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. A profiled screen plate for removal of polysilicon fines from larger chunks of polysilicon in a screening plant for the mechanical classification of polysilicon, the screen plate comprising: a feed region for receiving a feed of 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 continue into the region having slots so that the entire screen plate is profiled such that the height of the peaks and valleys extending across the profiled region to the end of the takeoff region are constant, the screen plate having slots instead of valleys at its end in the direction of conveyance, the height of the peaks and the maximum width of the slots in the takeoff region configured such that a fines fraction of polysilicon chunks is removed from the feed of polysilicon, wherein the fines fraction removed is defined as silicon chunks which can pass through a mesh screen having square mesh apertures of 8 mm×8 mm in size when chunks having chunk sizes of 20 mm to 250 mm are being classified, and is defined as silicon chunks which can pass through a mesh screen having square mesh apertures of 1 mm×1 mm when chunks having chunk sizes of 0.1 to 5 mm are being classified.

2. The screen plate of claim 1, which is constructed of elemental silicon, or has a covering of elemental silicon.

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

4. The screen plate of claim 1 which is made of one or more materials selected from the group consisting of plastic, ceramic, glass, diamond, amorphous carbon, silicon and metal.

5. The screen plate of claim 1, 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.

6. The screen plate of claim 1, comprising a coating of titanium nitride, titanium carbide, aluminum titanium nitride or DLC (diamond-like carbon).

7. The screen plate of claim 1, which is made of hard metal or which is lined or coated with a hard metal.

8. The screen plate of claim 1, wherein the slots have a width of up to 200 mm.

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

10. The method of claim 1, wherein the screen plate has an angle of inclination to the horizontal of from 5° to 20°.

11. The screen plate of claim 1, wherein the valleys have a depth of 20 mm.

12. The screen plate of claim 1, wherein an included angle of the profiled region is 45°.

13. A method for the mechanical classification of polysilicon employing a screening plant, comprising feeding polysilicon onto a profiled screen plate of claim 1, and vibrating the screen plate such that the polysilicon executes a motion in the direction of the takeoff region, wherein the fines fraction collects in the valleys of the screen plate and fall through the slots of the screen plate and is thus separated from the polysilicon feed.

14. The method of claim 13, wherein silicon chunks classified are of chunk size 0 to 2, and the fines are polysilicon chunks which can pass through said 1 mm×1 mm screen.

15. The method of claim 13, wherein silicon chunks classified are of chunk size 3 to 5, and the fines are polysilicon chunks which can pass through said 8 mm×8 mm screen.

16. The method of claim 13, wherein the profiled screen plate has a surface which contacts the polysilicon chunks which comprises elemental silicon.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a schematic diagram of the construction of a screen plate

LIST OF REFERENCE NUMERALS EMPLOYED

(2) 1 screen plate 2 feed region 3 profiled region of the screen plate 31 valleys of the profiled region 32 peaks of the profiled region 4 region having slots 41 slot 5 takeoff region

(3) 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.

(4) 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.

(5) 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.

(6) The screen plate 1 comprises—following on from the profiled region 3—a 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.

(7) 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.

(8) 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.

(9) Larger chunks are passed over the peaks 32 in the profiled region to the takeoff region 5.

(10) 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.

(11) 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.