Mill balls are classified according to manufacturing processes: Casting and Forging
Nowadays, on the market according to the ball mill ball manufacturing process can be divided into two methods: casting and forging, but their degree of wear-resistant is not the same. Due to the broken materials, grinding ball needs good wear resistance and enough toughness, usually alloy steel, high manganese steel, cast iron plus chromium iron and other materials with forging or casting method, with the corresponding heat treatment process is more economical, ball mill grinding ball according to the process and material can be divided into:
- Forging Steel Ball: Low carbon alloy steel ball, medium carbon alloyed steel ball, high manganese steel ball, rare earth Chromium Molybdenum Alloy Steel Ball;
- Cast Mill Ball: Low chromium cast ball, medium chromium cast ball, high chromium cast ball.
Which kind of grinding ball is the best on the market now? Let’s break it down.
1.FORGING STEEL BALLS:
Excellent surface quality, good impact resistance, strong toughness, excellent wear resistance, not easy to break and round. It is a processing method that the metal is heated to 700-1300 °C, and the forging machine is used to press the metal blank to produce plastic deformation so as to obtain the forgings with specific mechanical properties, shape, and size. Forging (forging and stamping) one of the two major components. By forging, the defects of as-cast porosity can be eliminated, and the microstructure can be optimized. At the same time, the mechanical properties of the forgings are better than those of the castings of the same materials because of the preservation of the complete metal streamline. For the important parts with high load and severe working condition, forgings are usually used except the simple shape of the rolled plate, profile or welding parts. In addition, forging steel ball must choose the most wear-resistant materials, such as the national standard of 60Mn, 65Mn, or some companies prefer to develop their own high-efficiency wear-resistant alloy steel materials, the same is the material, but produced in different steel plant, and the quality is not the same, and the forging quality depends on the materials, such as high manganese steel, has good impact resistance, toughness, wear resistance, and it’s not easy to break. Because of cheap, economical and durable features favored by the majority of users, such as international mining giant Rio Tinto, BHP Billiton, AngloGold, and the others uses forged steel ball.
FEATURES OF FORGING BALL PRODUCTION:
(1) Forging of heated metal materials into the molding machine. Forging can change the internal structure of metal material, refine the crystal and improve its mechanical properties.
(2) Heating equipment, forging equipment and many auxiliary tools must be used in forging production.
(3) Forging and pressing equipment mainly includes Steam Hammer, Air Hammer, Die Hammer, forging hammer, splint hammer, spring hammer, belt hammer, crank press, friction press, press, hole reaming machine, roll forming machine, etc.
2.CASTING BALL MILL BALLS:
Medium and low chromium cast balls’ wear resistance are weak, the broken rate is high, although cheap, but comprehensive cost-effective is not high, not recommended here. High-carbon cast ball has good hardness and is a kind of high-quality wear-resistant material. It has been widely used in dry ball mills in cement industry, but the toughness of high-chromium cast ball is poor, and it is easy to be broken in ball mills with a diameter bigger than 3 meters.
Material: generally speaking, the greater the hardness, the better wear resistance of the balls. To improve the wear resistance of the mill balls, it is necessary to increase its hardness, but with the increase in hardness, the impact toughness of the mill ball will decrease, and the hardness of the mill ball must also take into account the material and hardness of the lining board, not too high (smashing the lining board) Should not be too low (not wear-resistant) . Therefore, how to take into account the appropriate hardness of mill balls and good impact toughness is the key to improve the wear resistance of the grinding ball.
Mill ball commonly used materials are low carbon alloy, high manganese steel, high chromium cast iron, high carbon high manganese alloy steel.
- Low Carbon Alloy steel ball has good toughness and low price, in the same working condition, its service life than low chromium cast ball increased more than one times;
- High Manganese steel has good toughness, good workability, and low price. Its main characteristic is that under the action of significant impact or contact stress, the surface layer will produce work hardening rapidly, and its work hardening index is 5-7 times higher than that of other materials The wear resistance is improved greatly
- High Chromium cast iron is a kind of wear resistant material with excellent wear resistance, but it has low toughness, brittle fracture, and high price.
- The high carbon and high manganese alloy steels are mainly alloy structural steels containing CR, Mo, and other elements, with high hardness and good toughness, and Martensite, bainite or Bainite + martensite composite structure. The hardness of the steel ball is about HRC60, and the impact of toughness is more than 15J / CM2. Under the same working conditions, the service life of the steel ball is at least one times longer than that of the High Manganese Steel Ball.
However, the quenching and tempering heat treatment of steel ball is the key. After quenching and tempering heat treatment, not only the overall toughness reaches 12 joules / CM2, but also the plasticity and wear resistance are required. However, the general casting process can just reach 3-5 joules, which leads to a higher crushing rate Even if it is a high chromium cast ball, so in the case of greater strength, it is recommended to use forging. The manufacturing process of steel ball is also a critical factor in determining its service life. If there are defects on the surface or inside of the steel ball, such as shrinkage cavity, crack, transgranular and so on, not only the properties of the steel ball will be reduced, but also the steel ball will be broken. Therefore, reasonable forging, casting and heat treatment processes must be established in the production of steel balls. For example, for high chromium cast iron ball, measures such as vertical pouring, rational use of outer chill and strict control of casting temperature should be adopted, so that the steel ball can have good solidification sequence and feeding condition in casting, and then obtain dense inner structure And the phenomenon of coarse grain size is weakened. The heat treatment process of steel ball determines the realization of its mechanical properties and the distribution of carbides. As there are some chromium and other alloy elements in the composition of the steel ball, how to make these alloy elements form hard point carbide is also a factor to be considered in the heat treatment process. In a word, a reasonable production process and strict quality inspection means are the prerequisite to ensure the service performance of steel balls.
To sum up, forging is better than casting, the specific use of which steel ball is more appropriate also according to their operating conditions and economic strength. As the saying goes, there is no best, only better, do not buy expensive, just buy the right.