Preparation method of high-purity alumina thermal spraying powder for insulating ceramic bearing

Abstract

The application relates to the field of coating and surface treatment technology, and discloses a preparation method of high-purity alumina thermal spraying powder for insulating ceramic bearings, which comprises the following steps: selecting alumina powder with an average particle size of 1-50 microns; the alumina powder can be prepared by a chemical method or a physical method to ensure that the purity and particle size distribution of the alumina powder meet the requirements; mixing the alumina powder prepared in step one with a flowability improver, wherein the flowability improver is an organic compound and is used for improving the flowability of the alumina powder so that the alumina powder can be better sprayed on the surface of a ceramic bearing; and transmitting compressed air or gas through a spraying device to shoot the powder to the surface, ensuring uniform coverage and close adhesion, and meanwhile, the powder is melted and sprayed on the surface of the bearing by a high-temperature flame to form a uniform coating, so that the unqualified rate of the ceramic bearing is reduced, and the production cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of coating and surface treatment, in particular to a preparation method of high-purity alumina thermal spraying powder for insulating ceramic bearings. BACKGROUND

[0002] The preparation of high-purity alumina thermal spraying powder for insulating ceramic bearings generally involves a high-temperature thermal spraying process, in which high-purity alumina powder is heated to a molten state and then sprayed onto the bearing surface through a gas or powder spray gun. This technology helps to improve the performance of insulating ceramic bearings, making them perform well in electrical, mechanical and high-temperature environments.

[0003] Most of the existing preparation methods of high-purity alumina thermal spraying powder for insulating ceramic bearings cannot guarantee the uniformity of the coating, resulting in uneven or inconsistent thickness of the ceramic bearing surface, which affects the performance of the bearing, causing the bearing to rotate less smoothly, thereby increasing the rejection rate of ceramic bearings and increasing production costs. SUMMARY

[0004] In view of the shortcomings of the prior art, the present application provides a preparation method of high-purity alumina thermal spraying powder for insulating ceramic bearings, which solves the problem that most of the existing preparation methods of high-purity alumina thermal spraying powder cannot guarantee the uniformity of the coating, thereby affecting the performance of the bearing, increasing the rejection rate of ceramic bearings and increasing production costs.

[0005] To achieve the above purpose, the present application is implemented by the following technical scheme: a preparation method of high-purity alumina thermal spraying powder for insulating ceramic bearings, comprising the following steps:

[0006] Step one: select alumina powder with an average particle size of 1 to 50 microns, which can be prepared by chemical or physical methods to ensure that its purity and particle size distribution meet the requirements;

[0007] Step two: mix the alumina powder prepared in step one with a flowability improver, which is an organic compound designed to improve the flowability of the alumina powder for spraying onto the ceramic bearing surface;

[0008] Step three: add a binder to the mixed alumina powder in step two and mix it using a stirring device, the binder being an organic resin used to bond the mixture to the surface after spraying;

[0009] Step four: use a thermal spraying device to spray the mixed powder in step three onto the preheated insulating ceramic bearing surface by delivering compressed air or gas to ensure uniform coverage and tight adhesion;

[0010] Step five: during the thermal spraying process in step four, a burner is used to provide fuel and cooperate with oxidant to generate a flame, the flame melts the powder and sprays it onto the bearing surface to form a uniform coating, the volume ratio of combustion gas and oxidant is 1:1;

[0011] Step six: after the coating in step five is formed, an additional heat treatment step is carried out, which is to place the coating in a high temperature environment and sinter for 15-30 minutes to improve the density, mechanical properties and wear resistance of the coating, thereby improving the performance of the insulating ceramic bearing;

[0012] Step seven: after preparation, the coating has insulating properties and is suitable for the application of insulating ceramic bearings, which can improve the electrical insulation, wear resistance and corrosion resistance of the bearing and effectively prolong the service life of the bearing.

[0013] Preferably, the chemical method in step one is to convert appropriate raw materials into alumina powder through chemical reaction, the specific steps are as follows:

[0014] S1: react aluminum source with alkaline solution to form aluminum hydroxide precipitate

[0015] S2: the precipitate is washed and filtered to remove impurities;

[0016] S3: the aluminum hydroxide precipitate is dried and calcined to convert it into alumina powder, the alumina powder at this time is generally high-purity alumina powder with a purity of more than 99.9%.

[0017] Preferably, the aluminum source is aluminate, such as aluminum nitrate or aluminum sulfate, the alkaline solution is sodium hydroxide, and the alumina powder prepared by the chemical method needs to be treated with waste liquid and waste gas to ensure the quality of the obtained powder.

[0018] Preferably, the physical method in step one is to convert raw materials into alumina powder through physical process without involving chemical reaction, the specific steps are as follows:

[0019] S1: first, high-purity aluminum metal or alumina powder is put into a high-temperature furnace, and then transported by gas flow;

[0020] S2: at high temperature, the raw material undergoes physical change and finally forms alumina powder.

[0021] Preferably, the gas is hydrogen or nitrogen, and the alumina powder prepared by the physical method does not involve chemical reaction, so there is no need to treat waste liquid and waste gas.

[0022] Preferably, the flowability improver in step two is tested at different binder concentrations, and the optimal concentration of the alumina powder is selected based on the test results, and at the same time, the adhesion strength test, hardness test and microstructure observation are carried out for each concentration of the sample, and based on the test results, the amount of binder is further adjusted until the desired coating performance is achieved, and the optimal amount of alumina powder is obtained.

[0023] Preferably, the ratio of combustion gas and oxidizer in step five is achieved by mixing the combustion gas and oxidizer through a mixing device when they are supplied separately to the reactor, to ensure uniform ratio and achieve the required chemical reaction conditions, and at the same time, by monitoring and controlling the temperature, pressure, residual amount of oxidizer and other parameters in the reactor during the chemical reaction, the ratio of combustion gas and oxidizer can be adjusted in time, and the gas phase composition or other key parameters in the reactor are measured by sensors, and these information is compared with the required ratio, so that the supply of combustion gas and oxidizer is adjusted according to the feedback signals to maintain the required ratio.

[0024] Preferably, the binder in step three is epoxy resin, which is mixed with alumina powder and then chemically reacted, physically cross-linked and heat-cured to form a solid structure, providing good bonding performance.

[0025] Preferably, the preheating method of the preheated insulating ceramic bearing surface in step four is constant temperature furnace heating, infrared heating, laser heating and resistance heating.

[0026] Preferably, the flowability improver includes solvents, plasticizers, surfactants, polymer additives and acid anhydrides.

[0027] The present application provides a preparation method of high-purity alumina thermal spraying powder for insulating ceramic bearings.

[0028] 1、The present application uses compressed air or gas to deliver the powder to the surface through the spraying device, ensuring uniform coverage and tight adhesion, and at the same time, the burner provides fuel and oxidizer to generate a flame, which melts the powder and sprays it onto the bearing surface to form a uniform coating, thus ensuring the flatness or uniform thickness of the ceramic bearing surface, thereby reducing the rejection rate of ceramic bearings and reducing production costs.

[0029] 2、The present application completes the heat treatment of the formed coating by placing it in a high temperature environment and sintering it for a certain period of time, thereby improving the density and wear resistance of the coating, and thus improving the performance of the insulating ceramic bearing. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0031] Embodiment one:

[0032] The embodiment of the present application provides a preparation method of high-purity alumina thermal spraying powder for insulating ceramic bearings, comprising the following steps:

[0033] Step one: select alumina powder with an average particle size of 1 to 50 microns, and the alumina powder can be prepared by chemical or physical method to ensure that its purity and particle size distribution meet the requirements;

[0034] Step two: mix the alumina powder prepared in step one with a flowability improver, wherein the flowability improver is an organic compound designed to improve the flowability of the alumina powder for spraying on the surface of the ceramic bearing;

[0035] Step three: add a binder to the mixed alumina powder in step two, and use a stirring device to stir and mix, the binder is an organic resin used for the mixture to bond to the surface after spraying;

[0036] Step four: use a thermal spraying device to spray the mixed powder in step three onto the preheated surface of the insulating ceramic bearing by delivering compressed air or gas to ensure uniform coverage and close adhesion;

[0037] Step five: during the thermal spraying process in step four, use a burner to provide fuel and cooperate with an oxidizing agent to generate a flame, the flame melts the powder and sprays it onto the bearing surface to form a uniform coating, and the volume ratio of the combustion gas and the oxidizing agent is 1:1;

[0038] Step six: after the coating in step five is formed, an additional heat treatment step is performed, which is to place the coating in a high-temperature environment and sinter for 20 minutes to improve the density, mechanical properties and wear resistance of the coating, thereby improving the performance of the insulating ceramic bearing;

[0039] Step seven: after the preparation is completed, the coating has insulating properties and is suitable for application to insulating ceramic bearings, and the coating can improve the electrical insulation performance, wear resistance and corrosion resistance of the bearing and effectively prolong the service life of the bearing.

[0040] The chemical method in step one is to convert appropriate raw materials into alumina powder through chemical reaction, and the specific steps are as follows:

[0041] S1: reacting an aluminum source with an alkaline solution to form an aluminum hydroxide precipitate

[0042] S2: washing and filtering the precipitate to remove impurities;

[0043] S3: drying and calcining the aluminum hydroxide precipitate to convert it into aluminum oxide powder, which is typically high-purity aluminum oxide powder with a purity of 99.9% or higher.

[0044] The aluminum source is an aluminate salt, such as aluminum nitrate or aluminum sulfate, and the alkaline solution is sodium hydroxide. The chemically prepared aluminum oxide powder requires treatment of waste liquid and waste gas to ensure the quality of the obtained powder.

[0045] The physical method in step one is to convert the raw material into aluminum oxide powder through a physical process without involving chemical reactions. The specific steps are as follows:

[0046] S1: First, high-purity aluminum metal or aluminum oxide powder is put into a high-temperature furnace, and then transported by gas flow;

[0047] S2: At high temperature, the raw material undergoes physical changes and finally forms aluminum oxide powder.

[0048] The gas is hydrogen or nitrogen. The physical method of preparing aluminum oxide powder does not involve chemical reactions, so there is no need to treat waste liquid and waste gas.

[0049] In step two, the flowability improver is tested with different binder concentrations. Based on the test results, the best concentration of aluminum oxide powder with the best flowability and adhesion is selected. At the same time, the adhesion strength test, hardness test, and microscopic structure observation of each concentration sample are also carried out. Based on the test results, the amount of binder is further adjusted until the desired coating performance is achieved, and the best amount of aluminum oxide powder is obtained.

[0050] The detailed steps for testing the flowability improver with different binder concentrations are as follows:

[0051] S1: From the initial reference or experience, an initial binder concentration is selected, which can be used as the starting point for the test. This initial concentration may be based on previous similar applications or recommendations;

[0052] S2: Based on the selected initial concentration, a series of samples are prepared, each with a different binder concentration. This can be done by mixing aluminum oxide powder and binder and forming samples under appropriate conditions;

[0053] S3: Use appropriate rheometers or flowability testing equipment to measure the flowability of each sample. Flowability testing can be used to evaluate the flow characteristics of powder particles under different binder concentrations;

[0054] S4: Perform adhesion tests on each sample to evaluate the effect of binder concentration on powder adhesion;

[0055] S5: Record the data from the flowability and adhesion tests, including the binder concentration of each sample and the relevant test results;

[0056] S6: Repeat steps 2 to 5 using different binder concentration ranges to cover a wider range of concentrations;

[0057] S7: Based on the test results and data analysis, determine the optimal binder concentration range.

[0058] The ratio of combustion gas and oxidizer in step five is achieved by supplying the combustion gas and oxidizer separately to the reactor, mixing them together through a mixing device to ensure uniformity of the ratio and achieve the required chemical reaction conditions, while monitoring and controlling the temperature, pressure, and residual amount of oxidizer in the reactor during the chemical reaction process, the supply ratio of combustion gas and oxidizer can be adjusted in time, the gas phase composition or other key parameters in the reactor are measured by sensors, and these information are compared with the required ratio, so the supply of combustion gas and oxidizer is adjusted according to these feedback signals to maintain the required ratio.

[0059] The binder in step three is epoxy resin, which, after mixing with alumina powder, undergoes chemical reaction, physical crosslinking and thermal curing to form a solid structure, providing good adhesion performance;

[0060] Specifically, chemical reaction is a process that changes the molecular structure by forming or breaking chemical bonds. In the process of forming a solid structure, chemical reactions are usually introduced, such as polymerization, in which monomer molecules are connected together by covalent bonds to form larger molecules or polymers, these covalent bonds are very strong, so they can form a solid chemical structure in the material; physical crosslinking is a process of forming a structure in the material through physical forces rather than covalent bonds, these physical forces include van der Waals forces, hydrogen bonds, electrostatic interactions, etc., when there are these interactions between molecules, they can attract each other and form a solid network structure, for example, many elastomer materials, such as rubber, are formed by physical crosslinking, in which the crosslinking points between molecules are caused by physical attraction; thermal curing is a process of heating the material to promote the formation of a solid structure, usually, this involves heating the material to activate chemical reactions or rearrange molecules to introduce crosslinks or crosslinking points in the material, once the material has been thermally cured, it will have higher hardness and heat resistance, thermosetting resins, such as epoxy resin, are common examples, they need to be heated to form a solid structure.

[0061] The preheating method of the preheated insulating ceramic bearing surface in step four includes constant temperature furnace heating, infrared heating, laser heating and resistance heating.

[0062] Specifically, constant temperature furnace heating: place the insulating ceramic bearing in a constant temperature furnace and heat it uniformly at a predetermined temperature. This method is suitable for situations where high temperature accuracy and stability are required. The appropriate heating time and temperature can be selected according to the size of the bearing and the heat treatment requirements. Infrared heating: use infrared heating lamps or infrared heaters to heat the surface of the insulating ceramic bearing. Infrared heating can achieve rapid and local heating, which is suitable for small size and specific area heating requirements. Laser heating: use laser heating equipment to locally heat the surface of the insulating ceramic bearing. Laser heating has high energy density and precise energy control, which is suitable for local preheating. Resistance heating: place a resistance wire or resistance sheet on the insulating ceramic bearing and apply electricity to heat it. Resistance heating can provide uniform heating and controllable heating temperature, which is suitable for larger size or complex shape bearings.

[0063] Flow improvers include solvents, plasticizers, surfactants, polymer additives and acid anhydrides;

[0064] Specifically, solvents: adding solvents is one of the most common methods for improving flow. Solvents can reduce the viscosity of coatings or liquids, making them easier to apply or spray. Common organic solvents include acetone, dimethylformamide, methanol, ethanol, etc. Plasticizers: plasticizers are a class of organic compounds that can enhance the plasticity and flow of liquids. These compounds are usually compatible with polymers, improving the processing performance of materials. For example, phthalate plasticizers are commonly used in polyvinyl chloride resins. Surfactants: adding surfactants can reduce the surface tension of liquids, improve their wettability and permeability, which helps to form a uniform coating on the substrate. The choice of surfactant depends on the chemical properties of the system, such as non-ionic, ionic or mixed surfactants. Polymer additives: some high molecular weight polymers, such as polyvinyl ethers and polypropylene ethers, can be used as flow improvers. They form macromolecular chains in the liquid, reducing friction and improving flow. Acid anhydrides: acid anhydride compounds, such as phenolic anhydride, can be used as flow improvers in coatings and paints. They react with hydroxyl groups to form ester bonds, changing the molecular structure and reducing the viscosity.

[0065] Example two:

[0066] To distinguish this example from example one, three ceramic bearings identical to those in example one were used. The coatings were evenly applied to the ceramic bearings, and then the ceramic bearings with evenly applied coatings were placed in a high temperature furnace for sintering for 15 minutes, 20 minutes and 30 minutes respectively. The results are shown in Table 1.

[0067] Example Three:

[0068] To distinguish Example One and Example Two, one ceramic bearing same as Example One was used the same processing method as Example One but without the heat treatment step of Step Six, to get the insulating ceramic bearing, compared with the insulating ceramic bearing processed by the method in Example One, to get Table 2, in which the compactness detection is embodied by microhardness, the greater the microhardness, the better the compactness, the microhardness detection is detected by the same microhardness detection instrument on the insulating ceramic bearings of Example One and Example Two, the wear resistance detection is embodied by the wear depth, the deeper the wear depth, the worse the wear resistance.

[0069]

[0070] Table 1

[0071] Example one Example three Microhardness / MPa 865 534 Wear depth / μm 43 236

[0072] Table 2

[0073] Conclusion: From the data in Table 1 and Table 2, it can be concluded that the method in Example One can effectively improve the qualified rate, compactness and wear resistance.

[0074] Although the embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing a high purity alumina thermal spray powder for an insulated ceramic bearing, characterized by, The method comprises the following steps: Step 1: Selecting alumina powder with an average particle size of 1-50 microns, which can be prepared by chemical or physical methods to ensure its purity and particle size distribution meet the requirements; Step 2: Mixing the alumina powder prepared in Step 1 with a flow improver, which is an organic compound designed to improve the flowability of the alumina powder for spraying onto the ceramic bearing surface, the flow improver includes solvents, plasticizers, surfactants, polymer additives, and acid anhydrides, the solvents include but are not limited to acetone, dimethylformamide, methanol, ethanol, the plasticizers include phthalate plasticizers, the surfactants include but are not limited to nonionic, ionic and mixed surfactants, the polymer additives include but are not limited to polyvinyl ether and polypropylene ether, the acid anhydrides include phenolic anhydride; Step 3: Adding a binder to the mixed alumina powder in Step 2 and stirring with a stirring device, the binder is an organic resin used to bond the mixture to the surface after spraying; Step 4: Using a thermal spraying device to spray the mixed powder in Step 3 onto a preheated insulating ceramic bearing surface by delivering compressed air or gas to ensure uniform coverage and tight adhesion; Step 5: During the thermal spraying process in Step 4, a burner is used to provide fuel and cooperate with an oxidizing agent to generate a flame, the flame melts the powder and sprays it onto the bearing surface to form a uniform coating, the volume ratio of combustion gas to oxidizing agent is 1:1; Step 6: After the coating in Step 5 is formed, an additional heat treatment step is performed, which involves placing the coating in a high-temperature environment and sintering for 15-30 minutes to improve the coating's density, mechanical properties and wear resistance, thereby improving the performance of the insulating ceramic bearing; Step 7: After preparation, the coating has insulating properties suitable for the application of insulating ceramic bearings, this coating can improve the electrical insulation, wear resistance and corrosion resistance of the bearing, and effectively prolong the service life of the bearing.

2. The method of claim 1, wherein the high purity alumina thermal spray powder for insulating ceramic bearings is characterized by, The chemical method in Step 1 involves converting appropriate raw materials into alumina powder through chemical reactions, the specific steps are as follows: S1: Reacting aluminum source with alkaline solution to form aluminum hydroxide precipitate S2: Washing and filtering the precipitate to remove impurities; S3: Drying and calcining the aluminum hydroxide precipitate to convert it into alumina powder, the alumina powder at this time is generally high-purity alumina powder with a purity of 99.9% or higher.

3. The method of claim 2, wherein the high purity alumina thermal spray powder for insulating ceramic bearings is characterized by: The aluminum source is aluminate, such as aluminum nitrate or aluminum sulfate, the alkaline solution is sodium hydroxide, and the alumina powder prepared by the chemical method needs to be treated for waste liquid and waste gas to ensure the quality of the obtained powder.

4. The method of claim 1, wherein the high purity alumina thermal spray powder for insulating ceramic bearings is characterized by: The physical method in Step 1 involves converting raw materials into alumina powder through physical processes without involving chemical reactions, the specific steps are as follows: S1: First, high-purity aluminum metal or alumina powder is placed in a high-temperature furnace, then transported by gas flow; S2: At high temperature, the raw material undergoes physical changes and eventually forms alumina powder.

5. The method of claim 4, wherein the high purity alumina thermal spray powder for insulating ceramic bearings is characterized by: The gas is hydrogen or nitrogen, the physical method of preparing the alumina powder does not involve chemical reaction, thus no waste liquid and waste gas need to be treated.

6. The method of claim 1, wherein the high purity alumina thermal spray powder for insulating ceramic bearings is characterized by: The flowability improver in step two is tested at different binder concentrations, the optimal concentration of alumina powder is selected according to the test results, meanwhile, the adhesion strength test, hardness test and microstructure observation are conducted for each concentration of sample, and the amount of binder is further adjusted based on the test results until the desired coating performance is achieved, and the optimal amount of alumina powder is obtained.

7. The method of claim 1, wherein the high purity alumina thermal spray powder for insulating ceramic bearings is characterized by: The ratio of combustion gas and oxidant in step five is ensured to be uniform by mixing the combustion gas and oxidant together through a mixing device when they are supplied separately to the reactor, so as to achieve the required chemical reaction conditions, and during the chemical reaction process, the supply ratio of combustion gas and oxidant can be adjusted in time by monitoring and controlling the temperature, pressure, residual amount of oxidant and other parameters in the reactor, the gas phase composition or other key parameters in the reactor are measured by sensors, and these information are compared with the required ratio, thus the supply of combustion gas and oxidant is adjusted according to the feedback signals to maintain the required ratio.

8. The method of claim 1, wherein the high purity alumina thermal spray powder for insulating ceramic bearings is characterized by: The binder in step three is epoxy resin, which forms a solid structure after chemical reaction, physical cross-linking and thermal curing after mixing with alumina powder, providing good bonding performance.

9. The method of claim 1, wherein the high purity alumina thermal spray powder for insulating ceramic bearings is characterized by, The preheating method of the preheated surface of the insulating ceramic bearing in step four includes constant temperature furnace heating, infrared heating, laser heating and resistance heating.

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