Pistons and Other Parts of Aluminium.
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By Henry Sturmey.
We already use aluminium to quite a considerable extent in chassis construction, for the simple reason that, all other things being equal, the lighter a part can be made the better, seeing that this means less weight to drag about and consequently less fuel expenditure in the doing of it. Crankcases, gearboxes, and in many cases rear-axle differential cases, even in heavy truCks, are all made of aluminium, and it has apparently "come to stay." Can. it be used advantageously elsewhere? There is not much doubt but that it can be and that it Will be, in the not very distant future, because it has already been proved by experiment and more than experiment that it can be satisfactorily so employed.
Aluminium at X501) a Ton.
In America very much more has been done in this direction than with us, but, for the present, except in one direction, further progress is stopped by the price of aluminium, which has risen to close on £300 a, ton, being scarcer there than even with us. Seeing, however, that the American Aluntinium Co. is now expending a sum approximating 24,000,000 in the erection of new producing plant, it will not be long before this state ot things will be remedied. In the meantime it has been demonstrated that aluminium alloys have now been produced which are able to give satisfactory service• both for engine cylinders, pistons and connecting rods. So far as the first application is concerned, it is something to find that it is possible to produce an aluminium alloy which will not only withstand the heat generated by combustion, but also to withstand the expansion which follows the firing of the charge. ,
Its High Conductivity is a Useful Characteristic.
It has further been shown that aluminium can resist the tendency to crystallize under constantly repeated shocks of the explosions, and so far as the friction of the piston is concerned, that appears to be effectively met by shrinking in a thin steel liner.
Now there is more in this successful use of aluminium alloys for cylinder castings than meets the eye at first glance. It is not only the saving in weight which is gamed. Thera is very much more in it than that, and I look to it as a possibility that it May create a revolution in ear design even of commercial vehicles; there is the high conductivity of aluminium. As compared with cast-iron this is as 00 to 12, or thereabouts—rather more than that in favour of the alloy in fact—and, that being so, I see the possibility of arriving at suceess;with air cooling, which would do away at once with radiator, pump, water jackets and connections and effect a substantial saving alike in weight, :first cost, complication and upkeep expenditure. This development needs to be watched on this account.
Aluminium Alloy Piston.
So far as pistons and connecting rods are con
cer*
ned, now that it is proved to be possible for the
aluininiurn alloys to withstand the combined heat and hard work to which they are subjected in use, it. is not difficult to prognosticate their universal employment, at any rate, so far as the piston is concerned, in the near future. Indeed, aluminium alloy pistons are now being very largely employed in America in touring-car and aero engines, and they should be equally, or even more, advantageous in " truck " engines. They have been fully tested out in the most severe trials to which they could be put. ..M1 the American racing cars have used them last season without a
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single mishap to parts in use, two ears fitted with them having on one cccasion covered 350 miles at an average pace of over 102 m.p.h., and it is difficult to see how anything more severe could be done with any metal than that.
Results which May Accrue front Wider Use of Aluminium Alloys.
The great .advantage of their employment is, of course, the fact that it is the reciprocating parts i
which are being lightened, and how much this s done will be seen when it is stated that the particular aluminium alloy employed is something like 70 per cent. lighter than cast-iron, so that a saving of several pounds weight will he made in a commercial engine, and it is little realized by the man in the street how large a proportion of the power generated in the combustion chamber is absorbed in the work of starting the weight of the piston and connecting rod into rapid movement, stopping and reversing the direction of movement many hundreds of times a minute. With less work of this kind to do, there would be less need of heavy flywheels, the weight of which could be substantially reduced without disadvantage ; an engine would accelerate better and start easier and be more lively generally, but, above all, from the commercialvehicle user's point of view, there would be more power available for useful work, which means a better capacity for dealing with any work and, conversely, less consumption of fuel for the same work done, with a corresponding saving in the fuel bill. That this is not a fallacious notion is shown by tests which were made with an engine which, with cast-iron pistons weighing 4.75 lb., gave a maximum of 66 b.h.p. at 1550 revolutions. This was fitted with aluminium alloy pistons weighing 1.76 lb. arid run again, when the power developed at 1550 revs, went up to 77 b.h.p., whilst the maximum revolutions were increased until a maximum power of 84 b.h.p. was developed at 2200 revolutions, thus showing more than a 15 per cent. power increase at the same revolutions and a maximum power increase exceeding 25 per cent., which will be seen to be a very substantial and desirable improvement from the commercial user's point of view. British makers of engines must take up this development without delay, if they are to hold their own after the war.