Why the rubber compound will produce “self-sulfurization” during the period of placement

(1) Too much vulcanizing agent and accelerator are used.
(2) The capacity of rubber loading is large, the temperature of the refining machine is too high, and the film is not cooled enough; 
(3) or too early to add sulfur, the drug dispersion is uneven resulting in the accelerator and sulfur local concentration.
(4) improper parking, i.e., parking place temperature is too high, air circulation is not good.