WO2017050755A1 - Method for the production of open-pore, ceramic-bound abrasive tools - Google Patents

Abstract

The present invention relates to a method for producing open-pore, ceramic-bound abrasive tools having a pore fraction of between 20 and 80 % by volume, wherein a mixture of abrasive grains (31), binder (32) and pore forming agents is used, the pore forming agents comprising inorganic solid particles, in particular glass-like, crystalline and/or amorphous and/or semi-crystalline inorganic solid particles, with an average particle diameter of between 400 and 2000 μm.

Description

 Process for the production of open-pored, ceramically bound

 Grinding Tools

TECHNICAL AREA

The present invention relates to a method for producing open-pore, ceramic-bonded grinding tools and grinding tools produced by this method. STATE OF THE ART

Ceramic bonded abrasive tools are used in the art especially for surface treatment. For the production of the abrasive tools abrasive grains, for example those based on alumina, silicon carbide, diamond or CBN, with a binder and optionally further additives, such as. Fillers, abrasive substances, pore formers or temporary adhesives, processed into a mixture, which is then pressed to the desired shape. The resulting green body is then dried, optionally freed at suitable temperatures of the added Porenbildnem and then fired ceramic.

Depending on the application, the grinding tools have a certain porosity, the pores should allow efficient use of cooling lubricants and the absorption and removal of grinding chips, so that a high material removal is made possible with low thermal stress on the workpiece. It is common to add artificial pore formers to the mixture, which are substances that can be removed from the green body at low temperatures by evaporation, sublimation or burning. The best-known and still most commonly used pore-forming agent for ceramic-bonded grinding tools is naphthalene, which can be removed by sublimation at about 80 ° C. A disadvantage of the use of naphthalene is to be seen in particular in the toxicity and especially in the intense and typical odor, so that not only the employees in the production plants but also the residents are bothered by the exhaust air and endangered health. Despite appropriate Complex and cost-intensive protective measures do not completely eliminate nuisance and endangerment of the environment when naphthalene is used

avoid. Therefore, many attempts have been made in the past to

To replace naphthalene with alternative pore formers, but this often failed because these alternative substances not or insufficiently show the required for the production of ceramic bonded abrasive tools positive properties, such as. low springback after shaping, good mixing behavior, low tendency to swell in connection with the liquid

 Anfeuchtsystemen, stable homogeneous distribution and low tendency to separate in the finished mass, little exothermic and residue-free as possible

Burnout.

EP 2 540 445 A1 describes a process for the production of a bonded abrasive tool, wherein dicarboxylic acids and mixtures of dicarboxylic acids and hydrates of the dicarboxylic acids are used as pore formers. A disadvantage of this method is that in the decomposition of the dicarboxylic acids considerable volumes of gas are released, the mechanical

Damage to the green body can cause, what by a time and

costly temperature control must be avoided. In addition, the dicarboxylic acids must also be granulated with relatively great effort with the addition of binders to be used easily in the mixture for the green body can, which additionally complicates the production of grinding tools and expensive.

DE 196 28 820 A1 describes a method for the production of porous ceramic products, wherein the ceramic mass in the solid state present in the mass non-soluble or swellable, non-deformable acrylate glasses of polyacrylic or polymethacrylic, which are classified in a defined grain size, as burnable pore formers be added. A disadvantage of the method described in the above document is that the

Burning and decomposition products of the acrylate glass are released during burning in a narrow temperature interval, whereby the cleaning of the Exhaust combustion systems to be used in the short term extremely high load, which increases the risk of incomplete combustion and thus a

Pollution of the environment. In addition, even polyacrylates do not burn completely odorless, which is particularly noticeable negative when larger quantities are burned abruptly. In addition, there is a risk that by the burnout of the pore-forming agent for a short time

released large gas volumes are generated forces, causing the

Abrasive tools can be damaged. German Utility Model DE 20 2010 015 210 U1 discloses the use of thermoplastic granules as novel pore formers. The Scripture are no details to refer to which thermoplastic material and how this thermoplastic granules to be used. However, it has been found that even thermoplastic polymers are usually not completely odorless process. In addition, the processing of such pore-forming agent requires a very accurate and often complicated temperature control, thereby reducing the time and energy required for the production of the

Grinding wheels increased.

PRESENTATION OF THE INVENTION

There is therefore still a need for a pore-forming agent and a method for producing open-pored grinding tools, which overcomes the disadvantages of the prior art.

The object is achieved by a method for producing open-pore, ceramic bonded abrasive tools with a pore content between 20 and 80 vol.% By using a mixture comprising abrasive grains, binders and pore formers, wherein as a pore former inorganic solid particles having an average particle diameter between 200 and 2000 μηι be used. Suitable inorganic solid particles are inorganic

Compounds provided when heated in a temperature range Melt between 200 and 1200 ° C, decompose or volatilize and thereby release little or no polluting exhaust gases.

In this case, for example percarbonates can be used as inorganic solid particles, which decompose upon heating.

However, it is particularly advantageous to use glassy, crystalline and / or amorphous and / or semicrystalline inorganic solid particles as pore formers, the inorganic solid particles being melted, volatilized or decomposed on heating. When using melting particles, the melt deposits on the surface of the surrounding particles, in particular on the abrasive grains, wherein at the points where the inorganic

Solid particles templates, now pores are formed. Of course it is also possible, the inorganic solid particles in

Use combination with other pore formers, with a preferred

Embodiment of the present invention, the combination with thermoplastic polymers provides, with the two different pore formers complement each other advantageous. Thus, the inorganic solid particles can be used as needed or in addition to other pore-forming agents. If a combination with other pore formers is used, the mixture for producing open-pored, ceramic-bonded abrasive tools advantageously comprises at least one thermoplastic polymer as a further pore-forming agent. Through appropriate combinations can be ensured that the

 Pore formers have the required for the production of ceramic bonded abrasive tools positive properties, such. low tendency to swell, homogeneous stable distribution and low springback when pressing the mass, low pollution of the environment and the workplace as well as reduction of costs due to reduced burning time during the burn-out phase.

A particularly advantageous embodiment of the present invention provides that the pore formers are used in a defined, multimodal grain distribution, so that a defined pore space with different pore sizes in the targeted Abrasive tool can be generated, which is optimized for the respective grinding operation, wherein the size of the pores is adapted to the resulting chips in the grinding process and the coolant requirement. In this case, the pore formers are used in each case as granules with a grain fraction in a particle size range between 50 and 2000 μιτι.

The pore formers preferably have a multimodal particle size distribution with at least one coarse and one fine fraction and at least two

Grain size maxima in the range between 100 and 1000 pm, with the maximum of the finest fraction between 200 and 500 pm and the maximum of the coarsest fraction between 500 and 1500 pm. When using a Porenbildnermischung with a bi-modal particle size distribution of the average grain size d is ₅ o of the fine fraction is preferably between 100 and 400 pm and the average grain size d ₅ o of the coarse fraction 350 to 1000 pm.

For a pore-forming agent mixture having a trimodal particle size distribution, the mean particle size d _{50 of} the fine fraction is advantageously between 100 and 300 μm, the mean particle size d _{50 of} the middle fraction between 250 and 450 μm and the average particle size d _{50 of} the coarse fraction between 400 and 1000 μm.

The present invention also provides a grinding tool with a pore fraction between 20 and 80 vol.%, Which is prepared using a mixture, the inorganic solid particles, in particular glassy, crystalline and / or amorphous and / or semi-crystalline solid particles having an average particle diameter between 400 and 2000 pm as pore-forming agent.

The production of open-pored, ceramic-bonded grinding tools is usually carried out by the fact that to be used for the grinding process

Abrasive grains are presented in a defined grain size and are first mixed with a powdery binder. To the mixture is then added a liquid temporary adhesive, with the aid of which the ceramic binder, which is added as a powder, is fixed on the surface of the abrasive grain. As a temporary adhesive, for example, dextrin can be used. Subsequently, the

Pore formers and other additives added, the pore formers as well as the abrasive grains are used in solid form in a defined grain size, which is adapted to the size of the desired pores and preferably is approximately in the grain size range of the abrasive grains used. The shape of the glassy, crystalline and / or amorphous and / or semicrystalline inorganic used according to the invention as a pore former

Solid particles are advantageously adapted to the shape of the abrasive grains. In particular, fillers, grinding aids and moistening agents are used as other additives which, inter alia, serve to adjust the rheology of the composition so that pressing into a homogeneous green body is made possible or facilitated.

Further advantageous embodiments of the method according to the invention consist in mixing the pore-forming agent mixture with a temporary adhesive before it is introduced into the mass, whereby the homogeneity of the grinding tool can likewise be improved.

The process for producing the open-cell, ceramic-bonded

Abrasive tools begin with the production of a homogeneous mixture comprising abrasive grains, binders and pore formers, wherein as pore formers inorganic solids, in particular glassy, crystalline and / or amorphous and / or partially crystalline inorganic solid particles, with a middle

Particle size between 200 and 2000 μητι be used. This mixture is placed in a mold and pressed to a homogeneous green body. The green body is then dried and sintered in a temperature range below 1300 ° C.

The use of pore-forming mixtures with a multimodal distribution of pore formers results in grinding wheels that are also multimodal

Having pore distribution, wherein the pores have a mean diameter between 50 and 2000 μιη. It has been found that open-pored, ceramic-bonded grinding tools with a targeted multimodal pore distribution have advantages over the conventional grinding tools, since it is possible in this way, the grinding tool optimally the grinding conditions adapt. The benefits are reflected in particular in high

Abtragsleistungen at the same cool touch.

The open-pored, ceramic bonded abrasive tools according to the invention have a pore fraction of between 20 and 80% by volume and preferably have a multimodal pore size distribution with at least two pore size maxima in the range between 100 and 000 μm.

In an advantageous embodiment of the present invention has the

Abrasive tool a bi-modal pore distribution, the maximum of fine pores between 100 and 400 μιη and the maximum of the coarse pores between 350 and 1000 μιη.

A further advantageous embodiment provides grinding tools with a multimodal pore distribution, wherein the maximum of the finest pores between 100 and 300 μιτι, the maximum of the average pore between 250 and 450 μηη and the maximum of the coarsest pores between 400 and 1000 μηι.

Preferably, the maxima of the pore size distribution are at least 100 μιη apart.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described with reference to the drawings, which are given by way of illustration only and not

are interpreted restrictively. In the drawings show:

1 shows an exemplary ceramic bonded grinding tool.

 FIG. 2 shows a highly schematic flow chart of a method for producing an open-pored, ceramic-bonded grinding tool; FIG. and

Fig. 3 is a highly schematic sketch of the structure of an open-pored, ceramic bonded grinding tool. DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 shows an example of a ceramic bonded grinding tool in the form of a grinding worm for hard fine machining of gears. The invention is not limited to such grinding worms, but is applicable to any type of ceramic bonded grinding tools.

2, a simplified flow chart for the production of a ceramic bonded grinding tool is illustrated. First, abrasive grains, a ceramic binder, a pore-forming agent and optionally adhesive and additives are mixed (step 21). Subsequently, the resulting mass is removed from the mixer, sieved, placed in a mold and pressed with a hydraulic press (step 22). The green body thus obtained is optionally dried and fired in an oven (step 23).

The structure of a grinding tool made in this way is shown in FIG. 3 in strong

illustrated schematic form. The abrasive grains 31 are bonded to bond bridges 32 consisting of the ceramic binder. In between there is a plurality of differently sized pores 33. The mixture of abrasive grains 31, bonding bridges 32 and pores 33 forms a three-dimensional open network (not visible in the sectional view of FIG. 3). The shape, size and

Size distribution of the pores 33 depends strongly on the size of the pore formers.

The pores produced artificially with Porenbildnem have an irregular shape, which is derived from the geometry of the pore formers and the adjacent abrasive grains, but which can be approximately described as spherical. Their size can therefore be characterized by their average diameter.

Sizes for pores always refer to the following

determined by electron microscopy mean diameter. The abrasive grains also have any, usually irregular-polyhedral shape, but the

Usually also approximated by the spherical description. The abrasive grain size can be described in the usual way by the abrasive grain diameter, which in the case of sieve grains smaller than the light

Mesh size of the screen must be. Refer to size specifications for abrasive grains in the following always on the size of the abrasive grain determined by sieving. Likewise, size specifications or size distributions for pore-forming agents always refer to the sizes determined by sieving. Used pore formers

In the experimental examples, glass particles (Example A) were each

 Polyethylene (Comparative Example B) and naphthalene (Comparative Example C) as

Pore former used. The selected particle size of the pore-forming agent depends on the average diameter of the abrasive grain D _K and can be calculated therefrom with a factor F _x that is typical for the particular pore-forming agent. To ensure comparability of the examples, the factor Fx = 2.0 ± 1.0 was selected in all cases. This is summarized in Table 1 below.

Table 1: Pore formers used

Production of grinding wheels

For all discs tested, the same were given in Table 2

used raw material components, so that a direct comparison of the individual pore formers is possible by the grinding test, the amounts of the individual components are each based on the abrasive grain (100%). Table 2

The components were placed in a drum mixer and in 23

Mixing steps mixed for about 60 minutes, until optically a certain homogeneity and flowability of the mass was visible. Then the mass was removed from the mixer and sieved. The sieved mass was placed in a mold and pressed with a hydraulic press at pressures of 90 bar positive fit. The green bodies thus obtained had the dimensions (diameter x bore x height) 280 x 128 x 157 mm and were in an electric furnace up to a maximum temperature of 1200 ° C with a respective pore former

burned customized burning program.

During the processing of the masses until the wafers were burnt, no odor development was observed in the samples A and B, while the sample C showed the extremely strong and unpleasant smell of moth powder and tar already characteristic of the naphthalene during mixing and pressing. In the

Temperature treatment, in which the pore former initially reacted, pattern A was odorless, while pattern B had a slight but not unpleasant waxy odor. The burning of the sample disc C was again accompanied by an extremely strong odor nuisance.

grinding test The finished abrasive wheels had the properties described in Table 3 below. To test the discs was in a first step the

Grenzzeitspanungsvolumen or the equivalent Grenzspandicke h _eq _th until the occurrence of grinding burn and in a second step the

Grenzzeitspanungsvolumen or the equivalent limit chip thickness h _eq _ determined with respect to the exceeding of the permissible wear limit. Both values are also recorded in Table 3.

Table 3

* Abrasive burn limit = maximum achievable equivalent chip thickness h _eq _th, which can be used free of burn marks, ie without thermo-mechanical surface layer damage.

^** Wear limit = maximum achievable equivalent chip thickness h _eq _, which is applicable when a given wear criterion is maintained. The wheels were tested on a Reishauer RZ 260 machine using coconut oil and a diamond dressing tool. The workpiece was a test wheel made of 16MnCr5 material. In parallel, a comparative disk was examined as reference value (100%) in order to rule out possible influences of the workpiece batch. The grinding burn test was carried out by systematic enlargement of the

Axial feed (Z-feed) with otherwise identical cutting values and

Cutting conditions worked in three stages with three leveling strokes, a roughing stroke and a finishing stroke. In this way could in the 2nd stage for the

Schrupphub be guaranteed a uniform delivery. Of the

Grinding burn detection was carried out after the finishing stroke (3rd stage) by means of Nital etching.

The wear test was carried out with a comparable technology, whereby in the 2nd stage the roughing stroke with variable Z-feed was used and after the finishing stroke (3rd stage) the wear in the area of use of the grinding worm was determined during the roughing stroke. When exceeding one

Shape deviation of the profile fff> 6 μιη at a given grinding speed, the power limit is reached.

High wear resistance reduces dressing frequency and increases the number of workpieces that can be sanded in a dressing cycle, thus increasing productivity. The conditions with regard to odor development and the mechanical, physical and chemical processability found in the processing of the compositions A, B make it clear that the pore formers used are outstandingly suitable as substitutes for naphthalene. In addition, the inventive pattern A has the advantage that it can be processed much easier than the two comparative samples, since the use of inorganic solid particles no complicated firing curve must be driven, the burning out of the

Pore forming and taken into account with the prevents that suddenly develop large volumes of gas that can cause damage to the grinding tool. Rather, the glass melts during the sintering process and accumulates on the surface of the surrounding particles, while at the same places where the glass particles were positioned, pores are formed whose size depends on the size of the glass particles used. It stores the

Glass melt not only on the surface of the surrounding particles, but Also penetrates into cracks and capillaries of the grinding tool, which increases the strength of the bond and the entire grinding tool.

Thus, open-pored, ceramic-bonded abrasive tools using glassy, crystalline and / or amorphous and / or semi-crystalline inorganic solid particles can be produced much faster than pore formers. The manufacturing costs can be due to the lower energy consumption, the increased throughput per unit time and the lower committee in the

Production can be significantly reduced. Another advantage is the

Environmental compatibility added, especially if only inorganic

Solid particles are used as a pore former, the burning of the

Abrasive tool release any odorous or toxic gases.

Due to a targeted use of inorganic solid particles with different particle sizes grinding tools can be obtained with a homogeneous multimodal pore distribution, which is optimized for both the absorption of the chips and for flushing with the coolant. At the same time, the hardness of the disc can be optimized in this way. The grinding tests have shown that the grinding wheels according to the invention perform equally well or better than the standard or the conventional naphthalene-made disc both in the grinding burn test and in the wear test.

Claims

1. A process for the production of open-pored, ceramically bound  Abrasive tools having a pore content between 20 and 80% by volume, using a mixture of abrasive grains, binders and pore formers,  characterized in that  the pore-forming inorganic solid particles with a medium Particle diameter between 200 and 2000 μιη include. 2. The method according to claim 1,  dadu rch marked that  only inorganic solid particles are used as pore formers. 3. The method according to claim 1,  dadu rch marked that  the inorganic solid particles together with others  Pore formers, in particular thermoplastic polymers are used. 4. The method according to any one of claims 1 to 3,  characterized in that  the inorganic solid particles are glassy, crystalline and / or amorphous and / or partially crystalline solid particles. 5. The method according to any one of claims 1 to 4,  characterized in that the pore formers are present in a multimodal distribution with at least one coarse and at least one fine fraction, the maximum of the finest fraction lying between 200 and 500 μm, and the maximum of the coarsest fraction being between 500 and 1500 μm. Process for the production of open-pored, ceramically bound Grinding tools according to one of claims 1 to 5, comprising the steps:  - Preparation of abrasive grains, binders and pore formers  comprehensive homogeneous mixture,  Introducing the mixture into a mold,  Pressing the mixture into a homogeneous green body,  - Drying of the green body and  Sintering the dried green body at a temperature below 1300 ° C. An abrasive tool made using a method according to any one of claims 1 to 6, characterized in that the abrasive tool has a pore fraction between 20 and 80% by volume, the pores having an average diameter between 50 and 2000 μηη have. Grinding tool according to claim 7, characterized in that the grinding tool has a multimodal pore size distribution with at least two pore size maxima in the range between 100 and 1000 μιτι.