The sulfur in rubber moves to the surface and crystallizes on the surface, a phenomenon known as frosting.This happens to both unvulcanized and vulcanized rubber.When the unvulcanized rubber is sprayed with frost, the adhesion of the rubber material will be difficult, resulting in poor adhesion;If spray frost phenomenon is serious, in the manufacture of molded products or moving mold injection sheet products, ejected sulfur will be retained in the horizontal sag, so, easy to form a lack of glue.This is because the sulfur does not dissolve in the rubber in a short time.The first measure to prevent frosting of unvulcanized rubber is to reduce the sulfur content, but after reducing the sulfur content, the elastic modulus of vulcanized rubber will decrease sharply, and the hardness will also be reduced.Therefore, the reduction of sulfur with the amount of caution.
If the amount of sulfur is not reduced, the problem can be solved by adding insoluble sulfur.If all sulfur cannot be replaced with insoluble sulfur, half of the sulfur can be replaced with insoluble sulfur.This almost achieves the desired effect.The above method is applicable to the unvulcanized rubber used in factories facing outward processing.Sulphur, in particular, cannot be stored long in cold storerooms, which can induce frosting and the effect of insoluble sulphur.
After vulcanization of rubber products after a period of time will also occur frosting.As a precautionary measure, the problem of complete vulcanization should be noted before planning to reduce sulphur content.Curing temperature, curing time is appropriate, do not hope to consider a little longer curing time.But in any case, high temperature short time vulcanization is not suitable.Rubber products should avoid direct sunlight and sharp cooling after vulcanization and should be stored in a naturally ventilated place.In this case, cover the container with a cloth cover made of canvas, etc., to prevent frosting.Insoluble sulfur does not work in the frosting that occurs after vulcanization.
In addition, slightly different from frosting, there will be visible sulfur crystals in winter rubber slurry, if you use a magnifying glass, you can clearly see that this is some rhombic crystals.Once there is such a crystallization, in the brush coating of the glue will be at the end of the brush attachment crystals, in the glue coating surface concave;And with the gluing machine for gluing, it is in the blade of the scraping knife to form crystallization, like a strip of longitudinal glue mark.
The preventive measures are as follow: add insoluble sulfur equivalent to half of the required amount of sulfur in the sulfur mixture, only take the required amount from the mortar tank when using the mortar, and store the temporarily unused mortar in the mortar tank, and slowly stir it for use.