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Already the Employment of Nickel in Alloys for a Variety

3rd September 1937
Page 36
Page 36, 3rd September 1937 — Already the Employment of Nickel in Alloys for a Variety
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of Commercial-vehicle Parts has Contributed to Advancement, and More Progress May be Expected says a Metallurgical Authority

Nickel Alloys

a key factor in production progress

AODERN metallurgists claim that it lifiwas the discovery of the nickelalloy steels that first directed the attention of engineers to the enormous and since-realized possibilities of alloy steels. But not alone has nickel proved beneficial to the steel industry; its alloying with iron has also enabled a number of new materials to be developed—materials that have played and continue to play a great part in the progress of commercial motors. Some examples are given below.

The withstanding of the tendency to wear and crack has been one result in connection with the use of nickel iron for cylinder bloCks. The higher speeds of to-day, together with the increased power and acceleration obtained, have definitely caused an increase in this tendency, and the only means for efficiently and economically eliminating the trouble has been the employment of a nickel-chromium iron for the cylinders.

The use of this material creates a more uniform structure in the metal, and:, therefore, the expansion and contraction caused by intermittent heating and cooling are counteracted by the more uniform diffusion of temperature changes. Furthermore, the cylinders are denser and easier to cast with perfect soundness.

Harder Castings.

They do not chill, or show undue brittleness where the section is thin. Not only this, but the castings can be made harder without increasing the difficulty of machining. Thus, a more uniform cylinder metal, a greater resistance to rapid changes of temperature and a more durable cylinder block are obtained.

A typical nickel-chromium iron for cylinder blocks contains 2.8-3.3 per cent. carbon, 0.5-0.8 per cent. manganese, 1.5-1.75 per cent. nickel, 1.75-2.25 per cent. silicon, and 0.5-0.75 per cent. chromium.

Similarly, a nickel-chromium iron of somewhat different composition is being used for cylinder heads. These components have to withstand the maximum heat of the combustion, and for this reason are hotter than any other part of the engine, except the valves. Because of the cooling essentially concentrated on them, they have to withstand rapid fluctuations of temperature, which lead to cracks.

A suitable alloy for these parts demands ability to retain the original size, minimization of expansion under heat and greater toughness. Therefore, more nickel is included in the B40 composition of the iron, and the approximate analysis employed is 2.9-3.3 per cent. carbon, 0.5-0.8 per cent, manganese, 1.5-1.6 per cent. silicon, 2.0-2.5 per cent, nickel and 0.3 per cent. (maximum) chromium. Such a material is almost ideal for these components.

In the production of dies for automobile-part manufacture, a great deal of expense is involved. The die cost is made up of two .principal items— metal and machining. Therefore, the easier a die material is to machine, the less the dies will cost. Easy machining and solidity (i.e., absence of porosity) are indispensable requisites.

Three Valuable Features.

Obviously, if machining work were done on a die that proved, eventually, to be structurally unsound, money would be wasted. A third requisite is a considerable degree of hardness, to enable the die to stand up to its work.

Nickel-alloy cast-iron has been found to be a highly suitable alloy for these dies, because it combines the three main requisites specified. The approximate analysis of this material is as follows:—Carbon 2.9-3.0 per cent., manganese 0.6-0.7 per cent., silicon 1.25-1.5 per cent., chromium 0.8-0.8 per cent. and nickel 2.5-2.75 per cent.

One further advantage possessed by dies made from this material is that they are capable of acquiring a high polish, which minimizes scratching, and makes it possible to obtain deeper and more difficult pressings. They have also a considerable degree of resistance to abrasion and wear (approximately four or five times as great as that of ordinary grey iron).

Another application of nickel-allay iron is to large oil-engine liners. For these an alloy comprising 3.0 per cent. carbon, 1.65 per cent. silicon, 1.5 per cent, nickel and 0.3 per cent, chromium has been used with great success.

Reduced Cylinder Wear.

It has been found that after a brief running-in period, cylinders equipped with liners of this type take on a highly polished surface, wear less than castiron cylinders and create no problems of heat dissipation. Liner castings have also been made centrifugally to the dimensions destired, with an allowance for machining. It is claimed that large economies have thereby been effected, because of the saving in weight of metal obtained, and the reduction of stock needing to be tooled off.

Nickel-iron clutch plates have also been successfully manufactured from a nickel alloy containing 0 75 per cent. nickel, 3.2 per cent, carbon and 2.25 per cent. silicon. , A nickel metal, although not of the iron type, has helped to reduce ignition troubles. Used in the form of rotating electrodes and as electrodes in the distributor casing of coil-ignition distributors and magnetos for automobile electrical equipment, pure nickel has reduced to a minimum breakdowns due to failure of ignition. Extensive tests have shown it to be by far the most satisfactory metal for withstanding erosion by sparking. '

One of the most important uses of nickel-alloy iron is for camshafts and crankshafts. For these a nickel castiron of composition as follows is largely used:—Carbon 3.1-3.4, silicon 2.1-2.4, manganese • 0.5-0.75, chromium 0.75-1.0, nickel 0.2-0.4 and molybdenum 0.4-0.6 per cent. Piston rings have also been made from this material.

Oil-fuel 'meters, like most other appliances of measurement, have to be capable of retaining their initial accuracy throughout their lives. For this reason, corrosion must be reduced to a minimum, so that any " sticking " is avoided, and, with it, inaccuracies of measurement.

Prolonging Meter Accuracy.

For 'this reason, a nickel-chromium cast-iron has been used for the piston and all other parts, of the measuring chamber in these meters, and for ihe gear case and the gears of the intermediate train that transmits the movement to the register. By this means meter accuracy has been greatly prolonged_ For bushings, gears, piston rings and the like, a high-grade nickel-chromium iron has been used with an analysis of 2.8-3.0 per cent. carbon, 1.8-1.8 per cent. silicon, 0.65-0.85 per cent. manganese and 1.25-1.5 per cent. nickel.

This material has varying degrees of hardness, according to temperature. For instance, at 235 degrees C. it gives a Brinell hardness number of 450, and at 510 degrees C. 'a hardness number of 300. The alloy is readily machinable and can be heat-treated to give a high degree of mechanical strength.

It will thus be seen that the nickel irons promise to play an increasingly important part in the manufacture and maintenance of commercial vehicles. Experiment with and research intothese irons are daily continuing and almost each month sees new irons developed for specific purposes.


Organisations: Metallurgical Authority

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