WO2011092021A1

WO2011092021A1 - Grinding body with additional particles from recycled grinding bodies, and method for the production thereof

Info

Publication number: WO2011092021A1
Application number: PCT/EP2011/000386
Authority: WO
Inventors: Bernd-Arno Behrens; Matthias Kammler; Fabian Lange
Original assignee: Gottfried Wilhelm Leibniz Universität Hannover
Priority date: 2010-01-28
Filing date: 2011-01-28
Publication date: 2011-08-04
Also published as: DE102010006250A1

Abstract

In a first aspect, the invention relates to a grinding body (1) made of a compacted and sintered material. In particular, the invention relates to a grinding body (1) that has additional particles (4), in particular additional particles (4) that can be obtained from grinding bodies, in a predetermined region (3). The invention further relates to a method for producing said grinding bodies (1) and to grinding devices that contain grinding bodies (1) according to the invention, and to the use of additional particles (4) made from recycled grinding bodies (1) for producing said grinding bodies.

Description

GRINDING BODY WITH ADDITIONAL PARTICLES FROM RECYCLES

GRINDING BODIES AND METHOD FOR THE PRODUCTION THEREOF

In a first aspect, the invention relates to a grinding body made of pressed and sintered material. In particular, the present invention relates to an abrasive article which has additive particles, in particular abrasive particles, in a predetermined range. The invention also relates to a process for the preparation of these abrasive articles, as well as grinding devices containing abrasive articles of the invention, and to the use of recycled particulate filler particles for the production thereof.

The reuse of abrasive articles has long been a major problem with respect to the mechanical stresses in the operation of the abrasive articles. Because of these known problems, the use of recycled abrasive article material in abrasive articles is usually avoided altogether. Thus, to date, abrasive articles are made exclusively from new abrasive materials and suitable binders, since the requirements are very high, especially with regard to safety and product liability issues in particular rotating abrasive. Typically, abrasive particles of grain and binder are molded (pressed) into a (green) compact or green compact in a first step and then optionally sintered. Abrasive materials are subject to the most extreme mecha-

CONFIRMATION COPY niche stresses. Investigations have shown that the reduction in strength of the sanding base by vibrations is up to 50%. A problem of sintered workpieces, such as sintered abrasive articles, is their strength property. In the case of abrasives, the crack or fracture tendency also plays an important role. In this case, for example, the porosity of the abrasive body has an influence on the fracture toughness values of sintered workpieces such as grinding wheels. But also foreign parts, as well as all structural areas with abruptly changing properties, such as phase boundaries, are considered to be negative factors for the crack or break tendency. Therefore, it is usually tried to make the powder as homogeneous as possible. That is, it is generally considered that, due to the presence of foreign parts or particles having heterogeneous components of different diameters, the tendency of cracking increases and the strength of the abrasive article is deteriorated.

It is therefore considered that reuse of such abrasive body or parts thereof, especially with regard to the tangential stresses that occur and the above decrease in strength during operation, thus eliminates it. Therefore, abrasives are used only as building rubble and must be disposed of for a fee.

Various proposals for the reuse of abrasive articles have already been described. Thus, DE 44 465 91 A1 discloses the production of an abrasive article and this abrasive article itself. This recyclable abrasive has two sections, an outer grinding zone and a non-abrasive zone. This non-abrasive active zone is formed from a reusable, non-packaged, possibly reinforcing agent and / or filler contained organic plastic material and can be reused. On this non-abrasive zone, which forms a so-called basic body, there is the grinding zone of grain and binder. This grinding zone is applied to the body and associated with suitable thermosetting plastics. After use of the grinding wheel, the remainders of the grinding zone are removed mechanically and a new grinding zone is applied to the base made of preferably plastic.

The abrasive articles described herein, however, otherwise require extensive post-processing. Furthermore arise from the different materials of the grinding zone and the body strength problems, especially for the high demands in the grinding wheel area.

Also, the high safety requirements due to the mechanical stresses in operation require the development of improved in fracture toughness grinding wheels, especially grinding wheels. The object of the invention is therefore the provision of abrasive bodies with improved breaking strengths and methods for their preparation. Another object of the invention is to provide methods of making abrasive articles using abrasive article materials containing abrasive grain to enable recycling of spent abrasive wheels and to allow for later recycling of the abrasive articles.

This object is achieved by the invention specified in the patent claims 1, 11 and 13. The dependent claims contain advantageous developments of the invention.

In a first aspect, the present invention relates to abrasive articles comprising grain and binder having a first region adjacent to the abrasive surface forming the abrasive region, and a second region having a receiving region for attachment to a tool carrier forming a backing region, characterized in that second range of additional particles, the average diameter of these additional Particles equal to at least twice the mean diameter of the grain. That is, the second region is characterized by the fact that here, in addition to the grain and binder, additional particles are present which have at least twice the value of the mean diameter of the grain. Preferably, these additional particles have at least three times the diameter of the grain used in the second region, such as at least five times, for example at least ten times. The terms "grain" and "abrasive grain" are used interchangeably herein. In a preferred embodiment, the additional particles have at least twice the diameter of the average diameter of the grain used. In the case of spherical or platelet-shaped additional particles, the term "diameter" or "thickness" is understood here to mean the diameter, and in the case of angular or edge-shaped shapes, the thickness in relation to the axis perpendicular to the pressing direction. These terms are used interchangeably.

The mean diameter of the grain (abrasive grain) is understood to be the average diameter of the grain to be pressed, the same applies to the additional particles.

In one embodiment of the invention, the shape of the additional particles to be introduced is a non-edged additive particle. These non-angular additive particles can be present in particular in the form of lenses, spheres, in the form of broken grain forms or in stochastic forms. According to the invention is achieved by introducing the additional particles that due to the position, the shape and the proportion, the density distribution is changed in compacts such that the crack inclination or fracture tendency is not influenced or even reduced compared to an abrasive article without additional particles, while achieving an increase in strength becomes. In particular, the density distribution in the pressed and sintered workpiece is more homogeneous. In other words, in contrast to the general view, the introduction of the additional particles in the second region of the abrasive particles does not impair the density distribution in the abrasive article. Rather, it is even possible to achieve a targeted influence on the improvement of the strength properties.

In particular, the fracture crack tendency of the abrasive bodies, which is a major problem especially with abrasive wheels and constitutes a safety-relevant aspect when grinding wheels are used, is improved by introducing the additional particles into the second area of the wheels while improving the strength properties of the wheels. According to the invention, this makes it possible to provide abrasive articles in which material from spent abrasive articles is used.

The abrasive articles of the invention may e.g. prepared by the following procedure. In this case, after determining the densities in the grinding body or the compact, the position, shape and / or quantities of the additional particles to be introduced for influencing the density distribution in the compact or grinding body are determined. In this case, by introducing these additional particles in the predetermined amounts and positions, the density distribution and thus the breaking strength of the resulting abrasive article are positively influenced.

In particular, it has been found that an inhomogeneous density distribution, which may still be present after pressing, is improved by sintering in such a way that the density distribution in the grinding body is largely homogeneous. In particular, an improvement in the density distribution and thus an improvement in the breaking strength in the area of the tool holder of the grinding body is achieved. The area of the tool holder is exposed to the greatest loads during operation. At the same time, radial, tangential and axial loads as well as vibration loads meet each other.

By the targeted introduction of additional particles within this second Range can be caused an increase in strength of this area.

However, it would be assumed that the increase in strength due to the introduction of the additional particles is accompanied by an increase in the tendency to crack. According to general opinion, the introduction of a foreign body promotes this educational propensity considerably.

It has now surprisingly been found that this expected negative effect does not occur. On the contrary, the introduction of the additional particles, in particular porous additional particles allows an increase in strength without increasing the tendency to cracking.

That is, the abrasive particle of grain and binder in both areas has advantageous properties by the introduction of the additive particles in the second region. The abrasive body is formed in both areas of the same grain and binder.

This is due, in particular in the case of porous additional particles, to the fact that the bonding bridge behavior between the particles which are to be introduced by the binder also depends on the porosity of the latter. Larger porosities improve the bonding bridge behavior within the compact in comparison to those with lower porosities. It is assumed here that the respective porosity of the additional particles to be introduced results in an enlargement of the surface, which favors the formation of bond bridges between the individual additional particles or between the grain and additional particles. However, in general, the strength decreases with increasing porosity. In particular, the use of porous additional particles and of materials similar or equal to the material of the abrasive article, the bonding Improve bridge behavior introduced additional particles over non-porous additive particles. The added porous filler particles are particularly preferably those which are identical in their composition to the constituents of the abrasive article, the grain and binder. In a preferred embodiment, the porous additional particles are recycled particles of used abrasive articles. These grinding wheels are eg crushed and classified if necessary. When introducing these available from abrasive bodies available additional particles that have been correspondingly crushed and possibly classified, an increase in strength of the abrasive body can be found especially in the tool holder. Thereby, a substantial increase in strength can be achieved in the area in which these additional particles were introduced, without leading to an increase in the tendency to cracking. In particular, by prior preparation of a load analysis of the component, as in Behrens et al., Materials Science and Engineering, Vol. 38 (10), p. 816-820, a template for introducing the preferably recycled additional particles can be prepared, which are correspondingly introduced into the pre-prepared powder compact according to the recyklelten additional particles.

Preferably, the binders of the abrasive article are ceramic binders known in the art. In a preferred embodiment, the grinding wheels are designed as a grinding wheel, grinding pin, grinding cone or grinding segment. When the grinding wheel is designed as a grinding wheel, the first area is arranged on the outside in the radial axis and ends with the grinding surface, while the second area is arranged in the radial direction with respect to the first area. The introduced in the second region additional particles are preferably in the way that a gradient is formed. The gradient is designed such that it decreases in the direction of the first region. That is, preferably, the gradient decreases from the surface for the receiving area for attachment in the tool carrier, the tool holder.

Further preferably, the abrasive article is constructed such that the first region makes up at least a third of the distance between the abrasive surface and the surface with a receiving region of the tool carrier. As shown in FIG. 1, in a body having a radial axis, this distribution is such that the first area forming the grinding area is disposed radially outward with respect to the second area.

The additional particles which are introduced in the second region of the abrasive body, are in a preferred proportion of at least 0.5 vol .-%, preferably at least 1 vol .-% and preferably at most up to 50 vol .-% based on the total amount of grain in the grinding wheel. For example, For example, the amount of additive particles, based on the total amount of grain in the abrasive article, is between 1% by volume to 40% by volume, e.g. at least 3% by volume, such as at least 5% by volume and at least a maximum of 30% by volume, such as at least a maximum of 20% by volume. The introduced additional particles may be formed preferably lenticular or elongated.

When introducing these additional particles into the material to be pressed, e.g. by sprinkling, these additional particles are due to gravity perpendicular to the pressing direction. This has the consequence that in the increase in strength above the additional particles, the pressing of the blank, an increase in strength is achieved above the additional particles, longitudinally but geometry caused a negligibly small density reduction.

This long side of the geometriebedingt present small density reduction However, it is compensated during sintering, so that after sintering of the green body of the abrasive body shows a density distribution, which leads to an increase in strength, the cracking tendency is not increased, preferably even the tendency to cracking is reduced.

By density distribution is meant the quantitative detection of different densities within a pressed or sintered body.

Sintering is a heat treatment of powders or compacts, e.g. Greening, at temperatures below the melting point of the base material to increase the strength by binding of its particles with each other.

As a material to be pressed, the starting material for the pressing process, the grain with binder, is referred to below. As a compact, also called green compact, the product is named after the pressing process, in which the starting material has a certain relationship. This compact or green compact is then fed to further processing steps, such as sintering. With the aid of known pressing devices, the compacts can be produced from grain and binders and, if appropriate, further constituents. The introduction of the additional particles can also be carried out according to known methods.

Conventionally bonded abrasive bodies represent composite materials produced by molding technology, which in principle are composed of three components. These components consist of the actual abrasive, the abrasive grain, an application-specific selected binder and individually set pore spaces. With volume fractions V _K between 40 and 60% by volume, the abrasive, the grain, forms the largest fraction. These are usually corundum, silicon carbide, zirconium corundum (corundum and zirconium oxide in an electic composition) or industrial diamonds. As a further component are application specific selected binder, which ensures the cohesion of the abrasive body in the form of so-called binding bridges. For this purpose, a wide variety of materials such as porcelain or glassy ceramics, polymers, sintered bronzes and powder metallurgical rods are used. Ceramic bonded abrasive articles contain bond volumes V _B between 5 and 30% by volume, such as between 5 and 20% by volume. These are usually glassy amorphous melting porcelain-like sintering mixture whose starting materials usually consist of feldspar, kaolin, various quartzes, porcelain flours, lime spars, glass powder and various metal oxides.

As already stated above, density gradients in the pressed product, produced during the pressing of the material to be pressed, can lead to undesired distortions during the subsequent sintering process. This can lead to cracking during pressing, sintering and operation of the grinding wheels. It is therefore necessary to strive for the lowest possible density gradient during the production of the grinding wheels during pressing or during sintering.

In a further embodiment of the present invention, a corresponding method is provided which allows improvement of the density gradient, i. a more homogeneous density distribution. This homogeneous density distribution is achieved all the more surprising, although additional particles are introduced into the material to be pressed, which differ in size from the grain.

The method for producing the abrasive bodies further comprises the known methods for the production of pressed and sintered abrasive articles, as they are generally described and known in the prior art. The process is carried out in such a way that for the production of grinding bodies, the step of introducing additional particles into a mixture of grain and binder in a second region of a material to be pressed for the grinding body is carried out, these additive particles are additive particles according to the invention, and the step of compressing the additive particles containing Guts in the second region together with a first area containing no additional particles.

1 shows a section through a grinding wheel 1 according to the invention. The section through the grinding wheel shows a first region 2 which forms the grinding region and the second region 3. In the second region are the additional particles 4, which were introduced according to the invention in this area shown. The additional particles 4 are preferably porous additional particles, in particular additional particles recycled from used grinding bodies, obtained by comminution and, if appropriate, classifying the grinding bodies. Particularly preferably, the additional particles 4 are those which have the same composition as the abrasive body containing grain and binder. A surface of the first area forms the grinding surface 5. While the second area has a surface 6 with a receiving area for attachment to the tool carrier. The gradient of the introduced additional particles extending radially outward from the region of the tool holder is also shown. Preferably, the first region is formed such that it is at least a third of the distance between the surface 6 and the grinding surface 5. The grinding wheel according to the invention, as shown in the detail in Figure 1, is characterized by a high durability and reliability. In particular, these grinding wheels according to the invention are characterized in that they exhibit improved strength, without worsening the tendency to crack, in particular in the heavily loaded second region in the direction of the tool holder.

Claims

claims

1. abrasive body (1) comprising grain and binder having a first area (2) adjacent to the grinding surface (5) forming the grinding area, and a second area (3) having a receiving area for attachment to a tool carrier having a support area ( 6) is formed, characterized in that in the second region (3) in addition to the grain and binder additive particles (4) are present, wherein the average diameter of these additional particles corresponds to at least twice the mean diameter of the grain.

2. Abrasive body according to claim 1, wherein the additional particles (4) are porous additional particles of grain and binder.

3. The abrasive article of claim 1 or 2, wherein the additional particles (4) are porous additional particles of the same grain and binder, which form the abrasive body (1).

4. Abrasive body according to one of the preceding claims, wherein the additional particles (4) are obtained from grinding bodies used by crushing and optionally classifying.

5. Abrasive body according to one of the preceding claims, wherein the binder is a ceramic binder.

6. Abrasive body according to one of the preceding claims, wherein the grinding body (1) is in the form of a grinding wheel and wherein the first region (2) is arranged radially outward and the second region (3) with respect to the first region (2) radially is arranged inside.

7. The abrasive article according to one of the preceding claims, wherein the additional particles (4) present in the second region (3) are present in decreasing quantity in a gradient in the direction of the first region (2).

8. Abrasive body according to one of the preceding claims, wherein the first area (2) at least a third of the distance between the grinding surface (5) and the surface with a receiving area of the tool (6).

9. Abrasive body according to one of the preceding claims, wherein the proportion of additional particles (4) in the second region (3) of the abrasive article (1) at least 0.5 vol .-%, preferably at least 1 vol .-% based on the total amount of grain is.

10. Abrasive body according to one of the preceding claims, wherein the additional particles present in the second region are formed lenticular or elongated.

11. A method for producing abrasive articles (1) comprising the step of introducing additional particles (4) into a mixture of grain and

Binder in a second region (3) of a material to be compacted for the abrasive article, said additive particles (4) being those defined in any one of claims 1 to 9, and compressing the article containing said additive particles (4) together with said article a first area containing no additional particles (4).

12. The method of claim 1 1 for the production of abrasive bodies (1) according to any one of claims 1 to 9.

13. Grinding device comprising at least one grinding body (1) according to one of claims 1 to 10. Use of additional particles (4) of recycled abrasive bodies for producing abrasive bodies (1), these additional particles (4) being arranged in a second area (2) which does not form the grinding area (2) of the abrasive bodies (1).