Development status and production technology of wear resistant steel ball in China

At present, the total number of enterprises producing wear-resistant steel balls in China is generally about 1000-2000, among which there are more than 100 in Ningguo City of Anhui Province. In China, among the numerous steel ball production enterprises, most of them are small enterprises with an annual output of less than 2000 tons, and more than ten thousand tons are produced. These enterprises produce steel balls in a variety of methods, which can be generally summarized as sand mold, metal mold, centrifugal, EPC four mainstream casting processes, but also a small number of semi-solid molding and investment casting process. Among them, sand casting presents a state of polarization: one is the declining hand-made clay and sodium silicate sand molds. Single box or stacked box casting is adopted. Due to its poor performance and low production efficiency, at present, there are a few small enterprises applied in remote and backward areas, and most of them have been eliminated. The other type is typical of large-scale mechanized production, such as "disa" extrusion molding line, also known as "shooting extrusion vertical parting no box molding line". As long as hot metal is supplied, the single line production can be easily dried up to tens of thousands of tons per year. Magtor company of Belgium, which ranks first in the production of wear-resistant materials in the world, distributes in the production lines of wear-resistant steel balls all over the world, such as Thailand and India, with an annual output of about 600000 tons of steel balls, most of which are produced by Desa line. But this kind of production line equipment investment is big, the production cost is high, small and medium-sized enterprises should be cautious. The other is resin sand molding line (including old sand regeneration) which has been developing vigorously in recent ten years. After completing the maturation process of PC kiln similar to cement industry after 2000, and greatly reducing the investment cost, it has been developing rapidly. With its precise size, beautiful appearance and high labor productivity, it has shown great advantages in the production of small size steel balls and segments, especially high chromium microspheres and micro segments.

At present, metal mold is the most important technology in the production of casting ball. It can effectively improve the wear resistance and process yield of metal casting ball with excellent quenching effect. At the same time, its size standard, good appearance quality, especially low equipment investment and extremely simple operation method make it occupy more than 90% monopoly position in China's steel ball production enterprises. In the past, single mode was often used in metal mold, which can be divided into vertical type and horizontal type. In recent years, most of them use multi ball combined metal mold with higher production efficiency and lower labor intensity.

Centrifugal casting ball has excellent as cast microstructure and final mechanical properties, high yield, low energy consumption and less consumables. However, due to the limitation of single machine capacity, it is difficult to realize large-scale industrial production. At present, a small number of enterprises in China and India adopt this process.

EPC (lost foam) process has the advantages of good dimensional accuracy, high production efficiency and low labor intensity. The disadvantage is that its heat dissipation performance is poor, the microstructure of the steel ball is not compact enough, and the wear resistance is more than 30% worse than that of the metal mold with the same chemical composition. At the same time, the phenomenon of sand washing can not be avoided inside the steel ball, and the problem of high ball crushing rate exists in the application of large diameter mill.

Investment casting is an ancient production process, and the technology is quite mature. It has the advantages of high dimensional accuracy. However, there are many processes and high cost. At present, it is only used in the production of microsphere and micro segment by high chromium cast iron with poor fluidity.