Abstract
A shaped ceramic abrasive particle based on alpha-Al.sub.2O.sub.3 contains a proportion of 5% to 30% by weight of ZrO.sub.2. The alpha-Al.sub.2O.sub.3 has a medium crystallite size of 0.5 m to 3 m and the ZrO.sub.2 has a medium crystallite size of 0.25 m to 8 m.
Claims
1. A shaped ceramic abrasive particle based on alpha-Al.sub.2O.sub.3 comprising: a ZrO.sub.2 portion comprising from 5% by weight to 30% by weight of the abrasive particle, wherein the alpha-Al.sub.2O.sub.3 has an average crystallite size of from 0.5 m to 3 m and the ZrO.sub.2 has an average crystallite size of from 0.25 m to 8 m.
2. The shaped ceramic abrasive particle as claimed in claim 1, wherein the ZrO.sub.2 portion comprises from 10% by weight to 25% by weight of the abrasive particle.
3. The shaped ceramic abrasive particle as claimed in claim 1, wherein a ratio of the average crystallite size of the alpha-Al.sub.2O.sub.3 to the average crystallite size of the ZrO.sub.2 is from 0.4 to 7.
4. The shaped ceramic abrasive particle as claimed in claim 1, further comprising: a stabilizer that stabilizes the ZrO.sub.2, the stabilizer comprising less than or equal to 20% by weight of the abrasive particle, wherein the stabilizer includes at least one of yttrium oxide, magnesium oxide, calcium oxide, and cerium oxide.
5. The shaped ceramic abrasive particle as claimed in claim 1, further comprising: a MgO portion comprising less than or equal to 0.5% by weight of the abrasive particle.
6. The shaped ceramic abrasive particle as claimed in claim 1, further comprising: a SiO.sub.2 portion comprising from 0.01% by weight to 2% by weight of the abrasive particle.
7. The shaped ceramic abrasive particle as claimed in claim 1, further comprising: a Na.sub.2O portion comprising from 0.01% by weight to 0.5% by weight of the abrasive particle.
8. The shaped ceramic abrasive particle as claimed in claim 1, further comprising: a CaO comprising from 0.01% by weight to 0.03% by weight of the abrasive particle.
9. The shaped ceramic abrasive particle as claimed in claim 1, further comprising: a Fe.sub.2O.sub.3 comprising from 0.01% by weight to 0.2% by weight of the abrasive particle.
10. The shaped ceramic abrasive particle as claimed in claim 1, wherein a density of the abrasive particle is from 92% to 99.9% of a theoretical density of the abrasive particle.
11. An abrasive article comprising: a plurality of first shaped ceramic abrasive particles, each particle of the plurality of first shaped ceramic abrasive particles being based on alpha-Al.sub.2O.sub.3 and having a ZrO.sub.2 portion comprising from 5% by weight to 30% by weight of the abrasive particle, wherein the alpha-Al.sub.2O.sub.3 has an average crystallite size of from 0.5 m to 3 m and the ZrO.sub.2 has an average crystallite size of from 0.25 m to 8 m.
12. The abrasive article as claimed in claim 11, further comprising: a plurality of second shaped ceramic abrasive particles which are based on alpha-Al.sub.2O.sub.3 and are essentially free of ZrO.sub.2, wherein a proportion of second shaped ceramic abrasive particles being not more than 80%, of a total amount of shaped ceramic abrasive particles.
13. A process for producing shaped ceramic abrasive particles, comprising producing a slip from at least one alpha-Al.sub.2O.sub.3 powder, a ZrO.sub.2 powder, and a dispersion medium, 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; introducing the slip into depressions of a casting mold, the depressions having a defined geometry; drying the slip in the depressions to produce abrasive particle precursors, a solids content of the abrasive particle precursors being from 85% by weight to 99.9% by weight; removing the abrasive particle precursors from the depressions; sintering the abrasive particle precursors to produce the abrasive particles based on alpha-Al.sub.2O.sub.3 having a ZrO.sub.2 portion comprising from 5% by weight to 30% by weight of the abrasive particle and a density of from 92% to 99.9% of a theoretical density, the alpha-Al.sub.2O.sub.3 of the abrasive particle having an average crystallite size of from 0.5 m to 3 m and the ZrO.sub.2 of the abrasive particle having an average crystallite size of from 0.25 m to 8 m.
14. The process as claimed in claim 13, wherein the sintering of the abrasive particle precursors is carried out at a temperature of from 1300 C. to 1700 C.
15. The process as claimed in claim 13, wherein the drying of the slip is carried out at a temperature of from 25 C. to 60 C.
16. The process as claimed in claim 13, wherein the slip includes a humectant in a proportion of from 0.1% by weight to 10% by weight of the slip.
17-18. (canceled)
19. The shaped ceramic abrasive particle as claimed in claim 2, wherein the ZrO.sub.2 portion comprises from 15% by weight to 22% by weight of the abrasive particle.
20. The shaped ceramic abrasive particle as claimed in claim 5, wherein the MgO portion comprises from 0.02% by weight to 0.4% by weight of the abrasive particle.
21. The shaped ceramic abrasive particle as claimed in claim 6, wherein the SiO.sub.2 portion comprises from 0.02% by weight to 0.5% by weight of the abrasive particle.
22. The shaped ceramic abrasive particle as claimed in claim 7, wherein the Na.sub.2O portion comprises from 0.015% by weight to 0.2% by weight of the abrasive particle.
Description
FIGURES
[0057] The invention is elucidated in more detail below with the aid of the figures. The figures show:
[0058] FIG. 1 a schematic view of one embodiment of the shaped ceramic abrasive particle of the invention;
[0059] FIG. 2 a section of a schematic sectional depiction of one embodiment of the abrasive article of the invention;
[0060] FIG. 3 a graph depicting the abrasive performance of the abrasive article of FIG. 2;
[0061] FIG. 4 a flow diagram depicting the process steps for producing the shaped ceramic abrasive particle.
[0062] FIG. 1 schematically depicts an illustrative embodiment of a shaped ceramic abrasive particle 10 according to the invention. The geometric shape of the abrasive particle 10 is formed by a regular three-sided right prism having the side edges 12 and the height 14. The base area 16 and the top surface 18 are accordingly each formed by three side edges 12 of equal length. The base area 16 and the top surface 18 are of equal size and are separated from one another by the height 14. The three side faces 17 are formed by rectangles and are equal in size. In the illustrative embodiment of FIG. 1, the side edges 12 have a length of 1400 m. The height 14 is 410 m. In an alternative embodiment, the length of the side edge 12 can also be 1330 m and the height can be 14 400 m.
[0063] FIG. 2 shows a section of an illustrative embodiment of an abrasive article 50 according to the invention comprising abrasive particles 10 in a schematic sectional view. The abrasive article 50 in the embodiment depicted is 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 10. 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 from the prior art as flexible substrate for abrasive articles. The abrasive particles 10 are fastened to the support element 52 by means of a base binder 54, for example composed of phenolic resin. The layer of base binder 54 and abrasive particles 10 is coated with a covering binder 56, for example composed of phenolic resin.
[0064] The process of the invention for producing shaped ceramic abrasive particles is explained in more detail in the flow diagram of FIG. 4. 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, a ZrO.sub.2 powder and a dispersion medium, 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 a second step 120, the slip is introduced into depressions of a casting mold, with the depressions having a defined geometry. Drying of the slip in the depressions is then carried out in a third step 130 to give abrasive particle precursors having 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. Furthermore, 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.
[0065] FIG. 3 shows in graph form the abrasive performance of different abrasive articles which have been produced using shaped ceramic abrasive particles having different proportions of ZrO.sub.2. In the graph, the removal of material S measured in a grinding test in gram per plate is plotted on the y axis as measure of the abrasive performance, and the number of plates P which were ground in the grinding test is plotted on the x axis. A total of three grinding tests using three different examples of abrasive articles comprising shaped ceramic abrasive particles were carried out. In a first example according to the invention, an abrasive article comprising shaped ceramic abrasive particles having a proportion of ZrO.sub.2 of 22% by weight was used (hereinafter also referred to as variant AZ22). In a second example according to the invention, an abrasive article comprising shaped ceramic abrasive particles having a proportion of ZrO.sub.2 of 16% by weight was used (hereinafter also referred to as variant AZ16). In a third comparative example, an abrasive article comprising single-phase shaped ceramic abrasive particles which did not contain any ZrO.sub.2 (0% by weight of ZrO.sub.2) was used (hereinafter also referred to as variant A).
[0066] The abrasive particles of the variants AZ22, AZ16 and A were produced as follows. Firstly, a slip was produced (cf. FIG. 4, step 110) for each of the variants AZ22, AZ16 and A. For this purpose, the amounts of water as dispersion medium indicated in Table 1 and also Dolapix as dispersant were homogenized with the amounts indicated in Table 1 of pulverulent alpha-Al.sub.2O.sub.3, pulverulent ZrO.sub.2 (for the variants AZ22, AZ16) and pulvulerent MgO in a high-speed mixer. The pulverulent ZrO.sub.2 was partially stabilized ZrO.sub.2 (ZrO.sub.2 stabilized with 3 mol % of Y.sub.2O.sub.3). The further amounts indicated in Table 1 of the organic additives Optapix AC 112 as binder, Glydol N109 as wetting agent and glycerol as humectant were also added to the slip. The slip was subsequently milled in a ball mill. The finished slip had an average particle size of 0.2 m.
TABLE-US-00001 TABLE 1 Comparative Example Example 1 Example 2 example Variant AZ22 AZ16 A Water [g] 18.8 18.8 18.5 Al.sub.2O.sub.3 [g] 57.9 62.4 74.2 ZrO.sub.2 [g] 16.3 11.9 0 MgO [mg] 29 31 74 Wetting agent 0.6 0.6 0.6 GLYDOL N 109 [g] Binder 0.3 0.3 0.3 OPTAPIX AC 112 [g] Humectant 5.5 5.5 5.5 Glycerol [g] Dispersant 0.6 0.6 0.8 DOLAPIX CE 64 [g]
[0067] The finished slip was, for each of the three variants AZ22, AZ16 and A, introduced in a subsequent step into depressions of a casting mold, with the depressions having a defined geometry (cf. FIG. 4, step 120). Introduction of the slip into the depressions was carried out manually by means of a manual doctor blade. The casting mold had the shape of a plate having a thickness of 3 mm and consisted of silicone. The casting mold had a plurality of depressions having the same geometry. In order to arrive at shaped ceramic abrasive particles as shown in FIG. 1, the depressions in the casting mold were configured as negative shapes of a regular three-sided right prism having an edge length of 1.7 mm and a depth of 0.5 mm.
[0068] In a further step, the slip in the depressions of the casting mold was dried (cf. FIG. 4, step 130). Drying was carried out at a temperature of 40 C. for a time of about 1 hour. This made it possible to obtain abrasive particle precursors having a solids content of, for example, 96% by weight.
[0069] After drying, the abrasive particle precursors were removed from the depressions of the casting mold (cf. FIG. 4, step 140). For this purpose, the casting mold was bent through a small radius. The removal from the mold was additionally assisted mechanically by means of a brush.
[0070] In a subsequent step, the abrasive particle precursors were sintered to give abrasive particles (cf. FIG. 4, step 150). Sintering was carried out at a temperature of 1530 C. for a time of 120 minutes for the variants AZ16 and AZ22 and at a temperature of 1560 C. for a time of 180 minutes for the variant A. After sintering, the abrasive particles had a density of 98% (variant AZ22), 97% (variant AZ16) and 95% (variant A95) of the theoretical density. The abrasive particles had a content of ZrO.sub.2 of 16% by weight (variant AZ16, example 1 according to the invention), 22% by weight (variant AZ22, example 2 according to the invention) and 0% by weight (variant A, comparative example). In variant AZ22, the average crystallite size of the alpha-Al.sub.2O.sub.3 was 1.28 m, while in the variant AZ16 the average crystallite size of the alpha-Al.sub.2O.sub.3 was 1.39 m. The average crystallite size of the ZrO.sub.2 was 0.61 m in the variant AZ22 and 0.57 m in the variant AZ16.
[0071] The respective abrasive articles 50 in the form of abrasive disks which were produced using the abrasive particles AZ22, AZ16 and A had the following structure (cf. FIG. 2). A fiber disk composed of vulcanized fiber and having a diameter of 180 mm and a thickness of 0.8 mm was used in each case as support element 52. A mixture of phenolic resin (35-50% by weight) and chalk (30-45% by weight) was used as base binder 54. Here, the amount of base binder used was 100-120 g/m.sup.2 in the wet state. The amount of abrasive particles 10 which were applied to the support element 52 with base binder 54 was 640-740 g/m.sup.2. As covering binder 56, a mixture of phenolic resin (20-30% by weight), chalk/kaolin mixture 1:1 (30-40% by weight) and cryolite (5-20% by weight) was used for variants AZ22 and AZ16. In the case of variant A, a mixture of phenolic resin (20-30% by weight), chalk (35-45% by weight) and cryolite (5-20% by weight) was used as covering binder 56. The amount of covering binder used was 760-950 g/m.sup.2 in the moist state.
[0072] To determine the abrasive performance depicted in FIG. 3 of the respective abrasive articles produced using the abrasive particles AZ22, AZ16 and A, the following grinding test was carried out on a test stand. The respective abrasive article in the form of an abrasive disk was mounted on a support plate. As workpieces for grinding, use was made of steel plates composed of the materials 1.0332 and 1.8974 and having a machining area of 6 mm285 mm. To determine the removal of material per steel plate, the steel plates were weighed before and after the grinding test. During the grinding test, the steel plates composed of the materials 1.0332 and 1.8974 were ground alternately. The respective abrasive disk was operated at a speed of rotation of 4181 rpm and the workpieces were moved past the abrasive disk at a rate of advance of 1.5 mm/s. During the test, the workpieces were pressed onto the abrasive disk under a weight of 6 kg. 80 steel plates were machined using each of the three abrasive disks having the abrasive particles AZ22, AZ16 and A.
[0073] The graph in FIG. 3 shows a significantly improved abrasive performance for the two abrasive particles AZ22 and AZ16 compared to the single-phase abrasive particle A. Furthermore, the graph shows an improved abrasive performance for the abrasive particle AZ22 compared to the abrasive particle AZ16 in a first phase of the grinding test (up to about 35 plates) and conversely an improved abrasive performance for the abrasive particle AZ16 compared to the abrasive particle AZ22 in a second phase of the grinding test (from about 35 plates to 80 plates). In the first phase of the grinding test, the removal by wear of the abrasive particles is lower than in the second phase (from about 35 plates to 80 plates).
