We Must Win the Rubber
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THERE has been so much talk concerning the rubber position, the question of how much natural rubber in any form is now available in this country, and the possible supplies of. synthetic varieties from America, that many people have been left in a state of confusion. It was, therefore, particularly interesting to hear many of the hazy points brought into better promincnee by Dr. S. S. Pickles, D.Sc., F.I.C., in his paper read ,before'the Royal Society of Arts on February 16, a précis of which we published last week.
It will have been news to many of our 4eaders that there are so =fly synthetics which possess " rubbery " characteristics. All appear to have features which snake them suitable for particular -classes of product, but not many can be utilized in the production of tyres.
Pros and Cons of Rubber and Synthetics Natural rubber seems still to be the best material so far as its resilience is concerned. It is also easier to manipulate and possesses a natural adhesiveness, which renders it excellent as a bonding material between the carcass of a tyre and the. outer layers; including the tread.
On the other hand, a few synthetics give superior resistance to abrasion and should, consequently, possess a long wearing life. Many are also better in respect of their resistance to ageing, oxidation, and swelling or softening by contact with oil ; bet, in addition, they show a reduction of elasticity at Very low temperatures. If used for shock-absorption purposes, this is an important point to consider, not so mud" in this country but in others where extreme cold may be met, or when they arc used for such a purpose in aircraft.
As an important sideline, it is of interest to note that a small proportion of certain synthetics mixed with components for forming ebonite adds greatly to the strength of this material and increases its resistance to possible damage from shock or flexion. .
Important results altr expected from mixing synthetic and natural rubbers. The resulting compounds offer higher resistance to temperature and oil, but the proportion of natural rubber must not s of the Position be increased to too high a Rubbers, Their do not justify the addition.
Characteristics Questioned by us, Dr.
Pickles stated that overheating of tyres, as with the solid types and heavy pneumatics, may lead to selfAestruction, but if the temperature benot too high there is a tendency for the surface to harden, and the effect may not be so detrimental as with natural rubber.
Reports from America have suggested that whilst all-synthetic tyres can be employed satisfactorily for private cars, this does not seem to be the case with the large pneumatics employed for heavy vehiCles, where the heating effect is much more pronounced. Also. in these big tyres there is a tendency for the material to break away from the fabric. This may possibly be due to'the hardening through heat or the lack of tackin,ess. Therefore, with such tyres it is becoming the practice to use natural rubber for the body and to employ synthetic for the tread, which certainly opens the way for the employment of suitable synthetics, when they become available, fort recapping purposes, for which work they should give an even longer life than natural rubber.
One characteristic of such synthetic as Buna S is that its strength increases remarkably with the addition of a large percentage of carbon black, even to such a -hikh amount as 30 per cent. We do not know how the cost of carbon black compares with a synthetic when used in large quantities, but if it be not economic from the financial aspect it will reduce the synthetic required.
Our Experience with Synthetic Tyres About 18 months before the war we obtained a pair of 5.50 tyres for use on a'14 h.p. car. They were of German make, probably of Buna or a mixture of this with rubber. From their appearance and the formation of the tread, it seemed that they would possess good non-skid properties, but the first trial was almostdisastrous. Both were fitted to the rear wheels, and the skidding propensities were pronounced, even at comparatively low speeds. Fortunately, after a few hundred miles they settled down to their work, and after that we noted no difference between them and ordinary varieties of tyre. The reason appeared to us to be that the synthetic tread was so tough that it strongly resisted the incorporation of grit on the surface, for even after a few days one could run one's finger over the -tread and find it as smooth as the original surface, whereas most ordinary tyres quickly pick up enough sharp grit to give a roughened surface, affording good road-holding ability. After 5,000 miles the synthetic tyres shovved remarkably 'few cuts and abrasions. The test was summarily concluded by the laying up of the vehicle.
If it eventually be found necessary to employ a considerable proportion of naturalrubber with any synthetics which become available, it behoves us to be still more careful of our present stocks, and to use the synthetic at the points where wear occurs.
The Synthetic Position in America With regard to the rubber situation in America, the synthetics there are made mostly from petroleum and a certain amount from acetylene. The • farming. community in the is very powerful, and it 'has raised the point that at least part of the synthetic production should be from alcohol produced from potatoes, but Congress does not appear to be willing to budge in this matter. In Britain we appear to have a vast quantity of potatoes, and the production of these is growing. There should be ample to supply alcohol for the purpose in view, but one difficulty is that, already, about half the distilleries in the country have been closed down. .
There are, roughly, 60 types of plant from which various qualities of rubber can be produced, and some people are endeavouring to exploit these. We should not be misled, however, but give attention only to those plants which could become readily available and from which guaranteed results 'could be obtained.
Production Difficulties in Britain If we used petroleum as a basis, this would have to be imported and the position would be little, if any, better ; but we might be able to produce considerable quantities of acetylene from carbide of calcium. Normally, we import all our carbide, because of the difficulty of obtaining the great electric power necessary. The difficulty in the latter respect is chiefly one of economics. Electricity here is not cheap, but in war-time matters of finance go by the board_ However, we are assured that, whatever happens to civilian transport and other industries which depend largely upon rubber, there should be sufficient of this material, available to avoid any delay in the staging of our new fronts--of course, with the proviso that waste in any direction is stopped.
Speed in connection' with road transport means vastly increased wear of tyres. America has already imposed a maximum speed limit of 35 m.p.h. Here the commercial vehicle is not so much affected, because the maximum speed of the lighter types is 30 m.p.h. and of the heavier 20 m.p.h. ; but any tendencies which are displayed greatly to exceed these limits should, in the interests of the Nation, be treated with severity, although this applies less to the lower limit.