The ball mill steel balls on the market can be divided into two types according to the manufacturing process: casting and forging, but their wear resistance is different. Because of the crushed material, the steel ball needs good wear resistance and sufficient toughness. Usually, alloy steel, high manganese steel, cast iron and ferrochrome are used for forging or casting, and it is more economical to equip with the corresponding heat treatment process. , Ball mill steel balls can be divided into:
1. Forged steel balls: low carbon alloy steel balls, medium carbon alloy steel balls, high manganese steel balls, rare earth chromium molybdenum alloy steel balls;
2. Cast steel ball: low chromium cast ball, medium chromium cast ball, high chromium cast ball.
Which steel ball is the best on the market now? Let us analyze it now:
1. Forged steel balls:
Good surface quality, good impact resistance, strong toughness, good wear resistance, not easy to break and lose round. That is, the metal is heated to a temperature of 700-1300°C, and the forging machine is used to apply pressure to the metal blank to cause plastic deformation to obtain a processing method for forgings with certain mechanical properties, certain shapes and sizes. One of the two major components of forging (forging and stamping). Forging can eliminate defects such as loose as-cast during the smelting process and optimize the microstructure. At the same time, due to the preservation of complete metal flow lines, the mechanical properties of forgings are generally better than castings of the same material. For the important parts of related machinery with high load and severe working conditions, forgings are mostly used except for simpler shapes that can be rolled, profiles or welded parts. In addition, for forging steel balls to be wear-resistant, the most wear-resistant materials must be selected, such as national standard 60Mn, 65Mn, or high-efficiency wear-resistant alloy steel materials independently developed by some companies, and it is recommended to use steel produced by national super large steel plants. The quality of the materials produced in different steel plants is also different, and the quality of forgings is 80% dependent on the quality of the material. For example, the use of high manganese steel has good impact resistance, strong toughness and good wear resistance. , Not easy to break. Forged steel balls are favored by users because of their low price, economy and durability. For example, international mining giants Rio Tinto, BHP Billiton, and Anglo Gold all use forged steel balls.
Features of forging production:
(1) Forging the heated metal material into various shapes of tools, mechanical parts or blanks is called forging. Forging can change the internal structure of metal materials, refine crystals, and improve their mechanical properties.
(2) Forging production must use heating equipment, forging equipment and many auxiliary tools.
(3) 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.
2. Cast steel balls:
Low and medium chromium cast balls have poor wear resistance and high crushing rate. Although they are cheap, the overall cost performance is not high, so they are not recommended here. High chromium cast ball has excellent hardness and is a high-quality wear-resistant material. It has been widely used in dry ball mills in the cement industry. However, high chromium cast balls have poor toughness and are prone to breakage in ball mills with a diameter of more than 3 meters. The price is higher.
Influence of cast steel ball material: Generally speaking, the harder 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 as the hardness increases, the impact toughness of the steel ball will decrease. At the same time, the hardness of the steel ball must also take into account the material and hardness of the liner, not too high (Damage the liner), and should not be too low (not wear-resistant). Therefore, how to balance the suitable hardness and good impact toughness of steel balls is the key to improving the wear resistance of steel balls.
The commonly used materials for steel balls are: low carbon alloy, high manganese steel, high chromium cast iron, high carbon and high manganese alloy steel.
Low-carbon alloy steel balls have good toughness and low price. Under the same working conditions, their service life is more than twice that of low-chromium cast balls;
High manganese steel has good toughness, good manufacturability and low price. Its main feature is that under the action of greater impact or contact stress, the surface layer will quickly produce work hardening, and its work hardening index is 5-7 times higher than other materials. The wear resistance has been greatly improved;
High chromium cast iron is a kind of wear-resistant material with excellent abrasion resistance, but its toughness is low, brittle and broken easily and expensive.
High-carbon and high-manganese alloy steel is mainly alloy structural steel containing chromium, molybdenum and other elements, with high hardness and good toughness. Its matrix structure has martensite, bainite or bainite + martensite composite structure. The hardness of the steel ball is about HRC60, and the impact toughness is ≥15J/CM2. Under the same working conditions, its service life is at least one time longer than that of the high manganese steel ball.
But the quenching and tempering heat treatment of the steel ball is the key. After the quenching and tempering heat treatment, not only the overall toughness is required to reach 12 joules/CM2, but also considerable plasticity and wear resistance are required. However, the general casting process can only reach 3-5 joules, resulting in breakage The rate is higher, even for high chromium cast balls, so forgings are recommended when the working conditions are strong. 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, transcrystallization, 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 formulated in the production of steel balls. For example, for high chromium cast iron balls, vertical pouring and reasonable use of external cooling iron should be adopted, and the casting temperature should be strictly controlled. This can make the steel balls have a good solidification sequence and feeding conditions in the casting, and then obtain a dense internal structure. 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 make these alloying elements form hard point carbides is also a factor considered when formulating the heat treatment process. In short, formulating a reasonable production process and strict quality inspection methods are the prerequisites for ensuring the performance of steel balls.