624 



THE INDIA RUBBER WORLD 



[August 1. 1919. 



Al)ovf the cushion stock is laid the breaker strip of coarsely 

 woven fabric frictioned and coated on both sides, and rolled 

 tirmly into place with a hand roller. To prevent air pockets, the 

 edges of the breaker strip are bound with half-inch strips of 

 cushion stock rolled dowrn firmly. The breaker strip is of great 

 importance to the tire. It prevents separation of the tread ; 

 obviates the formation of mud boils, and reduces the possibilities 

 of fabric breaks resulting from stone bruises. 



The tread is ne.xt applied. First, however, 

 it must be built up with three or four strips of 

 black, white, gray or red unvulcanized tread gum 

 of suitable width and length sufficient to reach 

 around the entire circumference of the casing 

 In building up the tread the second widest ply. 

 J4-inch narrower than the widest ply, is placed at 

 the bottom. Above this are placed the required 

 number of piles, each J4-i"ch narrower than the 

 one beneath it, until finally the widest ply is 

 placed at the top. Each ply is rolled down se- 

 curely as laid with a flat hand-roller and all air 

 blisters removed by pricking with an awl. 



In applying the tread to the casing the second 

 widest ply is brought into contact with the breaker 

 strip, the tread is carefully centered all around 

 and pulled tight to prevent wrinkles. It is then 

 rolled down with a hand-roller or a tread-rolling 

 machine, all air blisters being pricked with an aw 

 of each tread ply are stitched down with a rotary wheel- 

 stitcher, and the splice trimmed off even with the surface of the 

 tread. 



■CAMEL BACK" TREAD GUM. 



To obviate the necessity of building up treads as needed, 

 there is a specially prepared unvulcanized tread gum called 

 "camel back," because it is built up to a hump in the center 

 where the thickness is needed. This requires only to be cut off 

 to the desired length; waste is thus reduced to the minimum and 

 ply separation, low spots, and air blisters are obviated. 



Manufacturers also supply endless retread bands with ribbed 

 and non-skid designs in all standard sizes to be applied instead 

 of built-up or "camel back" treads. 



VULCANIZING THE COMPLETE REPAIR. 



Plain retreads, retread bands, relines, recovers and rim cuts 

 entirely around are all vulcanized in a pot heater, also known 



The edges 



closed to In the different diameters. I'u insure a perfectly smooth 

 surface, a fabric pad should be wound around the coil. 



.Adjustable cast iron or aluminum segment cores are often 

 used instead of air-bags or coil springs. They are the exact 

 size and shape of the inside of the tire. Each segment is 

 ;/2-inch thick at the inside and ^-inch at the outside, making 

 them conform solid to the circle of the average tire. A sufficient 

 number of these segments is strung on two wires 

 I.) Ko nearly around the casing, and the adjust- 

 nu-Mt between the different casings is made by 

 using more or less segments. Where the coil 

 springs gaps apart to conform to the diameter of 

 liic casing, these segmental cores lie close to- 

 gether so that the casing can neither shrink nor 

 stretch in curing. 



Split curing rims, with clincher or straight- 

 side beads as required, are next put in place 

 upon the casing and the two sides clamped se- 

 curely together by bolts. A strip of wet muslin 

 cut on 45 degrees bias is stretched around 

 the casing as a surface liner, and over this a 

 heavy wet jacket. In the case of a re-covered 

 tire the light muslin jacket is put on before the 

 curing rims. 



The tire is ne.xt cross-wrapped with wet strips 

 of 8-ounce fabric IVi inches wide. The wrapping 

 should be even and very tight to insure uniform pressure, par- 

 ticularly on the side walls of the casing, and to help the beads 

 hold correct shape. The wrappings are wound completely around 

 the casing in one direction and then the operation is reversed 

 and the entire casing wrapped m the opposite direction. For 

 convenience in working, these strips of fabric are previously rolled 

 like surgeon's bandage, either by hand or with one of the several 

 rag rollers on the market. 



If an air-bag is used instead of coils or segmental cores, it is 

 inflated to 70 pounds pressure, and the casing is finally cured 

 in a kettle vulcanizer. Common cures are 45 minutes at 35 

 pounds steam pressure, and 40 minutes at 40 pounds. 



IN CONCLUSION. 



It seems unlikely that the price of tires will soon reach pre- 

 war levels. This, together with the greater spirit of thrift 

 engendered by the war, means that rebuilt tires will be used more 



Horizontal Retre.\ding Vulc.\nizer. 



Pot Vulcanizer. 



Wrapping Machinj 



as a kettle vulcanizer, or in a retread mold. In the case of a pot 

 heater a complete air-bag or an endless retreading coil is first 

 placed in the casing. Complete air-bags made of specially treated 

 gum and wound with fabric will give from 100 to 300 cures. End- 

 less retreading coils will last indefinitely. They are made of 

 tempered hard steel flat wire, long enough to accommodate cas- 

 ings of any diameter, and wound so that they may be opened or 



and more; that tire rebuilding has become and will continue to 

 be a great and growing business. Some 6,000,000 automobiles 

 are now in use in the United .States and the number increases 

 enormously every year. Allowing five tires to each car, four in 

 use and one spare, it is seen that some 30,000,000 tires are now 

 in use. Of these, probably one-third, or 10,000,000, could be re- 

 built annually. 



