1 Vulcanization temperature Vulcanization temperature is one of the basic conditions for rubber vulcanization reaction, which directly affects the rate of vulcanization reaction and the physical and mechanical properties of vulcanizate and thus affects the quality of the product. Like the general chemical reaction, the vulcanization reaction of the rubber finger sleeve depends on the temperature. As the temperature increases, the vulcanization reaction rate increases, the production efficiency is high, and more low-sulfur cross-linking bonds are easily formed. Conversely, the vulcanization temperature is low, vulcanization. The rate is slow, the production efficiency is low, and it is easy to generate more polysulfide crosslinks. Obviously, in order to obtain high production efficiency, the higher vulcanization temperature should be used as much as possible. In fact, the vulcanization temperature cannot be increased without limitation. Generally, the higher the vulcanization temperature, the lower the physical and mechanical properties of the finger rubber compound, and the higher the temperature. It can cause cracking of the rubber molecular chain and reversion of the rubber (especially natural rubber), which degrades performance and makes process control difficult. Therefore, the choice of vulcanization temperature should be considered in consideration of the type of the product, the type of rubber and the vulcanization system. The vulcanization temperature of the rubber is generally in the range of 120 to 190 °C.
2 Vulcanization pressure Vulcanization pressure refers to the pressure applied to the rubber product per unit area during vulcanization. The vulcanization pressure can be divided into normal pressure and high pressure. Generally, atmospheric vulcanization is suitable for thin-walled articles such as tapes, and molded articles require higher pressure.
The method of vulcanization and pressurization is to transfer the pressure to the model through a flat vulcanizing machine by a hydraulic pump, and then transfer the mold to the finger sleeve rubber, which is said to pressurize the plate; directly pressurize the vulcanization medium, such as steam pressure; pressurize with compressed air , that is, hot air pressurization; pressurization by an individual vulcanizing machine and injection pressure of a pressure injection machine.
The main effects of the pressure of vulcanization are as follows.
Preventing the product from generating bubbles during the vulcanization process, improving the compactness of the rubber compound. The moisture and other volatile substances contained in the rubber compound during vulcanization, and the hydrogen sulfide gas which may be formed during the vulcanization reaction, will volatilize and escape at high temperature. The compound produces bubbles. If a vulcanization pressure greater than the size at which the rubber may escape is generated during vulcanization, the generation of bubbles can be prevented and the compactness of the compound can be improved. Applying a higher vulcanization pressure can change the compactness of the compound. If only bubbles are prevented, a water absorbing agent such as gypsum or calcium oxide may be added to the rubber to achieve atmospheric pressure vulcanization.
b. Making the compound easy to flow and filling the cavity To produce a clear, full-bodied product, the finger-sleeve compound must flow and fill the cavity. In particular, the vulcanization pressure is more pronounced during the vulcanization induction period in which the rubber is in an uncrosslinked state. Experiments have shown that for molded rubber products, if the vulcanization temperature is 100~140~C, the vulcanization pressure should be 2~5MP. If the vulcanization temperature is 40 ~ 50 ~ C (such as injection molding filling), the vulcanization pressure should be 50 ~ 80MP. In this way, the rubber can flow well and fill the cavity.
. . When the compactness of the rubber compound is improved and the adhesion vulcanization of the rubber material and the skeleton material is improved, as the vulcanization pressure increases, the depth of the rubber penetrating into the cloth layer increases, thereby improving the adhesion between the rubber and the cloth layer and the resistance of the product. Flexibility. Experiments have shown that the vulcanization pressure (the internal pressure of the water tire) increases with the vulcanization pressure (the internal pressure of the water tire), and the flexural flexibility of the inner layer of the outer tire increases.
d. It helps to improve the physical and mechanical properties of vulcanizates. Experiments show that with the increase of vulcanization pressure, some physical and mechanical properties such as strength, dynamic modulus, fatigue resistance and wear resistance of vulcanized rubber are correspondingly improved. Experiments show that the wear resistance of tires vulcanized with 5.0MPa pressure is 10%-20% higher than that of tires vulcanized with 2.0MPa pressure. The ring pre-vulcanized tires produced by pressure of 6-7MPa are applied. The surface rubber has almost the same wear resistance as the new tire.
However, too high a vulcanization pressure is detrimental to the performance of the rubber because the high pressure, like high temperature, accelerates the thermal degradation of the rubber molecules, which in turn degrades the properties of the rubber compound. In addition, under high pressure, the structure of the textile material is also destroyed, resulting in a decrease in flex resistance. Excessive pressure requires high equipment, damage to equipment, and high power costs.
3 Vulcanization time As with many other chemical reactions, the progress of the vulcanization reaction depends on time. Under certain vulcanization temperatures and pressures, the degree of vulcanization meeting the design requirements can only be achieved after a certain curing time.
