Two questions will occur if the inner temperature of cement mill is too high. One question is working efficiency decreases for cement will stick to each other into a ball and this phenomenon will become serious with the temperature's raising. The other question is that the cement powder grinding is mixed with clinker and gypsum, while gypsum has a function of adjusting the cement condensing time. If the gypsum is too hot, it will lose water of crystallization and become semi-hydrated gypsum or anhydrous calcium sulfate. And the dissolubility is totally different from original content, which will have a great change on function of cement setting time, and cement will coagulate rapidly without usage. So, temperature controlling is very important for cement mill, generally under 100 °C with highest temperature no more than 120 °C.