Introduction and application of coal mill steel ball
I.Introduction mill steel ball
High Coal mill steel ball is the ball mill equipment grinding material medium, through the coal mill between the steel ball, between the mill steel ball and the material friction grinding effect, is an important basic parts, widely used in cement plants, power plants and so on.High and low chromium multi-element alloy steel ball, high and low chromium multi-element alloy casting and forging.
Now the market mill steel ball according to the manufacturing process can be divided into two kinds: casting and forging, but their degree of wear resistance is not the same.Due to the crushing material, the mill steel ball needs good wear resistance and enough toughness, usually with alloy steel, high manganese steel, cast iron plus chromium iron and other materials forging or casting method molding, with the corresponding heat treatment process is more economical, according to the process and material can be divided into:
- Forging steel balls: low carbon alloy steel balls, medium carbon alloy steel balls, high manganese steel balls, rare earth chromium-molybdenum alloy mill steel balls;
- Casting steel ball: low chromium ball, medium chromium ball and high chromium ball mill steel ball.
II. Forging Steel Ball
1, forged steel ball surface quality, good impact resistance, strong toughness, good wear resistance, not easily broken and out of round.Is the metal heating temperature of 700-1300℃, the use of forging machinery to apply pressure to the metal billet, plastic deformation to obtain a certain mechanical properties, a certain shape and size forging processing method.One of the two major components of forging (forging and stamping).Through forging, it can eliminate the defects such as the porosity of the cast state generated in the process of smelting, optimize the microstructure and structure, and the mechanical properties of forgings are generally better than castings of the same material due to the preservation of complete metal streamline.For the important parts with high load and severe working conditions in related machinery, forging is often used, except for the plate, profile or welding parts with simple shape that can be rolled.In addition, the forging steel ball to wear must choose the wear-resisting material, such as the national standard of 60 mn, 65 mn, or some company independent research and development of efficient wear-resistant alloy steel material, and recommended national oversize steel production of steel, is also a kind of material, the quality of the steel mill to produce in different range, and forging quality stand or fall of 80% depends on the stand or fall of material, such as high manganese steel, good impact resistance, strong toughness, good wear resistance, not easily broken.Forged steel balls are favored by the majority of users because of their low price, economical and durable features. For example, international mining giants Rio tinto, BHP billiton and anglogold all use forged steel balls.
- Features of Forging Production:
(1) forging the heated metal material into tools, mechanical parts or blank of various shapes is called forging.Forging can change the internal structure of metal materials, refine crystals and improve their mechanical properties.
(2) heating equipment, forging equipment and many auxiliary tools must be used in forging production.
(3) the forging and pressing equipment mainly includes steam hammer, air hammer, die forging hammer, mechanical hammer, splint hammer, spring hammer, belt hammer, crank press, friction press, hydraulic press, reaming machine, roll forging machine, etc.
III.Casting Steel Ball
- Low chromium cast steel balls have poor wear resistance and high breakage rate. Although they are cheap, their comprehensive cost performance is not high.High hardness casting ball is good, is a kind of high quality wear-resistant material, in the cement industry dry ball mill has been widely used, but high chromium casting ball toughness is poor, in the diameter of more than 3 meters in the ball mill is easy to break, and the price is higher.
- Influence of casting steel ball material: generally speaking, the harder the steel ball is, the greater its wear resistance will be.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, at the same time, the hardness of the steel ball should also give consideration to the material and hardness of the liner, not too high (break the liner), should not be too low (wear resistance).Therefore, how to give consideration to the suitable hardness and good impact toughness is the key to improve the wear resistance of mill steel balls.
Steel ball commonly used materials 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, and their service life is more than one times longer than that of low-chromium cast balls under the same working condition:
- High manganese steel toughness, technology is good, low price, its main characteristics are in the larger impact or contact stress under the action, the surface layer will quickly produce work hardening, the work hardening index is higher than other materials 5-7 times, wear resistance to be greatly improved:
- High chromium cast iron is a kind of wear-resistant material with excellent wear resistance, but its toughness is low, brittle and expensive.
- 4, high carbon and high manganese alloy steel mainly contains chromium, molybdenum and other elements of the alloy structure steel, high hardness, 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 ≥15 J/CM2. Under the same working conditions, the service life of the steel ball is at least I times higher than that of the high manganese steel ball.
The tempering heat treatment of mill steel balls is the key. After tempering heat treatment, the overall toughness is not only required to reach 12 joules /CM2, but also required to have considerable plasticity and wear resistance. However, the general casting process can only reach 3-5 joules, resulting in a high crushing rate.
The manufacturing technology of steel ball is also the key factor to determine its service life.If the steel ball surface or internal manufacturing defects, such as shrinkage hole, crack, crystal, will not only reduce the performance of the steel ball, and even cause the steel ball broken.Therefore, reasonable forging, casting and heat treatment processes must be developed in the production of mill steel balls.For example, for high chromium cast iron balls, vertical casting, reasonable use of external chillers, and strict control of casting temperature and other measures should be adopted, so that the steel balls in the casting have a good solidification sequence and conditions, so as to obtain a dense internal structure, and reduce the phenomenon of coarse grains.The heat treatment technology of steel ball determines its mechanical properties and the distribution of carbides.Since there is a certain amount of chromium and other alloying elements in the composition of steel balls, how to make these alloying elements form hard point carbides to give full play to the role is also a factor to be considered in the formulation of heat treatment process.In a word, the development of reasonable production technology and strict means of quality inspection, is to ensure that the mill steel ball to achieve the performance of the prerequisite.
Eternal Bliss Alloy Casting & Forging Co., Ltd.
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