800 



THE INDIA RUBBER WORLD 



August 1, 1921 



Foster 

 Friction Plug 

 RiBBER Sole 



a foremost place in the footwear niarkel, ii had tu light long and 

 hard for recognition. Some manufacturers of leather shoes per- 

 sisted in fostering the fallacy that rubber soles did more to harm 

 than to help the feet, and were so wedded to 

 old standards that it was only alter insistent calls 

 that they timidly ventured to make shoes with 

 rubber soles as "original equipment." Retailers 

 were equally reluctant to buy or display them, 

 and many unprogrcssive repair men took every 

 opportunity to "knock" them. The objections 

 made by the coV.blers were that the rubber soles 

 tore too easily while being stitched, that they 

 couM not be edged or finished as nicely as leather 

 soles, and that bulges or air pockets often de- 

 veloped under the soles. But the man who 

 wanted rubber soles on his shoes, and knew their 

 merits, often thought that the real reason why the 

 cobblers disUked putting on rubber soles was that 

 they wore too long. 



Now manufacturers are turning out shoes with 

 rubber soles that cost half the price of leather 

 ones and require fewer operations to attach and 

 finish them, yet are "tailored" as modishly as any leather shoe. 

 Finding that wearers are rapidly discovering the advantages of 

 rubber-soled shoes, retailers are actually adding to their stock 

 and variety, and may soon be pushing sales. The up-to-date 

 repair man scoflFs at the idea of any good rubber soling tear- 

 ing while being sewed on a shoe— a trouble easily avoided by 

 not pulling the stitches too tight. The rubber sole edges, he 

 says, can be buffed and finished in as dressy a fashion as 

 though of leather; and as for bulges or air pockets in the 

 sole center, they need not occur if a workman spreads his cement 

 on evenly. Ordinarily only a full sole is cemented, the taps being 

 generally nailed on. .\nother objection that is no longer raised 

 is that rubber soles tend to break across the foot. Many of the 

 old-time fiber soles did thus discredit the industry, but the mod- 

 ern sole does not crack. 



The rubber soling which will eventually find the widest 

 market is that which most fully meets these requirements: high 

 tensile strength, energy of resilience, light weight (a gravity that 

 will not exceed 1.15), a close grain that will resist cutting, at- 

 tractive appearance ("blooming" stock being decidedly passe), 

 and the property of holding its original life even in rough service. 

 As a result of intensive research and incessant experimenting, 

 rubber sole manufacturers are now producing several articles 

 that quite possess this exacting combination of qualities, and 

 which are as far ahead of the old-fashioned fiber sole as the 

 nitrogen-tungsten lamp is above the original carbon filament bulb. 



While accord- 

 ing the ingenious 

 and enterprising 

 manufactur- 

 ers their proper 

 share of credit, 

 it may be said 

 that several cir- 

 cumstances fa- 

 vored the devel- 

 opment of the 

 modern rubber 



sole. The war sent the price of leather up to an almost pro- 

 hibitive price, thus renewing an interest in leather substitutes, 

 and caused a sharp inquiry for rubber or fiber soles. The price 

 of crude rubber dropped to an unheard-of low figure, and the 

 price of reclaimed rubber began to fall rapidly as the value of 

 crude declined, while the volume of rubber scrap, especially dis- 

 carded tires, which afford an excellent and tough material for 

 soliitg compounds, began to increase immensely. Indeed, the 

 large amount of high-grade reclaim that has been available of 



Wi.vsi.ow Rubber Comi'ounu Tur.v Sole 



late has i)layed iiu Mii.ill p.iri in quantity pruduction of the mod- 

 ern rubber sole. 



QUEST FOR SOLING COMPOUNDS 



Visioning the time when cattle-raising and Katlicr production 

 W'Ould fail to keep pace with the growth of population, and 

 realizing the need of soles that would have all the merits and 

 none of the dcliciencics of those made of leather, yet be much 

 cheaper, rubber manufacturers began making soles nearly half a 

 century ago. The early products were heavy, awkward, and 

 practically all rubber. In trying to overcome old prejudices and 

 capture the public fancy a host of compounds was tried, but the 

 results were very discouraging. Then came the fiberized rubber 

 sole, an admirable effort to overcome the shortcomings of the 

 old rubber soles, and which met with a generous popular re- 

 sponse. The qualities were as various as the fillings, which 

 included practically every fibrous substance from leather refuse 

 to silk waste and paper pulp. 



Costly mistakes were made in marketing. Manufacturers of 

 some of the best goods blundered by making too many different 

 sizes and shapes, either making it hard for shoe men to apply 

 the soles or requiring them to carry too large an assortment. 

 They specialized too much and standardized too little, and made 

 no sustained advance. .Some unscrupulous makers injured the 

 trade greatly by flooding the market with inferior soles for which 

 extravagant claims were made and which only aroused resent- 

 ment against the whole rubber sole industry. 



Finally came the modern rubber sole, a real achievement, util- 

 izing all that was good in the soles that went before, obviating 

 all that was bad, and even eclipsing leather to a marked degree 

 while selling much more cheaply. Earlier mistakes in distribu- 

 tion were also avoided. The needs and convenience of manufac- 

 turer and repair man were studied, and the material was sup- 

 plied in stamped-out soles and taps in standard forms and sizes; 

 or in blocks, strips, and sheets from which the shoemaker or 

 cobbler could cut out his own patterns of full and half-soles. 

 The rapidly-growing popularity of these goods, the satisfaction 

 widely expressed, and the lack of fault-finding amply indicate 

 that the modern sole has won the public approval. 

 TYPES OF SOLING COMPOUNDS 



The search for a suitable sole stock to take tlie place of leather 

 has for many years been conducted by some of the foremost 

 experts in the rubber industry, and numerous patents have been 

 issued in this country and abroad for fabricated materials de- 

 signed to supplant sole leather. Nearly all of the mixtures thus 

 far used, or proposed, have a certain percentage of wool, cotton, 

 or leather fiber mixed with rubber and vulcanized, the amount 

 of fiber varying from 10 to 25 per cent. Leather fiber figured 

 prominently in the earlier compounds, but now it is rarely used 

 in excess of 5 per cent, the remainder of the fiber content being 

 cither of wood or cotton in a flocculent state. A typical modern 

 fiber sole compound is the following: 



Pti Cent 



Leather fiber .'to 5 



Other fiber 5 to IS 



New rubber 18 to 20 



Corp. 0:1 substitute 5 to 7 



Asphaltiim 2 to 5 



Reclaimed rubber 10 to 25 



Zinc oxide 18 to 20 



Maitnesium carbonate 1 to 6 



Siiluhur 1 to 6 



With whiting, lithopone, and litharge. 



A Danish sole leather substitute which has given good results 

 is composed of 3 pounds of Para rubber, 12 pounds of oil of 

 turpentine, mixed after the rubber has dissolved in the turpentine 

 with 3 pounds of 30 per cent ammonia. When the rubber mix- 

 ture acquires a grayish-white color 45 pounds of leather pulp, 

 which has been exposed to ammonia fumes, are added and the 

 whole kneaded to an even mass. 



An English formula for a leather-rubber which, though sim- 

 ple, gave much satisfaction, provided for 20 pounds of caoutchouc, 

 20 pounds of ground rags or other fiber, and 2 pounds of sulphur. 



