METHOD FOR PRODUCE A CERAMICLY BONDED GRINDING TOOL AND CERAMICLY BONDED GRINDING TOOL

Description

[0001] The invention relates to a method for manufacturing a ceramic-bonded grinding tool, in particular a honing ring. Furthermore, the invention relates to a ceramic-bonded grinding tool, in particular a honing ring, manufactured by such a method, comprising a base body and at least one abrasive material embedded in the base body via at least one inorganic bonding agent.

[0002] A grinding tool in the form of a honing ring is already known from EP 0 692 342 A2, in which, in the manufacturing process of the honing ring, a binder in the form of synthetic resin is mixed with fine-grained abrasive and ceramic-bonded coarse-grained abrasive in order to ensure increased fracture strength in the resulting honing ring through reduced brittleness due to the integrated synthetic resin.

[0003] Ceramic-bonded grinding tools are manufactured, for example, using a cold-pressing process, whereby the tool life and / or machining properties of the manufactured grinding tool depend significantly on the grain volume and / or bond volume relative to the pore volume of the grinding tool. In practice, adhesive systems in the form of dextrins have proven advantageous, but have proven inadequate for producing particularly dense specifications.

[0004] Grinding tools are already known from the documents CN 105 598 857 B, which forms the basis for the preamble of claim 1, US 4,881,950 A, CN 111 805 442 A and US 2003 / 194947 A1.

[0005] A disadvantage of the prior art is that grinding tools with a particularly high grain volume and / or bond volume cannot be produced in practice simply by modifying specifications, such as increasing the grain content and / or bond content in grinding tool blanks, because presses, in particular, are too weak for the necessary compaction of the grinding tool blanks. However, a high grain volume and / or bond volume is essential for grinding tool properties such as long tool life or favorable dressing characteristics, which can only be inadequately achieved with the prior art.

[0006] The objective technical object of the present invention is therefore to provide a method for producing a ceramic-bonded grinding tool that is improved compared to the prior art, as well as a ceramic-bonded grinding tool in which the disadvantages of the prior art are at least partially eliminated, and which are characterized in particular by a high grain volume and / or bond volume in the grinding tool in order to increase the service life and / or machining properties of the grinding tool.

[0007] This problem is solved by the features of claim 1.

[0008] According to the invention, the method therefore comprises the following process steps, to be carried out in chronological order: In a first process step, at least one abrasive, in particular corundum, SiC, aluminum oxide and / or superabrasive, at least one inorganic binder, in particular formed as a low-fire binder, and at least one organic binder, in particular in the form of epoxy resin, are provided and mixed; the at least one abrasive, the at least one inorganic binder and the at least one organic binder are pre-pressed into a cold-pressed green compact in a cold-pressing process step. The cold-pressed green compact is pressed into a hot-pressed green compact in a hot-pressing process step, the hot-pressed green compact is burned into a grinding tool blank, in particular a honing ring blank, in a burning process step, whereby during the burning process step the at least one organic binder is at least partially burned away, and the grinding tool blank is further processed into the grinding tool in which abrasive material is embedded in a subsequent process step.

[0009] This two-stage pressing process, followed by a firing process, enables the generation of very dense specifications with increased grain volume and bond volume compared to the state of the art. The grinding tool blanks and grinding tools produced by this process are particularly suitable for demanding grinding applications, with improvements in pressure resistance, hardness, wear behavior, etc., compared to conventionally manufactured ceramic-bonded grinding tools.

[0010] The increased grain and bond content allows for long tool life even during demanding grinding operations. For example, determining the mass density of the grinding tool, especially if its composition is known, can provide insights into its specifications. Microscopic examination of the grinding tool may be sufficient to determine its grain volume, bond volume, and porosity.

[0011] In this context, the technical term "green body" is defined as a blank during the manufacturing process for the formation of the grinding tool blank, whereby the cold-pressed green body, the hot-pressed green body, as well as the grinding tool blank can be removed from a press mold or an oven in a dimensionally stable form.

[0012] The post-processing of the grinding tool blank to form the grinding tool is generally arbitrary and can, for example, include machining steps such as broaching, scraping, milling, or the like. The performance in terms of dressing cycles of the honing rings produced according to the invention was significantly increased (by 300%) compared to conventional ceramic-bonded honing rings with high densities known from the prior art.

[0013] Instead of the dextrins typically used as adhesives for grinding tools or honing rings in practice, an organic binder is used as the adhesive according to the invention, which is particularly preferably an epoxy resin or synthetic resin. This offers the advantage that pressing process steps from the manufacturing area of ​​resin-bonded grinding tools can also be applied to ceramic-bonded grinding tools in order to achieve particularly dense specifications of grinding tools, whereas increases in grain volume and / or bond volume in ceramic-bonded grinding tools by pressing – especially at room temperature – are limited by physical and practically limited compaction.

[0014] In particular, the grain volume and bond volume can be increased by burning off the organic binder and melting the inorganic binder. For example, the mixture prepared for cold pressing contains 50 vol% to 65 vol%, preferably 55 vol%, grain volume and 10 vol% to 35 vol%, preferably 22 vol%, bond volume, which, in combination with a pore volume formed during the manufacturing process in the grinding tool blank, can result in 55 vol% grain volume and 20 vol% bond volume, making the grinding tool blank highly suitable for demanding abrasive grinding operations.

[0015] As stated at the outset, protection is also sought for a ceramic-bonded grinding tool, in particular a honing ring, manufactured by such a process, comprising a base body and at least one abrasive embedded in the base body via at least one inorganic binder, wherein the grain volume of the abrasive is in the range between 50 vol% and 65 vol%, in particular between 53 vol% and 58 vol%, and the binder volume is in the range between 10 vol% and 35 vol%, in particular between 18 vol% and 26 vol%. of the grinding tool, wherein the grain volume and the bond volume together amount to a maximum of 100 vol% of the grinding tool.

[0016] Differences between the sum of grain volume and bonding volume (inorganic binder and any organic binder) and the total volume of the grinding tool can, for example, be in the form of a pore volume.

[0017] It is particularly preferred that the grinding tool is manufactured by such a process.

[0018] Advantageous embodiments of the invention are defined in the dependent claims.

[0019] According to an advantageous embodiment of the invention, it is provided that the at least one organic binder is substantially completely burned off during the firing process step and / or is burned off to such an extent that an organic binder volume is a maximum of 15 vol%, preferably a maximum of 10 vol%, of the grinding tool blank.

[0020] The proportion of organic binder used in the two-stage pressing process with resin-bonded grinding tools can be reduced in the firing process step, whereby, depending on requirements (e.g., desired damping properties due to residual epoxy resin) for the grinding tool, the amount of remaining organic binder can be adjusted via operating parameters (e.g., pressure and / or temperature) in the firing process step.

[0021] Advantageously, the cold pressing process step and the hot pressing process step are carried out in separate pressing dies, preferably with the pressing die and / or the cold-pressed green body being preheated for the hot pressing process step.

[0022] Preferably, two press molds are used, with the press mold from the hot pressing process being preheated before, during, or after the cold pressing process in order to place a preheated, cold-pressed green compact into this press mold. Generally, it is also conceivable to preheat only the press mold or the green compact.

[0023] It has proven advantageous to press the cold-pressed green compact to a first dimension in the cold-pressing process step and the hot-pressed green compact to a second dimension different from the first dimension in the hot-pressing process step, preferably providing that the hot-pressed green compact is pressed to an outer diameter between 50 mm and 450 mm, an inner diameter between 20 mm and 300 mm and / or a width between 10 mm and 90 mm.

[0024] The press die of the cold pressing process step takes into account shrinkage in the subsequent process steps, whereby in the hot pressing process step the cold-pressed green body is further compacted in order to produce a grinding tool blank with desired dimensions after the flame-cutting process step.

[0025] According to an advantageous embodiment of the invention, it is provided that the at least one organic binder is essentially completely cross-linked in the hot pressing process step.

[0026] In general, during the hot pressing process, due to the temperatures present, at least one inorganic binder, unlike at least one organic binder, is not yet melted.

[0027] It has proven advantageous that in the firing process step at least one inorganic binder is melted, preferably that the firing process step is carried out in a furnace.

[0028] Due to the high temperatures in the combustion process step, the at least one binder burns out at least partially, preferably completely, and the grinding tool blank with high grain volume and / or bond volume is created through the combination of the at least one abrasive with the at least one inorganic binder.

[0029] An advantageous variant consists in using a pressure between 20 bar and 300 bar, preferably between 40 bar and 60 bar, and / or essentially room temperature in the cold pressing process step.

[0030] The cold pressing process step allows for the production of a dimensionally stable, cold-pressed green body with a substantially homogeneous mixture of the added components, suitable for further processing.

[0031] It is particularly preferred that a pressure between 270 bar and 310 bar, preferably 275 bar to 285 bar, and / or a temperature between 150 °C and 200 °C, preferably between 170 °C and 180 °C, is used in the hot pressing process step.

[0032] The hot pressing process step can result in a dimensionally stable, hot-pressed green body for the firing process step with cross-linked organic binder and existing inorganic binder.

[0033] In one embodiment of the invention, the firing process step is carried out at a temperature between 600 °C and 1300 °C, preferably between 900 °C and 1000 °C.

[0034] Depending on the choice of components of the organic and / or inorganic binders, a suitable temperature can be selected which ensures a stable bond – in particular of the at least one inorganic binder with the at least one abrasive – wherein the temperature is preferably selected such that the at least one organic binder burns off at least partially, preferably completely, during the firing process step and the at least one inorganic binder melts, preferably substantially completely, during the firing process step to embed the at least one abrasive, wherein no undesirable temperature-related damage (such as oxidation or splintering clumping due to excessively high temperatures) occurs to the at least one inorganic binder and abrasive.

[0035] According to a preferred embodiment of the invention, it is provided that, starting from a grain volume of an abrasive, the bonding volume of the binders and / or the pore volume of the cold-pressed green compact, the following steps are performed after the cold-pressing process: the hot-pressing process and / or the firing process. the grain volume of the grinding tool blank is increased to a range between 50 vol% and 65 vol%, preferably between 53 vol% and 58 vol%, and / or the bond volume of the grinding tool blank is increased to a range between 10 vol% and 35 vol%, preferably between 18 vol% and 26 vol%, and / or the pore volume of the grinding tool is reduced to a range between 10 vol% and 40 vol%, preferably between 22 vol% and 28 vol%. wherein the grain volume, bond volume and pore volume of the hot-pressed green body and / or grinding tool blank together do not exceed 100 vol%.

[0036] An increased grain volume and increased bond volume can produce a dense, solid, stable and / or, in particular, wear-resistant and / or tool breakage-resistant grinding tool.

[0037] Furthermore, it is preferably provided that the base body is ring-shaped and / or formed in one piece, wherein it is preferably provided that the base body has a toothing on an inner surface and / or on an outer surface that can be brought into contact with a toothed workpiece.

[0038] In a further embodiment, it can be provided that the at least one abrasive is at least partially, preferably completely, made of corundum, preferably precious and / or sintered corundum, SiC, aluminum oxide and / or superabrasive, preferably diamond and / or cubic boron nitride.

[0039] In this context, the technical term "superabrasive" is defined as an abrasive with particularly favorable abrasive properties and / or exceptionally high hardness, as is the case, for example, with diamond and cubic boron nitride (CBN). Gears, for instance, can be honed using this grinding tool.

[0040] According to an advantageous embodiment of the invention, the grinding tool is provided to have a maximum of 15 vol%, preferably a maximum of 10 vol%, organic bonding volume, wherein it is preferably provided that the organic bonding volume is formed from the group of thermoplastics and / or thermosets, particularly preferably essentially epoxy resin.

[0041] Thermoplastics and / or thermosets have proven to be particularly advantageous for the manufacture of grinding tools by the two-stage manufacturing process according to the invention, with epoxy resin exhibiting particularly advantageous properties with regard to bonding capacity and thermal behavior during the hot pressing process step and the firing process step.

[0042] According to an advantageous embodiment of the invention, the grinding tool comprises at least one, preferably exactly one, inorganic binder, wherein the at least one inorganic binder is formed in the form of a low-fire bond.

[0043] An example of low-fire bonding is synthetic technical glass, which is resistant to chemical attack and has an unlimited shelf life. Due to their material properties and machinability, low-fire bonding has proven particularly advantageous in the manufacture of grinding tools.

[0044] Advantageously, it is provided that the at least one inorganic binder comprises SiO2, Al2O3, B2O3 and / or at least one oxide comprising alkali and / or alkaline earth.

[0045] This allows high hardness and strength of the grinding tool to be achieved even at low furnace temperatures, whereby a bond with at least one abrasive, in particular diamond, cubic boron nitride and / or sintered corundum, can be produced particularly effectively.

[0046] In general, however, other inorganic binders are also conceivable, with particular preference given to inorganic binders which do not burn out during the firing process step due to sufficient temperature resistance.

[0047] It has proven advantageous for the grinding tool to have an outer diameter between 50 mm and 450 mm, an inner diameter between 20 mm and 300 mm and / or a width between 10 mm and 90 mm.

[0048] According to an advantageous embodiment of the invention, the grinding tool comprises a pore volume in the range of 10 vol% to 40 vol%, preferably between 22 vol% and 28 vol%, wherein the grain volume, the bond volume and the pore volume together amount to a maximum of 100 vol% of the grinding tool.

[0049] An effective reduction of the pore volume is particularly preferred for providing high densities of the grinding tool, whereby the pore volume present in the grinding tool can, to a certain extent, act to dampen forces acting on the grinding tool during an abrasive machining process.

[0050] The features of the method claims are applicable to the device claims and vice versa.

[0051] Further details and advantages of the present invention are explained in more detail below with reference to the description of the figures and the exemplary embodiments illustrated in the drawings. These show: Fig. 1 shows a preferred sequence of a method for manufacturing a ceramic-bonded grinding tool, schematically represented in a flowchart; Fig. 2 shows a ceramic-bonded grinding tool according to a particularly preferred embodiment in a perspective view.

[0052] Fig. 1 shows a method for producing a ceramic-bonded grinding tool 1 (see Fig. 2 ) in the form of a honing ring, wherein in a first process step an abrasive 2 – for example, corundum, SiC, aluminum oxide and / or superabrasive – is provided and mixed together with an inorganic binder 3 – for example, for low-fire bonding – and an organic binder 4 – for example, in the form of epoxy resin. The mixing of the mass to form the grinding tool blank 10 can generally take place in a press mold 12 of a cold pressing process step 5 or separately. The individual components of the mass to form a grinding tool blank 10 can generally be present in pure form or in mixture; for example, the abrasive 2 can be composed of corundum and superabrasive.

[0053] The abrasive 2, the inorganic binder 3, and the organic binder 4 are pre-pressed in cold-pressing process step 5 to form a cold-pressed green compact 6, which is schematically indicated to the right of the press mold 12 of cold-pressing process step 5. The cold-pressed green compact 6 has a central through-hole, which is generally not strictly necessary. The cold-pressed green compact 6 is pressed to a first dimension 13 in cold-pressing process step 5.

[0054] The cold-pressed green body 6 is pressed into a hot-pressed green body 8 in a hot-pressing process step 7, whereby the manufacturing process of the grinding tool blank 10 is subject to a two-stage pressing process.

[0055] In step 5 of the cold pressing process, a pressure of 50 bar and room temperature are used in this embodiment.

[0056] The hot-pressed green compact 8 is pressed in hot-pressing process step 7 to a second dimension 14 that differs from the first dimension 13. The hot-pressed green compact 8, which is schematically indicated to the right of the press die 12 of hot-pressing process step 7, was pressed to an outer diameter 15 of 300 mm, an inner diameter 16 of 138 mm and a width 17 of 27 mm, whereby the process can be adapted to any geometry and dimensions of the grinding tool blank 10 via the required press dies 12 and operating parameters such as pressure and temperature.

[0057] The cold pressing process step 5 and the hot pressing process step 7 are carried out in separate pressing dies 12, whereby the pressing die 12 and the cold-pressed green body 6 are preheated for the hot pressing process step 7.

[0058] In hot pressing process step 7, a pressure of 280 bar and a temperature of 180 °C are used according to this embodiment.

[0059] In general, the pressures and / or temperatures can vary during the pressing process steps 5, 7 and / or the firing process step 9, whereby material-characteristic properties of the grinding tool blank 10 can be adjusted by a pressure or temperature profile.

[0060] The organic binder 4 is fully cross-linked during step 7 of the hot pressing process.

[0061] The hot-pressed green body 8 is burned in a burning process step 9 to become the grinding tool blank 10 as a honing ring blank, whereby during the burning process step 9 the organic binder 4 in the form of epoxy resin is partially burned out.

[0062] In firing process step 9, the inorganic binder 3 is melted, with firing process step 9 being carried out in a furnace 18. In this embodiment, firing process step 9 is carried out at a temperature of 950 °C.

[0063] The organic binder 4 in the form of epoxy resin is burned off during the firing process step 9 to such an extent that an organic binder volume of 10 vol% of the grinding tool blank 10 is reached.

[0064] Starting from a grain volume of an abrasive 2, bond volume of the binders 3, 4 and pore volume of the cold-pressed green compact 6 after the cold pressing process step 5, the hot pressing process step 7 and the firing process step 9 are used in the embodiment shown. the grain volume of the grinding tool blank 10 was increased to 55 vol%, the bond volume of the grinding tool blank 10 was increased to 20 vol% despite the burnout process of epoxy resin in the combustion process step 9, and the pore volume of the grinding tool 1 was reduced to 25 vol%. wherein the grain volume, the bond volume and the pore volume of the hot-pressed green body 8 and the grinding tool blank 10 together each amount to 100 vol%.

[0065] The grinding tool blank 10 is further processed in a subsequent process step 11 to become the grinding tool 1 in which abrasive 2 is embedded.

[0066] Fig. 2 shows a ceramic-bonded grinding tool 1 in the form of a honing ring, which is produced by a method according to Fig. 1 was manufactured. The grinding tool 1 comprises a base body 19 and the abrasive 2, which is embedded in the base body 19 via the inorganic binder 3.

[0067] The base body 19 is ring-shaped and formed in one piece, wherein the base body 19 has a toothing 22 on an inner surface 20 that can be brought into contact with a toothed workpiece. In general, the toothing 22 can also be arranged on an outer surface 21.

[0068] The abrasive 2 consists of a mixture of superabrasives in the form of diamond and cubic boron nitride, wherein the abrasive 2 may alternatively or additionally also comprise other abrasives 2.

[0069] The grinding tool 1 verifies the dimensions of the burned grinding tool blank 10. Fig. 1 a slight shrinkage may generally occur during firing process step 9. The outer diameter 15 is 300 mm, the inner diameter 16 is 138 mm, and the width 17 is 27 mm.

[0070] The grain volume of the abrasive 2 is 55 vol% of the grinding tool 1, the bond volume of the bonding agents 3, 4 is 20 vol% of the grinding tool 1 and the pore volume is 25 vol% of the grinding tool 1.

[0071] The grinding tool 1 has 10 vol% organic binding volume, the organic binding volume being in the form of epoxy resin from the group of thermoplastics and thermosets.

[0072] The grinding tool 1 comprises an inorganic binder 3, wherein the inorganic binder 3 is in the form of a low-fire binder, the low-fire binder comprising SiO2, Al2O3, B2O3 and oxides of alkali and alkaline earth.

Claims

1. A method for producing a ceramically bonded grinding tool (1), in particular a honing ring, wherein the following method steps are carried out in chronological order: - in a first method step, at least one abrasive (2), in particular corundum, SiC, aluminum oxide, and / or a superabrasive, at least one inorganic bonding material (3), in particular formed as a low-temperature baking bond, and at least one organic bonding material (4), in particular in the form of epoxy resin, are provided and blended, - the at least one abrasive (2), the at least one inorganic bonding material (3) and the at least one organic bonding material (4) are pre-pressed in a cold-pressing step (5) to form a cold-pressed green body (6), - the cold-pressed green body (6) is pressed in a hot-pressing step (7) to form a hot-pressed green body (8), characterized in that - the hot-pressed green body (8) is fired in a firing step (9) to form a grinding tool blank (10), in particular a honing ring blank, wherein the at least one organic bonding material (4) is at least partly burned off during the firing step (9), and - the grinding tool blank (10) is post-processed in a subsequent method step (11) to form the grinding tool (1), in which abrasive (2) is embedded.

2. The method according to claim 1, wherein the at least one organic bonding material (4) is substantially entirely burned off during the firing step (9) and / or is burned off to such an extent that an organic bond volume is at most 15 vol.%, preferably at most 10 vol.%, of the grinding tool blank (10).

3. The method according to claim 1 or 2, wherein the cold-pressing step (5) and the hot-pressing step (7) are carried out in separate press molds (12), wherein it is preferably provided that the press mold (12) and / or the cold-pressed green body (6) is / are pre-heated for the hot-pressing step (7).

4. The method according to one of the preceding claims, wherein the cold-pressed green body (6) is pressed to a first extent (13) in the cold-pressing step (5) and the hot-pressed green body (8) is pressed to a second extent (14) that is different from the first extent (13) in the hot-pressing step (7), wherein it is preferably provided that the hot-pressed green body (8) is pressed to an external diameter (15) between 50 mm and 450 mm, an internal diameter (16) between 20 mm and 300 mm, and / or a width (17) between 10 mm and 90 mm.

5. The method according to one of the preceding claims, wherein the at least one organic bonding material (4) is substantially fully cross-linked in the hot-pressing step (7).

6. The method according to one of the preceding claims, wherein the at least one inorganic bonding material (3) is fused in the firing step (9), wherein it is preferably provided that the firing step (9) is carried out in a furnace (18).

7. The method according to one of the preceding claims, wherein - a pressure between 20 bar and 300 bar, preferably between 40 bar and 60 bar, and / or substantially room temperature is used in the cold-pressing step (5), and / or - a pressure between 270 bar and 310 bar, preferably 275 bar to 285 bar, and / or a temperature between 150°C and 200°C, preferably between 170°C and 180°C, is used in the hot-pressing step (7), and / or - the firing step (9) is carried out at a temperature between 600°C and 1300°C, preferably between 900°C and 1000°C.

8. The method according to one of the preceding claims, wherein, starting from a grain volume of an abrasive (2), a bond volume of the bonding materials (3, 4), and / or a pore volume of the cold-pressed green body (6) after the cold-pressing step (5), as a result of the hot-pressing step (7) and / or the firing step (9) - the grain volume of the grinding tool blank (10) is increased to a range between 50 vol.% and 65 vol.%, preferably between 53 vol.% and 58 vol.%, and / or - a bond volume of the grinding tool blank (10) is increased to a range between 10 vol.% and 35 vol.%, preferably between 18 vol.% and 26 vol.%, and / or - a pore volume of the grinding tool (1) is reduced to a range between 10 vol.% and 40 vol.%, preferably between 22 vol.% and 28 vol.%, wherein the grain volume, the bond volume and the pore volume of the hot-pressed green body (8) and / or of the grinding tool blank (10) together amount to at most 100 vol.%.

9. A ceramically bonded grinding tool (1), in particular a honing ring, manufactured by a method according to one of the preceding claims, comprising - a main body (19) and - at least one abrasive (2) that is embedded in the main body (19) by means of at least one inorganic bonding material (3), characterized in that - a grain volume of the abrasive (2) is in the range between 50 vol.% and 65 vol.%, in particular between 53 vol.% and 58 vol.%, and - a bond volume of a bonding material (3, 4) is in the range between 10 vol.% and 35 vol.%, in particular between 18 vol.% and 26 vol.%, of the grinding tool (1), wherein the grain volume and the bond volume together amount to at most 100 vol.% of the grinding tool (1).

10. The grinding tool (1) according to claim 9, wherein the grinding tool (1) is produced by a method according to one of claims 1 to 8.

11. The grinding tool (1) according to claim 9 or 10, wherein - the main body (19) is annular and / or formed in one piece, wherein it is preferably provided that the main body (19) has teeth (22) on an inner lateral surface (20) and / or on an outer lateral surface (21), which teeth can be brought into contact with a toothed workpiece, - the at least one abrasive (2) is formed at least in part, preferably entirely, of corundum, preferably high-grade corundum and / or sintered corundum, SiC, aluminum oxide, and / or a superabrasive, preferably diamond and / or cubic boron nitride.

12. The grinding tool (1) according to one of claims 9 to 11, wherein the grinding tool (1) comprises at most 15 vol.%, preferably at most 10 vol.%, organic bond volume, wherein it is preferably provided that the organic bond volume is formed from the group of thermoplastics and / or thermosets, particularly preferably substantially epoxy resin.

13. The grinding tool (1) according to one of claims 9 to 12, wherein the grinding tool (1) comprises at least one, preferably exactly one, inorganic bonding material (3), wherein the at least one inorganic bonding material (3) is in the form of a low-temperature baking bond, wherein it is preferably provided, that the at least one inorganic bonding material (3) comprises SiO2, Al2O3, B2O3, and / or at least one oxide comprising an alkali and / or alkaline earth.

14. The grinding tool (1) according to one of claims 9 to 13, wherein the grinding tool (1) has an external diameter (15) between 50 mm and 450 mm, an internal diameter (16) between 20 mm and 300 mm, and / or a width (17) between 10 mm and 90 mm.

15. The grinding tool (1) according to one of claims 9 to 14, wherein the grinding tool (1) comprises a pore volume in the range between 10 vol.% and 40 vol.%, preferably between 22 vol.% and 28 vol.%, wherein the grain volume, the bond volume and the pore volume together amount to at most 100 vol.% of the grinding tool (1).