Three-layer grinding wheel

Abstract

To provide a grinding wheel having at least three layers which can be manufactured at a lower cost than a conventional technique and is especially suitable for grinding ceramic balls.SOLUTION: A circular multilayer circulating grinding wheel (1) having a rotational axis (D) is provided. The grinding wheel (1) has at least three substantially flat layers including an inner layer (2) and two outer layers (3 and 4) immediately adjacent to the inner layer (2), of which at least the inner layer (2) has a proportion of diamond abrasive particles. The grinding wheel is characterized in that the grinding wheel (1) is for grinding of ceramic balls, that the substantially flat layer is arranged to extend outwardly from the rotational axis (D) and in a direction perpendicular to the rotational axis (D), and that proportion of diamond in the abrasive particles in the inner layer (2) is larger than that in the outer layers (3 and 4).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a grinding wheel having the features of the preamble of claim 1 and to the use of such a grinding wheel. [Background technology]

[0002] Grinding wheels consisting of a single uniform layer of abrasive material are generally known. For example, document WO2006 / 079444A1 shows a grinding wheel with a uniform layer of diamond-containing abrasive particles bonded with a synthetic resin for grinding ceramic balls. The grinding wheel is operated axially, and the balls to be ground run in grooves arranged concentrically with the rotation axis.

[0003] Multilayer grinding wheels are also known, for example, from document JP2003300166A, which describes a grinding wheel with three layers sandwiched axially atop one another. The grinding wheel is a component of a grinding device for precise radial cuts. Particularly good dimensional accuracy is achieved by having a central layer with relatively coarse abrasive particles made of diamond, and two axially adjacent outer layers made of fine-grained diamond abrasive particles. During use, wear of the two outer layers causes the grinding peripheral surface of the grinding wheel to become convex, so that the grinding wheel centers itself on the workpiece. Furthermore, document CN106944938 discloses a three-layer grinding wheel, in which the two outer layers contain a certain percentage of diamond abrasive particles, and the central or inner layer contains alumina and synthetic resin. This design improves heat dissipation through the inner layer of the grinding wheel.

[0004] Grinding wheels with a matrix containing uniform or equal amounts of diamond abrasive particles in all layers are expensive to manufacture. Three-layer grinding wheels with a center or inner layer that does not contain diamond abrasive particles are not suitable for grinding ceramic balls. Summary of the Invention

[0005] It is therefore an object of the present invention to create a grinding wheel having at least three layers that is cheaper to manufacture than the prior art and that is particularly suitable for grinding ceramic balls.

[0006] These objects are solved by a grinding wheel having the features of claim 1 and by the use of such a grinding wheel. Specifically, the present invention has the following features [1] to

[12] . [1] A multi-layer circulating grinding wheel (1) having at least three substantially flat layers including an inner layer (2) and two outer layers (3, 4) directly adjacent to the inner layer (2), wherein at least the inner layer (2) has a certain proportion of diamond abrasive particles, wherein the proportion of diamond among the abrasive particles in the inner layer (2) is greater than that in the outer layers (3, 4). [2] The grinding wheel according to [1], characterized in that the inner layer (2) has a diamond content of at least 50% by weight in the abrasive particles. [3] The grinding wheel according to [1], characterized in that the inner layer (2) has a diamond content of at least 75% by weight in the abrasive particles. [4] The grinding wheel according to [1], characterized in that the inner layer (2) has a diamond content of at least 90% by weight in the abrasive particles. [5] A grinding wheel according to [1] or [4], characterized in that the outer layers (3, 4) each have a diamond content of less than 90% by weight of the abrasive particles. [6] A grinding wheel according to [1], [3], [4], characterized in that the outer layers (3, 4) each have a diamond content of less than 75% by weight of the abrasive particles. [7] The grinding wheel according to any one of [1] to [4], wherein the outer layers (3, 4) each contain diamond in an amount of less than 50% by weight of the abrasive particles. [8] A grinding wheel according to any one of [1] to [7], characterized in that the grinding wheel (1) has exactly three layers (2, 3, 4) containing abrasive particles. [9] A grinding wheel according to any one of [1] to [8], characterized in that the outer layers (3, 4) have the same structure, in particular the same axial thickness.

[10] The grinding wheel according to any one of [1] to [9], wherein the inner layer (2) and the outer layers (3, 4) are made of synthetic resin bonding.

[11] Use of the grinding wheel (1) according to any one of [1] to

[10] for polishing balls.

[12] The use according to

[11] , characterized in that the grinding wheel (1) is externally connected to a metal support plate (13).

[0007] The grinding wheel is provided with an inner or central layer and at least two outer layers, the inner layer having a higher proportion of diamonds in the abrasive particles than the two outer layers directly adjacent to the inner layer, making it possible to save diamond abrasive particles compared to grinding wheels of uniform structure or wheels that differ only in particle size and not diamond content. Furthermore, such grinding wheels can be advantageously used for grinding ceramic balls, because the necessary guide grooves are quickly formed in the outer layer that comes into contact with the ball, and the inner layer must act preferentially, i.e., exclusively, to be worn, i.e., to effect the actual grinding process.

[0008] Advantageously, at least the inner layer is designed with abrasive particles bonded with a synthetic resin. It is even more advantageous if the two outer layers directly adjacent to each side of the inner layer have the same abrasive particles, and especially if these two outer layers have the same axial thickness.

[0009] When used for ball grinding, the new grinding wheel is preferably bonded to a metal backing plate on one outer side. The outer layer directly lying on the backing plate is then not used for grinding or guiding purposes during ball grinding. However, it has been found to be advantageous to provide this layer on the side opposite other outer layers of the same design, as this minimizes distortion of the entire grinding wheel, especially of the inner layer during manufacture. [Brief explanation of the drawings]

[0010] An example of an embodiment of the present invention will now be described with reference to the drawings. [Figure 1] FIG. 1 is a cross-sectional view of a three-layer grinding wheel in the radial direction. [Figure 2] FIG. 2 is the grinding wheel of FIG. 1 with guide grooves adapted for use in ball grinding. [Figure 3] FIG. 3 shows the grinding wheel from FIGS. 1 and 2 used for ball grinding in a corresponding device. DETAILED DESCRIPTION OF THE INVENTION

[0011] In FIG. 1, a grinding wheel 1 according to the present invention is shown diagrammatically in a dotted cross section. The grinding wheel 1 has an inner layer 2, which is sandwiched between a first outer layer 3 and a second outer layer 4. The inner layer 2 has a higher proportion of diamond in the abrasive particles than the two outer layers 3 and 4. For example, the inner layer 2 can have a diamond content of 50 weight percent (wt%), 75 wt%, or even 90 wt% of the abrasive particles. This figure is the percentage in the abrasive particles without the bonding matrix. In a preferred embodiment, the abrasive particles can also consist of 100% diamond. The particle size of the abrasive particles is not critical to the present invention. Suitable particle sizes are known from the prior art.

[0012] The two outer layers 3, 4 have essentially the same structure. They also contain abrasive particles, but contain only a low amount of diamond or no diamond at all. Therefore, the diamond content in these two layers can be less than 50% by weight, particularly less than 25% by weight, or even less than 10% by weight. In a preferred embodiment, the two outer layers 3, 4 are essentially free of diamond abrasive particles except for impurities or traces unavoidable in the manufacturing process.

[0013] If the inner layer 2 is not made of 100% diamond abrasive particles, the required total 100% can be supplemented with less expensive abrasive particles, such as corundum (Al2O3), especially high-grade corundum, silicon carbide (SiC), or other known abrasive particles. The two outer layers also contain conventional abrasive particles. In particular, in embodiments where the two outer layers 3, 4 do not contain diamond abrasive particles, all of the abrasive particles are selected from low-cost materials such as corundum, SiC, other abrasive particles, or a mixture of non-diamond abrasive particles as desired.

[0014] The inner layer 2 and the outer layers 3, 4 are produced by hot pressing with a synthetic resin bond. The ratio of abrasive particles to synthetic resin is suitably selected, as is common in the prior art. The pore volume of the grinding wheel according to the invention is preferably between 3 and 10%.

[0015] The essentially identical structure of the two outer layers 3, 4 ensures that the grinding wheel does not actually distort during or after manufacture, e.g., during the cooling stage. In the case of grinding wheels with an outer layer applied to only one side, sintering distortions are to be expected due to the different thermal conductivities and heat capacities of the materials, as well as due to the different thermal expansion of the materials.

[0016] The grinding wheel is a circular wheel, which is rotationally symmetrical about the axis D.

[0017] The thickness in the direction of axis D can be selected depending on the application. The dimensions of the grinding wheel and the individual layers 2, 3, 4 can therefore be selected depending on the application circumstances. The grinding wheel can also be selected to suit the needs of the grinding machine. In particular, the thickness of the outer layers 3, 4 can be smaller than that of the inner layer 2, as these serve primarily to stabilize the grinding wheel 3. Layer 3, which serves as a feed layer for the ceramic balls, is ground after heat pressing to the appropriate dimensions for the application (i.e., the ball diameter to be ground in use).

[0018] Figure 2 shows the grinding wheel 1 from Figure 1 in a similar cutaway, dotted representation. Here, in cross section, it can be seen that, compared to the initial situation in Figure 1, the upper outer layer 3 has subsequently (after hot pressing) been provided with guide grooves 5. The guide grooves 5 make the grinding wheel 1 suitable for use in ball grinding. The guide grooves 5 are concentric circumferential grooves, which are located on the outer surface of the outer layer 3 and are arranged symmetrically and concentrically with respect to the axis of rotation D.

[0019] Figure 3 shows the use of a grinding wheel 1 according to the invention for ball grinding on a machine with a vertical drive shaft. Figure 3 shows a schematic side view of an apparatus for ball grinding. Here, a stationary guide disc 10 is provided, which is preferably made of cast steel. The guide disc 10 has a circumferential guide groove 11 on its underside, in which a number of balls 12 to be ground are guided. From below, a backing plate 13 is provided with the grinding wheel 1, on which an inner layer 2 and two outer layers 3 and 4 are arranged, which is set to rotate by a drive shaft 15.

[0020] For polishing, pressure P is exerted from below on the stationary guide disc 10. The backing plate 13 is set to rotate by a drive means so that the ball 12 rotates in the guide groove 11, and in particular also in the guide groove 5 of the grinding wheel 1. Although the guide groove in the first outer layer 3 does not yet make any appreciable contribution to the polishing of the ceramic ball, the effective polishing process begins once the ball 12 moves freely through the layer 3 and comes into contact with the diamond-containing layer 2. The speed difference in different areas of the guide groove causes the abrasive particles to move against the surface of the ceramic ball. The abrasive particles then cause polishing of the ball's surface, thus improving the surface quality and ball shape.

[0021] The grinding wheels according to the invention can be used in ball grinders with vertical drive shafts as well as in ball grinders with horizontal drive shafts.

[0022] The advantage of the grinding wheel described in this context is that, especially when used for ball grinding, the entire thickness of the inner layer 2 can be used for the grinding process. The outer layer, made of inexpensive abrasive particles, serves only for the initial guidance of the ball blank in the guide groove 5 and for securing the grinding wheel to the backing plate 13. The support layer 4 has the additional advantage that the abrasive diamond-containing layer 3 can be used until penetration, thus achieving a reduction in diamond material waste, in contrast to single-layer discs. If both objectives are achieved by the diamond layer in the case of a single-layer diamond grinding wheel, the overall consumption of diamond abrasive particles is greater than in the case of the multi-layer grinding wheel described above, which has an inner layer containing a high proportion of diamond. Furthermore, if the layer 2 in which the ball moves is soft, on the one hand, the groove formation process occurs significantly faster than in a hard diamond layer, and on the other hand, this leads to a reduction in the number of low-quality ball batches.

Claims

1. 1. A circular, multi-layer, circulating grinding wheel (1) having a rotation axis (D), the grinding wheel (1) having at least three substantially flat layers, including an inner layer (2) and two outer layers (3, 4) immediately adjacent to the inner layer (2), the inner layer (2) being disposed between the two outer layers (3, 4) in the axial direction of the rotation axis (D), the inner layer (2) and the two outer layers (3, 4) all containing abrasive particles, at least the inner layer (2) containing a certain proportion of diamond abrasive particles, the grinding wheel (1) being designed so that a grinding groove (5) for guiding a ball when grinding the ball is formed on the axially outer surface of the outer layer (3), the substantially flat layers being disposed so as to extend outward from the rotation axis (D) and in a direction perpendicular to the rotation axis (D), and the proportion of diamond among the abrasive particles in the inner layer (2) is greater than that in the outer layers (3, 4).

2. 2. Grinding wheel according to claim 1, characterized in that the inner layer (2) has a proportion of diamonds in the abrasive particles of at least 50% by weight.

3. 2. Grinding wheel according to claim 1, characterized in that the inner layer (2) has a proportion of diamonds in the abrasive particles of at least 75% by weight.

4. 2. Grinding wheel according to claim 1, characterized in that the inner layer (2) has a proportion of diamonds in the abrasive particles of at least 90% by weight.

5. 5. Grinding wheel according to claim 1 or 4, characterized in that the outer layers (3, 4) each have a proportion of diamond in the abrasive grains of less than 90% by weight.

6. 5. Grinding wheel according to claim 1, 3 or 4, characterized in that the outer layers (3, 4) each have a proportion of diamond in the abrasive grains of less than 75% by weight.

7. 5. Grinding wheel according to any one of claims 1 to 4, characterized in that the outer layers (3, 4) each have a proportion of diamond in the abrasive particles of less than 50% by weight.

8. A grinding wheel according to any one of the preceding claims, characterized in that the grinding wheel (1) has exactly three layers (2, 3, 4) containing abrasive particles.

9. Grinding wheel according to any one of the preceding claims, characterized in that the outer layers (3, 4) have the same structure, in particular the same axial thickness.

10. Grinding wheel according to any one of the preceding claims, characterized in that the inner layer (2) and the outer layer (3, 4) are made of synthetic resin bond.

11. Use of a grinding wheel (1) according to any one of claims 1 to 10 for grinding ceramic balls.

12. 12. Use according to claim 11, characterized in that the grinding wheel (1) is externally connected to a metal support plate (13).

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