WONDERS OF TYRE TESTING

Hawera Star, Volume LI, 3 January 1931, Page 12

WONDERS OF TYRE TESTING

TRIALS WHICH TYRES- UNDERGO

Picture a shallow circular pit at about 30ft-. diameter, lined with con- ‘ crete. From a pillar in the centre a long arm extends radially and the outer end of this arm is supported by a wheel and tyre. As the wheel is driven by an electric motor the whole contraption whirls round and round the central pillar with the tyre l ceaselessly tracing out a circular path.. Just to make things more .difficult the tyre may :be forced to run over a oed of rougn and sharp .stones, or a granite block may be fixed to the track in such a position that the cover must rub harshly against it to represent the effect of kerb scraping. To safeguard the apparatus in the event of a puncture a smaller auxiliary 7 wheel is carried alongside the tyre tested. This is just one of a large number - of devices for testing tyres which are emn toyed in the test house at Fort DunTj,p. It is a large and impressive building, packed with machinery, and the interior is maintained at a steady temperature, winter and summer. Although tyres can be tested in every conceivable way in this building it still remains necessary to maintain a large fleet of vehicles of all types for roadtest purx>oses. These are 'run for thousands of miles at high speeds and in certain matters (such as tread wear) provide information which cannot yet be obtained in the laboratory. A large number of machines in the test house are of a type, in which a wheel and tyre are carried by a stub axle on a loaded lever. The load can bo varied by shutting a heavy weight along the lever and can be taken up to a maximum of five tons. This forces the tyre downwards on to a large revolving drum by which it is driven. Sometimes transverse bars are bolted to the drum to give the cover of the tyre a pronounced blow several time® per revolution. In this way the strength of the carcase can be investiAgd. Should deflation occur a contact is made and d strident electric bell warns the man in charge. It will Ire realised that even with a la rue drum the deflection of the tyre is not quite the same as would be the case were it pressed upon a flat surface. To get over this .difficulty for certain special tests the research staff employs the unusual plan of mounting two tyres and wheels one above the other, forced together with a flat belt between them.

Another ingenious machine is emdloved to ascertain the effect of impact upon an inflated cover, such as is caused in practice by running over a kerb. The machine resembles the guillotine. An electric motor at the top raises a sliding cross-bead carrying the striker, and the tyre is mounted on a rim at the bottom. The cross-head can be released from any desired height a. p to about 13ft. and, after the drop, strikes the cover with great force, orodu.cing a localised .stress of high magnitude. To prevent it from giving the cover a second; blow it is neatly caught on the rebound by an automatic trip gear. Fan belts are also tested, this being done on -a clever piece of apparatus which carries two 'bolts on differential mi I leys running at about _ d.fiOO r.p.m. Owing to the differences in the pulley diameters the belts are continually working against each other and so are subjected to a never-ending slipping action.