April 1, 1916.] 



THE INDIA RUBBER WORLD 



333 



Pressure Cure of Rubber Footwear. 



A RUBBER boot or shoe is made by assembling upon a 

 form or last the various pieces of unvulcanized rubber- 

 ized fabrics and sheeted stock which form the lining, 

 stay pieces, exterior waterproof and wearing parts of the boot 

 or shoe. This work is done by hand, and the thorou.t;hness 

 with which the tacky stock is made to adhere by the process 

 of hand rolling has much to do with the length of service 

 obtainable from the goods. 



Boot and shoe making is 

 generally done by piece work 

 and hurriedly, therefore there 

 are liable to be some small 

 places in the goods where 

 adhesion is imperfect and any 

 air confined between the 

 plies, prevents contact and 

 weakens the structure. 



Such faulty work may not 

 always be discovered by in- 

 spection, and is liable to de- 

 velop unlooked-for failures in 

 service. 



The usual method of cur- 

 ing rubber boots and shoes 

 consists in exposing them on 

 racks in large, dry heaters 

 where the temperature of the 

 air is slowly raised by steam 

 circulating in coils beneath 

 the racks. Moisture and vola- 

 tile products escape by nat- 

 ural ventilation through open- 

 ings in the roof of the heater. 

 The air, a poor conductor of 

 heat, circulates slowly and 

 without pressure. The work- 

 ing conditions are therefore 

 not under positive control, 

 and the time of vulcanization 

 is long, usually from eight to 



ten hours. The fact that the goods, during vulcanizing, are 

 not under pressure permits the formation of blisters wherever 

 included air or moisture is present. The loss from this cause 

 is sometimes very considerable, and difficult to remedy. Other 

 defects of the dry heater system of curing are irregularity of 

 cure, due to faulty circulation of the air; excessive space 

 required to handle the goods, because the cure is protracted 

 unduly, and large cost for operation. Notwithstanding these 

 defects and drawbacks, the dry heater has remained the 

 standard method for curing footwear since the earliest days 

 of rubber manufacturing. 



The rubber boot and shoe industry is indebted to Hon. 

 A. O. Bourn of Bristol, Rhode Island, for the introduction of 

 the first practical process for the pressure cure of footwear, 

 which he developed in his own works at Providence, R. I. 

 Since his invention several others have been perfected, the 

 work chiefly of American manufacturers. These methods of 

 pressure cure mark the most important recent advance in the 

 boot and shoe branch of the rubber industry, because they 

 bring under control and obviate many of the troubles and 

 inconveniences inherent in the older process of curing foot- 

 wear. 



Manufacturers are now able, by these inventions, to control 

 the vulcanized process and produce better goods with fewer 



"seconds." It is now possible to expel all air trapped be- 

 tween the plies in making, and under pressure to cure the 

 shoe structure compactly together. Pressure cure, by direct 

 steam, also allows the use of tough wearing and oil resisting 

 mechanical stocks, such, for example, as automobile tire tread 

 compound. 



Other important advantages, due to these improved 

 methods, are great economy of space formerly devoted to 

 heaters, and a very important 

 saving of time in vulcanizing. 

 These points materially in- 

 crease the curing capacity of 

 a factory while the effective- 

 ness of the process not only 

 produces better goods, but 

 permits the manufacture of 

 boots and shoes of any de- 

 sired color. This matter of 

 freedom in color selection is 

 an important one from a trade 

 viewpoint, adding markedly 

 to the variety and attractive- 

 ness of the goods. 



No data are available for 

 ascertaining the reduction in 

 cost attributable to pressure 

 cure, over open cure for foot- 

 wear. Undeniably a favor- 

 able margin exists which 

 makes it possible for the 

 manufacturer t o readjust 

 qualities and values; a matter 

 of first importance to the us- 

 ers of the goods. That such 

 a readjustment does take 

 place may be illustrated by 

 the authentic account of a 

 pair of pressure-cured boots 

 worn by a certain car inspec- 

 tor. The story is to the effect 

 that he subjected these boots to 26 months of actual service, 

 or 760 days of wear, walking in this period 5,728 miles. The 

 boots were provided with soles of tough automobile tire tread 

 stock, but their endurance is justly credited, in part, to the 

 compactness attained by reason of the pressure used in cur- 

 ing. Such wearing quality would not be expected from the 

 best rubber boot vulcanized by the customary process. 



In the manufacture of mechanical goods the standard 

 methods of cure have commonly been pressure methods by 

 steam heat, applied either in an atmosphere of steam or by 

 steam licated molds. The patented processes of pressure cure 

 for boots and shoes are adaptations of these means to the 

 special conditions of footwear manufacture by evolving cer- 

 tain general methods for removing trapped air and curing the 

 goods compactly. 



These methods may be considered in three groups: 



1. Consolidation of structure of the goods by pressure of 

 air or non-oxidizing gases and the application of their heat 

 or that of steam. 



2. Removal by vacuum of entrapped air and vulcanization 

 by pressure and heat applied by air, non-oxidizing gases or steam. 



3. Compression of the goods by inflation or otherwise, in a 

 mold heated internally or externally, by steam, for vulcaniza- 

 tion. 



