The difference between ball mill and rod mill

The grinding equipment widely used in concentrators are ball mills and rod mills. Both have similarities in appearance and grinding principle, but there are also differences in structure, performance, use, and other aspects. This article analyzes their similarities and differences from seven aspects and tells everyone how to choose a ball mill and a rod mill. From the analysis of the crushing mechanism, whether the ball mill or the bar mill, when the cylinder rotates, the grinding medium (ball or rod) installed in the cylinder body is lifted to a certain height with the rotation of the cylinder body under the action of the friction force and the centrifugal force, then it is dropped at a certain linear velocity, so that it impacts, grinds, and squeezes the material in the cylinder and to crush it. Their working principle is similar, but the ball mills and rod mills differ greatly in details, as shown below: 1. Shape structure analysis The ratio of the cylindrical shape of the two is different. The ratio of the length and the diameter of the barrel of the rod mill is generally 1.5-2.0, and the inner surface of the liner on the end cap is a vertical plane. The ratio of barrel length to diameter of the ball mill is small, and in most cases the ratio is only slightly greater than 1. In addition, the rotation speed of the rod mill barrel is lower than the working speed of the same specification ball mill so that the medium in the barrel mill works in a diarrhea state. 2. Species analysis (different ways of ore discharge) In ball mills, lattice-type ball mills and overflow ball mills (named from different configurations of ore-outlet structures) are commonly used. The rod mill does not use grid plate to discharge ore, only the overflow type and open type, the diameter of the hollow shaft of the discharge end is generally larger than the same size ball mill. 3. Grinding media analysis Rod mills commonly use 50-100mm diameter steel rods as grinding media, while ball mills use steel balls as grinding media. The difference in grinding bodies is the main difference between the two mills. The contact between the balls of the ball mill is point contact, and the contact between the bars of the rod mill is line contact, so the operating characteristics of the two equipments are significantly different. 4. Media filling rate analysis The media filling rate refers to the percentage of grinding media occupied by the mill volume. For different grinding methods, mill structure, operating conditions and media shapes, the media filling rate has a suitable range, too high or too low will affect the grinding effect. Usually, the filling rate of the ball mill is 40%-50%, and the rod mill is 35%-45%. 5. Performance analysis The process characteristics of the rod mill are rougher product, but uniform particle size, less coarse particles and slime, and lighter over- comminuted, the particle size characteristics of the rod mill product are related to the condition of the rod mill. The performance characteristics of the ball mill are high production capacity, strong adaptability to materials, high fineness of the materials, fine particle size, easy fine grinding, and significant energy saving, but the phenomenon of excessive comminution is serious. 6. Stability analysis The ball mill has no inertial impact during operation, which ensures the normal and efficient operation of the equipment, reduces the downtime of the equipment and improves the production efficiency. 7. Use analysis When tungsten ore and other rare metal ore are used in gravity or magnetic selection, rod mills are often used to prevent over-comminution; In the two stage grinding process, a rod mill is generally used as the first stage grinding equipment, which has a large production capacity and high efficiency. When dealing with soft or less hard ore, a rod mill can be used instead of a short head cone crusher for fine smashing, which is not only simple in configuration, but also low in cost, and can simplify dust removal in a work shop. The ball mill, due to its fine grinding material, is prone to comminution and is not suitable for re-election in metal processing.