EP0050233B1 - Diamond grinding wheel for processing stone - Google Patents

Description

The invention relates to a diamond grinding wheel for stone processing, in particular by means of a hand grinding machine, consisting of a support to be placed on the drive spindle and provided with a central coolant bore and a ring-shaped coating made of bonded diamond grain connected to it and forming the grinding surface, for guide grooves extending from the central coolant bore has the coolant and between these recesses, which are designed such that when the grinding surface engages the workpiece, coolant cannot pass outwards from the center.

Such grinding wheels are used in stone processing in particular for edge breaking, for grinding out lettering and for grinding smaller surfaces. The diamond grain is generally embedded in a sintered metal powder and the coating formed in this way is glued or soldered to a carrier disc, which in turn is attached to the carrier of the grinding disc. Since it is wet grinding, precautions must be taken to ensure that, on the one hand, the engaging surface of the tool is always wetted with coolant and, on the other hand, the grinding sludge that forms is removed. Furthermore, the shape of the grinding wheel must be designed in such a way that an optimal grinding performance is obtained with reasonable effort on the machine. In terms of increasing the grinding performance, it would be beneficial in itself to provide the largest possible grinding surface, but this would in turn require a pressure and thus an effort that cannot be applied by hand. Therefore, taking into account the coolant and grinding sludge removal, a compromise must always be made between grinding performance on the one hand and contact pressure on the other.

In a known embodiment, the covering consists of two narrow rings, the outer of which is concentric with the carrier disk, the inner, however, is arranged eccentrically (DE-B-1 270 982). This grinding wheel has the disadvantage that it easily runs out of the working position due to the eccentric arrangement of the inner ring. Due to the narrow design of the rings and the eccentric arrangement of the inner ring, the engagement surface of the tool is also relatively small.

In a further known embodiment (DE-B-1 577 584) a narrow outer ring concentric with the carrier disk is also provided. In this embodiment, the eccentric inner ring of the abovementioned grinding wheel is replaced by a plurality of ring segments which run outwards from the center of the carrier wheel and are otherwise curved in the circumferential direction. Due to the symmetrical arrangement of these ring segments, this grinding wheel does not run out, but it has the disadvantage that, due to the many edges on the ring segments, it can get stuck, the surface to be machined is ground unevenly or even these edges break out on the workpiece.

If, as is known per se, the ring-shaped grinding surface is simply widened in order to increase performance, this requires, as already indicated, a higher pressing force, since a larger proportion of diamond grain is engaged per unit of time. Certain improvements can be achieved in that a grained softer material, e.g. B. carbon particles are embedded, which are removed or broken out during the grinding process and thus lead to a porous surface. As a result, the engagement surface is reduced despite the large grinding surface (large ring width). With these grinding wheels, it is also known to form three to four grooves in the grinding surface, that of the coolant guide. and the grinding sludge discharge. However, this construction, which is advantageous in terms of the technical concept, presents considerable difficulties in terms of production technology. If the homogeneous distribution of the diamond grain in the metal powder is not easy to achieve before sintering, the addition of carbon particles creates a three-component system in which a homogeneous distribution of all three components is almost impossible. In particular, a homogeneous distribution of the carbon particles cannot be achieved due to their different grain shape and their specific weight. In practice, this then leads to the grinding wheel having “soft spots” in an uneven distribution and size, which in turn causes wear on the tool unevenly.

In the case of the grinding wheel mentioned at the beginning (US Pat. No. 3,386,214), the same problem is solved in that the covering has a large number of small bores in the manner of a perforation. In addition, radial coolant guide grooves are incorporated into the grinding surface, which start at the coolant bore and open into transverse distributor grooves at a distance from the periphery. Furthermore, radially extending depressions are arranged in the edge area, which run out at the periphery. Since, as already mentioned, abrasive coverings of this type are produced using sintering technology, the grooves, recesses and bores running in different directions and with different lengths can only be formed with great manufacturing outlay. The coolant distribution and maintenance is also insufficient. Furthermore, there will be uneven wear on the grinding surface, since the grooves and depressions do not follow the rotational symmetry of the grinding wheel.

Based on this prior art, the object of the invention is to propose a design in which, on the one hand, there is no uneven wear, on the other hand, effective coolant guidance and coolant maintenance on the grinding surface is possible and which furthermore enables simple manufacture of the covering.

This object is achieved according to the invention in that the guide grooves extend inclined in the circumferential direction of the grinding wheel up to the outer circumference of the coating and in that the depressions designed as grooves extend directly or approximately from the coolant bore on the one hand and do not extend to the outer circumference of the coating on the other hand.

In addition to the coolant guide grooves, the depressions provided according to the invention lead to a reduction in the effective grinding area, so that conversely the width of the annular coating and thus the area on the workpiece which is covered by the grinding wheel can be relatively large. Due to the symmetrical arrangement of the recesses, also in connection with the coolant guide grooves, any imbalance can be avoided. Likewise, this and an optimization of the ratio of the ring width to the free surface of the depressions prevent uneven wear of the grinding surface. While the guide grooves primarily serve to guide the coolant from the inside to the outside and at the same time distribute it over the grinding surface, the recesses arranged in between can be used to hold the coolant in order to ensure a uniform film of liquid on the grinding surface and at the same time for constant removal of the grinding sludge.

Usually, the bond of the diamond grain is achieved by sintering a metal powder, the coating having two layers, of which only the later outer layer contains the diamond grain, while the layer later forming the back of the coating is free of diamond grain. The sintering takes place in a shape adapted to the outline of the covering, so that the grooves and the depressions can easily be molded in by means of appropriate shaped pieces which are inserted into the sintering mold on the occasion of the production of the covering.

According to a preferred embodiment, however, it is provided that the covering consists of a plurality of sector-shaped sections, which are embedded in a rubber-elastic mass in an annular arrangement with formation of the coolant guide grooves and the depressions, and a disk which carries the investment material and which is connected to the carrier .

Building on the previously described production technology for the covering, the procedure in this embodiment is that a closed ring with the two layers is first produced in a conventional manner, then the ring is separated into the sector-shaped sections and finally these are cast in an annular mold with the investment material . At the same time, the support disk can be pressed into the investment material or can also be retrofitted, e.g. B. be glued.

Due to the last-mentioned design, each individual sector-shaped section is elastically supported, so it can deflect when pressed onto the workpiece. In this way, hollow grinding work can be carried out without difficulty. At the same time, this elastic mounting of the abrasive coating is perceived by the user as pleasant.

Since the grinding wheel with the coolant guide grooves and the depressions acts like a pump wheel during circulation and as a result the coolant is led away too quickly, i.e. would not be distributed sufficiently over the grinding surface, the recesses are designed so that they prevent the coolant from passing through from the inside out. If the depressions are also designed as grooves, it is provided that these grooves are closed, at least on the outer and possibly inner edge of the annular covering, up to the level of the grinding surface. It is therefore not a matter of continuous grooves, but of groove-shaped depressions which on the one hand act as a kind of pockets and thus retain the coolant, and on the other hand prevent the coolant from being discharged to the outside too quickly.

The investment material advantageously consists of a cold castable plastic, e.g. B. based on polyurethane, which makes the manufacture of the grinding wheel particularly easy.

Advantageously, but not essential to the invention, the covering is designed as a separate washer, which is detachably attached to the carrier and centered on a pin of the carrier by means of a central recess and at the same time is secured against rotation.

This design has the advantage that when the tool is changed, not the entire carrier, which generally sits on the drive spindle with a thread, but only the covering has to be loosened. This initially results in a reduction in price, since only one carrier is required for a large number of coverings. In terms of application technology, this design has the advantage that the carrier, which sticks to the drive spindle in particular after a long period of operation, no longer has to be laboriously detached.

According to one embodiment, the ring disk is held magnetically on the carrier. Such a magnetic holder cannot get stuck even after a long period of operation; rather, only the same force needs to be applied to release it. In particular, the magnetic holding force can be designed in such a way that the covering is held sufficiently firmly by the carrier and cannot be thrown off by jerky movements of the grinding machine, but on the other hand can be lifted off by tensile force, if necessary, using a tool.

If the material forming the diamond grain cannot be magnetized sufficiently, the coating can have a separate layer made of a ferromagnetic material, which in the embodiment with the sector-shaped sections is formed, for example, by the carrier disk. The holding magnet is arranged on the carrier, for example it has on one or more permanent magnets embedded in the face facing the covering.

As already indicated, with conventional grinding wheels there is a central coolant hole in the carrier. In order to avoid an unimpeded passage of the coolant jet in relation to the surface to be ground when the grinding wheel is off-center, the coolant bore is generally covered on its exit side by a baffle plate, so that the coolant is distributed to the outside. In the proposed separation of the covering from the carrier, a central centering pin is provided, which makes it more difficult to attach a baffle plate because of the canting that occurs as a result. It is therefore provided according to a further exemplary embodiment that the centering pin on the carrier is provided with two eccentrically arranged coolant bores which are connected to the central coolant bore. Due to the eccentric arrangement of the two coolant holes, the coolant is properly distributed.

• Fig. 1 eine teilweise geschnittene Seitenansicht einer ersten Ausführungsform der Schleifscheibe;
• Fig. eine Ansicht auf die Stirnseite des Trägers;
• Fig. 3 eine Ansicht auf die Schleiffläche des Belags;
• Fig. 4 einen der Fig. 1 ähnlichen Schnitt einer zweiten Ausführungsform der Schleifscheibe;
• Fig. 5 eine Draufsicht auf die Trägerscheibe gemäss Fig. 4;
• Fig. 6 eine der Fig. 1 entsprechende Ansicht einer dritten Ausführungsform;
• Fig. 7 eine den Fig. 2 und 5 entsprechende Ansicht auf die Stirnseite des Trägers und
• Fig. 8 eine Draufsicht auf die Schleiffläche der Ausführungsform gemäss Fig. 6.

The invention is described below with reference to exemplary embodiments shown in the drawing. The drawing shows:

• Figure 1 is a partially sectioned side view of a first embodiment of the grinding wheel.
• Fig. A view of the end face of the carrier;
• 3 shows a view of the grinding surface of the covering;
• 4 shows a section similar to FIG. 1 of a second embodiment of the grinding wheel;
• FIG. 5 shows a top view of the carrier disk according to FIG. 4;
• 6 shows a view corresponding to FIG. 1 of a third embodiment;
• Fig. 7 is a FIGS. 2 and 5 corresponding view of the end face of the carrier and
• 8 is a plan view of the grinding surface of the embodiment according to FIG. 6.

The grinding wheel 1 consists, for example, of a cast metal carrier 2 in the form of a plate and a covering 3 which is detachably fastened to the end face thereof can be attached to a hand grinder. For this purpose, the extension 4 has at least two diametrically opposed flats 5 on the outside for the attack of a wrench. Furthermore, the central threaded bore is used in a known and therefore not shown manner for supplying a coolant.

1 to 3, permanent magnets 7 are embedded in the end face 6 (see FIG. 2) of the carrier 2, three of which are provided in the embodiment shown. The end face 6 of the carrier 2 is surmounted by a central centering pin 8, on which the coolant line in the attachment 5 opens out via two eccentric bores 9. Furthermore, a further bore 10 is provided eccentrically in the end face 6 of the carrier 2.

The covering 3, which is the actual tool, is produced, for example, from a metal powder by sintering, diamond grain being embedded in the metal powder. The covering 3 is designed as a wide ring, which is centered with its central, in this case circular recess 11 on the pin 8 of the carrier 2. Furthermore, the covering 3 has on its rear side a molded-on pin 12 which engages in the bore 10 on the carrier 2 and thus secures the covering 3 against rotation. In the position shown in FIG. 1, the ring disk forming the covering 3 is held on the carrier 2 by means of the permanent magnets 7.

In Fig. 3, a view of the grinding surface of the covering 3 is shown. The covering 3 has a small number - in the exemplary embodiment shown three - guide grooves 14 which start from the central recess 11 and extend to the outer circumference of the covering 3. They serve to distribute the coolant emerging at the bores 9 of the centering pin of the carrier 2 (FIG. 1) over the grinding surface 13 and at the same time to remove the grinding sludge. Between the coolant guide grooves 14, a plurality — in the exemplary embodiment shown, between two guide grooves each having three — are arranged in the form of grooves 15, which — like the coolant guide grooves 14 — are inclined in the circumferential direction.

In the embodiment shown in the lower half of FIG. 3, the grooves 15 are instead closed only at their outer ends 17 and at their inner ends 18, so that a direct passage of coolant from the central recess 11 to the outer circumference of the lining 3 not possible. Instead of this design, the grooves 15 can also be closed only at the outer end 17. This embodiment has the advantage that the coolant is stored in the grooves 15, so that a wet running of the grinding wheel is always ensured.

In the exemplary embodiment according to FIGS. 4 and 5, instead of the magnetic holder or in addition to this, a mechanical fastening in the form of head bolts 19 is provided, which are locked in curved recesses 20 by rotating the lining 3 and carrier 2. The grooves 20 have circular extensions 21 for inserting the bolt head.

In FIG. 4, a covering 3 can also be seen, which consists of two layers 22, 23, of which the layer 22 forming the grinding surface 13 contains the diamond grain bound, while the layer 23 has the fastening means - here the head bolts 19. In the case of a magnetic holder, the layer 23 consists of a ferromagnetic material.

6 to 8, an annular permanent magnet 7 is embedded in the end face 6 (FIG. 7) of the carrier 2 and is surrounded by a non-magnetizable ring 24 is. The end face 6 of the carrier 2 is surmounted by a central centering pin 8, which in this embodiment has two diametrically arranged flats 25. The coolant line in turn opens out on the centering pin 8 via two eccentric bores 9.

The abrasive coating 3 is designed as a wide ring and consists of several sector-shaped sections 26 (FIG. 8) which are fixed in an investment material 27, for example by casting. They are arranged in the investment material 27 in the form of a ring at a distance from one another. In this way, on the one hand, the continuous coolant guide grooves 14 and, on the other hand, a plurality of groove-shaped depressions 15 are formed, which, as shown in the illustration in FIG. 1, can be formed in that the gap present between two adjacent sector-shaped sections 26 is only present at its outer ends 17 and possibly its inner ends 18 is filled with the investment material or else in that the investment material 27 projects only at these points up to the grinding surface 13 of the covering 3. (See Fig. 6, right half).

The investment 27 is seated on a support disk 29 (FIG. 6) made of a ferromagnetic material, which has a recess 28 in the center, which corresponds to the centering pin 8 on the carrier 2.

Claims (12)

1. Diamond grinding wheel for working stones, particularly by a hand-grinding machine, consisting of a back-up support (2) to be fixed to the driving spindle and having a central duct (11) for a coolant, and consisting furtheron of a ring-like coating (3) forming the grinding surface, joined up with the support and being made up of bonded diamond grains, said coating having grinding grooves (14) for the coolant, extending from the central duct (11) and between said grooves having recesses (15) designed for limiting flow of said coolant outwards from the central duct when the grinding surface (13) engages the workpiece characterized in that

a) said grinding grooves (14) being sloped in the direction of turning of said grinding wheel (1) and extended to the perimeter of said coating (3).

b) said recesses (15) being formed as grooves starting on the one hand directly of nearly said central duct (11) for the coolant, and not reaching on the other hand the perimeter of said coating (3).

2. Grinding wheel according to claim 1 wherein said coating (3) consisting a number of sector-like parts (26), placed in a ring-structure forming the grinding grooves (14) and the recesses (15), being bedded in a rubber-elastic substance (27) and consisting furtheron a disk (28) carrying the bedding substance (27) joined up with the support.

3. Grinding wheel according to claim 1 or 2, wherein said recesses (15) are closed (17, 18) only at the perimeter and if necessary at the inner edge of the ring-like coating (3) up to the hight of the grinding surface (13).

4. Grinding wheel according to claim 3, wherein the recesses (15) are closed by the bedding substance (27) at the perimeter and if necessary at the inner edge of the ring-like coating (3) up to the hight of the grinding surface.

5. Grinding wheel according to claim 2, wherein the bedding substance (27) is composed of a plastic material, e.g. on polyurethane base, castable while cold.

6. Grinding wheel according to claims 2 and 5 at which the coating (3) has two layers, both produced by powder metallurgy, only the outer one containing the diamond grains wherein at first a closed ring is made of said two layers (22, 23), and the ring is cut in the sector-like parts (26) being cast with the bedding substance (27) in an annular casting mould the bedding substance (27) being joined with a carrying disk (28) while or after the casting, e.g. by pasting.

7. Grinding wheel according to claims 1 to 6, wherein the coating (3) is formed as a separate ring wheel, fixed detachable on the support (2) and being centered with its center (11) on a tappet (8) of the support (2).

8. Grinding wheel according to claim 7, wherein the coating (3) having in the center a cutout (20) for centering and torsional fixing to the tappet (8) of the support (2).

9. Grinding wheel according to claims 1 to 8, wherein the coating (3) is fixed magnetically on the support (2).

10. Grinding wheel according to claim 9, wherein the support (2) is made up at least partially of permanently magnetic material (7) on the side facing the coating (3) and of ferromagnetic material on the other side.

11. Grinding wheel according to claim 9 or 10, wherein the permanently magnetic material (7) is placed ring-like on the support (2) round the tappet (8) corresponding to the cutout (20) in the coating (3).

12. Grinding wheel according to claims 1 to 11, wherein the tappet (8) on the support (2) has two eccentric located coolant-ducts (9) connected with the central coolant-duct of the support (2).

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