The particle size of the material entering vertical roller mill is larger than the maximum particle size allowed by the material inlet, and the proportion of bulk material is large, which increases the circulating load in vertical roller mill, causes the material layer in the membrane to be unstable, and causes an increase in slag.Material segregation. Due to the material itself and the untimely feeding time, the abrasive material is excessively concentrated, which increases the circulating load and causes slag spitting.The material has poor grindability. Improper clinker ratio and more difficult-to-grind components increase the circulating load in the membrane and cause slag spitting.The influence of fly ash. Some cement plants choose to use fly ash instead of clay ingredients. Due to the high moisture content of fly ash in the rainy season, it is mixed with limestone in the homogenization plant without being dried. When the vertical mill is running, the fly ash adheres to the three valve plates of the feeding chute and the inlet mill. The more it hangs, the more it hangs, and it suddenly collapses into vertical roller mill to a certain extent, causing the internal load of vertical roller mill to suddenly increase and the slag spit to increase sharply.