JP2000263447A - Abrasive material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grinding wheel, which can facilitate accurate polishing of a material of hard quality, and very excellent in polishing efficiency as compared with a diamond electro-deposited grinding wheel in the past. SOLUTION: This abrasive material consists of alumina long fiber, diamond abrasive grain, and matrix resin, with the fiber end of the alumina long fiber serving as an abrasive treatment end. This abrasive material is formed in a compound structure of a fiber rich part consisting of the alumina long fiber and the matrix resin and an abrasive grain rich part consisting of the diamond abrasive grain and the matrix resin. The abrasive material comprises, for instance, an UD sheet layer arranging all the alumina long fiber in the same direction to be bound by a thermosetting resin matrix and an abrasive grain layer binding the diamond abrasive grain by the thermosetting resin matrix, the abrasive grain is arranged in at least one surface of obverse/reverse flat surfaces, and a tip end part of the alumina long fiber is integrally formed in flat plate shape so as to be hit to a polishing surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abrasive material such as a grinding wheel, and is suitable for polishing hard materials such as cemented carbide, high-hardness steel, and hardened steel. The present invention relates to an abrasive material suitable for precision polishing fine parts such as ribs and bosses by hand polishing or using a vibration tool or a rotary tool.

[0002]

2. Description of the Related Art In recent years, molds made of high-hardness steel or hardened steel having a Rockwell hardness C (HRC) of 50 or more and cemented carbide having a higher degree have been increasing. The abrasive material capable of polishing these hard materials is mainly diamond. However, conventional diamond whetstones are formed using diamond abrasives as a binder with metal or thermosetting resin, and are widely used for grinding and cutting hard materials, but are rarely used for polishing. It can be said that there was no diamond grindstone suitable for precision polishing. The reason is that when precision polishing is conventionally performed, it is common to polish with a wooden or bamboo spatula using diamond powder or diamond paste, and this method requires a long time for polishing and requires skill. There was a problem and the appearance of the solid whetstone type was strongly desired, but the whetstone could not cope with the work unless it was small and thin, and at the same time, the whetstone itself required considerable strength and elasticity. This is because forming the diamond whetstone into such a shape was brittle and impractical.

On the other hand, as a method of reinforcing a grindstone, a method of blending various reinforcing fibers is widely known. For example, Japanese Patent Application Laid-Open No. 63-52972 proposes a method of reinforcing with short fibers of silicon carbide fiber, carbon fiber, silicon nitride fiber, boron fiber, and alumina fiber. The publication also discloses that a method of reinforcing with long fibers was known before that time. However, up to now, there has been no known whetstone composed of the three components of the reinforcing fiber, the abrasive grains, and the matrix resin that can precisely polish a hard material. In other words, while polishing of a hard material requires both excellent polishing properties and high grindstone strength, conventionally known fiber-reinforced grindstones have not sufficiently satisfied this requirement.

[0004]

As described above, in the fiber-reinforced grindstone, when the abrasive content is emphasized to increase the abrasive content, the strength is reduced, while the strength is emphasized and the fiber content is increased. If this is attempted, there is a problem that practical polishing properties cannot be obtained. The present inventors have attempted to solve this problem and provide an abrasive having excellent practicality and sufficient practical strength.

[0005]

In order to achieve the above object, the abrasive of the present invention comprises alumina long fibers, diamond abrasive grains, and a matrix resin as essential components. By dividing the distribution state of long fibers and diamond abrasive grains into two regions, that is, an alumina long fiber rich area and a diamond abrasive grain rich area, excellent polishing properties were exhibited and strength was improved. With such an arrangement of the alumina continuous fiber and the diamond abrasive grains, it is possible to mix necessary and sufficient abrasive grains for polishing without lowering the strength of the abrasive. Furthermore, by using a specific alumina long fiber as a reinforcing fiber, higher strength was achieved as an abrasive. That is, the polishing material of the present invention is an abrasive material comprising an alumina continuous fiber, diamond abrasive grains, and a matrix resin, wherein a fiber end of the alumina continuous fiber is a polished end, as described in claim 1. Further, it is characterized in that it is formed in a composite structure of a fiber-rich portion composed of the alumina long fiber and the matrix resin, and an abrasive grain-rich portion composed of the diamond abrasive and the matrix resin. Claim 2
An abrasive according to the present invention is characterized in that, in the abrasive according to the first aspect, the fiber-rich portion is formed of a UD sheet of alumina long fiber. The abrasive according to claim 3 is:
The abrasive material according to claim 1, wherein a plurality of cord-like elements each composed of a fiber-rich portion and an abrasive-grain-rich portion provided in parallel with the longitudinal direction are formed in a bundle. The abrasive according to claim 4 is the abrasive according to any one of claims 1 to 3, wherein the content of diamond abrasive grains is 10 to 2 or less.
0% by weight. The abrasive according to claim 5 is characterized in that, in the abrasive according to any one of claims 1 to 4, the filaments of the alumina long fibers mainly consist of filaments having a flat cross section. The abrasive according to claim 6 is the abrasive according to claim 5, wherein a ratio of a major axis to a minor axis of the cross-sectional shape is 1.3 to 1.8. Further, the abrasive according to claim 7 is the abrasive according to any one of claims 1 to 6, wherein a bending strength when a load is applied perpendicularly to a longitudinal direction of the long alumina fiber is 500 Mpa or more, The flexural modulus is 50 GPa or more. The abrasive according to claim 8 is the abrasive according to any one of claims 1 to 7, wherein the thickness is 0.45 to 1.2.
mm in the shape of a flat plate.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The fibers used in the polishing material of the present invention are alumina long fibers. Glass fibers, carbon fibers, silicon carbide fibers, and the like are known as reinforcing fibers, but when used as an abrasive, there is a drawback that they slip on the polished surface, and alumina fibers are most suitable. It is considered that the reason is that, in the case of alumina fibers, the tips of the fibers are sequentially crushed during polishing.

As the diamond abrasive used for the polishing material of the present invention, a commercially available diamond abrasive having a number of about 100 to 1,000 is most preferably used, but is not limited thereto.

As the matrix resin for bonding the alumina fibers and abrasive grains of the present invention, a thermosetting resin such as an epoxy resin, a phenol resin, a polyimide resin, a polymaleimide resin, and an unsaturated polyester resin is preferable.

The abrasive of the present invention is characterized in that the distribution of the reinforcing fibers and the abrasive grains constituting the abrasive is separated into a fiber rich portion and an abrasive grain rich portion so that the abrasive particles are not contained in the fiber layer. As a result, the abrasiveness and practical strength, which are the objects of the present invention, are achieved by the high abrasiveness of the abrasive grain-rich portion and the abrasiveness and strength retention of the fiber-rich portion with alumina fibers.

The formation of the abrasive-rich portion and the fiber-rich portion is basically performed by binding alumina fibers with a matrix resin containing no abrasive and forming a fiber-rich portion. The method for forming the diamond abrasive grains is not particularly limited as long as the diamond abrasive grains are contained only in the matrix resin integrally formed with the fiber-rich portion and separately formed in another area.

For example, the fiber-rich portion may be formed of a UD sheet or a winding sheet of alumina long fiber, and these sheets may be formed in a single layer or a multilayer structure. Specifically, a UD sheet layer in which all of the alumina long fibers are arranged in the same direction and bound by a thermosetting resin matrix, and an abrasive layer in which diamond abrasive grains are bound by a thermosetting resin matrix. In this case, the abrasive layer may be arranged on at least one surface of the front and back flat surfaces, and may be integrally formed in a flat plate shape such that the tip of the alumina long fiber hits the polishing surface. The fiber-rich portion made of the UD sheet may be formed in any shape, such as being wound into a rod.

Further, for example, by cutting the UD sheet provided with the diamond abrasive grain layer into a thin string shape, a string-shaped element having a fiber rich portion and an abrasive grain rich portion in parallel with the longitudinal direction is provided. A plurality may be prepared, and these may be formed into an arbitrary shape such as a flat plate shape or a round bar shape to form an abrasive.

The abrasive of the present invention has a thickness of, for example, 0.45 to 0.45.
What is necessary is just to form it as a flat plate of 1.2 mm and a width of about 3 to 20 mm.

The abrasive content of the abrasive of the present invention is 10
Preferably, it is about 20% by weight. Since the abrasive of the present invention has sufficient abrasiveness when the total abrasive content of the abrasive is 20% by weight or less, it is not necessary to contain more abrasives, and the strength decreases and the abrasive material is consumed quickly. Or become. On the other hand, if it is less than 10% by weight, the polishing properties are basically insufficient.

It goes without saying that the alumina fiber used in the present invention has better strength. The tensile strength of alumina fibers was at most about 100 kg / mm ^{2 for} short fibers and fragile long fibers at the beginning of development.
About 50 to 200 kg / mm ² are produced. The alumina long fiber used in the present invention has a tensile strength of 1.8 GPa (about 1 GPa).
80kg / mm ² ) or more, tensile modulus 180Gpa (about 180ton)
/ mm ² ) or more.

As described above, the strength of alumina fibers is not always high as compared with carbon fibers and the like. Therefore, there is a limit even if high-strength alumina fibers are used to improve the strength of the grindstone. The inventors of the present invention have conducted intensive studies and found that the strength of the grindstone is further improved when the filament group of the fibers is mainly made of alumina fibers having a flat cross section. That is, the alumina fibers used in the present invention preferably have a filament group mainly having a flat shape, not a normal circular cross section. Specific examples of the flat shape include an elliptical shape, a cocoon shape, and a raindrop shape, and these may be mixed. The filament may be mixed with the filament having a round cross section, but the number of filaments having a round cross section is preferably as small as possible.
% Is preferable. The flat shape preferably has a ratio of the major axis to the minor axis in the range of 1.3 to 1.8. The reason that the strength of the grindstone is further improved by using such a fiber having a flat cross-sectional shape is that the bonding area between adjacent filaments and abrasive grains increases through the matrix resin, and the molded body may generate external stress. When receiving and destroying,
It is presumed that the phenomenon that the fiber comes off from the matrix resin, that is, the so-called pull-out phenomenon, hardly occurs.

Since the abrasive of the present invention is used for polishing hard materials, it is practically preferable that the specific strength of the abrasive is 500 MPa or more and the flexural modulus is 50 GPa or more. A bending strength of about 800 MPa is required in order to almost eliminate the fear of breakage of the abrasive during use. Such a strength can be obtained by using an alumina fiber having a tensile strength of 1.8 Gpa or more and a tensile modulus of 180 Gpa or more in the layered structure of the present invention. In addition, if the cross-sectional shape of the filaments constituting the alumina fiber bundle is mainly flat, a polishing material with higher strength can be obtained. It is more preferable that the bending strength is 1,000 Mpa or more.

[0018]

Embodiments of the present invention will be described below. (Example 1) The number of filaments is 1000 with a fiber diameter of 10 μm.
Alumina fiber roving yarn (Al ₂ O ₃ 85
Weight%, SiO ₂ 15 weight%, average tensile strength 2.5Gp
a, 100 parts by weight of an epoxy resin (Epicoat 828 manufactured by Yuka Shell Epoxy), 80 parts by weight of tetrahydroxymethyl phthalic anhydride (HN2200 manufactured by Hitachi Chemical Co., Ltd.), and imidazole (2E4MZ-)
CN (Shikoku Chemical Industry Co., Ltd.) The resin composition was dipped in a tank of 2 parts by weight and impregnated with the resin composition, and the excess resin was wound around a rotating drum having a diameter of 330 mm while being squeezed with a steel roller. At this time, the yarn is traversed so that the yarns do not overlap on the drum, and the yarns adjacent to each other are not separated too much. Carefully cut open and allow thickness to 0.25
mm, a width of 250 mm, a length of about 1000 mm, and a sheet-like molded product in which fibers were arranged in one direction. Subsequently, this was heated at 115 ° C. for 30 minutes to be semi-cured, divided into four equal parts, and
Four UD prepregs of alumina long fiber having a side of 250 mm were obtained.

Using three UD sheets obtained as described above, artificial diamond abrasive grains (No. 170-200, manufactured by EID) are evenly adhered to one side of each of the two UD sheets. With the sheet that does not adhere
The three sheets are laminated so that the surface of the remaining sheets to which the diamond abrasive grains adhere is on the outside, and at this time, the fiber directions of the upper and lower sheets are shifted by about 5 degrees in different directions about the fiber direction of the middle sheet as an axis ( The upper sheet and the lower sheet were shifted by about 10 degrees in the fiber direction), and were cured with a heating and pressure molding machine at a temperature of 160 ° C. and a pressure of 30 kg / cm ² for 3 hours. Eighty flat sticks each having a width of 10 mm and a length of 50 mm were cut out from the obtained molded plate, and used as a grindstone for polishing. The average thickness of the whetstone is 0.5mm and the content of diamond abrasive grains is about 1
2.5 wt%, flexural strength 840 Mpa, flexural modulus 5
It was 7.3 GPa.

The grinding performance of this grindstone was measured as follows. NAK80 high hardness steel electric discharge machined product (hardness HRC50 of electric discharge machined surface, surface roughness Ra as polishing test work)
The stick whetstone is attached to a polishing tool (Turbo-Lap Swing TLS-07 manufactured by UHT) using a polishing tool (approximately 10 μm), and the vibration is applied to the whetstone by air pressure at 17,000 reciprocations / minute to apply a total load of about 250 g. A polishing test was performed by pressing the side of the stick against the surface.
The polishing time at this time and the surface roughness Ra (μ
Table 1 shows the relationship with m). Further, the weight loss of the test piece after polishing was measured, and the relationship between the polishing time and the cutting amount was shown in Table 2. Furthermore, using the same grindstone, the cemented carbide (V-30, HR
(A89.0, surface roughness Ra of about 1 μm) was subjected to an abrasion test under the same conditions. Table 3 shows the results.

(Example 2) Four UD prepreg sheets were manufactured under the same conditions as in Example 1, and after attaching diamond abrasive grains (No. 100-120) to one surface of each sheet, the fiber direction of all sheets was adjusted. First, the surfaces of the two sheets on which the diamond abrasive grains are not adhered are aligned with each other, and the surfaces of the remaining sheets on which the diamond abrasive grains are not adhered are also aligned, and the same as in Example 1. To form a molded plate having a thickness of 1 mm. From this plate, 80 flat stick-shaped grindstones having a width of 10 mm and a length of 50 mm were cut out. The content of the diamond abrasive grains in the grindstone was about 17% by weight, the bending strength was 596 Mpa, and the flexural modulus was 58.6 Gpa. A polishing test was performed on this grindstone under the same conditions as in Example 1 except that the angle between the stick and the work was 45 degrees and the load was 700 g. The results are shown in Tables 1 and 2. Further, using the same grindstone, a cemented carbide (V-30, HRA 89.0, surface roughness Ra about 1 μm)
An abrasion test was performed on the workpiece under the same conditions. Table 3 shows the results. As can be seen from the results shown in Tables 1 and 2, in both Examples 1 and 2, the level of Ra = 0.5 μm or less, which is usually required as the surface roughness of the cemented carbide mold, is easily obtained in a short time. Has been achieved.

(Comparative Example 1) In Example 1, 40% by weight of the same diamond abrasive grains as used in Example 1 were previously mixed with the resin composition, and the roving yarn of alumina fiber was constantly mixed with the resin tank while stirring. Except for the dipping, a UD prepreg sheet was prepared under the same operation and conditions as in Example 1. Since this sheet already contains diamond abrasive grains, the abrasive grains are not attached to the sheet surface, and the fiber direction of each sheet is shifted in the same manner as in Example 1 to laminate three sheets. Then, pressure treatment was performed to form a plate, and a stick having the same dimensions was cut out. The distribution state of the abrasive grains in this whetstone is random unlike Example 1, the content is about 15% by weight, the thickness of the stick is 0.5 mm, the bending strength is 362 MPa, and the bending elastic modulus is 35.2 GPa. there were. When a polishing test of the same NAK material as in Example 1 was performed,
The stick broke during polishing.

Comparative Example 2 A stick-shaped grindstone was manufactured under the same conditions as in Comparative Example 1, except that the amount of diamond abrasive grains mixed with the resin was changed to 15% by weight. The abrasive content of the grindstone is about 5% by weight, the thickness is 0.48mm, and the bending strength is 5
At 43 Mpa and the flexural modulus was 52.4 GPa, the strength reached a practical level. However, when the same NAK material as in Example 1 was subjected to the polishing test, as shown in Tables 1 and 2, the polishing performance was extremely high. It was low.

(Comparative Example 3) A commercially available diamond electrodeposited file (diamond file for ribs HTL2-200, thickness 0.3 mm, width 6 mm, length 72 mm, diamond abrasive grain No. 200) having the same abrasiveness as in Example 1 Conduct the test,
The results are shown in Tables 1 and 2. In addition, a polishing test of the cemented carbide was performed under the same conditions as in Example 1, and the results are shown in Table 3.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

As is clear from the above tables, according to the present invention, the surface roughness (Ra) at the same polishing time was obtained despite the same initial surface roughness as compared with the conventional diamond electrodeposition stick. Is extremely low, and a grinding wheel with excellent cutting efficiency and high polishing efficiency can be obtained.

Example 3 Monofilament is 0.25
Alumina long fiber bundles having 1,000 filaments in TEX (87% by weight of Al ₂ O ₃ , 13% by weight of SiO ₂ , specific gravity 3.2, average fiber diameter 1 obtained from specific gravity and TEX)
0 μm, average tensile strength 2.5 Gpa obtained from this diameter, average tensile elasticity 220 Gpa, filaments with a cross section of a cocoon-shaped cross section, and a short axis to long axis ratio of 1 .5. In addition, the filament with a round cross section was hardly observed), and this alumina-based long fiber bundle was wound in parallel,
While traversing so that the gap between adjacent fiber bundles is as small as possible, a rotating drum with a diameter of 330 mm
The fiber bundle was wound up to 0 mm, a polyfilm was applied on the fiber layer, and a roller was rolled from above to open the fiber bundle, thereby completely eliminating a slight gap between the fiber bundles. Subsequently, an epoxy resin composition having the following composition was applied to this fiber layer with a hand roller, dried, and then cut open in the rotation axis direction to obtain a UD prepreg sheet. Epoxy resin composition Epicoat 828 (manufactured by Yuka Shell Epoxy) 100 parts by weight Boron trifluoride monoethylamine 3 parts by weight Methyl ethyl ketone (MEK) 25 parts by weight A 220 mm × 220 mm sheet is cut out from this sheet and heated at 115 ° C. for 15 minutes. After pre-curing (preliminary curing), diamond abrasive grains (No. 400) of 375 to 400 mesh were sprinkled and adhered to both sides of the sheet as uniformly as possible using a 200 mesh sieve. At this time, the diamond content was adjusted to about 12% by weight while weighing the whole. Next, the sheet was cut by a cutting machine to a width of about 1 mm along the fiber direction. 55 pieces of the obtained string-like objects were each 10 mm in width × 10 mm in depth × 220 in length.
mm in a groove of a groove-shaped mold, and press the top of the mold with the convex part of the mold, apply hot pressing, and compress to a thickness of 1 mm.
The mixture was heated at 0 ° C. for 1 hour, and further heated at 170 ° C. for 3 hours to cure the epoxy resin composition. As a result of observing the cross section of the cured product with an electron microscope, a large number of fiber layers (some of which are partially bent) having a width of about 1 mm and a thickness of about 0.2 mm were arranged in an irregular direction. A diamond abrasive layer having a thickness of about 0.05 mm was observed at the boundary surface.

A part of the molded product is put into a crucible, weighed, baked in air at 650 ° C. for 1 hour to burn the resin, weighed, and further baked at 1,200 ° C. for 3 hours to burn diamond. After that, it was weighed and the diamond content was calculated. As a result, it was 12.4% by weight.

The average strength of the molded body was determined by measuring ten test pieces. As a result, the bending strength was 1,210 Mp
a, It was determined that the flexural modulus was 106 Gpa and that it had sufficient strength as a wrapping material.

The test wrapping material has a thickness of 1
The molded body cut into a stick shape of mm x 10 mm x 50 mm in length was mounted on a special air tool (Turbo-Lap Swing TLS-07 manufactured by UHT), and a vibration of 17,000 reciprocations per minute was given to load approximately The polishing test of the cemented carbide test piece was performed while applying 700 g. Used cemented carbide (V10 wire cut, Rockwell hardness A = 90)
Surface roughness before polishing was Ra = 2.291 μm, Rmax
= 19.175 μm, but as a result of polishing the polished surface of 30 mm × 15 mm for 10 minutes, Ra = 0.194 μm, R
max = 5.754 μm, and after 30 minutes Ra =
It reached 0.062 μm and Rmax = 0.931 μm, and the polishing property was extremely good. The sustainability and uniformity of the polishing performance were at a level with almost no problem.

As a means for confirming whether or not the wrapping material has practical strength, it is necessary to evaluate not only a strength test but also a situation close to actual polishing. The properties were evaluated as follows. The surface of the cemented carbide plate of the same material as the above-mentioned polishing test was machined in steps from the upper stage to the lower stage with the surface processed in a step shape (the step is 2 mm). We checked whether it could withstand the impact of falling from the tier to the lower tier. As a result, the wrapping material obtained in this example did not break or break, and had sufficient practical strength.

(Example 4) Forty cords obtained under the same conditions as in Example 3 were aligned, wrapped with a Teflon film to form a round bar, and set in a rubber press (liquid tank using silicone oil). 120 while pressing at 50 kg / cm ²
The film was heated at 150 ° C. for 30 minutes, further heated at 150 ° C. for 30 minutes, taken out, unwrapped, placed in an oven and heated at 170 ° C. for 3 hours to obtain a round bar-shaped molded product having a diameter of about 3.2 mm. Was. This was cut to a length of 50 mm with a diamond disc cutter, and then processed into a centerless rod into a round bar having a diameter of 3.0 mm. The diamond content of the round bar manufactured in this manner is 12.2% by weight, the strength is an average value of five pieces, the bending strength is 1,030 MPa, and the bending elasticity is 96 GPa.
It was determined that the steel had sufficient strength as a rotary tool.

An inverted conical hole is drilled from a 5 mm thick DC53 hardened steel plate (Rockwell hardness C = 61) by electric discharge machining (hole diameter: 3 mm, cone angle: 60 degrees). A 1 mm diameter through-hole was prepared as a test piece. The surface roughness of the inner wall of the cone is Ra = 2.488 μm, R
max = 18.219 μm. Next, the round bar was attached to a special rotating tool, the tip was machined to the same conical shape as the test piece using a diamond file, and the inner wall of the test piece was polished by rotating at 30,000 rpm for 1 minute. The surface roughness was measured every time. The strength during use was not a problem at all, and no breakage or cracking of the round bar was observed. The surface roughness was Ra = 0.925 μm and Rmax = 6.31 after 3 minutes of polishing.
The thickness reached 3 μm, which was sufficient for practical use.

[0036]

As described above, according to the present invention, rough polishing is performed on hard materials such as high-hardness steel having a Rockwell hardness C (HRC) of 50 or more and hard metals having higher hardness. It can be used commonly for finishing and polishing, and can also be applied to precision polishing of fine parts and small areas such as grooves and corners of ribs and boss molds, usually required for surface roughness of cemented carbide molds The present invention provides a polishing whetstone and a polishing method which have a polishing efficiency at which a level of Ra = 0.5 μm or less can be easily achieved in a short time and have excellent precision polishing properties.

Claims (8)

[Claims] 1. A polishing material comprising an alumina continuous fiber, diamond abrasive grains, and a matrix resin, wherein a fiber end of the alumina continuous fiber is a polished end. A polishing material formed in a composite structure of a fiber-rich portion made of a diamond abrasive grain and a matrix resin. 2. The abrasive according to claim 1, wherein the fiber-rich portion is formed of a UD sheet of long alumina fibers. 3. The abrasive according to claim 1, wherein a plurality of cord-like elements each comprising a fiber-rich portion and an abrasive-rich portion provided in parallel with the longitudinal direction are formed by convergence. 4. The content of diamond abrasive grains is 10 to 20.
The abrasive according to any one of claims 1 to 3, wherein the amount is% by weight. 5. The abrasive according to claim 1, wherein the filaments of the alumina long fibers are mainly composed of filaments having a flat cross section. 6. The abrasive according to claim 5, wherein a ratio of a major axis to a minor axis of the cross-sectional shape is 1.3 to 1.8. 7. The method according to claim 1, wherein the bending strength is 500 Mpa or more and the bending elastic modulus is 50 Gpa or more when a load is applied perpendicularly to the longitudinal direction of the alumina long fiber. The abrasive according to any one of the above. 8. The abrasive according to claim 1, wherein the abrasive is formed in a flat plate shape having a thickness of 0.45 to 1.2 mm.