Planetary Ball Mill is the key equipment for crushing materials after crushing. It can be divided into dry and wet grinding methods. Ball mills are widely used in cement, silicate products, new building materials, refractory materials, fertilizers, ferrous and non-ferrous metal beneficiation and glass ceramics and other production industries, dry or wet grinding of various ores and other grindable materials.
Classification of ball mills
Ball mill is one of the most widely used high-fine grinding machines in industrial production. Ball Mill, Overflow Ball Mill, Ceramic Ball Mill, Lattice Ball Mill.
Ball mills can be divided into dry and wet grinding methods. According to different discharge methods, they can be divided into grid type and overflow type. According to the shape of the cylinder, it can be divided into four types: short cylinder ball mill, long cylinder ball mill, tube mill and cone type mill.
Scope of application of ball mill
Ball mills are widely used in cement, silicate products, new building materials, refractory materials, fertilizers, black and non-ferrous metal beneficiation and glass ceramics and other production industries, dry or wet grinding of various ores and other grindable materials. Ball mills are suitable for grinding various ores and other materials. They are widely used in mineral processing, building materials and chemical industries. They can be divided into dry and wet grinding methods. According to the different discharge methods, it can be divided into two types: lattice type and overflow type.
The working principle of ball mill
The ball mill is composed of a horizontal cylinder, a hollow shaft for feeding and discharging materials, and a grinding head. The cylinder is a long cylinder, and the cylinder is equipped with a grinding body. Generally, it is a steel ball, which is loaded into the cylinder according to different diameters and a certain proportion, and the grinding body can also be made of steel. It is selected according to the particle size of the grinding material. The material is loaded into the barrel by the hollow shaft at the feed end of the ball mill. When the ball mill barrel rotates, the grinding body is attached to the barrel liner due to the action of inertia, centrifugal force and frictional force. It is taken away by the cylinder, and when it is brought to a certain height, it is thrown down due to its own gravity, and the falling grinding body crushes the material in the cylinder like a projectile.
The material enters the first chamber of the mill spirally and evenly from the feeding device through the feeding hollow shaft. There is a stepped lining plate or a corrugated lining plate in the chamber, and various specifications of steel balls are installed inside. The rotation of the cylinder generates centrifugal force to bring the steel balls to a certain level. When it falls after the height, it has a heavy impact and grinding effect on the material. After the material reaches the rough grinding in the first warehouse, it enters the second warehouse through the single-layer partition board. The warehouse is inlaid with a flat lining plate and has steel balls to further grind the material. The powder is discharged through the discharge grate to complete the grinding operation.
During the rotation of the cylinder, the grinding body also slips off. During the sliding process, the material is subjected to a grinding action. In order to effectively utilize the grinding action, when grinding the material with a larger particle size, the grinding body is placed on the grinding body. It is divided into two sections by the partition board, that is, it becomes a double warehouse. When the material enters the first warehouse, it is crushed by steel balls. When the material enters the second warehouse, the steel section grinds the material, and the qualified material is hollowed out from the discharge end. Shaft discharge, when grinding materials with small feed particles, such as No. 2 sand slag, coarse fly ash, the barrel of the mill can be a single-silo mill without partitions, and the grinding body can also be made of steel.
The raw materials are fed into the hollow cylinder through the hollow journal for grinding, and the cylinder is equipped with grinding media of various diameters (steel balls, steel bars or gravel, etc.). When the cylinder rotates at a certain speed around the horizontal axis, under the action of centrifugal force and frictional force, the medium and raw materials in the cylinder will leave the cylinder when the gravity of the cylinder is greater than the centrifugal force as the cylinder reaches a certain height. The inner wall is projected to fall or roll down, breaking the ore due to the force of the impact. At the same time, during the rotation of the mill, the sliding movement of the grinding media between each other also produces a grinding effect on the raw materials. The ground material is discharged through the hollow journal.
The structure of the ball mill
The ball mill is composed of feeding part, discharging part, rotating part, transmission part (reducer, small transmission gear, motor, electric control) and other main parts. The hollow shaft is made of cast steel, the inner lining can be removed and replaced, the large rotary gear is processed by casting gear hobbing, and the cylinder is inlaid with a wear-resistant lining plate, which has good wear resistance. The machine runs smoothly and works reliably.
The main body of the ball mill includes a cylinder, which is inlaid with a lining made of wear-resistant material, a bearing that carries the cylinder and maintains its rotation, and a driving part, such as a motor, and transmission gears, pulleys, V-belts, etc.
As for the parts called blades, they are generally not the main parts. The inner spiral in the inlet of the component at the feeding end can be called the inner spiral blade, and the inner spiral in the outlet of the component at the discharging end can also be called the inner spiral blade.
In addition, if a screw conveyor is used in the auxiliary equipment at the discharge end, there will be parts called screw blades in the equipment, but strictly speaking, it is no longer a part of the ball mill.
According to the material and ore discharge method, dry ball mill and wet grid ball mill can be selected. The energy-saving ball mill adopts self-aligning double-row radial spherical roller bearings, with low running resistance and remarkable energy-saving effect. In the barrel part, a conical barrel is added to the discharge end of the original barrel, which not only increases the effective volume of the mill, but also makes the distribution of the medium in the barrel more reasonable. This product is widely used in non-ferrous metals, ferrous metals, non-metallic beneficiation fields and chemical and building materials industries for material grinding.
Advantages of ball mill
- save energy. It adopts full hydraulic operation, easy to use, easy to realize automation, and its reliability and life are greatly improved
- The design of the discharge section is flexible. The design of the discharge port is reasonable, and customers can choose the iron remover according to their own needs
- Rotary part. The cylinder body, lining plate, medium, partition plate and discharge grate plate of the rotary part are all composed of high-quality original parts.
- The feeding volume of the feeding section is large. Reasonable feeding port design increases the feeding amount
- High grinding efficiency and good lining quality. Liners and grinding bodies are made of alumina ceramic, quartz, SILEX or special materials, and hard minerals are designed without iron pollution
- Closed system to reduce dust. The ultra-fine ball mill and classifier form a closed system, negative pressure conveying, small dust, reducing damage to human body
Accessories for Ball Mills
Ball mill accessories include ball mill gear, ball mill pinion, ball mill hollow shaft, ball mill ring gear, ball mill large ring gear, ball mill steel ball, ball mill partition plate, ball mill transmission device, ball mill bearing, ball mill end lining and so on.Among them, the selection of ball mill gear material.
According to the different working conditions of large gears, large gears are usually made of the following materials:
- (1) Medium carbon structural steel
- (2) Medium carbon alloy structural steel
- (3) Carburizing steel
- (4) Nitrided steel
The structure of the large gear of the ball mill has various shapes due to different use requirements, but from the technical point of view, the gear can be regarded as composed of two parts, the ring gear and the wheel body. According to the distribution form of the gear teeth on the ring gear, it can be divided into straight teeth, helical teeth, herringbone teeth, etc.
How to improve the efficiency of ball mill
(1) Increase the effective volume
Increasing the effective volume of the ball mill can increase the productivity of the mill year-on-year. The lining plate is thick and heavy, which increases power consumption, reduces the effective volume of the cylinder, and reduces the production efficiency of the ball mill. If the magnetic liner is selected, the effective volume of the cylinder can be increased, and the weight is relatively reduced, and the power consumption is reduced. However, the choice of thinner magnetic liner also has certain drawbacks. Due to its small thickness, the impact resistance is not as good as the current Cr-Mn-Mo alloy cast steel liner, which is prone to cracking. For example, for the lining problem, some manufacturers use grooved annular linings, which increase the contact surface of the ball ore, strengthen the grinding effect, and have the ability to lift the ore, reduce energy consumption, and are widely used.
(2) Increase the filling rate and rotation rate
The processing capacity of the ball mill increases with the increase of the filling rate of the steel balls. Increasing the filling rate increases the probability of the steel balls to grind the ore and the self-grinding effect of the ore. When the filling rate of steel balls is 45%, the load of the ball mill is the largest, and when the filling rate exceeds 45%, the load of the ball mill decreases greatly with the increase of the filling rate. This is mainly because with the increase of the filling rate, the throwing point of the steel ball is raised, and the action point of the impact force of the falling steel ball accelerates to approach and exceed the center of rotation, and the resultant moment is greatly shortened and becomes a negative value from 0 to 0. The load required by the impact resultant moment dropped by the steel ball (containing ore) changes from large to 0, until it becomes the power that pushes the cylinder to rotate (that is, the resultant force action point exceeds the center, and the resultant moment is negative).
(3) Change the shape of the grinding medium
The ellipsoidal medium can be used instead of the current spherical medium. Compared with the spherical medium, the elliptical sphere has the following advantages:
Compared with the ball with the same diameter, the elliptical ball has a 62% increase in weight, strong impact force, and improved crushing capacity;
The point contact between the ellipsoids is replaced by line contact, and the contact area is 4 times larger than that of the spheres, which has selective crushing and good screening effect on materials, and the product particle size is uniform, reducing the phenomenon of over crushing;
Compared with the ball of the same diameter, the surface area of the elliptical ball is increased by 8%, which increases the contact surface between the steel ball medium and the material and improves the grinding capacity;
The line contact between the elliptical ball and the mill liner replaces the point contact of the ball, which reduces the wear of the steel ball medium to the liner, reduces the impact of the steel ball medium and the mill liner, thereby reducing the steel ball medium and the mill liner. The wear of the machine lining plate prolongs the service life;
The ellipsoid also has antistatic and anti-moisture properties, which can reduce the adsorption of fine powder and reduce the phenomenon of full grinding.
Compared with the spherical sphere, the elliptical sphere can greatly improve the crushing and grinding capacity of the ball mill, and at the same time, the equipment loss can be reduced accordingly.
How to choose a ball mill
- 1. Ensure the production capacity of the mill. The selected grinding equipment can complete the specified output under the condition of ensuring the required grinding fineness.
- 2. The production capacity should be higher than the design. The design should consider the change of ore hardness and fineness. Generally, the ore in the deep part of the ore deposit becomes hard or thin, so the selected grinder should also be able to adapt to it, and at the same time ensure the smooth production in the initial stage.
- 3. Grinding test must be done. When there is no actual data as a basis for the design, it is necessary to request a grinding test, especially for a large-scale ore dressing plant, the selection calculation and proportional enlargement of the grinding machine should be carried out from the obtained basic data.
- 4. Appropriate consideration of large-scale equipment. Large-scale equipment is a design trend since the 21st century. Due to the large-scale equipment, the overall equipment is light in weight, occupies less land, has fewer production systems, fewer operators and auxiliary systems, and the corresponding investment and production costs are low. However, the operation and management level of large-scale equipment is high, and if the operation rate is slightly reduced, the output of the concentrator will be greatly reduced.
- 5. Select equipment with high operating rate. There are also good and bad old and new in the same type of equipment. Rod mills and autogenous mills sometimes have lower operating rates, but they are still applicable under certain conditions. In principle, equipment with a high operating rate should be selected to reduce maintenance and downtime.
- 6. Understand the hardness, grade and other properties of minerals, and try to choose an energy-saving ball mill;
- 7. Know the fineness required for mineral grinding, and select the aperture of the closed plate and the position of the bin according to the fineness required by the mineral;
- 8. According to the requirements of output, choose the diameter and length of the ball mill appropriately
- 9. Choose a new generation of transformed ball mill, it is best to buy it from a professional ball mill manufacturer corresponding to your mineral type
- 10. Select the module of the large teeth and small teeth of the ball mill, as well as the manufacturer of the motor and the subtraction machine. According to the price of the ball mill, the material of the lining plate and the thickness of the grinding steel plate are required.
How to replace the steel ball in the ball mill
The main function of the steel ball in the ball mill is to impact and crush the material, and also play a certain role in grinding. Therefore, the purpose of grading steel balls is to meet the requirements of these two aspects. The quality of the crushing effect directly affects the grinding efficiency, and ultimately affects the output of the ball mill. Whether it can meet the crushing requirements depends on whether the gradation of the steel balls is reasonable, mainly including the size of the steel balls, the ball diameter series, and the size of the balls of various specifications. proportion, etc.
In determining these parameters, in addition to considering factors such as the size of the ball mill, the internal structure of the ball mill, and product fineness requirements, the characteristics of the materials to be milled (ease of grinding, particle size, etc.) should also be considered.
In order to effectively pulverize the material, the following principles must be followed when determining the gradation:
First of all, the impact force of the steel ball must be large enough so that the steel ball of the ball mill has enough energy to break the granular material, which is directly related to the maximum diameter of the steel ball.
Secondly, the steel ball must have enough impact times on the material, which is related to the filling rate of the steel ball and the average ball diameter. When the loading amount is certain, under the premise of ensuring sufficient impact force, the diameter of the grinding body should be reduced as much as possible, and the number of steel balls should be increased to increase the number of impacts on the material to improve the crushing efficiency.
Finally, the material has enough residence time in the mill to ensure that the material is fully pulverized, which requires the steel ball to have a certain ability to control the flow rate of the material.
The so-called two-level ball distribution method is to use two different sizes of steel balls with a large difference in diameter for grading. The theoretical basis is that the gaps between the large balls are filled by small balls to fully increase the bulk density of the steel balls. In this way, on the one hand, the impact capacity and the number of impacts of the mill can be improved, which is in line with the functional characteristics of the grinding body, and on the other hand, the higher bulk density can enable the material to obtain a certain grinding effect. In the two-stage ball distribution, the function of the large ball is mainly to impact and crush the material, and the function of the small ball is to fill the gap between the large balls and increase the bulk density of the grinding body to control the flow rate of the material and increase the grinding capacity. It plays the role of energy transmission and transfers the impact energy of the large ball to the material; the third is to expel the coarse-grained material in the gap and place it in the impact area of the large ball.