Review of Progress in
Page 39
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Motor. Metallurgy
Developments in a Number of Important Directions Indicate Fields of Use in the Commercial-vehicle Industry for Some of the Latest Steels and Alloys
A SURVEY of developments in the
commercial-motor industry reveals the extent to which the newer, as well as the established, steels and alloys are being employed. For example, the magnetic properties of a steel containing 29 per cent, of nickel, at low ternperatures, are being employed in generators and speedometers. Small pieces of nickel steel function at low temperatures to raise automatically the charging time 'of the generator, or to correct the speedometer reading.
A new light aluminium alloy, into the composition of which a percentage of nickel enters, has been produced for use as a bearing metal. It has been severely tested under actual road conditions, and is now being fitted to bigend and main bearings of commercial vehicle engines.
A new device is the " choke stove," which provides rapid starting from cold and allows a considerably reduced warming-up time. The invention incorporates a tube of nickel-copper alloy running through the exhaust manifold, where it is immediately in the flame.
Gears of 5 per cent. nickel steel have proved their ability to stand up to heavy service. In one instance, a commercial vehicle covered 750,000 miles without transmission trouble, when furnished with gears of this steel.
Alloy Cast Irons Finding Increasing Favour The use of alloy cast irons is also extending. Recently, a new light lorry has been introduced in the United States incorporating a high-strength alloy cast iron, containing 1.5 per cent, of nickel and 0.5 per cent. of chromium, for crankcase and cylinder block. The engine of this vehicle is air cooled, and the crankcase weighs about 85 lb.
Brake drums are being made from chromium-molybdenum cast iron, where exceptionally hard conditions are likely to be experienced.. Long, steep hills, climbed with heavy loads, generate considerable heat in these drums, which often rise to a temperature of over 425 deg. C. Water cooling is sometimes employed, and, on occasion, this effect does not start until the drum is already at a good heat. The result is a sharp chilling of the metal.
In the United States, where trailers carrying heavy loads of logs are frequently run long distances in mountainous country, brake drums have been made from an electric-furnace cast iron containing 0.25-0.45 chromium and 0.45 per cent. molybdenum.
This iron is strong and tough, and offers much greater resistance to wear and abrasion than ordinary iron. It does not " grow," warp, or break down, when subjected to repeated heatings at rather high temperatures, • followed by sudden cooling. The introduction of molybdernim into the analysis lessens the liability to distort or lose form, so that pounding, which is a frequent cause of breakdown, is largely eliminated. The iron has a maximum stress of 45-50 tons per sq. in.
For piston rings, a new hypereutectic silicon-aluminium alloy has been developed. This contains age-hardening constituents and is closely controlled as regards impurities. Marked advantages in engine operation are derived from the light weight and high thermal conductivity of this alloy, which has a satisfactory elastic modulus (15,000,000 lb. per sq. in.), combined with a moment of inertia amounting to only one-third that of a good-quality piston-ring cast iron. It is stated that the thermal expansivity of the alloy is the lowest of any useful aluminium alloy commercially produced. The metal is employed either heat treated to 180 Brinell for piston-ring use, or to 110 Brinell for piston use.
Tyre Chains from Case-hardened Steel Tyre chains are being made from a
case-hardened carbon-molybdenum steel. The chain links are manufactured from wire of several diameters, ranging from 0.172 in, to 0.375 in.. according to the type of service for which they are required. The steel contains 0.15-0.2 per cent. carbon, 0.6-0.8 per cent. manganese, 0.2-0.3 per cent. silicon, and 0.15-0.25 per.cent. molybdenum.
Road springs for certain British commercial vehicles are being made from silico-manganese steel leaves with inset bronze hushes. Gearboxes on the same vehicles are made from a copper-siliconnickel-aluminium casting alloy.
In cylinder liners, four main lines of research and experiment are producing results, These are liners hardened by heat treatment, nitrogen-hardened cast iron, austenitic cast iron, and chromium plating. The heat-treated alloy-iron liners have their value when abrasion is considerable, but are less satisfactory when corrosion also is encountered. Austenitic cast iron will withstand corrosion, as well as a considerable degree of abrasive wear; such irons invariably contain' a percentage of nickel.
Nitrogen-hardened liners are suitable for petrol engines, where abrasive wear is likely. Chromium-plated bores are still largely in the experimental stage. For exceptionally severe service, a chromium cast iron, containing 32 per cent. of chromium, appears to give the most promising results, but a 13 per cent, chromium cast iron is also suitable.
A recent application of stainless steel is the first tank car of welded columbium-containing stainless steel. The columbium addition lessens the risk of weld decay. Lightweight stainless-steel semi-trailers are also in service; these measure 30 ft. in length with a height of 11 ft. 8 ins. Each trailer weighs 6,300 lb. Bodies and integral frames are built complete of stainless steel, a net weight saving of about 3,000 lb.
being effected, as against standard
construction.
Chromium-molybdenum case-hardening steels are being used for gearwheels and shafts in German commercial vehicles, as a substitute for nickelchromium steels. If oil-hardening types of these steels be called for, nickel or vanadium in small percentages is 90MCtimes added to the analysis. •
In clutch mechanisms, nickel-alloy cast-iron flywheels have been found to give a more satisfactory wear factor and greater resistance to scoring than either a low-carbon steel, or a straight, unalloyed cast iron. A steel containing 1 per cent. nickel and 0.45 per cent. carbon is being employed for the splined centre hub of the driven plate. This steel has excellent broaching and machining properties, combined with a high degree of wear resistance; 3 per cent, nickel-chromium case-hardening steel is being used for the splined shaft upon which the driven plate slides. This material has a core strength of 50-65 tons.
The heavier commercial vehicles are using nickel-alloy cast iron for clutch cover and outboard bearing sleeves and for pressure plates, whilst the clutch shaft is of nickel-chromium casehardening steel, although nickelchromium-molybdenum steel is also being used for the last named. For inlet and exhaust valves 3.5 per cent. nickel steel is being used.
Germany Develops Centrifugally Cast Brake Drums The centrifugal casting of brake drums has been developed in Germany. Substantially, the drum is built tip of two parts, the back of sheet steel, the flange of which is furnished with dovetailed recesses to facilitate close welding and to raise the safety factor, and the centrifugally cast-on iron rim. The iron and steel are intimately fused together by fusion welding, the carbon of the cast iron penetrating to a goad depth into the steel. It is not necessary to pm-heat the sheet steel.
Recent advances in the art of electric welding have rendered it feasible to produce, as a commercial article, tubing of stainless steel of gauge as fine as 40, i.e., 0.003 in. thick. The tube can be corrugated into flexible hose, whilst end fittings can be welded on for attachment of the tubing, wherever it is to be used.
A new magnetic clutch-brake combination having positive clutch, friction clutch, and friction brake, has been developed. The clutch discs are being made of nickel-copper-chromium cast iron, which is non-magnetic. Whilst this device has been designed mainly for electric-motor use, the significant point for commercial-vehicle designers is the use of this alloy iron for clutch discs.