A method for preparing ceramic hollow spheres applied to ceramic CBN grinding wheels

Abstract

A kind of ceramic hollow ball preparation method applied to ceramic CBN grinding wheel, comprising: carbon microspheres and resin type binder are mixed, and mixed with ceramic binder, mixed with organic release agent, sintering, in the sintering process, carbon microspheres, resin type binder, organic release agent are all carbonized, only ceramic binder after solidification is left to obtain ceramic hollow ball, the regularity of carbon microspheres shape and size and the uniformity of ceramic binder outside carbon microspheres have great influence on the quality of ceramic hollow ball obtained by sintering, in order to improve mixing efficiency and reduce the deformation probability of carbon microspheres, this paper adopts the mixing mode of planetary mixer, pressure vessel internal circulation and fluid mixing from the actual production, through the selection of size-stable carbon microspheres and low-cost organic release agent, ceramic hollow ball with stable quality can be prepared;The size stability and breakage rate of the hollow ball prepared by the method of the application are better than those of the market products, which can greatly improve the roughness stability of the surface of grinding wheel workpiece and effectively reduce the grinding wheel dressing frequency.

Description

Technical Field

[0001] This invention relates to the field of ceramic hollow sphere preparation technology, specifically a method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels. Background Technology

[0002] CBN grinding wheels are grinding wheels whose main component is cubic boron nitride (CBN). Under poorly cooled grinding conditions, the grinding heat cannot be carried away by the coolant from the grinding area in time, directly causing burns and discoloration of the workpiece surface, and even cracks, leading to workpiece scrap. In surface grinding, due to the large contact area, grinding debris cannot be discharged from the grinding area in time, repeatedly grinding within the grinding area, increasing the surface roughness of the workpiece or causing scratches, resulting in grinding defects. The workpiece cannot reach the desired state, leading to workpiece scrap.

[0003] Without solving the above problems, ceramic hollow spheres are usually used as common pore-forming fillers for ceramic CBN, mainly playing the roles of chip containment and cooling during the grinding process.

[0004] The existing state of the ceramic hollow spheres used in memory is as follows:

[0005] (1) The sphere is incomplete, open or solid. During the grinding wheel production process, the ceramic binder will fill the sphere, making the sphere a solid ceramic sphere. It cannot play the role of chip containment and cooling during the grinding process. In addition, the solid ceramic sphere has high hardness and will scratch the workpiece during the grinding process.

[0006] (2) The wall thickness is uneven and it is easy to break. During the mixing and molding process of grinding wheel production, the ball breaks and loses its original structure, making it unusable.

[0007] This invention proposes a method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, which solves some or all of the above-mentioned technical problems. Summary of the Invention

[0008] A method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, the specific steps of which are as follows:

[0009] S1: Mix and stir the carbon microspheres that meet the size range with the resin-based binder until homogeneous;

[0010] S2: Add the ceramic binder to the mixture from step S1 and continue mixing.

[0011] S3: Add the organic release agent to the mixture from step S2 and mix well to prevent adjacent mixtures from sticking together.

[0012] S4: Sinter the mixture prepared in step S3 to obtain hollow ceramic spheres.

[0013] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, the carbon microspheres are in a semi-dry state after being mixed with the resin-type binder in step S1, and the carbon microspheres have good fluidity.

[0014] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, the mixing method of carbon microspheres and resin-based binder in step S1 is as follows: carbon microspheres are placed in a certain proportion of resin-based binder and stirred evenly in a planetary mixer.

[0015] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, the mixing method of carbon microspheres and resin-type binder in step S1 is as follows: carbon microspheres are placed into a pressure vessel with a pressure of P1, and the circulating air inside the pressure vessel is turned on. The resin-type binder is added to an atomizer with the outlet end of the atomizer extending into the pressure vessel. The atomized resin-type binder is then rapidly injected into the pressure vessel at a pressure greater than P1, where P1>P0, and P0 is standard atmospheric pressure.

[0016] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, the mixing method of carbon microspheres and resin-based binder in step S1 adopts a fluid mixing method, and the specific steps are as follows: Figure 3 As shown, carbon microspheres and resin-based binders are conveyed through pipelines in a predetermined ratio. The carbon microspheres are conveyed through pipeline A1, while the resin-based binder is fed through an atomizer located within pipeline A2. Pipeline A3 is located downstream of pipeline A in the flow direction. Pipelines A1, A2, and A3 are all connected to pipeline A. Positive pressure gas is introduced into pipeline A3. As the positive pressure gas flows downstream along pipeline A, it creates negative pressure upstream of the flow direction of pipeline A. The atomized droplets of the resin-based binder and the carbon microspheres flow along pipeline A under the influence of this negative pressure, completing the mixing process. This mixing method avoids the problem of poor initial mixing between the carbon microspheres and the resin-based binder. Relying solely on mechanical stirring not only significantly prolongs the stirring cycle but, in more severe cases, can cause damage and deformation of the carbon microspheres, directly affecting the final molding quality of the hollow ceramic spheres. It is important to further emphasize that in cases of poor initial mixing, subsequent mechanical stirring alone cannot meet the high mixing requirements.

[0017] The mixing of the ceramic binder in step S2 and the organic release agent in step S3 can be carried out using the above-mentioned fluid mixing method or by using a planetary mixer.

[0018] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, the gas flow rate in pipe A3 remains constant; or, the gas flow rate in pipe A3 switches between V1 and V2, with V2 > V1.

[0019] Optionally, when the positive pressure of the gas in pipe A3 switches between V1 and V2, the feeding of carbon microspheres and resin binder stops. By intermittently switching the flow rate of the positive pressure gas in pipe A3, the carbon microspheres with resin binder can be flushed by the sudden change in gas flow rate while being mixed, thus preventing the carbon microspheres from adhering to the pipe surface. If high efficiency is required, feeding can continue while flushing with airflow.

[0020] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, a non-straight pipe length section (bending section, curved section, spiral section) is provided behind the flow direction of pipe A. By providing a non-straight pipe length section, the fluid mixing uniformity can be locally improved.

[0021] Preferably, in the method for preparing a ceramic hollow sphere for use in ceramic CBN grinding wheels, the A3 pipe is located in front of the non-straight pipe length segment.

[0022] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, the resin-type binder is epoxy resin, phenolic resin, or phenolic epoxy resin.

[0023] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, the organic separator includes starch or polyethylene powder.

[0024] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, the ceramic binder comprises one or more of borosilicate glass, feldspar, nepheline powder, clay, lithium carbonate, and chromium trioxide.

[0025] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, the amount of ceramic binder is precisely calculated based on the inner and outer diameters of the ceramic hollow spheres, ensuring that both the amount of ceramic binder and organic release agent are in excess. This ensures that the surface of the carbon microspheres is covered with a uniformly distributed ceramic binder, and that there is sufficient organic release agent between adjacent carbon microsphere intermediates to prevent them from sticking together.

[0026] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, after the organic release agent is uniformly coated on the outer surface of the carbon microsphere intermediate body in step S3, the mixed carbon microspheres are poured in, and excess ceramic binder and excess organic release agent are sieved out.

[0027] Preferably, in the method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, step S2 is performed in environment P4; or, compaction treatment is performed in environment P4 between steps S2 and S3, where P4 > P0. After the mixture in step S2 is compacted in a positive pressure environment, it is beneficial for the ceramic binder to be compacted on the surface of the carbon microspheres, which helps to improve the forming hardness and regularity of the ceramic hollow spheres. The compaction step cannot be set after S3, otherwise the mechanical release agent components will penetrate into the ceramic binder layer, and the surface quality of the sintered ceramic hollow spheres will be unstable.

[0028] Preferably, in the method for preparing ceramic hollow spheres for ceramic CBN grinding wheels, different sintering temperatures are applied to different ceramic binders in step S4. This is mainly to ensure that all raw materials except the ceramic binder are burned and carbonized during the sintering process, leaving a solidified ceramic shell.

[0029] This invention utilizes dimensionally stable and regularly shaped carbon microspheres as the core support structure for the fabrication of hollow ceramic spheres. A resin-based binder and a ceramic binder are sequentially and uniformly coated onto the surface of the carbon microspheres. An organic release agent is used to prevent adhesion. The carbon microspheres and organic release agent are then carbonized into ash through sintering, and the ceramic binder solidifies, ultimately yielding hollow ceramic spheres with stable dimensions and regular shapes. This invention emphasizes the uniformity of the resin-based binder coating on the carbon microsphere surface. By providing multiple selectable mixing methods, a specific mixing method can be chosen based on requirements for high work efficiency and the desired quality level of the hollow ceramic spheres, meeting various practical needs. Furthermore, the ceramic hollow spheres produced in this invention have low material costs and low manufacturing costs. Attached Figure Description

[0030] The specific embodiments are further described below with reference to the accompanying drawings, wherein:

[0031] Figure 1 This is the arrangement of carbon microspheres after mixing before sintering, as described in Specific Implementation Example 1 of this invention;

[0032] Figure 2 The ceramic hollow sphere (including the overall and cross-sectional views) is prepared according to the method described in Specific Embodiment 1 of this invention.

[0033] Figure 3 This is a simplified schematic diagram of the mixing device in specific embodiment 4 of the present invention;

[0034] Figure 4 This is a simplified schematic diagram of the mixing device in specific embodiment 4 of the present invention;

[0035] The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0036] Specific implementation case 1:

[0037] Materials: 200g 100-120 mesh carbon microspheres, 400g ceramic binder, 4g epoxy resin, 300g flour.

[0038] Tools and equipment: 120 / 140 mesh sieve, 80 / 100 mesh sieve, 60 / 70 mesh sieve, 10 sheets of 200*200 aluminum foil, 10 sheets of 220*220*10 mullite slabs, 36 10*10*10 mullite blocks, mixing equipment, sintering furnace.

[0039] Production steps:

[0040] S1. Mix 200g of 100-120 mesh carbon microspheres and epoxy resin using a mixing device;

[0041] S2. Add 400 grams of ceramic binder to the mixing equipment and continue mixing;

[0042] S3. Add 300 grams of flour to the mixing equipment and continue mixing to prevent the mixture from sticking together.

[0043] S4. Pour the mixed carbon microspheres onto a 120 / 140 mesh sieve to remove excess ceramic binder and flour. The added ceramic binder and flour are in excess to ensure the quality of the final hollow ceramic spheres.

[0044] Place the aluminum foil flat on the mullite slab, and then evenly spread the mixed carbon microspheres (after removing excess ceramic binder and flour) on the aluminum foil.

[0045] Separate the mullite slabs with mullite blocks and stack them up in order (e.g., ...). Figure 1 (As shown).

[0046] The mullite slab was placed in a sintering furnace for sintering at 800℃ for 8 hours. During the sintering process, the epoxy resin, flour and carbon microspheres carbonized into ash at 400℃, the ceramic binder began to soften at 600℃, and the ceramic binder solidified into a hollow sphere between the carbon microspheres and flour at 800℃.

[0047] The sintered object is placed on a lower 80 / 100 mesh sieve and an upper 60 / 70 mesh sieve for sieving.

[0048] Those retained on the 80 / 100 mesh sieve are ceramic perforated balls (such as...). Figure 2 (As shown).

[0049] The size and weight of the carbon microspheres involved in this specific implementation case, as well as the amount of ceramic binder, epoxy resin, flour, and sintering temperature, should not be regarded as a limitation on the scope of protection. The specific selection can be made according to the required size of the hollow ceramic spheres and the performance parameters of the resin-type binder, ceramic binder, and organic release agent.

[0050] The mixing equipment in Specific Implementation Case 1 can be any one of Specific Implementation Cases 2 to 4, or other mixing methods in the prior art can also be used.

[0051] Specific Implementation Case 2:

[0052] In specific implementation case 1, the mixing equipment is a planetary mixer (Germany EKA Eurostar 60 Di gita l planetary mixer). In step S1, carbon microspheres and resin binder are mixed in the planetary mixer for 3 minutes. In step S2, ceramic binder is added to the planetary mixer and mixed for 3 minutes. In step S3, flour is added to the planetary mixer and mixed for 3 minutes.

[0053] Specific Implementation Case 3:

[0054] In specific implementation case 1, the mixing equipment is a pressure vessel (pressure tank 0.6 cubic meters / 8 kg). In step S1, carbon microspheres are put into the pressure vessel, and the internal circulation air of the pressure vessel is turned on. Epoxy resin is injected into the pressure vessel through an atomizer and mixed for 5 minutes. In step S2, ceramic binder is introduced into the pressure vessel and mixed for 5 minutes. In step S3, flour is added into the pressure vessel and mixed for another 5 minutes. The pressure relief valve is opened, and the mixed material is flushed out of the pressure vessel.

[0055] Specific Implementation Case 4:

[0056] The mixing equipment in Specific Implementation Case 1 is as follows: Figure 3As shown, carbon microspheres and epoxy resin of uniform size are placed in their respective storage tanks, and carbon microspheres are quantitatively fed into pipe A1 and epoxy resin into pipe A2 (quantitative feeding of particles and liquids is existing technology and will not be described in detail here). The epoxy resin is atomized by an atomizer, and positive pressure gas is introduced into pipe A3. The gas flow rate is any value between 5 m / s and 20 m / s. In this specific implementation, the airflow velocity in pipe A3 is 7 m / s and 15 m / s respectively (other data can also be used, such as 10 m / s and 20 m / s. The specific airflow velocity can be set within a reasonable range. This is not a limitation on the airflow velocity, but only an example). The two airflow velocities are alternated. The 15 m / s blowing velocity can flush the carbon microspheres with airflow to ensure smooth airflow in the pipe. The positive pressure gas in pipe A3 creates a negative pressure suction in pipe A, which simultaneously transports and mixes the carbon microspheres and epoxy resin atomized droplets, achieving fluid mixing without mechanical stirring equipment. This ensures the initial mixing degree of the carbon microspheres and epoxy resin, and further improves the mixing degree during fluid transport. At the same time, it greatly shortens the mixing time, avoids carbon microsphere deformation, and improves the quality stability of hollow ceramic balls.

[0057] In step S2, the ceramic binder is mixed in the same way as described above, and the starch is mixed using a planetary mixer. Since the uniform coating of epoxy resin binder on the surface of carbon microspheres in S1 directly affects the mixing effect of ceramic binder and starch in the later stage, the mixing result in step S1 is quite critical.

[0058] The data obtained from the experiments of grinding wheels for connecting rod end faces using the ceramic hollow spheres prepared in specific implementation cases 2-4 are shown in the table below:

[0059]

[0060] The data in the table above shows that when ordinary ceramic hollow spheres are added to workpieces processed with commercially available materials, the surface roughness of the grinding wheel decreases sharply with the increase in the number of workpieces processed, and dressing is required after processing 5000 workpieces. However, when ceramic hollow spheres produced using the methods in embodiments 2-4 of this invention are used, the surface roughness of the grinding wheel decreases significantly with the increase in the number of workpieces processed, and the frequency of dressing is significantly reduced. Comparing the ceramic hollow spheres produced in embodiments 2-4 separately, the ceramic hollow spheres obtained by different mixing methods (planetary mixer, pressure vessel, and fluid mixing) have significantly different effects on the surface roughness when applied to grinding wheel workpieces. Based on this, the morphology of the ceramic hollow spheres observed after image magnification is shown in the table below:

[0061]

[0062] As shown in the table above, the pass rate of the outer diameter of ceramic hollow spheres produced by different mixing methods—planetary mixers, pressure vessels, and fluid mixing—gradually increases. This is mainly because the direct mixing of carbon microspheres and epoxy resin during the planetary mixer process cannot ensure uniform epoxy resin adhesion to the surface of each carbon microsphere. Further observation of the regularity of the ceramic hollow spheres reveals that the regularity of the hollow spheres produced by the planetary mixer is relatively low. This is presumably because the prolonged contact mixing process causes some carbon microspheres to undergo shape compression changes. In contrast, the mixing methods of pressure vessels and fluid mixing not only improve the uniformity of epoxy resin distribution on the surface of the carbon microspheres but also prevent deformation of the carbon microspheres during mixing. Even so, due to the simplicity of planetary mixing and its low production cost, it is highly practical in many fields. The specific mixing method can be selected according to actual needs.

[0063] Specific Implementation Case 5:

[0064] Based on the specific implementation case 4

[0065] Optionally, when the airflow speed alternates, i.e., during the process of increasing the airflow speed from 7m / s to 15m / s, the transmission of carbon microspheres and epoxy resin is suspended, and when the airflow speed returns to 7m / s, the transmission of carbon microspheres and epoxy resin continues.

[0066] Optionally, a straight pipe section (e.g., [missing information]) can be installed behind pipe A in the direction of flow. Figure 3 The aforementioned), the length section of the corrugated pipe ( Figure 4 The aforementioned section can also be a spiral pipe length segment. By setting a non-linear pipe length segment, the fluid mixing uniformity can be locally improved.

[0067] Specific Implementation Case 6:

[0068] Based on Specific Implementation Case 1, after the mixing in step S2 is completed, the mixture is placed in a pressure vessel and the ceramic binder is compacted by positive pressure. The pressure during the compaction process is 2P0, 1.5P0, or 3P0.

[0069] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels, characterized in that: The steps are as follows: S1: Mix and stir the carbon microspheres and resin-based binder until homogeneous. The mixing of carbon microspheres and resin-based binder adopts a fluid mixing method. The specific steps are as follows: carbon microspheres and resin-based binder are conveyed through different pipes according to a set ratio. The carbon microspheres are conveyed through pipe A1, and the resin-based binder is fed through an atomizer and pressed into pipe A2. Pipe A3 is located behind the flow direction of pipe A. Pipes A1, A2, and A3 are all connected to pipe A. Gas is introduced into pipe A3. As the gas in pipe A3 flows backward along pipe A, it will form a negative pressure in front of the flow direction of pipe A. The atomized droplets of resin-based binder and carbon microspheres flow along pipe A under the guidance of negative pressure, and the mixing is completed during the flow. After the carbon microspheres are mixed with the resin-based binder, the surface is in a semi-dry state. S2: Add the ceramic binder to the mixture from step S1 and continue mixing. S3: Add the organic release agent to the mixture from step S2 and mix well to prevent adjacent mixtures from sticking together. S4: Sinter the mixture prepared in step S3 to obtain hollow ceramic spheres.

2. The method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels as described in claim 1, characterized in that: The gas flow rate in pipe A3 remains constant, or the gas flow rate in pipe A3 is set to V1 and V2, with V2 > V1.

3. The method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels as described in claim 2, characterized in that: The gas flow rate in pipe A3 is set to V1 and V2. When the gas flow rate in pipe A3 is switched, the carbon microspheres and resin binder stop feeding.

4. The method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels as described in claim 1, characterized in that: A non-linear pipe section is provided behind the flow direction of pipe A, and the connection point between pipe A3 and pipe A is located in front of the non-linear pipe section.

5. The method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels as described in claim 1, characterized in that: The resin-type adhesive is epoxy resin, phenolic resin, or phenolic epoxy resin; the organic release agent includes starch or polyethylene powder.

6. The method for preparing ceramic hollow spheres for use in ceramic CBN grinding wheels as described in claim 1, characterized in that: Step S2 is performed in environment P2; or, between steps S2 and S3, compaction is performed in environment P2, where P2 > P0.

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