Continuous vulcanization

The most common compound for peroxide cross-linking of PE in the wire and cable industry is dicumyl peroxide (DCP), which decomposes at 120-125°C (248-257°F), generating free radicals needed for the process plus by-products (carbinol, acetophenone, and methane). The production line for continuous vulcanization of wire and cables by peroxide must be about 200 m (61 ft) long. 2 The plant space required for radiation cross-linking using... 

Ultrahigh-frequency (UHF) energy may be used for preheating and precuring rubber compounds for continuous vulcanization (CV) of rubber, containing carbon black, for such applications as weather stripping, tubing, hose, and. in some instances, tire tread compounds. 

In each step of vulcanization, the section of the belt to be vulcanized is gripped and stretched hydraulically to minimize or eliminate elongation during use. The difliculties of press cure may, however, be avoided by adopting continuous vulcanization with a Rotocure equipment in which the actual curing operation is carried out between an internally steam heated cylinder and a heated steel band. Rotocure is also useful for the vulcanization of transmission belts and rubber sheeting. 

Vulcanization of the phase interface of a rubber blend is important to provide strength and dynamic performance. This interfacial covulcanization is difficult in blends of low unsaturation rubbers such as EPDM with high diene elastomers. It can be approached by fast accelerators such as thiuram di- and tefrasulfides. Yoshimura and Eujimoto (1999) and later Corish (1967) showed that initial separate DMA peaks merge on continued vulcanization to give a single peak. 

The following provides a generalized comparison of the continuous vulcanization modes. 

The following is a generalized comparison of the advantages and the limitations of each of the continuous vulcanization modes. See also Cure Time. 

Peroxide cross-linking employs the thermal degradation of a peroxide to form free radicals. These then abstract a hydrogen atom from the polymer, producing a free radical site. Two radicals then combine to produce a chemical bond. The peroxide is usually present in the polymer as supplied and is not added as a separate material. The thermal reaction usually takes place in a high-temperature continuous vulcanization (CV) tube, immediately after the compound has left the extruder die. 

The compound is shaped and cured in a single line operation which produces very long lengths of tubes or cables. While there are several methods of continuous vulcanization, they employ pressureless systems and are based on the... 

Processing temperature °C 200-316 (vulcanization) 0-50 (moisture cure) 250-500 (extrusion vulcanization) 180-200 (continuous vulcanization in steam) 60-90 followed by 130-200 (peroxide cure) ... 

The cost of processing TPEs can be significantly less than that for conventional thermoset rubber. No vulcanization is needed. For example, no million-dollar continuous vulcanization unit is necessary for weather-stripping extrusion. Molding cycles are much shorter since all that is necessary is to cool the molten article below its hardening temperature. 

Rubber weatherstripping for automotive exteriors is usually produced from compounds based on EPDM. These weatherstrips can be dense (no voids), cellular (closed cell structure), or semidense. Weatherstripping is commonly extruded and cured in a continuous vulcanization unit (CVU). Some new production lines are switching over to thermopiastic elastomers (TPEs), which eliminate the curing step, with a reduction in production costs. 

Rubber bands (sometimes also called elastic bands, lackey bands, or gum-bands) are manufactured by slicing with heat along the width of an extruded rubber tube on a mandrel. Therefore a rubber band is actually produced from slices of a cured rubber tube. Usually, rubber bands are made from rubber compounds based on natural rubber. Rubber-band tubes are commonly cured in a continuous vulcanization unit. 

CR compounds can be used in aU vulcanization processes, such as compression and injection molding, hot air, steam autoclaves, and continuous vulcanization (salt baths, microwave-hot air cure, CV-cure). 

Continuous vulcanization may be accomplished in a salt bath or in open steam. It is best if the extrusion is first wrapped with a Mylar tape to exclude moisture,... 

Compounding Vamac for continuous vulcanization without external pressure. DuPont Technical Bulletin HHSD 141. 

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