Abstract
A shaped ceramic abrasive particle, in particular on the basis of alpha-Al.sub.2O.sub.3, includes at least three faces, at least two faces of which form a common vertex on which at least one corner common to the three faces lies. The abrasive particle has at least one structural weakening element. The disclosure also relates to an abrasive article including the abrasive particles, and a method for producing the abrasive particles.
Claims
1. A shaped ceramic abrasive particle comprising: at least three faces, of which at least two faces form a common edge on which at least one corner common to the at least three faces is located; and at least one structure-weakening element.
2. The shaped ceramic abrasive particle as claimed in claim 1, wherein the at least one structure-weakening element is formed as one of (i) an open recess in material of the abrasive particle and (ii) a closed recess in the material of the abrasive particle.
3. The shaped ceramic abrasive particle as claimed in claim 1, wherein the at least one structure-weakening element is located eccentrically to a center of gravity of the abrasive particle.
4. The shaped ceramic abrasive particle as claimed in claim 2, wherein the at least one structure-weakening element is configured as the open recess in the material and is located on one of (i) one of the at least three faces, ii) the at least one edge, and (iii) the at least one corner of the abrasive particle.
5. The shaped ceramic abrasive particle as claimed in claim 2, wherein the at least one structure-weakening element is configured as the closed recess in the material and is at a distance which is in a range from 1% to 50% of an average diameter of the abrasive particle from one of (i) one of the at least three faces, (ii) the at least one edge, and (iii) the at least one corner of the abrasive particle.
6. The shaped ceramic abrasive particle as claimed in claim 2, wherein the at least one structure-weakening element includes a plurality of structure-weakening elements configured as open recesses in the material and/or as closed recesses in the material.
7. The shaped ceramic abrasive particle as claimed in claim 2, wherein the at least one structure-weakening element has an essentially convexly curved shape having a radius of curvature of from 10 m to 200 m.
8. The shaped ceramic abrasive particle as claimed in claim 1, wherein the at least one structure-weakening element is configured as at least one of a material projection and a material overhang at the at least one edge and/or at the at least one corner of the abrasive particle.
9. The shaped ceramic abrasive particle as claimed in claim 8, wherein the at least one of the material projection and the material overhang is realized extends along at least 10% of a length of the at least one edge.
10. The shaped ceramic abrasive particle as claimed in claim 8, wherein the at least one of the material projection and the material overhang has a thickness of from about 10 m to 100 m.
11. The shaped ceramic abrasive particle as claimed in claim 8, wherein the at least one of the material projection and the material overhang extends for a distance of at least 20 m, beyond the at least one edge.
12. The shaped ceramic abrasive particle as claimed in claim 8, wherein the at least one of the material projection and the material overhang defines an angle in the range from 10 to 90 with at least one of the at least three faces.
13. An abrasive article comprising: a plurality of shaped ceramic abrasive particles, each of which comprises: at least three faces, of which at least two faces form a common edge on which at least one corner common to the at least three faces is located; and at least one structure-weakening element.
14. The abrasive article as claimed in claim 13, further comprising: a total number of abrasive particles, which includes the plurality of ceramic abrasive particles, wherein the plurality of shaped ceramic abrasive particles comprises at least 5%.
15. A casting mold for producing shaped ceramic abrasive particles, comprising: a plurality of mold cavities, each cavity of the plurality of mold cavities having a lower mold surface, a mold side wall and a depth T.sub.F between the lower mold surface and a surface of the casting mold, wherein the mold side wall and the surface of the casting mold are joined by a radius of curvature of at least 25 m.
16. The casting mold as claimed in claim 15, wherein a cross-sectional geometry of the plurality of mold cavities parallel to the lower mold surface is selected from the group consisting of a triangle, a rectangle, a star, an isogon, a regular polygon, and an irregular polygon.
17. A process for producing the shaped ceramic abrasive particles as claimed in claim 1.
18. The shaped ceramic abrasive particle as claimed in claim 2, wherein the abrasive particle is based on alpha-Al.sub.2O.sub.3.
19. The shaped ceramic abrasive particle as claimed in claim 2, wherein the at least one structure-weakening element is formed as a void, a bubble, a pore, an indentation, a notch, a hollow or a crater in the material of the abrasive particle.
20. The shaped ceramic abrasive particle as claimed in claim 7, wherein the at least one structure-weakening element has a spherical, ball-like shape having a radius of curvature of from 25 m to 50 m.
Description
DRAWINGS
[0065] The invention is illustrated in the following description with the aid of working examples depicted in the drawings. The drawings, the description and the claims contain numerous features in combination. A person skilled in the art will also advantageously look at the features individually and put them together to form purposeful further combinations. Identical reference numerals in the figures denote identical elements.
[0066] The figures show:
[0067] FIG. 1 a schematic view of an embodiment of a ceramic shaped abrasive particle according to the prior art;
[0068] FIG. 2 a schematic view of an embodiment of a ceramic shaped abrasive particle according to the invention having at least one structure-weakening element configured as open recess in the material;
[0069] FIG. 3 a schematic view of an embodiment of a ceramic shaped abrasive particle according to the invention having at least one structure-weakening element configured as closed recess in the material;
[0070] FIG. 4 a schematic view of an embodiment of a ceramic shaped abrasive particle according to the invention having at least one structure-weakening element configured as material projection;
[0071] FIG. 5 a schematic view of an alternative embodiment of a ceramic shaped abrasive particle according to the invention having at least one structure-weakening element configured as material projection;
[0072] FIG. 6 a schematic view of an embodiment of a ceramic shaped abrasive particle according to the invention having at least one structure-weakening element configured as material projection, a structure-weakening element configured as closed recess in the material and also a structure-weakening element configured as open recess in the material;
[0073] FIG. 7 a section of a schematic sectional view of an embodiment of the abrasive article according the invention;
[0074] FIG. 8 a flow diagram to indicate the process steps for producing a shaped ceramic abrasive particle according to the invention.
[0075] FIG. 1 schematically depicts (in particular not true-to-scale) an illustrative embodiment of a shaped ceramic abrasive particle 10 as is known from the prior art. The geometric shape of the abrasive particle 10 is formed by a regular three-sided right prism having the side edges and the height edges 12a having the height 14. Side edges and height edges will hereinafter also be referred to collectively as edges 12, 12a. The base area 16 and the top surface 18 are accordingly formed in each case by three side edges 12 of equal length. The base area 16 and the top surface 18 have the same size and are separated from one another by the height 14. The three side faces 17 are formed by rectangles and have essentially the same size. In the illustrated embodiment of FIG. 1, the side edges 12 have a length 13 of 1400 m. The height 14 is 410 m. In an alternative embodiment, the length 13 of the side edge 12 can also be 1330 m and the height 14 can be 400 m. The ceramic abrasive particle 10 is produced on the basis of alpha-Al.sub.2O.sub.3.
[0076] The shaped ceramic abrasive particle 10 depicted by way of example in FIG. 1 forms, in the following, the starting basis for the presentation of working examples of the proposed shaped ceramic abrasive particle 20, 20a-e, which according to the invention has at least one structure-weakening element 22, 22a-d. The proposed shaped ceramic abrasive particle 20, 20a-e is likewise produced on the basis of alpha-Al.sub.2O.sub.3 and has at least three faces, here by way of example two side faces 17 and the top surface 18, of which at least two faces form a common edge 12, 12a, for example a side face 17 and the top surface 18 form a side edge 12, on which at least one corner 19 which is common to the three faces is located.
[0077] In the following figures, which each depict illustrative embodiments of the abrasive particle 20, 20a-e according to the invention in views which are likewise schematic and not true-to-scale, the reference numerals for labeling the side edges, faces, etc., have not been inserted for reasons of claritythey can, however, be carried over directly from FIG. 1. The nomenclature for the abrasive particle 10 introduced by means of FIG. 1 can be carried over directly to the following working examples.
[0078] FIG. 2 depicts an illustrative embodiment of the ceramic shaped abrasive particle 20a according to the invention having four structure-weakening elements 22a configured as open recesses 24-30 in the material. A first structure-weakening element 22a is configured as an open recess 24 in the material in the form of a hollow or indentation on the at least one corner 19 of the abrasive particle 20, 20a. A second structure-weakening element 22a is configured as an open recess 26 in the material in the form of a hollow or indentation on the top surface 18. Third and fourth structure-weakening elements 22a are configured as open recesses 26, 28 in the material in the form of a hollow or indentation on a side edge 12 or on a height edge 12a. The structure-weakening elements 22a are in this case present eccentrically to the center of gravity of the abrasive particle 20, 20a, which is located in the center of the abrasive particle 20, 20a (not shown in more detail).
[0079] FIG. 3 depicts an illustrative embodiment of the ceramic shaped abrasive particle 20b according to the invention having three structure-weakening elements 22b configured as closed recesses 32 in the material. The three structure-weakening elements 22b are each configured as closed recess 32 in the material in the form of a void, in particular a bubble, completely within the interior of the material of the abrasive particle 20, 20b. The structure-weakening elements 22b are likewise positioned eccentrically to the center of gravity of the abrasive particle 20b, which in the abrasive particle 20, 20b depicted in FIG. 3, too, is located in the center of the abrasive particle 20, 20b (not shown in more detail). The structure-weakening elements 22b are each at a distance 34, which is about 20 m-30 m, from one of the at least three height edges 12a.
[0080] The structure-weakening elements 22, 22a, 22b depicted in FIGS. 2 and 3 each have an essentially convexly curved, in particular spherical, shape, with a radius of the convexly curved recess in the material being about 50 m. It may be remarked that, in one illustrative embodiment of the abrasive particle 20, a plurality of structure-weakening elements 22a, 22b configured as open recesses 24-30 in the material and as closed recesses 32 in the material can be provided simultaneously in the abrasive particle 20 (cf. FIG. 5).
[0081] FIG. 4 depicts an illustrative embodiment of the ceramic shaped abrasive particle 20c according to the invention having a structure-weakening element 22c configured as material projection 36 on two side edges 12 and the corner 19 between the two side edges 12. FIG. 4a shows the abrasive particle 20c in a schematic perspective view, while FIG. 4b shows a plan view and FIG. 4c shows a side view of the abrasive particle 20c (cf. coordinate system shown for orientation). The broken line indicates edges 12, 12a of the abrasive particle 20c in the original geometry (cf. FIG. 1) which are not visible, with the edges 12, 12a either being located on the rear side of the abrasive particle 20c or no longer being present because of the material projection 36. In the working example depicted, the material projection 36 runs along at least 45% of the length of one of the side edges 12 (left-hand and right-hand edge 12), indicated by the curly bracket 38. The material projection 36 has an approximate (average) thickness 40 of about 25-30 m. Furthermore, the material projection 36 extends by an (average) distance 42 of about 60 m beyond the side edge 12. The material projection 36 encloses an angle 44 of about 85 with the top surface 18. Here, the material projection 36 is joined on by means of a curved, in particular continuous, transition which can be described by a radius of curvature 46. In the working example depicted in FIG. 4, the radius of curvature is about 70 m.
[0082] FIG. 5 depicts an alternative, illustrative embodiment of the ceramic shaped abrasive particle 20d according to the invention having a structure-weakening element 22d configured as material projection 36 at a side edge 12, in particular at a corner 19. FIG. 5a shows the abrasive particle 20c in a schematic perspective view, while FIG. 5b shows a plan view (cf. coordinate system depicted for orientation). The broken line likewise indicates edges 12, 12a of the abrasive particle 20d in the original geometry (cf. FIG. 1) which are not visible, with the edges 12, 12a either being located on the rear side of the abrasive particle 20d or no longer being present because of the material projection 36. The material projection 36 has the shape of a nose at one of the corners 19, in particular also at a height edge 12a.
[0083] FIG. 6 depicts an illustrative embodiment of the ceramic shaped abrasive particle 20e according to the invention having a structure-weakening element 22b configured as closed recess 32 in the material, having a structure-weakening element 22a configured as open recess in the material and having a structure-weakening element 22c configured as material projection 36 and two side edges 12 and the corner 19 between the two side edges 12. The abrasive particle thus has a plurality of different structure-weakening elements 22, 22a, 22b, 22c.
[0084] FIG. 7 shows a section of an illustrative embodiment of an abrasive article 50 according to the invention with abrasive particles 20, 20a-e in a schematic sectional view. The abrasive article 50 is, in the embodiment depicted, a coated abrasive article 50 having a support element 52 made of vulcanized fiber. The support element 52 made of vulcanized fiber serves as flexible substrate for the abrasive particles 20, 20a-e. Vulcanized fiber is a composite material composed of cellulose, in particular cotton fibers or cellulose fibers, and is adequately known to a person skilled in the art as flexible substrate for abrasive articles from the prior art. The abrasive particles 20, 20a-e are fastened by means of a base binder 54, for example composed of phenolic resin, to the support element 52. The layer of base binder 54 and abrasive particles 20, 20a-e is coated with a covering binder 56, for example composed of phenolic resin.
[0085] The process according to the invention for producing shaped ceramic abrasive particles will be illustrated with the aid of the flow diagram of FIG. 8. The production process 100 comprises the following steps. In a first step 110, a slip is produced from at least one alpha-Al.sub.2O.sub.3 powder and a dispersion median, with the slip having a solids content of from 50% by weight to 90% by weight and an average particle size of from 0.1 m to 8 m. In one embodiment of the process, a ZrO.sub.2 powder can additionally be used. In a second step 120, the slip is introduced into depressions in a casting mold (not shown in more detail), with the depressions having a defined geometry. The casting mold has, in particular, a plurality of mold cavities, with the plurality of mold cavities comprising a lower mold surface, a mold side wall and a depth between lower mold surface and surface of the casting mold. The mold side wall and the surface of the casting mold are, in this working example, joined by a radius of curvature of 70 m (cf. explanation of FIG. 4). Drying of the slip in the depressions is then carried out in a third step 130 to give abrasive particle precursors which have a solids content of from 85% by weight to 99.9% by weight. After drying of the slip, the abrasive particle precursors are removed from the depressions in a fourth step 140. In addition, the abrasive particle precursors are sintered in a fifth step 150 to give abrasive particles based on alpha-Al.sub.2O.sub.3 having a content of ZrO.sub.2 of from 5% by weight to 30% by weight and a density of from 92% to 99.9% of the theoretical density, with the alpha-Al.sub.2O.sub.3 having an average crystallite size of from 0.5 m to 3 m and the ZrO.sub.2 having an average crystallite size of from 0.25 m to 8 m.
