(1) The additives in the rubber compound are not uniformly dispersed during mixing.
 (2) There are many impurities in the vulcanizing agent, impurities of small molecules become decomposed in advance, and bubbles remain in the product.
 (3) The mixing temperature is low, there is water, and the water is not volatilized. When the temperature is high, the sulfur is easy to melt or scorch when the sulfur is added to the open mill.
 (4) Insufficient parking time or production without use.
 (5) The rubber is not hot-melted uniformly, and the surface is not smooth when it is released.
 (6) When the rubber compound is hot-melted on the open mill, the surface is covered with air, and the outflow rubber compound has the phenomenon of trapping air.
 (7) Insufficient vulcanization, air bubbles appear unfamiliar;
 (8) The temperature of the roller of the open mill is not strictly controlled, the temperature of the hot refining rubber supply temperature, and the temperature of the extruding and discharging rubber are not strictly controlled, and there are air bubbles on the surface of the semi-finished product.