The manufacture of rubber goods : a practical handbook for the use of manufacturers, chemists, and others . ictionrim is drawn into the shell, and the roller begins to turn. Thespeed of the roller is accurately regulated, so that when the brakeis on fairly hard it takes up exactly as much sheet as the calenderspay out. As the diameter of the roll, with its alternate layers ofcloth and rubber, increases, the brake is slackened and the frictionpulley allowed to slip round, so that the speed of rotation of the 52 RUBBER MANUFACTURE. roll decreases as its circumference increases. After a little pr
The manufacture of rubber goods : a practical handbook for the use of manufacturers, chemists, and others . ictionrim is drawn into the shell, and the roller begins to turn. Thespeed of the roller is accurately regulated, so that when the brakeis on fairly hard it takes up exactly as much sheet as the calenderspay out. As the diameter of the roll, with its alternate layers ofcloth and rubber, increases, the brake is slackened and the frictionpulley allowed to slip round, so that the speed of rotation of the 52 RUBBER MANUFACTURE. roll decreases as its circumference increases. After a little practicethe calender-man can adjust the brake to a nicety, so that thesheet is rolled up without being stretched or creased. In thisway the thinnest Para sheet (0*2 mm. thick) can be calendered,and a uniform thickness will be maintained, since the sheets arenot stretched, and cannot draw up unevenly. To entirely do awaywith drawing up, the sheet should be left in the running clothuntil it is quite cold* and only then unrolled and made up. It should be mentioned that the bottom roll should be so adjusted(. Fig. 23. as to gently press the rubber against the face of the running 23 illustrates the principle of a modern set of three-rollcalenders. Such three-roll calenders are chiefly used for runningrubber sheet of the better qualities, which must be as free from air-bubbles as possible. But they also come in for doubling the sheetson the calenders, since it is only with great difficulty that, forexample, a sheet in a pure rubber quality, f mm. thick, can beobtained in long lengths quite free from air-blisters. In that casethe calendering takes the following course : in order, for example,to produce a sheet 1 mm. thick, a sheet J mm. thick is first runas described, and wound on to the wooden roller. This is thenmounted on the axle of the feeding roller (unwinding apparatus), THE RAW MATERIAL. 53 and the running-cloth, with the «heet of rubber upon it, is passedbetween the
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