A method for preparing CBN grinding wheels

Abstract

This invention provides a method for preparing a CBN grinding wheel, comprising the following steps: melting the raw materials of a ceramic binder, quenching them in water, and then crushing them to obtain a ceramic binder; impregnating the CBN grinding wheel metal matrix in a CBN grinding wheel impregnation slurry, drying and curing it to obtain a CBN grinding wheel blank; sintering the CBN grinding wheel blank and then machining it to obtain the final product; the raw materials of the ceramic binder, by weight percentage, include 10-15% boric acid, 5-6% lithium carbonate, 30-49% silicon dioxide, 28-40% bismuth oxide, 2-3% calcium fluoride, 2-3% nickel oxide, 2-3% cobalt oxide, and 2-3% titanium oxide; the CBN grinding wheel impregnation slurry, by weight percentage, includes 40-45% CBN abrasive, 10-15% the ceramic binder, 33-36% ethanol, 8-10% alcohol-soluble phenolic resin, and 0.5-1% silane coupling agent.

Description

Technical Field

[0001] This invention relates to a method for preparing a small-diameter internal grinding ceramic-bonded cubic boron nitride (CBN) grinding wheel, belonging to the field of grinding. Background Technology

[0002] Currently, the ferrous metal parts processing industry frequently requires grinding small-sized internal holes, such as the inner holes of miniature bearings, optical molds, and miniature compressor end caps. Currently, these parts are generally machined using electroplated CBN grinding wheels. Electroplated grinding wheels can be manufactured by electroplating and bonding CBN abrasive directly to the surface of the grinding wheel substrate using an electroplated metal as a binder, forming a metal / CBN abrasive working layer. This process can easily produce CBN grinding wheels with diameters less than 15mm and arbitrary heights. However, the working layer of this process is very thin, consisting of only one layer of CBN abrasive, resulting in a short service life. For example, when machining the inner hole of a 5mm diameter miniature bearing, a single electroplated grinding wheel can only process 30-50 parts.

[0003] Ceramic-bonded cubic boron nitride (CBN) grinding wheels offer advantages such as high grinding efficiency, low grinding force, good dimensional retention, high grinding precision, and long service life. They are currently widely used in the forming and precision grinding of metal materials such as cast iron, mold steel, high-speed steel, high-alloy steel, and bearing steel, and are considered the ideal tool for grinding ferrous metals. However, current CBN grinding wheels are produced using a dry-pressing and pressureless sintering process. When using this process to form internal grinding wheels with small diameters and large heights (diameter less than 15mm, wheel height to diameter ratio greater than 3), the CBN abrasive generates significant friction with the forming steel mold during dry pressing, resulting in a grinding wheel with high density at both ends and low density in the middle. This uneven density leads to uneven wear during internal grinding, with less wear in the high-density areas and more wear in the low-density areas. This uneven wear significantly affects the machining accuracy of CBN grinding wheels. Therefore, providing a method for preparing ceramic-bonded CBN grinding wheels with small diameter and large height has become an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing small-diameter internal grinding CBN wheels using a ceramic binder. This method employs an impregnation-slurry method to prepare small-diameter internal grinding CBN wheels. This method can prepare internal grinding wheels of any diameter, and in particular, it can produce high-quality small-diameter, high-height internal grinding CBN wheels. The working layer thickness of these wheels can reach over 1 mm, and the wheel density and microstructure are uniform, enabling high-precision grinding of the internal holes of ferrous metal parts.

[0005] Specifically, the present invention is achieved through the following technical solution:

[0006] A method for preparing a CBN grinding wheel includes the following steps:

[0007] The raw materials for ceramic binder are melted, quenched in water, and then crushed to obtain the ceramic binder.

[0008] The CBN grinding wheel metal substrate is impregnated in CBN grinding wheel impregnation slurry, dried and cured to obtain a CBN grinding wheel blank; the CBN grinding wheel blank is then sintered and machined to the required dimensions.

[0009] The raw materials of the ceramic binder, by weight percentage, include 10-15% boric acid, 5-6% lithium carbonate, 30-49% silicon dioxide, 28-40% bismuth oxide, 2-3% calcium fluoride, 2-3% nickel oxide, 2-3% cobalt oxide, and 2-3% titanium oxide.

[0010] The CBN grinding wheel impregnation slurry comprises, by weight percentage, 40-45% CBN abrasive, 10-15% ceramic binder, 33-36% ethanol, 8-10% alcohol-soluble phenolic resin, and 0.5-1% silane coupling agent.

[0011] The method for preparing the CBN grinding wheel includes the step of ball milling and mixing the raw materials of the ceramic binder;

[0012] The mass ratio of balls to material in the ball mill mixture is 1.2:1;

[0013] The ball milling mixing process uses corundum ceramic balls;

[0014] Of the corundum ceramic spheres, 30% are corundum spheres with a diameter of 10mm and 70% are corundum spheres with a diameter of less than 10mm.

[0015] The rotational speed of the ball mill mixing is 360 r / min;

[0016] The ball milling mixing speed is 60 r / min;

[0017] The ball milling mixing time is 1-2 hours.

[0018] The melting temperature is 1250-1300℃;

[0019] The heating rate for the melting process is 3-5℃ / min;

[0020] The holding time for the smelting process is 1-2 hours.

[0021] The crushing method is ball milling.

[0022] The grinding balls used in the ball milling process are zirconia grinding balls;

[0023] The ball-to-material mass ratio for ball milling is 1.2:1;

[0024] The zirconia grinding balls comprise 30% zirconia balls with a diameter of 50 mm, 40% zirconia balls with a diameter between 20 and 50 mm, and 30% zirconia balls with a diameter less than 20 mm.

[0025] The rotational speed of the ball mill crusher is 300 r / min;

[0026] The ball mill crushing time is 24 hours.

[0027] After the raw materials for ceramic binders are melted, quenched in water, and crushed, the process also includes grinding and drying steps.

[0028] The grinding process includes a ball milling step using grinding balls;

[0029] The grinding process uses a ball-to-material mass ratio of 1.2:1.

[0030] The grinding balls used in the process consist of 50% corundum balls with a diameter of 20 mm and 50% corundum balls with a diameter of less than 20 mm; the rotation speed used in the grinding process is 300 r / min.

[0031] The drying process includes the steps of passing the material through a 320# sieve and then drying it in a drying tower.

[0032] The preparation method of the CBN grinding wheel impregnation slurry includes the following steps:

[0033] Ethanol and a silane coupling agent are mixed and then added to the CBN abrasive and the ceramic binder and stirred and mixed. Then, alcohol-soluble phenolic resin is added and stirred and mixed. The silane coupling agent includes KH560.

[0034] The material of the CBN grinding wheel metal matrix includes H13 steel;

[0035] The impregnation includes a pretreatment step of the CBN grinding wheel metal substrate;

[0036] The pretreatment includes soaking in 1 wt% dilute hydrochloric acid for 0.5-1 minute, washing and drying, followed by soaking in acetone for 10-15 minutes and drying.

[0037] The curing temperature is 100-120℃;

[0038] The curing time is 4-6 hours.

[0039] The sintering process includes heating to 400-450°C at a rate of 2-3°C / min, holding at that temperature for 1-2 hours, and then heating to 600-650°C at a rate of 2-4°C / min, holding at that temperature for 1-1.5 hours.

[0040] A CBN grinding wheel prepared by the aforementioned method.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] The method provided by this invention first prepares a special ceramic binder through a melting method. Then, the binder is mixed with CBN abrasive and related additives to prepare an impregnation slurry. The working layer of the ceramic-bonded CBN grinding wheel is formed using the impregnation slurry method, followed by sintering and subsequent processing to obtain the ceramic-bonded CBN grinding wheel. Compared with the traditional dry pressing method for preparing ceramic-bonded CBN grinding wheels, this method can produce small-sized, high-height CBN internal hole grinding wheels. After sintering, the binder exhibits good bonding to the CBN abrasive, resulting in a uniform microstructure. Simultaneously, during the sintering process, the molten binder forms good wetting and bonding with the metal substrate surface, firmly adhering the CBN grinding wheel working layer to the metal substrate surface. Compared with CBN grinding wheels prepared by electroplating, the working layer thickness of the CBN grinding wheel prepared by this invention can exceed 1 mm. When grinding the inner hole of a cast iron compressor end cover with a diameter of 14mm, the grinding wheel operates at a speed of 20,000 rpm, the cooling medium is water, and the roundness error of the parts machined by the 140 / 170 grit electroplated CBN grinding wheel is 3.31μm, the cylindricity error is 2.11μm, and the service life is 182 parts. The parts machined by the 140 / 170 grit ceramic-bonded CBN grinding wheel prepared by the process of this invention have a roundness error of 3.02μm, a cylindricity error of 1.84μm, and a service life of 890 parts.

[0043] In summary, under the same process parameters, the ceramic-bonded CBN grinding wheel prepared by this invention has slightly better processing accuracy than the electroplated CBN grinding wheel with the same grit size, and its service life is more than 4.5 times longer than that of the electroplated grinding wheel. Attached Figure Description

[0044] Figure 1 The diagram shows the contact angle of the ceramic binder with an H13 steel substrate prepared in Example 1 and Comparative Example 2. Figure 1 Image a shows the contact angles of the binder samples of Comparative Example 2 (without nickel oxide and cobalt oxide) and the 1H13 steel substrate after sintering at 650°C for 1 hour. The image indicates that the contact angle between the binder sample without nickel oxide and cobalt oxide and the H13 steel substrate after sintering at 650°C for 1 hour is 68 degrees. Figure 1b shows that the contact angle between the binder sample of Example 1, containing 2 wt% nickel oxide and 2 wt% cobalt oxide, and an H13 steel substrate was 37 degrees after sintering at 650°C for 1 h. From Figure 1 It can be seen that the addition of nickel oxide and cobalt oxide can improve the wettability of the molten binder on the H13 steel substrate at the sintering temperature.

[0045] Figure 2 XPS analysis of titanium in the sample after sintering at 650°C for 1 h with a binder sample containing 3 wt% titanium oxide in Example 1 and CBN abrasive was shown. Figure 2 This indicates that the titanium oxide added to the binder sample will form Ti-B bonds with the boron elements on the surface of the CBN abrasive after sintering at 650℃ for 1 hour.

[0046] Figure 3 The wetting of the CBN abrasive by the binder after mixing with CBN abrasive samples containing 3 wt% titanium oxide and binder samples without titanium oxide in Examples 1 and 2 and sintering at 650°C for 1 h is shown. Figure 3 a indicates that after the binder sample without titanium oxide was mixed with CBN abrasive and sintered at 650℃ for 1 hour, no climbing phenomenon of binder was observed on the surface of CBN abrasive, indicating that the binder had poor wettability to CBN abrasive. Figure 3 b indicates that after the binder sample containing 3wt% titanium oxide was mixed with CBN abrasive and sintered at 650℃ for 1h, the binder exhibited a significant climbing phenomenon on the surface of the CBN abrasive, indicating that the binder had good wettability on the CBN abrasive.

[0047] Figure 4 The macroscopic morphology of the ceramic-bonded CBN grinding wheel prepared in Example 1 is shown (grind wheel diameter 10.5 mm, working layer height 35 mm). Figure 4 This indicates that the process of the present invention can produce ceramic-bonded CBN grinding wheels with small diameter and large working layer height (diameter less than 15 mm, grinding wheel height to diameter ratio greater than 3).

[0048] Figure 5 The image shows the microstructure of the working layer of the ceramic-bonded CBN grinding wheel prepared in Example 1. The image indicates that the ceramic binder and CBN abrasive have good bonding in the sintered ceramic-bonded CBN grinding wheel.

[0049] Figure 6 The image shows the microstructure of the ceramic-bonded CBN grinding wheel working layer prepared in Example 2. The image indicates that the microstructure of the CBN grinding wheel working layer is uniform after sintering.

[0050] Figure 7The image shows the microstructure at the interface between the CBN grinding wheel working layer prepared in Example 2 and the H13 metal matrix. The image indicates that the interface between the CBN grinding wheel working layer and the H13 metal matrix is ​​dense and has good adhesion after sintering.

[0051] Figure 8 The end face morphology of the ceramic-bonded CBN grinding wheel prepared in Example 1 is shown (grind wheel diameter 10.5 mm, working layer height 35 mm, working layer thickness 2 mm). The image shows that the working layer thickness of the CBN grinding wheel prepared by this invention can exceed 1 mm.

[0052] Figure 9 The test diagrams of roundness and cylindricity errors of bearing end cap parts machined by electroplated CBN grinding wheels with a grit size of 140 / 170 are shown as a comparison with Example 1. Figure 9 The results show that the roundness error of the bearing end cap part machined by the electroplated CBN grinding wheel with a particle size of 140 / 170 is 3.31μm and the cylindricity error is 2.11μm.

[0053] Figure 10 The images show test results for the roundness and cylindricity errors of the bearing end cap part machined by the CBN grinding wheel prepared in Example 1. The images show that the roundness error of the bearing end cap part machined by the CBN grinding wheel prepared in Example 1 is 3.02 μm, and the cylindricity error is 1.84 μm. Detailed Implementation

[0054] The present invention will be further described below with reference to the embodiments.

[0055] This invention provides a method for preparing a small-diameter internal grinding wheel with ceramic bond CBN, comprising the following steps:

[0056] (1) Preparation of ceramic binder:

[0057] (a) The weight percentage formulation of the binder is as follows:

[0058] Boric acid (chemically pure) 10-15%, lithium carbonate (chemically pure) 5-6%, silicon dioxide (chemically pure) 30-49%, bismuth oxide (chemically pure) 28-40%, calcium fluoride (chemically pure) 2-3%, nickel oxide (chemically pure) 2-3%, cobalt oxide (chemically pure) 2-3%, and titanium oxide (chemically pure) 2-3%.

[0059] The weighed raw materials are poured into a planetary mixer. The corundum mixing jar has a diameter of 300 mm. Corundum ceramic balls are added at a ball-to-material mass ratio of 1.2:1, with 30% of the balls being 10 mm in diameter and 70% being smaller than 10 mm in diameter. The mixing jar rotates at 360 r / min and revolves at 60 r / min. After mixing the raw materials for 1-2 hours, the mixture is removed to obtain the binder smelting raw material.

[0060] (b) Melting and crushing of the binder

[0061] Heat the crucible furnace to 1250-1300℃ at a rate of 3-5℃ / min, plug the furnace with a stopper, and pour in the mixed raw material powder, filling the crucible to 2 / 3-4 / 5 of its volume. Place a heat-resistant steel trough filled with water at the furnace outlet. When the furnace temperature reaches 1250℃, hold it at that temperature for 1-2 hours, then lift the stopper to allow the molten binder to flow into the water for water quenching.

[0062] Collect the water-quenched ceramic binder fragments and pour them into the corundum grinding jar of a horizontal ball mill (400mm diameter). Add water of equal weight to the binder, and add zirconia grinding balls at a ball-to-material mass ratio of 1.2:1. 30% of the zirconia balls are 50mm in diameter, 40% are 20-50mm in diameter, and 30% are less than 20mm in diameter. The grinding jar rotates at 300 rpm. After grinding the raw material for 24 hours, pour the slurry into a receiving tray.

[0063] (c) Drying and sieving of the binder

[0064] The slurry is dried at 100-110℃. After it is completely dry, the material is scooped up with a plastic shovel and poured into the corundum ball mill jar of a horizontal ball mill (400mm diameter). Zirconia grinding balls are added at a ball-to-material mass ratio of 1.2:1, with 50% of the balls being 20mm in diameter and the other 50% being smaller than 20mm. The ball mill jar rotates at 300 rpm. After milling for 4-6 hours, the powder is poured out and passed through a 320# sieve. The sieved binder is then sealed in a bag and placed in a drying tower for later use.

[0065] (2) Preparation of CBN grinding wheel impregnation slurry

[0066] CBN grinding wheel impregnation slurry composition by weight percentage:

[0067] The composition includes 40-45% CBN abrasive, 10-15% ceramic binder, 33-36% anhydrous ethanol, 8-10% alcohol-soluble phenolic resin, and 0.5-1% silane coupling agent KH560.

[0068] First, measure an appropriate volume of anhydrous ethanol, then add silane coupling agent KH560 in proportion, stir at high speed for 10-20 minutes at a stirring speed of 3000-5000 rpm, then add CBN abrasive and ceramic binder in weight ratio, and stir at 2000 rpm for 0.5-1 hour; then add alcohol-soluble phenolic resin in proportion, and stir at 2000 rpm for 0.5-1 hour to obtain a highly dispersible CBN grinding wheel impregnation slurry.

[0069] (3) CBN grinding wheel matrix treatment

[0070] According to the dimensional drawings of the CBN grinding wheel substrate, the blank made of H13 steel is machined into the CBN grinding wheel substrate. The machined grinding wheel substrate is then soaked in 1wt% dilute hydrochloric acid for 0.5-1 minute, then removed and rinsed with clean water. After drying at room temperature, the substrate is then soaked in anhydrous acetone for 10-15 minutes, removed, and dried at room temperature. This completes the CBN grinding wheel substrate treatment.

[0071] (4) Impregnation treatment of CBN grinding wheels

[0072] According to the position and height of the CBN grinding wheel working layer, the designated position of the CBN grinding wheel metal substrate treated in step (3) is immersed in the CBN grinding wheel impregnation slurry prepared in step (2). After the designated position of the grinding wheel substrate is immersed in the impregnation slurry for 1-2 minutes, it is taken out. The grinding wheel substrate after impregnation is hung to dry at room temperature, and then placed in an oven to cure at 100-120 degrees for 4-6 hours. After that, it is cooled with the oven to obtain the CBN grinding wheel blank.

[0073] (5) Sintering of ceramic-bonded CBN grinding wheels

[0074] The CBN grinding wheel blank is placed in a pit furnace and heated to 400-450℃ at a heating rate of 2-3℃ / min, and held for 1-2 hours. Then, the temperature is increased to 600-650℃ at a heating rate of 2-4℃ / min and held for 1-1.5 hours. After the furnace is closed, the CBN grinding wheel is allowed to cool naturally in the electric furnace. When the furnace temperature is below 70℃, the CBN grinding wheel blank is removed from the furnace to obtain the sintered ceramic-bonded CBN grinding wheel blank.

[0075] (6) Machining of sintered ceramic-bonded CBN grinding wheel blanks

[0076] The sintered ceramic bond CBN grinding wheel blank is clamped on a universal tool grinder. According to the dimensions of the ceramic bond CBN on the drawing, the outer circle and end face of the CBN grinding wheel are ground with an electroplated diamond grinding wheel. After the dimensions are qualified, the finished ceramic bond CBN grinding wheel is obtained.

[0077] The present invention will be further explained below:

[0078] (1) Preparation of binder

[0079] After the raw materials of the binder are mixed evenly, a molten glassy substance is formed after melting at 1250℃. Boric acid is transformed into boron trioxide, and lithium carbonate is transformed into lithium oxide. Lithium oxide provides "free oxygen" to boron trioxide and bismuth trioxide, causing boron trioxide to transform from a layered structure to a boron-oxygen tetrahedral structure, and bismuth trioxide to transform from an octahedral structure to a bismuth-oxygen tetrahedral structure. The boron-oxygen tetrahedra, bismuth-oxygen tetrahedra, and silicon-oxygen tetrahedra formed by molten silicon dioxide are connected through the atoms at the tetrahedral endpoints, forming a three-dimensional spatial network structure of the binder. This three-dimensional network structure gives the binder better mechanical properties and chemical stability. The addition of lithium carbonate and bismuth oxide also significantly reduces the melting temperature and softening point of the binder, allowing the binder powder after grinding wheel preparation to be sintered at 600-650℃. Calcium fluoride provides F- to the binder; at some sites in the three-dimensional network structure of the binder, F- replaces oxygen (O). 2- Adding small amounts of nickel oxide and cobalt oxide to the binder reduces the integrity of the three-dimensional network structure, lowers the viscosity and surface tension of the binder at the sintering temperature, and promotes the wettability of the binder to the CBN abrasive and H13 steel matrix at the sintering temperature. When a small amount of nickel oxide and cobalt oxide are added to the binder, the nickel and cobalt ions fill the voids in the three-dimensional network structure after the binder melts. When the grinding wheel prepared using this binder is sintered at 600-650℃, the binder becomes a molten viscous fluid. Because the voids in the three-dimensional network of the binder are filled with a certain amount of nickel and cobalt ions, whose ionic radii are close to those of iron atoms in the H13 steel matrix, they can easily undergo a displacement reaction. Some iron atoms on the surface of the H13 steel grinding wheel metal matrix become Fe ions, replacing the nickel and cobalt ions and entering the three-dimensional network of the molten binder, thus improving the wettability and adhesion strength between the binder and the H13 steel grinding wheel metal matrix. When a small amount of TiO2 is added to the binder, TiO2 participates in the three-dimensional network formation of the binder in the form of titanium-oxygen tetrahedra during the binder melting process. After the binder is made into a CBN grinding wheel, at the sintering temperature of the CBN grinding wheel, the boron-rich layer on the surface of the CBN abrasive begins to diffuse into the binder through the interface, forming Ti-B chemical bonds with the titanium ions enriched at the interface. Therefore, adding a small amount of TiO2 to the binder can significantly improve the wettability between the ceramic binder and CBN. The binder is melted, water-quenched, and crushed to obtain a binder slurry. After drying, the slurry is ball-milled and crushed through a 320# sieve to obtain binder powder with a particle size of less than 50 micrometers.

[0080] (2) Preparation of CBN grinding wheel impregnation slurry

[0081] In the CBN abrasive wheel impregnation slurry, anhydrous ethanol serves as the dispersion medium. During the subsequent drying process, anhydrous ethanol dries faster than water, and it does not undergo hydrolysis with the binder. The silane coupling agent KH560 acts as a dispersant; after hydrolysis in the ethanol solution, the resulting Si-OH bonds form Si-O-Si bonds with Si atoms on the binder surface, modifying the binder's surface and improving its dispersibility in the slurry. Alcohol-soluble phenolic resin acts as a temporary binder, curing during the subsequent slurry drying process to bond the binder and CBN abrasive to the abrasive wheel substrate, facilitating the subsequent sintering process.

[0082] (3) CBN grinding wheel matrix treatment

[0083] Based on the dimensional drawings of the CBN grinding wheel matrix, an H13 steel billet was machined into the CBN grinding wheel matrix. H13 steel was chosen as the material because it is a high-temperature mold steel with good chemical stability. It will not produce harmful chemical reactions with the molten binder during the subsequent grinding wheel sintering process. Furthermore, it exhibits good dimensional stability after high-temperature sintering, preventing deformation and ensuring the dimensional accuracy of the grinding wheel matrix. The machined grinding wheel matrix was immersed in 1wt% dilute hydrochloric acid for 0.5-1 minute, then removed to remove the oxide layer from the surface. After rinsing with clean water and air-drying at room temperature, the matrix was immersed in anhydrous acetone for 10-15 minutes, then removed to degrease the surface with acetone and air-dry at room temperature, resulting in a clean grinding wheel matrix ready for the subsequent impregnation process.

[0084] (4) Impregnation treatment of CBN grinding wheels

[0085] According to the position and height of the CBN grinding wheel working layer, the designated area of ​​the surface-treated CBN grinding wheel metal substrate is immersed in the CBN grinding wheel impregnation slurry. After immersing the designated area of ​​the grinding wheel substrate in the impregnation slurry for 1-2 minutes, it is removed. The viscous impregnation slurry will leave a slurry layer with a thickness of about 1-3 mm on the substrate surface. The grinding wheel substrate is then hung to dry at room temperature, during which time the ethanol in the slurry will completely evaporate. Then it is placed in an oven and cured at 100-120 degrees Celsius for 4-6 hours. At this time, the phenolic resin in the slurry cures, bonding the binder and CBN abrasive to the surface of the grinding wheel substrate, giving the obtained CBN grinding wheel blank a certain strength.

[0086] (5) Sintering of ceramic-bonded CBN grinding wheels

[0087] The CBN grinding wheel blank is placed in a pit furnace and heated to 400-450℃ at a rate of 2-3℃ / min, and held for 1-2 hours. At this temperature, the phenolic resin begins to decompose and carbonize. The temperature is then increased to 600-650℃ at a rate of 2-4℃ / min and held for 1-1.5 hours. At this temperature, the binder powder softens and becomes a glassy viscous fluid, which wets and coats the CBN abrasive and the metal substrate surface in contact with the CBN grinding wheel. After the furnace is closed, the CBN grinding wheel cools naturally in the electric furnace, and the binder hardens, firmly bonding the CBN grinding wheel working layer to the H13 metal substrate surface, resulting in a sintered ceramic-bonded CBN grinding wheel blank.

[0088] (6) Machining of sintered ceramic-bonded CBN grinding wheel blanks

[0089] The sintered ceramic-bonded CBN grinding wheel blank does not meet the dimensional accuracy requirements of the CBN grinding wheel working layer. Therefore, the sintered CBN grinding wheel blank is clamped on a universal tool grinder, and the outer circle and end face of the CBN grinding wheel are ground with an electroplated diamond grinding wheel according to the dimensions of the ceramic-bonded CBN grinding wheel on the drawing. After the dimensions are qualified, the finished ceramic-bonded CBN grinding wheel is obtained.

[0090] The present invention will be further described below with reference to specific embodiments.

[0091] Example 1

[0092] This embodiment provides a specific process for preparing a small-diameter internal grinding ceramic-bonded cubic boron nitride (CBN) grinding wheel, the steps of which are as follows:

[0093] (1) Preparation of ceramic binder:

[0094] (a) The weight percentage formulation of the binder is as follows:

[0095] Boric acid (chemically pure) 10%, lithium carbonate (chemically pure) 6%, silicon dioxide (chemically pure) 40%, bismuth oxide (chemically pure)

[0096] 32%, calcium fluoride (chemically pure) 3%, nickel oxide (chemically pure) 3%, cobalt oxide (chemically pure) 3%, titanium oxide (chemically pure) 3%.

[0097] The weighed raw materials are poured into a planetary mixer. The corundum mixing jar has a diameter of 300 mm. Corundum ceramic balls are added at a ball-to-material mass ratio of 1.2:1, with 30% of the balls being 10 mm in diameter and 70% being smaller than 10 mm in diameter. The mixing jar rotates at 360 r / min and revolves at 60 r / min. After mixing the raw materials for 2 hours, the mixture is removed to obtain the binder smelting raw material.

[0098] (b) Melting and crushing of the binder

[0099] The crucible furnace is heated to 1300℃ at a rate of 3℃ / min. A plugging rod is inserted, and the mixed raw material powder is poured in, filling 4 / 5 of the crucible volume. A heat-resistant steel trough filled with water is placed at the crucible furnace outlet. When the furnace temperature reaches 1250℃, it is held for 2 hours. The plugging rod is then lifted to allow the molten binder to flow into the water for water quenching.

[0100] Collect the water-quenched ceramic binder fragments and pour them into the corundum grinding jar of a horizontal ball mill (400 mm in diameter). Add water of equal weight to the binder, and add zirconia grinding balls at a ball-to-material mass ratio of 1.2:1. The zirconia balls should be 30% of the weight being 50 mm in diameter, 40% being 30 mm in diameter, and 30% being less than 20 mm in diameter. The grinding jar rotates at 300 r / min. After grinding the raw materials for 24 hours, pour the slurry into a receiving tray.

[0101] (c) Drying and sieving of the binder

[0102] The slurry was dried at 110℃. After it was completely dry, the material was scooped up with a plastic shovel and poured into the corundum ball mill jar of a horizontal ball mill (400mm diameter). Zirconia grinding balls were added at a ball-to-material mass ratio of 1.2:1, with 50% being 20mm diameter corundum balls and 50% being 10mm diameter corundum balls. The ball mill jar rotated at 300 r / min. After milling for 4 hours, the powder was poured out and passed through a 320# sieve. The sieved binder was then sealed in a bag and placed in a drying tower for later use.

[0103] (2) Preparation of CBN grinding wheel impregnation slurry

[0104] CBN grinding wheel impregnation slurry composition by weight percentage:

[0105] 140 / 170#CBN abrasive 40%, ceramic binder 15%, anhydrous ethanol 36%, alcohol-soluble phenolic resin 8%, silane coupling agent KH5601.

[0106] First, measure an appropriate volume of anhydrous ethanol, then add silane coupling agent KH560 in proportion, stir at high speed for 20 minutes at a stirring speed of 5000 rpm, then add CBN abrasive and ceramic binder in weight ratio, and stir at 2000 rpm for 1 hour; then add alcohol-soluble phenolic resin in proportion, and stir at 2000 rpm for 1 hour to obtain a highly dispersible CBN grinding wheel impregnation slurry.

[0107] (3) CBN grinding wheel matrix treatment

[0108] According to the dimensional drawings of the CBN grinding wheel substrate, the blank made of H13 steel is machined into a CBN grinding wheel substrate. The machined grinding wheel substrate is then soaked in 1wt% dilute hydrochloric acid for 1 minute and then taken out. After rinsing the grinding wheel substrate with clean water, it is air-dried at room temperature. The substrate is then soaked in anhydrous acetone for 15 minutes and then taken out and air-dried at room temperature, thus completing the CBN grinding wheel substrate treatment.

[0109] (4) Impregnation treatment of CBN grinding wheels

[0110] According to the position and height of the CBN grinding wheel working layer, the designated position of the CBN grinding wheel metal substrate treated in step (3) is immersed in the CBN grinding wheel impregnation slurry prepared in step (2). After the designated position of the grinding wheel substrate is immersed in the impregnation slurry for 1-2 minutes, it is taken out. The grinding wheel substrate after impregnation is hung to dry at room temperature, and then placed in an oven. After curing at 120 degrees for 4 hours, it is cooled with the oven to obtain the CBN grinding wheel blank.

[0111] (5) Sintering of ceramic-bonded CBN grinding wheels

[0112] The CBN grinding wheel blank is placed in a pit furnace and heated to 450°C at a rate of 3°C / min. It is held at this temperature for 1 hour, then heated to 650°C at a rate of 4°C / min and held for 1 hour. After the furnace is closed, the CBN grinding wheel is allowed to cool naturally in the electric furnace. When the furnace temperature is below 70°C, the CBN grinding wheel blank is removed from the furnace to obtain the sintered ceramic-bonded CBN grinding wheel blank.

[0113] (6) Machining of sintered ceramic-bonded CBN grinding wheel blanks

[0114] The sintered ceramic bond CBN grinding wheel blank is clamped on a universal tool grinder. According to the dimensions of the ceramic bond CBN on the drawing, the outer circle and end face of the CBN grinding wheel are ground with an electroplated diamond grinding wheel. After the dimensions are qualified, the finished ceramic bond CBN grinding wheel is obtained.

[0115] The roundness error of the bearing end cap part machined by the CBN grinding wheel prepared in Example 1 is 3.02 μm, and the cylindricity error is 1.84 μm.

[0116] Example 2

[0117] (1) Preparation of ceramic binder:

[0118] (a) The weight percentage formulation of the binder is as follows:

[0119] Boric acid (chemically pure) 12%, lithium carbonate (chemically pure) 6%, silicon dioxide (chemically pure) 34%, bismuth oxide (chemically pure) 40%, calcium fluoride (chemically pure) 2%, nickel oxide (chemically pure) 2%, cobalt oxide (chemically pure) 2%, titanium oxide (chemically pure) 2%.

[0120] The weighed raw materials are poured into a planetary mixer. The corundum mixing jar has a diameter of 300 mm. Corundum ceramic balls are added at a ball-to-material mass ratio of 1.2:1, with 30% being 10 mm diameter balls and 70% being 5 mm diameter balls. The mixing jar rotates at 360 r / min and revolves at 60 r / min. After mixing the raw materials for 1 hour, the mixture is removed to obtain the binder smelting raw material.

[0121] (b) Melting and crushing of the binder

[0122] The crucible furnace is heated to 1250°C at a rate of 4°C / min. A plugging rod is inserted, and the mixed raw material powder is poured in, filling the crucible to 2 / 3 of its volume. A heat-resistant steel trough filled with water is placed at the furnace outlet. Once the furnace temperature reaches 1250°C, it is held for 2 hours. The plugging rod is then lifted to allow the molten binder to flow into the water for water quenching.

[0123] Collect the water-quenched ceramic binder fragments and pour them into the corundum grinding jar of a horizontal ball mill (400 mm in diameter). Add water of equal weight to the binder, and add zirconia grinding balls at a ball-to-material mass ratio of 1.2:1. The zirconia balls should consist of 30% with a diameter of 50 mm, 40% with a diameter of 30 mm, and 30% with a diameter of 10 mm. The grinding jar rotates at 300 r / min. After grinding the raw materials for 24 hours, pour the slurry into a receiving tray.

[0124] (c) Drying and sieving of the binder

[0125] The slurry is dried at 100-110℃. After it is completely dry, the material is scooped up with a plastic shovel and poured into the corundum ball mill jar of a horizontal ball mill (400mm diameter). Zirconia grinding balls are added at a ball-to-material mass ratio of 1.2:1, with 50% of the balls being 20mm in diameter and the other 50% being smaller than 20mm. The ball mill jar rotates at 300 rpm. After milling for 4-6 hours, the powder is poured out and passed through a 320# sieve. The sieved binder is then sealed in a bag and placed in a drying tower for later use.

[0126] (2) Preparation of CBN grinding wheel impregnation slurry

[0127] CBN grinding wheel impregnation slurry composition by weight percentage:

[0128] The composition consists of 40% CBN abrasive with a particle size of W3.5, 13% ceramic binder, 36% anhydrous ethanol, 10% alcohol-soluble phenolic resin, and 1% silane coupling agent KH5601.

[0129] First, measure an appropriate volume of anhydrous ethanol, then add silane coupling agent KH560 in proportion, stir at high speed for 20 minutes at a stirring speed of 5000 rpm, then add CBN abrasive and ceramic binder in weight ratio, and stir at 2000 rpm for 1 hour; then add alcohol-soluble phenolic resin in proportion, and stir at 2000 rpm for 1 hour to obtain a highly dispersible CBN grinding wheel impregnation slurry.

[0130] (3) CBN grinding wheel matrix treatment

[0131] According to the dimensional drawings of the CBN grinding wheel substrate, the blank made of H13 steel is machined into the CBN grinding wheel substrate. The machined grinding wheel substrate is then soaked in 1wt% dilute hydrochloric acid for 1 minute and then taken out. After rinsing the grinding wheel substrate with clean water, it is air-dried at room temperature. Then, the substrate is soaked in anhydrous acetone for 10 minutes and then taken out and air-dried at room temperature, thus completing the CBN grinding wheel substrate treatment.

[0132] (4) Impregnation treatment of CBN grinding wheels

[0133] According to the position and height of the CBN grinding wheel working layer, the designated position of the CBN grinding wheel metal substrate treated in step (3) is immersed in the CBN grinding wheel impregnation slurry prepared in step (2). The designated position of the grinding wheel substrate is immersed in the impregnation slurry for 1 minute and then taken out. The grinding wheel substrate after impregnation is hung to dry at room temperature and then placed in an oven. After curing at 100 degrees for 4 hours, it is cooled with the oven to obtain the CBN grinding wheel blank.

[0134] (5) Sintering of ceramic-bonded CBN grinding wheels

[0135] The CBN grinding wheel blank is placed in a pit furnace and heated to 400°C at a rate of 2°C / min, held for 1.5 hours, and then heated to 650°C at a rate of 4°C / min, held for 1.5 hours. After the furnace is closed, the CBN grinding wheel is allowed to cool naturally in the electric furnace. When the furnace temperature is below 70°C, the CBN grinding wheel blank is removed from the furnace to obtain the sintered ceramic-bonded CBN grinding wheel blank.

[0136] (6) Machining of sintered ceramic-bonded CBN grinding wheel blanks

[0137] The sintered ceramic bond CBN grinding wheel blank is clamped on a universal tool grinder. According to the dimensions of the ceramic bond CBN on the drawing, the outer circle and end face of the CBN grinding wheel are ground with an electroplated diamond grinding wheel. After the dimensions are qualified, the finished ceramic bond CBN grinding wheel is obtained.

[0138] The roundness error of the bearing end cap part machined by the CBN grinding wheel prepared in Example 2 is 3.08 μm, and the cylindricity error is 1.89 μm.

[0139] Example 3

[0140] The difference from Example 1 is that

[0141] The weight percentage formulation of the binder is as follows:

[0142] Boric acid (chemically pure) 15%, lithium carbonate (chemically pure) 5%, silicon dioxide (chemically pure) 30%, bismuth oxide (chemically pure) 40%, calcium fluoride (chemically pure) 3%, nickel oxide (chemically pure) 3%, cobalt oxide (chemically pure) 2%, titanium oxide (chemically pure) 2%.

[0143] The roundness error of the bearing end cap part machined by the CBN grinding wheel prepared in Example 3 was 3.11 μm, and the cylindricity error was 1.92 μm.

[0144] Example 4

[0145] The difference from Example 1 is that

[0146] The weight percentage formulation of the binder is as follows:

[0147] Boric acid (chemically pure) 10%, lithium carbonate (chemically pure) 6%, silicon dioxide (chemically pure) 48%, bismuth oxide (chemically pure) 28%, calcium fluoride (chemically pure) 2%, nickel oxide (chemically pure) 2%, cobalt oxide (chemically pure) 2%, titanium oxide (chemically pure) 2%.

[0148] The roundness error of the bearing end cap part machined by the CBN grinding wheel prepared in Example 4 is 2.95 μm, and the cylindricity error is 2.13 μm.

[0149] Comparative Example 1

[0150] The difference from Example 1 is that

[0151] The weight percentage formulation of the binder is as follows:

[0152] Boric acid (chemically pure) 12%

[0153] Lithium carbonate (chemically pure) 6%

[0154] 36% silica (chemically pure)

[0155] Bismuth oxide (chemically pure) 40%

[0156] Calcium fluoride (chemically pure) 2%

[0157] Nickel oxide (chemically pure) 2%

[0158] 2% cobalt oxide (chemically pure).

[0159] The roundness error of the bearing end cap part machined by the CBN grinding wheel prepared in Comparative Example 1 was 4.32 μm, and the cylindricity error was 2.78 μm.

[0160] Comparative Example 2

[0161] The difference from Example 1 is that

[0162] The weight percentage formulation of the binder is as follows:

[0163] Boric acid (chemically pure) 12%, lithium carbonate (chemically pure) 6%, silicon dioxide (chemically pure) 38%, bismuth oxide (chemically pure) 40%, calcium fluoride (chemically pure) 2%, titanium oxide (chemically pure) 2%.

[0164] The roundness error of the bearing end cap part machined by the CBN grinding wheel prepared in Comparative Example 2 was 5.14 μm, and the cylindricity error was 2.12 μm.

[0165] Comparative Example 3

[0166] The difference from Example 1 is that

[0167] The weight percentage formulation of the binder is as follows:

[0168] Boric acid (chemically pure) 12%, lithium carbonate (chemically pure) 6%, silicon dioxide (chemically pure) 36%, bismuth oxide (chemically pure) 40%, nickel oxide (chemically pure) 2%, cobalt oxide (chemically pure) 2%, titanium oxide (chemically pure) 2%.

[0169] The roundness error of the bearing end cap part machined by the CBN grinding wheel prepared in Comparative Example 3 was 4.47 μm, and the cylindricity error was 2.84 μm.

[0170] Example 5

[0171] The difference from Example 1 is that the CBN grinding wheel impregnation slurry has the following mass percentage composition:

[0172] 45% CBN abrasive with a particle size of W3.5

[0173] The composition includes 10% ceramic binder, 36% anhydrous ethanol, 8% alcohol-soluble phenolic resin, and 1% silane coupling agent KH5601.

[0174] The roundness error of the bearing end cap part machined by the CBN grinding wheel prepared in Example 5 was 2.98 μm, and the cylindricity error was 1.82 μm.

[0175] Example 6

[0176] The difference from Example 1 is that the CBN grinding wheel impregnation slurry has the following mass percentage composition:

[0177] The composition consists of 43% CBN abrasive with a particle size of W3.5, 13% ceramic binder, 33% anhydrous ethanol, 10% alcohol-soluble phenolic resin, and silane coupling agent KH5601.

[0178] The roundness error of the bearing end cap part machined by the CBN grinding wheel prepared in Example 6 was 2.79 μm, and the cylindricity error was 1.72 μm.

Claims

1. A method for preparing a CBN grinding wheel, characterized in that, Includes the following steps: The raw materials for ceramic binder are melted, quenched in water, and then crushed to obtain the ceramic binder. The CBN grinding wheel metal matrix is ​​impregnated in CBN grinding wheel impregnation slurry, dried and cured to obtain CBN grinding wheel blank; The CBN grinding wheel blank is obtained by sintering and then machining its dimensions. The raw materials of the ceramic binder, by weight percentage, include 10-15% boric acid, 5-6% lithium carbonate, 30-49% silicon dioxide, 28-40% bismuth oxide, 2-3% calcium fluoride, 2-3% nickel oxide, 2-3% cobalt oxide, and 2-3% titanium oxide; the CBN grinding wheel impregnation slurry, by weight percentage, includes 40-45% CBN abrasive, 10-15% of the ceramic binder, 33-36% ethanol, 8-10% alcohol-soluble phenolic resin, and 0.5-1% silane coupling agent. The CBN grinding wheel's metal matrix is ​​made of H13 steel.

2. The method for preparing CBN grinding wheels as described in claim 1, characterized in that: This includes the step of ball milling and mixing the raw materials of the ceramic binder; The ball-to-material mass ratio in the ball milling mixture is 1.2:1; the ball milling mixture uses corundum ceramic balls. Of the corundum ceramic spheres, 30% are corundum spheres with a diameter of 10mm and 70% are corundum spheres with a diameter of less than 10mm. The rotational speed of the ball mill mixing is 360 r / min; The ball milling mixing speed is 60 r / min; the ball milling mixing time is 1-2 h.

3. The method for preparing CBN grinding wheels as described in claim 1, characterized in that: The melting temperature is 1250-1300℃; The heating rate for the melting process is 3-5℃ / min; The holding time for the smelting process is 1-2 hours.

4. The method for preparing CBN grinding wheels as described in claim 1, characterized in that: The crushing method is ball milling. The grinding balls used in the ball milling process are zirconia grinding balls; The ball-to-material mass ratio for ball milling is 1.2:1; The zirconia grinding balls comprise 30% zirconia balls with a diameter of 50 mm, 40% zirconia balls with a diameter between 20 and 50 mm, and 30% zirconia balls with a diameter less than 20 mm. The rotational speed of the ball mill crusher is 300 r / min; The ball mill crushing time is 24 hours.

5. The method for preparing CBN grinding wheels as described in claim 1, characterized in that: After the raw materials for ceramic binders are melted, quenched in water, and crushed, the process also includes grinding and drying steps. The grinding process includes a ball milling step using grinding balls; The grinding process uses a ball-to-material mass ratio of 1.2:

1. The grinding balls used in the process consist of 50% corundum balls with a diameter of 20 mm and 50% corundum balls with a diameter of less than 20 mm; the rotation speed used in the grinding process is 300 r / min. The drying process includes the steps of passing the material through a 320# sieve and then drying it in a drying tower.

6. The method for preparing CBN grinding wheels as described in claim 1, characterized in that: The preparation method of the CBN grinding wheel impregnation slurry includes the following steps: After stirring and mixing ethanol and silane coupling agent, the CBN abrasive and the ceramic binder are added and stirred and mixed. Then, alcohol-soluble phenolic resin is added and stirred and mixed. The silane coupling agent includes KH560.

7. The method for preparing CBN grinding wheels as described in claim 1, characterized in that: The impregnation includes a pretreatment step of the CBN grinding wheel metal substrate; The pretreatment includes soaking in 1 wt% dilute hydrochloric acid for 0.5-1 minute, washing and drying, followed by soaking in acetone for 10-15 minutes and drying.

8. The method for preparing CBN grinding wheels as described in claim 1, characterized in that: The curing temperature is 100-120℃; The curing time is 4-6 hours.

9. The method for preparing CBN grinding wheels as described in claim 1, characterized in that: The sintering process includes heating to 400-450°C at a rate of 2-3°C / min, holding at that temperature for 1-2 hours, and then heating to 600-650°C at a rate of 2-4°C / min, holding at that temperature for 1-1.5 hours.

10. A CBN grinding wheel prepared by the method for preparing a CBN grinding wheel according to any one of claims 1-9.

Images