CN110695864B

CN110695864B - Electrostatic sand planting method for coated abrasive tool and application thereof

Info

Publication number: CN110695864B
Application number: CN201910974308.9A
Authority: CN
Inventors: 翟建昌; 徐焕明; 孟霞; 姚刚
Original assignee: Zibo Riken Mt Coated Abrasives Co ltd
Current assignee: Zibo Sangong Taishan Coated Abrasives Co ltd
Priority date: 2019-10-14
Filing date: 2019-10-14
Publication date: 2021-04-20
Anticipated expiration: 2039-10-14
Also published as: CN110695864A

Abstract

The invention provides a thin planting method of a coated abrasive tool and application thereof. The sand planting method comprises the following steps: (1) a belt with continuous concave points or through holes is used as a sand planting belt, so that the grinding materials fall into the concave points of the sand planting belt without overflowing, or a part of the grinding materials are discharged through the through holes, and a part of the grinding materials are left on the surface of the belt; (2) when the static sand planting is carried out, the grinding materials in the concave points or the grinding materials remained outside the through holes move along with the belt, and are distributed on the base material coated with the primer under the action of an electric field; the pits or through holes are regularly and continuously distributed on the belt in an array, so that each pit or through hole on the belt has the same surrounding environment. The invention can ensure that the grinding materials can be uniformly and quantitatively distributed on the sand-planting belt to achieve the purpose of quantitatively diluting and planting the sand, and the grinding materials can be firmly fixed on the base material, thereby effectively improving the grinding capability of the grinding material product, reducing the sand drop rate and prolonging the grinding service life of the grinding tool.

Description

Electrostatic sand planting method for coated abrasive tool and application thereof

Technical Field

The invention belongs to the field of manufacturing of coated abrasive tools, and particularly relates to a sparse planting method of a coated abrasive tool and application thereof.

Background

The coated abrasive is an abrasive in which an abrasive is uniformly coated on a substrate such as paper, cloth, chemical fiber, or other composite materials with an adhesive. According to the shape of the coated abrasive tool, the coated abrasive tool can be divided into a sheet shape (such as sheet sand paper and abrasive cloth), a roll shape (such as abrasive belt), a belt shape (such as abrasive cloth sleeve), a disc shape (such as vulcanized fiber paper abrasive disc) and the like. Coated abrasives, such as sandpaper or abrasive belts, have a tendency to accumulate abrasive dust on the abrasive surface of the abrasive article during the grinding process, so that the abrasive article has a reduced ability to continue grinding without severe wear and loss of abrasive particles, due to the reduced grinding efficiency caused by the clogging of the abrasive dust. This is especially true when working with easily clogged materials, which often results in a short service life of a piece of intact sandpaper or sanding belt.

In the past, the above problems have been solved by using a large amount of cooling liquid during the grinding process, or by blowing with compressed air, brushing with a brush, or the like. However, some materials are not suitable for processing by cooling liquid; the cooling liquid is easy to cause pollution in some working environments; compressed air blowing or brush brushing or the like may interfere with the continuity of the grinding work or the like. Abrasive products of the sparse planting sand mold are developed later, particularly for machine grinding, abrasive belts or sand paper with various specifications can be manufactured, and the abrasive belts or the sand paper are adhered, wrapped by rollers or pressed on some specific machine tools for grinding.

At present, the coating mode of coated abrasive tools such as sand paper or abrasive belt is mainly electrostatic sand planting, and the abrasive materials are bonded on a base material adhered with glue solution by controlling the voltage between two polar plates. Fig. 1 shows a schematic diagram of a method and apparatus for electrostatic sand-planting. When sand is planted, abrasive particles fall on a smooth belt and are adhered to a base material with primer through voltage between two polar plates. For the electrostatic sand planting technology, the effect of thin sand planting is usually realized by changing the amount or composition of a primer layer, reducing the sand falling amount and the like. However, in actual production, the shakeout amount is realized by controlling the clearance of the sand box, and when the particle size of the abrasive particles is relatively small, the precision of simply controlling the clearance of the sand box cannot realize the rare planting sand, especially the fine abrasive with P1000. Therefore, the sand planting machine used in the prior art has limited capacity of controlling the sand falling amount, and the degree of sand planting in a diluted mode by adopting the method is limited. And the sand planting amount is adjusted by controlling the primer amount, so that when the primer amount is too small, the abrasive is not firmly bonded and is easy to fall off, thereby influencing the quality of the coated abrasive tool.

Accordingly, there remains a need for improved thin-laid sand techniques in the field of coated abrasives, particularly in the field of the manufacture of sandpaper or coated abrasives and the like.

Disclosure of Invention

The invention provides an electrostatic sand planting method for a coated abrasive tool, which comprises the following steps:

(1) a belt with continuous concave points is used as a sand planting belt, so that the grinding materials fall into the concave points of the sand planting belt without overflowing;

(2) when the static is planted with sand, the abrasive material in the concave points is distributed on the base material coated with the primer under the action of the electric field along with the movement of the belt.

According to the technical scheme of the invention, the pits are regularly and continuously distributed on the belt to form an array, so that each pit on the belt has the same surrounding environment, namely, when any two adjacent pits in the array are described by one vector, if the vector is moved in parallel, when one end of the vector falls on one pit in the array, the other end of the vector inevitably falls on the other adjacent pit in the array. For example, the array may be in the form of a square array, a diamond array, or the like. In one embodiment of the invention, the array is a square array, wherein the sides of the square are parallel to the direction of belt travel. In another embodiment of the invention, the array is a square array, wherein the diagonal of the square is parallel to the direction of belt travel.

Preferably, the pit array is such that the distance from any pit to its neighbouring pit is the same.

The cross section of the concave point is not limited, and can be circular, polygonal (such as triangle, quadrangle, pentagon, hexagon, etc., equilateral, or non-equilateral) or other irregular shapes. All the pits on the belt may be of the same shape or a collection of shapes. For the belt to be inexpensive to manufacture, it is preferred that all of the dimples on the belt be circular or square or diamond in shape, etc.

The longitudinal section of the concave point can be in the shape of a rectangle or a square with the same width, or in the shape of a trapezoid with a large opening and a small bottom, or in the shape of an arc.

The opening area of each pit is not particularly limited, and the object of the present invention can be achieved by ensuring that the total area of the opening areas of all the pits on the belt is 40 to 70% of the total area of the belt, for example, 50 to 65%, illustratively 60%. The open area of each pit can be easily calculated and designed by those skilled in the art according to the total area of the belt, the ratio of the sum of the open areas of the pits to the total area of the belt, and the pit array density. Of course, it will be understood by those skilled in the art that the open area of the pits should be at least larger than the projected area of the abrasive particles used in order not to impede the movement of the abrasive particles falling within the pits in the electrostatic sanding process in the presence of an electric field. In the present invention, the opening area of the pit means the area of the shape of the opening of the pit on the belt surface.

The size of the opening of the pit depends on the grit size of the abrasive used, but it will be understood by those skilled in the art that it should be at least larger than the grit size of the abrasive used to allow the abrasive to fall into the pit. When the abrasive used is a mixed abrasive, the pits are sized to accommodate the maximum abrasive particle size. In the present invention, the opening size of the pit means the minimum diameter length of the shape of the pit opening on the belt surface. For example, if the dimple shape is a circle, the opening size is the diameter of the circle; if the pit shape is a square, the opening size is the side length of the square; if the pits are irregularly shaped, the opening size is the length of the narrowest part of the shape. For example, for an abrasive with a particle size of P100, the opening size of the pits can be 150-200 μm; for P150 abrasives, the open size of the pits can be 90-120 μm, and the like.

According to the technical scheme of the invention, the abrasive can be selected from any abrasive with a common grain size, and is preferably a fine grain size abrasive, such as P100 and fine abrasive. In some embodiments of the invention, the abrasive is P320 and is a fine abrasive, illustratively, the abrasive is selected from the group consisting of P320 and P1000. The opening size of the pits is related to the grain size of the abrasive, for example, the abrasive with P320-P600 grain size, and the opening size of the pits is preferably 48-60 μm; the abrasive material with the granularity of P800-P1500 preferably has the pit opening size of 23-27 mu m; the P2000 is a fine abrasive, and the preferred pit opening size is 12-15 μm.

The depth of the pits may be designed according to the thickness of the belt or the particle size of the abrasive, and those skilled in the art will appreciate that the depth of the pits should not exceed the thickness of the belt. Preferably, the depth of the pits is not too deep to avoid excessive abrasive build-up in the pits. Of course, the depth of the pits should not be too shallow to retain abrasive. In one embodiment, the depth of the pits may be slightly greater than the particle size of the abrasive used. When the abrasive used is a mixed abrasive, the depth of the pits should be greater than the particle size of the largest abrasive.

According to the technical scheme of the invention, in the step (1), when the abrasive overflows the pits, the abrasive on the overflowing part can be scraped to ensure that no abrasive exists on the belt surface except the pits.

The invention also provides another alternative mode, the belt with the concave points in the step (1) is replaced by a belt with through holes regularly and continuously distributed in an array shape, so that a part of the grinding materials flowing out of the sand box are discharged from the through holes, and a part of the grinding materials are remained on the surface of the belt.

The through holes are regularly and continuously distributed on the belt to form an array, so that each through hole on the belt has the same surrounding environment, namely, when any two adjacent through holes in the array are described by one vector, if the vector is moved in parallel, when one end of the vector falls on one through hole in the array, the other end of the vector necessarily falls on the other adjacent through hole in the array, and the distribution of the solid part on the belt surface is also regular and continuous. For example, the array may be in the form of a square array, a diamond array, or the like. In one embodiment of the invention, the array is a square array, wherein the sides of the square are parallel to the direction of belt travel. In another embodiment of the invention, the array is a square array, wherein the diagonal of the square is parallel to the direction of belt travel.

Preferably, the through-hole array is such that the distance from any through-hole to its neighboring through-hole is the same.

The cross section of the through hole is not limited, and may be circular, polygonal (for example, triangle, quadrangle, pentagon, hexagon, etc., may be equilateral, and may be non-equilateral), or other irregular shapes. The cross sections of all the through holes on the belt can be in the same shape or can be a combination of various shapes. For the sake of inexpensive belt production, the through-holes preferably have a cross section of a circular shape, a square shape, a rhombic shape, or the like.

The through-hole may have a vertical cross section having a width equal to that of the vertical cross section, for example, a rectangular or square cross section, or may have a vertical cross section having a larger size and a smaller size, for example, a trapezoidal cross section. To facilitate the discharge of the abrasive, the longitudinal section is preferably as wide as the upper and lower sections.

The open area of each through-hole is not particularly limited as long as it is ensured that the total open area of the through-holes on the belt occupies 30 to 60%, for example 35 to 50%, exemplarily 40% of the total area of the belt. The person skilled in the art can conveniently calculate and design the opening area of each through hole according to the total area of the belt, the ratio of the total area of the openings of the through holes and the array density of the through holes. Of course, it will be understood by those skilled in the art that the open area of the through-holes should be at least larger than the projected area of the abrasive particles used in order not to impede the discharge of abrasive material from the through-holes. Wherein the "total opening area of the through-holes" refers to the sum of the opening areas of all the through-holes facing the substrate; the "opening area of the through-holes" refers to the area of the shape in which a single through-hole is opened on the belt surface facing the base material.

Also, the size of the opening of the through-holes depends on the size of the abrasive used, but it should be understood by those skilled in the art that it should be at least larger than the size of the abrasive used so that the abrasive can be discharged through the through-holes. When the abrasive used is a mixed abrasive, the size of the opening of the through-hole should be such that the largest abrasive can pass through. In the present invention, the opening size of the through-hole refers to the minimum aperture of the through-hole. For example, if the through-hole is a cylindrical hole, the opening size is the diameter of the cylinder; if the through hole is in a truncated cone shape, the opening size is the diameter of the circle of the small truncated cone surface in the truncated cone shape; if the through hole is a rectangular parallelepiped hole whose cross section is square, the opening dimension is the side length of the square. For example, for an abrasive with a particle size of P100, the opening size of the through-holes may be 150-200 μm; the abrasive of P150 may have an opening size of 90 to 120 μm or the like.

According to the technical scheme of the invention, in the step (1), the amount of the abrasive falling from the sand box to the sand planting belt can be adjusted according to the width of the belt, and the sand falling speed can be 1-9g/s, such as 1.6-7g/s, and as an example, 8.7g/s, 6.5g/s and the like, taking the width of the sand box as 0.1m as an example.

According to the technical scheme of the invention, in the step (2), the movement speed of the belt is 3-8 m/min.

According to the technical scheme of the invention, in the step (2), the operation conditions of the electrostatic sand planting comprise: the voltage is 1-100kV, for example 30-70kV, 40-60 kV.

Further, the operating conditions of the electrostatic sand-planting further comprise: the distance between the upper polar plate and the lower polar plate is 1-100mm, for example 70-100 mm.

The skilled person in the art has the corresponding ability to select and adjust the conditions of voltage range, polar plate distance, belt movement speed and the like according to the type of the used abrasive and the conditions of granularity, environment temperature and humidity and the like.

According to the technical scheme of the invention, the base material can be selected from paper, cotton cloth, chemical fiber, plastic film or other composite materials. Such as kraft paper, water-resistant kraft paper, vulcanized fiber paper, latex paper, PET film, nonwoven fabric, paper cloth, sandwich mesh cloth, and the like.

According to the present invention, the primer may be a primer commonly used in the art, including but not limited to animal glue (e.g., hide glue, gelatin, bone glue, etc.), resin (e.g., phenolic resin, epoxy resin, alkyd resin, urea resin, polyurethane, polyvinyl acetate, etc.). Further, the coating amount of the primer on the base material is 5-20g/m²E.g. 6-10g/m². The skilled person will have the corresponding ability to select and adjust the amount of primer according to the requirements of industry standards, the type of abrasive used and its particle size.

According to the present invention, the method is applicable to various abrasives including, but not limited to, brown corundum, white corundum, chrome corundum, zirconium corundum, black silicon carbide, green silicon carbide, iron oxide, synthetic diamond, cubic boron nitride, and the like.

The electrostatic sand planting method is suitable for the same-direction electrostatic sand planting, the reverse electrostatic sand planting, the side electrostatic sand planting and other types of electrostatic sand planting modes comprising a sand box and a belt.

Further, the invention provides application of the electrostatic sand-planting method in preparation of a coated abrasive tool.

The invention further provides a preparation method of the coated abrasive tool, wherein the method comprises the steps of obtaining a base material subjected to sand planting by adopting the electrostatic sand planting method, and drying, optionally coating glue and curing to obtain the coated abrasive tool.

According to the technical scheme of the invention, the drying and curing can be carried out by adopting the operation known in the field. For example, the temperature of the drying is 70 to 90 ℃, preferably 75 to 85 ℃, and exemplarily 80 ℃.

According to the technical scheme of the invention, the post-treatment such as coiling and cutting can be further included after the curing.

Further, the invention provides a coated abrasive tool prepared by the electrostatic sand-planting method. The density of the grinding material on the coated grinding tool is reduced, and the discharge of grinding chips during grinding is facilitated.

Further, the present invention provides a sand planting device used in the above electrostatic sand planting method, the device comprising: the device comprises a sand box, an upper polar plate, a lower polar plate and a belt for carrying abrasive materials, and is characterized in that the belt is provided with concave points or through holes which are regularly and continuously distributed, and when the belt is provided with the concave points which are regularly and continuously distributed, the device further comprises a scraping device for scraping the abrasive materials which escape from the concave points on the belt.

The pits (or through holes) are regularly and continuously distributed on the belt to form an array, so that each pit (or through hole) on the belt has the same surrounding environment, namely, when any two adjacent pits (or through holes) in the array are described by one vector, if the vector is moved in parallel, when one end of the vector falls on one pit (or through hole) in the array, the other end of the vector necessarily falls on the other adjacent pit (or through hole) in the array. For example, the array may be in the form of a square array, a diamond array, or the like. In one embodiment of the invention, the array is a square array, wherein the sides of the square are parallel to the direction of belt travel. In another embodiment of the invention, the array is a square array, wherein the diagonal of the square is parallel to the direction of belt travel.

Preferably, the pit array or the through-hole array is such that the distance from any pit (or through-hole) to its neighboring pit (or through-hole) is the same.

The shape of the cross section of the concave point (or the through hole) is not limited, and may be a circle, a polygon (for example, a triangle, a quadrangle, a pentagon, a hexagon, etc., which may be equilateral, or an equilateral), or other irregular shape. All the pits (or through holes) on the belt may be of the same shape or a collection of shapes. For the sake of inexpensive belt production, it is preferable that all the pits (or through holes) in the belt have a circular, square, or rhombic shape.

The through-hole may have a vertical cross section having a width equal to that of the upper and lower portions, for example, a rectangular or square shape, or may have a large opening and a small bottom, for example, a trapezoidal shape. To facilitate the discharge of the abrasive, the longitudinal section is preferably as wide as the upper and lower sections.

The open area of the pits, the total area of the open areas, the opening size and the depth are as described above.

The total opening area and the opening size of the through holes in the belt are also as described above.

According to the technical scheme of the invention, the sand planting device further comprises a base material roll and a bottom glue groove, the base material provided by the base material roll passes through the bottom glue groove, and the base material is conveyed between the polar plates through the conveying component.

In one embodiment of the invention, the scraping device for scraping off the abrasives escaping from the concave points on the belt is a scraper which is arranged above the belt and is in contact with the upper surface of the belt, and the scraper is positioned in front of the sand box along the running direction of the belt.

In one embodiment of the invention, the scraping device is a scraper arranged at the sand outlet end of the sand box and on the front end edge along the running direction of the belt, and the lower edge of the scraper is in contact with the upper surface of the belt. The scraping plate can be integrally formed with the sand box, and can also be detachably connected with the sand box body.

The included angle alpha between the scraper and the belt is as follows: alpha is more than 0 degree and less than 180 degrees, preferably, alpha is more than 10 degrees and less than or equal to 170 degrees.

The invention has the beneficial effects that:

the invention replaces the belt with smooth surface with the sand planting belt with continuous concave points or through holes, so that the abrasive can be uniformly and quantitatively distributed on the sand planting belt, the purpose of quantitatively planting sand is achieved, the abrasive can be firmly fixed on the base material, the grinding capability of the abrasive product is effectively improved, the sand drop rate is reduced, and the grinding service life of the grinding tool is long.

The sand planting method is particularly suitable for a fine abrasive.

Drawings

Fig. 1 is a schematic diagram of an electrostatic sand-planting apparatus in the prior art. Reference numerals: 1 ' -substrate roll, 2 ' -bottom glue groove, 3 ' -upper polar plate, 4 ' -lower polar plate, 5 ' -belt, 6 ' -sand box and 8 ' -oven.

FIG. 2 is an example of the shape and distribution of pits (or through holes) on the belt for sand-planting according to the present invention: (a) circular, (b) quadrilateral.

FIG. 3 is an example of a square matrix form of pits (or through holes) on the belt for sand planting of the present invention: the arrows in the figure represent the belt running direction, (a) the side length of the square in the square matrix is parallel to the belt running direction, and (b) the diagonal of the square in the square matrix is parallel to the belt running direction.

Fig. 4 is a schematic view of an embodiment of the electrostatic sand-planting apparatus of the present invention. Reference numerals: 1-substrate roll, 2-bottom glue groove, 3-upper polar plate, 4-lower polar plate, 5-belt, 6-sand box and 7-scraper.

FIG. 5 is a schematic view of a dimple belt used in an embodiment of the present invention, where a and b are the horizontal and vertical spacing distances, respectively, of adjacent dimples and d is the diameter of a circular dimple.

Detailed Description

The technical solution of the present invention will be further described in detail with reference to specific embodiments. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

Unless otherwise indicated, the conventional raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods.

[ SAND-PLANTING DEVICE ]

The sand planting device shown in fig. 4 includes: the base material roll comprises a base material roll 1, a bottom glue groove 2, an upper pole plate 3, a lower pole plate 4, a belt 5 for carrying abrasive materials and a sand box 6, wherein the base material provided by the base material roll passes through the bottom glue groove, the base material is conveyed between the pole plates through a conveying part, and the belt is provided with concave points which are regularly and continuously distributed (the arrangement characteristics of the concave points are shown in figure 5). The device also comprises a scraper 7 for scraping the abrasive materials out of the pits on the belt, the scraper 7 is arranged above the belt and is in contact with the upper surface of the belt, and the scraper 7 is positioned in front of the sand box 6 along the running direction of the belt 5.

Different belts were used in the following examples and comparative examples, a belt having circular pits according to the characteristics of the present invention (the pit arrangement characteristics are shown in fig. 5) was used in the examples, and a conventional smooth belt was used in the comparative example, but the belts in the examples and comparative examples were each 1600mm wide, and the method for producing the coated abrasive was the same: the latex paper suitable for the coated abrasive tool is used as a base material, phenolic aldehyde primer is coated on the base material, abrasive materials fall onto a belt through a sand box, and after electrostatic sand planting, the belt is dried, is coated with phenolic aldehyde glue solution, and is dried and cured to obtain the product. The sand falling amount is changed by adjusting the clearance of the sand box.

For the example using abrasive P320 grit, the belt pits and their distribution data are as follows: d is 50 μm, a is 10 μm, and b is 5 μm. The total open area of the pits is 60% of the belt area.

For the example using abrasive P1000, the belt pits and their distribution data are as follows: d is 20 μm, a is 5 μm, b is 5 μm, and the total area of the openings of the concave points occupies 50% of the belt area.

In the examples the direction of belt movement is in the same direction as the direction of sandpaper movement.

The latex paper, the phenolic base glue and the phenolic compound glue solution in all the examples and the comparative examples are the same, and the coating amount of the compound glue is 45g/m²。

The electrostatic sand-planting voltage in all the examples and the comparative examples is about 25kV, and the belt speed is 6 m/min.

The abrasives used were AP320 (corundum, particle size P320) and AP1000 (corundum, particle size P1000), respectively.

The sand planting amount and the grinding effect of the obtained product are measured and compared:

the sand planting amount is measured according to the industry standard ZBJ 43009-90 of the people's republic of China.

The grinding life test method comprises the following steps: and punching the sample back velvet into a 6-inch disk, grinding the automobile putty by using a full-automatic grinding machine, and observing the blocking condition and the grinding service life. The blocking condition is observed by naked eyes, and when the blocking occurs, a large piece of putty is adhered to the surface of the sand paper at the corresponding blocked position on the sand paper. The grinding life is judged by recording the weight change of the ground workpiece in the same time interval, when the weight of the ground workpiece does not change any more in the same time interval, namely the sand paper can not be ground at all, and the time from the beginning of grinding to the occurrence of the phenomenon is recorded as the grinding life.

TABLE 1 determination of the conditions for sand-setting of the abrasive AP320 and the product properties thereof

Table 2, sand-planting conditions for abrasive AP1000 and product performance measurement thereof

As can be seen from tables 1 and 2, the coated abrasive obtained by the electrostatic sand-planting method of the present invention has a reduced sand-planting amount, an anti-clogging effect during grinding, and a prolonged grinding life, compared to the coated abrasive obtained by electrostatic sand-planting using a smooth belt under the same conditions.

As can be seen from comparison between example 1 and comparative example 2 in table 1, although a certain degree of thin planting sand can be achieved by reducing the amount of the primer, on one hand, the degree of the thin planting sand reduction is limited, and on the other hand, the abrasive is easy to fall off due to the reduction of the amount of the primer, and finally, the grinding life of the grinding tool is shortened.

As can be seen from the comparison between example 1 and example 3 in Table 1, for the abrasive material having a coarse particle size of P1000, the degree of the thin planting sand can be increased by using a concave belt and adjusting the amount of the falling sand. Of course, too low a sand planting amount will reduce the grinding life of the sand paper, and the skilled person can select and match the sand planting method according to the requirement.

As can be seen from the comparison between comparative example 3 and comparative example 4 in Table 2, for P1000 with fine abrasives, the sand falling amount cannot be adjusted by a sand box, and the decrease of the primer amount cannot effectively improve the planting sand density, but the abrasive is easy to fall off due to the decrease of the primer amount, and finally the grinding life of the grinding tool is shortened. The embodiment 2 adopting the electrostatic sand planting method of the invention can obtain the effect of rare sand planting and simultaneously ensure that the grinding service life of the grinding tool is prolonged.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An electrostatic sand-planting method for a coated abrasive tool is characterized by comprising the following steps:

(1) a belt with continuous concave points is used as a sand planting belt, so that the grinding materials fall into the concave points of the sand planting belt without overflowing; the total area of all the concave points on the belt is 40-70% of the total area of the belt in terms of the opening area of the concave points;

2. An electrostatic sanding method according to claim 1 wherein the pits are regularly distributed in an array on the belt.

3. An electrostatic sanding method according to claim 1 wherein the dimples are regularly and continuously distributed in an array on the belt, the array of dimples being such that the distance from any dimple to its adjacent dimple is the same.

4. An electrostatic sanding method according to claim 1 wherein the pits are circular, polygonal or other irregular shape in cross-section.

5. An electrostatic sanding method according to claim 1 wherein all of the dimples on the belt are of the same shape or a collection of shapes in cross-section.

6. An electrostatic sand-planting method as claimed in claim 1, wherein the longitudinal section of the concave point is equal in width from top to bottom, or has a large opening and a small bottom, or has an arc shape.

7. An electrostatic sanding method according to any one of claims 1-6 wherein the abrasive is a fine grit abrasive.

8. An electrostatic sanding method according to claim 7 wherein the abrasive is P100 or finer.

9. An electrostatic sanding method according to any one of claims 1-6 wherein in step (1), when the abrasive overflows the pits, the overflow is scraped to ensure that the belt surface except the pits is free of abrasive.

10. An electrostatic sand planting method according to any one of claims 1 to 6, wherein in the step (1), the amount of the abrasive falling from the sand box to the sand planting belt is adjusted according to the belt width.

11. An electrostatic sand planting method according to any one of claims 1 to 6, wherein in the step (2), the moving speed of the belt is 3 to 8 m/min.

12. An electrostatic sand planting method according to any one of claims 1 to 6, wherein in the step (2), the voltage of the electrostatic sand planting is 1 to 100 kV.

13. An electrostatic sand planting method according to any one of claims 1 to 6, wherein the distance between the upper and lower electrode plates of the electrostatic sand planting is 1 to 100 mm.

14. An electrostatic sanding method according to any one of claims 1-6 wherein the substrate is selected from paper, cotton, chemical fibres, plastic film or other composite materials.

15. An electrostatic sand-planting method according to any one of claims 1 to 6, wherein the primer is coated on the substrate in an amount of 5 to 20g/m²。

16. An electrostatic sand-planting method according to claim 1, characterized in that the belt with concave points in the step (1) is replaced by a belt with through holes which are regularly and continuously distributed in an array, so that a part of the abrasive flowing out of the sand box is discharged from the through holes, and a part of the abrasive is remained on the surface of the belt, during the electrostatic sand-planting, the abrasive remained on the surface of the belt is distributed on the base material coated with the primer under the action of an electric field along with the movement of the belt, and the total area of the through holes on the belt accounts for 30-60% of the total area of the belt.

17. An electrostatic sand-planting method according to claim 16, wherein the through-hole array is such that the distance from any through-hole to its adjacent through-hole is the same.

18. An electrostatic sand-planting method according to claim 16, wherein the cross section of the through hole is circular, polygonal or other irregular shape.

19. An electrostatic sanding method according to claim 16 wherein all of the perforations in the belt are of the same shape or a collection of shapes in cross-section.

20. An electrostatic sand-planting method according to claim 16, wherein the through-hole has a vertical cross-section of the same width or a shape having a large opening and a small bottom.

21. An electrostatic sanding method according to any one of claims 16 to 20 wherein the abrasive is a fine grit abrasive.

22. An electrostatic sanding method according to claim 21 wherein the abrasive is P100 or finer.

23. An electrostatic sanding method according to any one of claims 16 to 20 wherein the amount of abrasive falling from the sand box onto the sanding belt is adjusted according to the belt width.

24. An electrostatic sanding method according to any one of claims 16 to 20 wherein the belt is moved at a speed of 3 to 8 m/min.

25. An electrostatic sand planting method according to any one of claims 16 to 20, wherein the voltage of the electrostatic sand planting is 1 to 100 kV.

26. An electrostatic sand planting method according to any one of claims 16 to 20, wherein the distance between the upper and lower electrode plates of the electrostatic sand planting is 1 to 100 mm.

27. An electrostatic sanding method according to any one of claims 16 to 20 wherein the substrate is selected from paper, cotton, chemical fibre, plastics film or other composite materials.

28. An electrostatic sanding method according to any one of claims 16 to 20 wherein the primer is applied to the substrate in an amount of from 5 to 20g/m²。

29. Use of an electrostatic sanding process as defined in any one of claims 1 to 28 for the manufacture of coated abrasive articles.

30. A method for preparing a coated abrasive tool, wherein the coated abrasive tool is obtained by drying, optionally coating, and curing a base material after being subjected to sand-planting by the electrostatic sand-planting method according to any one of claims 1 to 28.

31. The method of claim 30, wherein the curing further comprises a post-treatment of coiling and cutting.

32. A sand planting apparatus for use in an electrostatic sand planting method according to any one of claims 1 to 28, the apparatus comprising: the belt comprises a sand box, an upper polar plate, a lower polar plate and a belt for carrying abrasive materials, and is characterized in that the belt is provided with concave points or through holes which are regularly and continuously distributed, and when the belt is provided with the through holes, the sum of the opening areas of the through holes on the belt accounts for 30-60% of the total area of the belt; when the belt is provided with the pits which are regularly and continuously distributed, the device further comprises a scraping device for scraping the grinding materials which escape from the pits on the belt, and the total area of all the pits on the belt accounts for 40-70% of the total area of the belt based on the opening area of the pits.

33. The apparatus of claim 32, wherein the pits are regularly and continuously distributed in an array on the belt.

34. The apparatus of claim 32 wherein the pits are regularly and continuously distributed in an array on the belt, the array of pits being such that the distance from any pit to its neighboring pit is the same.

35. The apparatus of claim 32, wherein the pits are circular, polygonal, or other irregular shape in cross-section.

36. The apparatus of claim 32, wherein all of the pits in the belt have the same cross-sectional shape or a collection of shapes.

37. The device of claim 32, wherein the longitudinal section of the concave point is equal in width from top to bottom, or has a large opening and a small bottom, or has an arc shape.

38. The apparatus of claim 32, wherein the perforations are regularly and continuously distributed in an array on the belt.

39. The apparatus of claim 32, wherein the plurality of through-holes are arranged in a regular continuous array on the belt, the array of through-holes being such that the distance from any through-hole to its neighboring through-hole is the same.

40. The device of claim 32, wherein the through-hole has a cross-section of a circle, polygon or other irregular shape.

41. The apparatus of claim 32, wherein the cross-sections of all the through-holes in the belt are the same shape or a collection of shapes.

42. The device of claim 32, wherein the through hole has a vertical cross section of a same width or a shape having a large opening and a small bottom.

43. The apparatus of any one of claims 32 to 42, wherein the scraping means for scraping away the abrasive material escaping from the pits on the belt is a scraper disposed above the belt in contact with the upper surface of the belt, said scraper being located forward of the flask in the direction of travel of the belt.

44. The apparatus of any one of claims 32 to 42, wherein the scraping means is a scraper disposed at a front end edge of the sand outlet end of the flask in a belt running direction.

45. The apparatus of claim 43, wherein the angle α of the flight with respect to the belt is: alpha is more than 0 degree and less than 180 degrees.

46. The apparatus of claim 45, wherein the angle α of the flight with respect to the belt is: alpha is more than or equal to 10 degrees and less than or equal to 170 degrees.

47. The apparatus of claim 44, wherein the angle α of the flight with respect to the belt is: alpha is more than 0 degree and less than 180 degrees.

48. The apparatus of claim 47, wherein the angle α of the flight with respect to the belt is: alpha is more than or equal to 10 degrees and less than or equal to 170 degrees.