Rubber Tyre Manufacture

RUBBER TYRE MANUFACTURE Rubber tyres may be considered in two classes— (a) Solid or cushion tyres being those in which the rubber portion fulfils the combined functions of carrying the load, ab sorbing the shocks of meeting road surface irregularities, and re sisting abrasion.

(b) Pneumatic tyres—in which the load is carried and the shocks absorbed mainly by compressed air. The structure of the pneumatic tyre is primarily designed to provide a non-extensible covering with impermeable lining to contain and restrain under compression the column of air. This covering is provided with a rubber tread portion which takes up the abrasive wear of road contact and protects the contained column of compressed air. Such a structure has, as distinct from a solid rubber or cushion tyre, no capacity in itself either to carry load or to absorb shocks. It is entirely dependent on the contained compressed air to enable it to function, and is therefore correctly named a "pneumatic" tyre.

Solid Tyres,

although at some time used for all types of road vehicles and for the earliest motor cars, have now practically dis appeared from American highways because of legislation which discouraged their use. Large sizes have been supplanted by large pneumatic tyres, but small solid tyres are still used exten sively on industrial trucks and tractors. Some of these are made with metal base bands to which the rubber is firmly at tached. These bands are the full width of the base of the tyre and are dove tailed to secure firm anchorage of a hard rubber layer interposed between the metal and the soft rubber constituting the main portion of the tyre. This type of tyre is forced over the periphery of the wheel in an hydraulic press and remains fixed for the period of its life. In other cases the tyre is vulcanized directly to the rim of a metal wheel instead of to a separate band.

Cushion Tyres.

This title is somewhat loosely applied to a number of variations of the solid tyre which are designed to provide greater deflection under load and increased cushioning against shocks. These objectives

are attained by the use of softer rubber compounds and by insertion of cavities in the tyre.

The cavities may be circumfer ential grooves in the centre of the tyre, indentations in the sides or holes extending through the rubber transversely. Such modi fications reduce the volume of rubber and hence the load carry ing capacity. Both solid and cushion tyres are still used on military vehicles.

Pneumatic Tyres.

Whilst Thompson (Patent No. 10990 of 1845) was the first to conceive the possibility of supporting a road vehicle on a contained column of compressed air, and did in fact equip a horse-drawn brougham with 5-in. air-inflated tyres, it was to J. B. Dunlop (Patent No. 10607 of 1888) that the introduc tion of the pneumatic tyre must be credited; for from the produc tion of his first crude inflated tyres at Belfast in 1888, the manufacture of pneumatic tyres has continued without break, with constant improvement in the product, until to-day it is essential to all high speed road motor transport, and has remained since its introduction the only equipment of cycles of all forms.

The simplest form of pneumatic tyre is that known as the single-tube tyre. It consists of an endless tube of rubber-coated cotton fabric having on its inner face an impermeable rubber lin ing, and on its outer surface a covering of rubber to protect the fabric from wet or damage, with an additional thickness of rubber on the tread portion to resist road wear. Single-tube tyres were used on bicycles in America for many years; but because of the difficulty of repairing them they are no longer manufactured. They never had any considerable use as equipment for motor cars.

The necessity for a ready means of repairing resulted in tyres taking the form of a separate inflatable inner tube, with a de tachable outer cover. Out of a multitude of types of detachable covers introduced in the early '9os, two emerged—the Wired On or Straight Side type and the Beaded Edge or Clincher type.