Hardness of minerals can reflect mineral composition and physical property, which is an immutable factor. It is difficult for Raymond Mill to crush the minerals with features of compact structure, small crystal and large hardness. These minerals will take Raymond Mill much time to process to suitable sizes, and it affects the capacity badly. On the contrary, materials with small hardness are easy to be processed and the capacity of Raymond Mill is large.
Because of immutability of hardness, we should take positive attitude to materials with large hardness, for example, we can find the most suitable puple density and amount of returned sand. At the same time, it requests that reduce the sizes of materials which have been crushed, and find suitable proportioning when the conditions are eligible.