Janiary 1. 1916.] 



THE INDIA RUBBER WORLD 



163 



Standard Tire Fabrics. 



IT is not an exaggeration to say that the automobile tire has de- 

 manded quite as much thought, inventive skill and scientific de- 

 velopment as any other part of the modern motor car. The 

 tire is not a mere cushion, with the road on one side and the 

 wheel with its burden on the other. It is not a passive medium 

 of translation even when placed upon a forward wheel, and when 

 attached to the rear axle its service is virtually that of a prime 



Its stresses and strains are many. When driving straight 

 ahead, the blows delivered to tlie tire differ in magnitude ac- 

 cordmg to the size and nature of the road's inequalities, the 

 speed, the weight of the car and its load. Then there is another 

 series of stresses, lateral ones, when the forward wheels are 

 turned from side to side in 

 steering. Finally come the 

 reverse stresses produced by 

 skidding and the application of 

 the brakes. 



Because of its elasticity and 

 resiliency rubber is peculiarly 

 fitted for the cushioning service 

 required ; but rubber possesses 

 little strength. Therefore, in 

 order to keep its yielding with- 

 in bounds, it is necessary to 

 incorporate with the rubber a 

 suitable restraining material. 

 Cotton fabric is universally 

 used for this purpose, as it is 

 not so sensitive to high tem- 

 peratures, and is not likely to 

 chafe. 



Tire fabrics are made today 

 either of Sea Island or of 

 Egyptian cotton. The former 

 originated upon a single island 

 off our southern seaboard. 

 The filament is a long, fine, 

 silky one, and it contains more 

 natural wax, and is whiter 

 and better than the Egyptian 

 staple. But there is not enough of the original island crop to 

 supply the demand, and substantially all of it goes into the 

 fabrication of expensive yarns used in making fine lace. But 

 seeds of the original island staple have for years been planted in 

 suitable soil on the mainlands of Florida and Georgia, and thence 

 comes the present supply of this superior cotton, which is used 

 in the best tires. According to figures. Sea Island cotton enters 

 into something like 25 per cent of the tire fabrics, while the re- 

 maining 75 per cent are woven out of Egyptian cotton. 



The cross-section of any standard pneumatic tire makes clear 

 at a glance the general arrangement of the different plies of 

 fabric, the duty of each varying with the position occupied in 

 the finished product. The purpose of this fabric and rubber 

 carcass is to protect and hold the inflated inner tube and. at the 

 same time, transmit to the outermost part of the tire, called the 

 tread, the driving impulse exerted at the hub of the wheel. The 

 carcass serves as a barrier between the inner tube and the blows 

 incident to irregularities of the roadbed, and here resiliency is 

 desired to obtain the cushioning effect which makes for the com- 

 fort of the occupants of the car. 



The greatest care is exercised in the building of the carcass, 

 and in order that it may do efficiently the work expected of it, 

 tire fabrics have undergone an evolution wliich has demanded a 



great deal of experimenting. Originally, a heavy, square-woven 

 canvas was employed, but even when made of the very best ma- 

 terial it failed to give satisfaction. This was particularly so 

 when speeds increased and the weight of the cars was aug- 

 mented. The ordinary square weave, with single threads in the 

 warp and the filler, did not answer, and this was noticeably so 

 when the successive plies were laid straight, i. c, with the warp 

 running parallel with the circumference of the rim and the filler 

 spanning the tire at right angles to the tread. When subjected 

 to the varying stresses of service, one set of threads would be 

 taut and the other slack, and, in consequence, there was a lack 

 of cooperation. 



This was in part overcome by cutting the material on the bias, 

 and laying it on the tire core 

 so that both warp and filler 

 threads crossed it diagonally 

 the texture representing a se- 

 ries of multiple diagonals, criss- 

 crossing so that they pointed 

 in the direction in which the 

 wheel revolved. As a result, 

 all of the threads took the 

 stresses more nearly in line 

 witli their lengths, and offered 

 a longer bearing surface. Also, 

 they spanned a bigger arc, and 

 were supported by a larger 

 underlying volume of air 

 within the inner tube. This 

 meant a wider distribution of 

 the blow or a bigger area of 

 contact in surmounting a stone, 

 or any other road inequality, 

 and reduced to just that extent 

 the chance of a bruise or 

 rupture. 



As a matter of fact, cotton 

 tliread is not inherently elastic, 

 and it is quite apparent that 

 a suitable tire fabric should 

 possess this characteristic. 

 :anvas is devoid of this de- 



-■\rmv 



luck 



or square-woven 



sideratum : in truth, stiffness rather than elasticity is what 

 is commonly found in sailcloth. How, then, have the makers 

 of tire fabrics secured strength, in the first place, out of a 

 weak filament, and then so combined the threads that the 

 carcass might better perform its part and approach closer to 

 the ideal requirements for an envelope that should "bend or 

 suffer distortion of its normal circular shape without friction or 

 resistance other than the contained air-pressure?" The auto- 

 mobile tire does not perfectly meet this ideal standard, but it is 

 a good approximate, thanks to the ingenuity of the fabric builders. 

 The desired degree of elasticity is imparted by a process of 

 weaving, the threads being subjected to tension that gives to the 

 warp and filler threads a wavy form. This is technically called 

 "crimp." In short, the thread is virtually thus converted mto a 

 spring. It is this crimping that does the trick and provides the 

 necessary measure of elasticity. In weaving this type of tire 

 fabric the warp threads are given about 6 per cent more crimp 

 than those in the filler, the purpose of this being to offset one of 

 the consequences of calendering. As the fabric passes between 

 the rolls, some of the crimp in the warp is always ironed out. 

 To balance this, additional crimp is put in the warp threads at 

 the time of weaving, and when the frictioned fabric issues from 



