DE1592142A1 - Process for making alpha aluminum oxide abrasive grain - Google Patents

Description

dg apt

Method of manufacture; of Ot-aluminum oxide abrasive grain

The most commonly used abrasive in practice CX-Alurniniumoxyd ^ is used for precision grinding wheels, produced by :, dai3 burned bauxite ores in electric arc furnace to be melted down. Of the Electricity demand is relatively high. Xm small size will Aluminum oxide abrasive grain is also produced by means of tempering. For this, lower temperatures are required than for melting, however, winter clay is not suitable for Prazifjionnschleifen but only for the (irobsohleifen, how to clean (i

BATH

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The invention now relates to the production of abrasive grain from Ct aluminum oxide with better grinding properties, especially with regard to the application for precision grinding, as alurainium oxide, the was produced by, for example, melting or sintering. Particularly high yields are achieved according to the invention and a wide range of grain sizes; no melting or sintering is required *

Mach the inventive method are individual <X-Alumina crystals from a solution of a molten Hold flux and evaporation of the flux ^ e ^. It does this by heating a granulate of one Mixture of aluminum oxide ores such as bauxite and a, normally solid flux for aluminum dioxide at a temperature preferably between about 1 "1" and 1 100 C. The flux melts and the aluminum oxide dissolves in this melt. Eventually it becomes a considerable one Part of the flux evaporated to precipitate the aluminum oxide dissolved therein. The rest of the flux with the Aluminum oxide is cooled, one obtains a solidification Mass of impurities containing flux and precipitated Aluininiumoxyd-ßinkri stallen, surprising liesulbate is achieved when in the presence of water vapor e.g. in an ul'en with an "steam containing atmosphere -" - is heated.

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It is preferred to have a small amount of seed crystals vonft aluminum oxide in the starting mixture of bauxite and flux-to be introduced} at least a considerable amount The proportion of seed crystals should have a grain size essentially below approx. 2.38 mm (-Ö mesh), however, they must not be so thin that they dissolve in the flux melt. The crystals are essentially larger than the grain size of the Bauxite. It is not absolutely necessary to use seed crystals, but if seed crystals are used, see above the dissolved aluminum oxide crystallizes from the flux melt at this on. In addition, however, new crystals are also formed by precipitation.

The flux preferably has a melting point above about 500 and l4üO °, in particular to about HOO ⁰ U. It is therefore considerably lower than the melting point of alumina, the 20IiU is ⁰ U. The flux preferably contains a crystallization promoter or mineralizer in the form of inorganic compounds of sulfur, boron, lead or halogens. The aluminum oxide crystals precipitated in this way are single crystals and represent an abrasive grain with microscopic pores. At least the main part has a grain size of not much larger than approx. but not -we me in the sense of the, abrasives industry.

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ORIGINAL

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The formation of the plates varies with the composition of the heating mass and the conditions below Maybe the crystals have been formed, it's surprising This new abrasive grain has better properties in precision grinding shows alumina produced by smelting in the normal way. The precision grinding wheels made from this material with glass or silicate bond, as is common practice, show surprisingly improved properties versus those of fused clay or sintered clay β It is believed that one of the reasons for the improved grinding properties of the product according to the invention compared to fused clay or sintered clay lies in the fact that they are relative in relation to these are free from mechanical stresses and loads, mechanical and thermal stresses occur with these known ones "Product .. by cooling and during the granulation process of the quenched melt.

The largest part, for example, 90: b, the precipitated crystals have a size of a grain of between about 2 and 0,0b ') ö mm (IBO mm to b mesh) preferably 0,1'i to 1.7 (100 to 10 mesh).

For economic reasons, the concentration of aluminum oxide ores in the Ausgan;? .Sgemisch voraugavieiRO not less than about Λ weight Jj, not insbcsondei'e

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be less than H-O or k $% . Good crystals can be obtained down to a concentration of ψ / ο aluminum oxide ore. The higher the concentration of iron in the starting mixture, the better. The results are obtained with a concentration of iron between 65 and 70 wt Ore concentration without the inclusion of seed crystals is given by the solubility in the flux.

A preferred flux contains cryolite or lead oxide or ilmenite or a mixture of iron oxide and titanium

oxyrl; however, excellent results are achieved with all of these 3 substances. But you can also use one or more of the following ¹ substances as a flux: alkali metal, aluminum, lead, boron, alkali, potassium aluminum fluoride, iron or alkali sulfates, fluoroborates, aluminates, borates, boron oxide, manganese oxide, Titanium oxide, iron oxide, chromium oxide, borax, manganese chloride, zirconium oxychloride, soda, lithium carbonate, alkali silicofluoride, lead silicates «,

Generally speaking, any inorganic flux can be used in the flux Be a substance which is inert to aluminum oxide; lot and at a temperature well below the melting point of alum-iniuffloxyd melts, provided that

8AD OWGINAL

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In this substance aluminum oxide dissolves and it dissolves at a temperature significantly higher than the melting temperature, however, significantly lower than the melting point of the aluminum oxide volatilize loudly, each boiling point the flux should be lower than the melting point of aluminum oxide.

In a G-emic of llraenit, cryolite and lead oxide, the proportions may fluctuate widely "Excellent results are obtained at about the same i-iengen of cryolite and lead oxide with a lesser proportion of llraenit, for example ₉ about 'j> / ^ the amount of either cryolite or ßleioxydo The lead of the lead oxide and the fluorine of the cryolite act as mineralizers, the substances themselves serve as!

It was found that the presence of both BIeials also fluorine compounds with optimal crystal sizes of aluminum oxide lead. Are all lead compounds as lead oxide is applied, the crystal size is less; only fluorine compounds are used, x \ rie cryolite, thus the crystals become larger than when only lead oxide is used, but they are still smaller than when only lead oxide is used one (Yeinish of lead oxide and cryolite.

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The aluminum ores j processed in this way are bauxites, generally burned, of the most diverse origins, but other materials containing aluminum oxide such as high alumina Clays, chemically processed bauxite, e.g. alumina from Bayer-W -, finely divided aluminum oxide waste, such as dust from gas cleaning, is used. All these starting materials are to be found in the following under the term "aluminum oxide ore" is understood,

: The unit of the aluminum oxide ore - in contrast to agglomerates - is generally 2 ^ / U or less, in particular up to * y / u .. U The largest part of the particles as they are in nature · from:.: .. _s liegeii- _tt: a in i'Orm of aggregates or Ägglomeraten ago, the Big zwisehen lumps and down to the particle size schwanicto It is vränschenswert to crush das'Erz, eg in a Ball mill to reduce the larger agglomerates in order to obtain a mineral material of essentially uniform size. If flux in the form of a powder is then added to the ground ore and carefully mixed, this intimate mixture is particularly suitable for The process according to the invention. Water is then added before or during the crushing and wiping. Ore and fluids are ground in an aqueous dilution and mixed. / ₀ Solids -

0 0 9844/1348

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but also diluted with, for example, 5> S i''eststoi'i'en, depending on the amount of water used. The mixture is dried and the cake granulated. This (iranulate is then either heated or, if the proportion of undersize or oversize of the granulate is too large, pelletized and these pellets are then granulated under controlled conditions in order to achieve a granulate of uniform size with as little undersize and oversize as possible, e.g. an ivorn fraction between 1.2 - 4 mm (5 to Io mesh) without tails.

It was found to be there to some extent the smaller the crystal sizes obtained in the case of aluminum oxide the smaller the particle size of the granules or pellets subjected to the process according to the invention be, were. The U-size of the U-ranulate can vary over wide areas, but it is preferred dart the main part is not larger than approx. 12 ,? or 25.4 mm (1 or 2 mesh), so. about Iy mm (3/4 inch), and not much finer than about υ, Β4 or 1.2 mm (Io or 20 mesh). On the other hand, the grain size of the granules made of aluminum oxide ore and JVlura mean lower, e.g. about υ, 30 or 0.42 mm (40 or '5µ mesh) if smaller crystal sizes of the aluminum oxide is sought. Outstanding results are achieved by mannit eiiior granulate size between approx

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BATH ORIGINAL

1.2 to ^ ram (5 Dis Ib or 2ü mesh).

This treatment according to the invention hate to be applied of u-ranulate from an intimate; en u-emic of aluminum oxyder ore and flux has a considerably larger one Grain size as the particle size of the ore and the Flux.

The grain size information touches on the in "ώΙΐΐΚϋΙχ'ΊΚ

OE iiliiUOHIuliirJJJATlUijD ll'ö-jyij ABliÄSI \ Γϋί GHAM SIZüS, pü du shed by the united btates Department of Uornmerce, iieprint of October, l ^ bO "recommended specification,

The aluminum oxide seed crystals used can have been produced by precipitation or melting. It is preferred to incorporate them in the oil or in the pellets made from oil and flux, adding to the outlet from the oil and. Fluxes are added particles, for example in "the aqueous Aufschiäminung 'of bauxite, and fluxes zumindeßt the ilauptteil the /.eimkristalle should be coarser (at least about 3 or k times as rough) than the Teilchengrdsse of alumina tiirzes" 6 IE are thus not completely dissolved in the flux during the inhibition and are present in the melt as crystals, even if the particles of the aluminum

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Oxyd ore are already dissolved * The dissolved aluminum oxide then separates from the melt on the seed crystals away. Single crystals are formed by grain growth. At least the majority of the seed crystals should be essentially smaller than 2.3 µm (δ mesh), otherwise it will be the size of the finished crystals too large, i.e. the seed crystals should not be too large, so that the main part of the finished product is coarser than approx. 2.38 mm (b mesh) *

The grain size of the granules of aluminum oxide ore and flux is much larger than that of the vein crystals, compared to these, they are also very porous.

The preferred size range of the seed crystals is between 3-1 times (in particular 5 or 6 times) the particle size of the alurainium oxide ore in the starting material and about 3 or k. Part (preferably 8th or y. L'eil) of the desired size of the finished aluminum oxide crystals,

i stalls with approx. 30 / rev lead to excellent results. The optimal (j size of the seed crystals ultimately depends on the desired number of crystals, the particle size the alumina ores and the ore concentration in the starting material. If the ore concentration is low, so the crystal growth on the nuclei is so lower, so that

larger seed crystals can be used without this makes the finished product too coarse. The (ireaus der

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Seed crystals thus represent a possibility of the crystal size of the aluminum oxide abrasive grain. When heated, the fluorine content of the granulate melts and the ore particles dissolve in this melt, the seed crystals remain solid. Us is therefore evident the precipitated crystals or formed in each i ^J eliets or may G-ranulat are smaller than the original pellets or üranulat and that lie in lvrist'allgrösse gexcLssen mass of the hawser of the above-ranulats itself depends. .

The temperature can increase rapidly or gradually Maximum temperature increased. It should also be a considerable amount of flux is evaporated. : ^ d the temperature over certain Dtufen during a certain B * eriod increased, the load time can be at the maximum The temperature should be low, the lower the entire heating-up time is, deBto better, as this way the process is more economical However, the optimal time depends essentially in each case on the structure of the starting material.

Ke; is preferred dai3 the temperature is raised slowly, for example üoer * ca 2 to Ju ^ h, to a temperature above the melting point of the kapp i ^il luidmittelüj z.ß. lüüü to 13OU ⁰ G. This melts the flux and leaves the aluminum oxide in the

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Melt dissolved. Then the temperature is set to the maximum

• at
between approx. 1350 and 16 (Ju G - a period of time - zoB. 2 to 2 ^ h, preferably 2 to 15 h If the temperature increase until the flux melts is chosen slowly, then a dissolution of the seed crystals in the melt is generally avoided. When the maximum temperature is reached, the evaporation of the flux prevents the seed crystals from dissolving. A sufficient amount is required The amount of flux removed by evaporation depends on the maximum temperature, the length of the reaction time, the composition of the flux and the proportion used in the starting material Flux off.

Rapid cooling is desirable, e.g. by quickly cooling the furnace to room temperature. This can take 1 to 3 hours take advantage of. Slow cooling is uneconomical; · In some cases this also leads to undue crystal growth. ■

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After solidification, a glassy base material is obtained with impurities, especially from the ore, and residual flux. This is made up of the embedded aluminum oxide crystals by treating with mineral acids such as sulfur, acid and then with a strong base such as caustic soda or vice versa removed.

It was found that the presence of water vapor during heating leads to outstanding results “water vapor can be introduced into a gas-heated furnace in the usual way, for example by adding steam-containing combustion gases be introduced together with the granules of aluminum oxide and flux. The mixture is in a Atmosphere heated by combustion gases. The amount of water vapor is not particularly important, but you can do without it DariiDf good results can be achieved.

Ausganpspemisch: burnt bauxite (provenance Surinam) k ^l j weight .- ^, ITrnenite 15 u-ew .- ^, cryolite 20 wt .- #, ßieioxyd 20 wt .

The GemiBCh was ground with equal parts of water in a ball mill 2 ^L l · h. The particle size of the main portion of the ore was a maximum of 5 / U · 5 wt

, jonmelztunerde _s uorn ^ roiwe approx. 6 '^ u { zvxj iw: -.: \\\)

BATH ORIGINAL

lÄ-32 yo

x \ rurcLe added to the mill and left in it for 5 minutes without any appreciable milling effect. The Aufschlämrüung: was discharged and dried at 15O ⁰ G. The search was broken into and turned to pellets φ IT? now (7 ir.c: _),> V. ■ · ': - ·. 50 mm (2 inch) agglomerated and processed in a granulator to a grain size of 1.20 - 4 min (5 Dis Io aesh).

The Lrranulat was then händiscü on refractory Plexten of aluminum oxide, C-ize 12,7XlUjIUxD Iy ^ ¹ J cm (5x ^ x1 / 0 inch) aufsetragen and this in a BrenngefäJ or Uffel ^, 0 1? Ö cm (7 ")> Height 7, ö cm (3 ¹¹ ) - on top of each other; esta.pelt. Each muffle was placed on round, 12.7 cm thick, refractory plates and now about b hoof finely stacked, and the connection between the refractory plate and The muffle is not tight, but a small space exists so that the i? 'Luü5aiit.tel can escape. The products were now in an atmosphere containing pollutant gases and water vapor; used ^.:

Another type of ufeiisetzens fdnrte to guteii n; however rgebniüsen _o In this jyall v / aren his, auifelii present, the granulate was thus the öi'onatmosptiiire DIRC ^ t aur.genet: ·::. The hrintallentwiclilu-UiA 'utid- die Aarsbcute v; ia ·'u:; of it !, "ή '? Unt.t :!' / ei'U'cndung "the H

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^{The furnace was heated up to "" 1200 0} G at a speed of approx. 50 C / h, then quickly set to 1550 ⁰ U "and held at this temperature for 12 h. The feed was then switched off; the" The furnace could cool down quickly to room temperature. The furnace was cleared out and the process product was removed from the burning plates with the help of a metal spatula the individual aluminum oxide crystals within polycrystalline aluminum oxide aggregates. This urea was removed by treating it with acid and laupe, leaving behind individual crystals of aluminum oxide. This leaching out was achieved in that the product was stirred for 30 minutes in a hot, 24% sulfuric acid solution, washed for 10 minutes with water, then for 30 minutes in a hot,

touched

10 ü-evf. - ^ igen a at ronlauge / and was finally washed for 10 min

and dried /. A batch of 22.7 kg (50 lbs) showed the following Sieve analysis, mesh (12)

1.80 ^ 1.68 mrn 3.55 / * Γ, 41 "mm 5.51g 1.19 ram 5.28 # 0.8 ^ mm 4, ^ 9 / & 0/72 mm 10.82 ^ 0.59 mm 9.6O # 0, ^ - 8 mm • 9.96 ^ 0.3 ^ mm 5,93J ^ 0.25 mm $ 4.10 0.21 mm 0.177 mm 7.32? V 0.1 lb5 mm 0 0 98A4 / 13 ^ 8 BAD ORlGlNAt

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mesh ■

(100) 11.65 / ä Ό, 149 mm

(100) 4.33 # 0.149 mm

99.90%

The specific gravity of 2 pistons of the Korni'rak-tion with 0.3 ^ t-mm (4-6 mesh), with -3 »V? g / ciir determined. Chemical Analysis of these two samples:

Sample O j 09/6 2.99%

ad lüü? i

The material obtained consisted of precipitated, microporous, individual alumina ürlstallen. Of the The main part has a grain size of - essentially between. 2.3ö mm (Örnesh) and 2 mm (10 me.sh). They showed an indigo blue color and a leafy appearance. The micropores were very large in terms of size uniform, the crystals showed no tension.

Sample 1 , 0? Fo 0 .17% 0 , 21 96

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The thus obtained alumina crystals became on Precision grinding wheels 203x12.7x31.75 mm (8xö, 5xl, 25 inch) processed and the grinding properties compared to similarly structured grinding Discs based on fused alumina using the same types of binder. It was found that the grinding performance of the grinding wheels with the inventive Aluminum oxide crystals those with fused alumina were significantly superior.

The energy requirement for heating according to Example 1 was significantly lower than that for melting aluminum

Lead oxide and llmenite are not essential, however Yield and size of the aluminum oxide crystals by their Presence increased.

The seed material is not essential, but it appears have a favorable effect on the grain size and the yield of the end product. There were seed crystals with a size between 7 ^ and 48 / U (200 to 300 mesh) examined. Received optimal results one with a grain size around 65 / U (220 mesh). The pelletizing of the starting mixture is obviously not essential with regard to the chemical and physical processes in the Production of the sole grain according to the method according to the invention, vertoeaoert; however "the working conditions are essential

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and represents a preferred embodiment of the invention Procedure.

The exhaust gas from the furnace contained substantial amounts of ji'luor and lead »Even so, the flux melted every particle and in it the ore had dissolved, it did not come to pass a melting together of the whole hate.

Also a starting mixture of 80% bauxite and 2O> 6 k'ryolite led to comparable results, but the yield and the grain size of the crystals were lower.

When the maximum temperature, 135 ^ C was, so the grain size was less than a maximum of 155o Üfentemperatur ⁰ G.

Example 2 to 4- ■

Example 1 was repeated with a Ausgangegemisch from 90/0 bauxite and 10% cryolite (Example 2), 90 # bauxite and 10 $ Kaliuüifluorborat (Example 3) and 95 / ^ bauxite and ^L j / a sodium sulfide (Example 4 x). 5 u-ew _e -> b (7th alumina single crystals with a size of around opyu (22u mesh) were used as seed crystals. The granules of bauxite and flux, approx. 2 min (10 mesh), were used for 6 h Maintained 1550 degrees above sea level.

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In a modification of Examples 2 to 4, as

the following substances on £: extfandt: cryolite, borax, __ sodium chloride, "G-aleiuiafluorid, lithium fluoride, iJatriumfluorid, Boric acid, lead oxide. The crystal size was smaller as. in Example 1 and the yield is not quite as high.

.Boir .p iel ';

.for game 1 was repeated using 'jO / o iVonerae aas the "Bayer process, that is, with a relatively pure aluminum oxide, and 13» 5 / ilmenite, 18;? & cryolite and l j lead oxide The results were substantially the same. of example 1.

Example 6

Example 1 was repeated, but this time the uranulate made of aluminum oxide ore and fuel, heated to the maximum temperature and then at this temperature for 12 hours "bzvf. 2 ^ h held. The results are the same as those of the example fadeable.

Instead of sulfuric acid as a strong mineral acid to remove the glass around it, you can also use hydrochloric acid or Use plus & acid. Instead of Watrionlau ^ e one can also Potash, LitMumhydroxyd, trisodium phosphate and the like. As use strong base.

0 0 9 8 4 4/1348 claims

Claims (1)

'ΕΛ TA'DJ bPß ü U Hi 1. Process for the production of behieir grain from aluminum Oxyd-ivri stalls by precipitating out of a solution, which admittedly denies that an emisk of aluminum oxide ore and a normally solid flux can be heated until the flux has melted and the aluminum oxide dissolves in this melt, then iveiter heated to .Abdampfen of substantially iien ^ s of ./lui-Jmittels which cools ivristailmasse 'and finally _f; ; lasif; e round mass removed from the aluminum oxide crystals. 2. The method according to claim 1, characterized in that g e ic e η η - draws that one is heated to a temperature between and 10Ou ^{0 C.} 3.. Method according to Ansoru-ch 1 or 2, characterized in that κ ^e k 0 ^ is heated in ü-epenwart by water vapor. ^ i-. \ / Ei'i'ahren according to claim 1 to '}, thereby ge ic e η η ζ ei c h.-n e t that bauxite is used as an aluminum oxide ore. . ■■■ '-. 0098AA / 1 3A8 1.592.U2 IA-32 ybo 5. The method according to claim 1 to 4, characterized ge κ e no ζ eic h. η e 't, _ dad to as i / luiirnibbel such zwisonen with an N ochmelzpunKt ¹ and 1400 Juo υ applied. ö.. ^{Process according to claim 1} , characterized in that a fluid containing a mineralizer in an inorganic compound of iron, boron, lead or halogens is terminated. V. The method according to claim 1 to ü, whereby μ e κ e η η - ζ -, i without b, da.J. ina.n as i-'luiömitbel Kryolib, llmenit, I-31eioxide, Chroraozyd, or feron'-iine used ύ. . / learned, according to claims 1 to V, thereby ^ e ic e η η ζ ο i η eb, that one ends with marriage crystals made of aluminum oxide, the grain of which is essentially larger than the particle size of the aluminum oxide short . 9. The method according to claim 1 to B, characterized in that in the off {'; anirs {', emisch an aluminum oxide content not essentially below ?. 'Y / o is used. 10, method according to claim 1 to y, thereby geke η η ζ eich η et, d-att the Oemiach made of aluminum oxide ore and fluid with in ^! '' uses a form of cfranulate with a grain size between approx. 0.42 and 25 mm. 009844/1348 ^ «" «" «■ T5-92U2 Ho method according to claim 10, characterized in that te n e η η - draws, since: d one applies a mixture of that by, -. ', seen from. v7asaer to the finely divided η ^ rzaa unu. [■■ Luirfmittel, drying dos r.uchens and üranuiier & n produced has been. 12. method according to claims Iu, daaurca _t e λ e; i η draws ,. one may turn off _; -anj. s ^ -einiscli uses that by corrugating and then irranuline construction oxo; euumiuhue> - orn ^ rrö π ne herge π be 111 been i r <t <, 13. Proceed as per instructions 1 to 12, thereby drawing - e \ z --.- "_ι η, that one lan μ sam on an 'x'enH) oratur only the melting point of the yluiJmittel- and only then on the i'e.nioerabur between Vyjü and loüü ° w ywü Abdainpfen the essential r'luiammittelmen ^ e heated. ._ 9844/1348 BADORiGlNAL