Cement and Energy

The optimisation of a grinding plant can only be reached with Phe search for a compromise between : • • Output in tph. Specific energy in kWh/t. Wear and tear in g/t. As already shown, the transfer of energy to the grinding media is made through the liners, causing the grinding media to be loaded with kinetic energy. The profile of the liners must regulate the activation of the grinding media so that a sufficient quantity grist is available between the grinding media and the shell liners. Furthermore, the activation must be controlled so that a regulated grinding process is made possible. Difterent sizes of gri nding media are used to regulate the grinding in the milling chambers of the mill. 1n the fi rst chamber, the balls should produce a crushing .....:ct called cataracting. In the second chamber, the chopping up of the grist is achieved through friction, a process known as cascading. In the course of the grinding ring, the size of the gri ndin g media decreases (Figure 3). Cataracting Cascading Figure 3. Analysis of ball charge movement. ' ' ' ' ~,--r-/ ,. __ ,. : j: ---------~·--------- Figure 4a. Trapped grinding balls transfer shear force to other grinding media. Figure 4b. No shear force is caused through grinding media being trapped. Both forms of grinding described underlie the activation of the grinding media, which in turn produces the movement of the grinding media. At present, there are two fundamental kinds of liners u.s.ed in_,th.e first chamber of a cement mill. liolteu lmers The advantage of this form of liners is the simplicity of installation. However, in the screw holes small particles of grinding balls become trapped, and because of this shear force is transferred to other grinding media (Figure 4a). This of course is a disadvantage, which results in the worsening of the activation. Higher wear on parts and ;~. 1 higner energy consumption is also produced. liolt, es-s liners The advantage of this form of liners is that no shear force is caused through grinding media being trapped (Figure 4b). However, the disadvantage of this form of liners is the difficulty of installation. Special tools are required for the installation, and there is the danger of considerable tension being transferred to the mill shell. Also, it must not be forgotten that through higher demands of precision this kind of liners causes higher production costs. To make the grinding media circulation possible, the second grinding chamber has the task of activating the gri nding media. In addition, grinding media arc classified, and the specific structure of the grinding media and the amount of grist particles are increased. For this reason, classifying liners and activators are combined in the second grinding chamber (Figure 5). The bolt head joins with the surface of the key. ·~' I Figure 5. Classifying liners and activators are combined in the second grinding chamber. 3