In the process of vulcanizing rubber products with special sulfur powder for rubber, we found that sulfur is difficult to dissolve in rubber, and when the temperature changes, the dissolved sulfur may be separated from the rubber again due to the change in solubility, and precipitate on the surface of the rubber. The phenomenon of sulfur spraying.
Hazard of sulfur spraying phenomenon: After sulfur spraying of rubber products, it will not only affect the appearance of the product, but also reduce the surface adhesion of the rubber and make the aging resistance of the product worse.
Causes of sulfur spray phenomenon: When adding sulfur during mixing, the mixing temperature is too high or the mixing is uneven, which will cause more sulfur to dissolve in the mixture or local compounds. When the amount of sulfur dissolved in the rubber mixture exceeds the saturation solubility limit or the room temperature supersaturation solubility limit, it will crystallize and precipitate from the rubber, resulting in the phenomenon of sulfur spraying. Excessive sulfur content or severe lack of sulfur in the production of rubber products is also the cause of sulfur spraying.
Ways to avoid sulfur spray:
1. Control the amount of sulfur: Usually, the amount of sulfur in rubber should be controlled between 0.3-4 parts, and the amount of sulfur in soft rubber should not exceed 3-3.5 parts per 100 parts of raw rubber; semi-hard rubber and hard rubber The amount of sulfur in rubber is high, among which the amount of sulfur in semi-hard rubber is between 20-30 parts, and the amount of sulfur in hard rubber can be increased to 30-47 parts.
2. Adjust the production formula and process: Generally, in order to prevent rubber products from spraying sulfur, rubber product manufacturers will use an appropriate amount of reclaimed rubber or grooved carbon black in the rubber compound to improve the rubber quality rubber mixing process and vulcanization process; The use of an appropriate amount of selenium in the rubber product formulation of the vulcanizing agent can also reduce the phenomenon of sulfur spraying; when mixing in the production process, the sulfur should be mixed at the lowest possible temperature, and a small amount of softener should be added before adding the sulfur.