SCREEN PLATE FOR SCREENING PLANTS FOR MECHANICAL CLASSIFICATION OF POLYSILICON

Abstract

Polysilicon chunks or granules are classified into size fractions using a mechanical screen having a profiled surface having peaks and valleys, and terminating in widening slots through which a polysilicon size fraction falls. The device is effective and the slots are resistant to clogging.

Claims

1.-10. (canceled)

11. A screen plate for a screening plant for the mechanical classification of polysilicon, comprising: a feed region for receiving polysilicon, a profiled region having peaks and valleys, and a region having slots which follow on from the valleys, and a takeoff region, wherein the slots increase in size toward the direction of the takeoff region, and wherein the peaks of the profiled region also continue into the region having slots so that the entire screen plate is profiled, the screen plate having slots instead of valleys at its end in the direction of conveyance.

12. The screen plate of claim 11 which is made of one or more materials selected from the group consisting of plastic, ceramic, glass, diamond, amorphous carbon, silicon and metal.

13. The screen plate of claim 11, comprising a metallic main body and a coating or lining of one or more materials selected from the group consisting of plastic, ceramic, glass, diamond, amorphous carbon and silicon.

14. The screen plate of claim 12, comprising a metallic main body and a coating or lining of one or more materials selected from the group consisting of plastic, ceramic, glass, diamond, amorphous carbon and silicon.

15. The screen plate of claim 11, comprising a coating of titanium nitride, titanium carbide, aluminum titanium nitride or DLC (diamond-like carbon).

16. The screen plate of claim 11, which is made of hard metal or which is lined or coated with a hard metal.

17. The screen plate of claim 11, wherein the slots have a width of up to 200 mm.

18. The screen plate of claim 11, wherein an opening angle of the valleys of the profiled region is greater than 1 and less than 180.

19. The screen plate of claim 11, wherein the valleys of the profiled region are from 1 to 200 mm deep.

20. A method for the mechanical classification of polysilicon employing a screening plant, comprising feeding polysilicon onto a screen plate of claim 11, and vibrating the screen plate such that the polysilicon executes a motion in the direction of the takeoff region, wherein small particle-size polysilicon collects in the valleys of the screen plate and falls through the slots of the screen plate and is thus separated from the polysilicon feed.

21. The method of claim 20, wherein the screen plate has an angle of inclination to the horizontal of from 5 to 20.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The polysilicon may be polycrystalline chunks or granular polysilicon.

[0023] Small particle-size polysilicon is to be understood as meaning a proportion of the polysilicon feed amount which is to be removed by means of the screening plant. The small particle-size polysilicon is thus the fraction to be removed.

[0024] The small particle-size polysilicon may be polycrystalline silicon particles which are to be removed from a target fraction comprising granular polysilicon or polysilicon chunks.

[0025] In another embodiment the polysilicon feed is polysilicon chunks comprising a fines fraction. The fines fraction is to be removed with the screen plate.

[0026] The size class of polysilicon chunks is defined as the longest distance between two points on the surface of a silicon chunk (=max. length):

chunk size (BG) 0 0.1 to 5 mm
chunk size 1 3 to 15 mm
chunk size 2 10 to 40 mm
chunk size 3 20 to 60 mm
chunk size 4 45 to 120 mm
chunk size 5 100 to 250 mm

[0027] In what follows, for the chunk sizes 3 to 5 all chunks or particles of silicon of a size such that they may be removed by a mesh screen having square mesh apertures of 8 mm8 mm in size are referred to as a fines fraction.

[0028] For the chunk sizes 0 to 2 the same analysis applies, the mesh aperture width here being defined as 1 mm1 mm.

[0029] The screen plate comprises a feed region in which the feeding of the polysilicon is effected.

[0030] In one embodiment the polysilicon is conveyed to the screening plant and delivered to the feed region of the screen plate by means of a conveying channel.

[0031] The screen plate further comprises a profiled region having flutes or grooves, or generally, depressions and elevations, so that the profiled region has valleys and peaks.

[0032] During the motion of the polysilicon on the profiled region small chunks or small silicon particles (small with respect to the target fraction) or fines fraction collect in the valleys of the profiled region.

[0033] In one embodiment the polysilicon feed comprises chunks of the size classes 3 to 5 and a fines fraction according to the abovementioned definition. During the motion of the polysilicon on the profiled region, the fines fraction collects in the valleys of the profiled region.

[0034] In one embodiment the polysilicon feed comprises chunks of the size classes 0 to 2 and a fines fraction according to the abovementioned definition. During the motion of the polysilicon on the profiled region the fines fraction present in the polysilicon collects in the valleys of the profiled region.

[0035] Following on from the profiled region the screen plate comprises a region having slots. The slots are arranged immediately behind the valleys of the profiled region in the direction of conveyance. As a result, the fines fractions of the polysilicon present in the valleys of the profiled region are selectively passed to the slots of the region.

[0036] In one embodiment the peaks of the profiled region also continue into the region having slots so that the entire screen plate is profiled, the screen plate, however, having slots instead of valleys at its rear end in the direction of conveyance.

[0037] The removal of the fines fraction or of small chunks/particles is thus effected via the slots of the screen plate.

[0038] In one embodiment the removed fines fractions or small chunks/particles are received by a receiving container disposed below the slots of the screen plate. Larger chunks are passed over the peaks of the profiled region to the takeoff region.

[0039] In one embodiment the takeoff region is connected to a conveying channel via which the larger chunks are discharged. It is likewise possible for a further screen plate to follow on subsequently in order to remove a further fraction from the polysilicon.

[0040] The slots widen in the direction of conveyance. Surprisingly, this makes it possible to effectively avoid blockage of the openings/slots. Accordingly, the associated problems which are observed in the prior art and entail a high level of cost and inconvenience do not occur.

[0041] The separation accuracy is markedly higher than for bar screens resulting in a marked reduction in the amount of outsize removal and a consequent increase in yield.

[0042] The invention thus provides a screen plate which may be employed in all types of screening plants, where the fines fraction or small particle-size silicon material collects in valleys in the first region of the screen plate and is selectively removed through widening screen slots in the last region of the screen plate.

[0043] In one embodiment the screen plate is made of one or more materials selected from the group consisting of plastic, ceramic, glass, diamond, amorphous carbon, silicon, or metal.

[0044] In one embodiment the screen plate is lined or coated with one or more materials selected from the group consisting of plastic, polyurethane, ceramic, glass, diamond, amorphous carbon, or silicon.

[0045] In one embodiment the parts of the screen plate coming into contact with the polysilicon are lined or coated with one or more materials selected from the group consisting of plastic, polyurethane, ceramic, glass, diamond, amorphous carbon, or silicon.

[0046] In one embodiment the screen plate is made of hard metal or is coated or lined with a hard metal.

[0047] In one embodiment the screen plate comprises a metallic main body and a coating or lining of one or more materials selected from the group consisting of plastic, ceramic, glass, diamond, amorphous carbon, or silicon.

[0048] In one embodiment of the invention the plastic used in the abovementioned embodiments is selected from the group consisting of PVC (polyvinyl chloride), PP (polypropylene), PE (polyethylene), PU (polyurethane), PFA (perfluoralkoxy), PVDF (polyvinylidene fluoride) or PTFE (polytetrafluorethylene).

[0049] In one embodiment the screen plate comprises a coating of titanium nitride, titanium carbide, aluminum titanium nitride or DLC (diamond-like carbon).

[0050] The size of the slots depends on the fraction to be removed and may be up to 200 mm.

[0051] In one embodiment a separation step at 10 mm is to be effected (screening off polysilicon smaller than 10 mm), the slots having a width of 10 mm at their end (beginning of the takeoff region).

[0052] The implementation of the profiled region of the screen plate depends on the fraction to be removed. The depth and the angle of the valleys in the profiled region are to be configured such that the fraction to be removed, i.e. the fines fraction for example, collects there.

[0053] The angles of the valleys may be flat to extremely acute and may be greater than 1 and less than 180. The depth of the valleys may be from 1 to 200 mm. For example an angle of 45 and a depth of 20 mm are suitable for removing a 10 mm fraction.

[0054] Excitation of the screen plate may be effected either with a planar vibratory screening machine or with a shaker screening machine. Vibration drives (for example magnetic drives) or imbalance drives may likewise be provided.

[0055] In one embodiment the screen plate has an inclination to the horizontal. Angles of inclination of 0-90 are possible. Angles of inclination between 5 and 20 are preferred since gravity then aids conveyance over the screen plate.

[0056] The features cited in connection with the abovedescribed embodiments of the method according to the invention may be correspondingly applied to the apparatus according to the invention. Conversely, the features cited in connection with the abovedescribed embodiments of the apparatus according to the invention may be correspondingly applied to the method according to the invention. These features of the invention and the features recited in the claims and also in the description of the figures may be realized either separately or in combination as embodiments of the invention. Said features may further describe advantageous implementations eligible for protection in their own right.

BRIEF DESCRIPTION OF THE FIGURES

[0057] FIG. 1 is a schematic diagram of the construction of a screen plate

LIST OF REFERENCE NUMERALS EMPLOYED

[0058] 1 screen plate [0059] 2 feed region [0060] 3 profiled region of the screen plate [0061] 31 valleys of the profiled region [0062] 32 peaks of the profiled region [0063] 4 region having slots [0064] 41 slot [0065] 5 takeoff region

[0066] The screen plate 1 comprises a feed region 2 in which feeding of the polysilicon is effected. The polysilicon may, for example, be conveyed to the screening plant and delivered to the feed region 2 of the screen plate 1 by means of a conveying channel.

[0067] The screen plate 1 further comprises a profiled region 3. This profiled region 3 provides flutes or grooves or depressions of another kind, so that the profiled region 3 has valleys 31 and peaks 32.

[0068] The fines fraction present in the polysilicon collects in the valleys 31 of the profiled region 3 during the motion of the polysilicon on the profiled region 3.

[0069] The screen plate 1 comprisesfollowing on from the profiled region 3a region 4 having slots 41. The slots 41 are arranged immediately behind (in the direction of conveyance) the valleys 31 of the profiled region 3. As a result the fines fractions of the polysilicon present in the valleys 31 of the profiled region 3 are selectively passed to the slots 41 of the region 4.

[0070] The peaks 32 of the profiled region 3 preferably also continue in the region 4 so that the entire screen plate 1 is profiled but has slots 41 instead of valleys 31 in the region 4.

[0071] The removal of the fines fraction is thus effected via the slots 41 of the screen plate 1. The removed fines fractions may, for example, be received by a receiving container disposed below the slots 41 of the screen plate 1.

[0072] Larger chunks are passed over the peaks 32 in the profiled region to the takeoff region 5.

[0073] The slots 41 widen in the direction of conveyance. It has been found that this makes it possible to effectively avoid blockage of the openings/slots.

[0074] The description hereinabove of illustrative embodiments is to be understood as being exemplary. The disclosure made thereby enables a person skilled in the art to understand the present invention and the advantages associated therewith and also encompasses alterations and modifications to the described structures and methods obvious to a person skilled in the art. All such alterations and modifications and also equivalents shall therefore be covered by the scope of protection of the claims.