180 



THE INDIA RUBBER WORLD 



[December 1, 1919. 



RUBBER SPONGE MANUFACTURE IN FRANCE 

 AND AMERICA. 



ACCORDING to A. Hutin in "Le Caoutchouc ct la Gutta 

 Pcrcha," the manufacture of rubber sponges, which flour- 

 ished chiefly in Germany before the war. has been commenced 

 in France. 



There arc numerous recipes both for the rubber compound and 

 for the liquids utilized to produce the spongj' effect by liberating 

 gases during vulcanization that form bubbles of uniform size 

 distributed equally throughout the mass. One of the best com- 

 pounds follows: Para rubber, 4<jO parts by weight; golden sul- 

 phuret of antimony, containing 2 per cent of free sulphur, 60 

 parts; washed chalk, 90 parts; lime, 1 part; sulphur, 30 parts; 

 carbonate of magnesia, 20 parts ;lithopone, ISO parts; zinc white, 

 79 parts; barium sulphate, 40 parts; wheat starch, 40 parts; olive 

 oil, 15 parts; castor oil, 15 parts. 



The rubber is worked between slightly warmed rollers for four 

 to five hours to render it quite soft. Mixing takes an hour, as 

 follows : the softened rubber is first treated with the mixed 

 ciils added in small quantities, then the starch is added, next the 

 intimately mixed ingredients and finally the sulphur constituents. 



The liquid for causing the formation of bubbles is composed 

 of 90 per cent alcohol, 120 parts; aniline blue, 1 part; amyl ace- 

 tate, 2 parts. The mixer rolls are kept well cooled and run 

 slowly to reduce loss by volatilization, the liquid being sprinkled 

 on the mass by degrees. If added too quickly the liquid does not 

 become intimately incorporated with the mass. About 40 to 45 

 minutes is the average time required. The mixing rolls are set 

 close together and later the distance is gradually increased. Air 

 bubbles must not be allowed to occur in the mixture or unduly 

 large cavities will be formed thereby during vulcanization. 



The mass is ne.xt made up into rectangular cakes about V/i by 

 lYi by ZYa inches in a press, the dimensions being such that 

 the cakes do not come in contact with the walls of the vulcan- 

 izer. The thickness of the cakes is important. If too thick, 

 vulcanization may be imperfect ; if too thin, an overcure may 

 result. The forming press must be kept cool and the cakes vul- 

 canized at once on removal from it. The upper surface of the cake 

 is wiped with benzine and painted over lightly with oil, while the 

 lower is merely oiled and the sides covered with silk paper. 



The vulcanizer is of rectangular section and jacketed for steam, 

 which is admitted at a pressure of 65 to 70 pounds per square 

 inch for fifteen minutes before vulcanization is begun. The cake 

 is then laid on a piece of wire gauze in the vulcanizer and cov- 

 ered with a light cotton fabric. Vulcanizing time and conditions 

 must be ascertained by practical experience. Steam must not be 

 allowed to come in direct contact with the cake. 



AMERICAN METHOD. 



In general, .\merican practice in the manufacture of rubber 

 sponge follows that recorded above. It was developed first in the 

 laboratory of The B. F, Goodrich Co. at Akron, Ohio, shortly 

 following the appearance of the first commercial rubber sponge 

 which originated in Russia in 1897. 



It is found advantageous to set aside the rubber sponge mixing 

 to age for several days; even as long as a week or ten days does 

 no harm. The inflating material commonly used is carbonate of 

 ammonium in powder form. 



In preparation for vulcanization the stock is run out by a 

 tubing machine in the form of a bar of appropriate cross-section 

 to inflate to the thickness of sponge desired. The raw stock is 

 cut approximately one-third the bulk of the cured product 

 and laid in an aluminum trough for curing in open steam. 



Before vulcanization is begun the heater is charged with air at 

 45 pounds' pressure, which pressure is subsequently gradually 

 displaced with steam pressure, to be later still displaced by air 

 pressure under which the cured sponge is held until cooled suffi- 

 ciently to obviate all danger of internal splitting. 



-Vs soon as removed from the vulcanizer the thin skin or sur- 

 face of the bar of spongy rubber is promptly broken to prevent 

 damage by excess internal pressure. The walls of the sponge 

 cavities are systematically broken by passage of the cured bar of 

 sponge through an ordinary clothes wringer. This establishes 

 connection with the outer air throughout the mass ind renders 

 the finished sponge light and absorbent. 



The sponge is completed by cutting it from the cured rough 

 form by means of a hand cutting die, after which the outer 

 skin or surface rubber is removed by a machine knife with 

 rapidly revolving blades soinewhat after the style of a lawn- 

 mower blade. By properly housing the blade of such a cutter it 

 is possible to remove the surface from the sponge by simply 

 passing it lightly over a suitable opening which permits the blade 

 lo oonie into contact with the rubber. 



THE GERMAN RUBBER MARKET. 



In .^n .\rticle on the development of a German rubber market, 

 ■^ the "Gummi-Zeitung" comments on the experiences of the 

 German rubber industry during the war. German's rubber in- 

 dustry in the year 1913 worked up in round numbers 16,000 tons 

 of rubber, of which a third was exported in the form of rubber 

 goods. During the war as time went on the boundaries were 

 closed more and more to the importation of rubber. If the in- 

 dustry in spite of the steadily increasing demands of the army 

 was able to satisfy them, this was due to three circumstances : 



(1) Certainly hitherto no substitute material had been found 

 which in any degree possesses the quality of natural rubber and 

 could compete with it, but certain materials have value as help- 

 ing Para rubber as additions and their use in special cases will 

 continue even after the war. Still, when great demands are made 

 on the materials they cannot take the place of new rubber. In 

 other cases the Germans set aside rubber entirely and used other 

 materials in its stead (as in the case of elastic metal tires). 



(2) The working up of old rubber was improved and for this 

 reason we may expect in the future a saving in rubber, as we 

 have not yet got the ideal regeneration process and for good ma- 

 terial we must in the future turn to new rubber. 



(3) An important part in the German rubber economy was 

 played by synthetic rubber, which was prepared in the last year 

 of the war to the amount of 2,000 tons. This is the methyl 

 rubber of the color factory formerly Friedrich Bayer & Co. in 

 Leverkusen, which to he sure can be properly used in hard rubber 

 goods only. But during the war they have succeeded in making 

 progress in the preliminary for the manufacture of better kinds 

 of artificial rubber. They have learned to prepare acetone out of 

 calcium carbide and further isoprene out of acetone and setacety- 

 lene. There is no doubt that German science working on a scien- 

 tific basis will become master of the difficulties in case it has an 

 inducement to continue on the way it had entered upon. 



What seems lo be the future of the rubber market? In answer- 

 ing this question we must consider that the production of 

 rubber and still more the consumption of rubber is very exten- 

 sible. If there is a shortage of rubber and prices rise, the planta- 

 tions can increase their tapping and all sources of rubber which 

 are stopped up now by low prices will flow again. The consump- 

 tion can be easily limited by substitute and the increased prepa- 

 ration of old rubber. On the other hand, if the market is flooded 

 the plantations can limit their production and a few wild rubbers 

 like the African will be more or less driven out while the con- 

 sumption on account of the many ways in which rubber can be 

 utilized will quickly increase. These means of regulating will ap- 

 parently give the rubber market a certain steadiness. 



Variations in price and surprises such as marked the period of 

 the rubber crisis of 1913 may for the present be disregarded. 

 Thus, in the rubber market in London in the first half-year of 

 1919. prices are steadily held to the line of development around 



