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Light Alloys and the Post-wai :ommercial Motor

14th May 1943, Page 28
14th May 1943
Page 28
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Page 28, 14th May 1943 — Light Alloys and the Post-wai :ommercial Motor
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Presenting Brief Notes on Technique and Economics of the Application of Aluminium and Magnesium in Engine, Frame, and Body Assemblies

By F. A. Allen

THERE is, of course, no novelty in the application of aluminium

• alloys to automobile engineering. One attempt, at least, has been made to construct an all-aluminium car, and Captain Eyston's "Thunderbolt " was largelydesigned for light-alloy cornponents. There are good reasons, however, for supposing that light alloys will find increased and novel uses in the post-war commercial motor.

War-time service needs for light metals have resulted in greatly increased production of these materials, and it is likely that steel will be in short supply immediately after the war, whilst aluminium alloys will be comparatively free.

It is a fact, further, that new methods of fabrication, developed to meet the aircraft production programme, will be available to the commercial-vehicle constructor. The uses to which light alloys have Been put in aircraft suggest many post-war commercial-motor applications.

Wrought and Cast ' Forms Available

Lightalloys include the well-known aluminium-base alloys and the more recently developed magnesium alloys, which are some 40 per cent, lighter than the aluminium compositions. .Aluminium alloys may be obtained in the form of extrusions, forgings, castings or sheet. Extrusions and castings are the form indicated for structural

work; the first-named may also be used for decorative beading and a multitude of similar work in coach bodies.

Forgings will undoubtedly be used for pistons and other high-strength engine parts. In this connection, it is of interest to designers to know that the technique of forging can be used to develop directional properties, so tbat components having greater • strength in the areas of greatest stress can be made. Aluminium-alloy aircraft propellers are made at the present time according to this technique.

Castings are made by one of three methods. There is the ancient method of pouring molten metal into a sand mould; the modification of pouring into a metal mould or die (permanent-mould ..casting in America, and, perhaps less accurately, gravity die-casting in England) and, thirdly, the use of pressure to force molten metal into a metal mould, this method being known as pressure die-casting, or, in the U.S.A., as just die-casting.

Of the methods outlined, permanentmould castings give the best lob for stressed parts, for quicker solidifica tion results in a finer grain. Also, this technique possesses the great advantage over sand casting in that it gives work either nearer to, or actually at, finished dimensions.

Pressure die-castings can be produced in large quantities with great speed, but owing to present imperfections in the process the castings are not sound enough to recommend them for every use. They are employed, however, in large quantities for handles and dashboard fittings.

Whether a part sEall be produced as a sand casting or a permanent-mould casting depends, to a great degree, on economics, for a small number of castings would be prohibitively expensive if made by the permanent mould method. •

An obvious use for light-alloy sheet is in bodybuilding. It may be welded, and it is of interest that structural members may be pse-fabricated by a drop-hammer method which is, at the present time, being actively developed by the Ministry of Aircraft Production. The great advantage of the 'system lies in its simplicity; this results in low manufacturing costs.

Commercial carrying companies engaged in the transportation, of food

stuffs, such as margarine, milk and beer, should remember that aluminium is, in the American phrase, iriendly-tofood, and such commodities may be carrie'cl without fear of contamination.

It is well known that tankers require heat insulation to prevent rise in temperature during the summer months, and here again aluminium is used in the form of thicknesses of foil, the outer shell being painted with an aluminium pigmented paint to reflect the sun's rays. •

What has been 'ivritten concerning aluminium-alloy extrusions, forgings and castings applies, in general, to magnesium alloys also. There are, however, two observations that. must be made. First. thgy suffer in comparison with aldininium alloys in respect of the efficiency with which protection against corrosion may be given, one magnesium alloy providing a notable exception.

Magnesium-alloy castings or,forgings would, therefore, be found only in internal engine positions, and in. such places where, working away from the atmosphere and perhaps in continuous lubrication, corrosion attack would be negligible. This statement presupposes that there is no major advance in protective treatment before the end of the W8 r.

In order to prevent a wrong impression being given of the properties of

magnesium alloys, it should be added that cast magnesium-alloy wheels and rims were tried many years ago on buses in Berlin, and excessive corrosion was noticed only after salt had been thrown on the winter streets to melt the snow. Furthernabre, Many of the American and British aeroplanes have magnesium-alloy landing wheels as standard equipment.

The other note that should be made is in respect of fire risks. The use of magnesium -incendiary bombs has, unfortunatelY, given the impression to non-metallurgists that magnesium in any shape or form is inflammable. This is not so; incendiary bombs are a very special instance in which magnesiurri is induced, somewhat reluctantly, to burn by a filling having the property of producing an extremely high temperature more than sufficient initially to melt the magnesium con -tamer.

Magnesium dust, in common with other dusts; either metallic. or nOn metallic, will ignite . comparatively easily. Machine-shop fires during turning or milling 'operations are not unknown, but in every case they result from incorrect tool-cutting angles or bluntness.

To clinch the argument that magnesium is 'not particularly hazardous in fire risk, the test may be instanced in which an open tank made of magnesium sheet was filled with petrol which was ignited. The petrol burned away without any suspicion of burning the magnesium container.

To the above brief outline of the mechanical and structural possibilities of light alloys should be added some account of advantages that would arise from their wider use in motor vehicles.

Light Alloys and Higher Pay-load

It is obvious that for any taxation class of commercial vehicle, pay-load can be increased only if unladen weight be reduced. Light alloys suggest a means for doing this. Take, for example, a laden vehicle of the maximum Weight of 22 tons. An average' chassis of such a type will weigh about 5 tons 15 cwt., which could be reduced to 5 tons if light alloys be used fairly extensively in positions likely to be adequately served by these materials. The trody weight could be reduced from 2 tons 15 cwt. to I ton in a similar manner.

It will thus be seen that the original pay-load could be increased by 2 tons 10 cwt., representing a saving of 18.5 per cent.

Further examples of the economic advantage of the use of light-alloy applications may be quoted. By 'applying aluminium sheet and fabrications to body,. a weight saving equivalent to seven normal passengers was achieved; a tanker normally harrying 3,060 gallons was redesigned in terms of a light-alloy tank and underframe and it was thus possible ,to increase the load by 850 gallons.

A striking example from the same source of information shows a weight saving through incidental causes, for it was found that the use of a wooden floor in an open lorry resulted in an increase of 400 lb. through absorption of rain water. This unnecessary, unprofitable load would be obviated by the use of light-alloy sheet flooring—

a standard semi-manufactured product, by the way.

It is a fact that much greater energy is required to deform aluminium than steel (realization of this fundamental lies at the back of successful industrial production of aluminium stampings and pressings), but this has an important bearing on what might be termed resistance to accident hazard. If, for the sake of argument, a vehicle constructed largely of steel has a crash sufficiently seelous to smash it, a crash of the same mechanical force would be likely only to deform a light-alloy vehicle to a third of the extent.

Perhaps, not the least important advantage of light metal for chassis and body construction, lies '.in the ease with which deformation within the plastic range may be rectified. The fact that, without undue weight, greater rigidity may be, obtained, is, in a measure, a safeguard against buckling and.denting.

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Locations: Berlin

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