A New Dunlop Cord Fabric
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OWING to the fact that all cotton cord used in Dunlop pneumatid tyres is produced at mills controlled by the company, in Rochdale, Lancs., it has been found possible to develop a new kind of cord fabric which, as shown by careful tests, confers an increased life upon the tyre cover. Some years of experiment lie behind this important development, during which hundreds of tests have been made -with cotton cords and their properties, when built into a pneumatic tyre.
Each cord consists of a number of threads spun from cotton fibres, and when produced by the orthodox methods the material shows considerable variation in its physical properties. By employing special machinery, however, the Dunlop Rubber Co., Ltd., Fort Dunlop, Birmingham, has contrived a method of spinning the cords which ensures absolute consistency in the product.
To check these points, some interesting laboratory tests have been devised, which correspond closely with those which are commonly used to try out metals. There is a tensile machine, which automatically plots a graph of stress and strain when a cotton cord is loaded, an impact test produced
by a swinging pendulum, and a fatigue test in which pieces of cord are weighted and are pulled to and fro by cranks.
Pieces of fabric are also tested in various ways, one of which consists of applying water pressure and measuring the pressure needed to cause a tear and the amount of stretch which occurs. Full-scale tests are, of course, also carried out upon completed tyres in the laboratory and on the road. This is the usual practice of the Dunlop Rubber Co., Ltd.
Apart from the cord itself, the fabric is now produced by a novel method. A large number of cords is taken from drums through eyelets, and is guided in line through the rolls of a calendering machine. Here the cards are straight away embedded in rubber without using transverse threads to hold them together. The cover of a giant pneumatic tyre is, of course, built up of a large number of plys of this fabric, each layer of cords running obliquely across the cover at right angles to the cords above and below. Naturally the strength and durability of the cover depend largely upon the properties of the cotton cords out of which it is built.