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Machinery and equipment
Date: 2015-04-02
Browse number: 115

1. Make tools with ceramic materials

In machining of metal materials, machining is the most basic and reliable method of precision machining. In modern machining, ceramic tool materials play more and more important roles in high speed cutting and difficult cutting materials due to their excellent heat resistance, wear resistance and chemical stability. Ceramic tool material mainly includes alumina, silicon nitride and theron series. Other ceramic materials such as zirconia and titanium boride are also used as tool materials.

2. Alumina series

Pure alumina ceramics contain more than Al 2 O 3 99%, with low strength, poor thermal shock resistance and fracture toughness. Carbide, nitride and boride materials have high strength and hardness and can be used as the reinforcing phase in Al 2 O 3 ceramics. Such substances include TiC, TiN, TiB 2, Ti(CN), WC, ZrC, etc. Al 2 O 3 - Ti(CN) cutting material was prepared by repeated hot pressing process, with bending strength up to 820MPa, fracture toughness 7.4mpa #m1P2, vickers hardness 20.4gpa. The cutting test shows that this material is suitable for continuous cutting cast iron and hardened steel, especially for batch cutting hardened steel. The whisker is a widely used reinforced and toughened ceramic material. The whisker of SiC and Si 3 N 4 are mainly used to enhance Al 2 O 3. The SiC whisker ACTS as a reinforcing bar in Al 2 O 3 matrix and disperses the stress in the matrix. This ceramic tool has high fracture toughness, strength and hardness and is very suitable for processing nickel base heat-resistant alloys and various cast iron and non-metallic brittle materials with low cutting speed. The addition of Si 3 N 4 whiskers into Al 2 O 3 matrix can improve the thermal impact resistance of ceramics. Zirconia phase transition toughening is a widely used toughening process suitable for cutting nickel-chromium-iron heat-resisting alloy. ZrO 2 - Al 2 O 3 composite was prepared by adding 15% partially stable zirconia in Al 2 O 3 material and 1 550 e vacuum sintering for 2 h. This type of ceramic tool has good toughness and thermal shock resistance, but poor wear resistance, mainly used in rough machining of cast iron and alloy.

3. Silicon nitride series

Silicon nitride is a kind of cutting tool material after alumina material. It is higher in strength and fracture toughness than alumina materials. Its bending strength is generally up to 900~ 1,000mpa, fracture toughness is 5~ 7MPa#m1P2, hardness is 91~ 93HRA, heat resistance is up to 1,300 ~ 1,400e, it is not easy to generate cracks, and it can obtain stable service life. The strength and toughness of si3n4 ceramics can be further improved by the method of thermal pressure self-toughening, that is, the sintering process can be controlled so that some si3n4 grains can develop into bar grains with a large length-diameter ratio (the length-diameter ratio can be as high as 3-8), thus obtaining the effect similar to whisker toughening, and the fracture toughness can be as high as 10.02mpa #m1P2. This self-toughening ceramic cutter is a tool material suitable for cutting cold cast iron and hardened steel, especially for intermittent cutting. The performance of si3n4 composite ceramics is much better than that of hot-pressed si3n4 ceramics, which are made by adding appropriate compound fortifier such as metal carbides to the si3n4 matrix. In Si 3 N 4, Al 2 O 3, Y 2 O 3, TiC, TiN, MgO and other components can be added, so cold pressing and sintering can be adopted to reduce the cost. B-theron is made by adding Al 2 O 3 to Si 3 N 4 and sintering it, which has the characteristics of Al 2 O 3 and Si 3 N 4. Its thermal hardness is higher than that of cemented carbide and Al 2 O 3. When the temperature of tool tip is higher than 1,000 e, it can still be cut at high speed. Its biggest characteristic is can raise cutting speed, increase feed amount, raise

Metal cutting rate, prolong tool life. Nanomaterials have been the focus of research in recent years and have been widely used in all aspects of materials science. Si-c-n nano-powder was used as reinforcing phase, Si3N4 as matrix, and Y2 O3 and La2 O3 as sintering auxiliaries. The room temperature and high temperature mechanical properties than silicon nitride single-phase ceramics has improved greatly, the fracture toughness were 11.78 Mpam1 Mpam1/2/2 and 14.69 (1350 ℃), the bending strength of 934 MPa and 696 MPa, respectively (1 350 ℃ temperature)

4. Make bearings with ceramic materials

Traditional bearings are made of metal with oil as the lubricating medium. However, there are many disadvantages in use, such as not suitable for high temperature, high speed, chemical corrosion occasions, oil leakage and pollution of the environment easy to be lubricated. Ceramic bearings can make up for the lack of metal bearings.

Si3 N4, with its excellent performance, has become the preferred material for manufacturing ceramic rolling bearings and has been applied in many fields such as high-speed lathes, aerospace engines, chemical machinery and equipment. For example, NORTON inc. Of the United States has used the Si3N4 ceramic bearings in the space shuttle hydraulic pumps. Pharmaceutical equipment and printing and dyeing and fishing equipment. It has been proved that the use of ceramics as a rolling bearing material is successful. Ceramic materials used for making sliding bearings (water lubricated) mainly include oxide ceramics and non-oxide ceramics. Oxide ceramics mainly includes alumina, zirconia, etc. Non-oxide ceramics mainly include carbide and nitride. The results show that the wear resistance of non-oxide ceramics is better, among which Sialon and Si3N4 are the best. Mo2 FeB2

It is a newly developed ceramic sliding bearing material with good heat resistance, wear resistance, corrosion resistance and good weldability with steel. Ceramic bearings have the following advantages: high speed: the weight of ceramics is only 40% of the weight of the same volume of steel, which can reduce centrifugal loads and skid, making ceramic bearings 20 ~ 40% higher than the speed of traditional bearings. Long life: the hardness of ceramic material is much higher than that of steel. In addition, ceramics also have high compressive strength, which is about 5~ 7 times as much as steel according to specific materials and test types. When there are impurities in the bearing, the ceramic bearing seldom produces spalling failure, so the ceramic bearing usually has a longer service life.

Low heat: the friction coefficient of ceramics is about 30% of that of steel, so the ceramic bearing produces less heat, which can extend the life of the bearing.

Low thermal expansion: the thermal expansion of silicon nitride is approximately 20% of that of steel, which is beneficial for use in environments with large temperature variations. However, when choosing steel for its shaft and bearing seat, corresponding measures must be taken to adapt the degree of fit.

Corrosion resistance: the inert chemical properties of ceramic materials give ceramic bearings excellent corrosion resistance.

Insulation: ceramic material does not conduct electricity, which can protect bearing and bearing seat from arc damage.

High temperature resistance: the allowable working temperature of ceramic bearings is 1.090e. The strength and hardness of ceramic materials will not decrease even at high temperature, so this material is very favorable for bearings used in high temperature environment.

5. Make casting - ceramics with ceramic materials

Ceramic mold casting is a method of casting with ceramics as the casting material. The casting precision and surface quality are excellent. It can be done without cutting or with little cutting.

Production: the basic principle of metal mold with high refractoriness, small coefficient of thermal expansion of refractory as aggregate, use after hydrolysis of ethyl silicate as binder made into ceramic slurry, in under the action of catalyst, after grouting, glue, hardening, demoulding, burner and roasting process made of smooth surface and high dimensional precision ceramic mold. Ceramic casting is widely used in the manufacture of moulds, such as forging die, die, die casting die, glassware die, etc. Compared with machining mold, the cost is reduced by 20% ~ 40% and the manufacturing cycle is shortened by 50% ~ 80%. For example, the cylinder cover mold of Shanghai santana car adopts the ceramic mold of precision casting H13 steel, and the surface roughness Ra value is 6.3 ~ 12.5

Lm, the size accuracy is up to 0.35 P100, which can meet the production requirements and replace the imported mold. The manufacturing cost is only 25% of the imported mold.

6. Make sand jet nozzle with ceramic materials

The ceramic material has high hardness and good abrasion resistance, instead of cast iron, steel and hard alloy, it is made into sandblasting nozzle and used with various dry or wet sandblasting and shot blasting machines. The purpose of surface treatment (surface enhancement and surface modification, surface cleaning, surface abrasive cutting, etc.) can be achieved by using compressed air or grinding fluid pump to spray abrasive to the surface of the part at high speed through the spray gun and sanding nozzle. The preparation process of a new ceramic sanding nozzle is: B4 C powder and (W, Ti) C powder are mixed in a certain proportion with ethanol as the medium through 150

H's enhanced ball mill makes the average particle size below 0.8 Lm, and then through hot pressing

Form a shape. Mechanical property test and erosion wear test showed that, with the increase of (W, Ti) C content, the density of the ceramic sandblasting nozzle material increased significantly, the grain was refined significantly, and the bending strength and fracture toughness were greatly improved.

7. Foam ceramic filter

Foam ceramic is a kind of porosity of 70% ~ 90%, the volume density of 0. 3 ~ 0. 6 gP, with three dimensional network skeleton and connectivity of pore structure of porous ceramic products, in addition to the high temperature resistance, corrosion resistance and other general ceramics have performance, but also has low density, high porosity, large specific surface area, the characteristics of fluid from one sex, thus has been successfully used for molten metal filter, improve castings quality, reduce scrap rate. At present, many kinds of foam filters (such as Al2O3, ZrO2, SiC, SiN, etc.) have been developed.

Aluminum alloy and copper alloy are easy to absorb gas and mix into non-metal inclusions in the process of melting and forming casting, thus reducing the casting performance and processing performance. Therefore, the impurities in the metal liquid are removed with a filter. For aluminum alloy and copper alloy castings, cordierite foam ceramic filter is usually used. The rejection rate of casting can be reduced from 30% ~ 40% to 3% ~ 4%. Foam ceramic filter is also suitable for casting filtration of nodular cast iron, alloy steel and stainless steel. The steel and iron material has a large proportion and a high melting point, which requires high temperature strength, softening temperature and thermal shock resistance of foamed ceramics. Aluminum oxide or silicon carbide foamed ceramic filter sheets are usually selected, and the size of filter mesh is 2~ 3.

8. Ceramic pump

Structural ceramics have excellent wear-resisting and corrosion-resistant properties. They are made into ceramic pumps to deliver fluid containing particles, strong corrosive fluid or high pure fluid, which shows better performance than metal materials. The newly developed ceramic pumps include magnetic driven centrifugal pumps, horizontal centrifugal pumps, liquid ring vacuum pumps, twin screw pumps and gear pumps. Ceramic materials are generally used in key parts of contact fluid (such as impeller, axle housing, shell, end cover, etc.). The materials used include zirconia, silicon nitride and alumina. The service life of structural ceramic pump is generally longer, for example, the service life of silicon nitride ceramic twin-screw pump is 10 times that of the existing pump.

9. Other products of opposite sex

Some processing machinery parts are made of plastics, chemical fiber, rubber, etc., which are easy to be worn, corroded by additives and degradation during processing. The replacement of structural ceramic parts can make up for this deficiency. For example, the cylinder lining, kneading plates, screw parts, nozzles and moulds of the extruder made of ceramic materials such as zirconia and alumina. Its service life is 3~ 6 times of alloy steel, and its size is stable for a long time, which improves the processing quality of plastic products.

When stainless steel drawing, the metal mold and workpiece are easy to adhesive wear, so that the workpiece surface scratch, die life reduced. Using silicon nitride ceramic mould can overcome these shortcomings. Due to the difference between silicon nitride ceramics and stainless steel materials, it is not easy to stick between the mold and the workpiece. In addition, silicon nitride ceramics have high hardness and wear resistance, which can significantly improve the die life. Using silicon nitride ceramic to make the seal ring of the end cover of submersible pump, thermocouple sleeve, etc.

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