Ball mill ball is a basic component of ball mill. How does the steel balls help the ball mill work? The ball mill grinds the material and produces grinding and stripping effect through the collision friction between the ball and the material. Steel grinding balls are widely used in cement plants, power plants, etc., especially precision industrial steel balls play a huge role in the development of the national economy.
Materials of ball mill balls
The material of ball mill steel ball mainly includes high carbon steel, alloy steel, stainless steel, ceramics, and so on. Here are the details:
- Chromium steel balls: containing 0.5% to 2.0% chromium, high hardness, good wear resistance, strong corrosion resistance, suitable for grinding iron ore, metal ore and other hard materials. 3
- Stainless steel ball: Mainly made of 304 and 316 stainless steel, good corrosion resistance, and strong oxidation resistance, suitable for grinding chemical, pharmaceutical, food, and other industries of materials.
- Carbon steel ball: Mainly made of high carbon steel and medium carbon steel, good wear resistance, suitable for grinding color pigments, ceramics and other industries of materials.
- Ceramic ball: It is made of alumina, yttrium oxide and other ceramic materials as the main raw materials, with high hardness, good wear resistance, strong corrosion resistance and other characteristics, suitable for grinding ceramics, powder metallurgy, and other materials.
- Perlite ball: It is mainly made of natural perlite, with high hardness, low wear, corrosion resistance, and other characteristics, suitable for grinding sponge manganese ore, hematite, and other materials.
- High manganese steel ball: high manganese steel itself has good toughness, the main feature is that the surface can be rapidly hardened when encountering a large impact force, and the wear resistance can be improved in use.
In addition, the ball mill steel ball also has high chromium cast iron, high carbon and high-magnesium alloy steel, and other materials.
Processing of ball mill balls
The ball mill balls on the market can be divided into cast steel balls and forged steel balls according to their production process, but their wear resistance is not the same. Generally speaking, cast steel balls are suitable for dry grinding operations, and forged steel balls are suitable for wet grinding operations.
Due to the broken material, the steel ball needs good wear resistance and enough toughness, usually with alloy steel, high manganese steel, cast iron and chromium iron and other materials with forging or casting method molding, with the corresponding heat treatment process is more economical, ball mill steel ball according to the process and material can be divided into:
- Forged steel balls: low carbon alloy steel balls, medium carbon alloy steel balls, high manganese steel balls, rare earth chromium molybdenum alloy steel balls;
- Casting steel ball: low chromium casting ball, medium chromium casting ball, high chromium casting ball.
How to select ball mill balls
What kind of steel ball is best on the market now? Now let’s break it down:
Forged steel ball
Good surface quality, good impact resistance, strong toughness, good wear resistance, not easy to break and round. That is, the metal is heated at a temperature of 700-1300℃, and the metal blank is pressurized by forging machinery to produce plastic deformation to obtain a certain mechanical properties, a certain shape and size of the forging processing method. One of the two components of forging (forging and stamping). Through forging can eliminate the metal in the smelting process of the as-cast loose and other defects, optimize the microstructure, and because of the preservation of the complete metal flow line, the mechanical properties of the forgings are generally better than those of the same material. For important parts with high load and severe working conditions in related machinery, forgings are mostly used in addition to plates, profiles or welding parts with simple shapes that can be rolled. In addition, forged steel ball to wear must choose the most wear-resistant materials, such as the national standard 60Mn, 65Mn, or some companies independently developed high-efficiency wear-resistant alloy steel materials, and it is recommended to use the steel produced by the national large steel mill, the same material, the quality produced in different steel mills is also different. The quality of forgings 80% depends on the quality of the material, such as the use of high manganese steel, good impact resistance, strong toughness, good wear resistance, not easy to break. Forged steel balls are favored by the majority of users because of their cheap price, economic and durable characteristics, such as international mining giants Rio Tinto, BHP Billiton, Anglo Gold, etc., all use forged steel balls.
Forging production features:
- Forging the heated metal material into tools, mechanical parts or blanks of various shapes is called forging. Forging can change the internal structure of metal materials, refine the crystal and improve its mechanical properties.
- Forging production must use heating equipment, forging equipment and many auxiliary tools.
- Forging equipment mainly includes steam hammer, air hammer, die forging hammer, mechanical hammer, splint hammer, spring hammer, belt hammer, crank press, friction press, press, reaming machine, roll forging machine, etc.
Casting steel ball
Low and medium chromium casting ball has poor wear resistance, high crushing rate, although cheap, but the comprehensive cost performance is not high, it is not recommended here. High chromium casting ball has good hardness and is a high-quality wear-resistant material, which has been widely used in cement dry ball mills, but the toughness of high chromium casting ball is poor, and it is easy to break in the ball mill with a diameter greater than 3 meters, and the price is high.
The effect of casting steel ball material: Generally speaking, the greater the hardness of the steel ball, the greater the wear resistance. To improve the wear resistance of the steel ball, it is necessary to increase its hardness, but with the increase of hardness, the impact toughness of the steel ball will be reduced, and the hardness of the steel ball should also take into account the material and hardness of the lining board, which can not be too high (smashing the lining board), nor should it be too low (not wear-resistant). Therefore, how to balance the appropriate hardness and good impact toughness of the steel ball is the key to improve the wear resistance of the steel ball.
Steel ball commonly used materials include low carbon alloy, high manganese steel, high chromium cast iron, high carbon and high manganese alloy steel. Low carbon alloy steel ball has good toughness and low price, under the same working condition, its service life is more than 1 times longer than that of low chromium cast ball;
High manganese steel toughness, good process, low price, its main feature is that under the action of greater impact or contact stress, the surface layer will quickly produce work hardening, the work hardening index is 5-7 times higher than other materials, wear resistance has been greatly improved;
High chromium cast iron is a kind of wear-resistant material with excellent anti-wear properties, but its toughness is low, brittle breakage is easy to occur and its price is expensive.
High carbon and high manganese alloy steel is mainly alloy structural steel containing chromium, molybdenum and other elements, high hardness, good toughness, its matrix structure is martensite, bainite or bainite + martensite composite structure. The hardness of the steel ball is about HRC60, the impact toughness is ≥15J/CM2, and the service life is at least 1 times higher than that of the high manganese steel ball under the same working conditions.
But the quenching and tempering heat treatment of the steel ball is the key, after the quenching and tempering heat treatment not only requires the overall toughness of 12 joules /CM2, but also requires considerable plasticity and wear resistance, but the general casting process can only reach 3-5 joules, resulting in a high crushing rate, even if it is a high chromium cast ball, so it is recommended to use forgings when the strength of the working condition is large. The manufacturing process of the steel ball is also a key factor in determining its service life. If there are defects in the surface or internal manufacturing of the steel ball, such as shrinkage holes, cracks, crystal penetration, etc., it will not only reduce the performance of the steel ball, but even cause the steel ball to break. Therefore, reasonable forging, casting and heat treatment processes must be developed in the production of steel balls. For example, for high chromium cast iron balls, vertical casting and rational use of external cold iron should be adopted, and the casting temperature should be strictly controlled, so that the steel balls can have a good solidification sequence and feeding conditions in the casting, and then obtain dense internal organization, and weaken the phenomenon of coarse grains. The heat treatment process of the steel ball determines the realization of its mechanical properties and the distribution of carbides. Since the composition of the steel ball contains a certain amount of chromium and other alloying elements, how to give full play to the role of these alloying elements to form hard point carbides is also a factor to be considered when developing the heat treatment process. In short, the development of a reasonable production process and strict quality inspection means is to ensure that the steel ball to achieve the prerequisite for performance.
In summary, forgings are better than castings, and the specific steel ball used is more suitable according to their working conditions and economic strength. As the saying goes, there is no best, only better, don’t buy expensive, only buy the right.
