Cement Milling (Ball Mill) Part I

- ديسمبر 22, 2020

The mechanical elements of a tube mill can roughly be subdivided into internal and external parts. The mill internals have a direct function with regard to the grinding process and include principally the wear parts of a mill such as mill liners, diaphragms and grinding media.

The external parts of a standard tube mill consist of mill shell, mill heads, mill bearings, feed and discharge equipment and include also the mill drive.

In the following the external parts of the tube mill are described under special consideration of the process technological aspects. The mill internals are described in separate chapters.

MECHANICAL COMPONENTS OF TUBE MILLS

The first tube mills were of a rather simple design, consisting basically of a drum equipped with some wear plates and filled with some balls.

In the course of increasing plant capacities and the development of new energy saving processes the design of the mechanical components of a tube mill were changed considerably.

Fig. 1 and Fig. 2 show the different design features of modern tube mills. The dimensions and design of the mill shell, the mill heads and the mill bearings are basically dictated by the required grinding capacity whereas the design of the feed and discharge devices are selected according to process considerations such as wet grinding or drying / grinding.

Fig. 1 indicates a typical arrangement of a tube mill for cement grinding, consisting of two grinding compartments, two trunnion bearings and a central drive

Fig. 2 shows an air swept mill equipped with an overhanging drying compartment and driven by a girth gear / pinion drive. On the inlet side the mill is provided with a slide shoe bearing whereas the outlet part of the mill is supported by a conventional trunnion bearing. The raw material is fed into the gas stream entering the mill and the ground material is swept out by the mill exhaust gas

Two compartment mills as shown in Fig. 1 are also used for dry grinding of raw materials. The air swept mill as shown in Fig. 2 is principally used for drying/grinding of very wet raw materials (or coals).