The following points should be noted when designing the compound formula for continuous vulcanization：
(1) Rubber types and vulcanization temperature: Continuous vulcanization is usually carried out at high temperatures above 200 ℃. Due to the oxidation of the rubber surface at high temperatures, high temperature vulcanization when the rubber contains volatile components is unfavorable to the performance of the product, so the maximum vulcanization temperature should be controlled. For details, see Table 1-1.
|
Types of rubber |
Maximum vulcanization temperature, ℃ |
Remark |
|
NR,IR,BR |
230 |
The surface of rubber is oxidized and sticky at high temperature |
|
SBR,CR,Butyl rubber,BR |
About 300 |
|
|
All kinds of oil-filled rubber |
About 250 |
Oil volatilization occurs at high temperatures |
|
EVA/EPR/EPDM |
About 210 |
The peroxides decompose at high temperatures, making the rubber porous |
Table 1-1 The highest vulcanization temperature of various rubbers
(2) Vulcanization system: In order to achieve rapid vulcanization and prevent deformation of initial vulcanization products, it is appropriate to use rapid vulcanization system. Due to the large L/D value of the vacuum extruder used, the adhesive must have sufficient scorch stability. The use of zinc dithiocarbamate in styrene butadiene rubber can achieve rapid flat vulcanization and good processing stability. In the non-sulfur modified neoprene rubber, the accelerator ETU and DETU compound has fast vulcanization speed, good vulcanization state and compression permanent deformation, but the scorch stability is not good, so the anti-scorch agent can be used.
(3) Fillers and softeners should avoid using fillers with high moisture content to avoid porosity in vulcanized products. The water content of talc powder and silicate system is the least, and the water content of clay filler is higher, and it must be dried at high temperature or used with calcium oxide, a hygroscopic agent. In order to prevent the deformation of the product, in addition to the use of high viscosity rubber or partial cross-linked rubber, it can also be used with high structure carbon black, fine particle silicate, etc., by improving the viscosity of the rubber material Mooney method. Operating oils with low boiling point components should be avoided, and operating oils with less reduction at high temperatures are beneficial to continuous vulcanization.
(4) Ultra-high frequency vulcanization in the microwave electric field, the thermal effect of the rubber material with small polarity is very bad, so in addition to the use of nitrile rubber, neoprene rubber and other polar rubber, it must also be used with high wear-resistant hard carbon black or white carbon black.
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