August 1, 1921 



THE INDIA RUBBER WORLD 



819 



Probably 2 to 5 per cent would be sufficient for tbis purpose, and 

 the results thus obtained would be of real value in determining 

 the variation in the rate of cure, because in this way the condi- 

 tions of vulcanization would be more uniform than is the case 

 at present, and the results more truly comparable. 



ONAZOTE— EXPANDED VULCANIZED RUBBER> 



Pure rubber with or without the addition of vulcanizing mate- 

 rials when subjected to high gas pressures and high temperatures 

 in an autoclave, tends on release of the pressure or on cooling, 

 to lose the greater part of the occluded gases. The mass may 

 be made to retain large (|uantities of gas under pressure by the 

 addition of substances which reinforce or close the pores of the 

 thin walls which constitute the reticulated structure. Substances 

 of a waxy or resinous nature serve this purpose. The addition 

 of such substances also lowers the pressure necessary for com- 

 plete gas penetration, 75 atmospheres usually being sufficient. 

 When using crepe plantation rubber, high melting point ceresine 

 wax and light magnesia in equal parts to the extent of five to 

 ten per cent of the weight of raw rubber with sufficient red anti- 

 mony and sulphur to effect hot vulcanization, are sufficient for the 

 purpose. 



As an aid in retaining the gas pressure a strongly resistant rub- 

 ber skin is readily obtained by covering the raw material of the 

 expanded rubber with a rubber compound which will not itself 

 retain gas under pressure and will form a strong resisting cover 

 for the gas expanded material. This skin of rubber being vul- 

 canized to the expanded rubber interior, becomes an integral part 

 of the whole during the process of vulcanization, and is, therefore, 

 enabled to withstand punctures and external injury without de- 

 crease of efficiency of the expanded rubber. 



The apparatus employed for producing and curing expanded 

 rubber consists of two principal parts or metal tubes fitted with 

 removable steel end caps. One of these shells is placed inside the 

 other. The inner one contains the rubber and controls the pres- 

 sures at the beginning and end of the process when apphed to the 

 material to be treated. Central openings through the steel end- 

 caps are suitably arranged atld fitted with adjustable check and 

 pressure valves controlling the pressure automatically at certain 

 stages of the process. .\ similarly constructed outer shell controls 

 and operates the application of the high gas pressure to the inner 

 one. 



In making expanded rubber it is of utmost importance to provide 

 a sealing matter of high melting point which will readily permit 

 the gases to pass through the rubber when submitted to high 

 gas pressure, and afterwards automatically to seal permanently 

 gas-tight all porosity. To effect this a waxy or resinous matter 

 is used as a flux which produces a liquid state by the action of 

 heat and facilitating the entry of gas through the rubber. 



The natural extent of pressure capable of retention by the rub- 

 ber substance, without the skin support referred to above, is not 

 over two atmospheres. To obtain a product holding a higher 

 pressure requires the use of a substance capable of absorbing 

 high pressure and to control the expanding action of the gas by 

 a strong resilient skin which will not retain the gases. It is 

 very necessary that this should be done during the expansion 

 process. 



The shell, loaded with rubber mixing and tightly capped, is placed 

 in a heated chamber at 200 degrees F. and kept there until thor- 

 oughly heated. If a substance is required to contain five atmos- 

 pheres' pressure when fully expanded, the check and pressure 

 valves are set at 100 pounds before insertion of the shell into the 

 outer tube or "gun." The pressure is supplied to the apparatus 

 by means of high-pressure cylinders or a pump. 



When the pressure enters the inner shell through the regulat- 

 ing valve, heat is applied by a steam jacket surrounding the 

 "gun" and gradually increased simultaneously with the gas pres- 



sure until the full vulcanizing temperature is reached, which is 

 usually about 305 degrees F. 



It is necessary to maintain a pressure of about 70 to 75 atmos- 

 pheres until the vulcanization is complete, usually in two hours, 

 more or less. The quality or fineness of the froth formation is 

 determined by causing a sudden drop in pressure when the tem- 

 perature has lowered to 50 degrees F. The pressure trapped in 

 the inner shell by the automatic valve at 100 pounds acts as a 

 resilient counter-pressure to the rapid expansion within the con- 

 tents of the shell and prevents its disruption. To exhaust the 

 pressure from the shell, a gas-releasing device is employed. 



Commercially the expanded rubber described is known as Ona- 

 zote and weighs only four pounds per cubic foot. This material 

 was one of the novelties exhibited at the Fifth International Rub- 

 ber Fxhibitiiin in London last June, 



PLANTATION SCRAP RUBBERS i 



Scrap rubbers generally give low values for ultimate tensile 

 strength and elongation, the inferiority being due to the presence 

 of foreign matter not removed by w-ashing; the mineral constitu- 

 ents, particularly the particles of sand, are mainly responsible. 



Repetition of earlier experiments confirm the results previously 

 recorded, that (1) smoking usually lengthens time of cure of 

 sheet rubber without markedly affecting the mechanical properties 

 of the rubber, (2) that different methods of drying have little 

 effect on the vulcanizing and mechanical properties, (3) that 

 rubber allowed to remain in a moist condition is quick curing, 

 and, (4) tliat thin crepe rubber cures slowly, whereas blanket 

 crepe approximates in this respect to ordinary sheet. 



^''Causes of The Inferiority of Planlation Scrap Rubber." Bulletin of 

 the Imperial Institute, IS, 1920, l-i2. 



^C. L. Marshall, Dunoon, Doyle Gardens, Harlesden, London, British 

 Patent No. IS.^.Ue. 



CHEMICAL PATENTS 



THE UNITED STATES 



RUBBER Compounding Mixture. A fluid mixture consisting 

 of a resinous substance and a relatively non-volatile solvent. 

 —George J. Chertofif, Cleveland. Ohio. United States patent No. 

 1,379.743. " 



Manufacture of Rubber. A process for i'rep.\ring high- 

 grade raw rubber direct from the latex without evaporating, dry- 

 ing or smoking, as follows : First, treating the latex, as soon as 

 practicable after being tapped from the trees, with a dilute aqueous 

 solution of alkalinized phenol to preserve the latex in a fluid and 

 sound condition for any required length of time prior to coagula- 

 tion ; second, adding thereto a dilute solution of a suitable acid 

 in sufficient quantity to neutralize the alkalinity of the preservative 

 treatment and acidify the latex, whereby nascent phenol is lib- 

 erated and energetic coagulation of the contained rubber in the 

 late.x takes place; and third, subjecting the coagulum of rubber 

 to a mechanical dehydrating treatment. — Samuel Cleland Davidson, 

 Belfast, Ireland. United States patent Xo. 1.380,640. 



Art of Compounding Rubber. The method of producing vul- 

 canized rubber by dissolving an accelerator, mixing the solution 

 with a compounding ingredient, incorporating the mixture with 

 rul)lK:r, and vulcanizing the rubber compound. — Clayton W. Bed- 

 ford, assignor to The Goodyear Tire & Rubber Co., both of .^kron, 

 Ohio. United States patent No. 1,380,765. 



Fabric for Airships and Process. The process consists in 

 coating a basic material, proofed with rubber, with a film of oil 

 of the class which dries by polymerization. — Henry A. Gardner, 

 Washington, D. C. United States patent Xo. 1,381,412. 



Fabric for .'Virships and Process. The process consists in 

 treating a cloth base with a fireproofing solution, removing the 

 excess solution by passage through a series of rollers, and coating 

 the cloth with a dope containing an oil of the class which dries 

 by polymerization. — Henry A. Gardner, Washington, D. C. United 

 States patent Xo. 1,381,413. 



Treatment of Rubber Latex. In the coagulation treat- 

 ment of rubber latex which, while still in perfectly fresh con- 

 dition after being tapped, has been preserved with an alkalized 



