Agglomerate abrasive grain comprising incorporated hollow microspheres

Abstract

An agglomerate abrasive grain includes a mixture of individual abrasive grains and hollow bodies, wherein the abrasive grains and the hollow bodies are held together via a binding matrix of aluminosilicate and alkali silicate, and the agglomerate abrasive grain has an open porosity and a closed porosity in each case ranging from 5% by volume to 40% by volume, wherein the total porosity of the agglomerate abrasive grain is less than 50% by volume.

Claims

1. An agglomerate abrasive grain comprising a plurality of individual abrasive grains incorporated into a binding matrix, wherein: the abrasive grains are selected from the group consisting of corundum, fused corundum, sintered corundum, alumina zirconia, silicon carbide, boron carbide, cubic boron nitride, diamond, and mixtures thereof; the binding matrix is obtained from a mixture of an aluminosilicate, an alkali sodium silicate, and water; the aluminosilicate and the alkali sodium silicate having a molar ratio of Al.sub.2O.sub.3 to SiO.sub.2 ranging from 1:2 to 1:20; the binding matrix is hardened at temperatures below 500 C.; the agglomerate abrasive grain has an open porosity ranging from 5% by volume to 25% by volume, the agglomerate abrasive grain further comprising hollow bodies that are incorporated into the binding matrix and that provide the agglomerate abrasive grain with a closed porosity, wherein the hollow bodies are 5% to 40% by volume of the agglomerate abrasive grain, and the sum of closed and open porosity is less than 50% by volume of the agglomerate abrasive grain; further wherein the abrasive grains and the hollow bodies have an average particle diameter ranging from 5 m to 250 m, and wherein the ratio of the average particle diameter of the abrasive grains to the average particle diameter of the hollow bodies ranges from 2:1 to 1:2.

2. The agglomerate abrasive grain according to claim 1, characterized in that the percentage by volume of the abrasive grains to the percentage by volume of the hollow bodies has a ratio ranging from 9:1 to 1.5:1.

3. The agglomerate abrasive grain according to claim 2, characterized in that the percentage by volume of the abrasive grains to the percentage by volume of the hollow bodies has a ratio ranging from 6:1 to 2:1.

4. The agglomerate abrasive grain according to claim 1, characterized in that the agglomerate abrasive grain comprises from 10% by volume to 80% by volume of abrasive grains, from 5% by volume to 40% by volume of hollow bodies, from 5% by volume to 40% by volume of binding matrix, and from 5% by volume to 25% by volume of open pores.

5. The agglomerate abrasive grain according to claim 1, characterized in that the hollow bodies are selected from the group consisting of hollow bodies on the basis of aluminum oxide, silicon oxide, zirconium oxide, titanium oxide, cerium oxide, and/or mixtures thereof.

6. The agglomerate abrasive grain according to claim 5, characterized in that the hollow bodies are hollow spheres made of glass.

7. The agglomerate abrasive grain according to claim 1, characterized in that the agglomerate abrasive grain comprises from 5% by weight to 30% by weight of binding matrix, from 60% by weight to 95% by weight of abrasive grains, and from 0.3% by weight to 20% by weight of hollow bodies.

8. A method for producing agglomerate abrasive grains according to claim 1, wherein a mixture of individual abrasive grains and hollow bodies are incorporated into a binding matrix of aluminosilicate and alkali sodium silicate having a molar ratio of Al.sub.2O.sub.3 to SiO.sub.2 ranging from 1:2 to 1:20, the method comprising: mixing the abrasive grains and hollow bodies with the binding agent of aluminosilicate, alkali sodium silicate, and water, drying the agglomerate abrasive grain green bodies obtained in this manner at a temperature ranging from 80 to 150 C.; classifying the dried agglomerate abrasive grain green bodies to a defined abrasive grit size; and hardening the dried and classified agglomerate abrasive grains at a temperature below 500 C.

Description

EXAMPLE 1

Comparison

(1) For the production of the comparative example, 3 kg of abrasive grains (ZK40 P180, Treibacher Schleifmittel) were mixed with 25 g of metakaolin (OPACILITE, Imerys) and 333 g of corundum micro grain (ESK P1400F, Treibacher Schleifmittel) in an intensive mixer (type RO1, Eirich) for 5 minutes in counter flow. One part of the mixture for the granules production was subsequently placed onto a rotating pelletizing table (type TR04, EIRICH) at 200 rpm and at an incline corresponding to stage 8 to 9 and was thereby sprayed with a diluted sodium silicate solution (30%). While successively adding grain mixture and sodium silicate, granules that formed are conveyed to the edge of the dish granulator due to the force of gravity and were collected. A total of 500 g of sodium silicate solution was added. The agglomerate abrasive grain green bodies obtained in this way were classified, wherein a fraction in the range of between 1180 m and 850 m was separated, subsequently dried in a drying chamber with recirculating air for one hour at 125 C., and then calcined in a rotary kiln at 450 C.

EXAMPLES 2 TO 5

(2) The production of examples 2 to 5 was carried out such as example 1, wherein, however, 10% by volume of the abrasive grains were in each case successively replaced by hollow spheres on the basis of silicon oxide and aluminum oxide (e-spheres, Erbslh) comprising an average particle diameter of 80 m. 300 g of abrasive grain (ZK40 P180) were in each case replaced by 34.5 g of e-spheres.

EXAMPLES 7 TO 9

(3) The production of the samples was carried out such as example 4, wherein, however, the portion of open pores was varied by different quantities of binder. Only 250 ml of a diluted sodium silicate solution together with 12.5 g of metakaolin and 166.5 g of corundum fine grain as binder were thereby used for example 7. 750 ml or 1000 ml, respectively, of sodium silicate solution together with 37.5 g or 50 g, respectively, of metakaolin and 499.5 g or 666 g, respectively of ESK P1400F were thereby used for examples 8 or 9, respectively.

EXAMPLES 10 AND 11

(4) The production of the agglomerate abrasive grains was carried out analogously to example 4, wherein, however, hollow bodies having a lower average particle diameter were used in example 10 and hollow bodies having a larger average particle diameter were used in example 11, while alumina zirconia ZK 40 P 180 was still used as individual abrasive grains.

(5) Grinding Tests

(6) Vulcanized fiber discs, by means of which a rod of steel 1.4301 (X5CrNi18-10; V2A) comprising a diameter of 20 mm was abraded, were produced from agglomerate abrasive grains having an average grain size of approx. 1 mm, which grains were produced according to the above-described examples 1 to 11. Five grinding intervals of 30 seconds were thereby carried out in each case with a wheel speed of 30 m/s, an rpm of 2700, and a contact pressure of 20 N. In addition to the material removal, the grain wear was measured and the G-ratio was calculated therefrom. Furthermore the surface was optically evaluated, wherein a differentiation was made between very good=completely homogenous surface, good=homogenous surface comprising slight irregularities, medium=substantially homogenous surface comprising clearly visible irregularities and bad=inhomogeneous surface.

(7) The composition and some physical data of examples 1 to 11 are summarized in Table 1 below.

(8) TABLE-US-00001 TABLE 1 Composition (% by vol.) abrasive hollow Bulk Fracture Example grain body open Density Strength No. ZK40 P180 binder (80 m) pores g/cm.sup.3 CFF (N) 1 65.9 15.3 18.8 0.92 19 (comparison) 2 61.1 15.8 6.8 16.3 0.88 17.5 3 53.5 15.5 13.4 17.6 0.85 17 4 47.7 15.8 20.4 16.1 0.81 14.5 5 39.8 15.4 26.6 18.2 0.72 13 6 32.6 15.1 32.6 19.7 0.68 11.5 (comparison) 7 46.6 7.7 20.0 25.7 0.74 10.5 8 46.0 22.8 19.7 12.5 0.86 17.5 9 44.0 29.2 18.9 7.9 0.90 24 hollow body 10 49.1 16.3 20.9 13.7 0.82 15.2 (55 m) 11 44.7 14.8 19.2 21.3 0.78 14.8 (120 m)

(9) Remarks: The percentages per volume of open pores were determined by mercury porosimetry. Based on the determined values, the percentages by volume for the abrasive grains, the binder matrix and the hollow bodies were then calculated with respect to the used quantities. For this purpose, a specific weight of 4.0 g/cm.sup.3 was assumed for the abrasive grains as well as for the fine grain used for the binder matrix, a specific weight of 2.4 g/cm.sup.3 was assumed for the siliceous binder (metakaolin and sodium silicate), and a specific weight of 0.46 g/cm was supposed for the hollow spheres made of glass.

(10) The results of the grinding tests are summarized in Table 2 below:

(11) TABLE-US-00002 TABLE 2 Grinding Tests ZK40 P180 Grain Wear Example No. Removal (g) (g) Surface G-Ratio 1 10.8 0.7 bad 15.4 (comparison) 2 14.5 0.8 good 18.2 3 15.8 0.85 very good 18.6 4 16.4 0.87 very good 18.8 5 17.0 1.0 very good 17.0 6 15.4 1.4 very good 11.0 (comparison) 7 14.8 0.88 very good 16.8 8 15.7 0.93 good 16.9 9 14.4 1.0 medium 14.4 10 13.4 0.8 good 16.8 11 12.5 1.2 very good 10.4

(12) Based on the comparative example 1, which does not include any hollow bodies, a part of the individual abrasive grains was successively replaced by hollow bodies in examples 1 to 6. By replacing 10% by volume of the abrasive grains with hollow bodies (example 2), a considerable improvement of the G-ratio (quotient of material removal and wear) can already be identified, wherein in particular the surface quality is also considerably improved. Even though the fracture strength of the agglomerate abrasive grains is decreased by further replacing individual abrasive grains with hollow spheres, this does not have a negative effect with respect to the grinding test, because the cutting ability of the agglomerate abrasive grain is increased, which is reflected in the high removal rate. At the same time, the fracture strength of the agglomerate abrasive grain is still high enough to keep the grain wear within limits, so that high G-ratios result. The best results are achieved when replacing approx. 30% by vol. of the individual abrasive grains with hollow bodies (example 4). Higher portions of hollow bodies, as in examples 5 and 6, in which approx. 40% by vol. or approx. 50% by vol., respectively, of the abrasive grains are in each case replaced by hollow bodies, lead to a destabilization of the agglomerate abrasive grains, so that an increased grain wear, still having very good removal rates, leads to decreased G-ratios, wherein an excellent workpiece surface quality, however, can always be observed, in particular with the examples comprising large portions of hollow bodies.

(13) The ratio of open pores to closed pores was varied in examples 7 to 9. The increase of the open porosity in example 7 leads to a considerable deterioration of the fracture strength and to an increased grain wear resulting therefrom and to a decreased G-ratio in comparison with example 4. Even though the decrease of the open porosity in examples 8 and 9 results in an increase of the fracture strength, this, however, does not have a positive effect on the grinding result, because a high grain wear can be identified despite the high fracture strength of the agglomerate abrasive grains. The high grain wear is possibly caused by the fact that the bonding of the agglomerate abrasive grains having a lower open porosity into the abrasive being no longer optimal, whereby a break-out of the entire agglomerate abrasive grain from the bond is made possible, which is favored even more by the high facture strength of the agglomerate abrasive grain. The correlation between the open porosity and the bonding into the abrasive follows from the possibility of infiltrating liquid binding agent into the open pores during the bonding of the agglomerate abrasive grain and thus anchoring the agglomerate abrasive grain in the abrasive.

(14) The particle size of the hollow bodies was varied in examples 10 and 11, whereby it can be summarized that the best results were obtained, when the particle size of the hollow bodies corresponds approximately to the particle size of the abrasive grains. Particularly good results were obtained when the average particle size of the hollow bodies was slightly larger than the average particle size of the abrasive grains.

(15) In this context, it is to be pointed out once again that the above-described principles and advantageous embodiments of the agglomerate abrasive grains according to the invention apply in particular to the machining of surfaces, when materials are used, which are to be treated moderately, using pressures, which are not too high. Other principles, which are the subject matter of further tests, might possibly apply for other materials and other grinding conditions.

EXAMPLES 12 TO 17

(16) The production of examples 12 to 17 was carried out such as examples 1 to 6, wherein, however, semi-friable aluminum oxide FRPL having the grit size P320 was used instead of the alumina zirconia ZK40 having the grit size P180 as individual abrasive grains. The particle size of the hollow bodies was adapted accordingly, wherein hollow bodies with the identification Q-cel 5070 (Potters, Ballotini GmbH) on the basis of silicon oxide having an average diameter of 55 m instead of the hollow bodies on the basis of silicon oxide and aluminum oxide having an average diameter of 80 m were now mixed with the semi-friable aluminum oxide. The other conditions were maintained.

(17) To produce the comparative example 12, a mixture of 3 kg of abrasive grains (FRPL P320, Treibacher Schleifmittel), 25 g of metakaolin (OPACILITE, Imerys) and 333 g of corundum micro grit (ESK P1400F) were mixed in an intensive mixer (type RO1, Eirich) for 5 minutes in counter flow. One part of the mixture for the granules production was subsequently placed onto a rotating pelletizing table (type PR04, EIRICH) at 200 rpm and at an incline corresponding to stage 8 to 9, and was thereby sprayed with a diluted sodium silicate solution (30%). While successively adding grain mixture and sodium silicate, granulates that formed are conveyed to the edge of the dish granulator due to the force of gravity and were collected. A total of 500 g of sodium silicate solution was added. The agglomerate abrasive grain green bodies obtained in this manner were classified, wherein a fraction in the range of between 1180 m and 850 m was separated, subsequently dried in a drying chamber with recirculating air for one hour at 125 C., and then calcined in a rotary kiln at 450 C.

(18) For examples 13 to 17, 10% by vol. of the abrasive grains was in turn replaced successively by 10% by vol. of hollow spheres comprising an average diameter of 55 m.

EXAMPLES 18 TO 20

(19) The production of examples 18 to 20 took place as in example 15, wherein, however, the portion of open pores was varied by different quantities of binder. Only 250 ml of a diluted sodium silicate solution together with 12.5 g of metakaolin and 166.5 g of ESK P1400F were thereby used as binder for example 18. 750 ml or 1000 ml, respectively, of sodium silicate solution together with 37.5 g or 50 g, respectively, of metakaolin and 399.5 g or 666 g, respectively, of ESK P1400F were thereby used in each case for examples 19 and 20.

EXAMPLES 21 AND 22

(20) The production of the agglomerate abrasive grains took place analogously to example 15, wherein, however, hollow bodies comprising a lower average particle diameter (30 m) were used in example 21 and hollow bodies comprising a larger average particle diameter (80 m) were used in example 22, while semi-friable aluminum oxide FRPL P320 was still used as individual abrasive grains.

(21) Grinding Tests

(22) Vulcanized fiber wheels, by means of which a rod of steel 1.4301 (X5CrNi18-10; V2A) comprising a diameter of 20 mm was abraded, were produced from agglomerate abrasive grains having an average grain size of approx. 1 mm, which grains were produced according to the above-described examples 12 to 22. Five grinding intervals of 30 seconds were thereby carried out in each case with a wheel speed of 30 m/s, an rpm of 3700, and a contact force of 30 N. In addition to the material removal, the grain wear was measured and the G-ratio was calculated therefrom. In addition, the surface was evaluated optically, wherein a distinction was made between very good=completely homogenous surface, good=homogenous surface comprising slight irregularities, medium=substantially homogenous surface comprising clearly visible irregularities and bad=inhomogeneous surface.

(23) TABLE-US-00003 TABLE 3 Composition (% by vol.) abrasive grain hollow Bulk Fracture Example FRPL body open Density Strength No. P320 binder (55 m) pores g/cm.sup.3 CFF (N) 12 63.9 14.8 21.3 0.94 22.5 (comparison) 13 58.2 15.0 6.4 20.4 0.90 18 14 50.2 14.5 12.5 22.8 0.85 15 15 43.1 14.3 18.5 24.1 0.78 14.8 16 37.3 14.4 24.8 23.5 0.72 13.7 17 31.4 14.5 31.4 22.7 0.63 13.4 (comparison) 18 44.8 7.4 19.2 28.6 0.9 17.2 19 44.2 22.0 19.0 14.8 0.85 18.8 20 42.9 28.5 18.4 10.2 0.87 21.4 hollow body 21 42.2 14.0 18.1 25.7 0.76 17.4 (30 m) 22 45.3 15.0 19.4 20.3 0.73 18.2 (80 m)

(24) The composition and some physical data, such as fracture strength and bulk density, of the agglomerate abrasive grains obtained according to examples 12 to 22 are summarized in Table 3. The percentages by volume of abrasive grains, binder and hollow bodies were calculated on the basis of the measured open porosity as in the case of the examples presented in Table 1.

(25) The results of the grinding tests are summarized in Table 4 below:

(26) TABLE-US-00004 TABLE 4 Grinding tests FRPL P320 Grain Wear Example No. Removal (g) (g) Surface G-Ratio 12 1.8 0.2 bad 9.0 (comparison) 13 2.2 0.18 good 12.2 14 2.3 0.22 very good 10.5 15 2.6 0.18 very good 14.4 16 2.6 0.21 very good 12.4 17 2.3 0.24 very good 9.6 (comparison) 18 2.2 0.19 good 11.6 19 2.2 2.1 good 10.5 20 2.4 2.6 medium 9.2 21 1.9 0.2 medium 9.5 22 1.6 0.2 very good 8.0

(27) Examples 12 to 22 were established according to the same model as examples 1 to 11. It was possible to confirm the principles, which had already been found in the case of the agglomerate abrasive grains made up of the coarser abrasive grains. The best results were thus obtained with an agglomerate abrasive grain, in the case of which approx. 30% by vol. of the individual abrasive grains are replaced by hollow bodies (example 15). It was also confirmed for the agglomerate abrasive grains made up of finer abrasive grains that hollow bodies and abrasive grains should advantageously have the same particle sizes, which follows from the comparison of examples 21 and 22 with example 15.