Metallurgical Progress
Page 39
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Benefits the Motor industry OF late, metallurgy has not received its fair share of general publicity as regards the work it has done on behalf of the commercial-motor industry. In the present article a few developments of special interest in this direction have been summarized. One may mention, first, the excellent work on lead bronzes, for automobile use, carried out by the Germans, who have been experimenting with bronzes containing over 20 per cent, of lead, but with little or no tin, for bearing metals.
Another interesting feature is the continued development of the alloy cast irons. Nickel-chromium cast. iron, for example, is being employed for brake drums, and is hardened and tempered in advance of machining. It is stated to offer full resistance to heat cracks, to lift the tensile strength from about 24 tons to 26 tons per sq. in., and to provide a hard surface for braking without any deleterious effect on the shoe facings.
New Alloy Steels for Use in Spring Manufacture.
The me of alloy steels of complex type for springs is a further development, due to the work of the metallurgist. In the United States of America no fewer than 45 new coaches have been fitted with springs made from a special chromium-vanadium steel, which has been found to give smooth riding qualities.
A new range of alloys for permanent magnets is not the least of the new discoveries. These magnets are used in speedometers, electric clocks, etc., and the novel alloys now being adapted contain nickel, cobalt and copper. They have given most promising results, and are said to have excellent working properties, and tensile strengths much higher than those of the iron-base alloys, together with better impact figures. Their magnetic characteristics compare very well with those of other magnet alloys.
Cylinder liners have been successfully nitrogen-hardened, and have been found, in petrol engines, to offer great resistance to abrasive wear, if not in oil engines, whilst another direction in which the metallurgist is at present experimenting is that of chromium plating the cylinder bores, which, at the moment, is being done commercially.
Trailer side-rails have been made, with great succeas, from a nickel:. copper alloy steel. The object of using this steel is to save weight, without in any way losing strength. Approximately 50 per cent, higher strength can, in fact, be obtained without change of weight. The. same alloy steel is being widely, used in commercial-vehicle construction for frames, body sheets, etc. _ _
A new alloy for valve seats is the direct result of the metallurgical research work being carried out daily in this country. This is a chromiumcarbon-silicon-iron alloy which offers extreme resistance to oxidation under heat; great hardness, given by a suitable heat-treatment; a tensile strength of from 45 tons to 55 tons per sq. in.: and a Brinell hardness figure of 387 at a temperature of 500 dogs. C. For inserts, this alloy is said to be much superior to either Stellite-faced ,seats or heat-treated high-speed steel.
In punching and forming various parts, such as fenders, radiator shells, head lights, etc., an alloy cast iron containing 3.3 per cent. carbon, 1.25 per cent. silicon, 0.75 per cent. manganese, 1.5 per cent, nickel, and 0.75 per cent, chromium has been used for the dies. This material is said to give the dies a high machinable hardness and wear-resisting structure, which ensure a longer service life and greater manufacturing economy than is obtainable with ordinary cast-steel dies.
• Another discovery of metallurgical character is that vanadium, in small quantities, added to cast iron, produces a wide range of alloy irons highly suitable for such commercial-vehicle parts as brake drums, oil-engine cylinder heads, cylinder blocks, piston rings, clutch plates, heavy gears, exhaust manifolds, cylinder, liners, and dies. These irons give a higher transverse strength and wear resistance than ordinary iron castings, as well as improved tensile strength and Brinell hardness. These advantages are gained without any loss of machinability, Germans Experiment With Cast Iron for Bearings.
The Germans, hampered by a shortage of raw materials and an internal economy that compels them to concentrate on substitutes, have been experimenting with cast iron for bearings, as a retern to an old condition, They claim to have obtained satisfactory results with a cast iron having a tensile strength of 16.5 tons per sq. in., ground and polish-finished, which is said to have withstood considerably higher bearing pressures, without seizing,. than a .cast-bronze bearing. Nickel-chromium-molybdenum iron has been developed for valve guides, and is said to have superior wear resistance, as well as resistance to growth, to that of ordinary cast iron. Nickel-cadmium cells have greatly improved accumulators for engine starting, etc. Nickel-molybdenum steel has proved attractive as an alternative alloy steel for engine gears, whilst a 1 per cent, nickel steel is being widely employed for connecting rods and caps.
Another valuable advance is the discovery that cadmium-base bearing alloys, plated with indium, will overcome the corrosive attacks of lubricants containing organic acids. The indium addition harms neither the fatigueresistance nor other bearing properties. The indium is electrolytically deposited as a thin coating on the bearing surface, which is afterwards heated so as to ensure diffusion of the indium into the surface layers of the parent alloys.
Corrosion-resisting Metals for Cooling Systems.
Copper-nickel alloys have been found advantageous for radiators and oil coolers, and, in particular, they provide ample resistance to the corrosive action of special cooling liquids in radiators. High nickel alloys for sparking-plug electrodes have been found exceptionally serviceable for high-class engines. They have good electrical properties combined with erosion resistance.
As an alternative to the alloy for valve inserts referred to earlier, high nickel-copper alloy may be quoted. It has been found one of the best allround metals for this purpose, having good oxidation resistance with a low rate of wear.
A development that promises to be extremely important is the alloying of cast irons with the element boron, but this is, at the moment, only in the experimental stage.
Carbon-vanadium steels are being used in America for connecting-reds. Sheet work for commercial vehicles is being made, in certain British works, from an aluminium-copper-silicon alloy. The strengthening members are made from a nickel-aluminium alloy, rivets are of aluminium alloy, and bolts of cadmium-plated steel. The result is an extremely light vehicle which enables an increased pay-load to be secured.
Another type of alloy, containing magnesium, is being used for pistons. This contains 1.5-2.5 per cent. copper, 1.4-1.8 per cent. magnesium, 1.2-1.5 per cent. iron, 0.5-2.0 per cent. nickel. 0.02-0.12 per cent, titanium, and not more than 2.0 per cent. aluminium. For gears, a chromium-molybdenum case-hardening steel is also proving highly satisfactory. L.S.