Silicon nitride-based ceramic material and preparation method of ceramic bearing bush

Abstract

The invention discloses a silicon nitride-based ceramic material and a preparation method of a ceramic bearing bush. The silicon nitride-based ceramic material comprises the following raw materials: silicon nitride and a sintering aid, the sintering aid comprises aluminum oxide, aluminum nitride and ytterbium oxide; the raw materials comprise the following components in parts by weight: 80-92 parts of silicon nitride, 2-4 parts of aluminum oxide, 3-8 parts of aluminum nitride and 3-8 parts of ytterbium oxide. By optimizing the material formula, the capacity of aluminum elements and oxygen elements in silicon nitride is improved, so that the silicon nitride has the characteristics of high strength, high hardness, high fracture toughness and high thermal shock resistance of silicon nitride and the characteristics of refractory property, corrosion resistance and oxidation resistance of aluminum oxide; the requirements of a high-aluminum-zinc unit on moderate hardness, good toughness and strong thermal shock resistance of a bearing bush material can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of supporting journal bearing materials for hot-dip coating equipment in the cold rolling process. More specifically, it relates to a silicon nitride-based ceramic material and a preparation method of a ceramic journal bearing, and particularly to a silicon nitride-based ceramic material and a ceramic journal bearing for supporting the journal bearings of the zinc pot roll system of a hot-dip high-aluminum zinc unit. Background Art

[0002] The hot-dip high-aluminum zinc unit is a production line for continuously producing hot-dip aluminum-zinc coated strip steel. The hot-dip coating process is completed in a zinc pot, which is specifically divided into a hot-dip aluminum-zinc unit and a hot-dip high-aluminum zinc-aluminum-magnesium unit. Among them, the metal bath composition used in the zinc pot of the hot-dip aluminum-zinc unit is 55% Al + 1.6% Si + the rest is Zn; the metal bath composition used in the hot-dip high-aluminum zinc-aluminum-magnesium unit is 55% Al + 1.6% Si + 2% Mg + the rest is Zn; in the above-mentioned hot-dip high-aluminum zinc unit, the temperature of the molten metal is 590 - 600 °C.

[0003] Combined Figure 1 As shown in the hot-dip high-aluminum zinc unit, the strip steel 100 obliquely enters the zinc pot. After the strip steel 100 is turned by the sink roll 3, it vertically goes up and passes through two positioning rolls, usually called the front and rear stabilizing rolls 1 and 2, and then leaves the surface of the zinc bath; the strip steel 100 undergoes the so-called "hot-dip coating" in the zinc bath and forms a corresponding zinc coating. Obviously, the three rolls in the zinc bath, including the sink roll 3, the front stabilizing roll 1, and the rear stabilizing roll 2, are rotating mechanical equipment that is integrally immersed in the high-temperature molten metal. Sliding bearings, which are also commonly referred to as "bush journal bearings" in the industry, are required to support both sides of each of the three rolls. Figure 2 It is a schematic diagram of the bush journal bearings of the zinc pot roll system of the hot-dip high-aluminum zinc unit. Among them, the bushing 4 refers to the component installed on the shaft head of the roll system and rotates with the roll system during use. The journal bearing 5 refers to the component that matches the bushing to form a friction pair and does not rotate itself.

[0004] When continuously hot-dip coating high-aluminum zinc on strip steel, the composition and temperature of the metal bath have an important impact on the continuous hot-dip coating process of strip steel. The aluminum element in the zinc liquid is added as a beneficial element, but at the same time, aluminum will also accelerate the corrosion rate of the strip steel and iron facilities in the zinc pot at high temperatures. Therefore, the friction materials such as the bushings and journal bearings of the zinc pot rolls in the hot-dip coating production line are usually produced with corrosion-resistant materials. However, nickel-based alloys, cobalt-based alloys, austenitic stainless steels, hot work die steels, and high-speed steels all have deficiencies such as poor corrosion and wear resistance to zinc liquid, low hardness, and short service life. Currently, the bearing life of the zinc pot roll system of the high-aluminum zinc unit is generally relatively short, about 7 - 10 days, and there is a need for a breakthrough in materials in the industry.

[0005] Silicon nitride was discovered more than a hundred years ago and has excellent high-temperature resistance and chemical corrosion resistance. However, since it is a covalent bond compound and cannot be densified by ordinary sintering methods, useful materials could not be made until the 1960s when reaction sintering and hot pressing sintering technologies made breakthroughs, and thus it has gradually been used in industries such as bearings, cutting tools, and cast aluminum.

[0006] In existing hot-dip production lines, the shaft sleeves in the zinc pots usually use round or arc-shaped zirconia, alumina, or silicon nitride ceramic bars, which are welded and fixed on-site. However, zirconia and alumina materials have poor thermal shock resistance, and silicon nitride materials have low sintering activity and are difficult to densify, all of which affect the service life of the ceramic shaft sleeves.

[0007] There are also reports in the industry of using silicon nitride for shaft sleeves. However, the working conditions of the high-aluminum zinc unit determine that the ceramics used have triple requirements for hardness, toughness, and thermal shock resistance. The silicon nitride ceramics reported currently have high hardness but poor material toughness and often fail prematurely in actual use. In view of the above situation, it is necessary to re-develop a material suitable for the shaft of the zinc pot roller in the hot-dip high-aluminum zinc production line around the above triple requirements to meet the personalized needs of the high-aluminum zinc unit for shaft sleeve materials. Summary of the Invention

[0008] Aiming at the defects existing in the prior art, the purpose of the present invention is to provide a silicon nitride-based ceramic material and a preparation method of a ceramic shaft sleeve. By optimizing the material formula and increasing the content of aluminum and oxygen elements in silicon nitride, it combines the characteristics of high strength, high hardness, high fracture toughness, high thermal shock resistance of silicon nitride and the refractoriness, corrosion resistance, and oxidation resistance of alumina, and can meet the requirements of the high-aluminum zinc unit for the shaft sleeve material with moderate hardness, good toughness, and strong thermal shock resistance.

[0009] To achieve the above purpose, the present invention adopts the following technical solutions:

[0010] The first aspect of the present invention provides a silicon nitride-based ceramic material, the raw materials of which include silicon nitride and sintering aids; the sintering aids include alumina, aluminum nitride, and ytterbium oxide;

[0011] The raw materials include the following components by weight: 80 - 92 parts of silicon nitride, 1 - 3 parts of alumina, 3 - 11 parts of aluminum nitride, and 3 - 9 parts of ytterbium oxide.

[0012] Preferably, the dosage of the sintering aids is 8 - 20 wt% of the total amount of the raw materials.

[0013] Preferably, the particle sizes of the silicon nitride, alumina, aluminum nitride, and ytterbium oxide are 0.2 - 0.8 μm.

[0014] Preferably, the silicon nitride-based ceramic material is prepared by the following preparation method:

[0015] Mix silicon nitride, sintering aids and deionized water, and add a forming agent and mix evenly to obtain an aqueous slurry with a solid content of 50-55%. Then, perform ball milling and mixing, add an antifoaming agent and a dispersant during the ball milling process. After the ball milling is completed, spray drying is used to prepare the silicon nitride-based ceramic material.

[0016] Preferably, the addition amount of the forming agent is 1-2 wt% of the total content of the raw materials, the addition amount of the antifoaming agent is 0.1-0.5 wt% of the total content of the raw materials, and the addition amount of the dispersant is 1-2 wt% of the total content of the raw materials.

[0017] Preferably, the forming agent is selected from polyethylene glycol or polyvinyl alcohol; the antifoaming agent is selected from n-octanol; the dispersant is selected from polyacrylic acid.

[0018] Preferably, the particle size of the silicon nitride-based ceramic material is 40-80 μm, and the loose bulk density > 0.8 g / cm 3 .

[0019] The second aspect of the present invention provides a preparation method of a ceramic bearing bush, including the following steps:

[0020] S1, cold isostatic pressing, subject the silicon nitride-based ceramic material as described in the first aspect of the present invention to cold isostatic pressing to obtain a cylindrical green ceramic body;

[0021] S2, dewaxing and pre-sintering, subject the green ceramic body to dewaxing under negative pressure carrier gas in a nitrogen protection atmosphere to obtain a pre-sintered ceramic blank;

[0022] S3, gas pressure sintering, rough machine the pre-sintered ceramic blank, then send it into a sintering furnace, and perform gas pressure sintering in a nitrogen-containing gas to obtain a semi-finished ceramic bearing bush;

[0023] S4, grinding, grind the semi-finished ceramic bearing bush to obtain a ceramic bearing bush.

[0024] Preferably, in the step S1, during the cold isostatic pressing process, the pressure is 250-280 MPa, and the pressing time is 8-10 min.

[0025] Preferably, in the step S2, during the dewaxing process, place the silicon nitride-based ceramic green body in an atmosphere furnace, under a nitrogen protection atmosphere, first keep it warm at room temperature for 1-2 h, then heat it up to 80-120 °C and keep it warm for 3-4 h, heat it up to 250-280 °C and keep it warm for 2-4 h, heat it up to 400-450 °C and keep it warm for 2-3 h, heat it up to 900-950 °C and keep it warm for 2-3 h, heat it up to 1100-1350 °C and keep it warm for 1-2 h, and then cool it down at a cooling rate of 2-5 °C / min.

[0026] Preferably, in the step S3:

[0027] During the air pressure sintering process, the sintering temperature is 1750 - 1950 °C, and the sintering time is 2 - 4 h: and / or the nitrogen-containing gas used during sintering is a mixed gas of nitrogen and argon or nitrogen.

[0028] Preferably, in the step S4, the Vickers hardness HV10 of the ceramic bearing bush is 1200 - 1450 kg / mm 2 , and the fracture toughness is 6.2 - 6.6 MPa·M 1 / 2 .

[0029] Advantages of the present invention:

[0030] 1. For the preparation method of a silicon nitride-based ceramic material and a ceramic bearing bush provided by the present invention, first, the formula of the silicon nitride-based ceramic material is optimized to increase the solid solution amount of aluminum and oxygen elements in silicon nitride, so that it takes into account the characteristics of high strength, high hardness, high fracture toughness, high thermal shock resistance of silicon nitride, as well as the refractory, corrosion resistance, and oxidation resistance of alumina;

[0031] 2. The bearing bush prepared by the present invention can meet the working conditions requirements of a high-aluminum zinc unit, can be used for a long time, has good structural stability during use, has a small contact area between the ceramic bearing bush and the bushing, low friction resistance, fast running-in speed at the initial stage of startup, stable wear, and can achieve the purpose of stable, low-resistance, and long-life operation of the bushing and bearing bush. Description of the drawings

[0032] Figure 1 is a schematic diagram of the zinc pot roll system of an existing hot-dip high-aluminum zinc unit;

[0033] Figure 2 is a schematic diagram of the shaft sleeve and bearing bush of the zinc pot roll of an existing hot-dip high-aluminum zinc unit. (a) is an assembly drawing of the shaft sleeve and bearing bush of the zinc pot roll of the hot-dip high-aluminum zinc unit, and (b) is a cross-sectional view of the shaft sleeve and bearing bush of the zinc pot roll of the hot-dip high-aluminum zinc unit;

[0034] Figure 3 is a flow chart of the preparation method of the ceramic bearing bush of the present invention;

[0035] Figure 4 is a metallographic schematic diagram of the ceramic bearing bush prepared in Example 1 of the present invention;

[0036] Figure 5 is a structural schematic diagram of the ceramic bearing bush prepared in Example 1 of the present invention pre-installed on the bearing seat. (a) is a three-dimensional view of the ceramic bearing bush; (b) is a cross-sectional schematic diagram of the ceramic bearing bush in the A - A direction; (c) is a cross-sectional schematic diagram of the ceramic bearing bush in the B - B direction. Detailed implementation manners

[0037] To better understand the above technical solution of the present invention, the technical solution of the present invention will be further described below in conjunction with the drawings and embodiments.

[0038] A silicon nitride-based ceramic material provided by the present invention, the raw materials thereof include silicon nitride and sintering aids; the sintering aids include alumina, aluminum nitride and ytterbium oxide; the raw materials specifically include the following components in parts by weight: 80-92 parts of silicon nitride, 1-3 parts of alumina, 3-11 parts of aluminum nitride, and 3-9 parts of ytterbium oxide.

[0039] In a specific embodiment, the amount of the sintering aid used is 8-20 wt% of the total amount of the raw materials.

[0040] For the above-mentioned raw materials used, the particle sizes of silicon nitride, alumina, aluminum nitride and ytterbium oxide are all in the range of 0.2-0.8 μm. Among these raw materials: alumina and aluminum nitride as sintering aids can reduce the sintering temperature of the silicon nitride-based ceramic, which is more conducive to densification. At the same time, the aluminum atoms in aluminum nitride can also replace a part of the silicon atoms in the silicon nitride lattice to improve the toughness of the material. Ytterbium oxide plays a role in refining grains and improving the strength of the grain boundary phase in the material.

[0041] The preparation method of the silicon nitride-based ceramic material of the present invention is as follows: Mix silicon nitride, sintering aids and deionized water, and add a small amount of molding agent and mix evenly to obtain an aqueous slurry with a solid content of 50-55%. Then, perform ball milling and mixing, and add an antifoaming agent and a dispersant during the ball milling process. After the ball milling is completed, spray drying is used to prepare a silicon nitride-based ceramic material with a certain particle size and fluidity; during the ball milling process, the ratio of material to ball is 1:2-3, and the ball milling time is 36-48 h.

[0042] In the above process, the addition amount of the molding agent is 1-2 wt% of the total content of the raw materials, the addition amount of the antifoaming agent is 0.1-0.5 wt% of the total content of the raw materials, and the addition amount of the dispersant is 1-2 wt% of the total content of the raw materials. In a specific embodiment, the molding agent is selected from polyethylene glycol (PEG) or polyvinyl alcohol (PVA); the antifoaming agent is selected from n-octanol; the dispersant is selected from polyacrylic acid.

[0043] The particle size of the above-prepared silicon nitride-based ceramic material is 40-80 μm, and the loose bulk density > 0.8 g / cm 3 .

[0044] Combined Figure 3 As shown, the present invention also provides a preparation method of a ceramic bearing bush, including the following steps:

[0045] S1, cold isostatic pressing, subject the above-prepared silicon nitride-based ceramic material to cold isostatic pressing to obtain a cylindrical ceramic green body;

[0046] Specifically, weigh according to the proportion of the components of the silicon nitride-based ceramic material. Add silicon nitride, alumina, aluminum nitride, and ytterbium oxide powders to deionized water, and add a small amount of molding agent, defoaming agent, and dispersant. After mixing evenly, obtain an aqueous slurry with a solid content of 50-55% (the solid content here is silicon nitride, alumina, aluminum nitride, ytterbium oxide powders, and molding agent). Then, carry out ball milling and mixing (the ratio of material to ball is 1:2-3, and the ball milling time is 36-48 h). Then, use spray drying to obtain a silicon nitride-based ceramic material with a particle size of 40-80 μm and a loose bulk density > 0.8 g / cm 3 of the silicon nitride-based ceramic material;

[0047] Put the above-prepared silicon nitride-based ceramic material into a rubber sleeve with a diameter of 38-40 mm, a height of 130-150 mm, and a wall thickness of 2-3 mm. After filling it tightly and blocking both ends, place it in a cold isostatic press and press it at a pressure of 250-280 MPa for 8-10 min to obtain a cylindrical green ceramic body;

[0048] S2, dewaxing and pre-sintering. Carry out dewaxing of the green ceramic body under a negative-pressure carrier gas in a nitrogen protection atmosphere to obtain a pre-sintered ceramic blank;

[0049] Specifically, place the above green ceramic body in an atmosphere furnace for dewaxing and pre-sintering. The specific process is as follows: Dewaxing under a negative-pressure carrier gas in a nitrogen protection atmosphere. The dewaxing process is: room temperature (1-2 h), 80-120 °C (3-4 h), 250-280 °C (2-4 h), 400-450 °C (2-3 h), 900-950 °C (2-3 h), 1100-1350 °C (1-2 h), (cooling rate 2-5 °C / min); that is, first keep warm at room temperature for 1-2 h, heat up to 80-120 °C and keep warm for 3-4 h, heat up to 250-280 °C and keep warm for 2-4 h, heat up to 400-450 °C and keep warm for 2-3 h, heat up to 900-950 °C and keep warm for 2-3 h, heat up to 1100-1350 °C and keep warm for 1-2 h, and then cool down at a cooling rate of 2-5 °C / min.

[0050] S3, gas pressure sintering. Rough process the pre-sintered ceramic blank, and then send it into a sintering furnace to carry out gas pressure sintering under a nitrogen-containing gas to obtain a semi-finished ceramic bearing shell;

[0051] Specifically, a pre-fired ceramic blank is rough-machined using a lathe, machining center, etc. to obtain a ceramic strip blank with a diameter of 30 ± 0.5 mm and a length of 112 ± 0.5 mm, with beveled cut surfaces at both ends. Then, the ceramic strip blank obtained from rough machining is placed flat in a graphite boat and placed in a sintering furnace, and pressure sintering is carried out under a nitrogen-containing gas. The sintering temperature is 1750 - 1950 °C, and the sintering time is 2 - 4 h to obtain a semi-finished ceramic bearing shell. The nitrogen-containing gas used during sintering is a mixed gas of nitrogen and argon or nitrogen. When using a mixed gas of nitrogen and argon, the volume fraction of nitrogen is 5 - 10%.

[0052] S4. Grinding process: The semi-finished ceramic bearing shell is ground to obtain a ceramic bearing shell.

[0053] The semi-finished ceramic bearing shell obtained after pressure sintering is ground (outer diameter centerless grinding, bevel cutting, surface grinding can be used), and finally a ceramic bearing shell with a surface roughness of Ra0.8 is obtained.

[0054] The obtained ceramic bearing shell is tested, and its Vickers hardness HV10 is 1200 - 1450 kg / mm 2 , and the fracture toughness is 6.2 - 6.6 MPa·M 1 / 2 , which can meet the working conditions of the high-aluminum zinc unit.

[0055] The preparation method of the silicon nitride-based ceramic material and the ceramic bearing shell of the present invention will be further introduced below with specific examples;

[0056] Example 1

[0057] The purpose of this example is to prepare a ceramic bearing shell with a diameter of 26 mm, a length of 100 mm, and beveled cut surfaces at both ends. The specific process is as follows:

[0058] (1) Preparation of silicon nitride-based ceramic material: The particle sizes of alumina, aluminum nitride, and ytterbium oxide powders are all in the range of 0.2 - 0.8 μm. Weigh the silicon nitride, alumina, aluminum nitride, and ytterbium oxide powders as shown in Table 1 and add them to deionized water, then add PVA powder with a solid powder content of 1%, stir and mix evenly to obtain an aqueous slurry with a solid content of 50%. Then, put it into a stirred mill for ball milling and mixing. The material-to-ball ratio is 1:2, and the ball milling time is 40 h. During the ball milling process, add 0.1% defoaming agent (n-octanol) and 1% dispersant (polyacrylic acid) of the solid powder. After ball milling, spray drying is used to obtain a silicon nitride-based ceramic material with a particle size of 40 - 80 μm and a loose bulk density > 0.8 g / cm 3 .

[0059] (2) Cold isostatic pressing: The silicon nitride-based ceramic material is placed into a rubber sleeve with a diameter of 38 - 40 mm, a height of 130 - 150 mm, and a thickness of 2 - 3 mm. After being fully filled and the two ends being blocked, it is placed in a cold isostatic press and pressed at a pressure of 250 MPa for 9 minutes to obtain a cylindrical green ceramic body.

[0060] (3) Dewaxing and pre-sintering: The cylindrical green ceramic body obtained by cold isostatic pressing is placed in an atmosphere furnace for dewaxing and pre-sintering to obtain a pre-sintered ceramic blank. The process is dewaxing under a negative pressure carrier gas in a nitrogen protection atmosphere. The dewaxing process is: room temperature (1 - 2 h), 80 - 120 °C (3 - 4 h), 250 - 280 °C (2 - 4 h), 400 - 450 °C (2 - 3 h), 900 - 950 °C (2 - 3 h), 1100 - 1350 °C (1 - 2 h), (cooling rate 2 - 5 °C / min)

[0061] (4) Gas pressure sintering: The pre-sintered ceramic blank is roughly processed using a lathe, machining center, etc. to obtain a ceramic bar blank with a diameter of 30 mm and a length of 112 mm with beveled ends on both sides. The roughly processed ceramic bar blank is placed flat in a graphite boat and placed in a sintering furnace for gas pressure sintering. At 1750 - 1950 °C, the sintering time is 2 - 4 h, the gas type is nitrogen, and the gas pressure is 4 - 6 MPa. After sintering, a semi-finished ceramic bearing bush is obtained.

[0062] (5) Grinding: The semi-finished ceramic bearing bush is subjected to external diameter centerless grinding, bevel cutting, and surface grinding to obtain the required ceramic bearing bush, and its surface roughness is Ra0.8.

[0063] (6) Testing: The ceramic bearing bush prepared above is tested. Its Vickers hardness HV10 is 1300 - 1450 kg / mm 2 inside, and the fracture toughness is 6.4 - 6.5 MPa·M 1 / 2 , and when used at the large-scale production site, it can meet the working conditions of the high-aluminum zinc unit.

[0064] Combined with Figure 4 the metallographic schematic diagram of the cross-section of the ceramic bearing bush shown, it can be seen that the ceramic bearing bush prepared in this embodiment has long rod-shaped grains intertwined. The relatively fine grain diameter also hinders the propagation of cracks, providing the high hardness and fracture toughness required by the material.

[0065] Combined with Figure 5 shown, the ceramic bearing bush 7 prepared in this embodiment is pre-installed on the bearing seat 6 made of a stainless steel frame, and then installed as a whole at the production site for use, and it can meet the working conditions of the high-aluminum zinc unit.

[0066] Example 2

[0067] The purpose of this embodiment is to prepare a ceramic bearing bush with a diameter of 26 mm, a length of 100 mm, and beveled ends at both ends. The specific process is as follows:

[0068] (1) Prepare silicon nitride-based ceramic materials: The particle sizes of alumina, aluminum nitride, and ytterbium oxide powders are all in the range of 0.2 - 0.8 μm; Weigh silicon nitride, alumina, aluminum nitride, and ytterbium oxide powders as shown in Table 1 respectively, add them to deionized water, and then add PEG powder with a solid powder content of 1%, stir and mix evenly to obtain an aqueous slurry with a solid content of 50 - 55%. Then put it into a stirred mill for ball milling and mixing, with a material-to-ball ratio of 1:3 and a ball milling time of 48 h. During the ball milling process, add 0.5% defoaming agent (n-octanol) and 2% dispersant (polyacrylic acid) based on the solid powder. After ball milling, spray drying is used to obtain silicon nitride-based ceramic materials with a particle size of 40 - 80 μm and a loose bulk density > 0.8 g / cm 3 ³.

[0069] (2) Cold isostatic pressing: Put the silicon nitride-based ceramic materials into a rubber sleeve with a diameter of 40 mm, a height of 150 mm, and a thickness of 2 - 3 mm. After filling it tightly and blocking both ends, place it in a cold isostatic press and press it at a pressure of 260 MPa for 8 min to obtain a cylindrical ceramic green body.

[0070] (3) Dewaxing and pre-sintering: Place the cylindrical ceramic green body obtained by cold isostatic pressing in an atmosphere furnace for dewaxing and pre-sintering to obtain a pre-sintered ceramic blank. The process is negative pressure carrier gas dewaxing under a nitrogen protection atmosphere. The dewaxing process is: room temperature (1 h), 80 °C (3 h), 80 °C (4 h), 250 °C (2 h), 250 °C (2 h), 400 °C (2 h), 400 °C (3 h), 900 °C (2 h), 1100 °C (1 h), 1100 °C (cooling rate 2 °C / min).

[0071] (4) Gas pressure sintering: Use a lathe, machining center, etc. to process the pre-sintered ceramic blank to obtain a ceramic strip blank with a diameter of 30 ± 0.5 mm and a length of 112 ± 0.5 mm with beveled ends at both ends; Place the roughly processed ceramic strip blank flat in a graphite boat and place it in a sintering furnace for gas pressure sintering. At 1870 °C, the sintering time is 2.5 h, the gas type is a mixed gas of nitrogen and argon, the gas pressure is 4 MPa, and the volume fraction of nitrogen in the mixed gas is 8%. After sintering, a semi-finished ceramic bearing bush is obtained.

[0072] (5) Grinding process: Perform outer diameter centerless grinding, bevel cutting, and surface grinding on the semi-finished ceramic bearing bush to obtain the required ceramic bearing bush with a surface roughness of Ra0.8.

[0073] (6) Detection: The prepared ceramic bearing bush is detected, and its Vickers hardness HV10 is 1200 - 1450 kg / mm 2 within, and the fracture toughness is 6.2 - 6.6 MPa·M 1 / 2 , and when used at the large-scale production site, it can meet the working conditions of the high-aluminum zinc unit.

[0074] Example 3

[0075] The purpose of this example is to prepare a ceramic bearing bush with a diameter of 26 mm, a length of 100 mm, and inclined cut surfaces at both ends. The specific process is as follows:

[0076] (1) Preparation of silicon nitride-based ceramic material: The particle sizes of alumina, aluminum nitride, and ytterbium oxide powders are all in the range of 0.2 - 0.8 μm; according to the silicon nitride, alumina, aluminum nitride, and ytterbium oxide powders shown in Table 1, they are weighed and added to deionized water respectively, and then PEG powder with a solid powder content of 1% is added. After stirring and mixing evenly, an aqueous slurry with a solid content of 53% is obtained. Then it is put into a stirred mill for ball milling and mixing, the material-ball ratio is 1:2, the ball milling time is 36 h, and during the ball milling process, 0.4% defoaming agent (n-octanol) and 1.5% dispersant (polyacrylic acid) of the solid powder are added. After the ball milling is completed, spray drying is used to obtain a silicon nitride-based ceramic material with a particle size of 40 - 80 μm and a loose bulk density > 0.8 g / cm 3 of.

[0077] (2) Cold isostatic pressing: The silicon nitride-based ceramic material is loaded into a rubber sleeve with a diameter of 45×45 mm, a height of 150 mm, and a thickness of 2 - 3 mm. After being fully filled and blocked at both ends, it is placed in a cold isostatic press and pressed at a pressure of 280 MPa for 10 min to obtain a cylindrical ceramic green body.

[0078] (3) Dewaxing and pre-sintering: The cylindrical ceramic green body obtained by cold isostatic pressing is placed in an atmosphere furnace for dewaxing and pre-sintering to obtain a pre-sintered ceramic blank. The process is negative pressure carrier gas dewaxing under a nitrogen protection atmosphere. The dewaxing process is: room temperature (1 h), 80 °C (3 h), 80 °C (4 h), 250 °C (2 h), 250 °C (2 h), 400 °C (2 h), 400 °C (3 h), 900 °C (2 h), 1100 °C (1 h), 1100 °C (cooling rate 2 °C / min).

[0079] (4) Gas pressure sintering: The pre-fired ceramic blank is processed by a lathe, a machining center, etc. to obtain a ceramic strip blank with a diameter of 30±0.5 mm and a length of 112±0.5 mm and beveled surfaces at both ends; the roughly processed ceramic strip blank is placed flat on a graphite sintering boat and placed in a sintering furnace for gas pressure sintering at 1820°C for 3 hours. The gas type is a mixture of nitrogen and argon, the gas pressure is 4.5 MPa, and the volume fraction of nitrogen in the mixture is 10%. After sintering, a ceramic bearing semi-finished product is obtained.

[0080] (5) Grinding: The semi-finished ceramic bearing is subjected to centerless grinding and bevel grinding on the outer diameter to obtain the required ceramic bearing with a surface roughness of Ra0.8.

[0081] (6) Testing: The ceramic bearing prepared above was tested and its Vickers hardness HV10 was 1300-1450 kg / mm 2 The fracture toughness is 6.4~6.5MPa·M 1 / 2 , used in large production sites, can meet the working conditions of high aluminum zinc units.

[0082] Table 1 Composition and content of raw materials used for silicon nitride-based ceramic materials in the embodiment (by weight)

[0083]

[0084] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A silicon nitride-based ceramic material, characterized in that, Its raw materials include silicon nitride and sintering aids; the sintering aids include alumina, aluminum nitride and ytterbium oxide; The raw materials include the following components by weight: 80-92 parts of silicon nitride, 2-4 parts of alumina, 3-8 parts of aluminum nitride, and 3-8 parts of ytterbium oxide.

2. The silicon nitride-based ceramic material according to claim 1, characterized in that, The dosage of the sintering aids is 8-20 wt% of the total amount of the raw materials.

3. The silicon nitride-based ceramic material according to claim 2, characterized in that, The particle sizes of the silicon nitride, alumina, aluminum nitride and ytterbium oxide are 0.2-0.8 μm.

4. The silicon nitride-based ceramic material according to claim 2, characterized in that, The silicon nitride-based ceramic material is prepared by the following preparation method: Mix silicon nitride, sintering aids and deionized water, add a forming agent and mix evenly to obtain an aqueous slurry with a solid content of 50-55%, then carry out ball milling and mixing, add an antifoaming agent and a dispersant during the ball milling process, and obtain the silicon nitride-based ceramic material by spray drying after the ball milling is completed.

5. The silicon nitride-based ceramic material according to claim 4, characterized in that, The addition amount of the forming agent is 1-2 wt% of the total content of the raw materials, the addition amount of the antifoaming agent is 0.1-0.5 wt% of the total content of the raw materials, and the addition amount of the dispersant is 1-2 wt% of the total content of the raw materials.

6. The silicon nitride-based ceramic material according to claim 5, characterized in that, The forming agent is selected from polyethylene glycol or polyvinyl alcohol; the antifoaming agent is selected from n-octanol; the dispersant is selected from polyacrylic acid.

7. The silicon nitride-based ceramic material according to any one of claims 1 to 6, characterized in that, The particle size of the silicon nitride-based ceramic material is 40 to 80 μm, and the loose bulk density > 0.8 g / cm 3 .

8. A method for preparing a ceramic bearing bush, characterized in that, It includes the following steps: S1, cold isostatic pressing, subject the silicon nitride-based ceramic material according to any one of claims 1-7 to cold isostatic pressing to obtain a cylindrical green ceramic body; S2, dewaxing and pre-sintering, subject the green ceramic body to dewaxing under negative pressure carrier gas in a nitrogen protection atmosphere to obtain a pre-sintered ceramic blank; S3, gas pressure sintering, rough process the pre-sintered ceramic blank, then send it into a sintering furnace, and carry out gas pressure sintering in a nitrogen-containing gas to obtain a semi-finished ceramic bearing bush; S4, grinding process, grind the semi-finished ceramic bearing bush to obtain a ceramic bearing bush.

9. The method for preparing a ceramic bearing bush according to claim 8, characterized in that, In the step S1, during the cold isostatic pressing process, the pressure is 250-280 MPa and the pressing time is 8-10 min.

10. The method for preparing a ceramic bearing bush according to claim 8, characterized in that, In the step S2, during the dewaxing process, place the silicon nitride-based ceramic green body in an atmosphere furnace, under a nitrogen protection atmosphere, first keep it at room temperature for 1-2 h, then heat it to 80-120 °C and keep it for 3-4 h, heat it to 250-280 °C and keep it for 2-4 h, heat it to 400-450 °C and keep it for 2-3 h, heat it to 900-950 °C and keep it for 2-3 h, heat it to 1100-1350 °C and keep it for 1-2 h, and then cool it at a cooling rate of 2-5 °C / min.

11. The method for preparing a ceramic bearing bush according to claim 8, characterized in that, In the step S3: During the gas pressure sintering process, the sintering temperature is 1750-1950 °C and the sintering time is 2-4 h: and / or the nitrogen-containing gas used during sintering is a mixed gas of nitrogen and argon or nitrogen.

12. The method for preparing a ceramic bearing bush according to claim 8, characterized in that, In the step S4, the Vickers hardness HV10 of the ceramic bearing bush is 1,200 - 1,450 kg / mm 2 , and the fracture toughness is 6.2 - 6.6 MPa·M 1 / 2 .

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