As we have mentioned repeatedly in our articles, the right choose of lining plate is very important. 10-15 years ago there was only one main purpose of lining plates was protection of the mill hull from mechanical damage.
To date, the design of the lining plates is based on the need to form a grinding line, which will ensure the maximum efficiency of the grinding process by steel grinding balls.
Lining plates differ in size, material and method of attachment to the mill casing and the shape of surface.
According to the type of profile, lining plates can be smooth, stepped wavy, combined, corrugated, cellular, heeled and other.
Lining plate’s durability and the lift height of steel grinding balls depend on the geometric shape of the lining plate surface. When designing new types of liners one of the objectives is the reduction in slipping of grinding balls and grinded material over the lining surface, which improves the grinding quality and, as a result, increases mill productivity. Ring lining plates are more durable than liners with smooth and wave working surface. This is because the liners projections get stronger under the impact of the steel grinding balls. Figure 1 below shows the type of lining plates, which are currently used in existing enterprises.
Figure 1. The type of lining plates
Types of liners profiles: a – single-wave, b – two-wave, c – cascade, d – block, e – profile with lifting axle, f – unified profile, g – flat, h – steel cylinder, i – stepped, j – heeled, k – cone-step, l – rubber.
Cylinder lining plates are used for rational grinding balls distribution according to their size in the direction of grinding material.
Cone-step liners with heeled surface and wave shape. The sorting of steel grinding balls is the distribution the balls in different diameters by length of the mill. The lining is set so that the working surface of the plate forms a set of short truncated cones, which are facing the loading side with their larger base. This liners arrangement guarantees the distribution of grinding balls with a decreasing diameter to the movement of the grinding material. Larger balls in the loading location to destroy large pieces of material. At a distance from the loading location, smaller balls are located to destroy small pieces of material.
The adhesion between material, grinding balls and liners occurs due to the heel or wavy surface. Heel dimensions are equal to the diameter of the largest grinding balls. It was established, that the lining plates quickly abraded with the smaller diameter of the heels because of the small clutch with grinding balls.
There are some shortcomings of cone-step liners: reduction in the effective capacity of the mill, deterioration of heel surface at the place of large grinding balls exploitation, the difficulty in design and producing.
One of the most common types of lining is stepped lining plate.
Rubber lining plate is used under the following conditions of mill operation: environment should be neutral, pH acidity not more than 8-10 units, temperature not higher than 80°C, the diameter of the loading grinding balls is not more than 80 mm, the particle size of the loading material shall not exceed 20 mm.
The lining plate inside the mill drum is arranged so that the gaps (oriented along the axis of housing rotation) between the plates form a straight line. The gaps (direction transverse of housing rotation) form a zigzag line (figure 2).
Figure 2. The types of liners arrangement
There are two types of liners arrangement:
а) a zigzag line;
б) a straight line.
The lining plates arranged straight lines along and across the mill casing are also widely used in production. Therefore, the arrangement of liners there is only then the ball mill is intended for grinding of non-aroid materials (for example, coal).