EP1851004B1 - Abrasive wheels and production thereof - Google Patents

Abstract

An abrasive device for a grinding tool. The abrasive device includes abrasive grains material-lockingly connected with one another by a bonding agent. The abrasive grains have an approximately spherical contour. The abrasive device further includes a porosity of at least 35 percent. The present disclosure also relates to a method for producing the abrasive device.

Description

The invention relates to abrasive articles, preferably a grinding tool, in particular abrasive tools, in which the abrasive bodies are fixed in a material-locking manner on a carrier. The carriers may preferably be flexible and the respective grinding tools may be in the form of, for example, bands or plates (pads).

So is in DE 26 08 273 A a sheet or belt-shaped grinding tool and a method and an apparatus for producing such grinding tools known. In addition, it is noted that in such abrasive grinding wheels in spherical form, which are interspersed over the entire diameter with organic binders, to be used.

According to this known teaching, the production of such abrasive bodies should take the form of spherical abrasives of a plurality of abrasive grains being formed from a suspension made of abrasive grains and an organic binder matrix in a stirred vessel within the suspension and held in suspension by the stirring. In this case, the drop-shaped abrasive bodies formed from a plurality of abrasive grains are bound by the binder in the suspension. After the spherical abrasive particles have reached sufficient strength in the suspension, they should then be separated from the liquid components by, for example, decantation or other processes.

Subsequently, the spherical abrasive bodies can then be cleaned with a solvent outside and then dried, whereupon they are then available for the production of abrasive tools.

By introducing air or propellant into the suspension, a slight porosity can be established at the spherical droplets forming the abrasive bodies, which in any case should form below 35% closed pores, with a preferred range of 7 to 15% of the volume closed pores are to be formed.

At the in DE 26 08 273 A As a result, abrasive articles having a downwardly greatly limited outer diameter potential can be obtained, and also the abrasive articles thus obtained can only be produced from relatively large abrasive grain fractions. Thus, 200 μm are explicitly named as the smallest outer diameter for grinding wheels and 3 μm as the smallest mean grain size of the abrasive grains.

With such grinding tools, which have been produced with corresponding abrasive, but is a very fine grinding surface processing on various workpieces, as is particularly desirable during the processing or post-processing of decorative lacquer layers and in particular in vehicle construction, not possible.

In addition, the life of such grinding tools is limited.

In the WO 01/85393 A there are disclosed abrasive articles each consisting of abrasive grains formed from abrasive grains. These abrasive grains are bonded together by means of a ceramic binder. These abrasive articles are used for the surface treatment of, for example, glass.

Each abrasive article has a porosity formed by introducing an organic binder and expelling it by burning. The product usable as an abrasive article then has only the ceramic binder.

It is an object of the invention to produce grinding wheels of a grinding tool, which are suitable for a very fine grinding machining of surfaces of workpieces.

According to the invention this object is achieved with abrasive articles having the features of claim 1. They can be produced by a method according to claim 14. Advantageous embodiments and further developments of the invention can be achieved with the features described in the subordinate claims.

The grinding tools according to the invention for grinding tools are formed from abrasive grains which are bonded to one another in a material-locking manner by means of a binder. The grinding wheels have an at least approximately spherical outer contour and a porosity of at least 35%. More preferably, a porosity of above 40% can be maintained in the abrasive articles.

They can be formed from abrasive grains whose particle size in the range between 0.05 and 10 .mu.m, preferably between 0.1 to 3 .mu.m.

With such small abrasive grains abrasive bodies can then be made available whose outer diameter is in the range between 10 and 150 microns, preferably between 25 and 80 microns.

For use on abrasive tools, a production or a classification can be made so that for the individual grinding wheels to be used on a grinding tool, a narrow outer diameter range, quasi a constant grain size of such abrasive has been met.

In the case of the abrasive bodies according to the invention, a maximum deviation of the particle size of the abrasive grains used for an abrasive body should be maintained at a maximum of 20% about an average value for a predefinable particle size.

The abrasive bodies of the invention can be used both with a spherical / spherical outer contour for grinding tools, in which a homogeneous distribution of cohesively bonded by a binder abrasive grains has been complied with and therefore the porosity over the entire volume of an abrasive body is almost constant.

In a further embodiment, the abrasive bodies formed correspondingly with a spherical outer contour can also be completely hollow on the inside and form a correspondingly porous shell around a cavity cohesively bonded abrasive grains. In this case, a porosity of at least 35% may also have been maintained in the shell.

The binder used for the cohesive bonding of abrasive grains should have ≤ 10% by mass with a respective abrasive article, whereby binder contents ≤ 5% by weight may be sufficient.

The abrasive grains may be selected from SiC, Al ₂ O ₃ (corundum), BN, WC / CO, WC, diamond, zirconium corundum, SG-Kom (abrasive grains from the sol-gel or sintering process), with corresponding mixtures of these chemical Compounds for the production of respective grinding wheels can be used.

As binders, for example, different phenolic resins, polyurethane, epoxy resins, urea resins and PVB (polyvinyl butyral) can be used.

A large number of grinding bodies can then be fixed in a material-locking manner on a carrier, as already mentioned in the introductory part, on tape-shaped or sheet-shaped carriers. In this case, the cohesive fixing can in turn likewise be used with a binder, preferably an organic binder and particularly preferably the same binder with which the abrasive grains are also adhesively bonded to form an abrasive body.

The abrasive particles may have been fixed in the form of a single layer as uniform as possible, equidistant arrangement on at least one surface of a carrier. However, it is also possible to fix abrasive bodies in multiple layers on a carrier or to apply abrasive particles as a heterogeneous filling on the carrier and then to firmly fix them again.

In a preferred form, grinding tools with at least approximately constant outside diameters should have been applied and fixed on a carrier for a grinding tool.

Abrasive particles can be tempered again after their actual production, and this should be done in a temperature range between 150 and 200 ° C, preferably at about 175 ° C over a period of two hours.

However, such tempering can also be carried out simultaneously with the cohesive fixation of the grinding bodies on the respective carriers with the formation of the cohesive fixation.

UV curing of the grinding wheels after their actual production and cold hardening by means of suitable binder systems would also be possible.

The abrasive articles according to the invention can be produced by means of a suspension formed from a binder, solvent and abrasive grains, in which, if appropriate, further additives can also be present.

In contrast to the prior art, small droplets and agglomerates are formed from and not in the suspension, from which the solvent is expelled, for example by evaporation, after drop formation.

With the aid of a heat treatment, which can also be carried out in addition to the expulsion of the solvent, then the actual formation of the abrasive body with formation of cohesive connections of each adjacent abrasive grains, by a corresponding activation of the binder used.

The drops, as already indicated, should not be formed within the suspension but in a gas atmosphere, for example air or nitrogen.

This can be achieved for example by the known per se method of spray drying, freeze drying or spray freeze drying.

But there are also other manufacturing possibilities conceivable in which emerge from a suspension, which is received in a container, correspondingly small drops in a gas atmosphere and subsequently, as already mentioned, expelled the solvent and the cohesive connection of the abrasive grains of a drop by appropriate activation of the used binder can be carried out for the eventual formation of an abrasive article. Due to the special spherical alignment of the individual abrasive grains on the surface of the forming abrasive body, a high initial roughness depth is avoided.

The grinding tools formed with abrasive bodies according to the invention can now be used for very fine machining of workpiece surfaces which, as in the general part of the description, have also been shed with additional protective layers, such as coating layers. The achievable very small outer diameters in combination with the small particle sizes of the abrasive grains used for the production of abrasive articles have an advantageous effect.

In particular, by the relatively high porosity, which can be readily adjusted at up to 70%, can also be achieved for a prolonged period of use of abrasive tools according to the invention, since the corresponding available open pore volume can relatively absorb a relatively larger attrition, as is the case with the solutions known from the prior art.

Since, as a rule, the individual abrasive grains of the individual abrasive particles are not wetted over their entire surfaces with the binder and therefore only small surface areas have been wetted with binder for the cohesive connection of the individual adjacent abrasive grains, with which in turn the cohesive connection of the adjacent abrasive grains Abrasive bodies has been produced, when using the grinding tools can replace individual abrasive grains and release free pores for a further absorption of abrasion during grinding.

The invention will be explained in more detail by way of example in the following.

• Figur 1 eine FESEM-Aufnahme eines erfindungsgemäßen Schleifkörpers mit einer Vergrößerung von 1400:1;
• Figur 2 eine FESEM-Aufnahme eines innen hohlen Schleifkörpers mit einer Vergrößerung von 1350:1;
• Figur 3 einen Bildausschnitt einer FESEM-Aufnahmee eines Teilbereiches eines erfindungsgemäßen Schleifkörpers mit einer Vergrößerung von 5000:1.

Showing:

• FIG. 1 a FESEM image of an inventive abrasive article with a magnification of 1400: 1;
• FIG. 2 a FESEM image of an internally hollow wheel with a magnification of 1350: 1;
• FIG. 3 a picture detail of a FESEM images of a portion of a grinding wheel according to the invention with a magnification of 5000: 1.

Before taking in the FIGS. 1 to 3 A FESEM image was taken of a preparation which makes it possible to reproduce the internal structure of the abrasive particles without errors.

With the FIGS. 1 to 3 It is also clear that the individual abrasive bodies have been produced with a correspondingly increased porosity, which can be maintained at least above 35%, preferably at least 40 and generally at about 70%.

With FIG. 2 should be suggested that even inside hollow grinding wheels can be easily produced.

For the production of in the FIGS. 1 to 3 shown abrasive grains, abrasive grains of SiC were used with a particle size of about 5 microns. The correspondingly produced abrasive particles had an approximately spherical outer contour with outer diameters of approximately 50 μm, whereby in some cases after the production of abrasive bodies a classification to this diameter range of approximately 50 μm was carried out.

For the preparation suspensions were prepared with different binders and also different solvents.

Thus, an aqueous suspension with polyurethane binder prepared in the suspension in a proportion of 2 to 4% by mass and the designated SiC abrasive grains was prepared. The proportion of SiC in the suspension was 40-70% by mass.

Instead of a polyurethane, however, it was also possible to use phenolic resin (eg novolak) as binder with proportions of 2 to 4% by mass for the preparation of the suspension, acetone being added as the solvent to the suspension.

From this suspension, abrasive particles were formed by spray drying using a two-fluid nozzle from the resulting droplets of the suspension, the respective solvent, ie water or acetone, being expelled in advance and the respective binder corresponding to the cohesive connection between adjacent abrasive grains for the individual abrasive bodies has been activated. In this case, a temperature in the range of 250 to 120 ° C was maintained for the corresponding drying / activation.

Subsequently, the abrasive bodies were further annealed at a temperature of about 175 ° C over a period of about two hours to increase their overall strength.

The abrasive articles then had a porosity in the range between 60 and 70% and could subsequently be fixed in a material-locking manner to a corresponding carrier for the production of grinding tools, as already mentioned in the general part of the description.

Claims (17)

1. Abrasive bodies for an abrasive tool, the abrasive bodies being formed from abrasive particles that are intimately connected to one another by means of a binder and having at least approximately a spherical outer contour, characterized in that the abrasive particles are bonded by a synthetic resin, such as phenolic resin, polyurethane, epoxy resin, urea resin or polyvinyl butyral (PVB) as the binder, and in that the abrasive bodies have a porosity of at least 35 per cent.
2. Abrasive bodies according to Claim 1, characterized in that they are formed from abrasive particles with a particle size in the range between 0.05 and 10 µm.
3. Abrasive bodies according to Claim 1 or 2, characterized in that they are formed from abrasive particles with a particle size of between 0.1 and 3 µm.
4. Abrasive bodies according to one of the preceding claims, characterized in that the outside diameter of the abrasive bodies lies in the range between 10 and 150 µm.
5. Abrasive bodies according to one of the preceding claims, characterized in that the outside diameter of the abrasive bodies lies in the range between 25 and 80 µm.
6. Abrasive bodies according to one of the preceding claims, characterized in that a maximum deviation of the particle size of 20 per cent is maintained for abrasive particles of an abrasive body.
7. Abrasive bodies according to one of the preceding claims, characterized in that the porosity of > 35% is homogeneously distributed in the abrasive bodies.
8. Abrasive bodies according to one of the preceding claims, characterized in that the abrasive bodies are hollow inside.
9. Abrasive bodies according to one of the preceding claims, characterized in that the proportion of binder in an abrasive body is ≤ 5% by mass.
10. Abrasive bodies according to one of the preceding claims, characterized in that the abrasive particles are selected from SiC, corundum (Al₂O₃), BN, WC/Co, WC, diamond, zirconium corundum and SG grain, i.e. abrasive particles from the sol-gel or sintering process.
11. Abrasive bodies according to one of the preceding claims, characterized in that the binders are UV-, temperature- or cold-curing.
12. Abrasive bodies according to one of the preceding claims, characterized in that a multiplicity of abrasive bodies are intimately fixed on a carrier.
13. Abrasive bodies according to one of the preceding claims, characterized in that abrasive bodies are fixed on a carrier in one or more layers or as a homogeneous or heterogeneous bed.
14. Method for producing abrasive bodies according to one of Claims 1 to 13, characterized in that small drops are formed from a suspension containing a binder, a solvent and abrasive particles, then the solvent is driven out of the drops and the binder is activated by means of at least one heat treatment to form intimate connections between neighbouring abrasive particles, of the individual abrasive bodies obtained from a single drop, the binder consisting of synthetic resin, such as phenolic resin, polyurethane, epoxy resin, urea resin or polyvinyl butyral (PVB).
15. Method according to Claim 14, characterized in that drops are formed from the suspension in a gas atmosphere.
16. Method according to Claim 14 or 15, characterized in that the abrasive bodies are produced by spray drying.
17. Method according to Claim 14 or 15, characterized in that the abrasive bodies are produced by freeze drying or spray freeze drying.

Images