WO2009053084A1

WO2009053084A1 - Production of molded bodies from ultrapure silicon

Info

Publication number: WO2009053084A1
Application number: PCT/EP2008/009001
Authority: WO
Inventors: Armin Müller; Jens Piotraschke; Raymund Sonnenschein; Torsten Sill; Christian Beyer; Dietmar Kaden; Christos G. Aneziris; Dieter Melzer; Berndt Lieber
Original assignee: Jssi Gmbh
Priority date: 2007-10-27
Filing date: 2008-10-24
Publication date: 2009-04-30
Also published as: EP2052848A1; DE102008044687A1

Abstract

The invention relates to a device for forming a molded body from a powder, comprising at least one molding chamber (25) for accommodating a powder limited by at least one side of at least one molding chamber wall (26), a supply device (1) for conveying the powder into the at least one molding chamber (25) and a compression unit (2) for compressing the powder in the at least one molding chamber (25), wherein the at least one molding chamber wall (26) is made of a non-metallic material, at least in the region of the side facing the molding chamber (25).

Description

Preparation of high-purity silicon molds

The invention relates to an apparatus and a method for producing moldings from a powder.

For example, in order to be able to further process the silicon powder produced from monosilane in a deposition process, it is advantageous to increase the material density and form it. For this purpose, a Walzenkompaktierungs- method is usually used, in which, however, it is due to the process to the occurrence of an adverse fines. Such a fine fraction makes it difficult to handle the compacted material and, moreover, has to be laboriously separated off and returned.

Another problem in the production of ultrapure silicon for photovoltaic applications is the contamination of the silicon dust in the treatment, especially in the compaction of the powder. In this case, in particular, any contact of the silicon powder with metallic surfaces and with oxygen is disadvantageous.

The invention is thus based on the object to provide an apparatus and a method for shaping a molded article from a powder, in which the resulting fine fraction is reduced and the purity of the powder is at least largely preserved.

This object is achieved by the features of claims 1 and 7. The core of the invention consists in forming in a cold isostatic dry die process, in particular, the metal chamber used for compacting the powder mold chamber. The compact tion of the powder is thus carried out in an at least almost metal-free environment. In contrast to roll compaction, in which the shaping takes place by means of linear forces and inevitably produces a fine fraction, stable and abrasion-resistant semi-finished products with a reduced fines content can be produced by cold isostatic pressing. By means of the device according to the invention, a very high freedom of contamination could be achieved.

Further advantageous embodiments of the invention will become apparent from the dependent claims. Additional features and details of the invention will become apparent from the description of several embodiments with reference to the drawings. Show it:

1 shows a cross section through a portion of the device GE measured a first embodiment with the slider of

Intermediate member in a first position,

2 shows a cross section through a portion of the device according to FIG. 1 with the slider of the intermediate member in a second position, FIG.

3 shows a cross section through a portion of the device according to FIG. 1 with the punch in a lower position for compressing the powder in the mold chamber, FIG.

4 shows a cross section through a portion of the device according to FIG. 1 with the plug in an upper position for removing the molded article from the mold chamber, FIG. 5 shows a cross section through a partial region of the device according to a further exemplary embodiment,

6 shows a cross section through a partial region of the device according to a further exemplary embodiment,

7 is a plan view of a device according to another embodiment,

8 is a sectional view taken along the line VIII-VIII through the embodiment of the apparatus of FIG. 7,

Fig. 9 sectional view taken along the line IX-IX through the embodiment of the apparatus of FIG. 7, and

10 shows a sectional view along the line X-X through the exemplary embodiment of the device according to FIG. 7.

A first exemplary embodiment of the invention will be described below with reference to FIGS. 1 to 4. A device for shaping a molded article from a powder comprises a supply device 1 and a compression device 2. The device further comprises an intermediate element 3 displaceably arranged between the supply device 1 and the compression device 2 and a base frame 4 which at least the compression device 2 is attached.

First, the construction of the feeder 1 will be described. The supply device 1 comprises a particular designed as a funnel 5 Befύll element. The funnel 5 is formed substantially rotationally symmetrical to a first, vertically oriented longitudinal axis 6. The funnel 5 has a funnel interior 12 with an upper inlet opening 7 and a lower outlet opening 8. Both the inlet opening 7 and the outlet opening 8 are closed gas-tight. The funnel 5 comprises a downwardly conically tapering upper part 9 and a downwardly adjoining this lower part 10. The lower part 10 is formed substantially hollow cylindrical. The upper part 9 and the lower part 10 are made of a non-metallic material at least on their side facing the funnel interior 12. The funnel interior 12 facing side of the upper part 9 and the lower part 10 is in particular carried out with an abrasion-resistant hard material layer. It is intended to form the funnel 5 made of stainless steel. It is also possible to form the funnel 5 from a glass or vitreous material. The funnel 5 is designed in particular in layered construction.

The funnel 5 comprises a funnel wall 11, which is largely gas-impermeable. In the area of the funnel wall 11, in particular in the lower part 10, however, a first degassing device 13 is provided. The first degassing device 13 comprises a porous structure 14 in the funnel wall 1 1, at least one filter element 15 and a first vacuum device 16. By means of the vacuum device 16, the funnel interior 12, in particular in the region of Parts 10 can be acted upon by negative pressure. The porous structure 14 and the filter element 15 are designed such that they prevent penetration of the powder in the hopper interior 12 into the vacuum device 16. For this purpose, in particular the filter element 15 has openings which are smaller than the smallest expected size of the powder located in the funnel interior 12. The filter element 15 is advantageously exchangeable bar. The porous structure 14 comprises a porous plastic, in particular a plastic fleece, combined with a metallic support fabric. The plastic is resistant to abrasion and has sufficient purity for use in photovoltaics. The porous structure 14 is designed in particular in layered construction.

In addition, the feed device 1 comprises a first feed screw 17 arranged in the hopper 5. The feed screw 17 comprises a shaft 18 arranged rotatably drivable along the longitudinal axis 6 and at least one gear 19 wound helically around the shaft 18. Both the shaft 18 and the passage 19 are made at least on their funnel interior 12 facing surface of a non-metallic material. The screw conveyor 17 is in particular made of a hardened steel and has an abrasion-resistant hard material layer on its surface. The passage 19 is advantageously over its entire length on the circumferential side of the funnel wall 11 at. However, a gap with a gap of a few millimeters between the passage 19 and the funnel wall 11 is also possible. On the shaft 18, a scraper 20 is also arranged to prevent bridging of the powder in the hopper interior 12 above the screw conveyor 17. The scraper 20 is located on the funnel wall 1 1 and is rotatably supported by the shaft 18 about the longitudinal axis 6. Between the scraper 20 and the funnel wall 11 may also be provided a gap with a gap of a few millimeters.

The intermediate member 3 is designed in particular as a horizontally displaceable slider 21. The slider 21 radially encloses an upwardly and downwardly open cavity 22. The cavity 22 is rotationally symmetric to a cavity axis 23. It has a radius r _H , which at least as is large as the inner radius r _{ü of} the lower part 10 of the funnel 5. The slider 21 is in the horizontal direction, that is perpendicular to the longitudinal axis 6 between a first position shown in Fig. 1, in which the cavity axis 23 with the longitudinal axis 6 coincides, and a second position shown in Fig. 2, in which the cavity axis 23 coincides with a second longitudinal axis 24, displaceable. In the direction of the longitudinal axis 6, the slider 21 and thus the cavity 22 has a height h. The cavity 22 thus has a volume V _H = π xr _H ² x h. The slider 21 has a removal slide 39 forming end wall 37. It may also be provided a separate removal slide 39.

In the first position of the slide 21 shown in FIG. 1, the cavity axis 23 and the longitudinal axis 6 coincide. In this position, the slider 21 thus there is a barrier-free transition from funnel interior 12 in the lower part 10 of the funnel 5 to the cavity 22 of the slider 21. The cavity 22 is in this position of the slider 21 at its lower, the funnel 5 opposite end by the Basic frame 4 powder-tight finished. In the second position shown in FIG. 2, in which the slide 21 is displaced by at least twice the radius Γ _{H of} the cavity 22 in the direction perpendicular to the first longitudinal axis 6 with respect to the first position, the slide 21 forms a closure of the outlet Opening 8 of the funnel 5.

The compression device 2 comprises a substantially cylindrical, rotationally symmetrical with respect to the second longitudinal axis 24 formed mold chamber 25 with a ring cylindrical shape chamber wall 26. The mold chamber 25 is formed substantially rotationally symmetrical to the second longitudinal axis 24. The lower end of the mold chamber 25 is closed by a plug 27. The plug 27 lies in its 1, to the gas-tight position shown in FIGS. 1 to 3 on the mold chamber wall 26. It forms the lower closure of the mold chamber 25. The plug 27 is displaceable along the direction of the second longitudinal axis 24. It can be lowered to open the mold chamber 25 down. However, it is also for removing a mold located in the mold chamber 25 upwards, that is, in the mold chamber 25 can be inserted. The plug 27 is releasably secured against displacement along the second longitudinal axis 24 by pins or notched plates, not shown in the figures.

The plug 27 has an insert 28, which is oriented in particular centrally, parallel to the second longitudinal axis 24 and made of a finely porous material, in particular of an abrasion-resistant plastic combined with a metallic support fabric. On the side of the plug 27 facing the mold chamber 25, a further filter may additionally be provided in the region of the insert 28. To the insert 28, a second degassing device 65 is coupled to a second negative pressure device 29. By means of the second vacuum device 29, the mold chamber 25 can be controllably acted upon by the insert 28 with negative pressure.

The mold chamber wall 26 includes an outer sleeve 30 having at least one pressure feed opening 31. The mold chamber wall 26 also includes a die 32 which is disposed on the inside of the sleeve 30. The die 32 is at least on its side facing the mold chamber 25 side of a non-metallic material. It is in particular made of an abrasion-resistant elastomer. It is flexible, in particular elastic. It has a high resistance to alternating stress while remaining dimensionally stable. To the pressure supply port 31 in the sleeve 30, a pressure chamber 33 is coupled. Instead of The pressure chamber 33 can be provided with any, in particular a hydraulic pressure-generating device. By means of the pressure-generating device, the die 32 can be pressurized from the outside. By pressurizing the die 32 with pressure, the mold chamber 25 is compressible, in particular uniformly, in particular isostatically compressible. In a particularly preferred embodiment, the plug 27 is slidable along the second longitudinal axis 24 to support the uniform, in particular isostatic, compression of the mold chamber 25. The pressure for applying pressure to the die 32 can be regulated by means of a regulating device 34. In the area between the control device 34 and the mold chamber 25, a pressure measuring device 41 is provided which measures the pressure acting on the female mold 32 and thus on the mold chamber 25.

The mold chamber 25 has an upper filling opening 35. The filling opening 35 and thus the mold chamber 25 can be closed in a gas-tight manner by means of a punch 36 displaceable along the second longitudinal axis 24. The punch 36 is formed substantially cylindrical. The punch 36 has an outer circumference which corresponds to the inner circumference of the hollow space 22. He is advantageously at his lower, the

Mold chamber 25 facing end formed peripherally formed. The punch 36 is displaceable along the direction of the second longitudinal axis 24 by at least the amount of the height h of the slider 21. The punch 36 is thus as shown in Fig. 3 in the second position of the slider 21 accurately inserted into the cavity 22. In a lower position of the punch 36, the punch 36 is gas-tight against the die 32. The mold chamber 25 is closed in this position of the punch 36 by means of the punch 36 gas-tight upwards. The mold chamber 25 with the die 32 is thus in particular powder-tight to the environment separated.

The stamp 36 has at least partially on a surface of a hard material layer. It can also be formed at least on its surface of ceramic, for example silicon nitride, silicon carbide or silicon oxide in proportions of at least 90% or a mixture of these. In particular, the punch 36 is at least in the mold chamber 25 facing region of its surface, which closes the mold chamber 25 in the lower position of the punch 36 and thus forms part of the mold chamber wall 26, made of a non-metallic material.

In the closed state, that is, with the plug 27 and the punch 36 in their respective closed position as shown in Fig. 3, the mold chamber 25 in the relaxed, that is acted upon neither with negative pressure from the inside nor with overpressure from the outside state an inner, free volume V _κ . The volume V _{K of} the mold chamber 25 is approximately as large as the volume V _{H of} the cavity 22. The volume V _{H of} the cavity 22 is in particular at least as large as the volume V _{K of} the mold chamber 25. The volume V _{H of} the cavity 22 may advantageously be slightly larger than the volume V _{κ of} the mold chamber 25th

The function of the device will now be described. The device is used to produce fusible silicon silicon powder, wherein the silicon melt is suitable for the production of polycrystalline silicon blocks and / or silicon single crystals for use of the produced silicon in the photovoltaic. The supply device 1 provides for supplying a predetermined amount of the powder into the In this case, the cavity 22 in the slide 21 of the intermediate member 3 of the predosing of the introduced into the mold chamber 25 powder amount is used.

To fill the mold chamber 25, first the funnel 5 is filled with a powder to be compacted, in particular with silicon powder, in particular with ultrafine, highly pure and highly dispersed silicon powder obtained from a monosilane in a deposition process. The primary particles of the silicon powder have a mean diameter of 0.01 .mu.m to 100 .mu.m, in particular from 0.1 .mu.m to 20 .mu.m, in particular 2 .mu.m to 5 .mu.m. By means of the screw conveyor 17, the powder is introduced into the cavity 22. Here, the mounted on the shaft 18 of the screw conveyor 17 scraper 20 prevents bridging of the powder above the passage 19th

Before and / or in particular during filling, the funnel interior 12, in particular in the lower part 10 of the funnel 5 with negative pressure, in the range of 50 mbar to 1000 mbar, in particular from 100 mbar to 600 mbar is applied by means of the vacuum device 16, which leads to a withdrawal of gas from the powdery starting material. The powder is thus already precompressed in the hopper 5, whereby the filling of the mold chamber 25 is optimized and the compression ratio for the molding is reduced. When the funnel interior 12 is subjected to negative pressure by the vacuum device 16, the filter element 15 and / or the porous structure 14 prevent the powder from penetrating into the vacuum device 16. Preferably, the powder is also prevented by the geometric pressure Embodiment of the passage 19 of the screw conveyor 17 in particular in the upper part 9 of the funnel 5 pre-compressed before filling the cavity 22 in the intermediate member 3. Once the desired amount of powder is present in the cavity 22 of the intermediate member 3, the slider 21 from its first position shown in Fig. 1, in which the cavity axis 23 coincides with the first longitudinal axis 6 in the horizontal direction, that is perpendicular to the longitudinal axis 6, in the second position shown in Fig. 2, in which the cavity axis 23 coincides with the second longitudinal axis 24, moved. In this second position, the slide 21 closes the outlet opening 8 of the funnel 5. It can be provided in particular to couple the drive device of the screw conveyor 17, not shown in the figures, to the position of the slide 21 such that the conveyor screw 17 only is then driven when the slider 21 is in the first position, as shown in Fig. 1.

After the slider 21 has been moved to the second position with the cavity 22 in which the precompressed powder is located, the powder pre-dosed in the cavity 22 is introduced into the mold chamber 25. The introduction of the powder into the mold chamber 25 takes place under the action of the gravitational force. It is supported by a negative pressure generated in the mold chamber 25 by means of the second vacuum device 29 in the range from 50 mbar to 1000 mbar, in particular in the range from 100 mbar to 600 mbar. The filling of the mold chamber 25 can be monitored by means of the pressure-measuring device 41. To monitor the filling of the mold chamber 25, other sensors, in particular weight meter or level sensors can be provided.

Finally, the punch 36 is inserted along the direction of the second longitudinal axis 24 down into the cavity 22 and along along the second longitudinal axis 24 is displaced until it sealingly closes the Befϋll opening 35 of the mold chamber 25. This ensures that the powder present in the cavity 22 is completely transferred into the mold chamber 25. In addition, by the vertical displacement of the punch 36, the powder in the mold chamber 25 can be precompressed, in particular if the volume V _{H of} the cavity 22 in the intermediate member 3 is slightly larger than the volume V _{K of} the mold chamber 25. Once the Form chamber 25 on the one hand from the bottom through the stopper 27 on the other hand from above sealed by the punch 36 gas-tight to the outside, the die 32 is pressurized to compress the powder in the mold chamber 25 from the pressure chamber 33 from the outside. The pressurization is done in particular hydraulically. But it can also be provided pneumatically. For pressing a molding pressures in the range of 100 to 1600 bar, in particular in the range of 200 to 600 bar used. The pressure which is applied to the die 32 via the pressure chamber 33 and the pressure feed opening 31 in the sleeve 30, acts uniformly over the entire circumference of the die 32. The mold chamber 25 thus becomes at least approximately uniform in the radial direction, in particular quasi-isostatic, in particular isostatic compressed, which leads to an at least largely isostatic compression of the powder in the mold chamber 25. Due to the largely isostatic compression, internal stresses in the shaping, which can lead to the formation of cracks, are avoided. The pressure curve can also be controlled variable time, in particular can be specifically avoided by adjusting the pressure holding time or the pressure profile locally occurring pressure peaks in the shaping. As a result, the cracking and the occurrence of increased fines can be selectively prevented. The compaction of the molding can be further improved by targeted degassing of the mold chamber 25 by means of the second degassing device 65. For this purpose, during the compression of the powder by pressurization of the die 32 from the outside by means of the second negative pressure device 29, the mold chamber 25 is pressurized from the inside with negative pressure in the range from 50 mbar to 1000 mbar, in particular from 100 mbar to 600 mbar.

After pressing the molding in the mold chamber 25, it must be removed from the mold chamber 25. For this purpose, the punch 36 is first moved along the second longitudinal axis 24 out of the cavity 22 into its upper starting position. Then, the slider 21 is shifted in the horizontal direction to its first position. Finally, the plug 27 is displaced upwardly along the second longitudinal axis 24, that is, through the mold chamber 25 to the position shown in Fig. 4, whereby the finished molding is removed from the mold chamber 25. If the slide 21 is now displaced into the second position with plugs 27 inserted into the mold chamber, the finished molding is pushed out of the press area by the end wall 37 of the slide 21.

Advantageously, the movements of the plug 27, the punch 36 and the slider 21 are coupled together, in particular by a mechanical coupling. As a result, the operation of the device can be simplified and achieve an increase in performance.

It has been found that molded articles having a bulk density of 0.04 to 2 grams / cm ³ , in particular 0.5 to 1.5 grams / cm ³ , in particular 0.8 to 1, are obtained with the device according to the invention and the method according to the invention. 2 grams / cm ³ and a fines below 5%, in particular below 1%, in particular below 0.1% of the material used in the case of contamination of the silicon powder with respect to metals by less than 1 ppm, in particular less than 0, 1 ppm, in particular less than 0.01 ppm. Furthermore, the moldings have a nip tensile strength in the range from 0.03 N / mm ² to 1 N / mm ² , in particular from 0.1 N / mm ² to 0.9 N / mm ² . The moldings are melted at a temperature of at most 1500 ⁰ C to form a homogeneous silicon melt.

Particularly advantageous is to arrange the entire device in a gas-tight closed reaction space. In order to avoid surface reactions of the silicon powder with oxygen, an inert gas device, not shown in the figures, is provided for replacing the oxygen contained in the reaction space by a protective or inert gas, preferably nitrogen or argon. The compaction of the powder can thus be carried out in an oxygen-free atmosphere.

Preferably, the supply device 1 is at least partially evacuated from the gas by means of the first degassing device 13 and the compression device 2 by means of the second degassing device 65 during the filling process of the mold chamber 25 in order to remove the powder even before the compression provide largely free of gas in the mold chamber 25 and thereby minimize the formation of pores in the molding. Another advantage of filling under reduced pressure is the pre-compaction of the powder thereby achieved, which in turn results in a higher final density of the moldings.

In the following, a further embodiment will be described with reference to FIG. Identical parts are given the same reference numeral as in the first exemplary embodiment, to the description of which reference is hereby made. Structurally different but functionally similar parts receive the same reference numerals with a following a. The main difference compared to the first embodiment is that the lower part 10a of the funnel 5 is arranged obliquely at a certain angle b, in particular at an angle b in the range of 30 ° to 60 °, to the first longitudinal axis 6, that through the Outlet opening 8a of the lower part 10a of the funnel 5 exiting powder can enter directly into the mold chamber 25. An intermediate member 3 is not necessary in this embodiment. In the region of the outlet opening 8a, a cross-section reducing element 40 for additional compression of the powder at the end of the screw conveyor 17 is provided. The cross-section reducing element 40 is designed in particular as a sieve. Further, the mold chamber 25 at its lower end to a removal opening 38. After completion of the compacting operation of the molding in the mold chamber 25, the plug 27 is moved to remove the molding from the mold chamber 25 along the direction of the second longitudinal axis 24 downward, whereby the removal opening 38 is opened and the finished molding is removed from the mold chamber 25. The finished molding is then removed from the horizontally displaceable removal slide 39 from the area between the plug 27 and the mold chamber 25.

In the following, a further embodiment will be described with reference to FIG. Identical parts are given the same reference numerals as in the first embodiment, to the description of which reference is hereby made. The supply device 1 is formed essentially as in the embodiment according to FIG. 1. The compression device 2, however, is essentially as in the embodiment formed according to FIG. 2. The main difference compared to the first and second exemplary embodiment is that the feed device 1, in addition to the first screw conveyor 17 arranged in the hopper 5, as the second screw conveyor, has a horizontally arranged feed screw 43 with a rotationally driven feed shaft 44 and a feed -Gang 45 has. In the area of the feed screw 43, a third degassing device 66 with a third vacuum device 42 corresponding to the first degassing device 13 is also provided.

It should be noted at this point that the various elements of the exemplary embodiments, in particular the supply device 1, the compression device 2 and the elements provided for removing the finished molding from the mold chamber 25 can be freely combined with one another.

A further embodiment of the invention will be described below with reference to FIGS. 7 to 10. Identical parts are given the same reference numerals as in the first embodiment, to the description of which reference is hereby made. Structurally different, but functionally similar parts receive the same reference numerals with a d followed. The main difference with respect to the first exemplary embodiment is that a cyclic permutation device with a plurality of mold chambers 25 designed as a round-clock table 46 is provided. The round-stroke table 46 includes an upper cover plate 47 and a rotatable rotary unit 48 disposed below it. In the rotary unit 48, a plurality of mold chambers 25 are arranged. The number of mold chambers 25 is in particular 6. However, another number is also conceivable. The mold chambers 25 are special uniformly arranged on a circle about a vertically oriented axis of rotation 49, so that the angular distance between each two adjacent mold chambers 25 is the same in each case. The angular distance between two adjacent mold chambers 25 is thus 360 ° / n _s, where n denotes the number of mold chambers 25 in the rotary unit 48. The rotary unit 48 is radially symmetrical with respect to the axis of rotation 49, that is, it turns on a rotation by an angle of 360 ° / n in itself.

The rotary unit 48 is rotatably mounted about the rotation axis 49 on a pin 50. In the pin 50, a vacuum supply line 51, which communicates with the second negative pressure device 29, integrated. The vacuum feed line 51 in the journal 50 comprises in particular a first, vertical section 63 arranged along the axis of rotation 49 and a second, horizontally arranged section 64. The first section 63 and the second section 64 abut one another in such a way that the negative pressure Feed line 51 is formed continuously. The first portion 63 is further connected to the degassing device 29 in connection. In addition, in the pin 50, a hydraulic supply line 52 for connection of the pressurizable die 32 is provided with the pressure chamber 33. The pressure chamber 33 is not shown in the figures. It is arranged in particular in the region of the axis of rotation 49 on the upper cover plate 47. The rotary unit 48 is friction and sealed by bearings 53 and seals 54 mounted on the pin 50. As seals 54 in particular elastic O-rings are provided. Alternative embodiments of the seals 54 are also possible. The rotary unit 48 is rotatable about the axis of rotation 49 by means of a drive unit 55. The drive is in particular indexed and clocked, the angular distance between two Index positions just equal to the angular distance 360 ° / n between two adjacent mold chambers 25 in the rotary unit 48 corresponds.

With regard to the structure of the mold chambers 25, in particular the mold chamber walls 26, reference is made to the preceding embodiments.

The rotary unit 48 comprises the massive base frame 4d. In the basic position 4d, a vacuum connection line 56 and a hydraulic connection line 57 are provided for each mold chamber 25.

Hereinafter, starting from a first angular position, the features of the six angular positions of the round-clock table 46 are described with respect to the axis of rotation 49 of the device, wherein the rotary unit 48 is currently in an index position. It is clear that by a rotation of the rotary unit 48 by a rotation angle of 60 °, the device passes into itself, with only the positions of the individual mold chambers 25 are cyclically reversed. During operation of the device, however, the respective angular positions correspond to certain, different filling states of the mold chambers 25 and different compression states of the powder located in the respective mold chamber 25.

To each of the mold chambers 25 with its longitudinal axis 24 is provided along the longitudinal axis 24 displaceable plug 27d. Each stopper 27d has a respective first latching element 58, designed as a notch, for example, and a correspondingly designed second latching element 59. By means of the latching elements 58 and 59 of the plug 27 d and a Locking device 60 in the base frame 4d, the plug 27d can be fixed in two vertical positions. The latching device 60 is designed in particular as a pneumatic cylinder, which can be brought into engagement with the latching elements 58, 59 designed as a bore or notch. In the latched position, the plug 27d is secured against displacement along the longitudinal axis 24.

In a first angular position with respect to the axis of rotation 49, the supply device 1 is arranged on the upper cover plate 47 of the round-cycle table 46. As a feeder 1, a feeder 1 according to any one of the preceding embodiments is provided. In the first angular position with respect to the axis of rotation 49, the longitudinal axis 24 of one of the mold chambers 25 coincides with the longitudinal axis 6 of the funnel 5 of the feed device 1. The lower outlet opening 8 of the trichter- 5 opens into the filling opening 35 of the mold chamber 25 in this angular position.

In this first angular position with respect to the axis of rotation 49, the second section 64 of the negative pressure supply line 51 in the journal 50, which runs from the axis of rotation 49 in the direction of the first angular position, pushes the negative pressure connecting line 56 in the base frame 4d of the rotary shaft. Unit 48 and the insert 28 d in the plug 27 d just in such a way that the mold chamber 25 can be acted upon by means of the second vacuum device 29 with negative pressure. In this case, the seals 54 ensure a sealed transition from the vacuum feed line 51 to the vacuum connecting line 56.

In the first position, the stopper 27d is in its lower position, that is to say the latching device 60 is connected to the first latching device. Element 58 engaged. The mold chamber 25 can be filled with powder from the supply device 1 in this position.

In a rotated by 60 ° in the rotational direction about the axis of rotation 49 second angular position of the round-clock table 46, the filling opening 35 of the mold chamber 25 is closed by the upper cover plate 47 of the round-cycle table 46. According to the embodiment shown, the mold chamber 25 is in this position neither with the negative pressure supply line 51 nor with the hydraulic supply line 52 in connection. However, it is also possible to form the vacuum supply line 51 in such a way that the mold chamber 25 can also be acted upon with negative pressure in this second position. The second angle position is provided as a buffer station.

In a rotated by a further 60 ° in the rotational direction about the axis of rotation 49 third angular position of the round-clock table 46, the loading of the mold chamber 25 is provided with pressure from the pressure chamber 33. In this position, the hydraulic supply line 52 communicates with the hydraulic connection line 57 sealed by the seal 54 in combination. The filling opening 35 of the mold chamber 25 can be closed in this position with the punch 36d. The punch 36d is displaceable in the vertical direction for rotation of the rotary unit 48, in particular can be raised. The chamfered edges of the punch 36d, when engaged in the fill port 35 of the mold chamber 25, aid in the precise locking of the rotary unit 48 in the respective index position. It is possible to design the vacuum feed line 51 in the journal 50 in such a way that the mold chamber 25 can also be subjected to negative pressure in the third angular position. The third angular position corresponds functionally to the compression device 2 of one of the exemplary embodiments described above. A fourth, about 60 ° rotated in the direction of rotation about the axis of rotation 49 angular position is provided for removal of the molding from the mold chamber 25. For this purpose, the upper cover plate 47 on a removal recess 61. The plug 27d in this angular position is displaceable in the vertical direction to an upper position for removal of the molding from the mold chamber 25. In the upper position of the plug 27d, the latching means 60 may be engaged with the second latching member 59 of the plug 27d. The removal recess 61 in the upper cover plate 47 is bounded by a vertical guide surface 62. The guide surface 62 is formed such that the guided out of the mold chamber 25 by means of the plug 27 d in a further rotation of the rotary unit 48 in the direction of rotation along the guide surface 62 slides while a predetermined path to the peripheral edge of the rotary unit 48 is transported. The guide surface 62 extends in particular to the peripheral boundary of the round-clock table 46. At this point, for example, under the round-clock table 46, a catching device, not shown in the figures may be provided for collecting the finished moldings.

In a fifth, again rotated by 60 ° in the rotational direction about the axis of rotation 49 angular position, the plug 27d is still in the mold chamber 25. However, the filling opening 35 is at least largely completed in this position of the upper cover plate 47 , so that the molding can not slip back into the mold chamber 25 even with a lowering of the plug 27 d in its lower position. In a sixth angular position, the plug 27d is again moved from its upper to its lower position. The displacement of the plug 27 is done in particular pneumatically or hydraulically. Alternatively, a mechanical displacement of the plug 27d is conceivable. In particular, the displacement of the plug 27 d may also be coupled to the rotation of the rotary unit 48. It can be done, for example, during rotation of the rotary unit 48 about the axis of rotation 49. For this purpose, in particular mechanical guide elements in conjunction with the plug 27d are conceivable. In the sixth angle position, the mold chamber 25 is ventilated. For this purpose, the upper cover plate 47 of the round-cycle table 46 is executed in this position upwards finally with a gap of 2 mm.

The sixfold radial symmetry of the rotary unit 48 represents only one possible embodiment and should not be construed as limiting.

It is also conceivable to form a round-clock table 46 and a rotary unit 48 with only three-fold radial symmetry. In this case, a first position for filling the mold chamber 25, a second position for compressing the powder in the mold chamber 25 and a third position for removal of the molding is provided. Other embodiments of the rotary unit 48 with a different radial symmetry are also possible.

Claims

Patentaπsprüche

1. A device for molding a molded article from a powder comprising a) at least one at least partially by at least one side of at least one mold chamber wall (26) limited form chamber (25) for receiving a powder, b) a supply device ( 1) for feeding the powder into the at least one mold chamber (25) and c) compacting means (2) for compressing the powder in the at least one mold chamber (25), d) the at least one mold chamber - Wall (26) at least in the region of the mold chamber (25) facing side consists of a non-metallic material.

2. Device according to claim 1, characterized in that the mold chamber (25) by means of a punch (36) is closable, wherein the punch (36) at least in the mold chamber (25) facing portion of its surface from a non metallic material.

3. Device according to one of the preceding claims, characterized in that at least one vacuum device (13, 29, 42) is provided.

4. Device according to one of the preceding claims, characterized in that the device is arranged in a gas-tight closed reaction space, wherein an inert gas device for replacing the oxygen obtained in the reaction space by an inert gas.

5. Device according to one of the preceding claims, characterized in that the supply device (1) comprises at least one screw conveyor (17, 43).

6. Device according to one of the preceding embodiments, characterized in that a cyclic permutation device is provided with a plurality of mold chambers (25).

7. A method for producing moldings from a powder comprising the following steps:

Providing at least one mold chamber (25) at least partially enclosed by at least one side of at least one mold chamber wall (26) for receiving a powder, filling the at least one mold chamber (25) with a powder,

Compacting the powder in the mold chamber (25), - wherein for compacting the powder, the mold chamber (25) with

Pressure is applied.

8. The method according to claim 7, characterized in that the

Pressurization of the mold chamber (25) is hydraulically.

9. The method according to any one of claims 7 or 8, characterized in that the mold chamber (25) in the radial direction at least approximately uniform, in particular quasi-isostatic, in particular isostatically compressed.

10. Silicon, produced by the method according to any one of claims 7 to 9, characterized in that a) the silicon in the form of a homogeneous, compressed molding of a compacted powder is present, b) the forming an average nip tensile strength in the range of 0.03 N / mm ² to 1 N / mm ² , in particular from 0.1 N / mm ² to 0.9 N / mm ² , c) the molding has an average bulk density of 0.04 g / cm ³ to 2 g / cm ³ , d) the primary particles of the silicon powder of the molding have a mean diameter in the range of 0.01 .mu.m to 100 .mu.m, in particular 0.1 .mu.m to 20 .mu.m, in particular 2 .mu.m to 5 .mu.m, and e) the shaping at a temperature of at most 1500 ⁰ C to a homogeneous silicon melt is melted.

11. Use of the device according to one of claims 1 to 6, characterized in that it is the powder to be compacted silicon powder.