1) prevents rubber from generating bubbles during vulcanization and improves the compactness of products.
2) Driving the filling flow of the rubber compound to fill the mold cavity.
3) Improve the adhesion between the rubber mixture and the cord fabric and the flex resistance of the product.
4) Improve the physical and mechanical properties of vulcanized rubber (i.e. products).
Usually, the selection of curing pressure needs to consider several factors, namely, the formula of rubber compound, the plasticity of rubber compound, and the structural form of molding die (filling pressure, injection pressure, injection pressure, etc.). ), the type of curing equipment (flat curing press, injection pressure curing press, injection curing press, vacuum curing press, etc. ) and the structural characteristics of the product. The general principles of vulcanization pressure selection are: the pressure of soft rubber should be small, and the pressure of hard rubber should be large; The pressure of thin-walled products should be small, and the pressure of thick-walled products should be large; The product with simple structure needs less pressure, and the product with complex structure needs more pressure; The pressure that requires high mechanical properties of products should be greater, and vice versa; When the curing temperature is higher, the curing pressure can be lower, and when the curing temperature is lower, the curing pressure can be higher.
Vulcanization pressure should be set within the system pressure range of vulcanization equipment according to product quality, combined with experience or through trial production.
Usually in engineering applications, in order to improve production efficiency, the vulcanization time is shortened by increasing the vulcanization temperature within the allowable range.
Therefore, increasing the curing temperature can shorten the curing time. The high temperature vulcanization process includes injection vulcanization and electric heating plate vulcanization, both of which can be vulcanized at 160℃ or even higher. In recent years, there is a trend to adopt high temperature vulcanization in industry. In addition, the continuous vulcanization process with molten liquid as heating medium has also begun to adopt high temperature vulcanization. In the process of rubber injection molding, because the rubber compound has been preheated and plasticized by the screw, a higher vulcanization temperature (such as 175~ 183℃) can be adopted, which has little effect on rubber reversion or over-vulcanization. For example, when EPDM is molded at 160℃, its positive vulcanization time is 60 minutes. If it is changed to 200℃, it will be injected.
The curing time of injection molding is only 4 minutes. Generally, the vulcanization time of small products made of rubber can be l-2mm.
Vulcanization effect is an index to measure the vulcanization degree of rubber compound. If the vulcanization effect is large, it shows that the vulcanization degree of the rubber compound is deep; The vulcanization effect is small, indicating that the vulcanization degree of the rubber mixture is shallow. The curing effect is equal to the product of curing strength and curing time. The so-called vulcanization strength refers to the degree of vulcanization or the vulcanization speed of rubber achieved in a unit time at a certain temperature.
High curing strength means that the curing reaction speed is fast and the curing time required to reach the same curing degree is short; The curing strength is small, indicating that the curing reaction speed is fast.