Rubber overvulcanization

It refers to the state of the rubber compound at high temperature for a long time.

"Dead Glue"
Due to the early vulcanization of the mixed rubber with vulcanizing agent added during processing or parking, the resulting rubber is called dead rubber, which is actually a scorched rubber. In the actual processing process, in order to avoid the danger of scorch and make the rubber compound have better in-mold fluidity, it is often solved by adding an anti-scorch agent. The compound exhibits early vulcanization during processing or during pre-vulcanization parking. The main reasons for the scorch of the rubber compound are improper formula design, such as inappropriate type of accelerator, excessive dosage; excessive temperature during mixing, extrusion, and calendering; excessive parking temperature and long time of rubber compound. In addition to improving the formula and process for the above reasons, preventing the scorch of the rubber compound can also be achieved by using an anti-scorch agent to prolong the scorch time of the rubber compound.

Cause:
(1) Improper formula design, unbalanced vulcanization system configuration, and excessive amount of vulcanizing agent and accelerator.

(2) For some types of rubber that need to be masticated, the mastication does not meet the requirements, the plasticity is too low, and the gum is too hard, resulting in a sharp temperature rise during rubber mixing. Roller temperature of rubber mixer or other roller devices (such as remixer, calender) is too high and cooling is not enough, which may also lead to scorch on site.

(3) When the rubber compound is unloaded, the film is too thick, the heat dissipation is poor, or it is not cooled, that is, it is stored in a hurry, coupled with poor ventilation in the warehouse, high temperature and other factors, resulting in heat accumulation, which will also cause scorch.

(4) The management of the rubber material is not good during the storage process. After the remaining scorch time is used up, it is still not used, and natural scorch occurs. Difficulty in processing; affect the physical properties of the product and the smoothness of the outer surface; even lead to disconnection at the joint of the product.

Solution:
(1) The design of the rubber compound should be appropriate and reasonable. For example, the accelerator should be used in multiple ways as much as possible. Scorch is suppressed. In order to adapt to the high temperature, high pressure and high speed rubber mixing process, an appropriate amount (0.3 to 0.5 parts) of anti-scorch agent can also be used in the formula.

(2) Strengthen the cooling measures for rubber materials in rubber mixing and subsequent processes, mainly through strict control of machine temperature, roll temperature and ensuring sufficient cooling water circulation, so that the operating temperature does not exceed the critical point of scorch.

(3) Pay attention to the management of semi-finished rubber materials, each batch of materials should be followed by a flow card, implement the "first-in, first-out" inventory principle, and stipulate the maximum storage time of each vehicle material, which shall not be exceeded. The warehouse should have good ventilation conditions.

(4) The vulcanization system is adjusted, and the sulfenamide accelerator is used, which greatly improves the anti-scorch performance.

(5) Improve the storage and processing conditions of the rubber compound, such as strengthening cooling;

(6) Use anti-scorch agent.