OCR Text |
Show Molding Rubber The bureau of standi ri Is says that rubber is tie; poured Into melds in a molten condition, but l-i molded In steam heated prex s, the temperature tempera-ture of the moldM being high enough to cause the rubber to become plastic and assume the sWipo of lite mold. Hard robber contains at least 21 per j cent of combined sulphur. Vulcanlzu Hon must tderefore be prolonged and the rubber comj ound must contain sul'icliut sulphur to produce the grade of hard rubber desired. , |