Difference between ball mill and rod mill

Ball mills and rod mills have been widely used in concentrators. To many people, they are like a pair of "twins", which seems difficult to distinguish. When the overall operation cost of grinding equipment is high, its selection is particularly important. This paper analyzes the similarities and differences between ball mill and rod mill from many aspects to help you better choose the appropriate grinding equipment.

Common points of ball mill and rod mill:

Appearance: from the appearance, ball mill and rod mill are long barrel equipment.

Classification: ball mill and rod mill are the key grinding equipment for crushing materials after crushing.

Structure: basically the same structure, which is a horizontal cylindrical structure. The cylinder is equipped with grinding medium, feeder, pinion, feeding end, feeding end, transmission mechanism, etc.

Principle: the working principle of ball mill and rod mill is the same. Both of them drive the cylinder to rotate through the transmission device. After the grinding medium is raised to a certain height, it is thrown out at a certain linear speed. Under the action of force, the material is impacted, ground and extruded, so as to achieve the effect of grinding the material.

Difference between ball mill and rod mill:

1、 Difference in shape and structure

Although the shapes of ball mills and rod mills are very similar, the cylinder proportions of the two are different. In most cases, the cylinder length / diameter ratio of the ball mill is only slightly greater than 1; In the rod mill, the barrel length / diameter ratio is generally 1.5~2.0, and the lining surface on the end cover is vertical.

In addition, in order to keep the internal medium in the draining state, the barrel speed of the rod mill is lower than the working speed of the ball mill of the same specification.

2、 Classification (by ore discharge form)

Ball mill can be divided into overflow type and format, and rod mill can be divided into overflow type and open type.

At present, there are mesh ball mills and overflow ball mills commonly used in ball mills (this is determined by the structure of different ore discharge departments); Because there is no grid in the rod mill, there are only overflow type and open type. The diameter of the central shaft at the discharge end is larger than that of the ordinary ball mill of the same specification.

3、 Differences in grinding media

The grinding medium of the ball mill is steel ball, and the medium of the rod mill is steel rod. The difference of abrasives is the biggest one.

Due to different abrasives, their working methods are also different. There is a point contact between the ball mill and the material, a line contact between the rod mill and the material, and the gap between the rods is a regular strip, which has a certain screening effect on the material.

4、 Media loading rate difference

The filling rate refers to the percentage of grinding medium in the volume of the mill. Generally, the ball milling filler is 40% - 50%, and the rod milling filler is 35% - 45%. Due to different grinding methods, mill structures, working conditions and medium shapes, the filling rate of medium has a certain range, and too high or too low will affect the grinding effect.

5、 Performance analysis

The performance characteristics of ball milling are high production capacity, strong adaptability to raw materials and high fineness of raw materials. The discharge degree is generally between 0.074~0.4 mm. The discharge particle size is small, which is easy to be finely ground, and is remarkable in energy saving. However, the phenomenon of over crushing in ball milling is serious.

The rod mill is characterized by rough products, uniform particles, less coarse sand and low degree of over crushing. The discharge particle size is generally 0.833~0.147 mm, and the particle size characteristics of rod mill products are related to the conditions of rod mill ore.

6、 Stability analysis

Good ball milling stability. Because the ball mill is not impacted by inertia during operation, the normal and efficient operation of the equipment is ensured, the downtime of the equipment is reduced, and the production efficiency is improved.

7、 Different scope of use

Rod mills are usually used for gravity or magnetic separation of metal ores (such as tungsten tin ore and rare metal ore) to prevent over crushing; The same is true for fragile materials such as coal; In the second stage grinding process, rod mills are usually used as primary grinding equipment, with high production capacity and efficiency. Using rod mill instead of short head cone crusher to fine grind soft or not too hard ore is not only simple in configuration, but also low in cost, and can simplify the dust removal work in the workshop.

Ball mills are widely used in metal, non-metal or stone ball mills. However, due to the fine grinding material, it is prone to over crushing, which is not suitable for the production line of metal beneficiation and re concentration.

The above is the analysis of the similarities and differences between ball mill and autogenous mill, so how to choose in production? Generally speaking, you can choose from raw materials, particle size effect of finished products, and production mode.

(1) According to raw material selection:

In the production process, if fragile materials such as tungsten tin ore, rare metal ore and coal need to be processed, rod mills should be selected; If you need to process fragile materials such as aluminum ash, lime, slag, molybdenum ore, it is best to use a ball mill.

(2) Selection based on the influence of finished product particle size:

The size of this product is 1~3 mm, which is used for rough grinding and rod grinding.

The particle size of the product is less than 0.5mm, which is used for fine grinding, and the ball mill is selected.

Rod mill products are rougher than ball milling, but more uniform.

(3) Select according to production mode

When using gravity or magnetic separation of rare metals, in order to avoid the harm caused by excessive powder in the work, rod mills are generally used for the production and processing of materials; The production and processing of cement plants mostly use ball mills.

For the selection of grinding equipment, comprehensive consideration should be given to selecting appropriate grinding equipment according to different needs and scenarios, so as to ensure that the equipment matches the process flow and avoid economic losses.