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U.S.A. Is Retreading 10,000,000 Tyres a Year

3rd April 1942, Page 21
3rd April 1942
Page 21
Page 21, 3rd April 1942 — U.S.A. Is Retreading 10,000,000 Tyres a Year
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/ Operating Records Show Big Resultant Economies and No Rise in Failures: Hints on When to Retread and How to Judge Used Tyres' Suitability

AA S in this country, America is employing more and more the practice of retreading tyres with a view to economy of materials and labour. About 10 years ago the number of tyres retreaded in the U.S.A. was less than a million. In 1941 it was over •six millions, whilst it was estimated before the nation became involved directly in the war that the number for 1942 would be 10 millions.

As a result of an investigation into the matter by the American Army, every suitable tyre possessed by this Service is now retreaded. The Navy and certain Government departments are following the same policy. For some six years the U.S.A. post office has been having its tyres retreaded by the thousand, despite the fact that it is in a position to buy new tyres very favourably. It is Of interest that this departments' operating cost records show that a big saving has been effected by this measure and that no increase in breakdowns on the road, due to tyre trouble, has occurred. This last point is important, because it constitutes an excellent answer to those in this country who are still doubtful about the reliability of retreaded . tyres.

Retreading Officially Encouraged Operators in America are encouraged by the authorities to have tyres retreaded as much as possible and it is understood that among commercial vehicles well over 50 per cent, of the tyres in use are reconditioned by this process. Sometimes the operation is performed several times on the same cover if the casing be a particularly good one.

Retreading from bead to bead is not generally favoured, mainly because it entails double curing of the rubber and fabric at the sides. Usual methods are:—

(I) Removing the whole tread, including the breaker strip, exposing the upper cord layer for inspection, and applying a new wide-wing camel-back including a new breaker strip.

(2) Buffing the old tread, leaving the breaker strip with some rubber still on it and using a short-wing camel-back. This is called " full-recapping." (3) Preparing the tyre as in the secgnd case, but applying only a shoulder capping stock instead of a shortwing camel-back. This is known as "top-capping."

Economies False and Real Less rubber is obviously needed for the second and third processes, with marked savings. Rubber can be further conserved, by forming a shallow tread, but the saving here is not real because it shortens the tyre life, whilst the labour expended is the same. Inferior rubber and mixtures containing an excess of reclaimed rubber are similarly uneconomic.

It is debatable whether the first process is preferable on economic grounds. The use of more rubber is involved, labour costs are higher and so are those of heating and equipment_ Against these points is the certainty of the tyre running its proper mileage, because a really thorough examination, prior to retreading, can be made only in this case. Apparently, however, the efficacy of inspection from inside is so great that a sufficient degree of security from failure can be given in this way and processes 2 and 3 are definitely favoured by the majority.

Removal of old rubber is done by cutting with a knife by hand or by machine, or by buffing with a wheel carrying sharp steel -points and revolving at high speed. Buffing needs to be done carefully or the finished tyre may be out of balance. Moreover, with some of the older equipment, it is easy to scorch the tyre and new rubber will not adhere properly to burned rubber.

With modern equipment, the tyre is suspended in a device which, while giving it rotation, automatically feeds it up to the buff. Thus the minimum of skill, effort and attention is demanded.

Revolving tables are used to facilitate the application of the rubber solution.

• Full-circle moulds are usually employed for the actual retreading operation. It is essential that they be a proper fit, and, in this'connection, it is worthy of mention that frequently moulds, of the correct dimensions of the tyre when new, do not fit, because inflation and load stresses have permanently distorted the casing.

Faults of some old-type moulds are that they are liable to distort the tyre, to apply too much heat and to produce ar.shallow tread. In the case of sectional moulds, although it is easier to place the tyre in position and they entail less effort, labour costs are higher because of the repetition of the operations for each tyre.

For Checking and inspecting To complete the equipment there should be tyrebalancing machines, measuring appliances, devices for testing the rubber, and, of course, inspecting apparatus, which we have purposely left to the last so as to he able to enlarge upon the subject without interrupting the sequence of our outline of tho operations just named.

Hydraulically operated inspection stands are usually employed. Examination is made for ply separation, chafing of cords, small holes, cuts and cracks. Stones and gravel have a tendency to wander from the outside to the inside, whilst even minute openings will permit the entry of wet and sand. Dangerous separation of plies ensues.

Even if an otherwise sound-looking tyre shows Loo many spots, indicating such penetration, it should be rejected. A small number of minor defects is permissible, but no hard and fast rule can be laid down. Decisions must rest with the expert who can rely upon his general impressions.

Tieing up with this matter of inspection is the question: when should a tyre be withdrawn from service for retreading? It is all important; indeed it is the crux of the matter.

Experts in the U.S.A. and elsewhere say that where retreading has not proved economical it is almost always due to an attempt to run the original tread too far. 'our conclusions have been reached, How to Ensure Success (1) Withdraw the tyre just before the non-skid pattern has worn off. (2) Select tyres for retreading carefully, always consulting an expert. (3) Retread only first-grade tyres. (4) Remember that mileage is not wasted by withdrawing the tyre early. No rubber is removed by the capping processes. Some advice on when not to retread may also be valuable. Reject tyres which are (a) not of first-class make, (b) worn into the fabric casing, (c) weak at the bead, (d) badly cracked or cut at the side walls, (e) damaged by cuts or breaks extending through more than one ply, (1) showing ply separation, (g) evidencing having been run underinflated, (h) apparently the worse for having been subjected to constant overloading. It is popularly thought that a tyre should be retreaded only once, but that is by no means the limit. An analysis of records from 300 large American fleets showed that 42 per cent, were retreading many tyres more than once, that 18 per cent, often retread twice and that 8 per cent, have retreaded the same tyre from three to as many as eight times.

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Organisations: American Army, Navy
People: Used Tyres

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