Progress in Metallurgy
Page 54
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That Benefits the Commercial-vehicle industry
There is Always Something New in Metals and Some of the Latest Products Have Invaluable Uses in the Motor Industry
nAY by day patient investigation and L./research into metals for the commercial-motor industry proceeds, and almost every month sees some new development or discovery of practical
importance. Recently, for example, bearing metals have been the subject of extensive tests, and it has been demonstrated that the introduction of nickel into graphitized alloys produces bearings with a higher starting load capacity than is found with non-graphitized non-nickel-containing bearing alloys.
A nickel containing white metal, with a high lead percentage, prevents, to a great extent, the possibility of seizure during the running-in period. Furthermore, the coefficient of friction is con siderably lessened. It • is obvious. therefore, that the graphitization of bearing metals is, in itself, advantageous, whilst the addition of nickel emphasizes this improvement.
For heavily stressed parts such as connecting rods, pistons, cylinder heads, bearings, body parts, wheels, axles and other components, a new nickel-containing aluminium alloy has been developed, known as R.77. This has the following typical percentage analysis: copper, 1.5-3.0; zinc, 4.0-6.0: magnesium, 2.0-4.0; iron, up to 0.6; silicon, up to 0.6; nickel, up to 1.0; titanium, up to 0.3; the rest being aluminium.
This new material has valuable mechanical characteristics, and can be supplied in most wrought forms, e.g., pressed, rolled, extruded, drawn, etc.. Having a specific gravity of 2.8, it possesses, also, a high strength-toweight ratio.
Aluminium Alloys for Bodies.
Aluminium alloys have been used with considerable success in the construction of bodies. For example, aluminium-copper-silicon alloy sheets have been used for this work, whilst strengthening members have been made from a nickel-aluminium alloy. Similarly, rivets have been made from an aluminium alloy.
The result has been to lighten body weights very considerably. One per cent, nickel steel has also been used for commercial-vehicle bodies, its application being to the four main posts and the longitudinal members. Its employment has enabled light sections to be used without any increase in weight in comparison with wood, but with a much higher strength factor and longer life.
Of extraordinary interest is the range of new stainless steels of ferritic type invented by an Englishman, Mr. W. P. Digby. These are known as " Cypritic " stainless steels, and their base analysis is 10 per cent. copper, 18 per cent, chromium, and 72 per cent. iron Their resistance to corrosion is not So
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high . as that of the standard 18.8 austenitic stainless steels, but it is claimed to be considerable.
Practical experiments with the material in use have been successful and mechanical properties are good, particularly the impact figure. Welding presents no difficulties and intercrystalline corrosion is negligible. The chief advantage of these new steels is their low cost, because nickel IS replaced by copper, which is relatively cheap. Forging and rolling can both be done without difficulty, and th-i steel takes a satisfactory polish.
Stainless Steels in Experimental Stage.
It must be remembered, however, that these stainless steels are still largely in an experimental state, and the claims made for them should be closely examined. The new steels are being developed chiefly in America and British metallurgists, puzzled by the entirely unorthodox structure of _the steel from the point of view of corrosion resistance, are doubtful whether the claims made will be borne out.
Nevertheless, reports indicate that these new steels must be seriously considered, as it is possible that their introduction may completely revolutionize the use of stainless steel in the commercial-vehicle industry.
In the United States a nickel. chromium steel has been successfully employed for trailer frames, and it ;s said that by this means their weight has been reduced by 30 per cent. The steel is used in the as-rolled condition, but even without heat-treatment, and with a carbon percentage below 0.15 per cent., the strengths obtained are high enough to allow the section dimensions to be reduced to the extent mentioned. An interesting feature is the extension of the use of alloy irons in the production of tyres. Used for tyre moulds, an alloy iron of the base analysis 1.5 per cent nickel, 0.6 per cent, chromium has proved highly successful. The material has a dense, close-grained structure, free from either hard carbide segregations or porosity, is easily machined, and can be given the high degree of polish necessary in these dies.
Alloy irons have also been used for brake drums where high resistance to wear, and the ability to withstand swift fluctuations in temperature, are desirable. The material used is a 1.5 nickel, 0.5 per cent. chromium iron. This has a Brinell hardness of about 260, and possesses sufficient toughness together with heat and wear resistance. The same iron has also been used for oil-engine cylinder sleeves, but of a slightly harder quality (Brinell 300), and easily machineable.
In tools, a new development is the portable band file. This is a device for continuous filing and consists of short file segments mounted on a steel band. The ends of the segments are so made that they interlock with one another and present an uninterrupted surface to the work. Smooth flow, together with a locking mitre principle, produce a tool somewhat on the lines of .a helical-gear tooth construction.
New Steel for Permanent Magnets.
The extension to use in speedometers' and magnetos of the new nickel-ironcobalt-aluminium steels for permanent magnets lends interest to the attempts being made to improve the magnetic
properties of these materials. Chromium arid manganese have been added as alloys, and a suggested new alloy of this type contains 20-22 per cent. nickel, 9-12 per cent. aluminium, and 5-10 per cent. cobalt. The chromium and manganese percentages have not been disclosed, but it is claimed that certain improvements have been secured by their addition.
To provide a range of magneto, speedometer, and electric-lamp magnets of a more malleable type than the nickel-aluminium-cobalt and nickelaluminium magnets at present being used, which are obtainable in only the cast form, a new range of nickel-copper magnet alloys has been invented in Germany. Some remarkable claims are made for these, but their magnetic characteristics are not so good as those of the existing alloys.
On the other hand, their relatively low cost and malleability combined with the high magnetic properties which they admittedly possess, make it possible to employ them for types and forms of magnets not hitherto obtainable in other than the less-valuable