DE1577574A1 - Drum abrasives - Google Patents

Description

The Carborundum Company ² July 5th Ι9ββ

Buffalo Avenue 1577574

Niagara Falls, New York, USA

Drum abrasives

The invention relates to a drum abrasive or the like. and a method for its production. The drum abrasive is used in particular to remove surface irregularities as well as for finishing or surface finishing of products.

The drum grinding is a surface treatment in which a mixture of metallic or non-metallic Parts, abrasives and various means into one Container is introduced, which is then used for the purpose of surface treatment of the parts mentioned, e.g. for removal, round corners, for deburring, descaling, polishing or the like. set in rotation or subjected to vibration. When piercing metal parts, drum grinding is more economical than grinding, Hand washing is generally preferred. The machining process can be accelerated with drum grinding and also achieve a more even finish than with hand sanding or other sanding methods. Of the includes the term "drum grinding" as used hereinafter surface processing by rollers or drums as well as such under the action of a vibratory movement. . ■ '■; ; ■■■■ '.

255.

VI ■ .. "■■ .... - 2 -

909881/0801

- "2 - ■

Drum abrasives come in several types and forms known. Should the drum abrasive be used to remove Metal from metallic products, it is desirable that the amount of metal removal, i.e. H. the grinding performance as high as possible and at the same time the loss of abrasive is low in order to keep the processing costs low. On the other hand, is the amount of metal removal too low, drum grinding is often no longer possible perform economically.

Those previously generally used for drum grinding Means consisted predominantly of porcelain or of molten, emery-like ceramic materials. the Porcelain-based abrasives have an exceptionally long service life on rotating or vibrating machines and thus the advantage of a low abrasive loss, but the grinding performance (i.e. the Material removal from the workpiece) is extremely low. the fused ceramic emery materials also exhibit not -both properties, namely long service life and high grinding performance (material removal). Recently an improved abrasive has been developed which consists of finely broken bauxite, which is produced by extrusion put into "abrasive form" and then sintered. Although such sintered bauxite materials refer to their wear resistance and service life are superior to the aforementioned substances, their grinding performance is certain surface treatment processes are less than satisfactory. There is therefore a considerable amount of money on the part of the industry. Need for a drum-type abrasive that "enables a high abrasive performance with a long service life."

909881/0801

biö Erfinätang aims at an abrasive made of sintered bauxite that meets the aforementioned requirements corresponds, whose Sehleifwirfcuhg is considerably larger than that of the well-known bauxite abrasive.

^ invention consists of the Tronimel abrasive preformed, sintered bodies, which are melted in addition to bauxite Ali ^ iniumoxjdteilehen (alumina particles) in im have substantially uniform distribution in the bauxite.

The shaped bodies preferably contain about 10 to 80% molten aluminum oxide (alumina). The preferred range of aluminum oxide is approximately between 20 and 60 ° .

By adding finely divided burnt or melted aluminum oxide to the bauxite and then shaping and sintering these materials, an abrasive is obtained which has surprising properties As a drum abrasive, a grinding effect that is considerably greater than that of a sintered material made exclusively from bauxite, and which is also considerably greater - ± έΨ ·,

ÖJ3- ¹ - - ι.

as the drum loops known otherwise, including. borrowed the fired ^ ceramic emery materials. It has also shown that the abrasive effect of the invention Abrasive with increasing content of powdery, melted Aluniniura oxide to which bauxite rises rapidly.

The drum abrasive according to the invention can advantageously be produced by first using the Bauxite is crushed into microcrystalline particles that

Pt 9G9881 / 0801

BATH ORIGINAL

then a mixture of the crushed bauxite and fine broken molten aluminum oxide is produced, which is then brought into the appropriate Forra or to Molded bodies "is processed, which are subjected to the sintering process will. An abrasive produced in this way has when used for the drum grinding process a 'grinding effect, which increases with an increasing proportion of powdery molten aluminum oxide and which in In each case is greater than the grinding effect of the known, sintered bauxite materials, polygamy "do not contain aluminum oxide. By increasing the acting on the materials Heating temperature can also extend the life of the erfindungsg he. ate. Abrasive can be increased. In detail leaves the drum abrasive according to the invention - for example manufacture in the following way:

In its natural state, bauxite contains hydrated aluminum oxide and smaller amounts of silica, titanium compounds, Iron oxide and other impurities. For the process according to the invention, firing is preferred Bauxite used, although unfired bauxite can also be used is. ■ The burning and roasting is honored in the more important: the entire VJasser expelled from the bauxite. For example, the analysis of a typical fired Surinam bauxite Tolgende Verte on:

Frozent

P5.67

J, ^ 4

"J 3 -O

. ~ * 5,1j 3 pure

909881/0801

BATH ORIGINAL

Although Surinam bauxite is preferred, can Of course, also natural bauxite from other deposits or synthetic bauxite door the production use the abrasive of the invention.

The burnt bauxite is crushed to an average grain size no higher than about 5yU (microns). The comminution is preferably carried out in such a way that the majority of the microcrystalline particles of the comminuted bauxite has a grain size below 10 η , the grain portion above 2.0 π not being more than 5 yO and the average grain size between about 2.5 / u and 5

lies. The comminution of the bauxite to this fine grain size can be carried out in various ways. For example, the bauxite can be comminuted in a roller mill to minus Ao meshes and then ground in a ball mill, wet-on-ground, its grinding media .; _: Steel, flint or Aluffliniuraoxyd abrasives are made. The grinding process is carried out until the desired grain size is reached. On the other hand, the bauxite can also be comminuted in a jet mill that works with air or steam, with the resulting microcrystalline bauxite particles then in conventionally, for example ₄ in an oven 'dried.

Then, from the microcrystalline, comminuted bauxite and the finely applied molten aluminum oxide, a mixture is produced. The content of oil-fused aluminum oxide in the mixture can vary between about 10 % and "about 80 γ> of the mixture, the preferred range for the aluminum oxide content being between about 20 and 6o ρ ," ie, by increasing the Share of

fine aluminum oxide in the mixture, the grinding effect of the sintered material produced from the mixture can be increased. However, adding larger amounts of molten aluminum oxide increases the abrasive loss somewhat. These two factors must therefore be coordinated with one another in the manufacture of the drum abrasive according to the invention. If it is mainly the material decrease (grinding effect) that matters and the service life of the abrasive is of secondary importance, the mixture can contain up to 80% of fine molten aluminum oxide in order to achieve an abrasive with an extremely high abrasive effect. On the other hand, in those applications in which the service life of the abrasive is important, but on the other hand a sufficiently high abrasive effect is required, it is advisable to reduce the amount of molten aluminum oxide powder in the mixture. Under the same sintering conditions, for example, an abrasive can be produced which has io fo of powdered, molten aluminum oxide and about 90 j'o bauxite powder and which, with a slightly lower squint effect, causes less abrasive loss than abrasives that contain higher proportions of aluminum oxide.

According to the invention, this has powdery, fused alumina (Alumina) preferably a grain size of approximately 100 meshes (U.S. Standard Sieve Series) or a smaller grain size, the preferred grain size being around 24o see or is below. To the mixture can be a low Amount of a suitable organic temporary binder, such as starch, cellulose derivatives, waxes and the like or a inorganic binders such as bentonite are added. Such and others only temporarily creating a bond

\ - 7-τ-

909881/0801

■ '. <.' ■ "- -. 'BATH ORIGINAL ·: -

- 1 -

157757 A

Binders are known per se. In general, an amount of binder of about 2 to ^Q is sufficient in the process according to the invention. '%. _f where.the amount depends on the type of mixture and the particular binder used.

Then water is added to the dry mixture in order to obtain a plastic mass suitable for processing, the consistency of which allows the grinding wheel to be shaped and manufactured. The amount of water added largely depends on the type in which the forming, wii'd gebung made, the nature of the bauxite, the ^water, content thereof, and other conditions, in general, the amount of water added belauft to about 22 ° to 5 ° 1 loo per kg .trockener mixture..

After the dry constituents have been mixed with the water, molded bodies are produced from the plastic material, the shape of which corresponds to the desired shape of the grinding body. The shaping can, for example, by eating, casting, by ochleuderguß'o.dgl. take place. Preferably, the shaping, however, is done by extrusion, '- wherein the mass having a suitable consistency or the like by means of a pressing head. processed on a rod or column with the desired cross-section shape; is, of which then the grinding wheel of the desired length _; iii. more suitable. Ueise such as "barren means of moving wires Kesser \ be divided off. Bsi application of Strangpre3verfahrens ^l it is recommended that the dry ingredients before the Vermiscluins the nit '.vasser a small amount of herköm.nliöheii Plastisierers, viie z * B. To add Tennassee binding clay, vrobei .lie additions.isn ^ e, for example, is about 1 Ms' 5- ^.

909881/0801

BAD ORiGiNAL

The plastic mass can then be extruded. one Rod, column or the like. , leather of any cross-sectional shape, including a round or polygonal, e.g. triangular or square cross-sectional shape. In most use cases, bodies are triangular Cross-sectional shape preferable because "such. Shapes are common bring a higher grinding effect.

The drum abrasive means according to the invention can be produced with different dimensions, whereby the cross-sectional dimensions as well as the lengths of the abrasive bodies can vary as required. If triangular bodies are produced, they preferably have a length of about 0.3 cm to about ^! - 6.0 cm, while the thickness or length of the abrasive body is preferably about 0.3 to 6.0 cm. It goes without saying, however, that larger or smaller bodies are more appropriate for certain purposes.

If an organic binder is used as a temporary binder in the manufacture of the abrasive bodies, the bodies are preferably first of all ^: heated in an oxidizing atmosphere and at a temperature which is high enough to drive off the binder. However, this temperature should be around. Do not exceed ^{ΙΙ00 0 C;} it is preferably between about 750 and 100 ° C. The time required for the annealing of the binder depends largely on the binder used, the temperature of use and the type of drying process. determined by the Cf ens. If only an inorganic binder "such as bentonite" is used, the oxidation treatment will not be required.

909881/0801

BATH ORIGINAL

The molded bodies produced in this way are then heated to a higher temperature for sintering. Although a neutral or a reducing atmosphere can be provided, it is advisable to work with an oxidizing atmosphere, since this reduces the oxide impurities in the bauxite with the disadvantageous phenomena of swelling or the _; Formation of a glass mass, the bond between the individual particles of which is weakened, prevented or at least reduced to a minimum. Excellent results could be achieved by heating the moldings in cassettes or the like. can be achieved in a gas-fired furnace. It goes without saying, however, that other equipment tongues of known design can also be used for these purposes. By using a gas-fired oven, the oxidizing atmosphere can be created by letting the oven exceed the amount of air required for complete combustion of the gas 2o % excess air is supplied.

It is advisable to strictly adhere to the sintering time and the sintering temperature. If the sintering temperature is not sufficiently high or the sintering tent is not long enough, the resulting product does not have sufficient strength. On the other hand, if the sintering temperature is too high, the individual moldings can bake together so that they later have to be broken off from one another. Sintering temperatures are particularly suitable for the process according to the invention. Range between about l4oo ° C and I75o ° G. The sintering time can vary depending on the intended Sintartemperatur, · the '"application only coming atmosphere as well as the particle size and the Zusararnensetzuns of the mixture between 15 minutes ■ -..'':., And east. Hours at maximum temperature.

between about 50 minutes and 2 ^ hours where ■

Sintering temperature is J500 ° C.

909081/0801

After the sintering process: v / er den the grinding wheels with a normal speed in conventional high-temperature ovens brought to cool down. If desired, it can Abrasives are then subjected to post-processing to eliminate minor edge defects or during the cutting process to "remove any adhesions remaining on its surface. For this purpose, the abrasive can e.g. be wet in a rotating drum for about 15 to 5.0 minutes to be drummed. ... '.. -

The bulk density of the cut ice decreases with increasing contents of powdery, molten aluminum oxide. In the case of triangular grinding wheels, the triangle sides are generally approximately in each case. 2.2, which have a length and a thickness of .approximately 1.25 cm, irn. Range from about ϊβοσ to 2o8o kg / no. The bulk density increases with increasing sintering temperature !!, somewhat. The specific gravity of the sintered body is also dependent on the aluminum oxide content - generally in the range from about 5 to 3.1.

The drum loosening means produced according to the invention has a dense structure. Since the crystal form des'Schleifmittels depends on the amount of Alur.iiniumoxyd and the sintering temperature used, the description of the crystal structure like the following remarks are limited i ■. . "■. ...-" ■ -

If the abrasive is used at low sintering temperatures, d. H. .at temperatures of about 14oo C to about 1500 C is heated for a few hours, so the sintered

_ 11 _

90988170801

Fabric raikr öler is metallic bauxite with fine fused Alumina particles in an even distribution. At.. Application - sololler comparatively gsrinsec. Sintering temperatures can therefore use the molten aluminum oxide particles at least partially under a microscope from that

Crystalline bauxite can be differentiated. When _t iedo.ch sintered body at higher temperatures of about '155.0 ° C to 175o C ^G and the sintering temperature amounts to only about one hour so hoists the microscopic examination

the iiörper.in some cases, a tendency for recrystallization and / or crystal growth of the microcrystalline erkonnon bauxite to form a granoblastisehen in substantially crystalline structure, ie .a texture in which the liristalie unregeL.i ^'are ..3ig and sharp-edged and remember a mosaic. The wetness of such a crystal growth bs-vr. recrystallization is not just · depending on the sintering temperature ¹ and the Sinterzoit, but also on the amount of fine i? i 'dew substance contained Alur ;; niumoxyd.

In the following some examples of the execution of the * ' The applicable process procedure is specified.

Beisnia

First, the ebranite Suriname bauxite, which was about the mentioned above? ZiisaMrensetzus showed us to be a uikroliristallinen Powder-au ^ cs.-iahlar., Its average Fm'tikQl ^ .röBä .- 'r ^ vm'S, ^ / U. Fraud. Then there was a signing

the aacaiolgende 2usa!;: - ;; 3nsetEung made:. -;.

- 12 -

909851/0801 ■■ .--

, ... :: ': BAD ORIGINAL

proportion of

Surinam bauxite (mean size 2.5 λχ) 9o

molten aluminum oxide powder ■

(2 '^ ο stitches and finer) Io

Bentonite (2oo meshes and finer) 3

Tennessee Tie Tori (325 meshes and

finer) 2

v / ater 35

The dry fabrics were then added to a mixer and mixed for about 5 minutes. The water was then slowly added to the dry mix to make one for the Extrusion molding to get suitable cash register. The total quenching time was about 30 minutes. Subsequently was the material is removed from the mixer and placed in a drill or screw-like extruder introduced from which the Material through a triangular opening Press head was pressed out. The extruded rod became cut into the desired lengths using a wire cutter.

The moldings produced in this way were in flat cassettes are inserted and then introduced into a furnace heated with natural gas, in which they are charged with a low Excess air at a temperature of about 1490 ° C in were sintered for three hours. The bodies received passed made of triangular plates, the sides of which were each about 2.2 cm long and a thickness of 1.25 cm had »The specific weight of the sintered body was about 3 * 62.

909881/0801.? '& S0 X rS £ ■ '■ - ^BAD

Example II

A number of mixes have been made, as follows to prove:

1. The superior properties of the invention Drum abrasive versus a bauxite abrasive made in the same way, however has no fused alumina particles;

2. the abrasive effect depending on the proportions Aluminum oxide. .

ITn a Vergleichsbäsis to be created en, .the nachstehendaufgerührten -jeweils mixtures were subjected to the same standard procedure ₄ The preparation of the abrasive body was Jev / Eils in the direction indicated in B'eispiel I V'eise.

.,. , .ν '"- ■■"' -_.- ■■ ".. molten

lashing No. Bauxite alumina

- powder

Share share

1- loo ο

2 9o Io

^: y ₍ 8o. 2o

4 7o. ". '■. 3o

5 6o 4o 6- '5o. '5o 7 3o to

Further mixed components, ie bentonite binding clay and water in proportions of 3 or 2, or 35 % based on the abrasive component or abrasive components of the mixture were added to all of these mixtures. '

■; ■; ■ ..- ■■: - ■ ^:. '' ^: .. ■■■ '- w: - ■'

■; : 909881/0801, _B »OMSiNAL

Moldings produced from each mixture according to Example I heated v / urden, so that triangular plates were obtained, the triangle sides of an edge length of .each about 2.2 cn and which had a thickness of -approximately 1.2 p cm had. The resulting abrasive bodies were then used to determine their abrasive properties (property of material removal of the product to be treated) is evaluated. In the test procedure that is the same for all samples v / are the earbud examinations with the following mentioned apparatus as well as carried out under the conditions explained in detail below:

machine:

Pangborn Carborundum Yibrator (CVA-3) , with a capacity of approx

o, oC: 5

Speed: 2ooo ^: cycles / min .;

Middle:

Water:

Metal samples:

29.5 part of a non-abrasive polishing aid, containing a mixture of isopropanol and a non-chemical surfactant of the fatty acid all: ylolarnide type, dissolved in about βο; ί water,; 'e 1.9 1 V'asser;

1.9 1 at the beginning of the test and o.47 1 after 2 hours of flushing j

SA3. Ho. Io2o, cold rolled steel angles with the dimensions 6.35 om χ 6.35 cm χ o, p2 cm; ;

16 hours total; Abrasive rinsed every 2 hours and additives and water added. ^r ". - - .: - ^:

909881 / 0Mt

- 15 -

BATH ORIGINAL

The vibration machine up to about; 95 ",, * of your performance with abrasives filled, then the auxiliary means, water and the metal samples were admitted. The metal loss of the samples was after; 2 hours at a time by drying and lying down. The results of the experiment are given in Table I below:

Table I.

No. zaies
AIu mi
ni u in-
oxide-
powder Salute
gevricht 1 O 2 ^ o7 ο lc 2o34 3 2o 1935 Ii ' 3o 19o6 5 4o 19oc > -
U 5o ΙΓ-9Ο ι 7c lClo

Metal removed by abrasives. (^ q, total). -

Seemed rate

j \ [_ < 6th hours ρ l £ 12th 61 UL 69 93 IC 79 C- 1, o5 1, 1 " 32 1.46 1, 13th 1, 34 1, 54 o, F4 1, .l ^r 1.45 3, 71 1.95 2, 18th 2, 4i 2, 63 o,: -5 1, 13th 1, 42 1, 7o 1.97 2, 38 2, 82 2, 19th o, B2 .1, 65 2, o3 1, 56 3, ol 3, 41 3, 98 4, 51 1.65 1, 94 2.6o 2, 24 3, ^ 3 4, Fo ' 4, 5.52 5, 15th 1.23 1, 35 2.75 3, 42 4.17 4, 2o 5, δ, 1.12 2, Io 2.94 3y 74 4.54 5, 6, 1.25 3,

.112 .158, 164 .26o .34o .3B5 .416

+) Dui ⁱ chsc:-average ketallentung (in; t v. 'During the lo-hour holiday.

^ e hour

These experimental results are in the Pig. I and 2 graphically reproduced .: The graphic representation according to Fi.3. I times the increase in the leuall distance with increasing content of the 3.-abrasive filing by means of molten aluminum oxide (alumina), whereby; the. Curves I to "7. those listed in Table I. Mixtures I to 7 correspond to / from Table I and FIG it can be clearly seen that all abrasives fine alumni umoxyd show, regarding

90 98 8

- • 16— BAD ORIGINAL

superior to bauxite abrasives because of their abrasive properties « are, which aluminum oxide does not have.

The graph according to FIG. 2, which is also based on the test results of Example II, leaves the high grinding rate of the sintered bauxite and aluminum oxide existing drum abrasive according to the invention or the increase in the grinding rate with increasing content of Recognize aluminum oxide powder. , ".

As stated above, the abrasive loss increases in drum grinding with an increase in the proportion of fine-tune aluminum oxide in the grinding compound. By controlling the amount of alumina fines added as well as the Sintering it is possible to make an abrasive, which in terms of its grinding rate and its abrasive loss is set to an optimal value. This was with the previously available abrasives. such as the melted aluminum glasses not possible. With such glasses, the grinding rate is the abrasive a puncture of its content of abrasive material while the life of the abrasive is dependent on the strength of the composition of the abrasive bond. By lowering the content of abrasive material, there is an increase in the service life of such materials, however at the same time a decrease in the grinding rate is achieved.

To the grinding rate and the abrasive loss of the invention Abrasive with the known, consisting of molten Alurainlum ceramic masses abrasive compare, the following test was carried out:

- 17 -

909881/0801

Example III

A drum lift test was carried out in the manner described in Example II with seven samples of sintered bauxite abrasive. The abrasive samples consisted of sintered bodies made from the mixtures mentioned in the previous example. A commercially available abrasive , which au jo'ji consists of aluminum oxide ^{grain and 1} Jo% of ceramic glass mass and which is considered to be the most suitable for use in vibration machines, was also tested under the same conditions. The comparison test led to the results given in Fig. J5:

The grinding rate (lüirve A) of the abrasive consisting of a molten aluminum oxide ceramic mass corresponded approximately to the grinding rate of curve B, which corresponds to an abrasive according to the invention which contains 20 % finely divided molten aluminum oxide (alumina). The grinding loss of the burnt aluminum oxide ceramic abrasive (curve C) corresponded approximately to that of the abrasive ^{according to the invention, with a content of:} Q ; j finely divided burnt aluminum oxide according to curve D. In the range from 20 to about 50 ρ content Burnt Alui.iiniumoxid v / eist the abrasive according to the invention a "■ significantly higher grinding rate and a lower sole with toi loss than the known abrasive. ■ .-:

In the experiments described above, the pleasure of abrasives became obsolete (By using the abrasive when placing it in the i Vibration processing machine and through to completion dGx '7e:; - search carried out reweighing (after previous I.

90 9881/0801

BAD ORiGJNAt

Drying.) And determined by calculating the difference in weight.

The specified percentages, parts and ratios are based on weight, unless otherwise stated.

Patent claims:

. "- ν, _ ■ _ .. _: -:;. ·,:, _BA d ORIGINAL

98 81708OV ^ - 19 -

Claims (17)

- .19 · Claims 1. Drum abrasive or the like. made of sintered bauxite moldings, characterized in that the sintered moldings in the ■■ essentially made of bauxite and in-this, in. substantially evenly dispersed molten aluminum oxide particles exist. 2. Abrasive according to claim 1, characterized in that the shaped bodies contain about 10 to 8o \ l of molten aluminum oxide (alumina). ^ ' j5. Abrasive according to Claim 2, characterized in that the proportion of molten aluminum oxide is approximately 2o to 60 fo . 4. Abrasive according to one of Claims 1 to Os, characterized in that the shaped bodies have an essentially granoblastic crystalline structure. 5. Abrasives naöh one of claims 1 to 4, characterized ge <Kennzelehnet, that the specific weight of the molded body in Range from about 3> o to 3 * 7. 6. Verfaliren for the production of a sintered drum grinding: means according to one of claims 1 to 5j, characterized in that bauxite is crushed to an average particle size below about 5 / a and then mixed with molten Äluminiuiiioxydteilchen that is then from the 909881/0801 " ^2o " . BATH Mixture moldings are produced, which are then ^{vrer sintered at a temperature between about .lAoo 0} C and 175o ° C. 7. The method according to claim 6, characterized in that as Bauxite armored bauxite ore is used. S. The method of claim 7 or β * characterized in that a mixture of about 2o to 9o%, preferably 80 to 50% of crushed bauxite and about Io, preferably about 2o to 50 '/ ■> alumina is prepared to 80%. 9. The method according to any one of claims 6 to 8, characterized in that that the molten alumina particles have a grain size of about 100 mesh or smaller, preferably 24o stitches or smaller can be added. lo. Method according to one of Claims β to 9> characterized in that the mixture contains a small amount of a binder is added. . ... ' 11. The method according to any one of claims 6 to lo, characterized in, that the body made from the mixture for about 15 minutes to 6 hours at one temperature sintered between about 14oo ° C and 175o ° and then cooled will. ,. - 21 - 909 881 / _080T,:,:.: BADORiGiMAi, 12. The method according to any one of claims β to 11, characterized in that that bentonite is added as a binder. Method according to one of Claims 6 to 12, characterized in that that from the mixture by means of a spray head or the like .. strand-shaped bodies, preferably those with a triangular cross-section, are produced by extrusion, from which the sintered bodies are then divided off in the desired length. l4. Process according to one of Claims 6 to 14, characterized in that the molded bodies produced from the mixture subjected to sintering at such a temperature and for so long that 'the finely divided alurainium oxide particles as separate particles finely divided in the sintered Bauxite remain. ' 15. The method according to any one of claims 6 to 14, characterized in that that 'the sintering time and the sintering temperature are adjusted so that a substantially granoblastic crystalline structure is obtained. 16 / Method according to one of Claims β to 15, characterized in that that the mixture contains a small amount of a plastic ziere-r-s, / of a binder and so much water added that they are suitable for extrusion molding Maintains consistency. ■ '.-.- ■■ - ■ : ■ - 22 - 17. The method according to any one of claims β to 1β, characterized in that that bentonite is used as a binder and clay as a plasticizer. l8. Method according to one of Claims 6 to 17 *, characterized in that the cooled sintered bodies are removed for removal
small edge defects can be drummed for about 15 to 15 minutes. 909881/0801 - ^ßAD Empty soap