RU2594923C2 - Grinding tool for processing fragile materials and method of its manufacturing - Google Patents

Abstract

FIELD: metal processing.

SUBSTANCE: invention relates to abrasive processing. Grinding tool (1) includes core (2) and abrasive rim (4) containing abrasive particles (5) embedded into the matrix (6) containing a metal binding agent representing a fused bronze alloy and making 50-100 % of matrix volume, wherein metal binding agent contains silicon nitride in amount of 0.02-5.00 % of metallic binder, the silicon nitride is present in the form of grains with average size of less than 10 microns and more than 0.1 micron. Method involves fusing of abrasive particles together with metal powder containing copper and tin to produce matrix (6) in which abrasive particles (5) are embedded, and the matrix containing a metal binding agent represents fused bronze alloy; before fusing the metal powder is added with silicon nitride powder in such quantity that silicon nitride makes 0.02-5.00 % of metallic binder.

EFFECT: technical result consists in enhanced wear resistance ensuring even and predictable wear.

14 cl, 8 dwg

Description

FIELD OF THE INVENTION

The invention is a grinding tool, in particular a grinding tool for processing hard and / or brittle materials, such as tungsten carbide. The grinding tool may be, inter alia, a grinding wheel. The invention also relates to a method for manufacturing such a grinding tool.

BACKGROUND OF THE INVENTION

Grinding tools, such as grinding wheels, are used to process fragile materials. One of the applications of such grinding tools is the processing of tools that are made of hard metal (tungsten carbide). For example, a grinding tool can be used for machining, in which it is shaped by grinding drills or mills. If the preform to be shaped is made of a solid material, such as tungsten carbide, the abrasive tool should have abrasive particles of a very hard material. In practice, this usually means that the abrasive particles are diamond particles or borozone grains. Diamonds or grains of borozone for this purpose are commercially available and can be considered as standard components. Diamonds for this purpose can usually have a normal or average particle size of 50 microns (the particle size certainly varies) and have many sharp edges that can cut hard materials such as tungsten carbide.

A known type of grinding tool for this purpose is a core grinding wheel, which can be made, for example, of a metal material such as steel or aluminum. The core may also be made of non-metallic material, such as a polymeric material. The core can be made in the form of a disk, which can be mounted on the tool spindle for rotation around the axis of a metal core having a disk shape. An abrasive rim surrounds the core and is connected to it. The abrasive rim may contain abrasive particles embedded in the matrix by one or more binders. The material used in the abrasive rim is usually more expensive than the core material. For this reason, the abrasive rim has a smaller radial extent than the core (i.e., the abrasive rim is usually a smaller part of the grinding wheel, since it is more expensive).

During grinding, the abrasive rim gradually wears out. When it is completely worn out, the grinding wheel can no longer be used.

Known binders for abrasive rims of grinding wheels include polymeric binders, such as, for example, bakelite. Also, the binder may be a ceramic binder. It is also known about the use of metallic binders from bronze, which were produced by sintering. In such sintering operations, a metal powder containing copper and tin is sintered together with abrasive particles such as diamond particles or borosone grains. Sometimes, silver may be added, so that bronze contains copper (Cu), tin (Sn) and silver (Ag). In the past, practical experience has shown that Cu / Sn / Ag alloys perform well as bonding agents for abrasives and that such binders function well in the grinding process. Although the exact reason for this is not entirely clear. According to the inventors, the improved thermal conductivity caused by the addition of silver may explain why alloys containing silver perform well as binders for abrasive materials. However, silver is expensive, other bronze alloys can be used to reduce costs, and the present invention is also applicable to bronze alloys without silver.

Other known bronze combinations for this purpose include copper / tin / cobalt (Cu / Sn / Co) and copper / tin / nickel (Cu / Sn / Ni). In addition, it has been proposed that bronze combinations for this purpose could include copper / tin / titanium (Cu / Sn / Ti).

Another known system includes a composite material of a polymer binder and a metal binder, in which the metal powder is sintered together with the polymer material so that a matrix is formed in which the polymer binder and the metal binder (usually a bronze alloy, as described above) are closely intertwined with a friend at the microscopic level. In such composite materials, both the metal binder and the polymer binder form a chain. The corresponding chains of binders penetrate each other. Such a hybrid matrix, which contains both a metal binder and a polymeric binder, is disclosed, for example, in US Pat. No. 6,063,148.

In addition to metal and polymer binders, such composite materials typically include one or more fillers. One of these fillers may be graphite, which is used because of its lubricating properties.

The abrasive particles used may have various properties. For example, the fragility of diamonds can vary depending on the purpose of using a grinding tool. The properties of various diamonds can be selected to satisfy the properties of various binders (or binder compositions).

In a good grinding tool, the abrasive particles must be bonded in their matrix so that the grinding functions of the tool match the desired. Preferably, the grinding sharpening has good wear resistance, so that it can be used for a long period. However, good wear resistance is not the only desirable property and a grinding tool with the highest wear resistance is not necessarily the best choice. Another desirable property is low power consumption (i.e., so that the power needed to drive the grinding is not too high) and constant or at least predictable performance. If the grinding effect of the abrasive rim changes too often over time, this is difficult. This is especially true for grinding tool performance, the change of which cannot be predicted.

The degree of wear of the grinding tool under given conditions depends to a large extent on the properties of the matrix into which the abrasive particles are embedded. Thus, the composition of the matrix is important.

When a grinding tool is used for machining a workpiece, sharp angles and faces of abrasive particles act on the workpiece. Thus, a force is applied to the abrasive particles embedded in the matrix. During grinding, abrasive particles are damaged. Gradually, small pieces come off the abrasive particles so that the abrasive particles gradually wear out. When the abrasive particles in one area of the abrasive rim were completely worn, the workpiece collides with the matrix directly. The matrix, as such, is less solid than the workpiece, and it wears out quickly. As a result, fresh abrasive particles emerging on the surface of the abrasive rim can begin to act on the workpiece.

However, if the matrix that contains the abrasive particles is too weak, the abrasive particles may come off the matrix before they wear out. When this occurs in part of the surface of the abrasive rim, the workpiece comes in direct contact with a relatively fragile matrix and prematurely wear out the matrix. When this happens, power consumption drops instantly, as long as the matrix wears out so that fresh abrasive particles come to the surface. As a result, the abrasive rim of the grinding tool wears out faster than it did if the grinding tool had been programmed in advance. The consequence of this may be that grinding does not occur properly as the grinding tool is set to a mode based on assuming the diameter of the tool, which is now incorrect. This problem becomes more serious if the abrasive rim is so worn out that it is difficult to predict. For example, if wear occurs with abrupt steps that come at irregular intervals.

It is also desirable that the required power for grinding can be kept low so that energy consumption during grinding can be minimized.

Another desirable property of grinding tools is a high grinding coefficient. The grinding coefficient expresses the ratio between the volume of material removed with the grinding tool from the workpiece and the volume lost by the grinding tool (tool wear). A good grinding tool has a high grinding ratio.

Thus, it is an object of the present invention to provide a grinding tool that has good wear resistance. Further objectives of the invention should provide a tool with regular and predictable wear, the need for low power for a high coefficient of grinding. These goals are achieved using the present invention, which will be described below.

SUMMARY OF THE INVENTION

The invention relates to a grinding tool. The grinding tool is specifically designed to handle hard and / or brittle materials such as tungsten carbide, but the developed grinding tool can also be used to grind other materials. The grinding tool includes a core and an abrasive rim. The abrasive rim includes abrasive particles embedded in the matrix. The matrix contains a metal bonding agent, which is a sintered alloy of bronze. The metal binder makes up 50% -100% of the matrix volume. In accordance with the invention, the metal binder contains silicon nitride in an amount that is 0.02-5.0% by volume of the metal binder or, in some cases, 0.1-5.0% by volume of the metal binder.

Here, the matrix may also optionally contain a polymeric binder that has been sintered together with a metal binder so that the polymeric binder and the metal binder form a bonded chain.

Here, silicon nitride is 0.3-5.0% of the volume of the metal binder. For example, it can be 0.5-5.0% of the volume of the metal binder, 1.0-5.0% of the volume of the metal binder, or 0.5-3.0% of the volume, or 0.5-2, 0% of the volume.

Silicon nitride may be present in the form of grains with an average grain size that is preferably less than 10 microns, but also preferably above 0.1 microns. The size of such particles can be 1250 particles of a Tyler grid. Thus, particles can include particles up to 10 microns in size, although the average grain size is smaller.

When the polymeric binder is part of the matrix, the polymeric binder contains a polyimide or is made entirely or almost completely of polyimide.

The matrix may optionally further include fillers such as graphite. Graphite has lubricating properties that may be desirable in the grinding process.

The metallic binder is preferably a bronze alloy that contains copper, tin and silver.

The abrasive particles can be, for example, diamond particles or borosone particles. For both diamonds and borosone, abrasive particles can have an average particle size of 4-181 microns. In many embodiments, the abrasive particles may have a size of 46-91 microns. In embodiments of the invention, the abrasive particles may be coated with copper or nickel.

The invention also relates to a method for manufacturing a grinding tool being developed. The method includes sintering abrasive particles together with a metal powder. The result of sintering is a matrix in which abrasive particles are embedded. The matrix will thus contain a metal bonding agent. The metal powder contains copper and tin, so that the metal bonding agent is a sintered bronze alloy. According to the invention, silicon nitride in the form of a powder is added to the metal powder before sintering and to such an extent that silicon nitride comprises 0.02-5.0% by volume of the metal binder and preferably 5.0% by volume of the metal binder.

In embodiments of the inventive method, the metal powder may further comprise silver.

When reference is made to the relative proportion of silicon nitride in a metal binder, it should be understood that this refers to the volume fraction of powder used in the manufacturing process. In other words, the manufacturing method is that in a powder that is added before sintering, silicon nitride will be 0.02-5.0% of the volume of the metal binder (silicon nitride is calculated as part of the metal binder). It is assumed that silicon carbide particles will retain the same relative fraction of the total volume also after sintering.

Alternatively, the polymer is added to the metal powder before sintering, preferably in the form of a polyimide powder, so that a polymer binder is also formed, which is part of the matrix.

The method can be carried out as follows: the powder material for matrix binding agents is mixed with abrasive particles to form a mixture. The mixture is then pressed in a cold press. The densified mixture is then cured in an industrial furnace at a temperature of 380-520 ° C, preferably 400-500 ° C, for 120-150 minutes. After that, the compacted and cured mixture is placed in a press and is subjected to a pressure of 1500-2000 kg / cm ² . The pressure is then maintained until the mixture reaches a temperature below 300 ° C.

As an option, filler is added to the mixture of metal powder and abrasive particles before sintering. The filler may further comprise graphite.

Preferably, the matrix of the grinding tool under development is a matrix, which is a composite material, i.e. a matrix containing both metallic and polymeric binder; The solution of mounting crystals on a hybrid amplifier board can combine the best properties of a metal binder with the best properties of polymer binders. If sharpening is required, a hybrid matrix grinding tool can be re-sharpened more easily than a pure metal matrix. At the same time, a hybrid matrix grinding tool has better wear resistance than matrices using only a polymer binder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Schematic illustration of a grinding tool.

FIG. 2. Schematic representation of the cross section of abrasive particles interspersed in the abrasive rim of a grinding tool.

FIG. 3. A schematic cross-sectional view of a grinding tool that acts on a workpiece.

FIG. 4. A chart that displays power consumption for two different grinding tools.

FIG. 5. Schematic representation of the cross section of the first version of the developed grinding tool.

FIG. 6. Schematic representation of the cross section of the second version of the developed grinding tool.

7. A diagram that shows the wear of a grinding tool versus the silicon nitride content.

FIG. 8. A diagram that shows the grinding coefficient of a grinding tool as a function of silicon nitride content.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 depicts a grinding tool 1. The grinding tool may be, in particular, a grinding wheel that is designed to process hard and / or brittle materials, such as tungsten carbide. Such materials may be present in tool blanks, such as, for example, drills or cutters, and the grinding tool 1 of the present invention may be a grinding wheel that is used to shape such tools. The grinding tool 1 consists of a core 2 and an abrasive rim 4. The core 2 can be made of less expensive material, such as steel or other metal. Alternatively, the core may be made, for example, of a polymeric material. The core may also contain more than one material. For example, it can be made partially from a metal, such as steel or aluminum, and partially be a polymeric material. The core 2 can be made with a through hole or a cavity such that the grinding tool 1 can be mounted on a spindle (not shown) for rotational movement. In FIG. 2, the abrasive rim 4 contains abrasive particles 5 embedded in the matrix 6. The matrix 6, in turn, contains a metal bonding agent, which is a sintered bronze alloy. The metal binder makes up 50% -100% of the volume of the matrix 6, and embodiments are thus possible in which the entire matrix 6 consists of a metal binder. However, matrix 6 typically contains at least some other components. For example, it may contain a filler, such as graphite, which has lubricating properties. In most embodiments, matrix 6 will comprise a polymeric binder which can be formed from polyimide.

If the matrix 6 holds the abrasive particles 5 well, the abrasive particles 5 will emit small fragments and will wear out gradually. As a result, the wear of the abrasive particles will be relatively slow, so that the diameter of the grinding tool 1 can be substantially constant over a long period of time. In addition, the wear of the abrasive rim will go at a steady pace and the energy supply during operation will not change much.

If the matrix 6 is instead unable to hold the abrasive particles 5 firmly, it may happen that the abrasive particles detach before they are fragmented. As a result, they will be lost before their full abrasive potential is used. The abrasive tool 1 will wear out faster and the diameter of the grinding tool (e.g. grinding wheel 5) will decrease faster. The smaller diameter of the grinding tool 1 can lead to less accurate machining of the workpieces.

In FIG. 3, the grinding tool 1 acts on the workpiece 7. The workpiece can be, for example, a workpiece, which should be in the form of a drill. The grinding tool is rotated using a power source acting through, for example, a spindle (not shown). Thus, the abrasive rim 4 of the grinding tool acts on the workpiece 7 to cut / cut a groove in the workpiece. In FIG. 3, the workpiece has a core diameter in the transverse direction, which is determined by the action of the grinding tool 1. If the grinding tool 1 is worn so that its diameter decreases, the diameter of the core in the transverse direction will increase if wear is not compensated (for example, by changing the position of the grinding tool 1 with respect to to the workpiece 7). Therefore, it is highly desirable that wear is maintained at a low level and that wear that does not occur does not occur with sudden unpredictable surges.

It can also be added that when the abrasive particles 5 are properly gradually fragmented, it is good for the machinability of the grinding tool 1, that is, the ability of the grinding tool to re-sharpen itself. When the abrasive particles 5 are fragmented step by step, the wear on the matrix 6 can occur smoothly and the surface of the abrasive rim 4 does not clog so easily. If abrasive particles instead come off suddenly before they are properly fragmented, this tends to increase surface clogging; the surface of the abrasive rim 4 may become more contaminated with small particles 5 from the workpiece 7. This may require temporary removal of the grinding tool 1 from service so that the grinding tool 1 can be sharpened again. If the abrasive particles 5 are gradually fragmented, the risk of such clogging is less. When the abrasive particles are completely worn out, the new abrasive particles 5 can come to the surface more smoothly, which in itself contributes to the re-sharpening of the grinding tool (or, rather, the abrasive rim 4 of the grinding tool 1).

When abrasive particles come off the abrasive rim before they are completely fragmented, this usually manifests itself in the power consumption of the grinding tool; the force suddenly drops, and then begins to grow again after a while, the abrasive particles are held properly by the matrix so that they are allowed to fragment as they should, and this can also be seen on energy consumption. In this case, the particles tend to remain relatively constant over time (it should be noted, however, that usually there is always a gradual increase in the required power for working with the first workpieces so that less energy is required for the very first parts).

It was suggested in the article by E.D. Kizikova and P. Kebko (“Microadditives in the alloys of the Cu-Sn-Ti system”, Institute of Superhard Materials, Academy of Sciences of the Ukrainian SSR, Kiev, translated from “Metallurgy and heat treatment of metals”, No. 1, pp. 50-53, January 1987 ) that the Cu / Sn / Ti alloy, which should be used as a binder for diamond abrasive tools, must be reinforced with 0.01% silicon nitride (Si ₃ N ₄ ). According to the authors of this article, this addition leads to an improvement in the yield strength.

The inventors have considered what steps can be taken to improve the matrix's ability to hold abrasive particles. Not wanting to be bound by theory, the inventors believe that one of the reasons that metal binders release the abrasive particles embedded in it may be because dislocations inside the metal binder make the metal binder weak. Assuming that this theory is correct, the authors immediately suggested that it should be possible to improve the matrix and strengthen it with particles that block the arrangement in a metal binder. Therefore, the authors of the present invention have tried various additives to a metal powder, which was used for sintering a metal binder. One additive that was tested was alumina, which was added to the extent that corresponds to 1.0% of the volume of the metal binder. This led to some improvement, but the improvement was not as good as the inventors hoped. The inventors also tried to add 0.01% silicon nitride by volume. The improvement with this additive was even less than the improvement achieved with alumina.

The inventors then again examined whether an increased amount of silicon nitride would lead to better results. This was confirmed by tests conducted by the inventors. When silicon nitride was added in amounts significantly greater than 0.01% of the volume of the metal binder, it was found that a very significant improvement was obtained.

For example, the inventors tested compositions in which a metal binder was contained in an amount of 1.0% by volume of silicon nitride (Si ₃ N ₄ ). A grinding tool with this composition was then compared to a standard grinding tool using a hybrid matrix and which does not contain silicon nitride (Si ₃ N ₄ ). The grinding tools were two grinding wheels, in which the abrasive rim 4 was made in the form of a ring surrounding the core 2. Under comparable conditions, the diameter of a standard tool was erased by 136 μm, while the diameter of a grinding tool with an experimental composition was worn out only by 58 μm. The grinding coefficient for a tool with 1.0% silicon nitride was 2335. For comparison, a tool using 0.01% by volume of silicon nitride was erased by 94 μm, while a tool using 1.0% by volume of aluminum oxide was erased by 84 microns.

The test was carried out with a composition where silicon nitride was 5% of the volume of the metal binder. The wear resistance was still good, but not as good as that of a grinding tool with 1.0% by volume of silicon nitride. In addition, a tool with 5.0% silicon nitride had a higher energy consumption. The grinding coefficient was good, but not as good as in tools with 1.0% and 0.1% by volume.

The inventors also tested the grinding wheel, which had a shape and composition similar to other tested instruments, but in which silicon nitride was 0.1% of the volume of the metal binder. It was found that under the same test conditions under which other tools were tested, the tool wear with 0.1% by volume of silicon nitride was 62 μm and the grinding coefficient was 2084. Although the results were worse than those obtained with 1% by volume, this was still a very significant improvement over standard grinding tools.

The inventors also tested a grinding wheel, which had 0.02% silicon nitride content of the volume of the metal binder, but which in the rest was similar to the other grinding wheels tested. Under similar test conditions, a grinding wheel with 0.02% by volume of silicon nitride has a wear (reduction in diameter) of 58 μm and a grinding coefficient of 2283. Thus, the results were slightly better than the results obtained from a ratio of 0.1% of volume .

The results obtained allow us to conclude that significantly better results are obtained in the range of 0.02-5.0% by volume of silicon nitride (Si ₃ N ₄ ). It turned out that in this range both the grinding coefficient and wear resistance were significantly better than at 0% or 0.01%.

Tests for wear resistance and grinding coefficient were carried out for 0% by volume, 0.01% by volume, 0.02% by volume, 1.0% by volume and 5.0% by volume of silicon nitride.

The tools tested were grinding wheels, essentially of the type shown in FIG. 5, i.e. grinding tools with an abrasive rim 4, which surrounds the core 2, and where the grinding tool 1 rotates around axis A during operation. Wear resistance as a function of silicon nitride content can be seen in FIG. 7. Wear resistance, as a reduction in diameter, is shown in FIG. 7. As can be seen in FIG. 7, the wear resistance increased significantly when the silicon nitride content was increased from 0.01% to 0.02%. Wear resistance is still high to a silicon nitride content of 5.0% by volume of the metal binder. However, at 5.0% by volume of silicon nitride, the wear resistance was slightly lower compared to the resistance observed at a content of 0.02-1.0%. The inventors concluded that, therefore, the best wear resistance is obtained in the range from 0.02-5.0% by volume.

The grinding coefficient as a function of the silicon nitride content can be seen in FIG. 8. As can be seen in the figure, the best values were obtained with a silicon nitride content in the range from 0.02% -5.0%. In FIG. 8, it can also be established that the G-ratio falls in the right direction in the figure, although the grinding coefficient at 5.0% by volume is still good.

Thus, the authors of the present invention concluded that the metal bonding agent may contain silicon nitride in an amount that is 0.02-5.0% of the volume of the metal binder. Since energy consumption was higher at 5.0% by volume, the inventors came to the conclusion that values lower than 5.0% would have good wear resistance, but lower energy consumption compared to tools with a silicon nitride content of 5% by volume. Thus, the preferred range may be 0.02-3.0% by volume, 0.5-3.0% by volume, 0.5-2.0% by volume or 1.0% -2.0% of volume of metal binder.

At 0.1% by volume, energy consumption is generally lower than at 0.02% by volume. At 5.0% silicon nitride by volume, the power consumption was higher than with a content of 0.02%, but the energy consumption at 5.0% by volume was more especially, the power consumption was more predictable than at 0.02% by volume.

Particles of silicon nitride should preferably have a size of up to 10 microns (1250 units of Tyler mesh). For sieved particles, this usually means that the average grain size is less than 10 microns. The average particle size (D50) for silicon nitride particles can therefore be about 2-3 microns (depending on how the average particle size is measured). The specific surface area of the particles of silicon nitride may preferably be in the range of 5-6 m ² / g If the particles used are too small, this can lead to clogging and difficulties during production. In addition, in order to impart optimal strength to the metal binder, the authors suggest that particles of up to 10 μm should preferably be included.

Typically, matrix 6 should further comprise a polymer binder that has been sintered together with the metal binder so that the polymer binder and the metal binder form a bond chain (even if such a polymer binder is optional). Using a polymer binder allows you to improve the properties of the matrix and adapt it to various types of abrasive particles. The polymer binder may suitably be a polyimide or contain a polyimide. The reason for this is that polyimide is heat resistant and can withstand high temperatures during sintering. If a polymer binder is used, the polymer binder may be present in an amount up to 50% of the matrix volume (i.e., the amount of the polymer binder is in the range of 0-50% of the matrix volume). For example, a polymer binder may be present in an amount of 10-40% or 10-30% of the matrix volume.

Optionally, the polymeric binder may be formed by some other polymeric material. For example, it can be formed from polyamide imide, which is also able to withstand high temperatures. However, a polyimide is preferred since it has better grinding properties than polyamide imide.

The metal binding agent is preferably a bronze alloy that contains copper, tin and silver. Silver improves the desired properties of the metal binder.

The abrasive particles 5 can be either diamond particles or borosone particles. Diamonds are harder and have better abrasive properties, but borozone is more heat-resistant. In addition, diamonds can react chemically with certain materials.

The abrasive particles 5 can be either diamond particles or borosone particles. Particles can be in the range from 4 μm to 181 μm. Even if the particles are outside it, in each case, this range can be considered depending on the requirements. In many practical embodiments, the abrasive particles 5 could have an average particle size in the range of 46 μm to 91 μm, which is suitable for many grinding operations.

Abrasive particles 5, as an option, may have a coating of copper or Nickel. A copper or nickel coating can improve the bond between the abrasive particles 5 and matrix 6. However, the abrasive properties of the particles 5 will be slightly reduced if the particles have such a coating.

The relative proportion of abrasive particles 5 with respect to binders and fillers in the matrix 6 may vary depending on the requirements in each individual case. In many practical embodiments, the amount of abrasive particles may be 10-50% of the total abrasive rim volume (i.e., the total abrasive particle size and matrix). If the relative proportion of abrasive particles is higher than 50%, there is a significant risk that the matrix will no longer be able to hold abrasive particles. If the relative proportion of abrasive particles is less than 10%, then the grinding effect may become too small. The relative proportion of abrasive particles may preferably be in the range of 15-30% and a suitable value may be 25%.

Preferably, silicon nitride is present in the form of grains having an average grain size that is equal to or less than 10 microns but above 0.1 microns. For example, they may have an average size in the range of 1-10 microns or 2-9 microns. The authors suggest that particles of silicon nitride smaller than 0.1 μm can lead to clogging of particles of silicon nitride, which reduces their reinforcing effect.

Silicon nitride particles can have three different crystallographic structures, designated as α, β and γ phases (also known as trigonal phase, hexagonal phase and cubic phase). Phases α and β are the most common. Phase γ can only be synthesized at high pressure and high temperature. Any of these phases can be used. Preferably, phase α is used. The added silicon nitride particles can also be a mixture of particles of different phases.

Based on FIG. 4, a grinding tool according to the invention is compared with a standard grinding tool. The vertical axis represents power consumption, while the horizontal axis represents the number of workpieces that have been machined with the appropriate grinding tool. In FIG. 4 B5 is a grinding tool in accordance with the invention. While EZ is a standard grinding tool. As can be seen in FIG. 4, the tool, presented as B5, has a power consumption that rises immediately and then remains essentially constant. The energy consumption of the traditional instrument introduced by EZ is steeply increasing, and then suddenly drops before it rises again. This means that the abrasive particles of tool B5 slowly fragment, while the EZ is a grinding tool where the abrasive particles suddenly come off. In this regard, the tool will wear out faster.

It can also be added that B5 is a tool with both a metal and a polymer binder. The metallic binder is bronze, which contains copper, tin and silver. They were sintered using a metal powder, which contains 45% by volume of copper, 45% by volume of tin and 10% by volume of silver. In the tool according to B5, the polymer binder represents 1.0% of the total binder.

The grinding tool of FIG. 1 may have a cross section as shown in FIG. 5. In such an embodiment, the abrasive rim 4 is located radially outside the core 2 so that the rim 4 completely surrounds the core 2. The tests explained with reference to FIG. 4, 7, 8, were carried out on such a grinding tool. However, the present invention is not limited to such an embodiment. With reference to FIG. 6, it should be understood that the core 2 can extend at least as much in the radial direction as the abrasive rim 4. In FIG. 6, the grinding tool has an abrasive rim 4, which does not exceed the size of the core 2 in the radial direction. Meanwhile, the abrasive rim 4 has an axial extension that is different from the axis of the core 2 (the axial direction is the axis of rotation A of the grinding tool 1 when it is driven by the spindle, see Fig. 5 and 6). It should also be understood that the grinding tool 1 is not necessarily designed for rotation. Meanwhile, it can act on the workpiece by reciprocating motion. In the context of the claims, the term "core", therefore, should be understood in the broad sense of any supporting substrate for the abrasive rim. Similarly, the term "rim" should also be understood in a broad sense as any layer fixed to the core 2 so that abrasive particles can act on the workpiece.

In addition, the invention encompasses a method of manufacturing a developed grinding tool. The method includes sintering abrasive particles together with a metal powder that contains copper and tin, so that sintering results in a matrix into which the abrasive particles are embedded 5. The matrix contains a metal bonding agent, which is a sintered bronze alloy. In accordance with the invention, silicon nitride in powder form is added to the metal powder before sintering in such an amount that silicon nitride will be 0.1-5.0% of the volume of the metal binder.

The metal powder used is predominantly a metal powder with particles smaller than 44 microns in size, but they should preferably be larger than silicon nitride particles. Preferably, they should be at least twice as large. Suitable average size is 15-44 microns.

Metal powder may also optionally contain silver.

The metal powder may come in the form of pre-alloyed particles or in the form of particles of pure copper, pure tin, pure silver, etc.

The polymer may be added to the metal powder before sintering, preferably in the form of a polyimide powder, so that a polymer binder is also formed, which is part of the matrix 6.

The sintering method can be carried out so that the powder material for the binder matrix 6 is mixed with the abrasive particles 5. The mixture is compacted in a cold press. After this compaction, the mixture is cured in an industrial furnace at a temperature of 380-520 ° C, preferably 400-500 ° C or 440-460 ° C, for 120-150 minutes. The time required depends on the size. In a larger mold, more time is required. After that (preferably immediately afterwards), the compacted and cured mixture is placed in a press and subjected to a pressure of 1500-2000 kg / cm ² . The pressure is then maintained until the mixture reaches a temperature below 300 ° C.

For example, the inventors made a grinding tool in accordance with this method in a process where the temperature in the furnace was 450 ° C.

The abrasive rim 4 can also be made using spark plasma sintering (IPA). By this technique, the abrasive rim 4 can be made very quickly.

The rim with a matrix containing abrasive particles can be sintered separately, and then fixed (for example, glued) to the core 2. On the other hand, the abrasive rim 5 can be sintered directly on the core 2 so that it binds to the core during its formation. Before sintering, the core 2 can be electrolytically coated with copper on at least one surface of the core, which will intersect with the abrasive rim 4. The abrasive rim 4 can then be sintered on a surface with a copper coating so that a seam is formed.

The filler may be further added to the mixture of metal powder and abrasive particles 5 before the sintering operation. As explained previously, the filler may contain graphite. Other possible materials may include fillers, for example, alumina spheres.

Preferably, the bronze used in the metal binder is selected from the group consisting of copper - tin (Cu / Sn), copper - tin - cobalt (Cu / Sn / Co), copper - tin - nickel (Cu / Sn / Ni) or copper - tin - silver (Cu / Sn / Ag). Even more preferred is bronze with copper - tin - silver. Other bronze alloys may also be considered.

The proposed grinding tool can be used for processing hard and / or brittle materials. This does not exclude the possibility that the grinding tool can be used for other materials.

In embodiments of the invention, the matrix 6 may also, as an option, contain at least one ceramic component in the form of ceramic particles. The ceramic component may be, for example, a frit, and which contains SiO ₂ . The ceramic particles for the matrix may be a frit in the form of spherical particles having a particle size of 50-500 microns, depending on the size of the abrasive particles. For larger abrasive particles, larger ceramic particles will be used. Abrasive particles can be embedded in ceramic particles, while ceramic particles are embedded in a hybrid matrix with metal and polymer binders. Ceramic particles can be held by the matrix more strongly than abrasive particles will be held. The machining abrasive rim is thus improved. The ceramic component does not have such good wear resistance as a metal binder. By combining ceramics, metal and polymer binders, you can combine the best properties of these binders.

Claims (14)

1. A grinding tool (1), comprising a core (2) and an abrasive rim (4) containing abrasive particles (5) embedded in a matrix (6) containing a metal bonding agent, which is a sintered bronze alloy and constitutes 50-100% of the volume of the matrix, while the metal binding agent contains silicon nitride in an amount of 0.02-5.00% of the volume of the metal binder, and silicon nitride is present in the form of grains that have an average size of less than 10 microns and more than 0.1 microns. 2. A grinding tool (1) according to claim 1, wherein the matrix (6) also contains a polymeric binder, which has been sintered together with a metal binder to form bonded polymer and metal binders. 3. A grinding tool (1) according to claim 1 or 2, in which silicon nitride is 0.3-5.0% by volume of the metal binder, preferably 0.5-3.0% by volume, more preferably 0.5- 2.0% of the volume. 4. The grinding tool according to claim 2, in which the polymeric binder contains polyimide. 5. The grinding tool according to claim 1 or 2, in which the matrix further comprises a filler in the form of graphite. 6. The grinding tool according to claim 1, in which the metal binder is a bronze alloy that contains copper, tin and silver. 7. A grinding tool according to claim 1, wherein the abrasive particles (5) are diamond particles or particles of cubic boron nitride. 8. A grinding tool according to claim 7, in which the abrasive particles (5) have an average particle size in the range of 4-181 microns, preferably in the range of 46-91 microns. 9. A grinding tool according to claim 8, in which the abrasive particles (5) are coated with copper or nickel. 10. A method of manufacturing a grinding tool (1), comprising sintering abrasive particles together with a metal powder containing copper and tin, to obtain a matrix (6) into which the abrasive particles (5) are embedded, wherein the matrix containing a metal bonding agent is sintered bronze alloy, moreover, before sintering, silicon nitride is added to the metal powder in the form of a powder in such an amount that silicon nitride will be 0.02-5.00% of the volume of the metal binder, while the added silicon nitride is made in the form grains having an average grain size less than 10 microns and greater than 0.1 microns. 11. The method of claim 10, wherein the metal powder further comprises silver. 12. The method according to p. 10 or 11, in which the polymer is added to the metal powder before sintering, preferably in the form of a polyimide powder, with the formation of a polymeric binder, which is part of the matrix (6). 13. The method according to p. 10, in which the mixing of the powder material for the matrix binders (6) with abrasive particles (5), compacting the mixture in a cold press, curing the compacted mixture in an industrial furnace at a temperature in the range from 380-520 ° C , preferably 400-500 ° C, for 120-150 minutes, after which the compacted and cured mixture is placed in the press, subjected to a pressure of 1500-2000 kg / cm ² , which is held until the mixture reaches a temperature below 300 ° C. 14. The method according to p. 10, in which the filler is added to the mixture of metal powder and abrasive particles (5) before sintering, and the filler contains graphite.

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