Retreading Within the Scope of All Operators
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ANimportant development in connection with the atconditioning of worn tyres forms the subject of patent No. 555,976, by the Dunlop Rubber Co., Ltd., 1, 'Albany Street, London, NAVA, and Mr. Arthur Adams of the company's works, at Fort Dunlop.
It has always been considered something of a specialist's job to, carry out retreading work, and it is somewhat sFprising, therefore, to learn that, given certain simple equipment, the • process can be carried-out almost as readily as one would vulcanize an inner tube. Further, the fact that it is an advantage to perform the retreading with the tyre in position on the wheel, removes all need for the use of special tyre supports, or means for creating internal pressure.
Assuming it be desired to 'retread a worn cover, a level surface for the retread rubber is prepared by levelling off the old tread, preferably by means of a wire buff. No doubt a hand rasp , could be used, but it would seem essential that the finished surface be as free from bumps as possible, and that the tyre be left reasonably round. • This surface must be well cleaned, after which a suitably compounded rubber solution is applied, the pUrpose of which is to hold the retreadstrip in position. Next, .thls strip is well rolled down to the 'cover, so that the two make intimate contact, which means the expulsion of all possible air
retread strip, and -so restrain its outward movement when the tyre is pumped up, which is then done.
Up to this stage, the procedure has been almost precisely that followed in the normal process of retreading. It should here be mentioned that the tread strips, as supplied, ate ..premoulded, that is to say, the " curing " ring used plays no part in forming the pattern of the tread. For this reason the ring can'be a simple affair.
Normally, of course, it is usual to use steam-heated patterned moulds but, in this case, although it is necessary to apply heat it is only for the purpose of vulcanizing the retread strip in position. The source may be free steam, gas jets, or electricity. Should electricity be used, it would be possible to employ a resistance-or heater coil to surround the rim, which would give excellent heat distribution circumferentially.
This, then, is the broad outline of the scheme, which would seem to put tyre retreading Well within the scope of the average operator.
Although the foregoing deals with a complete remould, in that' a ,strip used right around the tyre, the process is equally effective if rubber blocks be put on separately, In this case, they would be put on reasonably close together, so as to prevent the form"a.. tion of a " flat " section between adjacent blocks.