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Brief introduction of alumina ceramic production process
Part 1:Features and Technical Indicators
Alumina ceramics are currently divided into two types: high purity type and common type.High-purity alumina ceramic materials with Al2O3 content above 99.9%, due to its sintering temperature as high as 1650-1990℃, transmission wavelength of 1 to 6 m, generally made of fused glass to replace the platinum crucible: use its light transmittance and alkali resistance metal corrosion as sodium lamp tube;In the electronics industry, it can be used as integrated electric subgrade board and high frequency insulation material.Ordinary alumina ceramic system is divided into 99 porcelain, 95 porcelain, 90 porcelain, 85 porcelain and other varieties according to the content of Al2O3, sometimes Al2O3 content in 80% or 75% also classified as ordinary alumina ceramic series
1. The hardness
The hardness of rockwell is hRA80-90, which is second only to diamond and far more than wear-resistant steel and stainless steel.
2. Excellent wear resistance
The wear resistance is 266 times that of manganese steel and 171.5 times that of high chromium cast iron.According to our customer tracking survey over the past ten years, the service life of the equipment can be extended at least ten times under the same working condition.
3. Light weight
Alumina ceramic density is 3. 5g/cm3, only -half of steel, which can greatly reduce equipment load.Main technical indicators of abrasion resistant ceramics: alumina content ≥95%, density ≥3.5g/cm3, Rockwell hardness ≥80 HRA, compressive strength ≥850 Mpa, fracture toughness K IC≥ 4.8mpa ● M1 /2, bending strength ≥290MPa, thermal conductivity 20W/m.K, thermal expansion coefficient: 7.2×10-6m /m.K.
Among them, 99 alumina ceramic materials are used for making high temperature crucibles, fireproof tubes and special wear-resistant materials, such as ceramic bearings, ceramic seals and water valves.Alumina ceramics are mainly used as corrosion-resistant and wear-resisting parts.Because part of talc is often mixed in 85 porcelain, the electrical property and mechanical strength are improved. It can be sealed with molybdenum, niobium, tantalum and other metals, and some of them are used as electrical vacuum devices.The production process is as follows:
Part 2: Powder preparation
The aluminum oxide powder is prepared into powder according to different product requirements and different molding processes.The particle size of the powder is below 1 m micron. In addition to the purity of alumina in 99.99%, ultra-fine grinding and uniform particle size distribution are also required for the manufacture of high-purity alumina ceramics.When using extrusion or injection molding, binder and plasticizer should be introduced into the powder, generally thermoplastic or resin with a weight ratio of 10-30%.The organic binder should be mixed with the alumina powder at 150-200℃ to facilitate the forming operation.There is no need to add binder for powder material formed by hot pressing process.If semi-automatic or full-automatic dry pressing is adopted, it has special technological requirements for the powder. Spray granulation is needed to treat the powder and make it appear spherical, so as to improve the fluidity of the powder and facilitate the automatic filling of the mold wall during the molding.In addition, in order to reduce the friction between powder and mold wall, 1~2% lubricant, such as stearic acid and binder PVA, should be added.
It is necessary to spray the powder for dry pressing molding, in which polyvinyl alcohol is introduced as binder.In recent years, a water-soluble paraffin wax was developed by a research institute in Shanghai as a binder for spray granulating Al2O. It has good fluidity under heating conditions.After spray granulation, the powder must have good fluidity, loose density and flow Angle friction temperature less than 30C.The particle size ratio is ideal to obtain the larger density of the green billet.
Part 3: Molding Method
The forming methods of alumina ceramic products include dry pressing, grouting, extrusion, cold isostatic pressing, injection, flow casting, hot pressing and hot isostatic pressing.In recent years, some molding technologies have been developed, such as filter press molding, direct solidification molding, gel molding, centrifugal grouting molding and free solid molding.Products of different shapes, sizes, complex shapes and precision require different forming methods.Abstract Introduction to its common forming:
Grouting molding: Grouting molding is the earliest molding method used for alumina ceramics.Due to the use of gypsum mold, low cost and easy to shape large size, complex shape parts.The key of grouting is the preparation of alumina slurry.Usually with water as the flux medium, then add the gel and binder, after fully grinding exhaust, and then pour into the gypsum mold.The slurry solidified in the mold due to the adsorption of water by the capillary.When hollow grouting, when the mold wall adsorption slurry to the required thickness, also need to pour out the excess slurry.In order to reduce the shrinkage, high concentration slurry should be used as far as possible.
It is necessary to add organic additives in alumina ceramic slurry to form a double layer on the surface of slurry particles to stabilize slurry suspension without precipitation.In addition, the binder such as vinyl alcohol, methyl cellulose, herbaecolamide and dispersant such as polyacrylamine and gum Arabic should be added to make the slurry suitable for grouting operation.
Part 4: Sintering technology
The technique of densifying granular ceramic billets to form solid materials is called sintering.Sintering is to remove the holes in the billet, remove a small amount of gas and impurities and organic matter, so that the particles grow and The heating device used in sintering is the most widely used electric furnace.Besides atmospheric sintering, there are also hot pressing sintering and hot isostatic sintering.Although continuous hot pressing sintering increases the output, the cost of equipment and mould is too high. In addition, because of axial heating, the length of products is limited.At present, some high value-added alumina ceramic products or special components needed for national defense, such as ceramic bearings, reflectors, nuclear fuel and barrel products, field use hot isostatic burning or high vacuum non-pressure sintering method.
In addition, microwave sintering, arc plasma sintering and self-propagating sintering techniques are also being developed.
SIMUWU company research and production of high vacuum non-pressure sintering equipment can achieve high density alumina ceramic products.The equipment operation is simple, intelligent operation temperature.The capacity of the equipment can be customized with different specifications and sizes. The function of personalized customized equipment can meet the production needs of customers.
Part 5：Finishing and packaging Processes
Some alumina ceramic materials need to be finished after sintering.If used as artificial bone products require a high surface finish, such as a mirror, to increase lubricity.Due to the high hardness of alumina ceramic material, it needs to be finished with harder polishing brick material.Such as SiC, B4C or diamond, etc.Usually from coarse to fine abrasive step by step grinding, final surface polishing.Generally, Al20o powder <1 m micron or Diamond paste can be used for grinding and polishing.Laser and ultrasonic grinding and polishing methods may also be used.Some alumina ceramic parts need to be packaged with other materials.
Alumina ceramics strengthening process, in order to strengthen alumina ceramics, significantly improve its mechanical strength, a new foreign alumina ceramics strengthening process.This process is novel and simple, the technical means adopted is on the surface of alumina ceramics, using electron ray vacuum coating, sputtering vacuum coating or chemical vapor deposition method, plating – layer silicon compound film, heating treatment in 1200C ~1580C, aluminum oxide ceramics toughened.The mechanical strength of the strengthened alumina ceramics can be greatly increased on the original basis and the alumina ceramics with ultra-high strength can be obtained.
Edited by: Lucky Hu;
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