Ball mills are widely used in metallurgy, mining, electric power, building materials, chemical industry and other fields. It is the most commonly used crushing equipment. Grinding media are balls or cylinders rolling in the ball mill. The grinding media of ordinary ball mills are mainly metal balls and cylinders. In the ceramic production industry, the main grinding media used are ceramic grinding media - followed by natural flint and pebbles. Currently listed in my country Ceramic grinding media mainly include alumina, zirconia, silicon carbide, silicon chloride and other series. Ball mills are widely used in metallurgy, mining, electric power, building materials, chemical industry and other fields. It is the most commonly used grinding equipment.

 

Grinding media are balls or cylinders rolling in the ball mill. The grinding media of ordinary ball mills are mainly metal balls and cylinders. In the ceramic production industry, the main grinding media used are ceramic grinding media - followed by natural flint and pebbles. Currently listed in my country Ceramic grinding media mainly include alumina, zirconia, silicon carbide, silicon chloride and other series. Resistance to The characteristics of corrosion, low price, and the problem of metal impurities in metal balls, so alumina ceramic balls are widely used in white cement, minerals, ceramics, electronic materials, magnetic materials, and powder of raw materials in coatings, paints and other industries. For grinding and processing, it is a high-quality grinding medium. In the building ceramic industry, the wear efficiency of alumina ceramic balls is 2O ~ 40 2s higher than that of natural flint and pebbles. 

 

1. Factors affecting wear resistance

The wear mechanism of alumina ceramics is divided into brittle fracture wear and plastic deformation wear. The wear characteristics of the former are grain shedding due to intergranular fracture, and the wear characteristics of the latter are micro-cutting through fractures. The wear rate of the former is higher than that of the latter. Much more, it is hoped that the wear of ceramics is a plastic deformation wear and internal factors of ceramics have an important influence on the mechanism of plastic deformation wear of ceramics. Alumina ceramic ball is a friction and wear component, and its wear rate is affected by internal factors and external factors, among which internal factors have a greater impact.

 

The wear-resistant alumina balls is closely related to the synergistic effect of its own material's mechanical properties and microstructure. That is, its internal factors l elastic modulus, degree of fatigue H, fracture toughness J, raw K, grain size size grain boundaries and porosity), and a lot of research has been done in recent years. The toughness and grain size of ceramics are the most studied internal factors and are most closely related to wear resistance. Toughness has a great influence on the friction and wear of ceramics. Because the smaller the grain size, the better the wear resistance of sea porcelain, so wear resistance Ceramics are developing in the direction of microcrystallization. However, the cost of nano-alumina ceramics is very high, and it is difficult to popularize and use in the field of engineering applications. Therefore, the research focus of alumina ceramic wear-resistant materials is several, and breakthroughs and development have been made in the range of um grain size.

 

2. Morphology of particles

Ceramics are made of pressed green bodies fired at high temperature. The green bodies are pressed from particles, so the sintering of ceramics is not only the sintering behavior between particles, but also the sintering behavior of the green body. Sintering is an important part of ceramic firing. There are quite a few factors that affect the sintering of the green body, and the internal factor is the characteristics of the powder. Powder properties are one of the important factors affecting sintering. Surface energy is one of the driving forces for particle sintering, and morphology has a great influence on the surface energy of particles, so the effect of particle morphology on ceramic sintering is considerable.

 

Particles with rough surface have relatively large specific surface area or surface energy, so their sintering driving force is large, sintering is easy, the sintering density is large, and the pores are small and few. Granular particles with smooth surface. The specific surface area or surface energy of this particle is relatively small, so its sintering driving force is small, it is not easy to sinter, and the sintering density of ceramics is relatively low. The voids are large and many. Compared with granular particles, plate-like particles have larger specific surface area, larger sintering driving force, easier sintering, and higher sintering density of ceramics. Compared with the green body composed of small hard agglomerates and no agglomerates, the porosity is large. The green body density is small, the density of ceramics is also small, and the sintered density of ceramics is low.

 

3. Particle size

When the grains are relatively small, the wear mechanism is mainly plastic deformation and partial transgranular fracture, resulting in slight wear; when the grains are relatively coarse, the wear mechanism is mainly grain boundary fracture, resulting in severe wear. Therefore, the smaller the grain size, the better the wear resistance of the ceramic. Therefore, a-AlO raw materials with small particle size should be used as much as possible in order to reduce the grain size of ceramics. In addition, compared with large particles, small particles have a relatively large specific surface area or surface energy. Therefore, the sintering driving force is large, the sintering temperature is low, and the sintering density is high.

 

 4. Burning aid

Appropriate sintering aids can reduce the sintering temperature, improve the microstructure of ceramics, improve the mechanical properties, and then improve the wear resistance of ceramic balls. The quality of sintering aids includes quantity, phase composition, chemical composition and fineness. The sintering aid is generally formulated with a ternary system of SiO-CaO-MgO. The use of sintering aids that emit gas and phase change at high temperatures should be avoided as much as possible, so as to avoid new defects, which will affect the densification and qualification rate of the product, and reduce the competitiveness of the product

 

5. Forming

Isostatic pressing technology is adopted to overcome the defects of other forming methods such as hollowness, delamination, low density and uneven density. The particle size, shape and additives of raw materials will affect isostatic pressing. The molding pressure and dwell time affect the density, sintering shrinkage, and sintering temperature of the green body. Therefore, it is necessary to use suitable raw materials and scientific molding process to ensure that the green body has good sintering characteristics.

 

6. Sintering system

Too high sintering temperature and too long holding time will promote Al0. As the crystal grows and the liquid phase increases, not only the strength but also the wear resistance will decrease. Of course, if the temperature is too low, the sintering density will decrease, and the wear resistance of the ceramic ball will decrease. If the sintering temperature is not suitable, even AlO. If the content is high, the wear resistance is not necessarily good, and the key depends on the phase composition and microstructure of the ceramic ball. The use of low-temperature fast-firing technology can obtain significant energy-saving benefits, and at the same time, it can inhibit the grain growth of alumina ceramic balls, which is beneficial to improve product strength and toughness, thereby improving the wear resistance of ceramic balls. The sintering aid greatly affects the fast burning at low temperature. Generally, the formula of SiO-Cat')-MgO ternary system is used.

 

7. Research progress

Researchers have carried out a lot of research on reducing the sintering temperature and improving the wear resistance with appropriate additives. Important progress has been made at an average of l~1.5/am. an Al. 0; Y-PSZ with l8~2O added in it, fired at 1650 C for 1h, its relative sintered density reached 988, and the wear rate was only l/5~l/8n of the usual 95 ceramic balls. For 95 ceramic balls, when the weight of 0.3 Mg0 is added, the wear resistance is excellent. The microstructure grains are fine and uniform, and the gas L is the least. . an Al. 0. The powder with suitable conversion rate is extremely important, and the conversion rate has a great influence on the quality of alumina ceramic balls. AlO. The conversion rate is high, its calcination temperature is relatively high, and the hardness of the material increases the grinding difficulty of the powder. Moreover, the sintering activity is small. If the sintering temperature is increased, it will not only increase the cost, but also cause grain growth, which is not conducive to the formation of uniform The microstructure, the wear resistance decreased. If Al:O. The conversion rate is low, its calcination temperature is relatively low, the hardness of the material is weakened, the grinding is relatively easy, and the sintering activity is large, but due to the crystal transformation of the product, the shrinkage is too much, resulting in cracking of the ceramic ball.

 

There are currently 75 A1Os on the market. Porcelain ball, 80 ~ 95 A1. O Ceramic balls and high-aluminum ceramic balls are relatively expensive. At present, most of the users are concentrated in some large-scale domestic and foreign enterprises and large national enterprises with higher product grades, but many small and medium-sized enterprises do not dare to care about them. This limits its popularization and application. In response to this problem, some people have developed wear-resistant ceramic balls by using the rich bauxite resources in my country. The performance of this product is not lower than the ceramic balls made of alumina powder with the same specific gravity, and the cost is only the same level of specific gravity. 50 ~ 70 of the alumina ceramic ball.

 

8. Application

The blanks and glazes used in the building and sanitary ceramics industry with wall and floor tiles as the leading products are ground by ball mills. Until now, most companies still use natural ball stones as grinding media. Due to poor wear resistance of natural ball stones and the unavoidable contamination of the glaze during the grinding process. At the same time, due to the low density of natural ball stones, the grinding efficiency is low. Seeking and using cheap and high-quality grinding media is one of the pursuits of ceramic enterprises. Since the 1950s, alumina ceramic balls have entered the field of ceramic production. In 1998, the total output of architectural ceramics in China was 1.594 × 10 m. The total output of sanitary ceramics is 1.45 million pieces, accounting for 13 and 1/5 of the world's output respectively. It is considered to be the world's largest producer of building sanitary ceramics, and from now to 2010. my country is expected to maintain building sanitary The status of the world's largest producer of ceramics. According to the ideal product structure, high-grade products are estimated to be about 40,000 t/a for high-grade ceramic balls, and the demand for high-grade porcelain balls should be around 50,000 t/a.