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Ball iron is a specialized form of iron shaped into balls and used in the grinding and milling industry for a variety of purposes. Though many industrial applications call for grinding balls made out of steel, ball iron is still used and in large demand in regions such as China and other Asian nations. The addition of key elements like chromium into the ball iron in the manufacturing process gives it added strength and fracture resistance.
Grinding balls can range in size from about 0.6–4.7 inch diameter (15-120 millimeters). Trace elements added include carbon and chromium. The higher the chromium content, which can be up to 30% of the mass of the ball, the stronger it is.
Many key industries make wide use of ball iron, the main one being the cement industry where they are used to grind lime lumps known as clinker that form during sintering. Other manufacturing sectors that use iron ball include the grinding of raw meal, and coal grinding for both power plant fuel supplies and in the mining industry. One of the larger manufacturers produces 7,000 metric tons of it per year and exports 80% of this to various nations around the world. Other companies export ball iron in the range of 4,500 to 12,000 metric tons per year, with some capable of producing 50,000 metric tons per year to nations and regions including South America, Europe, South Africa, and the Philippines.
Ball mills of small to large size also use iron ball in processing materials. These materials are produced as fine powders in chemical engineering factories. Companies that specialize in mineral processing equipment for these factories sell ball iron, and, along with it, various other types of milling balls including those made of high alloy steel, carbon alloyed steel, iron strengthened with nickel, and steel strengthened with manganese. They also do quality control using chemical, mechanical, and metallographic tests, and even ultrasound examinations to ensure that the product is uniform.
Though ball iron can be shaped spherically, it is given an ellipsoid or egg shape for more a effective grinding ability when used in large quantities. A typical minimum order quantity for a supply is 20 metric tons, though the price per metric ton is fairly low. In the industry, ball iron is sometimes referred to as wear-resistant material due to its durability. It won't crack or break even when dropped from a considerable distance, due to repeated drop testing during the manufacturing process.