Steel balls are widely used in mining, power plants, cement plants, steel plants, silica sand plants, coal chemical industry and other fields. The annual consumption is huge. my country is a big consumer of steel balls, with an annual steel ball consumption of millions of tons.
Due to different production methods, there are three main types of steel balls commonly used, namely cast steel balls, forged steel balls, and hot-rolled steel balls. In order to better explain the differences between steel balls in different production methods, let’s first understand The following influences the wear and failure mechanism of steel balls under normal working conditions: Steel balls in the abrasive bin of the mill It is brought to the highest point by the lining plate and falls under the action of gravity, while the material is "rubbed" and "grinded". The lining plate drives the grinding body to continuously drop, roll and slide in the mill, and wear/failure occurs. Mainly include cutting and chiseling wear, deformation wear, brittle shedding, fatigue wear, breakage rate, loss of roundness, etc.
Cutting and chiseling wear: During the grinding process, the hard and sharp particles in the grinding body cause wear to the steel balls when they move with each other. This is mainly reflected in the surface wear caused by the cutting action and the groove wear caused by chiseling.
Deformation wear: When the steel ball impacts the material relative to each other, under the repeated cutting/chiseling action and repeated deformation of the metal, cracks are generated due to fatigue, and the cracks expand and connect to form plow chip flakes, which fall off from the surface, causing wear.
Brittle spalling: During the impact of steel balls on each other, the reaction force of some steel balls on the lining plate causes the brittle metallographic structure of the steel balls (such as carbides) to crack, break, and peel off from the surface, causing wear.
Fatigue wear: During the rotation of the mill, the steel ball undergoes a fatigue process under the action of changing impact force, contact pressure, and shear stress. Generally, fatigue cracks are formed in the subsurface layer. The cracks extend parallel to the surface and extend toward the surface to form spalling. Produces microscopic layers and spalling pits.
Breaking rate: Steel balls whose broken area exceeds more than 1/3 of the total area of steel balls during use are called broken balls. The percentage of broken balls in the total amount of balls used during use is called the steel ball breakage rate.
Out of roundness: It is generally believed that a steel ball is out of roundness if the ratio of the difference between the maximum diameter and the minimum diameter of the steel ball to the tolerance diameter of the steel ball is greater than 7% after 2000 hours of use.
Impact factor
There are many main factors that affect the performance of steel balls, among which the main ones are:
1. Material: mainly refers to the type and proportion of alloy, which affects density and surface properties;
2. Density: It is related to the material and the production process. The higher the density, the better the overall performance;
3. Toughness/internal stress: mainly affects the crushing rate, mainly related to the heat treatment process;
4. Metallographic structure: affects density and crystal fineness, and has a greater impact on the breakage rate;
5. Heat treatment process: affects the hardness and metallographic structure, which is reflected in the wear resistance and breakage rate;
6. Hardness: divided into surface hardness and internal hardness, which are reflected in wear resistance and breakage rate;7.
7. Wear resistance: The higher the wear resistance, the better;
Cast steel ball
The steel balls produced by casting and smelting are called cast steel balls; the cast steel balls have been greatly improved to a certain extent by adjusting the alloy type and proportion. Overall, because the cast balls are produced using molds, there are inevitably some internal Blisters and pores, the structure is not very dense, so the density is smaller; in addition, there are generally pouring openings and rings on the surface; cast steel balls Due to different materials and processing techniques, the hardenability inside and outside the heat treatment is poor, the hardness of the inside and outside of the production-processed steel balls is greatly different, and the breakage rate of cast steel balls is large. Generally, the breakage rate of cast steel balls is 3%; the impact toughness of cast steel balls is about 3~ 6J/cm², poor performance in wear resistance and out-of-roundness; the advantages of cast steel balls are small production investment, low production cost and low price.
Forged steel ball
Steel balls produced by forging are called forged steel balls. The forged steel ball has a certain forging ratio during the forging forming process, which increases the density of the steel ball, changes the surface metallographic structure, and has stronger toughness, higher hardness, and better surface appearance; forging The crushing rate of steel balls is small, and the crushing rate of forged steel balls is 1%. Due to the small crushing rate, the powder extraction rate of the mill is increased, and the cost of mineral processing is reduced, which improves the production efficiency of the mill. The metallographic structure of forged steel balls is a fine needle-like martensite structure with high hardness. The impact toughness of forged steel balls is greater than 12J/cm², and its wear resistance and roundness are better. The disadvantages of forged steel balls are large equipment investment, low production efficiency, high production costs and high prices.
hot rolled steel ball
Hot-rolled steel balls are a new rolling process technology. They are formed by heating round steel bars and rolling them in a steel ball cross-rolling mill. They have certain properties of forged steel balls, with better surface, precise dimensions, and impact toughness greater than 12J. /cm2, has high hardness and good mechanical properties, and has excellent qualities of wear resistance, no deformation, and no cracking. Its anti-peel and anti-breakage performance is more than 10 times that of ordinary cast steel balls, and the general breakage rate does not exceed 1%. The investment of hot-rolled steel balls is relatively high and is not suitable for the production of various types and small batches. It is more suitable for large-scale production.
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