SI8511242A8 - Process for preparing grindstones - Google Patents

Description

TREIBACHER CHEMISCHE WERKE AG

Procedure for preparing sanders

FIELD OF THE INVENTION

The invention relates to abrasives and relates to a high abrasive abrasive based on alpha-A ^ O ^ and Al-oxycarbides, optionally further additives, in particular to a process for preparing such abrasives.

A technical problem

When melting a mixture of aluminum oxide or alumina-rich substances with a carbon-containing reducing agent and subsequent rapid cooling of the melt with increasing carbon content, the proportion of Al ^ C ^ in the finished product is greatly increased. As Al ^ C ^ is known to decompose in moist air and under the influence of heat when grinding, the grinding efficiency is greatly reduced by the presence of Al ^ C ^.

Therefore, there was a need to produce an abrasive that contained as little Al ^ C ^ as possible and had a suitable structure, following a favorable technological process.

The state of the art

The ED-PS O 022 420 is known to be an abrasive consisting of a combination of crystalline phases of aluminum oxide and at least one of the two aluminum oxycarbides A1 ₂ OC and Al ^ O ^ C, the mixture of aluminum oxide + carbon-containing substance being used in the ratio of proportions corresponding to the Al ^ C ^ mole fraction between 0.02 and 0.20 in the state diagram of Al ₂ 0 ₃ + Al ^ C ^. The molten mixture was then cured at a controlled rate of 10 to more than 100 ° C per minute. The cooled melt is then crushed, graded and used for grinding work by known methods.

Description of solution to a technical problem with implementation examples

The invention therefore relates to a process for the preparation of an alpha-Al ₂ 0 ₃ -based grinder and at least one of the two aluminum oxycarbides Al ₂ 0C and Al ^ OjjC, wherein the alumina mixture is melted with a carbon-containing substance and the molten product is rapidly cooled , whereby the process of the invention is carried out by melting the mixture of aluminum oxide or aluminum oxide-rich feedstocks, optionally with further additives, only with a carbon-containing reducing agent or together with a metal reducing agent and then melt rapidly cooled, after which the crushed milled grain is subjected to heat treatment at a temperature between 500 ° C and 1500 ° C for 3 minutes to 24 hours, the material being pre-treated or pre-treated with a surface layer consisting of 1 i cations, fine corundum grains, pigments and / or iron oxides.

Programmed heat treatment, in addition to removing harmful Al ^ C ^, is intended to translate the structure of the abrasive material into a special metastable equilibrium (rapid cooling of the melt leads to extreme imbalance in the structure) and to cure internal stresses and / or abrasions. mesh deformations.

Rapid cooling of the melt, preferably with a cooling time of more than 100 ° / min, is indispensable in order to ensure the formation of a suitable microcrystalline structure which, in addition to the components of the structure, conditions excellent grinding abilities.

E.g. The grinder obtained by slow cooling of the melt in the range of 50 ° C / min contains, in addition to alpha-Al ₂ O _3, both oxycarbide phases Al _a OC and Al ^ O ^ C, and the abrasive capacity is unsatisfactory due to the crystalline crystalline structure.

Adequate cooling of the melt can be effected by pouring it into a mold with defined plate spacing, by casting onto metal or non-metallic molds, or into a salt or metal melt.

Too long annealing or annealing at too high temperatures leads to a predominant equilibrium state in the structure, ie, the disappearance of the Al ₂ 0C phase, which adversely affects the abrasive capacity, as is clearly shown in the examples.

Further improvement of material properties could be achieved by the addition of one or more elements from the group Mg, Ca, Zr, Ti, Si, Cr and / or SE (rare earths) in the range of 0.1 to wt.%.

It was further found that the presence of both oxycarbide phases, namely Al ₂ OC and Al ₂ O 4 C, is advantageous for optimum abrasive ability, with the proportion of Al ₂ OC phase being preferably greater than that of Al 2 O 4 C.

Coke, carbon black, graphite, anthracite, amorphous carbon and / or carbide may be used as the carbon-containing reducing agent.

Al or Mg may also be used as a further reducing agent.

The excellent properties of the grain prepared according to the process of the invention can be further improved by coating which is applied to the coating material before or after annealing. The purpose of the coating is to provide an increased grain surface ₎ , thereby significantly improving the incorporation into the grinding tool.

To determine the grinding properties of the prepared sanders according to the invention of the FEPA (Federation of Europeene des Fabricants de Produits Abrasifs), grain toughness (grain breakdown) and grinding capacity were determined for P36 grain.

To determine the abrasive capacity, the resulting grain fraction 36 was applied to the fabric substrate with adhesive (artificial resin). By grinding on a C45 carbon steel shaft at constant pressure using a band grinding machine, we then determined the abrasive capacity (material per hour unit grinding) in comparison with corundum of eutectic composition containing zirconium oxide and the same cooling conditions of the melt. For an abrasive prepared by casting into an iron mold with a zirconium plate spacing of 5 to 7 mm, we have arbitrarily determined an index of 100.

Grain toughness (grain decay) was determined by the following method: 50 g of grain fraction.36 was filled into a screw-in steel cylinder containing 12 19 mm diameter steel balls with defined sieving analysis. The closed steel cylinder was then rotated for 10 minutes on a roller with a constant number of revolutions, and then a seeding analysis of the grain obtained was performed again. Grain decomposition is obtained from the ratio of medium grain size before and after grinding according to the formula grain decay% medium grain size after grinding .100 medium grain size before grinding

Since the decay of the grain does not depend on the specific properties of the material but also on the shape of the grain, the obtained values were corrected by the grain shape factor.

The invention is illustrated by the following examples.

EXAMPLE 1 (Comparative Example)

A mixture of 150 kg of calcined alumina (0.35 wt.%, 0) and 0.6 kg of carbon in the form of ground coke was melted in an electric arc furnace. The melt was then cast into a mold with 5 to 7 mm plate spacings. The solidified plate-material had a carbon content of 0.045 wt.% And the content _of Na ₂ 0 0,03 wt.%. The material was ground in industry-standard crushing machines and classified into FEPA grinding grain. To cure internal stresses and oxidize any carbides present, the grains were heat treated at 1200 ° C for 10 minutes.

The test results of both prepared annealed and annealed grinding grain as well as comparative zirconium corundum grain are listed in Table 1.

TABLE 1

grain breakdown by weight% grinding ability index eutectic Zr-corundum 38,2 1 00 grain »36 by Example 1 unwanted 48,7 49, 1 for example 36 annealed 41.5 65,0 X-ray fine structural analysis (hereinafter referred to as

RDA) of the material indicated that both the annealed and annealed material existed within the given evidentiary limits exclusively from alpha-Al ₂ 0 ₃ .

In the following cases 2 to 6, we proceeded essentially as in example 1. The changes relate to the use of the reducing agent and the type of annealing treatment (example 7).

EXAMPLE 2

3.5 kg of ground coke was used as the reducing agent. The hardened flat material contained 0.4 wt% C and 0.03 wt% at ₂ 0. The RDA showed that the material was predominantly alpha-Al ₂ 0 ₃ z a slight amount of A1 ₂ OC. We could not prove Al ^ C ^.

EXAMPLE 3

The addition of the reducing agent was 8 kg of ground coke. In the product, we found 1.1 wt% C and less than 0.02 wt% _{2 2} .

Based on RDA, the material is predominantly alphaAl ₂ 0 ₃ and Al ₂ 0C. We further found small quantities of Al ^ O ^ C and ^A1 4 ^c 3PRIMER 4

The carbon additive in the form of ground coke was 10 kg. The product contained 1.4% by weight of C and less than 0.02% by weight of ₂ 0.

The RDA has shown that the material consists predominantly of alpha-Al ₂ O ₃ , Al ₂ OC and Al ^ O ^ C. The Al ^ C ^ content increased significantly from 2 to 3% by weight of the product of Example 3.

EXAMPLE 5

The reduction agent was 16 kg. The product contained 2.4% by weight of C and less than 0.02% by weight of ₂ 0. The melting of the mixture resulted in significant evaporation of aluminum. In addition, the melt was very foaming, so the mixture had to be briquetted to prevent large dusts.

The RDA has shown that the product consists of alpha-Al ^ O; ,, Al ₂ OC and Al, and we have found about 4 to 5 wt.% ^A1 4 ^C 3 '

EXAMPLE 6

A mixture of 150 kg of calcined alumina and 25 kg of carbon in the form of ground coke was also briquetted here. As the briquettes melted, a considerable amount of aluminum evaporated and the melt foamed heavily. The fused product contained 4.5 wt% C, the Na ₂ 0 content was below 0.02 wt%.

The RDA showed that, in addition to alpha-Al ₂ 0 _3, a considerable amount of A1 ₂ OC and Al ^ O ^ C were present. The A1C content was 10% by weight.

EXAMPLE 7

To remove Al ^ C ^, to cure internal stresses, and to adjust the special metastable equilibrium in the structure, we subjected the annealed treatments from Examples 2 to 6 of the obtained graded granulation. The annealing temperatures were 1000 ° C, 1100 ° C, 1200 ° C, 13OO ° C, 1500 ° C and 18OO ° C. The annealing took 3, 5, 10, 20, 40, 60, 120 and 240 min. As the temperature treatment would only lead to the oxidation of the carbide into the possible oxycarbides, it was carried out at annealing time above 10 minutes under a controlled atmosphere (mainly an inert atmosphere). The carbon content after incineration should not be significantly lower than before.

We tested the products as described in the description.

The test results are listed in Table 2.

TABLE 2

Example no. annealing temperature 16 ° C glowing time Min. breakup grain wt.% index abrasive ability 2 unwanted 45,0 49,8 «1 1000 3 45,0 50.2 tt 10 41,3 60,2 tt 20 41,1 65,8 tt 40 40,8 60.3 n 120 42,8 51, 2 tt 1100 3 44,8 54.6 II 10 39,8 65,4 tt 20 42,8 65,1 tl 40 44.5 68,2 II 120 45,8 51, 5 II 240 46,3 50.8 tl 1200 5 40,8 58,4 tt 10 39.3 · 67.5 tl 20 39,8 67.3 11 40 43.5 58.1 II 60 44,9 51,1 11 240 48,0 47.1 tl 1300 3 41,8 59.5 tl 5 39,9 64,5 II 10 41.5 62,7 II 20 43,8 59,1 II 40 4 5.5 50.6 It 240 48.5 46.5 11 1400 3 39,2 63.5 II 10 43.5 58,2 II 60 48,1 46.5 1 » 240 48,2 46,4

<Continued e)

2 1500 3 45,3 52,5 H 5 44,6 52,5 II 20 48,6 44,6 II 60 51,2 41,2 II 240 51, 8 41,0 II 1800 3 4 '/, 2 50.3 II 5 46.5 51, 0 II 10 50.3 47,6 tt 60 55,8 40.1 tl 240 56.1 40,0 3 the cutter is one 41, 2 66,3 II 1000 3 41,3 67.1 II 5 40,8 69,4 H 10 39.1 78,2 11 15 38.5 95,4 II 20 37,8 102,3 II 40 37,8 100,1 11 60 38,9 91,4 II 120 41.5 68,3 II 240 42.3 60.5 II 1100 5 39,4 81,2 II 10 37,8 98.5 II 20 37,2 103,2 It 40 38.5 95,8 II 120 4 3.5 60,2 tl 1200 5 37.6 90,3 tl 10 37,0 100,5 II 20 36,8 105,6 11 40 38,8 88,3 II 120 42.3 61.7 H '1300 3 40.5 78.6 II 5 36,5 104,3 tl 10 35,8 106,2 II 20 37,3 100,8 II 40 39,8 81,4 II 120 42.1 60,2

(continued)

3 1500 3 41,6 88,4 tl 5 40.3 98.1 tl 10 42,8 87,3 II 40 45,8 61.4 • 1 120 52,5 54,3 tl 1800 3 43.5 67.3 II 20 52,5 45,1 II 240 58.3 39.5 1 « devour one 37,4 95,3 4 1000 5 35,4 104,5 II 10 34, 6 106,3 tl 20 34.3 108.5 II 40 35,8 106,3 II 60 38,9 97,2 I » 240 43,0 71,3 tl 1100 3 37,0 100,3 II 5 34.6 107,3 II 10 33,9 118.5 11 20 34.3 109,4 11 60 45,6 60.3 It 1200 3 35,8 102,6 II 5 33,9 114,8 1 « 10 32,4 130.3 It 20 35,9 104,6 II 40 39,9 90.5 II 240 56.1 41,3 II 1300 3 34.5 108.5 II 5 32,6 127.8 II 10 32,8 129.3 II 20 36,3 100,4 II 60 51.9 49,6 II 1500 3 36,5 105,2 II 5 43,2 78.5 II 40 58.6 44,6

(continued)

4 1800 3 44,3 60.5 II 5 51.6 52,3 M 10 60.4 40,6 II 120 60.8 40.3 5 devour one 35,8 105,6 1 » 1000 3 35,2 109.6 • 1 5 34, C 115.5 H 10 33,2 118.5 II 20 33,0 128.6 II 40 34.5 114,0 tl 60 35,8 108.6 tl 240 41.5 85,9 II 1100 3 35.1 108,2 II 5 33.6 118.4 II 10 32.9 129.6 II 20 32.5 136,3 tt 40 36,8 105,2 tt 240 55,6 45,8 II 1200 3 35,2 109.5 tl 5 32,8 132.3 II 10 32,4 145.6 II 20 34.3 117,6 tt 40 38.5 100,6 II 240 56,3 53,0 tt 1300 3 34.6 112.5 11 5 32,6 140.6 II 10 33,8 120,3 II 20 37,2 100,5 II 1 20 54, 6 51,3 11 1500 3 34.8 110.5 It • 5 40,2 98.3 H 20 53.5 55,3 II 240 61.5 40.5 H 1800 3 48,6 61.3 tl 40 61.3 39,8 II 240 60.3 39,4

(continued)

6 devour one 37,0 93,2 tl 1000 3 36,1 104,6 »1 10 34.5 111,4 tl 20 33,8 111,0 tl 40 35,8 105,4 II 60 41,3 90.6 II 240 48,7 65,3 tl 1100 3 35,3 108,4 'I 10 33,4 119.5 It 20 35,6 108,3 II 40 38,2 101,4 II 240 50.2 55,0 tl 1200 3 34.8 112,3 It 5 33.5 118.4 • 1 10 33,2 118.6 II 20 38.5 103,6 tl 240 55,4 48,3 It 1300 3 34.2 117,3 II 5 34.0 119,2 II 10 35,4 109.6 tl 20 40.3 98.4 1 « 60 48,3 61, 4 n 1500 3 39,2 100,8 11 5 40,0 96.4 II 40 60.5 44,6 II 240 71,0 28,0 II 1800 3 51.5 50.6 II 40 68,3 38,7 II 240 72.3 28,3 The RDA of annealed products is showed that e.g. by incandescent processing 10 minutes at 1200 ° C we did not could do more- to say Al ^ C ^. At there was lower temperatures it takes time

annealing correspondingly longer, at higher temperatures correspondingly shorter. Along with the oxidation of carbides, the Al ₂ 0C phase fraction also changed. It decreased slightly in favor of the Al4θ4 C phase ·

EXAMPLE 8 (Comparative Example)

A mixture of 150 kg of calcined alumina (0.35 wt% on ₂ 0) of 1.5 kg of MgO and 0.6 kg of ground coke was melted as in Example 1 in an electric arc furnace. The melt was then poured into a mold with 5 to 7 mm plate spacings. The cured material had a carbon content of 0.05% by weight, 1.03% by weight of MgO and 0.03% by weight of ₂ 0. It was ground, graded and annealed at 1200 ° C for 10 minutes. The grain properties of P 36 grain (FEPA standard) were tested as indicated in the description.

Table 3 lists the test results.

TABLE 3

Decomposition of grain by weight% of grain P 36 according to Example 8 non-calcined single grain P 36 of Example 8 annealed

45,8

40,2 index of grinding ability

55,8, 3

RDA has shown that this material consists of alphaAl ₂ 0 ₃ and MgO

Al ₂ 0 ₃

There was no significant change in the phase relations during annealing.

In the following Examples 9 to 15, we essentially proceeded as in Examples 1 and 8. The changes relate to the addition of the reducing agent, the addition of MgO and to the type of annealing treatment described in example 16.

EXAMPLE 9

A mixture of 150 kg of calcined alumina, 1.5 kg of MgO and 6 kg of carbon in the form of ground coke was melted in an electric arc furnace. The solidified product contained 0.8% by weight of C, 1.08% by weight of MgO and less than 0.02% by weight of ₂ 0. Based on RDA, there was a material of alpha-Al ₂ 0 ₃ and MgO compounds. 13 Al ₂ 0 ₃ , Mg-Al-0 and Al ₂ 0C. Al ^ C ^ content was below the limit of proof

EXAMPLE 10

150 kg of calcined alumina, 1.5 kg of MgO and 13 kg of ground coke were mixed well, briquetted and melted in an electric arc furnace. The product contained 2.0% by weight of C,

1.1 wt% MgO and less than 0.02 wt% Na ^ O. RDA has shown that the composition of this product is predominantly alpha-Al ₂ 0 ₃ , MgO.

Al ₂ 0 ₃ , A1 ₂ OC, AljjO ^ C and Al ^ C ^, the A1C3 content being 3 to 4% by weight.

EXAMPLE 11

Briquetted mixture of 150 kg of calcined alumina,

1.5 kg of MgO and 20 kg of ground coke were melted in an electric arc furnace. The solidified product contained in the mold

3.1% by weight of C, 1.1% by weight of MgO and less than 0.02% by weight of ₂ 0.

RDA showed alpha-Al ₂ 0 ₃ , MgO phases. 13 Al ₂ 0 ₃ , Al ₂ 0C, Al ^ O ^ C and Al ^ C ^, the Al ^ C ^ content being% by weight.

EXAMPLE 12

Mixture of 150 kg calcined alumina, 3 kg MgO and

0.6 kg of ground coke was melted and poured as described in Example 1. The product contained 0.05 wt% C, 1.95 wt% MgO and 0.03 wt% ₂ 0.

RDA has been shown to be the dominant phases of alpha-Al ₂ 0 ₃ and MgO. 13 Al ₂ 0 ₃ . In addition, Mg-Al-0 was found and carbides could not be determined.

EXAMPLE 13

150 kg of calcined alumina, 3 kg of MgO and 13 kg of ground coke were mixed and the mixture was briquetted. After melting and casting into the mold, we were given a product containing

1.96 wt% C, 2.04 wt% MgO and less than 0.02 wt% at ₂ 0.

According to the RDA, there was an alpha-Al ₂ 0 _{3 material} , MgO. 13 Al ₂ 0 ₃ , Al ₂ 0C, Al ^ OjjC and 4 to 5 wt% Al ^ C ^.

EXAMPLE 14

150 kg of calcined alumina were mixed well with 5.4 kg of MgO and 0.6 kg of carbon (ground coke) and placed in an electric arc furnace. The melt was poured into a mold with 5 to 7 mm plate spacings. The cured product contained 0.045 wt% C, 3.48 wt% MgO and 0.04 wt% Na ₂ 0.

REJA indicated that the product consisted of alphaAl ₂ 0 ₃ , MgO. 13 Al ₂ 0 ₃ , some Mg-Al-0 and spinel.

EXAMPLE 15

A mixture of 150 kg of calcined alumina, 5.4 kg of MgO and 13 kg of ground coke was briquetted and melted and poured as in Example 1. The product contained 1.94% by weight of C,

3.55 wt% MgO and less than 0.02 wt% at ₂ 0. Based on RDA, there was a material made of alpha-Al ₂ 0 ₃ , MgO. 13 Al ₂ 0 ₃ , Mg-Al-0 and oxycarbides Al ₂ OC and Al ^ O ^ C. In addition, there were 5 wt.% Al ^ C ^.

EXAMPLE 16

Analogous to that described in Example 7, the graded granules of Examples 9 to 15 were subjected to annealing treatment. The materials of Examples 12 and 14 were annealed each time for only 10 min. at 1200 ° C because they did not require the oxidation of carbides. All other products were grilled again at different temperatures for a long time.

The test results of P36 (FEPA) granulations obtained from Examples 9 to 15 are listed in Table 4.

TABLE.4 Example no. annealing temoature C incandescent time grain decomposition.% by weight index abrasive ability 9 devour one 42,9 65,3 It 1000 3 42,8 64,5 II 5 39.5 89,3 II 10 36,8 109,3 II 20 35,2 111,5 tl 40 34.8 113,2 II 60 37.5 105,3 II 120 39.6 92.5 II 240 40,2 90.6 II 1100 3 42.5 65,3 »1 5 38.6 96.4 II 10 35,2 115,6 It 20 34.5 120,1 II 40 36,3 112,3 II 60 38.5 100,3 II 240 44,4 68,3 II 1200 3 41,6 77,3 II 5 37,8 103,2 II 10 34.0 125,4 II 20 33,3 131,2 tl 40 38,4 101,6 II 60 41.5 81,3 n 1300 3 40,2 99.5 11 5 35,3 113,2 II 10 33.6 129.7 II 20 37.5 102,6

2C (continued)

9 1300 40 40.3 91,5 II 60 43,1 70.6 II 240 44,6 59,8 II 1500 3 38,4 100,5 II 5 38.6 100,3 II 10 39.3 95,4 II 20 41,2 80,3 II 60 44,6 60.5 II 1800 3 40.3 91, 2 tl 5 41.5 80.4 II 10 42.6 64,3 II 240 45,3 55,0 10 a rifle one 37.5 102,3 II 1000 3 36,7 109,9 II 5 35,2 118.6 It 10 33,0 132.6 II 20 32,3 150.5 11 40 32.5 150.5 II 60 34.7 118.6 II 120 40,8 100,3 It 1100 3 35,0 117,6 tt 5 33,3 129.4 It 10 32,0 151,3 tt 20 31.0 153,6 It 40 34.1 122.5 tt 60 36,3 113,1 tt 120 38,3 100,6 tt 1200 3 35.1 118.3 tl 5 32,0 154.6 II 10 31,4 160,2 tt 20 31.0 171, 3 tt 40 35,3 120.6 tl 120 44,6 67.5

2ΐ (continued)

10 1300 3 34.8 114.6 «1 5 32,0 151,8 η 10 32,3 148.5 ι » 20 32,8 138.4 I » 40 36,5 110,6 tl 60 42.6 67.3 tl 1500 3 34.5 115,3 II 5 37,2 108.5 II 40 48,3 51,3 II 240 54,1 45,8 II 1800 3 36,3 111,5 » 5 44,3 70,8 »1 20 50.4 50.6 tl 120 54,8 45,6 11 nezarJend 36,4 108,4 II 1000 3 36,4 110,6 II 5 34.8 120.5 II 10 33,2 128,4 rt 20 33,0 130.6 II 40 38.5 105,4 II 60 39,8 100,6 n 240 41,3 90,2 n 1100 3 35,2 117,4 II 5 33,0 126.5 II 10 32,8 140.8 It 20 32.1 145.6 II 40 35,8 115,3 II 60 39,9 100,3 II 240 48,6 50.3 II 1200 3 35,3 117,9 II • 5 32,8 138.8 II 10 32,0 159.6 n 20 32,3 141.8 It 40 39.6 102,5 II 60 45,2 80,3

2 (Continued) »»

11 1300 3 33,8 125,6 H 5 32,4 141.5 II 10 32,8 137,9 II 20 37,0 108.5 II 40 43.5 76,2 II 120 55,3 48,6 II 1500 3 34.2 118.5 II 5 38.6 101,2 II 20 48,3 50.6 II 240 61, 3 42.3 II 1800 3 41,6 85.7 II 10 51,3 50.6 II 240 66,8 42.0 12 unroasted® 43,2 65,8 II 1200 10 41,1 68.5 13 devour one 38,7 100,3 II 1000 3 38.5 100,4 II 10 35,8 116.5 II 20 34.3 128,4 II 40 34.0 130.0 II 60 36,0 110,2 II 1 20 38,2 101, 4 II 1100 3 36,7 108,4 II 5 35,3 119.6 M 10 34.7 125,4 N 20 33,9 135.6 II 40 35,0 121.6 in 60 38,4 101,4 »1 240 50.3 67.6 II 1200 3 36,3 112,3 H 5 34.5 121, 6 II 1 0 33.5 137.6 »1 20 33,4 145,2 II 40 37,8 105,6 II 60 40,2 100,4 II 240 49.5 54,3

j (continued)

13 1300 3 35,0 120,3 N 5 33,8 130,2 H 10 33,2 141, 6 II 20 37.6 108,4 II 60 47,3 65,2 n 1500 3 35,0 117,6 II 5 37.6 109,3 II 10 46.5 61.3 II 40 53,7 50.3 II 1800 3 44,3 73.5 II 10 49,3 58.6 II 60 65,4 40.3 14 devour one 46,8 61, 4 II 1200 10 43,3 75,6 15 devour one 40.3 90,8 It 3 38,7 95,3 II 10 36,8 109,8 II 20 34.8 115,6 II 40 34.5 118.6 f « 60 38.5 98.3 II 240 46,3 63,4 1 * 1100 3 38,1 102,4 II 5 36,8 108,9 II 10 35,3 118.4 It 20 34.0 128.5 II 40 36,3 109,4 II 60 40,2 93,5 tl 240 48.5 53,9 n 1200 3 35,8 115,9 II 5 35,7 120.6 II 10 33.5 130,2 II • 20 33,9 135.6 II 40 39.3 90,4 H 1300 3 34.0 128,4 II 5 33.6 137,4 II 10 35,2 121,3 II 20 38,4 100,8 H 120 54,3 50.0

(continued)

1500 3 34.8 115,2 5 39,2 90,0 10 44,6 71.5 40 54,3 50.6 240 63,4 42.5 1800 3 46.5 59,3 10 49,1 55,3 20 57,3 50.2 240 67,8 39.5

The RDA performed on annealed materials showed that with sufficiently annealed materials (eg 10 min at 1200 ° C), we could no longer determine Al ^ C ^ · In addition, the Al ^ O ^ phase appeared slightly more strongly. C, with the Al ^ OC phase fraction slightly smaller. A longer annealing process, especially at higher temperatures (above 1200 ° C), also showed a decrease in the Mg-Al-0 phase (if initially present).

EXAMPLE 17

A mixture of 150 kg of calcined alumina (0.35 wt% on ₂ 0) of 3.1 kg of zirconium oxide and 7 kg of carbon in the form of ground coke was melted in an electric arc furnace as described in Example 1. The melt was poured into a mold with plate spacing of 5 to 7 mm. The solidified product contained 0.91% by weight of C and

52.06 wt% Zr0 ₂ . The Na content _of 0 was below 0.02% by weight. The material was ground and graded, and the grain toughness and grinding ability index before and after annealing (10 min at 1200 ° C) were determined for P36 grain (FEPA standard). Because zirconium in the product was predominantly in the form of carbide or. of oxycarbide and suboxide, we had to partially perform the annealing treatment under an inert atmosphere, in order to avoid its excessive oxidation.

The RDA showed that the product was made up of alphaAl ₂ 0 ₃ and Al ₂ OC and zirconium carbide, suboxides and Al ^ C ^ could not be demonstrated. During annealing, except for the slight appearance of the Al ^ O ^ C phase, there was no significant change in the structure.

The results are in Table 5.

TABLE 5 grinder P36; non-annealed grinder P36, annealed grain decomposition by weight%

38,4

36,3 grinding ability index

101,6

110,4

EXAMPLE 18

150 kg of calcined alumina, 3 kg of SE oxide and 7 kg of ground coke were mixed and melted in an electric arc furnace. The melt was poured into a mold with plate spacings of 5 to 7. The solidified product contained 0.88% by weight of C, 2.1% by weight of SE-oxide and less than 0.02% by weight of ₂ 0. It was crushed, graded and in the P36 grain before and after annealing (10 min. at 1200 ° C) again determined grain decay and grinding ability index.

Based on the RDA, there was an unwanted product of alpha-Al ₂ 0 ₃ , Al ₂ OC and a phase that could not be further defined. We have not determined AljjC ^. Some Al ^ O ^ C was formed during annealing.

The results are presented in Table 6.

TABLE 6 grain breakdown wt% grinding ability index grinder P37 unbaked

39,8

92.5 grinder P36 annealed

35,4

115,6

EXAMPLE 19

110 kg of calcined alumina (0.35% by weight at ₂ 0),

1.5 kg of MgO and 28 kg of crushed Al ^ C ^ were mixed well and placed in an electric arc furnace. The melt was cooled rapidly as in Example 1. The product contained 0.83 wt% C, 1.1 wt% MgO and less than 0.02 wt% at ₂ 0. From the P36 grain obtained , before and after annealing (10 min at 1200 ° C), grain decay and abrasion index were determined. The RDA showed that the unroasted grain was composed of alpha-Al ₂ 0 ₃ , MgO. 13 Al ₂ 0 ₃ , Mg-Al-0 and Al ₂ 0C. On annealing, the Mg-Al-0 phase decreased slightly while slightly Al ^ O ^ C appeared.

Table 7 shows the test results.

TABLE 7 grinder P36 grinder P36 non-grilled single annealed grain decomposition%, 8

33,9 index of grinding ability

75,6

127.8

EXAMPLE 20

The mixture consisting of 135 kg of calcined alumina (0.35 wt% on ₂ 0), 8 kg of Aluminum meal, 1.8 kg of Mggrain and 7 kg of carbon in the form of ground coke was melted and cooled rapidly. The product contained 2,01% by weight

MgO, 1.89 wt% C and less than 0.02 wt% at ₂ 0. The product was ground and graded, and the grain breakdown and index were determined at P36 before and after annealing (10 min at 1200 ° C). grinding abilities. The RDA of the undesired product showed alphaAl ₂ 0 ₃ »MgO. 13 Al ₂ 0 ₃ , Al _a OC, Al ^ O ^ C and about 1 to 2 wt% Al ^ C ^ - Al ^ C ^ disappeared upon annealing. The ratio of Al ₂ 0C to Al ^ OjjC has shifted slightly in favor of Al ^ O ^ C. The test results are listed in Table 8.

TABLE 8

Grain breakdown grinding mass index% _ ability grinder P36 unroasted 39.5 95.6 grinder P36 annealed

34.5

120.6

8 EXAMPLE 21

According to Example 10, the P36 abrasive grain obtained was equipped with a coating to improve the bonding to the basic bond (artificial resin) on the abrasive belt. We made different types of coatings, with the following coatings:

after wetting the abrasive grain with a mediator of adhesion (water glass, colloidal.Si0 ₂ , starch, etc.), a real coating agent was applied in a forced mixer. Care must be taken to ensure that the grain is fully coated. We then burned the grains to achieve a surface structure with large surfaces and to achieve a good adhesion of the coating. If the coating required a firing temperature of about 1200 ° C, it was annealed and burned in one working step. At lower firing temperatures, the grains were annealed before coating.

Types of coatings

BROKER OPREMA MEANS FOR PAINTING TEMPERATURE Brandy 19.1. water glass Fe ₂ 0 ₃ 800 ° C 19-2. colloidal Si0 ₂ CaO 1200 ° C 19.3. colloidal SiO ₂ Zr0 ₂ . Si0 ₂ 1200 ° C 19.4. starch nerve 1200 ° C Table 9 presents the grain decay values

and the indexes of the grinding ability of the coated sanders thus prepared. On a case-by-case basis, the increased toughness of the grain results from the clogging of the cracks that have emerged from the crushing due to penetration of the adhesive.

9TABLE 9

grain breakdown by weight% grinding ability index grinder by 19.1. 32,4 175.6 grinder P ° 19.2. 30.5 185,3 grinder PO 19.3. 30,1 191,1 grinder PO 19.4. 32,0 174,8 From results individual cases is clearly evident

that the process according to the invention provides a grinder characterized by exceptional grain toughness and grinding ability. These last-- '\ -.

ness is reflected in a small grain breakdown and a high index of grinding ability.

-30Best Way to Economically Utilize Invention

150 kg of calcined alumina, 1.5 kg of MgO and 13 kg of ground coke were mixed well, briquetteed and melted in an electric arc furnace at 1200 ° C for 20 minutes. The product contained 2.0 wt.% C, 1.1 wt. % MgO and less than 0.02 wt. % Na ^ O. X-ray fine-structure analysis showed that the composition of this product was predominantly alpha-A ^ Og, MgO. 13 Al ^ O ^, A ^ OC, Al ^ O ^ C and Al ^ C ^, the Al ^ C ^ content being 3 to 4% by weight.

For

TREIBACHER CHEMISCHE WERKE AG:

Claims (10)

PATENT APPLICATIONS 1. A process for the preparation of alpha-Al ₂ 0 ₃ based abrasives and at least one of the two aluminum oxycarbides Al ₂ OC and Al ^ O ^ C, wherein the alumina mixture is ground with a carbon-containing substance and the molten product is rapidly cooled, characterized in that the mixture of aluminum oxide or aluminum oxide-rich feedstocks, optionally with further additives, is melted only with a carbon-containing reducing agent or together with a metal-reducing agent and then cooled rapidly, then from the solidified melt. the crushed grinding grain is subjected to a heat treatment at a temperature of between 5 0 0 C and 1500 ° C for 3 minutes to 24 hours, with the material being pre-or after the heat treatment optionally provided with a surface layer consisting of silicates, fine corundum grains, pigments and / or iron oxides. Method according to claim 1, characterized in that the crushed milled grain is subjected to heat treatment at a temperature between 1000 and 1300 ° C for 5 to 60 minutes. Process according to claim 1 or 2, characterized in that one or more elements from the group of magnesium, calcium, zirconium, titanium, silicon, chromium and / or rare earths in the range of 0.1 to 10% by weight are used as further additives. , preferably 0.5 to 5% by weight. 3Χ Process according to one of Claims 1 to 3, characterized in that coke, carbon black, graphite, anthracite and / or amorphous carbon are used for reduction. Process according to one of Claims 1 to 3, characterized in that a carbide, preferably Al 2 -C 4, is used as the reducing agent. Process according to one of Claims 1 to 3, characterized in that aluminum or magnesium is used as the reducing agent in addition to carbon or carbon-containing compounds. Method according to one of Claims 1 to 6, characterized in that rapid cooling of the melt is achieved by pouring it onto metal or non-metallic molds or between metal or non-metallic cooling plates. Method according to one of Claims 1 to 7, characterized in that the melt is cooled at a rate of more than 100 ° C / min. Abrasive obtained by the process according to any one of claims 1 to 8, characterized in that the carbon content of the aluminum oxycarbide and, if applicable, other carbides has a content of between 0.1 and 6.6% by weight, preferably between 1 and 3 wt.%. 10. Abrasive obtained by the method according to any one of claims 1 to 8, characterized in that its Al ^ C ^ content is less than 5% and preferably less than 0.5%.