Rubber vulcanization is an important process of rubber products processing, the purpose is to add vulcanization agent in rubber, and under certain temperature, pressure and time conditions, so that rubber macromolecular chain cross-linking reaction, the raw rubber into elastic and dimensional stable vulcanization rubber. In this process, the molecules of rubber form a three-dimensional network structure through cross-linking, so as to obtain high strength, high elasticity, high wear resistance, corrosion resistance and other excellent properties.
1. Vulcanization system and properties:
Different types of rubber react with crosslinking agents to produce different crosslinking bond structures, and the properties of vulcanized rubber are also different.
Typical vulcanization systems include common sulfur vulcanization system, semi-effective vulcanization system, effective vulcanization system and sulfur-free vulcanization system.
2, curing agent
Vulcanizing agent is a substance that can cross-link linear rubber molecules into a three-dimensional network structure. The earliest vulcanizing agent was sulfur, which is still widely used today. With the increase of synthetic rubber varieties and the development of its products, many compounds with vulcanization effect have been found. What is now called vulcanization is only a symbolic industrial term, and its essence is to cross-link linear rubber molecules to form a three-dimensional network structure, and all substances with this effect can be called vulcanizing agents.
3, vulcanization process conditions:
Sulfur dosage: The greater the dosage, the faster the vulcanization rate, the higher the degree of vulcanization achieved, but excessive will lead to "sulfur spraying". The solubility of sulfur in rubber is limited, and the amount varies according to the requirements of rubber products.
Vulcanization temperature: The temperature is 10℃ higher, and the vulcanization time is reduced by half. Rubber is a poor thermal conductor, thick rubber products are generally used gradually warming, low temperature long-term vulcanization.
Curing time: too short time will lead to insufficient curing degree, too long time will lead to high curing degree, only the appropriate curing degree can ensure the best comprehensive performance.
4, curing process:
It can be divided into four stages: induction, pre-vulcanization, positive vulcanization and overvulcanization, each stage has different characteristics.
Induction period: the time before the formal vulcanization begins, usually called the scorch time.
● Pre-vulcanization period: The process of formal vulcanization, in which the characteristics of this stage rise with the vulcanization time, so that positive vulcanization is achieved.
● Positive vulcanization period: After the pre-vulcanization, if the vulcanization continues, the physical properties of the vulcanized rubber will decline.
● Over-vulcanization period: If you continue to vulcanize, the process of physical properties of vulcanized rubber instead of decreasing.
The vulcanization induction period determines the scorch property and processing safety of the rubber, the crosslinking degree is low in the pre-vulcanization period, the physical properties of the vulcanized rubber in the positive vulcanization stage reach or approach the optimal point, the natural rubber in the over-sulfur stage will appear "back" phenomenon, and the fixed elongation strength of most synthetic rubber continues to increase.
5, traditional rubber vulcanization process:
Influencing factors: the higher the amount of sulfur, the faster the vulcanization rate, but excessive will "spray sulfur"; The vulcanization temperature is high, the vulcanization time is shortened, but the thermal conductivity of rubber is poor, and the thick products should pay attention to the uniform temperature; The curing time should be appropriate to ensure the best performance.
6, rubber vulcanization process:
According to the vulcanization conditions can be divided into cold vulcanization, room temperature vulcanization and hot vulcanization three categories.
Hot vulcanization can be divided into direct vulcanization, indirect vulcanization and mixed gas vulcanization.
7, injection molding vulcanization process:
The difference between injection pressure and mold pressure is that the temperature of the rubber material is different. Injection pressure can shorten the molding cycle, realize automatic operation, and has many advantages.
Notes for injection molding vulcanization process include using reasonable screw speed, back pressure, controlling the temperature of the injection machine, choosing the right nozzle diameter, and maintaining the right mold temperature and the best vulcanization conditions.
8, nitrogen vulcanization process:
The main advantages of nitrogen-filled vulcanization are energy saving and prolonged capsule life, which can save 80% steam and double the service life of the capsule.
The process of nitrogen vulcanization is characterized by first passing high temperature and high pressure steam, switching into nitrogen after a few minutes, and vulcanizing to the end of the "pressure variable temperature" process. Nitrogen purity requirements are high, it is recommended that enterprises prepare nitrogen systems to reduce costs.
8, variable temperature vulcanization process:
Key factors include shortening curing time, high temperature curing and temperature measurement.
The uneven temperature in the vulcanization process of thick rubber products is the main factor causing the uneven degree of vulcanization, and the rubber industry generally believes that the constant external temperature is very important for non-thick rubber products, but not for thick rubber products such as tires.
The discovery of vulcanization method greatly improved the properties of raw rubber, expanded the application range of rubber, and laid the foundation for the large-scale production of rubber. Until now, the vast majority of rubber is still using sulfur vulcanization process. Rubber vulcanization is a complex chemical and physical change process, through strict control conditions can make the rubber to obtain excellent properties. The discovery and development of this process had a profound impact on the rubber industry, making rubber a widely used material.
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