The Grinding ball mill is the most widely used equipment in industyr grinding, the grid  type ball mill and overflow ball millis used in the mineral processing industry and other industrial field .Dry type grid type ball mill is mainly used for industrial milling, mainly used for grinding materials industries.

Structure of ball mill

The ball mill is usually composed of cylinder, liner, feeder, hollow shaft, bearing, transmission device and lubrication system. The structure of the ball mill is introduced with the example of the 3200x5400mm overflow ball mill below.

1)Cylinder of ball mill

The  cylinder  is welded by a number of thick 30-32mm steel plates, with flange plates welded at both ends so as to connect to the casting end covers. The cylinder is equipped with a replacement liner. In order to make the liner contact tightly with the cylinder and buffer the impact of the steel ball on the cylinder, plywood is applied between the liner and the inner wall of the cylinder. In order to facilitate the replacement of the lining and the internal condition of the cylinder, a manhole  is opened on the cylinder body. The manhole is mostly rectangular, and the length is generally 350-550mm.


 

2)Feeding part of ball mill

The feeding part is composed of an end cover  with a hollow shaft neck, a joint feeder , a fan-shaped liner  and a shaft neck inner sleeve , etc. The inner neck of the hollow shaft can prevent the wearing of the inner surface of the axle neck. The inner surface of the inner sleeve is spiral and helps to feed. The feeder is bolted to the end of the inner sleeve. The general use of the joint feeder, followed by the drum feeder and worm feeder, and so on.

3)Discharge part of ball mill

The discharging part is made up o the end cover of the hollow neck,  the wedge , the center liner  and the inner sleeve  of the axle neck, and  radial bars are placed on the inner wall of the end cover, which is equivalent to the partition board. There is a latticed plate between each of the two bars and is pressed and fixed with a wedge. Wedge iron by the screw through the wall on the fastening ribs on the end cover. The center part uses the center liner to hold all the grid liners. The inner sleeve of the hollow shaft neck is made of a trumpet shaped blade at one end of the discharge grid to guide the pulp naughty from the partition board to flow down the blade. The whole discharge section is firmly fixed on the flange plate of the barrel as well as the feeding part.
 

4)Transmission part of ball mill

The transmission part is composed of large gear wheel, pinion, transmission shaft and elastic coupling. The mill barrel is driven by the gear drive device by the motor  through the couplings. The gear drive device is composed of a gear ring and a transmission gear installed at the end of the barrel. The transmission gear is mounted on the drive shaft, and the drive shaft is supported on the two double row centering rolling bearings in the bearing seat. The gear cover is fully covered with a dustproof cover.
 

5)Main bearing of ball mill

The hollow Journal of the ball mill is supported on the self aligning main sliding bearing. The main bearing is made up of the lower bearing seat , the bearing cap , the lower bearing bush with the Babbit alloy , the cylindrical pin  and the sealing ring. The bearing pedestal and the lower axle bush are made of spherical contact in order to compensate for the installation error. There is a cylindrical pin in the center of the base and the axle of the axle bush, which prevents the Bush from sliding out of the bearing seat. The oil entering the pipe is fanned into the journal bearing on the neck of the nozzle, and the oil after the lubrication is returned to the tank by the exhaust pipe.

Overflow ball and grid ball mill

The structure of the overflow ball mill is basically the same as that of the grid ball mill , but there is no material row in the cylinder end, and the reverse spiral blade is installed on the inner surface of the hollow neck bushing, which can return the pellets and coarse ore blocks in the pulp back to the mill.

Compared with the overflow type ball mill, the advantages of grid type ball mill is the discharge pulp surface is low, the pulp can pass rapidly, can reduce the overgrinding; the ball can be loaded, and the ball will not be discharged, good working conditions can be formed; under the same conditions, the production capacity is higher. And the power consumption is low, it is slightly complicated structure. But the overflow type ball mill has the advantages of simple structure, management and maintenance are convenient, so the operation rate is relatively high. Usually, the overflow type ball mill should be used with the fine grinding fineness, and the grinder type ball mill is suitable for the coarse grinding fineness. (The adverse effects of excessive grinding on ore dressing can be avoided ).

Working principle of ball mills

-The main component of overflow ball mill is a rotary cylinder supported by bearings which is revolved by transmitting machinery. Materials are put in cylinder through the feed opening and then thoroughly grinded. The falling course of iron balls and ores can produce huge falling impact and autogenous grinding. The continuous feeding of ores can create considerable pressure to make ores move from feed opening toward discharge opening. Finally, acceptable particles are discharged from the discharge opening. Hollow shaft with the anti-spiral blade returns the steel ball and the coarse ore.

-The main part of grid ball mill is a rotation cylinder rotating slowly by the transmission device. The material is fed from the cylinder inlet and grinded by the impact of steel ball and ore and self-grinding. Due to the continuously feeding material, the pressure pushes material to the outlet and the grinded material is discharged from the cylinder outlet. In wet grinding, material is taken out by water; in dry grinding, the material is taken out by air. The grid installed in the outlet of mill is relied for forced discharge. Low pulp surface in cylinder reduces the ore over-grinding, and prevent the steel ball out. Under the same production conditions, production capacity of grid mill is larger than overflow ball mill's. 

-Dry type ball mill is a grid ball mill of horizontal rotating device with outer gear drive device, two hoppers. Materials evenly spirally enter into the first hopper through hollow shaft, the warehouse has stepped lining board or corrugated liner board and different sizes of steel balls, the centrifugal force produced by cylinder rotation brings the steel balls to a certain height, then the falling balls pound and grind materials. After the rough grinding in the first hopper, by monolayer partition panel, the material will enter the second hopper, which has plane scale board with steel balls inside to grind material. The powder is discharged from grid plate and grinding operation is finished.

Liner and grinding medium of ball mill

liners and grinding media are important components of ball mills or indispensable for work, they are easy to wear and consume a lot.

1)Liners of ball mill

Liner material can be made of hard chromium steel, high manganese steel alloy cast iron, rubber and magnetic lining etc.. High manganese steel has enough impact toughness, and it can harden and become hard and wearable when subjected to a certain impact. Therefore, high manganese steel is widely used to make liners. However, high manganese steel processing technology requires high price and high price. For grinding , the impact resistance of liner is not high, and other alloy cast iron with wear-resistant and cheaper alloy can be selected. The defect of the metal liner is that it is not convenient for processing and forming, the quality is large and it is not easy to install and disassemble.

The geometry and configuration of the liner have a direct influence on the production efficiency of the mill. Therefore , there are several different shapes of liners to meet the needs in different situations. In general, it can be divided into two types of liner, smooth and unsmooth.

The smooth liner is suitable for fine grinding because of the larger sliding of the steel ball and strong grinding and stripping. The unsmooth liner can bring the steel ball to the higher place, have the greater impact force, and have the strong agitation to the steel ball and the ore, so it is suitable for the coarse grinding. The long strip liner has the advantages of simple manufacturing, no or less screw fixation, compression only with end cover liner or wedge layering, convenient installation and so on, which can also reduce the leakage of slurry along the screw hole and enhance the strength of the cylinder. In addition, angular spiral liner has been developed and adopted at home and abroad.

The rubber liner is usually a flat convex tree plate with an approximate rectangle, which is usually made up of a K or B shape with a cylindrical bar (i.e., a lifting liner). Sinonine company can provide various types, specifications and use of rubber liner, and the quality is excellent. It has been popularized in many factories and mines, and the use effect is very good.

The thickness of the metal liner is generally 50-150mm, and the thickness of the rubber liner is generally 40-80mm. The service life of the former is generally six months to 1 years, and the latter can be up to 3 years.

In recent years, the development of magnetic liner is rapid, its performance is increasing, and it is steadily popularizing and applying. The magnetic liners of ball mills are made of rubber or steel wrapped permanent magnetic materials, so they are divided into two kinds: metal magnetic liners and rubber magnetic liners. Magnetic liners can adsorb a layer of ferromagnetic material on the surface by magnetic force, so that materials and media can not directly contact with the lining surface during the working process, so as to reduce lining wear. At the same time, it can also be adsorbed on the wall of ball mill, and it is not fixed with bolts. As the magnetic liner is lighter and thinner than the manganese steel liner, it also has the effect of saving energy and improving the output. Because the granularity of first stage ball mill is large, the impact force is great, and the wear is serious, so the magnetic liner is generally only suitable for the second stage ball mill.

2)Grinding medium of ball mill

The grinding medium is essential for the ball mill, and the consumption is very large. It was all spherical, and then the casting and baseball media appeared. The diameter of the ball medium is about 15-125mm, and the diameter of the casting section is about 8-30mm, and the length is about 8-40mm. Steel balls can be made by forging, rolling and casting. Steel ball is divided into carbon steel ball and alloy steel ball. According to the content of carbon and alloy elements, there are high, medium and low carbon steel balls and high, medium and low alloy steel balls. The ball is divided into ordinary cast iron, alloy cast iron and natural multi element low alloy cast iron ball. After the steel ball is made, it can be further treated by heat treatment to increase its wear resistance. Generally, different size and different types of grinding balls should be selected according to various specific situations, so as to achieve the best grinding effect and get the best economic benefits.