- According to the physical property test and production experience of the finished product, shorten the curing time. This reduces the degree of over-vulcanization to a certain extent.
- Adopt high temperature vulcanization. In recent years, the vulcanization process of small tires has gradually developed towards high-temperature vulcanization, and considering the post-vulcanization effect, the vulcanization time is short, which has a certain effect on reducing the oversulfurization and improving the uniformity of the vulcanization degree.
- Carry out vulcanization temperature measurement, find the slowest vulcanization point in the product, and determine the vulcanization time based on this point. The effect is better than the previous two. Using this method can improve the vulcanization efficiency to different degrees and improve the uniformity of the vulcanization degree. However, since only the external temperature is examined in actual production, the actual temperature of each part of the tire is not known, and the temperature is not fixed every time, so the result calculated according to the temperature measurement and the actual vulcanization result have a large error.
- The simulation and prediction of the temperature field during the vulcanization of thick rubber products show that the uneven temperature is the main factor causing the uneven vulcanization of the tire casing. The rubber industry generally believes that a constant external temperature is an important condition to ensure quality, and it is necessary to do everything possible to achieve constant temperature from the equipment. This is true for non-thick rubber products, but not for thick rubber products such as tire casings. The tire is heated and vulcanized in the model, and the heat is transferred to all parts of the tire through the model. Rubber is a poor conductor of heat, the temperature rises slowly, and there are obvious temperature gradients in various parts of the early heating tire. It takes a long time to reach equilibrium.
Rubber products have a wide range of applications due to their special physical and mechanical properties. With the development of the times, many new requirements have been placed on the performance of rubber products. In order to meet these demands, various new technological production methods are constantly emerging and changing. Pressure injection vulcanization, nitrogen vulcanization, variable temperature vulcanization are just the epitome of many new technologies.
References: The original "China Plastic Rubber" "vulcanization" has its history, because the original natural rubber products were cross-linked with sulfur The agent is named after cross-linking. With the development of the rubber industry, a variety of non-sulfur cross-linking agents can now be used for cross-linking. Therefore, the more scientific meaning of vulcanization should be "crosslinking" or "bridging", that is, the process of forming a network polymer through crosslinking of linear polymers. Sulfur cross-linking occurs during the vulcanization process. This process refers to connecting one or more sulfur atoms to the polymer chain to form a bridge structure. The result of the reaction is the formation of an elastomer, whose properties have changed in many ways. The vulcanizing agent can be sulfur or other related substances. In terms of physical properties, it is the process of converting plastic rubber into elastic rubber or hard rubber. The meaning of "vulcanization" includes not only the actual cross-linking process, but also the method of generating cross-links.
The vulcanization process can be divided into four stages, the characteristics of each stage:
- It can be seen from the measurement of the fixed tensile strength of the rubber (or vulcanization instrument) that the entire vulcanization process can be divided into four stages: vulcanization induction, pre-sulfurization, normal vulcanization and oversulfurization (for natural rubber, vulcanization back to original).
- During the vulcanization induction period (scorch time), cross-linking has not started yet, and the compound 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 raw rubber itself, and mainly depends on the additives used. For example, the use of retardation accelerators can get a longer scorch time and has higher processing safety.
- After the vulcanization induction period is a pre-vulcanization stage where cross-linking proceeds at a certain speed. The degree of cross-linking during the pre-vulcanization period is low. Even if the tensile strength of the late vulcanizate is reached, the elasticity cannot reach the expected level, but the performance of tearing and dynamic cracking is better than the corresponding normal vulcanization.
- After reaching the positive vulcanization stage, the physical properties of the vulcanized rubber respectively reach or approach the optimal point, or achieve a comprehensive balance of performance.
- After the positive vulcanization stage (the vulcanization flat area), it is the oversulfurization stage. There are two cases: natural rubber has a "return" phenomenon (decreased in constant tensile strength), and most synthetic rubbers (except butyl rubber) have constant tensile strength Continue growing.
- For any rubber, not only crosslinking occurs during vulcanization, but also the production of chains and molecular chains break due to heat and other factors. This phenomenon runs through the entire vulcanization process. In the over-sulfur phase, if cross-linking is still dominant, the rubber will become hard and the tensile strength will continue to rise. On the contrary, if the rubber becomes soft, it will return to the original.