A sol-gel method based compact superhard abrasive and its preparation method and application

Abstract

The application discloses a kind of based on sol-gel method's accumulation superhard abrasive and its preparation method and application, belong to superhard material coating abrasive technical field.The accumulation superhard abrasive is made of superhard abrasive micro powder, magnesium phosphate modified epoxy resin composite binder and filler, wherein the magnesium phosphate addition amount is 3% to 9% of the mass of epoxy resin.Preparation, first by acrylamide, N,N'-methylene bisacrylamide and ammonium persulfate form polyacrylamide sol precursor, then join superhard abrasive micro powder, magnesium phosphate and filler and adjust to acidity, then join epoxy resin and curing agent, by in-situ gelation, mold forming and ladder curing obtain accumulation superhard abrasive.The method can inhibit micro powder settlement, improve abrasive distribution uniformity;Magnesium phosphate participates in epoxy resin ring-opening reaction under acidic conditions to form a composite bonding structure containing P-O-C bond, improve the heat resistance of binder and the strength of accumulation abrasive.

Description

Technical Field

[0001] This invention relates to the field of superhard material coated abrasives technology, specifically to a sol-gel method for depositing superhard abrasives, its preparation method and application, and particularly to a method for preparing depositable superhard abrasives by using a polyacrylamide in-situ gel network to fix micron-grade superhard abrasives and using magnesium phosphate modified epoxy resin as a composite binder. Background Technology

[0002] Superhard abrasive belts are widely used in the precision grinding and polishing of difficult-to-machine metals such as titanium alloys and stainless steel due to their high grinding efficiency, good surface finish, and wide applicability. Diamond and cubic boron nitride, as typical superhard abrasives, are important materials for preparing high-performance abrasive belts. However, micro-powder-grade superhard abrasives with particle sizes of W80-W1, especially below W5, face the following problems in the preparation of coated abrasives: on the one hand, both diamond and cubic boron nitride are high-resistivity materials, making them difficult to adapt to electrostatic abrasive coating processes; on the other hand, the small particle size makes it difficult to achieve uniform distribution and stable orientation when using gravity abrasive coating. Therefore, their application in superhard abrasive belts has long been limited.

[0003] To address the challenge of directly attaching fine-grained abrasive particles, existing technologies have proposed agglomerated or clustered abrasive techniques. These techniques involve using a binder to bond fine-grained abrasive particles into larger composite particles. For example, CN103273434A discloses an ultrafine diamond ceramic-bonded abrasive and its preparation method. This involves mixing diamond powder with a ceramic sol system, followed by spray drying and calcination to obtain spherical abrasive particles. While this technique can achieve the agglomeration and granulation of fine-grained diamond, the ceramic binder system results in brittle particles that are unsuitable for flexible abrasive belt applications. Furthermore, the random orientation of the spherical particles after attachment leads to inconsistent exposed cutting edges, affecting initial grinding efficiency and grinding stability.

[0004] The prior art CN1761552A discloses abrasive agglomerates and their applications, which achieve agglomeration by placing superhard abrasive grains in agglomerates. However, the agglomerates in this technology have irregular shapes, and also suffer from problems such as random orientation and inconsistent exposed cutting edges after sand planting. Furthermore, it does not propose an effective solution to the problem of easy sedimentation and difficulty in uniform distribution of micronized superhard abrasives during liquid phase preparation.

[0005] Existing technology CN105563353B discloses a process for preparing fine-grained abrasives using a sol-gel ceramic binder. This process disperses abrasives, a ceramic binder, and a pore-forming agent in a sol, followed by molding, drying, pre-processing, firing, and machining to obtain an integral abrasive. The sol-gel system in this technology is used to construct the ceramic framework after firing, and the process route revolves around high-temperature firing, resulting in an integral ceramic abrasive. This technology does not address the issue of preventing the sedimentation of micronized superhard abrasives in a resin system, nor does it address the preparation of discretely stacked abrasive particles that can be fixed onto a flexible substrate using a sand-planting process. Therefore, its technical object, molding mechanism, and applicable scenarios differ from those of this invention.

[0006] In the field of resin-bonded abrasives, the existing technology CN108857937A discloses a scheme to add dicalcium phosphate and magnesium phosphate to resin grinding wheels to improve the bonding strength between resin powder and abrasive. However, this technology mainly focuses on the overall formulation optimization of resin grinding wheels. The dicalcium phosphate and magnesium phosphate are used as conventional inorganic additives and do not involve the participation of magnesium phosphate in the ring-opening reaction of epoxy resin under acidic conditions to form a reactive composite bonding structure containing POC bonds. It also does not address the issues of gel bearing, stacking and molding, and sand-planting of micronized superhard abrasives.

[0007] Furthermore, existing technology CN112969769B discloses a tetrahedral shaped abrasive particle with a predetermined tilt angle, aiming to improve grinding performance through a specific single-particle geometry. However, this technology focuses on the shape of the shaped abrasive particle itself and does not address the composite abrasive system composed of micronized superhard abrasive, reactive inorganic-organic composite binder, and conductive / weight-adding filler, nor does it address the issue of suppressing micronized powder sedimentation through in-situ gelation to make micronized superhard abrasive suitable for electrostatic or gravity-based abrasive application.

[0008] Therefore, current technology lacks a solution that can simultaneously address the following issues:

[0009] (1) Micronized diamond or cubic boron nitride is prone to sedimentation and difficult to disperse uniformly in liquid systems; (2) Micronized superhard abrasives are non-conductive and lightweight, making them difficult to use for electrostatic and gravity abrasive application. (3) The existing resin binder has insufficient heat resistance and holding power, which causes the abrasive grains to fall off prematurely during high-speed grinding; (4) Existing abrasive systems focus on particle morphology design but lack the construction of a synergistic relationship between composition, process and sand planting.

[0010] Therefore, it is necessary to provide a new micron-grade superhard abrasive deposition molding technology to meet the comprehensive requirements of superhard abrasive belts for particle uniformity, heat resistance, strength, abrasive adaptability and grinding stability. Summary of the Invention

[0011] The purpose of this invention is to provide a superhard abrasive based on the sol-gel method, its preparation method and application, to solve the problems of uneven dispersion, difficulty in sand planting and insufficient heat resistance of resin binders in the prior art of micro powder-grade superhard abrasives.

[0012] This invention is not simply replacing the ceramic binder with epoxy resin, nor is it merely adding phosphate fillers to the resin system. The core of this invention lies in: using a three-dimensional gel network formed by in-situ polymerization of polyacrylamide as a temporary support and spatial fixation system for micronized superhard abrasives, suppressing micronized powder sedimentation and component segregation before low-temperature resin curing; simultaneously, introducing magnesium phosphate under acidic conditions of pH 2-3, allowing it to participate in the ring-opening reaction of the epoxy resin to form a reactive composite bonding structure containing POC bonds, thereby improving the crosslinking density, thermal stability, and holding power of the binder for micronized superhard abrasives; and then combining it with conductive / weight-adding fillers to obtain stacked superhard abrasives suitable for electrostatic and / or gravity-based abrasive planting.

[0013] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing superhard abrasive based on sol-gel method includes the following steps: (1) Preparation of sol precursor: Acrylamide monomer, crosslinking agent and initiator are dissolved in water and mixed evenly to obtain polyacrylamide sol precursor solution; (2) Preparation of mixed slurry: Add superhard abrasive powder, magnesium phosphate and filler to the polyacrylamide sol precursor solution obtained in step (1), adjust the pH to acidic, and disperse by ultrasonication to obtain mixed slurry; (3) Resin composite and in-situ gelation: Epoxy resin and its curing agent are added to the mixed slurry obtained in step (2), and the mixture is stirred and heated to allow the acrylamide monomer to polymerize in situ and form a wet gel encapsulating superhard abrasive powder, magnesium phosphate and filler. (4) Molding: The wet gel obtained in step (3) is injected into the mold, pre-dried and demolded to obtain the wet abrasive blank; (5) Curing and post-treatment: The wet blank of the abrasive obtained in step (4) is cured by step heating to cross-link the epoxy resin and densify the gel network. After drying and sieving, the superhard abrasive is obtained.

[0014] Preferably, in step (1), the mass concentration of the acrylamide monomer is 5%-20%, based on the total mass of the polyacrylamide sol precursor solution; the crosslinking agent is N,N'-methylenebisacrylamide; the initiator is ammonium persulfate; and the molar ratio of acrylamide monomer, N,N'-methylenebisacrylamide and ammonium persulfate is (60-70):(5-10):1.

[0015] Preferably, the superhard abrasive powder is diamond powder and / or cubic boron nitride powder, with a particle size of W80-W1, more preferably W10-W2, and even more preferably W5.

[0016] Preferably, the superhard abrasive powder accounts for 55%-80% of the total dry weight; the filler accounts for 3%-20% of the total dry weight.

[0017] Preferably, the filler includes metal micro powder, corundum micro powder and / or silicon carbide micro powder; the metal micro powder is at least one of copper powder, nickel powder, iron powder, titanium powder and aluminum powder, and the amount added is 3%-15% of the mass of the superhard abrasive micro powder; the amount added of corundum micro powder and / or silicon carbide micro powder is 2%-10% of the mass of the superhard abrasive micro powder.

[0018] Preferably, in step (2), dilute hydrochloric acid is used to adjust the pH to 2-3, preferably 2.5.

[0019] Preferably, the epoxy resin is bisphenol A type epoxy resin E51; the curing agent is polyamide curing agent 650. The amount of epoxy resin added is 20%-40% of the mass of the superhard abrasive powder, preferably 30%; the amount of curing agent added is 20%-35% of the mass of the epoxy resin, preferably 27.8%.

[0020] Preferably, the amount of magnesium phosphate added is 3%-9% of the mass of epoxy resin, more preferably 5%-9%, and even more preferably 7%. When the amount added is less than 3%, the improvement on thermal stability and strength is limited; when the amount added is more than 9%, it is easy to cause local agglomeration of inorganic phase, affecting the uniformity of slurry and the integrity of stacked particles.

[0021] Preferably, the in-situ polymerization temperature in step (3) is 40℃-60℃, and more preferably 50℃.

[0022] Preferably, the stepped temperature curing procedure in step (5) is as follows: 60℃ for 1 hour, 80℃ for 1 hour, 100℃ for 2 hours, 120℃ for 2 hours, 140℃ for 2 hours, 160℃ for 2 hours, and 180℃ for 2 hours.

[0023] The present invention also provides a superhard abrasive prepared by the above method. The superhard abrasive comprises superhard abrasive powder, a magnesium phosphate modified epoxy resin composite binder, and a filler, wherein the magnesium phosphate modified epoxy resin composite binder contains POC bonds.

[0024] The present invention also provides the application of the above-mentioned superhard abrasive in the preparation of superhard abrasive belts, which are used for fine grinding and polishing of titanium alloys or stainless steel.

[0025] In this invention, the role of the in-situ polyacrylamide gel network is not to form the final abrasive bonding phase, but rather to temporarily support and spatially fix the micronized superhard abrasive before resin crosslinking and curing, thereby ensuring the uniform distribution of micronized powder in the slurry and the uniform internal composition of the stacked particles after molding. This is fundamentally different from the sol-gel abrasive process that constructs a sintered ceramic skeleton through ceramic sol.

[0026] In this invention, magnesium phosphate is not used as a common inorganic filler, but participates in the ring-opening reaction of epoxy resin in an acidic environment to form a reactive composite structure containing POC bonds. This structure improves the crosslinking density and thermal stability of the system, and enhances the interfacial bonding between the binder and the superhard abrasive, thereby increasing the strength of individual abrasive particles and the abrasive grain retention capacity during grinding.

[0027] Compared with the prior art, the present invention has the following beneficial effects: The in-situ gel network of polyacrylamide effectively fixes micronized superhard abrasive, inhibits sedimentation and component segregation, and ensures uniform internal composition of the packed abrasive. By involving magnesium phosphate in the ring-opening reaction of epoxy resin under acidic conditions, a reactive composite binder containing POC bonds is constructed, which improves the binder's heat resistance, structural density, and retention of abrasive particles. By introducing conductive / weight-adding fillers, micro-powder-grade superhard abrasives can be adapted to electrostatic and gravity-based sand-planting processes after being deposited. This process does not require high-temperature sintering and is suitable for preparing discretely packed abrasive particles for flexible superhard abrasive belts; The technical effect of this invention comes from the synergistic effect of gel bearing, anti-settling, reactive composite binder and sand planting adaptation, rather than from a single known binder or a single particle shape. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0029] Figure 1 Infrared images of epoxy resins modified with different contents of magnesium phosphate; Figure 2 X-ray diffraction analysis diagrams of magnesium phosphate and magnesium phosphate modified epoxy resin before and after curing; Figure 3 Thermogravimetric analysis images of epoxy resins modified with different contents of magnesium phosphate; Figure 4This is a microstructure diagram of the superhard abrasive material prepared according to the present invention.

[0030] Figure 5 This is a process flow diagram of the present invention. Detailed Implementation

[0031] In this invention, the acrylamide monomer mass concentration refers to the percentage of acrylamide monomer in the total mass of the polyacrylamide sol precursor solution. The percentage of magnesium phosphate added in the epoxy resin mass refers to the ratio of the mass of magnesium phosphate to the mass of epoxy resin. The total dry basis mass refers to the total mass of the superhard abrasive powder, the cured composite binder, and the filler. The invention is further illustrated below with reference to embodiments. Unless otherwise stated, all percentages below are mass percentages.

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The polyacrylamide sol-gel system used in this invention has the following construction mechanism: ammonium persulfate (APS) decomposes upon heating to generate sulfate radicals (SO4). - The free radical attacks the double bonds of acrylamide (AM) monomers, initiating a chain polymerization reaction; at the same time, N,N'-methylenebisacrylamide (BIS) acts as a crosslinking agent, with its double bonds at both ends connecting to different polyacrylamide molecular chains, forming a three-dimensional crosslinked network structure.

[0034] The bearing mechanism of this gel system for ultrafine-grained superhard abrasive powders is as follows: the three-dimensional network structure forms a continuous skeleton in the liquid phase, encapsulating and fixing the diamond or cubic boron nitride powder within the network pores, effectively preventing the powder particles from settling under gravity. When the gel concentration reaches a critical value, the network density is high enough to achieve complete bearing of the powder.

[0035] Example 1 I. Determination of Polyacrylamide Gel Concentration Sol-gel systems were prepared with acrylamide monomer added at amounts of 1g, 2g, 3g, and 4g relative to 30g of diamond micropowder, corresponding to polyacrylamide monomer concentrations of 4%, 8%, 12%, and 16%. The prepared sols were allowed to stand, and the sedimentation of the diamond micropowder was observed.

[0036] The results showed that when the acrylamide concentration was 5.0%, the gel network strength was insufficient, and bottom sedimentation occurred after the slurry stood for 30 minutes. When the concentration was 10.0%, sedimentation was significantly reduced. When the concentration was 16.0%, there was no significant sedimentation in the slurry, and the fluidity was suitable. When the concentration was 20.0%, the viscosity of the slurry was too high, which was not conducive to injection molding. Therefore, the preferred acrylamide concentration was 10.0%-16.0%, and more preferably 16.0%.

[0037] II. Mechanism and Process of Magnesium Phosphate Modified Epoxy Resin The chemical mechanism of magnesium phosphate-modified epoxy resin lies in the following: Under acidic conditions (pH 2-3), the phosphate groups released from magnesium phosphate undergo a ring-opening esterification reaction with the epoxy resin, forming POC chemical bonds. This reaction achieves molecular-level composite of the inorganic and organic phases. The phosphate groups, as multifunctional reaction sites, participate in the construction of the epoxy resin's crosslinking network, significantly increasing the crosslinking density. Simultaneously, unreacted magnesium phosphate particles act as inorganic fillers, filling the micropores generated by the curing shrinkage of the epoxy resin and inhibiting the formation of internal defects.

[0038] Example 2: Preparation of magnesium phosphate modified epoxy resin composite binder Magnesium phosphate modified epoxy resin composite binder was prepared according to the following steps: (1) Place 70 mL of deionized water in a beaker, add the measured amount of magnesium phosphate, and stir for 20 minutes; (2) Slowly add dilute hydrochloric acid to adjust the pH value to 2-3; (3) Add magnesium oxide at a mass ratio of 10:1 to magnesium phosphate as a curing accelerator and continue stirring for 10 minutes; (4) Add 4g acrylamide, 0.96g N,N'-methylenebisacrylamide and 0.2g ammonium persulfate, and stir at 50°C for 30 minutes to initiate polymerization; (5) Add 9g of epoxy resin E51 and its curing agent low molecular weight polyamide 650, stir for 20 minutes and then use ultrasonic treatment until the system gradually gels.

[0039] III. Molding process of equilateral triangular tetrahedral abrasive deposits This invention uses a sol-gel combined extrusion molding process to prepare equilateral triangular tetrahedral stacked abrasives. The specific process includes four stages: gel injection molding, pre-drying with mold, isobaric extrusion demolding, and post-curing.

[0040] Example 3: Preparation of equilateral triangular tetrahedral abrasive (1) Gel injection molding: Prepare a wet gel according to the steps in Example 2, transfer it to a syringe, and slowly inject it into a pre-designed silicone mold with an equilateral triangular tetrahedral cavity. The mold cavity is an equilateral triangle with a side length of 1-2 mm and a depth of 0.8-1.5 mm to ensure that the abrasive has a regular tetrahedral structure after molding.

[0041] (2) Pre-drying with mold: Place the mold after injection into a 50℃ oven for 2-4 hours to pre-dry the wet gel initially to form an abrasive wet blank with a certain strength.

[0042] (3) Isobaric extrusion demolding: Isobaric extrusion device is used to apply uniform pressure to the mold and completely extrude the abrasive wet blank from the mold cavity. Isobaric extrusion can avoid deformation or damage caused by uneven stress on the wet blank.

[0043] (4) Post-curing: The demolded wet abrasive blank is placed in an oven and cured according to the following stepped temperature increase program: 60℃ for 1 hour, 80℃ for 1 hour, 100℃ for 2 hours, 120℃ for 2 hours, 140℃ for 4 hours, and 160℃ for 1 hour. After curing, it is dried and sieved to obtain equilateral triangular tetrahedral superhard abrasive.

[0044] IV. Preparation of Aggregate Abrasives with Different Magnesium Phosphate Contents Following the preparation method of Example 3, only the amount of magnesium phosphate added was changed to prepare abrasives with different magnesium phosphate contents, and the formulations are shown in Table 1.

[0045] Table 1. Formulation of abrasive materials with different magnesium phosphate contents

[0046] Example 4: Cubic boron nitride deposited superhard abrasive In Example 4, the diamond powder was replaced with 30.00g of cubic boron nitride powder, the copper powder was replaced with 2.00g of nickel powder, and the silicon carbide powder was replaced with 1.00g of corundum powder. The remaining steps were the same as in Example 4, and cubic boron nitride deposited superhard abrasive was obtained.

[0047] Preparation method using Mg7 as an example: (1) Preparation of sol precursor Weigh 70.00 g of deionized water, add 4.00 g of acrylamide, 0.96 g of N,N'-methylenebisacrylamide and 0.20 g of ammonium persulfate, and mechanically stir at 25 °C for 15 min to obtain a polyacrylamide sol precursor solution.

[0048] (2) Preparation of mixed slurry 30.00 g of cubic boron nitride micro powder, 0.63 g of magnesium phosphate, 2.00 g of copper powder and 1.00 g of silicon carbide micro powder were added sequentially to the above sol precursor solution. After stirring for 10 min, the pH was adjusted to 2.5 with 5% hydrochloric acid by mass, and then ultrasonically dispersed at 300 W for 20 min to obtain a uniformly mixed slurry.

[0049] (3) Resin composite and in-situ gelation Add 9.00g of bisphenol A type epoxy resin E51 and 2.50g of polyamide curing agent 650 to the mixed slurry, stir mechanically for 20min, and then place it in a constant temperature water bath at 50℃ for 30min to allow the acrylamide monomer to undergo in-situ polymerization and obtain a wet gel.

[0050] (4) Molding The wet gel is transferred to a syringe and injected into a mold. Preferably, the mold is designed as a regular tetrahedral cavity with an edge length of 1.50 mm, used to prepare stacked abrasive particles with regular shapes. After injection, the mold is placed in a 50°C oven for pre-drying for 3 hours to allow the wet gel to initially set.

[0051] (5) Demolding and curing The wet preform is extruded from the mold cavity using isobaric extrusion and then cured by stepped temperature increase according to the following procedure. After curing, it is dried and sieved to obtain the deposited superhard abrasive.

[0052] V. Comparative Examples Comparative Example 1: Preparation of Spherical Abrasive Grinding Using the same formulation and process as in Example 3 (Mg7), but replacing the mold with a spherical cavity in the extrusion molding step, spherical deposited abrasive was prepared. This was used for electrostatic sanding to prepare superhard abrasive belts. The results showed that the spherical abrasive exhibited random orientation after sanding, failing to achieve directional alignment, resulting in low initial grinding efficiency and poor stability during the grinding process.

[0053] Comparative Example 2: Irregularly aggregated abrasive A wet gel was prepared using the same formulation as in Example 4, but instead of using a regular mold, it was obtained by crushing, granulating, solidifying, and sieving to produce irregularly shaped abrasive aggregates. The results showed that this sample exhibited poor consistency at the exposed cutting edge after abrasive loading, and the grinding force fluctuation in the initial grinding stage was greater than that of the regularly shaped particle sample obtained in Example 4. This comparative example illustrates that a regular particle morphology is beneficial for improving grinding stability after abrasive loading. However, the core technological contribution of this invention lies in the synergistic construction of gel support, anti-settling, and reactive composite binder, rather than simply the shape itself.

[0054] Comparative Example 3: Preparation of deposited abrasives without sol-gel process The same formulation (Mg7) as in Example 3 was used, but the addition of monomers such as acrylamide was omitted. That is, the sol-gel process was not used, and diamond micron powder, magnesium phosphate, epoxy resin, etc. were directly mixed and then injection molded. The results showed that during the static standing process of the mixed slurry, the diamond micron powder underwent severe sedimentation, and the composition of the solidified abrasive was uneven between the upper and lower parts, making it impossible to obtain a qualified product with uniform composition.

[0055] Comparative Example 4: Preparation of pure epoxy resin bonded abrasive Using the same process as in Example 3, but with 0% magnesium phosphate added (i.e., Mg0 formulation), equilateral triangular tetrahedral abrasives with pure epoxy resin binder were prepared. These were used for electrostatic abrasive belt preparation. Results showed that the pure epoxy resin binder had poor heat resistance and was prone to thermal softening under high-speed grinding conditions, leading to premature abrasive grain detachment. The belt durability was significantly lower than that of the Mg7 sample of this invention.

[0056] Comparative Example 5: Without using a sol-gel system Using the same raw material formulation as in Example 3, but without acrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate, diamond micron powder, magnesium phosphate, copper powder, silicon carbide micron powder, epoxy resin E51, and polyamide curing agent 650 were directly mixed, molded, and cured. The results showed that the slurry underwent significant sedimentation during settling and molding, and the composition of the particles after curing was unevenly distributed, making it difficult to obtain a uniformly composed and qualified abrasive.

[0057] Comparative Example 6: Using silica sol instead of polyacrylamide gel system The same formulation as in Example 3, consisting of diamond micron powder, magnesium phosphate, copper powder, silicon carbide micron powder, epoxy resin E51, and polyamide curing agent 650, was used, but acrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate system were replaced with silica sol of equal solids content. The results showed that the silica sol system was insufficient in fixing the W5 diamond micron powder spatially, leading to sedimentation before molding; the cured particles were also more brittle, resulting in a higher demolding breakage rate than in Example 4.

[0058] Comparative Example 7: The proportion of raw materials in the gel system exceeds the scope of this invention. Using the same raw materials and process as in Example 4, the difference was that the molar ratio of acrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate was adjusted to 40:2:1 to obtain sample PAM-L; and then adjusted to 80:15:1 to obtain sample PAM-H. The results showed that the PAM-L sample had insufficient gel network crosslinking density, resulting in sedimentation after the slurry was allowed to stand; the PAM-H sample gelled too quickly, leading to poor slurry flowability and increased particle edge defects after molding.

[0059] VI. Application Examples Application Example 1: Application of equilateral triangular tetrahedral abrasive in the preparation of superhard abrasive belts using electrostatic sanding. The Mg7 deposited abrasive prepared in Example 3 was mixed with conductive fillers (metal micropowder, corundum-like micropowder) and coated onto the abrasive belt substrate using an electrostatic sand-coating process. During the sand-coating process, the equilateral triangular tetrahedral structure exhibited self-orientation characteristics; regardless of which face contacted the substrate, the exposed surface always featured sharp corners, achieving a uniform orientation of the abrasive grains on the abrasive belt surface. The prepared abrasive belt exhibited high initial grinding efficiency and stable grinding process, making it suitable for fine grinding and polishing of difficult-to-machine metal materials such as titanium alloys and stainless steel. The superhard abrasive belt prepared in Example 3 was used for fine grinding and polishing of titanium alloy TC4, with a belt linear speed of 20 m / s, a grinding pressure of 0.15 MPa, and a grinding time of 10 min. The results showed that compared with abrasive belts made using irregularly agglomerated deposited abrasive, the abrasive belt in this application had higher initial grinding efficiency, less grinding force fluctuation, and more stable surface quality. Abrasive belts made with cubic boron nitride deposited superhard abrasive from Example 4 were used for fine grinding and polishing of 304 stainless steel samples. The results show that the abrasive belt has less abrasive grain shedding and fewer surface scratches during continuous grinding, making it suitable for precision machining of stainless steel materials.

[0060] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0061] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing superhard abrasives based on the sol-gel method, characterized in that, Includes the following steps: (1) Preparation of sol precursor: Acrylamide monomer, crosslinking agent and initiator are dissolved in water and mixed evenly to obtain polyacrylamide sol precursor solution; 2) Preparation of mixed slurry: Add superhard abrasive powder, magnesium phosphate and filler to the polyacrylamide sol precursor solution obtained in step (1), adjust the pH to acidic, and disperse by ultrasonication to obtain mixed slurry; (3) Resin composite and in-situ gelation: Epoxy resin and its curing agent are added to the mixed slurry obtained in step (2), and the mixture is stirred and heated to allow the acrylamide monomer to polymerize in situ and form a wet gel encapsulating superhard abrasive powder, magnesium phosphate and filler. (4) Molding: The wet gel obtained in step (3) is injected into the mold, pre-dried and demolded to obtain the wet abrasive blank; (5) Curing and post-treatment: The wet blank of the abrasive obtained in step (4) is cured by step heating to cross-link the epoxy resin and densify the gel network. After drying and sieving, the superhard abrasive is obtained. The amount of magnesium phosphate added is 3%-9% of the mass of epoxy resin, and the magnesium phosphate participates in the ring-opening reaction of epoxy resin under acidic conditions to form a magnesium phosphate modified epoxy resin composite binder containing POC bonds.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass concentration of the acrylamide monomer is 5%-20%, based on the total mass of the polyacrylamide sol precursor solution; the crosslinking agent is N,N'-methylenebisacrylamide, the initiator is ammonium persulfate, and the molar ratio of acrylamide monomer, N,N'-methylenebisacrylamide and ammonium persulfate is (60-70):(5-10):

1.

3. The preparation method according to claim 1, characterized in that, In step (2), the superhard abrasive powder is diamond powder and / or cubic boron nitride powder with a particle size of W80-W1; the superhard abrasive powder accounts for 55%-80% of the total dry weight; and the filler accounts for 3%-20% of the total dry weight.

4. The preparation method according to claim 3, characterized in that, The filler includes metal micro powder, corundum micro powder and / or silicon carbide micro powder; the metal micro powder is at least one of copper powder, nickel powder, iron powder, titanium powder and aluminum powder, and the amount added is 3%-15% of the mass of the superhard abrasive micro powder; the amount added of corundum micro powder and / or silicon carbide micro powder is 2%-10% of the mass of the superhard abrasive micro powder.

5. The preparation method according to claim 1, characterized in that, In step (2), dilute hydrochloric acid is used to adjust the pH to 2-3; in step (3), the epoxy resin is at least one of bisphenol A type epoxy resins E51 and E44; The curing agent is at least one of polyamide curing agent 650, phenolic resin, 2-ethyl-4-methylimidazolium, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and m-phenylenediamine. The amount of epoxy resin added is 20%-40% of the mass of the superhard abrasive powder, the amount of curing agent added is 20%-35% of the mass of the epoxy resin, and the in-situ polymerization temperature is 40℃-60℃.

6. The preparation method according to claim 1, characterized in that, In step (5), the stepped temperature curing process includes sequentially holding at 60℃ for 1 hour, 80℃ for 1 hour, 100℃ for 2 hours, 120℃ for 2 hours, 140℃ for 2 hours, 160℃ for 2 hours, and 180℃ for 2 hours.

7. A superhard abrasive prepared by the preparation method according to any one of claims 1-6, characterized in that, The superhard abrasive comprises superhard abrasive powder, magnesium phosphate modified epoxy resin composite binder and filler, wherein the magnesium phosphate modified epoxy resin composite binder contains POC bonds.

8. The application of the superhard abrasive as described in claim 7 in the preparation of coated abrasives, characterized in that, The coated abrasive is made by electrostatic sanding and / or gravity sanding.

9. The application according to claim 8, characterized in that, The coated abrasive is an ultrahard abrasive belt, abrasive cloth, abrasive paper, or flap wheel, and is used for fine grinding and polishing of titanium alloys or stainless steel.

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