Aluminum oxide ceramic is a widely used ceramic, which is based on alumina (Al2O3) as a main component alumina ceramic material having good conductivity, mechanical strength and temperature resistance. The content of Al2O3 in high-purity alumina ceramics is above 99.9%, and the sintering temperature is as high as 1650 °C~1990 °C. Ordinary alumina ceramics are classified into 99 porcelain, 95 porcelain, 90 porcelain, 85 porcelain, etc. according to the Al2O3 content. Sometimes the Al2O3 content is 80% or 75%, which is also classified as ordinary alumina ceramic series. Among them, 99 alumina ceramic material is used to make high temperature crucible, refractory furnace tube and special wear-resistant materials, such as ceramic bearings, ceramic seals and water valve sheets; 95, 92 alumina ceramics are mainly used as ceramic grinding bodies and other corrosion resistant , wear-resistant parts; 85 porcelain is often incorporated into part of talc , which improves electrical properties and mechanical strength, and some are used as electric vacuum device devices.
The alumina powder entering the plant is prepared into a powder material according to different product requirements and different molding processes, and the powder particle size is below 1 μm. If high-purity alumina ceramic products are manufactured, in addition to the purity of alumina of 99.99%, it is necessary to exceed Finely pulverized and uniform in particle size distribution. When extrusion molding or injection molding is used, a binder and a plasticizer are introduced into the powder, generally a thermoplastic resin or a resin having a weight ratio of 10% to 30%, and the organic binder should be at 150 ° C with the alumina powder. Evenly mixed at ~200 °C to facilitate the molding operation. The powder raw material formed by the hot pressing process does not need to be added with a binder. If semi-automatic or fully automatic dry pressing is used, there is a special process requirement for the powder. It is necessary to treat the powder by spray granulation to make it spherical, which is beneficial to improve the fluidity of the powder and facilitate automatic filling during molding. Mold wall. In addition, in order to reduce the friction between the powder and the mold wall, it is necessary to add 1% to 2% of a lubricant such as stearic acid and a binder PVA.
For dry pressing, the powder spray is granulated, in which polyvinyl alcohol is introduced as a binder. A research institute in Shanghai has developed a water-soluble paraffin as a binder for Al2O3 spray granulation, which has good fluidity under heating. The powder after spray granulation must have conditions such as good fluidity, loose density, flow angle friction temperature of less than 30 ° C, and ideal particle ratio to obtain a larger bulk density. Alumina ceramic dry pressing forming methods are uniaxial or bidirectional, and the presses are hydraulic or mechanical, and can be semi-automatic or fully automatic. The maximum pressure of the press is 200 MPa, and the output can reach 15 to 50 pieces per minute.
During the dry pressing process, the uniform distribution of the powder particles is very important for the filling of the mold. The accuracy of the filling amount has a great influence on the dimensional accuracy control of the manufactured alumina ceramic parts. The powder particles have a maximum free-flowing effect of more than 60 μm and between 60 and 200 mesh, and the best pressure forming effect is obtained.
The technical method of densifying a granular ceramic body and forming a solid material is called sintering. Sintering removes the voids between the particles in the body, removes a small amount of gas and impurity organic matter, and causes the particles to grow and combine with each other. After a reasonable thermal system control, a microcrystalline ceramic structure mainly composed of corundum is formed.
The microcrystalline alumina ceramic grinding body has the following characteristics, and is particularly suitable for the application technology of the cement ball mill .
1. High hardness: measured by the Shanghai Institute of Ceramics, Chinese Academy of Sciences, its Rockwell hardness is HRA 80 ~ 90, the hardness is second only to diamond , far exceeding the wear resistance of wear-resistant steel and stainless steel.
2. Excellent wear resistance: measured by Powder Metallurgy Institute, Central South University, which is equivalent to 266 times the wear resistance of manganese steel, high chromium cast iron 171.5 times of. According to the customer tracking survey, under the same cement grinding conditions, the service life of the grinding body can be extended by at least 10 times.
3. Light weight: its density is 3.6 ~ 3.8g / cm3, only half of steel, can greatly reduce the equipment load.
4. The main technical indicators are as follows:
Alumina ceramic content ≥92%
Density ≥ 3.6g/cm3
Rockwell hardness ≥ 80HRA
Compressive strength ≥ 850MPa
Fracture toughness KΙC≥4.8MPa·m1/2
Bending strength ≥ 290MPa
Thermal conductivity 20W/m·K
Thermal expansion coefficient 7.2×10-6m/m·K
5. Development trend: Alumina ceramics is the most widely used material in advanced ceramics, and the following trends are accompanied by the development of the entire industry.
(1) The level of technical equipment will be rapidly improved: the development of computer technology and digital control technology has promoted the technological progress and rapid development of the advanced ceramic materials industry. Such as automatic control of continuous sintering kiln, high-power large-capacity grinding equipment, high-performance powder granulation equipment, and other net pressure forming equipment and other advanced equipment, effectively promote the overall level of the industry, at the same time, in production efficiency, Product quality and other aspects have also improved significantly.
(2) Continuous improvement of product quality: domestic microcrystalline alumina ceramic products have grown from scratch, the scale of the industry has grown from small to large, and the quality of products has gone from low to high, and has experienced a rapid development process.
(3) The scale of the industry will expand rapidly: microcrystalline alumina ceramic products, as the basic materials of other industries or fields, are affected and restricted by the development level of other industries. From the application of alumina ceramics, its application range is wider and wider, and the dosage is getting larger and larger, especially in the cement grinding system and building ceramics in the new dry process production.
