an emulsion.

Magneto-magnet Metals

Magnets for magnetos continue to constitute a whole branch of metallurgical research, Here lack of space prevents more than a brief examination of what is being done. It is sufficient to say that permanent magnet allays of large coercivi ties are being continually experimented with, and among these may be mentioned ailver-manganesealuminium, iron-molybdenum, ironneodymium, platinum-iron-cobalt, and palladium-iron. Another new magnet alloy contains 32 per cent. nickel, 12 per cent, aluminium, together with small percentages of titanium and a balance of iron.

In France petrol costs are high, and there is an increasing tendency to turn to gas as vehicle fuel. Compressed gas is carried in cy.linders made from nickel-chromium-molybdenum steel, to raise the ratio of strength to weight. Japan is using nickel-aluminium-copper for pistons, and nickel-chromium-iron for piston rings.

Novel and interesting developments of a somewhat. different type include the addition of about 3 per cent. of molybdenum to stainless steel, in order to eliminate pinhole corrosion, and the discovery of the fact that a wide range of tensile strength and hardness can be given to steel containing about 1.5 per cent, carbon and 1 per cent, silicon by modification of the heat treatment.

Lorry bodies are being constructed of low-alloy, high-tensile steel of copper, nickel, molybdenum type, which enables weight to be reduced without any loss of strength, whilst giving greater length of life owing to improved corrosion resistance.

Some attention should be paid to the coating of valves and inserts with an 80/20 nickel-chromium alloy. A method of dry cyaniding plain and alloy steels, such as the nickel and nickel-chromium steels, has been developed in America. This combines the processes of continuous nitriding and continuous gas carburizing. The case produced has considerable affinity with a cyanide case. The principle of the process is the employment of ammonia in conjunction with other gas carburizing mixtures, the constituents of the atmosphere being suitably modified, as is the time and the temperature of the treatment. A special technique is essential to the success of the method, which has already given promising results.

Progress in Nitricling Nitrogen hardening is a source of unending investigation, and the latest progress includes attempts to produce satisfactory nitriding of tantalumniobium and austenitic manganese steels. It has been found possible to nitride satisfactorily engine valves made from a steel containing 14 per cent. chromium, 14 per cent. nickel, and 2 per cent. tungsten. By nitriding stem and guide wear have been considerably lessened without any loss of hardness.

The French have been experimenting with the welding of nickel chromium air-hardened and case-hardened steels, and have discovered a useful method, designed to avoid brittleness. A nonhardening metal, e.g., austenitic nickelchromium steel, is first deposited on the surfaces of the chamfers to a depth rather greater than the thickness of the base metal.

The treated parts are annealed, thereby eliminating the brittle zone, and may afterwards be hardened and tempered if desired to produce the requisite mechanical characteristics. The parts are then assembled and the joints welded, employing austenitic electrodes, the weld being made wholly upon the deposited coating. This does away with the need for re-heat-treating the base metal,

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