It can be divided into four stages, each with its own characteristics. It can be seen from the measurement of the fixed tensile strength of the rubber (or the vulcanizer) that the entire vulcanization process can be divided into four stages: vulcanization induction, pre-sulfurization, normal vulcanization, and persulfurization (for natural rubber, vulcanization reversion).

Vulcanization induction period: During the vulcanization induction period (scorch time), the crosslinking has not yet started, and the rubber has good fluidity. This stage determines the scorch and processing safety of the compound. At the end of this stage, the compound begins to crosslink and lose fluidity. The length of the vulcanization induction period is related to the nature of the changes in the rubber molecules in the vulcanization of the raw rubber. It mainly depends on the auxiliaries used. For example, using a retardation accelerator can obtain a longer scorch time and has higher processing safety.

Prevulcanization: After the vulcanization induction period, the prevulcanization phase is carried out at a certain speed. The degree of cross-linking in the pre-vulcanization period is low. Even at the late breaking strength of the vulcanizate, the elasticity cannot reach the expected level, but the performance of tearing and dynamic cracking is better than the corresponding normal vulcanization.

Ortho vulcanization: After reaching the ortho vulcanization stage, the physical properties of the vulcanizate reach or approach the optimal point, respectively, or a comprehensive balance of properties is reached. After the normal vulcanization phase (vulcanized flat area), it is the oversulfurization phase. There are two cases: natural rubber "back to the original" phenomenon (decreased tensile strength), most synthetic rubber (except butyl rubber) fixed tensile strength Continue growing.

Persulfur: For any rubber, not only cross-linking occurs during vulcanization, but also rupture of the production chain and molecular chain due to heat and other factors. This phenomenon runs through the entire vulcanization process. In the over-sulfur stage, if the cross-linking still prevails, the rubber will be hard, and the elongation strength will continue to increase. On the contrary, the rubber will soften, and it will return to its original state.