THE INDIA RUBBER WORLD 



Cavitv Retread Mold. 



The beads and side walls 

 arc not subjected to any 

 steam whatever that might 

 impair the fabric through 

 iivercuring or cause sepa- 

 ration of the beads. No 

 wrapping is required, and 

 as the pressure of the mold 

 is everywhere uniform, no 

 edges of the plies nor low 

 spots will be visible, nor 

 will the tread be loose as 

 sometimes happens after 

 curing in a pot heater be- 

 cause of careless wrap- 

 ping. 



The use of a retread 

 mold is simple. After the 

 new tread has been applied, 

 an air bag is placed in the 

 casing which is mounted 

 on an ordinary rim. The 

 top half of the mold is 

 raised, the casing placed 

 within, and both halves are 

 bolted together. The air 

 bag is then inflated, steam 



is turned into the mold, with drip cocks opened and the ca 



remains in the mold until cured. 



When removed from mold and rim 



the tire has the appearance of a 



new casing. 



One of the advantages of the re- 

 tread mold is that the outward 



pressure exerts an even tension 



during the cure, so that each cord 



in the tire carries its share of the 



load and there are no wrinkles or 



buckles, causing one ply to work 



against another and develop a break. 



TWIN RETREADING MOLDS. 



With twin full-circle molds two .Sectional Cavity 



casings may be cured simultaneously, Vulcanizer. 



both of the same size or neighboring 



sizes, such as 30 by 3J4 and 31 by 4- 

 inch, according to the construction of 

 the molds. They may be provided 

 with ribbed or special non-skid tread 

 designs. The molds consist of three 

 sections, each cored to receive steam. 

 The center member is stationary, 

 mounted on edge and supported by 

 braced legs. It has one-half of each 

 mold machined on either side, while 

 each of the two outside hinged mem- 

 bers has the correspond- 

 ing half. Steam is ad- 

 milted to all three sec- 

 tions at their lowest 

 points and condensation 

 in the molds is removed 

 by the same pipes. The 

 two outside sections have 

 hinged, swing steam 

 joints directly under the main hinges and can be opened and 

 clo.sed without escape of steam, h'our bolts hold the three sections 

 of the mold together. Circular air bags are placed inside the cas- 



Pneumatic Truck Tire Sec- 

 tional Vulcanizer. 



25 to ISO pounds' pressure during the cure. 

 CAVITY RETREAD MOLXk. 

 When retreading is done 

 on a moderate scale, the cav- 

 ity retread mold is used. It 

 is similar in operation to 

 ihe ordinary sectional cavity 

 vulcanizers for curing tread 

 repairs, but is made to cure 

 one-third instead of one- 

 fourth or one-fifth of a 36- 

 inch diameter circle. 

 An objection to the principle on which all cavity retread molds 

 work is the fact that parts of casings larger or smaller than "36- 

 nch are subjected to a double cure. The circumference of a 36- 

 nch diameter circle is 113 inches, while that of a 30-inch casing 

 s only 94 inches ; obviously 

 when a 30-inch casing is 

 placed three times in the 

 mold for curing, 19 inches of 

 the casing is subjected to a 

 double cure. A 37-inch tire 

 requires four cures to cover 

 its circumference of 116j'4 

 inches, yet four applications 

 of the mold cover nearly 151 

 inches, so that about 34{/^ 

 inches are subjected to dou- 

 ble cure. 



SECTIONAL CAVITY 

 VULCANIZERS. 



Sectional cavity vulcan- 

 izers for curing outside fab- 

 ric and tread repairs consist 

 of one to five molds, steam 

 jacketed around the cavity, 

 cast en bloc or singly, and 

 made in either one-fourth or 

 one-fifth circle to measure 

 from IS to 18 inches long on 

 the tread. Three, four and 

 five-cavity outfits are most 

 common, and will accom- 

 modate all casings from 2!4 

 or ZYz to 5-inch. The molds 

 are mounted on substantial 

 and' some are equipped wi 



^ 



Inside Patch \'ulcanizer. 



Combination Sectional Vulc 



1 stands of convenient height, 

 self-contained boiler. Sepa- 

 rate molds of different sizes, 

 each standing on short metal 

 legs for mounting on a 

 wooden bench, are often as- 

 sembled with pipe connections, 

 according to local require- 

 ments. With a separate 



jCij t — ,1, |h^''"i; "lold for each size casing, no 



*^?,- i I r /J . i reducing shells are required, 



direct contact is always cer- 

 tain between the hot walls of 

 the vulcanizer and the casing, 

 and there is no uncertainty as 

 to evenness of cure. 

 Air-cooled flanges are a fea- 

 ture o* one make of sectional 

 cavity vulcanizers. One-eighth inch of heat-resisting material is 

 placed between the flanges and vulcanizer. causing both ends of 

 the cavity to remain cool while heat is maintained up to this heat 

 insulating material, thus obviating unsightly and damaging lumps 



nner Tubk Vulcanizer. 



