Page:The American Cyclopædia (1879) Volume III.djvu/749

 CAOUTCHOUC 739 The inner layer of the pipe is formed by a thick sheet of uncanvassed vulcanized rubber, which has been also prepared in one of the calenders. This is cut of the proper width, and wound round a long iron pipe used as a mandrel, and its edges are lapped over one another, firmly pressed together, and permanently joined by a small grooved roller held in the hand of the workman. Before being applied, the inner surface of this sheet of rubber must be coated over with a powder of some substance which will prevent adhesion to the mandrel, so that it may be removed after the hose is finished. The best substance is soapstone, or steatite. The lapping edge must be carefully left un- touched with this material, or perfect union will not be possible. Around this inner coat- ing are now successively wrapped two strips of the bias-cut rubber canvas, and over this another and outer coat of pure vulcanized rub- ber, making six coats in all, four of which are of rubber canvas. It is claimed that hose of two inches calibre, made in this manner, is capable of resisting a hydrostatic pressure of 400 Ibs. per square inch at a temperature of 60 F. Each length of hose is usually made 50 ft. long, which has been found the most convenient for use on the hose carriages, the lengths being joined as required by couplings. After every layer has been wound over its con- centric fellow, and also during the process, the workmen make use of their rollers to compress and consolidate the hose. After all the layers have been applied, the pipe is taken to another bench, where it is covered with four or five layers of cotton cloth, and then, with several others, it is placed upon a long carriage which runs upon rails into a large hollow cylinder Flo. 6. Vulcanizing Cylinder. which is heated by live steam, or steam which is not superheated, coming immediately from the boiler, and usually at a pressure which will give it a temperature of about 240 F. When the rubber has been confined in this cylinder, at this temperature, for eight or ten hours, the true vulcanization or union of the caoutchouc with the sulphur takes place, accompanied with the disengagement of sulphuretted hydrogen gas. This is one of the most important parts of the process of manufacture, and upon it, as well as upon the mixing of the ingredients, de- pend the strength and elasticity of the product. The heat should be raised gradually and main- tained at a determined point till the vulcaniza- tion is completed, and then should be immedi- ately withdrawn. In manufacturing engine hose, the New York gutta percha and rubber manufacturing company mix a certain amount of carbolic acid with the caoutchouc, which it is claimed preserves the hose and shortens the process of vulcanization. An ingenious regis- ter is in use at their factory, the invention of Mr. John Murphy, by which the application of a steam pressure gauge to clockwork records the different degrees of temperature, and their duration, which may have been reached during the vulcanizing process, which is generally performed during the night, under the care of one or two men. When caoutchouc is intend- ed for car springs, about 5 per cent, of white lead and variable proportions of carbonate of lime are added, with 6 per cent, of sulphur. This makes the product more solid and sub- stantial, and capable of supporting greater weight without too much compression, which is objectionable. In the manufacture of ebon- ite, as before stated, a much larger proportion of sulphur is used ; and in the cheaper kinds, when great strength is not required, various earthy substances are employed. But sulphur and caoutchouc alone, when properly mingled and raised to the required degree of heat, pro- duce the best article. The temperature neces- sary to effect the proper result varies with the proportion of the ingredients, and ranges from 250 to something over 300, this also being j more or less modified by the time employed. When India rubber is woven into fabrics, it is i prepared for the purpose by slicing it into threads, with knives worked by machinery and kept wet. These threads are wound upon cylinders in a state of tension, and are woven into the fabric in this condition. In the early manufacture of fabrics of this kind a process technically called "shirring" was employed. The elastic threads, in a state of tension, were passed between rollers, and then between two other rollers over each of which was passed a strip of cloth, cotton, or silk. This brought the threads between the two layers of cloth, and the latter having been prepared with a coating of India-rubber cement, they were held there. One of these shirring machines, together with a machine for cutting the threads, was the invention of James Bogardus of New York, and was extensively used for a number of years. The goods made by that process have however entirely given place to woven fabrics ; and the cutters now used are single circular knives, re- volving with high speed, cutting sheets wound upon cylinders, which are given a slow rotary as well as a side motion, by which the thread