Composite magnetic abrasive and preparation method thereof

Abstract

The present invention discloses a composite magnetic abrasive and a preparation method thereof, belonging to the field of magnetic abrasive technology. The technical problem to be solved by the present invention is how to improve the performance of magnetic abrasive particles themselves and reduce the preparation cost of magnetic abrasive particles. The technical solution is as follows: the composite magnetic abrasive includes an iron matrix, a binder and a whisker structure, wherein the whisker structure is a reinforced and toughened structure produced by the reaction of a sintering additive with two grinding phases or one of the two grinding phases at high temperature. The preparation method is as follows: (1) taking two grinding phases, an iron matrix and a sintering additive, adding a polyvinyl alcohol aqueous solution and mixing them uniformly to obtain a mixed material; (2) taking the mixed material and pressing it into a blank; (3) placing the blank in a drying oven for drying treatment to obtain a dried blank; (4) taking the dried blank and placing it in a sintering furnace for sintering treatment, wherein during the sintering process, the sintering additive reacts with the two grinding phases or one of the two grinding phases at high temperature to produce a reinforced and toughened whisker structure.

Description

Technical Field

[0001] The invention relates to the technical field of magnetic abrasives, in particular to a composite magnetic abrasive and a preparation method thereof. Background Art

[0002] In current magnetic grinding processes, the most commonly used grinding phase is an iron-based magnetic abrasive. Commonly used grinding phases include Al2O3, TiC, and SiC, and the iron matrix generally uses reduced iron powder. Furthermore, the existing magnetic abrasive production process is relatively simple, and its strength and toughness are low, resulting in a short service life. For example, while Al2O3-Fe magnetic abrasives can grind a workpiece, they cannot achieve continuous surface removal. After grinding the workpiece for a period of time, if further precision is desired, the process must be stopped and other grinding abrasives must be switched, significantly limiting grinding efficiency. Furthermore, the production cost of high-performance magnetic abrasives, such as those produced by the gas atomization rapid solidification method, is too high.

[0003] Therefore, how to improve the performance of magnetic abrasive particles and reduce the preparation cost of magnetic abrasive particles is a technical problem that needs to be solved urgently. Summary of the Invention

[0004] The technical task of the present invention is to provide a composite magnetic abrasive and a preparation method thereof to solve the problem of how to improve the performance of the magnetic abrasive particles themselves while reducing the preparation cost of the magnetic abrasive particles.

[0005] The technical task of the present invention is achieved in the following manner: a composite magnetic abrasive, comprising an iron matrix, a binder, and a whisker structure, wherein the whisker structure is a reinforced and toughened structure produced by a reaction between a sintering additive and two abrasive phases or one of the two abrasive phases at high temperature;

[0006] Among them, the iron matrix is ​​40-60 parts, the binder is 3-5 parts, the two grinding phases are 20-40 parts, and the sintering additive is 5-10 parts.

[0007] Preferably, the particle size of the iron matrix is ​​150-160 μm.

[0008] Preferably, the iron matrix is ​​made of one or more of reduced iron powder, spherical iron powder and carbonyl iron powder.

[0009] Preferably, the whisker structure is a thin and long structure with a size of 10-20 μm.

[0010] Preferably, the particle size ratio of the two grinding phases is 20:3-10:1, and the particle size of the grinding phase with a larger particle size does not exceed 20 μm.

[0011] Preferably, the two grinding phases are aluminum oxide and silicon carbide.

[0012] Preferably, the particle size of the sintering additive is 1-3 μm;

[0013] Sintering additives include manganese, chromium or copper. At high temperatures, the two grinding phases can react with them to harden, thereby strengthening and toughening the grinding phases. For the iron matrix, the magnetic phase distribution of the iron matrix is ​​changed, the density of effective magnetic atoms is increased, and the saturation magnetization intensity is improved. Manganese atoms cause grain refinement and generate new magnetic phases, thereby increasing the coercive force.

[0014] More preferably, the binder is a 5% by mass polyvinyl alcohol aqueous solution.

[0015] A method for preparing a composite magnetic abrasive, the preparation method is specifically as follows:

[0016] (1) taking 20-40 parts of the two grinding phases, 40-60 parts of the iron matrix, and 5-10 parts of the sintering additive, and adding 3-5 parts of a 5% by mass aqueous solution of polyvinyl alcohol and mixing them uniformly to obtain a mixed material;

[0017] (2) Taking the mixed material and pressing it into a blank with a pressure of 80-110 kN;

[0018] (3) placing the blank into a drying oven for drying to obtain a dried blank; wherein the drying temperature is 100-110° C. and the drying time is 10-12 hours;

[0019] (4) taking the dried blank and placing it in a sintering furnace for sintering treatment, during which the sintering additive reacts with the two grinding phases at high temperature to produce a reinforced and toughened whisker structure; wherein the sintering parameters are 1200°C-1250°C for 6-6.5 hours, a heating rate of 3-3.3°C / min, and a holding time of 2-2.5 hours;

[0020] (5) After sintering, the particles are manually crushed and sieved to obtain magnetic abrasive particles with a size of 150-220 μm.

[0021] Preferably, after the sintering treatment in step (4), during the cooling of the sintering furnace to room temperature, manganese reacts with silicon carbide to form manganese silicide whiskers; the manganese silicide whiskers are stable at high temperatures and grow in the form of whiskers; and free carbon is released when Mn reacts with silicon carbide, and the free carbon reacts with manganese at high temperatures to form manganese carbide whiskers; the manganese carbide whiskers grow through liquid phase mass transfer under a gas-liquid-solid (VLS) mechanism; the iron matrix reaches a level where it does not melt, so that the two grinding phases and the generated whisker structure can be embedded in the surface of the iron matrix.

[0022] The composite magnetic abrasive and the preparation method thereof of the present invention have the following advantages:

[0023] (1) Unlike conventional abrasive grains composed of two grinding phases, the composite magnetic abrasive of the present invention comprises a magnetic matrix, two grinding phases, a sintering additive, and a whisker structure produced by a high-temperature reaction between the grinding phase and the sintering additive. The sintering temperature is raised in a high-temperature sintering furnace to a temperature higher than the melting temperature of the sintering additive and lower than the melting temperature of the magnetic matrix. Two silicon carbide and aluminum oxide with a relatively large size difference react with Mn in a high-temperature environment to produce a whisker structure. Furthermore, in a high-temperature environment, the iron matrix is ​​melted but not dissolved, so that the grinding phase and the produced whisker structure can be embedded in the surface of the iron matrix. The sintering additive Mn melts at its melting point, further reinforcing the embedding of the two grinding phases in the iron matrix surface. The two grinding phases and the produced whisker structure further improve the strength and toughness of the magnetic abrasive grains, thereby enhancing their wear resistance, extending the service life of the magnetic abrasive grains, and greatly reducing the production cost.

[0024] (2) The composite magnetic abrasive processing of the present invention not only enhances the strength and toughness of the magnetic abrasive grains to extend their service life, but also reduces the cost of preparing the magnetic abrasive grains;

[0025] (3) The abrasive phase on the outer surface of the abrasive grain of the present invention comprises multiple layers. The inner matrix of the composite magnetic abrasive grain is an iron matrix, and the outer layer of the iron matrix is ​​embedded with two abrasive phases and a sintering additive after condensation, as well as a whisker structure generated by the abrasive phases and the sintering additive during the high-temperature sintering process. At the same time, the two abrasive phases have a relatively large difference in size, the purpose of which is to facilitate the fixing and embedding of the abrasive phases to each other, further extending the service life of the magnetic abrasive grain.

[0026] (4) The sintering additives of the present invention are manganese, chromium, copper, etc., which can react with the grinding phase and have a melting point below the sintering temperature, so as to further fix the grinding phase and the iron matrix;

[0027] (5) The present invention utilizes a high-temperature sintering furnace to raise the sintering temperature to a temperature higher than the melting point of the sintering additive and lower than the melting temperature of the magnetic matrix, embeds the two grinding phases into the surface of the magnetic matrix, and reacts the grinding phases and the sintering additives through a high-temperature reaction to produce a reinforced and toughened whisker structure, thereby increasing the strength and toughness of the magnetic abrasive particles and improving their wear resistance, thereby extending the service life of the magnetic abrasive particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below with reference to the accompanying drawings.

[0029] Attachment Figure 1 Microscopic SEM and EDS images of composite magnetic abrasive containing Mn additive;

[0030] Attachment Figure 2 Enlarged SEM and EDS images of composite magnetic abrasive whiskers containing Mn additives;

[0031] Attachment Figure 3Schematic diagram of the structure of SiC / Fe magnetic abrasive purchased on the market;

[0032] Attachment Figure 4 is the hysteresis curve of magnetic abrasive particles. DETAILED DESCRIPTION

[0033] The composite magnetic abrasive and its preparation method of the present invention are described in detail below with reference to the accompanying drawings and specific examples.

[0034] Example 1:

[0035] This embodiment provides a composite magnetic abrasive, which includes an iron matrix, a binder, and a whisker structure. The whisker structure is a reinforced and toughened structure produced by the reaction of a sintering additive with two abrasive phases or one of the two abrasive phases at high temperature.

[0036] Among them, the iron matrix accounts for 50% by mass in the composite magnetic abrasive; the binder accounts for 5% by mass in the composite magnetic abrasive; the two grinding phases account for 36% by mass in the composite magnetic abrasive; the sintering additive accounts for 9% by mass in the composite magnetic abrasive; the binder serves as a forming agent and is discharged during the sintering process.

[0037] The particle size of the iron matrix in this embodiment is 150-160 μm.

[0038] The iron matrix in this embodiment is one or more of reduced iron powder, spherical iron powder, and carbonyl iron powder.

[0039] The whisker structure in this embodiment is a long and thin structure with a size of 10-20 μm.

[0040] The particle size ratio of the two grinding phases in this embodiment is 20:3-10:1, and the particle size of the grinding phase with a larger particle size does not exceed 20 μm.

[0041] The two grinding phases in this embodiment are aluminum oxide and silicon carbide.

[0042] The particle size of the sintering additive in this embodiment is 1-3 μm;

[0043] Sintering additives include manganese, chromium or copper. At high temperatures, the two grinding phases can react with them to harden, thereby strengthening and toughening the grinding phases. For the iron matrix, the magnetic phase distribution of the iron matrix is ​​changed, the density of effective magnetic atoms is increased, and the saturation magnetization intensity is improved. Manganese atoms cause grain refinement and generate new magnetic phases, thereby increasing the coercive force.

[0044] The binder in this embodiment is a polyvinyl alcohol aqueous solution with a mass fraction of 5%.

[0045] Example 2 (SiC / Al2O3 / Fe composite magnetic abrasive containing Mn additive)

[0046] This embodiment provides a method for preparing a composite magnetic abrasive, and the preparation method is specifically as follows:

[0047] (1) Material preparation: 60 g of Fe powder with a particle size of 150 μm; 10 g of Al2O3 powder with a particle size of 10 μm-20 μm; 20 g of SiC powder with a particle size of 3 μm-1 μm; and 10 g of Mn powder with an average particle size of 1 μm-3 μm.

[0048] (2) Pressing the abrasive into a blank: Fe powder, Al2O3, SiC, and Mn were mixed to a certain degree, and then 3g of polyvinyl alcohol aqueous solution was added and mixed evenly. The mixture was placed in a press and pressed into a blank at a pressing force of 110KN;

[0049] (3) Drying: After pressing, place the product in a vacuum drying oven at 1120°C for 12 hours.

[0050] (4) Sintering: The blank is placed in a vacuum sintering furnace and sintered at 1200°C for 6 hours, with a heating rate of 3.3°C / min and a holding time of 2.5 hours. It is then cooled to room temperature in the furnace. During this process, Mn reacts with silicon carbide (SiC) to form manganese silicide whiskers (MnSi). These silicides are stable at high temperatures and grow in the form of whiskers. Mn reacts with silicon carbide (SiC) to release free carbon (C), which reacts with Mn at high temperatures to form manganese carbide whiskers (Mn2C). The whiskers grow through liquid phase mass transfer under the gas-liquid-solid (VLS) mechanism. The iron matrix reaches a level where it cannot be melted, so that the two grinding phases and the resulting whisker structure can be embedded in the surface of the iron matrix.

[0051] (5) Crushing: The sintered blank is first crushed into a suitable size manually and then the required composite magnetic abrasive particles are screened out with a sieve.

[0052] Example 3 (SiC / Al2O3 / Fe composite magnetic abrasive grains without sintering agent)

[0053] (1) Material preparation: 55 g of Fe powder with a particle size of 150 μm; 20 g of Al2O3 powder with a particle size of 10 μm; and 20 g of SiC powder with a particle size of 1 μm.

[0054] (2) Pressing the abrasive into a blank: Fe powder, Al2O3, and SiC were mixed to a certain degree, and then 4g of polyvinyl alcohol aqueous solution was added and mixed evenly. The mixture was placed in a press and pressed into a blank at a pressing force of 110KN;

[0055] (3) Drying: After pressing, place the product in a vacuum drying oven at 1120°C for 12 hours.

[0056] (4) Sintering: Place the blank in a vacuum sintering furnace and sinter at 1200°C for 6 hours, with a heating rate of 3.3°C / min and a holding time of 2.5 hours; then cool to room temperature in the furnace;

[0057] (5) Crushing: The sintered blank is first crushed into a suitable size manually and then the required composite magnetic abrasive particles are screened out with a sieve.

[0058] Example 4 (SiC / Fe composite magnetic abrasive)

[0059] (1) Material preparation: Fe powder with a particle size of 150 μm 55; SiC powder with a particle size of 10 μm 48

[0060] (2) Pressing the abrasive into a blank: Mix Fe powder and SiC to a certain degree, add 4.5 ethylene alcohol aqueous solution and mix evenly, put it into a pressing machine and press it into a blank with a pressing force of 110KN;

[0061] (3) Drying: After pressing, place the product in a vacuum drying oven at 120°C for 12 hours.

[0062] (4) Sintering: Place the blank in a vacuum sintering furnace and sinter at 1150°C for 6 hours, with a heating rate of 3.2°C / min and a holding time of 3 hours; then cool to room temperature in the furnace;

[0063] (5) Crushing: The sintered blank is first crushed into a suitable size manually and then the required composite magnetic abrasive particles are screened out with a sieve.

[0064] Example 5 (Al2O3 / Fe magnetic abrasive)

[0065] (1) Material preparation: 50 g of Fe powder with a particle size of 150 μm; 45 g of Al2O3 powder with a particle size of 10 μm;

[0066] (2) Pressing the abrasive into a blank: After mixing Fe powder and Al2O3 to a certain degree, add 3.5g of polyvinyl alcohol aqueous solution and mix evenly. Put the mixture into a pressing machine and press it into a blank with a pressing force of 110KN;

[0067] (3) Drying: After pressing, place the product in a vacuum drying oven at 120°C for 12 hours.

[0068] (4) Sintering: Place the blank in a vacuum sintering furnace and sinter at 1150°C for 6 hours, with a heating rate of 3.2°C / min and a holding time of 3 hours; then cool to room temperature in the furnace;

[0069] (5) Crushing: The sintered blank is first crushed into a suitable size manually and then the required composite magnetic abrasive particles are screened out with a sieve.

[0070] The structure of the composite magnetic abrasive material proposed in this embodiment for fully realizing fine processing is shown in the attached figure. Figure 1 As shown in the figure, it can be seen that there are two grinding phases, the sizes of the two grinding phases are quite different, smaller silicon carbide particles are also attached to the spherical alumina, and whiskers are generated on the surface of the iron matrix, which can achieve long-term and efficient grinding. Figure 2 This is the EDS image of the whisker structure. It can be seen that the main components of the whiskers are Mn and Si.

[0071] The structure of existing magnetic abrasive is as shown in the attached Figure 3 As shown in the figure, it can be seen that there is only one grinding phase. When the grinding phase fails, the life of this magnetic abrasive is exhausted, and long-term grinding cannot be achieved. In addition, the preparation cost is high, and the spherical structure is not uniform, so precision grinding cannot be achieved.

[0072] Attachment Figure 4 For the hysteresis curve of this composite magnetic abrasive, Figure 3 The saturation magnetization and coercive force of the composite magnetic abrasive particles can be read from the hysteresis curve.

[0073] The performance of magnetic abrasive particles is primarily evaluated by two indicators: saturation magnetization Ms and coercive force Hc. The saturation magnetization is the maximum magnetization that a magnetic abrasive particle can achieve when magnetized in an external magnetic field. The greater the saturation magnetization of a magnetic abrasive particle, the greater its magnetic field sensitivity, the faster its magnetization speed, the higher its relative magnetic permeability, and the better its ferromagnetic properties. During operation, the grinding pressure exerted by the magnetic abrasive particles on the workpiece and their ability to agglomerate with each other are also greater. After the magnetic abrasive particles are saturated magnetized, when the external magnetic field returns to zero, the magnetic induction intensity of the magnetic abrasive particles cannot return to zero. A certain magnetic field must be applied in the opposite direction of the external magnetic field to return the magnetic induction intensity to zero. This applied magnetic field is called coercive force. Therefore, magnetic abrasive particles with a large saturation magnetization and a small coercive force are preferred in magnetic particle finishing technology. Table 1 compares the saturation magnetization and coercive force of Examples 2 to 5 and commercially available SiC / Fe magnetic abrasive particles.

[0074] Table 1

[0075]

[0076] As can be seen from Table 1, in this embodiment, based on the sintering additive, the two abrasive phases react at high temperature to produce whisker structures, and the melting point of the sintering additive is reached during sintering, so that the two abrasive phases are combined together through the molten sintering additive. After cooling, the sintering additive also solidifies to make the combination stronger, further enhancing its performance and reducing the cost of preparing high-performance magnetic abrasive particles.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite magnetic abrasive, characterized in that: The composite magnetic abrasive comprises an iron matrix, a binder and a whisker structure, wherein the whisker structure is a reinforced and toughened structure formed by the reaction between a sintering additive and two grinding phases or one of the two grinding phases at high temperature; Among them, 40-60 parts of iron matrix, 3-5 parts of binder, 20-40 parts of two grinding phases, and 5-10 parts of sintering additives; The particle size of the iron matrix is ​​150-160 μm; the iron matrix is ​​one or more of reduced iron powder, spherical iron powder, and carbonyl iron powder; The particle size ratio of the two grinding phases is 20:3-10:1, and the particle size of the large grinding phase does not exceed 20 μm; the two grinding phases are made of aluminum oxide and silicon carbide; The particle size of the sintering additive is 1-3 μm; the sintering additive is manganese, chromium or copper.

2. The composite magnetic abrasive according to claim 1, characterized in that: Whisker tissue is a long and thin structure with a size of 10-20 μm.

3. The composite magnetic abrasive according to claim 1 or 2, characterized in that: The binder is a 5% by mass polyvinyl alcohol aqueous solution.

4. A method for preparing a composite magnetic abrasive, characterized in that: The preparation method is specifically as follows: (1) taking 20-40 parts of the two grinding phases, 40-60 parts of the iron matrix and 5-10 parts of the sintering additive, adding 3-5 parts of a 5% by mass aqueous solution of polyvinyl alcohol and mixing them uniformly to obtain a mixed material; (2) Take the mixed material and press it into a blank with a pressure of 80-110KN; (3) placing the blank into a drying oven for drying to obtain the dried blank; wherein the drying temperature is 100-110°C and the drying time is 10-12 hours; (4) The dried blank is placed in a sintering furnace for sintering. During the sintering process, the sintering additive reacts with the two grinding phases at high temperature to produce a reinforced and toughened whisker structure. The sintering parameters are 1200°C-1250°C for 6-6.5 hours, a heating rate of 3-3.3°C / min, and a holding time of 2-2.5 hours. (5) After sintering, artificial crushing is performed to screen out magnetic abrasive particles of 150-220 μm; In which, after the sintering treatment in step (4), when the sintering furnace is cooled to room temperature, manganese reacts with silicon carbide to form manganese silicide whiskers; the manganese silicide whiskers are stable at high temperatures and grow in the form of whiskers; and when Mn reacts with silicon carbide, free carbon is released, and the free carbon reacts with manganese at high temperatures to form manganese carbide whiskers; the manganese carbide whiskers grow through liquid phase mass transfer under a gas-liquid-solid mechanism; the iron matrix reaches a level that does not melt, so that the two grinding phases and the generated whisker structure can be embedded in the surface of the iron matrix.

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