A typical grinding mill comprises a generally cylindrical drum with openings at one or both ends of the drum. Spaced about the inside wall of the drum are a number of lifter bars which are elongate objects which stand proud of the inner drum surface. The material to be ground is introduced to the drum along with grinding media in the form of a number of steel balls. The drum is caused to rotate and, as it does so, the lifter bars serve to lift the material and grinding media as the drum rotates, rather than merely sliding along the inside wall of the drum. At a certain point in the rotation of the drum, the material and grinding media falls away from the lifter bar by action of gravity to impact at the lower region of the drum. The force of the impact causes the material to be broken into smaller pieces thus effecting a grinding action.
The lifter bars become worn during operation and have a limited service life. It is necessary to replace the lifter bars from time to time. This is typically carried out by way of a specialised machine known as a liner handler. The liner handler moves on wheels and has a hydraulically operated arm which can grasp and carry a lifter bar. Having picked up a lifter bar, the handler is driven to the opening of the mill and the hydraulic arm extended to introduce the lifter bar into the mill and to hold the lifter bar in place whilst securing bolts are tightened. However, in the case of smaller mills, there is often insufficient clearance at the opening of the mill to allow use of a liner handler. This necessitates manual installation of lifter bars.
The lifter bars can typically weigh of the order of 200 kg and so a crew of at least four men is typically required to physically carry each lifter bar into some mills and to hold each bar in position whilst various securing bolts are aligned and tightened. This is a very strenuous task. Further, the floor of the mill is curved and generally uneven and may be littered with a mixture of crushed material and steel balls. This material may move when stepped on by persons entering the mill which presents a further hazard when installing large lifter bars inside the mill. There is a risk of injury to the installers of the lifter bars. It would be advantageous to reduce this risk.