DE8613169U1 - Device for separating solid fine powders into grain size fractions - Google Patents

Description

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P36 16 300.7-09 - 2 -

DEVICE FOR SEPARATING SOLID FINE POWDERS INTO GRAIN SIZE FRACTIONS

The invention relates to a device for separating solid fine powders into grain size fractions.

Micrograins made of silicon carbide and electrocorundum in the range of 0 pm to 1 pm are currently used to produce so-called "modern ceramics". Obtaining such grain classes by sieving or processes using centrifugal force is extremely complex. In addition, such a grain size distribution is not yet optimal for the desired purposes, because within this range further subdivided grain classes are required, for example with grain sizes of 0 μιδ to 0.5 pm and 0.5 μιδ to δια.

The object underlying the invention is therefore to provide a device with which large quantities of sub-micro grains separated according to grain classes can be produced from powdered solid fine powders in an economical manner.

This object is achieved according to the invention in that the fine powder is suspended in a liquid, the suspension is allowed to sediment in a suspension column, suspension fractions are withdrawn one after the other from top to bottom at certain heights of the suspension column after certain sedimentation times and the fine powder contained in each suspension fraction is recovered.

This is done with a device that has a column-shaped suspension container,

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which has a connection for the suspension feed on its top and removal openings, staggered in height, that can be closed by slide valves for the respective suspension fraction.

In order to determine the particle size of dispersed particles in the size range of about 1 to 100 µm, it is already known to prepare a uniform suspension of a small amount of the powder to be examined in a suitable dispersion medium and then to allow this to sediment. Since, according to Stokes' law, there is a clear connection between the size and density of spherical particles and their rate of settling, the percentage distribution of the grain sizes can be deduced from the temporal course of the sedimentation (Römpp's Chemistry Encyclopedia, 1st edition, pages 3151 and 3152). With this so-called sedimentation analysis, the grain sizes of powders can be determined with the help of sedimentation, but the extraction of grain size fractions according to the invention cannot be derived from this in an obvious way.

According to the invention , sub-micro grains separated into grain class fractions can be produced economically from pul-

deformable ceramic fine powders can be obtained in large quantities with reasonable effort. For example, micropowders made of silicon carbide, corundum and tetrasodium diphosphate with a grain size distribution of 0 to 1.5 μιγ can be separated into grain size fractions of 0 to 0.5 pm, 0.5 to 1.0 m and 1.0 to 1.5 nti.

Embodiments of the invention are explained in more detail with reference to drawings, which show:

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Fig. 1 a device for carrying out the method and

Fig. 2 flow chart showing the extraction of grain size fractions from Edeikorund fine dust

The column-shaped sedimentation tank 1 shown in Fig. 1 has an inlet 2 on its upper side at height H, an outlet 3 on its lower side, an outlet 4 which can be closed by a slide valve 5 at height H ₁ and an outlet 6 which can be closed by a ^slide valve 7 0 at height H ₂ .

The column-shaped sedimentation tank 1 is filled via the inlet 2 over its entire height H with a suspension which has been prepared from a liquid and a solid fine powder or fine powder mixture of known grain size distribution, for example in the range from 0 to 1.5 \m .

After a sedimentation time t.. determined for the respective powder mixture in a preliminary test, the slide 5 at the outlet 4 is opened at the height H ₁ and the suspension fraction located at the height HH ₁ is allowed to drain. The sub-micro grain obtained from this suspension fraction essentially contains grains with a size of 0 to 0.5 µm.

After a total sedimentation time t ₁ + t», which was also determined in the preliminary test, the suspension column located above the outlet 6 with the height H ₁ - H ₂ is drained by opening the slide 7 and further treated. A fine powder with a grain size in the size range of 0.5 to 1.0 μπα is obtained. The suspension located in the sedimentation area below the outlet 6 above the height H ₂ , which contains the coarse particles

- 5 of the grains is withdrawn through outlet 3.

Fig. 2 shows schematically the separation of fine corundum dust into grain size fractions. The fine corundum dust stored in a container 10 is emulsified in a high-speed mixer 12 with a suspension liquid which is fed from a container 11 and consists of water with additives. Such additives are, for example, 0/5%

of an emulsifier in the form of a sodium salt of a polyalkylnaphthalenesulfonic acid and 0.2% of a sequestering agent . The emulsion or suspension discharged from the mixer 12 passes via the inlet 2 into the column-shaped sedimentation container 1. After a sedimentation time t., the suspension column HH ₁ of Fig. 1 is discharged via the outlet 4 into a centrifuge 16, to which water and drying agent can also be fed from a container 13. The filtrate discharged during centrifugation passes into a container 14 and is returned to the container for recycling via a line 15. The particle sludge accruing in the centrifuge 16 is dried in an oven 17, where it breaks down into a granular powder, which is packed in suitable containers in the station 18, observing the safety regulations for inert dusts.

The suspension fraction with the liquid height H ₁ - H_ discharged at the outlet 6 after the sedimentation time t.. + t_ by opening the slide 7 is then treated in the same way in the centrifuge 16 and the particle sludge obtained is dried in the oven 17 and packaged at a station 18 after determining the grain size distribution. The oversize grain discharged from the outlet 3 is fed into a container 13 for further processing.

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When preparing the suspension from liquid and fine powder as well as when recovering the powder after drying, ultrasound can be used if necessary.

The invention is explained in more detail using the following example.

The aim is to separate fine corundum dust into grain size fractions consisting of 40% with a grain size of 0.1 to 0.5 μια, 35% of 0.5 to 1 μια, 20% of 1 to 2 μια, 3% of 2 to 3 μια and 2% of over 3 μια. A column-shaped sedimentation tank 1 with a height H of 3 m is used. The outlet 4 is at a height H ₁ of 92 cm, the outlet 6 at a height H ₂ of 33 cm. After a sedimentation time of 30 minutes, the suspension column HH ₁ is allowed to drain without causing any turbulence by opening the slide valve 5. The fine powder of noble corundum obtained according to the treatment of Fig. 2 contains 75% of particles with a size of 0.1 to 0.5 μιδ, 15% with a size of 0.5 to 1 μιδ, 9% with a size of 1 to 2 μιδ, 1% with a size of 2 to 3 μιδ and no particles with a size over :) μιδ. The slide valve 7 of the outlet 6 remains closed. After a further sedimentation time of 10 minutes, this sedimentation fraction with the height H ₁ is removed at the outlet 3, which contains 5% of particles with a grain size of 0.1 to 0.5 μα, 15% with a size of 0.5 to 1 μα, 40% with a size of 1 to 2 μα, 30% with a size of 2 to 3 μα and 10% with a size of over 3 μα, the

Percentages refer to the respective frequency.

Claims (1)

P36 16 300.7-09 - 1 - Alfred Hempel 11 October 1988 GmbH S Co. KG DEAC-33753.1 Fi/mk DEVICE FOR SEPARATING SOLIDS FINE POWDERS INTO GRAIN SIZE FRACTIONS Claim for protection Device for separating solid fine powders into grain size fractions, characterized by a column-shaped suspension container (I)/ which has on its top a connection (2) for the suspension feed and is staggered in height by slides (5, 7) Has lockable removal openings (4, 6) for the respective suspension fraction. - 21-