Abrasive grains on basis of eutectic alumina zirconia

Abstract

Heat treated alumina zirconia abrasive grains based on Al.sub.2O.sub.3 and ZrO.sub.2 may be fused in an electric arc furnace, and may have a weight content of: Al.sub.2O.sub.3 between 52% and 62% by weight; ZrO.sub.2 and HfO.sub.2 between 35% and 45% by weight, with at least 6% by weight based on the total weight content of ZrO.sub.2 being present in the tetragonal and/or cubic high temperature modifications of ZrO.sub.2; Si-compounds between 0.2% and 0.7% by weight expressed as SiO.sub.2; carbon between 0.03% and 0.5% by weight; additives between 0.5% and 10% by weight; and raw-material-based impurities of less than 3% by weight. The heat treated alumina zirconia abrasive grains may be heat treated in air between 350° C. and 700° C. for a time period of one to six hours using a rotary kiln.

Claims

1. Abrasive grains based on Al.sub.2O.sub.3 and ZrO.sub.2 fused in an electric arc furnace and having a weight content of: Al.sub.2O.sub.3 between 52% and 62% by weight; ZrO.sub.2 and HfO.sub.2 between 35% and 45% by weight, with at least 60% by weight, based on the total weight content of ZrO.sub.2, being present in the tetragonal and/or cubic high temperature modifications of ZrO.sub.2; Si-compounds between 0.2% and 0.7% by weight, expressed as SiO.sub.2; carbon between 0.03% and 0.5% by weight; additives between 0.5% and 10% by weight; and raw-material-based impurities of less than 3% by weight, wherein the abrasive grains are characterized in that after quenching the melt, crushing the solidified fused product and screening it into grit sizes, the abrasive grains are heat treated in air between 350° C. and 700° C. for a time period of one to six hours.

2. The abrasive grains according to claim 1, characterized in that the additives are selected from the group consisting of reduced Ti-compounds, Y.sub.2O.sub.3, MgO, CaO, and/or mixtures thereof.

3. The abrasive grains according to claim 1, characterized in that the abrasive grains are heat treated in air between 400° C. and 600° C. for a time period of two to four hours.

4. The abrasive grains according to claim 1, characterized in that the additives comprise at least one reduced titanium compound in the form of oxides, suboxides, carbides, oxycarbides, oxycarbonitrides, and/or silicides.

5. The abrasive grains according to claim 1, characterized in that between 65% and 85% by weight of ZrO.sub.2, based on the total weight content of ZrO.sub.2, are present in the tetragonal and/or cubic high-temperature modifications.

6. The abrasive grains according to claim 1, characterized in that the abrasive grains have an improved grain fracture strength (CFF) according to Vollstaedt of at least 95 N.

7. The abrasive grains according to claim 1, characterized in that the abrasive grains have a minimized micro grit decomposition (MKZ) of less than 6%.

8. The abrasive grains according to claim 1, characterized in that the additives comprise a reduced titanium compound in the form of oxides, suboxides, carbides, oxycarbides, oxycarbonitrides, and/or silicides, whereby between 60% and 80% by weight of ZrO.sub.2, based on the total weight content of ZrO.sub.2, are present in the tetragonal and/or cubic high-temperature modifications, and whereby the abrasive grains have an improved grain fracture strength (CFF) according to Vollstaedt of at least 95 N.

9. A method for producing fused abrasive grains according to claim 1, the method comprising: mixing raw materials to produce abrasive grains having the following chemical composition: a) Al.sub.2O.sub.3 between 52% and 62% by weight; b) ZrO.sub.2 and HfO.sub.2 between 35% and 45% by weight, with at least 60% by weight of ZrO.sub.2, based on the total weight content of ZrO.sub.2, being present in tetragonal and/or cubic high-temperature modification; c) Si-compounds between 0.2% and 0.7% by weight expressed as SiO.sub.2; d) carbon between 0.03% and 0.5% by weight; e) additives between 0.5% and 10% by weight; and f) raw-material-based impurities of less than 3% by weight; fusing the mixture in an electric arc furnace; quenching the fused mixture to obtain a solidified product; crushing the solidified product and subsequently screening the crushed solidified product to obtain abrasive grains; and heat treating the abrasive grains at a temperature between 350° C. and 700° C. in air for a time period of one to six hours.

Description

(1) In FIGS. 1 to 6 the graphical progressions of the mechanical and crystallographic data summarized in table 1 are reproduced. Thereby demonstrate:

(2) FIG. 1 the graphical progression of the T-factor of sample A, B, and C with increasing temperatures;

(3) FIG. 2 the graphical progression of the CFF-value of sample A, B, and C with increasing temperatures;

(4) FIG. 3 the graphical progression of the MKZ-value of sample A, B, and C with increasing temperatures;

(5) FIG. 4 the influence of the temperature treatment on CFF-value and T-factor with respect to sample A;

(6) FIG. 5 the influence of the temperature treatment on CFF-value and T-factor with respect to sample B; and

(7) FIG. 6 the influence of the temperature treatment on CFF-value and T-factor with respect to sample C.

(8) From FIG. 1 the influence of the different stabilizers becomes apparent. Whereas sample A stabilized solely with Ti-compounds shows a continuous and significant decrease of the high-temperature phase with increasing treatment temperatures, there is, even at temperatures up to 850°, only a marginal decrease of the T-factor to be observed with respect to sample B stabilized only with Y.sub.2O.sub.3. For the mixed stabilized sample C, there is not till 500° C. then a significant decrease of the T-factor to be observed. Obviously, Y.sub.2O.sub.3 stabilizes the high-temperature phases more efficiently and more sustainably.

(9) Nevertheless, the curves in FIG. 2 reveal that the decrease of the high-temperature phases, respectively, the phase transitions does not influence the grain fracture strength (CFF) that much, up to a temperature of 750° C. The grain fracture strength is for all 3 samples nearly unchanged up to a temperature of 750° C. Of particular interest is the increase of the grain fracture strength at 500° C. of sample A stabilized only with Ti-compounds.

(10) The micro grit decomposition with increasing temperature illustrated in FIG. 3 shows for all 3 samples A, B, and C a similar, but variably pronounced progression. Thus, the micro grit decomposition decreases at the first temperature level up to 500° C. in order to subsequently increase different strongly with progressing temperature treatment dependent on the type of stabilization. Also in this case, it is of interest that sample A solely stabilized with titanium compounds shows the lowest increase of micro grit decomposition and consequently the lowest wear.

(11) The FIGS. 4, 5, and 6 illustrate in each case with respect to the different samples A, B, and C the changing of the T-factor in comparison with the changing of the grain facture strength (CFF), whereby also here the significant divergence of both curves in case of sample A only stabilized with Ti-compounds attracts attention.

(12) Additionally, grinding tests were carried out with some selected samples, in so doing a temperature treated sample was compared with the untreated original sample, respectively.

Cut-Off Wheel Test

(13) For this series of tests, cut-off wheels of the specification R-T1 180×3×22.5 were chosen. First, a pressing mixture consisting of 75% by weight alumina zirconia of grit size P36, 5% by weight liquid resin, 12% by weight powder resin from HEXION Specialty chemicals GmbH, 4% by weight pyrite, and 4% by weight cryolite was prepared. For the production of the wheels, 160 g of the pressing mixture were molded onto a commercially available fabric material and pressed at 200 bar and cured according to the resin manufacturer's instructions.

(14) For the cut-off test, round steel bars made of stainless steel X5CrNi18-10 (material number 1.4301) with a diameter of 20 mm were used. The cutting operations were performed at a wheel speed of 8,000 revolutions per minute and with a cutting time of 3 seconds. After 20 cuts the wheel wear was determined based on the reduction in diameter of the wheels. The G-ratio was calculated from the ratio of material removal and wheel wear. The results of the grinding tests are summarized in table 2.

(15) TABLE-US-00002 TABLE 2 sample G-ratio performance (%) A untreated 13.57 100% 500° C. 15.14 112% B untreated 9.12 100% 500° C. 10.36 113% C untreated 9.42 100% 500° C. 12.00 127%

(16) The results summarized in table 2 reveal that the grinding efficiency of all tested alumina zirconia abrasive grains is improved by a heat treatment of the finished abrasive grains. In the context of the present invention the influence of the type of stabilization was investigated and can be summarized as follows.

(17) The particular advantage of the stabilization with reduced T-compounds firstly consists in that the so-stabilized alumina zirconia (sample A) has per se a higher performance than samples B and C which are fully or partially stabilized with Y.sub.2O.sub.3. Another advantage of the stabilization with Ti-compounds is the fact that a cheap raw material (rutile sand) can be used as stabilizing additive. Actually, the price of Y.sub.2O.sub.3 is more than hundredfold the price of rutile sand. Furthermore, contrary to the fully or partially Y.sub.2O.sub.3-stabilized samples B and C, the grain fracture strength of the Ti-stabilized sample A is enhanced with increasing temperatures. Last but not least, sample A solely stabilized with titanium compounds shows the lowest increase of micro grit decomposition and consequently the lowest wear.