A method for preparing silicon nitride bearing ball with internal stress

Abstract

The present invention describes a method for preparing silicon nitride bearing balls with internal stress, belonging to the technical field of ceramic products. High-α-phase Si3N4 powder is the main material for silicon nitride bearing balls, Sb powder is the main material for providing internal stress, ALN is used to further improve the wear resistance of the material, Y2O3 is used to improve the densification of silicon nitride bearing balls. After adding Y2O3, pores can be seen under the electron microscope with a size of 0.5 μm. MgO is used to promote the transformation of α-phase Si3N4 powder to β-phase. Li2O and La2O3 form a high-temperature liquid phase to promote the densification of bearing balls. According to the property of cold expansion and hot contraction of antimony within a certain temperature range, the present invention performs molding by pressing at the shrinkage point of antimony, and then conducts a sintering process. After sintering, rapid cooling is completed when the temperature is lowered to the shrinkage point temperature to avoid the shrinkage point, and antimony is kept in the state of the expansion point all the time.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic products, and in particular to a method for preparing a silicon nitride bearing ball with internal stress. Background Art

[0002] In the field of modern industry and science and technology, bearing balls are key components, and their performance directly affects the operating efficiency and service life of mechanical equipment. As an advanced ceramic material, silicon nitride has shown significant performance advantages in the application of bearing balls due to its excellent physical and chemical properties. Silicon nitride bearing balls have shown broad application prospects in the field of modern industry and science and technology with their excellent performance characteristics such as high hardness, high temperature stability, corrosion resistance, light weight, low friction and quietness. With the continuous advancement of technology and the continuous expansion of the market, silicon nitride bearing balls will play an important role in more fields and provide strong support for technological progress and equipment upgrades in various industries.

[0003] As the global demand for clean energy grows, offshore wind power, as an important part of renewable energy, is welcoming opportunities for rapid development. Offshore wind power has the advantages of abundant resources, no occupation of land, and stable wind speed, but it also faces the challenges of a complex and changeable marine environment. In offshore wind power systems, wind turbines are core equipment, and bearings are one of the key components to ensure the reliable operation of wind turbines. As the core component of bearings, bearing balls play a vital role in them. Offshore wind farms are exposed to high humidity and high salt spray environments for a long time, which poses a severe test to the corrosion resistance of bearing balls. Ordinary metal bearing balls are prone to rust and corrosion in such an environment, which in turn affects the performance and service life of the bearings. Silicon nitride ceramic bearing balls can ensure reliability and durability in harsh marine environments.

[0004] The development trend of offshore wind power also poses new challenges to the performance of bearing balls. In order to improve power generation efficiency and reduce energy costs, modern wind turbines are moving towards large-scale and intelligent development, which means that bearings need to withstand greater loads and more complex working conditions. Higher requirements are placed on bearing balls in terms of dimensional accuracy, load capacity and fatigue life. Therefore, it is necessary to continuously optimize the design and manufacturing process of bearing balls and improve their performance indicators such as hardness and toughness to ensure that bearings can operate stably in large wind turbines. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing silicon nitride bearing balls with internal stress. The present invention dopes powdered antimony into the powder and utilizes the micro-expansion principle of antimony at low temperature to prepare silicon nitride bearing balls with internal expansion stress, thereby providing internal stress support for the silicon nitride bearing balls and further improving the bearing capacity and toughness of the bearing balls.

[0006] A method for preparing a silicon nitride bearing ball with internal stress, the steps of which are:

[0007] S1, Si with α phase content higher than 70% 3 N 4 powder, Sb powder, AlN, Y 2 O 3 、MgO、Li 2 O.La 2 O 3 , the sintering aid is put into a ball mill for ball milling until all particles have a particle size of less than 0.5 μm to prepare a mixed powder. 3 N 4 Powder is the main material of silicon nitride bearing balls, Sb powder is the main material for providing internal stress, ALN is used to further improve the wear resistance of the material, Y 2 O 3 Used to improve the density of silicon nitride bearing balls, adding Y 2 O 3 The pores can be seen under the electron microscope at 1 μm. MgO is used to promote the α-phase Si 3 N 4 The powder transforms to β phase, Li 2 O.La 2 O 3 A liquid phase is formed at high temperature, which promotes the densification of the bearing balls.

[0008] S2. Prepare a molding mold, which is used to mold silicon nitride bearing balls; the molding mold is composed of material one and material two; material one is graphite material, which is used to provide the mold shape; material two is a high temperature resistant, high strength, and high hardness material, which is used to provide supporting force; the molding mold is formed by bonding two symmetrical single molds, and the cavity part of the molding mold is spherical.

[0009] S3. In an oxygen-free air atmosphere at 80-200°C, two symmetrical single molds are pressurized and filled with mixed powders respectively; the two symmetrical single molds are both in a hemispherical upward state, and mixed powders are added to the single molds for calendering until the mixed powders fill the grooves and are higher than the grooves, forming hemispherical mixed powders.

[0010] S4. Place the single mold horizontally in an oxygen-free air atmosphere at 80-200°C, align and fit the two hemispheres of mixed powder, apply extrusion force to the two symmetrical molds, squeeze out the excess mixed powder, until the two symmetrical molds fit together, and lock the two symmetrical molds into a mold with powder.

[0011] S5. Place the mold with the powder into a high pressure sintering furnace for sintering.

[0012] S6, after sintering, slowly cool down to 100-200℃, take out the mold with powder after sintering, and quickly cool down to room temperature, open the mold, and take out the silicon nitride blank. Antimony has the lowest expansion rate at 100 degrees Celsius. This step is to maintain the expansion of antimony and achieve the effect of internal stress, quickly cool down the sintered blank, and skip the shrinkage process of antimony.

[0013] S7. Machining the silicon nitride blank to prepare bearing balls of required sizes.

[0014] Further, in step S1, Si 3 N 4 powder, Sb powder, AlN, Y 2 O 3 、MgO、Li 2 O.La 2 O 3 The mass fraction ratio of sintering aids is (70-83):(8-15):(3-5.0):(3-5):(1-3):(1-3):(1-3):(1-3).

[0015] Furthermore, the air environment in which the ball milling is performed in step S1 is an oxygen-free environment.

[0016] Furthermore, the second material in step S2 is silicon nitride material, silicon carbide material, or diamond material.

[0017] Furthermore, in step S3, the calendering molding is performed n times, where n is a positive integer ≥2.

[0018] Furthermore, in step S5, the sintering temperature is 1700° C.-1900° C., the sintering pressure is 4 atm-30 atm, the sintering time is 48 h-96 h, and the sintering gas is nitrogen or argon. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation of the present invention or the technical solution in the prior art, the drawings required for use in the specific implementation or the description of the prior art are briefly introduced below.

[0020] Figure 1 It is a flow chart of the preparation process of the present invention. DETAILED DESCRIPTION

[0021] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0022] Case 1: Si with α phase content higher than 70% 3 N 4 powder, Sb powder, AlN, Y 2 O 3 、MgO、Li 2 O.La 2 O 3 , sintering aid, with a mass fraction ratio of 75:9:5:2:3:3:1:1:1, were put into a ball mill for ball milling until the particle size of all particles was <0.5μm to prepare 6kg of mixed powder.

[0023] Preparation of the molding die: The molding die is symmetrical and divided into two halves. The molding die can be divided into a support material and a shaping material. The support material is silicon nitride material, and the shaping material is graphite material. Graphite material has high temperature resistance and lubricity. It is used to contact the bearing ball during molding. The graphite material is a thin component with a hemispherical groove. The shaping material can be mainly silicon nitride material and silicon carbide material. The shaping material is used to protect the graphite component and provide support for the graphite component.

[0024] The mixed powder and the mold are heated at 100°C in a nitrogen atmosphere for 20 minutes before operation. The mixed powder is added to the graphite groove until it is higher than the hemisphere. The graphite groove is placed on the silicon nitride support, and the powder is slowly rolled with a hydraulic column. After rolling, the mixed powder is continued to be added to the hemisphere, and the powder is continued to be slowly rolled with the pressure column. After repeated many times, ensure that the powder is compact and the powder position is still higher than the hemisphere. After the two hemispherical mold sets have completed the above operations, the two hemispherical mold sets are assembled. After the two hemispherical mold sets are assembled, they are placed horizontally, one side is fixed, and the other side is slowly rolled with a horizontal hydraulic press. After rolling, they are relaxed. The molds are always kept in a fitted state. Repeated many times, the bottom is placed to blow away the fallen granular powder with a hot air gun until the two hemispherical molds are fitted. After the hemispherical molds are fitted, they are locked with screws and nuts to keep the hemispherical molds tightly fitted. The screws and nuts are all made of silicon nitride. In actual production, in order to improve efficiency, the mold can prepare multiple ceramic bearing balls at one time.

[0025] The rolled mold is placed in a high-pressure sintering furnace for sintering at a sintering temperature of 1750°C, a sintering pressure of 20 atm, and a sintering time of 72 hours.

[0026] After sintering is completed, the temperature is slowly lowered and the pressure in the furnace is reduced to 1 atm. When the temperature drops to 200°C, the mold with the sintered powder is clamped out and placed in a large amount of water for rapid cooling to room temperature. After reaching room temperature, the screw nut is removed, the mold is opened, and the silicon nitride blank is taken out.

[0027] The silicon nitride blank is machined to prepare 12 bearing balls of required sizes. The 12 bearing balls are group A and are numbered A1-A12.

[0028] Case 2: Si with α-phase content higher than 70% 3 N 4 Powder, AlN, Y 2 O 3 、MgO、Li 2 O.La 2 O 3 , sintering aid, with a mass fraction ratio of 80:4:5:5:3:1:1:1, are put into a ball mill for ball milling until the particle size of all particles is less than 0.5μm to prepare 2kg of mixed powder.

[0029] The mixed powder is poured into two hemispherical molds and pressed into spherical bodies.

[0030] The spherical green body is subjected to cold isostatic pressing.

[0031] The spherical blank is debinded.

[0032] The spherical green body is sintered in a nitrogen atmosphere at a sintering temperature of 1750°C, a sintering pressure of 20 atm, and a sintering time of 72 hours to obtain a silicon nitride green body.

[0033] The silicon nitride blank is machined to prepare four bearing balls of required sizes. The four bearing balls are group B, numbered B1-B4, and group B is a conventional process control group.

[0034] The embodiment group was subjected to performance tests, including: bending strength; fracture toughness; hardness; and crushing load ratio.

[0035] The flexural strength is measured with reference to the standard GB / T 6569-2006 "Test method for flexural strength of fine ceramics"; the hardness is measured with reference to the standard GB / T 16534-2009 "Test method for room temperature hardness of fine ceramics"; the fracture toughness is measured with reference to the standard GB / T 23806-2009 "Test method for fracture toughness of fine ceramics - single-side pre-cracked beam method"; the crushing load ratio is measured with reference to the standard JB / T1255-2014.

[0036]

[0037] Comparing the above average data of group A with the reference group B, the bending strength of group A decreased slightly, but the decrease was not large; the fracture toughness of group A increased significantly; the hardness of group A decreased; and the crushing load ratio of group A increased significantly. The ceramic bearing ball prepared by the present invention has a slight decline in bending strength and hardness indicators, but the toughness and crushing load ratio are significantly improved, which are beneficial to the anti-aging and durability of the bearing ball.

Claims

1. A method for preparing a silicon nitride bearing ball with internal stress, characterized in that: The steps are: S1. Put Si3N4 powder with an α-phase content higher than 70%, Sb powder, AlN, Y2O3, MgO, Li2O, La2O3 and sintering aid into a ball mill for ball milling until all particles have a particle size of less than 0.5 μm to prepare a mixed powder; S2. Prepare a molding die, the molding die is used to mold silicon nitride bearing balls; the molding die is composed of material one and material two; material one is graphite material, used to provide the mold shape; material two is a high temperature resistant, high strength, high hardness material, used to provide support force; the molding die is formed by laminating two symmetrical single molds, and the cavity part of the molding die is spherical; S3, under 80-200°C and oxygen-free air atmosphere, pressurize and fill two symmetrical single molds with mixed powder respectively; the two symmetrical single molds are both in a state of hemispheres facing upwards, and the mixed powder is added to the single molds for calendering, and the calendering is performed until the mixed powder fills the groove and is higher than the groove, forming a hemispherical mixed powder; S4. Place the single mold horizontally in an oxygen-free air atmosphere at 80-200°C, align and fit the two hemispheres of mixed powder, apply extrusion force to the two symmetrical molds, squeeze out the excess mixed powder, until the two symmetrical molds fit together, and lock the two symmetrical molds into a mold with powder; S5, placing the mold with the powder into a high pressure sintering furnace for sintering; S6. After sintering is completed, the temperature is slowly lowered to 100-200°C, the mold with the powder after sintering is taken out, and the temperature is quickly lowered to room temperature, the mold is opened, and the silicon nitride blank is taken out; S7. Machining the silicon nitride blank to prepare bearing balls of required sizes.

2. A method for preparing a silicon nitride bearing ball with internal stress according to claim 1, characterized in that: In step S1, the mass fraction ratio of Si3N4 powder, Sb powder, AlN, Y2O3, MgO, Li2O, La2O3 and sintering aid is (70-83): (8-15): (3-5.0): (3-5): (1-3): (1-3): (1-3): (1-3).

3. The method for preparing a silicon nitride bearing ball with internal stress according to claim 1, characterized in that: The air environment in which the ball milling is performed in step S1 is an oxygen-free environment.

4. The method for preparing a silicon nitride bearing ball with internal stress according to claim 1, characterized in that: In step S2, the second material is silicon nitride material, silicon carbide material or diamond material.

5. The method for preparing a silicon nitride bearing ball with internal stress according to claim 1, characterized in that: The number of calendering processes in step S3 is n times, where n is a positive integer ≥2.

6. The method for preparing a silicon nitride bearing ball with internal stress according to claim 1, characterized in that: In step S5, the sintering temperature is 1700° C.-1850° C., the sintering pressure is 4 atm-30 atm, the sintering time is 40 h-108 h, and the sintering gas is nitrogen or argon.

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