How Metallurgical Research
Page 49
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Has Benefited the Motor Trade
AETALLURGICAL" research conIVItinues to he concentrated largely on the development of materials and processes of value to the motor industry, and in this article are enumerated some of the more recent results of this research. Cylinder performance in the commercial vehicle is an important matter, because it decides, to a large extent, the life of the engine.
A range of nickel-aluminium alloys has been developed, which has, on account of the light weight,, been of extreme value to the oil-engined commercial vehicle. These metals are used for cylinder heads, where they have the advantages of good heat conduct ivity, lightness, uniformity in mechanical properties and simplicity of casting.
A nickel-aluminium alloy is also being used for connecting rods in these oil engines, for which it has proved to be highly successful, eliminating many big-end troubles.A similar alloy, of slightly different composition, is employed for pistons in road-vehicle oil engines.
Piston trouble as a result of expansion under heat is a not-infrequent cause of engine seizure. To minimize this trouble, a method of regulating the expansion of the piston has been developed. Struts of Invar, an alloy containing nickel and iron, are cast into the piston. Invar is a material with a low coefficient of expansion and, as a result, the heat generated by the combustion chamber does not create sufficient expansion in the piston to cause seizing.
Alloy Steels that Withstand Heavy Shocks.
Wherever commercial vehicles have to withstand extremely heavy shocks and arduous 'service, exceptional strength is demanded in the frame or body. The use of alloy steels has been of great advantage in this direction. In one instance, the frame of the vehicle has been made throughout of nickel steel.
For cylinder heads which have to be shrunk on, and for similar motor components where low specific gravity, combined with high strength and easy casting, is required, a new alloy has been developed, .which consists of 2.5 per cent. copper, 1.5 per cent. nickel, .0,6: per:cent: magnesium, .1.2 per cent. iton, 1.2 per cent, silicon, and 0.15 per cent, cerium, the rest being aluminium. The special feature of this analysis is the inclusion of the alloy cerium, which tends to minimize brittleness, whilst giving to the castings a good, clean surface and a pleasing finish. The new material has high tensile strength at considerable temperatures, a high elastic limit and Brinell hardness, with also a high fatigue strength.
Many commercial vehicles have to operate in areas where the atmosphere is of a specially corrosive character, as in the neighbourhood of chemical works, blast furnaces, steel-manufacturing plant, etc. A lorry user has recently conceived the novel idea of mounting austenitic stainlessasteel name plates on the sides of the vehicle.
Seven plates, about 2 ft. 6 ins. long.
are used on each side. These are given a bright polished finish, and the lettering is painted in bright blue, straight on to the steel without any spe6a1 preparation being necessary, The plates are held in position by angle brackets drilled to receive bolts, and the lorry presents an attractive appearance.
To combat atmospheric corrosion, a new alloy steel has been placed on the market. It is a low-chromium coppersilicon alloy with a hig percentage of phosphorous in its composition, and claims are made that this steel will offer from four to six times as great a resistance to atmospheric corrosion as will an ordinary carbon steel of standard quality.
In the United States a chassis frame has been constructed entirely of tubular steel, and it is claimed that this new development ensures a great saving in weight.
A material which is becoming inCreasingly important in its application to commercial vehicles is the low carbon nickel manganese steel, with the following approximate composition :— Nieltel 4-7 per cent., manganese 0.35 per cent., and Carbon 0.07-0.20 per cent.' This steel has great uniformity of structure., and' in the softened state has the ability to be nia,chined as easily as a semi-hard carbon steel. It can be cold-formed or bent.
It is largely employed for ,transtnission shafts, steering roefs, cardan forks, back axles, bolts, gudgeon pins, etc. Its primary advantages are high mechanical strength and high elastic limit —a capacity to be cold-worked without fracture—and a great resistance to vibration and repeated shocks: A new steel for welded underframes, bus and lorry bodies and other purposes, is the copper-molybdenum alley material, which contains 1.5 per cent. copper, 0.2-0.3 per cent. molybdenum and low carbon. This steel can readily be welded and has high resistance to atmospheric corrosion. Its tensile strength is 34-44 tons per sq. in.
Invar has already been mentioned in connection with pistons as an alloy with a low coefficient of expansion. Stainless Invar is a . new discovery, made by Hakar iVlasurnoto, a Japanese. It contains approximately 54 per cent. cobalt, $6.5 per cent, iron and 9.5 per cent, chromium, as against the 63.5 per cent, iron and 36.5 per cent, nickel of the ordinary Invar metal.
This new material has a smaller coefficient of expansion under heat than has even fused silica. It is highly resistant to corrosion and its surface remains bright after long periods of immersion in strong corrosive agents. The material is too new for its application to the motor industry to have been fully realized as yet, but there is little doubt that, like Indar, it will soon be playing a part in the prevention of piston expansion.
Characteristics of a New Bronze for Dies.
A new bronze has been invented for the highly polished dies required in the manufacture of many motor parts. No final polishing is required by the stampings after manufacture in dies of this material. It has a Brinell hardness approaching 340. This is not so hard as ordinary die steels, but, in practice, it is found that the life of the dies is fully equal to that of steel, because no "picking up" of the stock. occurs as it passes through the die. When chassis frames are being stamped out in dies of the new bronze, it is the usual practice to back the dies with steel,
Another die-casting alloy is nickelcopper silicon, which has a tensile strength of 12 tons per sq.,in., and is employed in the manufacture of crankcases, gearcases, clutch covers, etc. By its means, the die-caster is able to obtain a perfectly accurate finish combined with stability in use.