Method for producing a coated grinding means

Abstract

A method for producing a coated abrasive includes producing or providing an intermediate abrasive product that comprises a substrate, a plurality of abrasive grains that are bonded to the substrate, and at least one layer of an uncured size coat that at least partially covers the abrasive grains with the uppermost size coat being uncured. The method further includes applying at least one grinding additive to the uppermost, uncured size coat with the grinding additive applied to the size coat in dry form. The method also includes curing the uppermost size coat. A coated abrasive is produced by the method and the coated abrasive is used to process a surface.

Claims

1. A method for producing a coated abrasive, comprising: applying at least one grinding aid in dry form to an uncured uppermost layer of a size coat of an intermediate abrasive product, the intermediate abrasive product including a backing, a multiplicity of abrasive grains bonded to the backing, and the size coat, which at least partly covers the abrasive grains; and curing the uppermost layer of the size coat after the application of the at least one grinding aid.

2. The method according to claim 1, wherein the applying of the at least one grinding aid includes scattering one or more of a powder, flakes, fibres, agglomerates, and capsules on the uppermost layer of the size coat.

3. The method according to claim 1, wherein at least 90% by weight of particles of the grinding aid have a size in the range from 0.1 m to 2 mm.

4. The method according to claim 1, wherein an average size of particles of the grinding aid is lower than an average size of the abrasive grains.

5. The method according to claim 1, wherein the grinding aid is applied at an application rate which lies in a range from 10 g/m.sup.2 to 500 g/m.sup.2.

6. The method according to claim 1, wherein the grinding aid is applied to the uppermost layer of the size coat in dry form by scattering.

7. The method according to claim 3, wherein at least 95% by weight of the particles of the grinding aid have a size in the range from 0.1 m to 0.5 m.

8. The method according to claim 3, wherein at least 99% by weight of the particles of the grinding aid have a size in the range from 0.1 m to 0.1 mm.

9. The method according to claim 3, wherein all of the particles of the grinding aid have a size in the range from 0.1 m to 0.1 mm.

10. The method according to claim 5, wherein the application rate of the grinding aid is in a range from 20 g/m.sup.2 to 400 g/m.sup.2.

11. The method according to claim 5, wherein the application rate of the grinding aid is in a range from 25 g/m.sup.2 to 250 g/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the text below, the invention is elucidated using a number of working examples and drawings. In the drawings:

(2) FIGS. 1a and 1b show schematic sectional views of a first known abrasive with wet-applied grinding aid before and after use;

(3) FIGS. 2a and 2b show schematic sectional views of a first inventive abrasive with dry-applied grinding aid before and after use;

(4) FIG. 3 shows a size distribution of particles of a grinding aid;

(5) FIG. 4 shows a photograph of a plan view of a second inventive abrasive with abrasive grains of size #36 and KBF.sub.4 as grinding aid, which has been applied dry at an application rate of 178 g/m.sup.2;

(6) FIG. 5 shows a photograph of a plan view of a second comparative example of an abrasive with abrasive grains of size #36 and KBF.sub.4 as grinding aid, which has been applied in liquid form by roll application;

(7) FIG. 6 shows a photograph of a plan view of a third inventive abrasive with abrasive grains of size #50 and grinding aid which has been applied dry;

(8) FIG. 7 shows a photograph of a plan view of a third comparative example of an abrasive with abrasive grains of size #50 and grinding aid which has been applied in liquid form by roll application;

(9) FIG. 8 shows a photograph of a sectional view of a fourth comparative example;

(10) FIG. 9 shows a photograph of a sectional view of a fourth inventive abrasive;

(11) FIG. 10 shows Abbott curves of a number of abrasives.

DETAILED DESCRIPTION

(12) The conventional coated abrasive shown schematically in FIG. 1a comprises a backing 1, abrasive grains 3, which are bonded by means of a make coat 2 to the backing 1, and also a size coat 4, which covers the abrasive grains 3. With the aid of a known roll process, a liquid additional coating 6 has been applied with the aid of rolls, and comprises a multiplicity of particles 5 of a grinding aid. As a result of the rolling, the particles 5 have been accumulated substantially between the individual abrasive grains 3. In this way, when a surface is being worked, a large part of the particles 5 do not come into contact at all with this surface. After use of the abrasive 1, a part of the abrasive grains 3 has been abraded, as evident in FIG. 1b. Up to this point in time, however, numerous particles 5 of the grinding aid have remained unused, and this is extremely inefficient economically.

(13) In contrast to this, FIG. 2a shows an inventive abrasive, in which the grinding aid has been applied dry as elucidated in more detail below. Here, the particles 5 of the grinding aid are disposed in the vicinity of the outer surface of the size coat 4. Moreover, they are distributed more homogeneously over this surface and are not accumulated in the regions between the abrasive grains 3. In this way, a larger fraction of the particles 5 of the grinding aid comes into contact with a surface to be worked, and is able there to develop its desired effect. This larger fraction has been abraded in the used state of the abrasive 1, which is shown in FIG. 2b.

(14) For the production of coated abrasives, first of all a multiplicity of intermediate abrasive products was provided. These intermediate products contained a backing 1 of vulcanized fibre with a thickness of 0.8 mm. Using a make coat 2, abrasive grains 3 composed of two different corundums with sizes of #36 and #50 were bound to the backing 1 at a rate of 800 g/m.sup.2 (grain size #36) and 570 g/m.sup.2 (grain size #50). The make coat 2, comprising phenolic resin and chalk, was applied at a rate of 178 g/m.sup.2 (grain size #36) and 175 g/m.sup.2 (grain size #50). Subsequently an uncured and therefore still liquid size coat 4 comprising phenolic resin/chalk was applied at a wet rate of 650 g/m.sup.2 (grain size #36) and 450 g/m.sup.2 (grain size #50).

(15) Potassium tetrafluoroborate (KBF.sub.4) was applied as grinding aid to the thus-produced intermediate abrasive product, in Examples 1 to 7 as per Table 1 and in Examples 8 to 11 as per Table 2.

(16) The potassium tetrafluoroborate powder was obtained from Solvay Fluor GmbH, 30173 Hanover, Germany. The size distribution of the powder particles is indicated by the cumulative distribution in FIG. 3.

(17) In Comparative Examples 1, 9 and 11, the grinding aid was applied in the form of a liquid additional coating. This liquid additional coating had the following composition:

(18) TABLE-US-00001 Phenolic resin 75% 12% by weight KBF.sub.4 50% by weight Cryolite 10% by weight Water 17% by weight Colorant, wetting agent, TiO.sub.2, 11% by weight plasticizer, thickener

(19) For producing the Inventive Examples 2 to 8 and 10, powder-form potassium tetrafluoroborate (KBF.sub.4) was applied in dry form to the still-uncured size coat. The potassium tetrafluoroborate was applied uniformly to the intermediate abrasive product by means of a conventional application station for powder-form media. The application rates are shown in Tables 1 and 2.

(20) In all of the examples (both as dry powder in the inventive examples and as dispersed particles in the comparative examples), the potassium tetrafluoroborate particles had an average size of 25 m in each case.

(21) For the abrasives of Examples 1 to 7, Table 1 records the total abrasion achievable with these abrasives with abrasive grains of grain size #36. This total abrasion was determined by punching the cured abrasive to form abrasive discs having a diameter of 180 mm. The abrasive discs were affixed to a grinding machine, operated at a cutting speed of 33.6 m/s, and pressed down with a force of 50 N perpendicularly in succession onto a multiplicity of adjacently disposed plates, 4 mm thick, made of stainless steel (X5CrNi18-10 1.4301). The rate of tangential advance was 1.5 m/min, with grinding taking place with a contact roll. The amount of material abraded was determined individually for each plate by differential measurement. Working was continued until the abrasion amount per plate had dropped to around 35% of the abrasion amount for the first plate. Table 1 reports the total abrasion hereby obtained, and the loss of covering, i.e. the mass of the original abrasive disc that was abraded therefrom in the course of working.

(22) As is evident from Table 1, the amount of grinding aid needed in the case of inventive dry application (Example No. 3) relative to the customary wet application (Example No. 1) is only around half in order to achieve approximately the same total abrasion.

(23) TABLE-US-00002 TABLE 1 Example No. 1 2 3 4 5 6 7 Application wet dry dry dry dry dry dry mode (comparative example, average values from 8 samples) KBF.sub.4 172 43 87 112 152 178 208 application (contained rate [g/m.sup.2] in 344 g/m.sup.2 wet-applied additional coating) Total 159 119 160 180 192 216 220 abrasion [g] Covering 3.5 2.9 3.0 3.1 3.4 3.4 4.0 loss [g]

(24) FIGS. 4 to 7 contain photographs of plan views of the coated abrasives 8 to 11 as per Table 2. FIGS. 4 and 5 therefore show abrasives with a grain size of #36, with FIG. 4 showing a grinding disc with grinding aid applied dry in accordance with the disclosure, and FIG. 5 showing an abrasive with wet-applied grinding aid. FIGS. 6 and 7 show abrasives with a grain size of #50.

(25) As is apparent from comparing the figures, the particles of the grinding aid in accordance with the inventive dry application (FIGS. 4 and 6) are present on the surface of the abrasive, and in particular also above the individual abrasive grains. Moreover, the particles of the grinding aid are distributed substantially homogeneously over the surface. In the case of the comparative examples with wet application (FIGS. 5 and 7), in contrast, the particles of the grinding aid have penetrated further between the abrasive grains and are therefore virtually no longer visible.

(26) TABLE-US-00003 TABLE 2 Example No. 8 9 10 11 FIG. No. 4 5 6 7 Grain size # 36 # 36 # 50 # 50 Application dry wet dry wet mode (comparative (comparative example) example) KBF.sub.4 178 172 (contained in 136 138 application 344 g/m.sup.2 wet-applied (contained in rate [g/m.sup.2] additional coating) 276 g/m.sup.2 wet- applied additional coating)

(27) FIG. 8 shows a photograph of a sectional view through a conventional abrasive, in which the grinding aid 5 is embedded in a liquid-applied additional coating 6. As can clearly be seen here, a large part of the grinding aid is located in the regions between the abrasive grains 3, where, however, it is completely unable to develop its intended effect.

(28) FIG. 9 shows a photograph of a sectional view through a further inventive abrasive. The abrasive grains 3 are bonded by means of a make coat 2 to a backing 1 composed of vulcanized fibre with a thickness of 0.8 mm. Backing 1, make coat 2 and abrasive grains 3 are covered by a layer of size coat 4. Located above this layer is a further layer of dry-applied grinding aid 5. As is also apparent from this figure, the layer of grinding aid 5 has a substantially homogeneous thickness. Moreover, it can be seen that the grinding aid 5 has virtually not penetrated into the layer of size coat 4. Furthermore, the particles of the grinding aid 5 are bonded directly by the size coat 4. There is therefore no need for further binding agent, of the kind necessary in the case of conventional, wet application of the additional coating.

(29) FIG. 10 shows Abbott curves for a number of abrasives, these curves having been determined in accordance with DIN EN ISO 4287. The first curve (1) was measured on a backing on which an abrasive grain mixture comprising corundum had been bonded. This mixture contained semi-precious corundum of grade P120 and ceramic corundum of grade #120. This backing had a difference in height of 436 m. The difference in height, here and below, refers to the difference in the heights of a point on the surface that is furthest removed from the backing, and a point on the surface that is situated closest to the backing; the difference in height, therefore, is equal to the difference of the ordinate values of the Abbott curve at 0% and at 100%.

(30) Following application of a size coat, the second curve (2) was obtained, with a difference in height of 368 m. The third curve (3) was determined for an inventive abrasive in which potassium tetrafluoroborate (KBF.sub.4) with an average grain size of 25 m was applied dry at a rate of about 64 g/m.sup.2; the difference in height here is 386 m. In comparison to this, the fourth curve (4) shows the result for a conventional abrasive in which the potassium tetrafluoroborate was applied in a dispersion; the resulting difference in height was 288 m. The dispersion was applied at a rate of 120 g/m.sup.2, giving an application rate of 54 g/m.sup.2 of the potassium tetrafluoroborate.

(31) As can be seen from FIG. 10, the third curve (3) of the inventive abrasive, with fractions of material of less than about 15%, lies above the fourth curve (4) of the conventional abrasive, while with higher fractions of material the third curve lies below the fourth. The reason for this is that in the case of dry application, a relatively large number of the particles of the grinding aid are located in the region of the highest elevations (in other words, in the region of a depth of cutting space of 0 m). In the case of wet application, in accordance with curve (3), a larger portion of the grinding aid has dropped into the region between abrasive grains, meaning that, here, the fraction of material is greater in the case of greater depths of cutting space. Moreover, the difference in height of curve (3) for the inventive abrasive is greater than the difference in height of the curve (4) for the conventional abrasive. The reason for this as well is that a large fraction of the particles of the grinding aid is located in the region of the highest elevations.