According to the curing conditions, it can be divided into three types: cold curing, room temperature curing and hot curing.
Cold vulcanization can be used for the vulcanization of thin film products. The products can be dipped in a carbon disulfide solution containing 2% to 5% sulfur chloride, and then washed and dried.
Room temperature vulcanization
When room temperature vulcanization, the vulcanization process is carried out at room temperature and atmospheric pressure, such as using room temperature vulcanization rubber (mixed rubber solution) for bicycle inner tube joints, repair and so on.
Thermal vulcanization is the main method of vulcanizing rubber products. According to the different curing media and curing methods, thermal curing can be divided into three methods: direct curing, indirect curing and mixed gas curing.
(1) Direct vulcanization, the product is directly placed in hot water or steam medium for vulcanization.
(2) Indirect vulcanization. Products are vulcanized in hot air. This method is generally used for certain products with strict appearance requirements, such as rubber shoes.
(3) Mixed gas vulcanization, air vulcanization is used first, and then direct steam vulcanization is used. This method can overcome the shortcomings of steam vulcanization that affect the appearance of the product, and can also overcome the shortcomings of long heat curing time and easy ageing due to the slow heat transfer of hot air.
The main factors affecting the vulcanization process
(1) Sulfur dosage. The larger the amount, the faster the vulcanization speed, and the higher the degree of vulcanization that can be achieved. The solubility of sulfur in rubber is limited. Excess sulfur will be precipitated from the rubber surface, commonly known as "sulfur spray". In order to reduce the sulfur injection phenomenon, it is required to add sulfur at the lowest possible temperature, or at least below the melting point of sulfur. According to the requirements for the use of rubber products, the amount of sulfur in soft rubber generally does not exceed 3%, the amount of sulfur in semi-rigid rubber is generally about 20%, and the amount of sulfur in hard rubber can be as high as 40% or more.
(2) Vulcanization temperature. If the temperature is 10 ° C higher, the curing time is shortened by about half. Because rubber is a poor thermal conductor, the vulcanization process of the product is different due to the temperature difference of its various parts. In order to ensure a relatively uniform vulcanization degree, thick rubber products are generally vulcanized by gradually increasing temperature and low temperature for a long time.
(3) Vulcanization time. This is an important part of the vulcanization process. The time is too short, and the degree of vulcanization is insufficient (also called undersulfur). Too long time, too high degree of vulcanization (commonly known as over sulfur). Only the appropriate degree of vulcanization (commonly known as normal vulcanization) can ensure the best comprehensive performance.
Compression set is one of the important performance indicators of rubber products. The magnitude of permanent compression of vulcanized rubber involves the elasticity and recovery of vulcanized rubber. The size of the permanent deformation is mainly dominated by changes in the rubber's recovery ability. Factors affecting the recovery ability include the interaction between molecules (viscosity), the change or destruction of the network structure, and the displacement between molecules. When the deformation of the rubber is caused by the stretching of the molecular chain, its recovery (or the size of the permanent deformation) is mainly determined by the elasticity of the rubber: if the deformation of the rubber is accompanied by the destruction of the network and the relative flow of the molecular chain, It can be said that it is unrecoverable, and it has nothing to do with elasticity. Therefore, all the factors that affect the elasticity and recovery of rubber are the factors that affect the compression and permanent deformation of vulcanized rubber. These factors include elasticity, impact elasticity (resilience), elasticity and modulus, permanent compression, permanent tear.
1. Elasticity—The elasticity of rubber should be a theoretical concept, which indicates the ease of rotation of the rubber molecular segment and side groups, or the compliance of the rubber molecular chain and the magnitude of the molecular force. For vulcanized rubber, its elasticity is also related to the density and regularity of the crosslinked network.
2. Elasticity and Permanent Deformation-It is often said that the elasticity of natural rubber is very good, but its permanent deformation is often very large. This is mainly because the natural rubber has a very high elongation. The damage and the displacement of the molecular chain are large, and the recovery process after the break is long and the unrecoverable part increases. If the permanent deformation of the fixed length is compared, the permanent deformation of natural rubber is not necessarily large.
3. The impact elasticity or resilience is measured under a constant load (or constant energy) condition. The elasticity of the elasticity is directly related to the degree of cross-linking  or the modulus of the vulcanizate. It expresses rubber elasticity and viscosity. (Or absorption) synthesis.
4. Compression permanent deformation is measured under constant deformation conditions, and its value is related to the elasticity and recovery ability of rubber.
In the range of higher strain rates, the dynamic stress-strain relationship of vulcanized rubber is related to the strain rate. The elastic modulus, yield stress, and flow stress all increase with the increase of the strain rate, so the material shows obvious results in dynamic experiments. Strain rate effect. Under low strain rate loading, vulcanized rubber is not sensitive to strain rate.