A Striking Demonstration of the Rubber-jointed Track
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FROM time to time we have referred to the original design of the rubberjointed track which has been evolved by Roadless Traction, Ltd., Gunnersbury House, Hounslow. The principle of employing rubber blocks, under initial compression, between the metal components of the track offers many advantages, in addition to durability. For example, there it no need for lubrication, much of the noise is cut out (practically the only sound emanates from the contact between the track plates and the ground Surface), and there is no metal-to-metal contact, except between the teeth of the driving sprocket and the rollers on the links. Further, the track being formed as an ellipse gives, instead of a flat surface for the lower run of the track, one which is slightly convex, thereby giving firmer contact over the whole of the area extending from the forward idling wheel to the back of the driving sprocket.
When it was first produced the rubber-jointed track was sho,wn to possess a much longer life than had usually been experienced with metal-jointed tracks. Iffor no other reason than this the rubber-jointed type had been found satisfactory, it would have done ' much to establish the future of the track-laying machine.
It was decided to demonstrate this longevity, and a duration test was evolved with the co-operation of the National Physical Laboratory. Links of a type suitable for employment in a 20-25-ton tractor were submerged in a
bath of sand and water—a condition which usually proves fatal to all-metal tracks after a short period of service. The tension on the rubber blocks was varied in the course of the tests from 4,64)0 lb. per sq. in. up to 12,500 lb. per sq. in. ; the rates of flexing also were changed. The lowest equivalent road speed was 10.65 m.p.h., whilst the highest rate, at which the bulk of the test was carried out, was 32 m.p.h. The latter figure is, of course, a really high one for a track-laying machine and shows all the more clearly the endurance .capabilities of the rubber joint. The high-speed test lasted for the equivalent of 88,000 miles, and slower-speed tests followed. As the track and its joints showed almost negligible wear, it was decided, after covering the equivalent of 39,040 miles, to stop the test.
To have accomplished nearly 40,000 miles and still for the joints to be in thoroughly sound working order is an important accomplishment and one which indicates that track-laying machines can now be produced for the most arduous overseas work, for which the particular type is, in many eases, the only commercial possibility.
At the Shipping, Engineering and Machinery Exhibition a RO"adlessequipped Fordson was shown on the stand of the Rubber Growers' Association. An interesting demonstration was afforded of the lack of friction in the tracks by coupling the tractor to a lever, pivoted in brackets bolted to the floor. The leverage was in the order of four to one, but it was possible easily to move the tractor, within the limits of travel permitted by the lever, one hand only being used. This demonstration dispelled from the minds of al/ who witnessed it and tested it personally the belief that a track-laying machine must of necessity involve large frictional losses. The tractor weighed 2-it tons.