When the rubber product is vulcanized, it produces a phenomenon of poor cracking at the position of the mold line, which is generally called “burning edge”. Once it appears, it often produces a large amount of waste products, which seriously affects the normal production. As a professional rubber manufacturer, the analysis of the reasons for this phenomenon is hoped to help everyone.
The reason for the rubber “burning edge”
Vulcanization of rubber is a complex chemical reaction. Due to the high temperature, a large amount of volatiles are generated during the vulcanization. When the rubber is vulcanized, the rubber is molded in a closed cavity due to the action of high pressure, and the volatiles generated by the vulcanization cannot be leaked to form a certain pressure. As the vulcanization reaction progresses, more and more volatiles are formed, and the internal pressure is getting larger and larger. Finally, the closed cavity is broken out along the mold line, and at this time, the vulcanization has been carried out for a while, and the rubber of the surface layer has been vulcanized. Loss of fluidity, defects caused by a large amount of volatile leakage, can not be compensated, left in the final product, causing “burning edge.”

Rubber products that are prone to “burning edges”
1. Thick-walled products, because the rubber heat transfer is difficult, the inner and outer rubber compounds are not easy to be vulcanized synchronously. Therefore, such products are likely to cause the edge of the product to be vulcanized and the inside is not vulcanized. 2. Low-hardness products, because such products are often formulated with a large amount of softener in the formulation, which will contain more low-boiling volatiles, which will escape in a large amount during vulcanization. Compared with high hardness rubber compounds, it is more prone to “burning edge” phenomenon.
3. The mold structure is designed to cause concentrated exhaust products. For example, a cylindrical or cylindrical product is divided into two semi-circular combinations, and all vulcanized volatiles are concentratedly discharged from the intermediate parting line position, often resulting in “burning” due to excessive concentration of exhaust gas.
Production practice shows that rubber products with the above characteristics are prone to “burning edge” phenomenon. Attention should be paid to the production.