Vulcanization

VULCANIZATION (from French volcaniser — to heat up), a process consisting of the conversion of soft gutta-percha and rubber into a hard, elastic, horn-like state. In medicine, V. is widely used in the manufacture of rubber dental prostheses. The process of V. consists of the combination of the carbon of the rubber with sulfur. During V., under the influence of high temperature and vapor pressure, the rubber enters into combination with the sulfur mixed with it, during which hydrogen sulfide is released. V. of prostheses is carried out at t° 160-165° (at a pressure of 6 atm.) in a so-called vulcanizer. If the content of sulfur in the vulcanized rubber is less than 20%, the object remains soft (for example, drainage tubes). The vulcanizer, Papin's boiler, is used for the vulcanization of small rubber objects, such as dental prostheses, seals, etc. The boiler is made of copper or bronze, in the form of a cylinder with a semicircular bottom and a removable lid. The objects to be vulcanized, embedded in plaster, are placed in the boiler, and water is poured in; the lid is pressed tightly by a screw located on a massive steel arc fixed near the edges of the boiler. In the lid there is a valve for the release of steam, a safety valve, a tube for inserting a thermometer, and often a manometer with an apparatus for regulating the steam pressure. The vulcanizer is heated by electricity, gas, alcohol, etc.