CA2421604C

CA2421604C - Powder feeding apparatus with a filling shoe and mask

Info

Publication number: CA2421604C
Application number: CA002421604A
Authority: CA
Inventors: Michael Thomas Silbermann
Original assignee: DORST Technologies GmbH and Co KG
Current assignee: DORST Technologies GmbH and Co KG
Priority date: 2002-03-06
Filing date: 2003-03-06
Publication date: 2007-04-24
Anticipated expiration: 2023-03-06
Also published as: DE10209746B4; DE10209746A1; CA2421604A1

Abstract

A method and apparatus for feeding a die, wherein a filling shoe (7) cyclically is driven into a feeding position above a die opening (2) embedded in the die (1) and into a non-feeding position situated away from the die opening (2) above the die's upper side (6) and wherein during the feeding position the pulverized or granulated powder (11) is being filled from the filling shoe (7) into a hollow space, which is built in the die opening (2) above of at least one punch (3 - 5) being moveable within it in an upward and in a downward direction. In order to prevent mixing of old powder with the new powder when the opening of the die is moved over again being already partly fed with powder it is suggested to put a mask (12) with at least one mask opening (13, 13a) above the die opening (2) before or during the moving of the filling shoe (7) over the die opening (2).

Description

POWDER FEEDING APPARATUS WITH A FILLING SHOE AND MASK
Background of the invention As can be seen from Fig. 5, there are generally known dies 1 comprising a die opening 2, in which at least one punch 3 - 5 is arranged being movable in an upward and a downward direction. A filling device having the form of a filling shoe 7 and having arranged at least one filling hose 8 for filling a filling shoe chamber 10 with powder, slides above the die surface 6. In order to move the filling shoe 7 forward and backward above the die surface 6 the filling shoe 7 is coupled to driven guide rods 9. Advantageously, the guide rod arrangement 9 reaches over bolts 9b, which laterally protrude out of the filling shoe 7. In order to feed the die opening 2 in an area above lowered punches 3, 4 with powder 11 the filling shoe 7 is moved over the die opening 2, being the filling shoe 7 previously already filled with powder.
It is a problem to feed the die opening 2 with different sorts of powder 11, and 11a, respectively, into different sections of the die opening. E. g., if the filling shoe 7 away from the die opening 2 is re-fed with powder 11a after previously being filled another kind of powder 11 in one die opening section, the result is, that, when following displacement of the filling shoe 7 over already fed area occurs, powder particles of powder 11a which is located in the filling shoe chamber 10 will mingle with superficial part=icles of the other powder 11 in the die opening 2. In case that the powder 11a being in the filling shoe chamber 10 has a clearly higher density than the powder 11 being in the die opening 2, then an even deeper and far-reaching mixing of powder 11 in the die opening 2 will take place. Especially, a break-down in the peripheral areas takes place, in the course of which the heavier powder 11a from the filling shoe chamber 10 along the edge of the die opening 2 penetrates deeply into the die opening 2, while away from it light powder 11 will be brought upward from the die opening 2 into the filling shoe chamber 10.
Summary of the invention The object of the invention is to improve a powder feeding apparatus, to improve a filling shoe for such an apparatus and to improve a method for feeding of a die opening with powder, respectively. Especially, there should be avoided that different powder materials are mixed together by being dragged along, and that superficial areas get polluted or mixed together. Furthermore and advantageously, the effect of break-down in the marginal areas of the die has to be avoided.
In one embodiment of a powder feeding apparatus, especially for metallurgical powders, the powder feeding apparatus comprises at least one die, comprising a die surface and at least one die opening within it, one, two or more punches being shiftable within the die opening in upward and downward direction, a feeding device, comprising a filling shoe being moveable above the die surface into at least one position above the die opening in order to feed it and into at least one position which is distant of the die opening, and a powder filling device for filling the powder, at least one mask comprising at least one mask opening, and at least one mask guiding device. Said mask guiding device comprises means to temporarily cover the die opening with the mask in such a way that the mask opening or the mask openings, respectively, are arranged above a part of the die opening which has to be filled with powder, when the filling shoe moves in direction to and over the die opening and for removing the mask from the die opening when or after the filling shoe moves away from the die opening.

In one embodiment a filling shoe comprises a filling shoe guiding device and a powder feeding device. A mask guiding device is configured for putting on a mask above a die opening having at least one mask opening when the filling shoe moves in direction to and over the die opening and for removing the mask from the die opening when the filling shoe moves away from the die opening.
In one embodiment method for feeding with pulverized or granulated material a die opening within a powder feeding apparatus and/or by means of a filling shoe, wherein a mask will be arranged upon the die opening before it will be fed, which comprises a die opening in order to feed a pre-determined space of the die opening in a well-directed way, at least one filling device will be driven into a feeding position above the die opening embedded in the die and into a non-feeding position away from the die opening above the die's upper side and wherein the pulverized or granulated material in the feeding position is being filled from the fil_Ling device into a hollow space, which is being built in the die opening above of at least one punch which is moveable in <~n upward and a downward direction within it. The mask with the mask opening is placed above the die opening before or during the moving of the filler device above the die opening.
The fundamental thought concerning such a powder feeding apparatus, the filling shoe being brought into action within it and the method for filling in a die opening with a pulverized or granulated material consists in covering with a mask the die opening already partially filled with powder in especially the fed areas, whereby the mask comprises one or more mask openings in these areas, where the die opening is to be fed with pulverized or granulated material in a further working process.

Advantageously, according to a powder feeding apparatus and with a die, with automatic control mechanism, at least a punch within a die opening and a feeding device, especially with a filling shoe, a mask is provided, having at least one mask opening, whereby for moving and/or transferring of the mask in addition a mask guiding device has to be provided.
The mask guiding device facilitates a temporary covering of the die opening with the mask in such a way that the mask opening and the mask openings, respectively, is/are arranged above a part of the die opening which subsequently has to be filled with powder. Furthermore, the mask guiding device facilitates the temporary removing of the mask from the die opening and from the area which surrounds the die opening.
Advantageously, the mask guiding device as such can be provided by a plurality of designs. On the one hand mask guiding devices can be designed which are part of the real feeding apparatus, e. g. drives, which can lift up and displace a mask or which can swivel a mask around a joint tied to the place and turn down the mask over the desired die opening. Further exemplary drives facilitate moving or swivelling of the mask, while the same slides over the die sur:Eace during the process, so that the filling shoe advantageously always can lie on the mask. The mask e. g. in form of a thin sheet can, advantageously, also be bended upward by means of a mask guiding device with in particular turning rolls in the front field of the filling shoe. By moving the filling shoe in direction of the die opening advantageously the mask will be bended downward by the filling shoe and will be put on the die opening and its surrounding area in the end. When the filling shoe moves backward the mask again will be bended or pulled upward through the mask guiding device, particularly carried out by elastic spring mechanisms or by the influence of weights, which can exercise a corresponding tensile force upon one end of the mask via turning rolls. Besides bending the mask by means of a guiding device a mask moving can therefore generally also occur via other forces F acting on the mask.
Advantageously, on the other hand mask guiding devices can be 5 provided, which already are part of the filling shoe. E. g.
there can be arranged a turning device on the upper side of the filling shoe, which, driven by means of a spring or a weight and particularly using a turning roll, pulls the front end of the mask upward particularly upward in a sloped direction above the filling shoe. According to a particularly simple embodiment, however, there can also be designed a mask leader which is arranged on the front side of the filling shoe in form of turning rails and which turns the mask coming out from the front side out of the filling shoe when being moved backward into an upper direction, particularly turns it in direction of the backward movement in upward direction over the filling shoe. When the filling shoe moves in direction of the opening of the die the mask via forward-movement of the filling shoe automatically again will be pulled in front of the filling shoe and under it. In order to make possible this automation the end of the mask which lies on the opposite side of the movable end of the mask purposefully will be fixed on a rigid piece relatively situated to the die.
Advantageously there can also be used mufti-material filler and mufti-material filling shoes, respectively, which in a first working step get inserted the powder via a first powder hose into their powder chamber in order to get filled in a further working step via a second filler hose another powder into their powder chamber. The filling shoe after the feeding of the filling shoe chamber then will be moved over the die opening in order to unload the contents of the filling shoe chamber into the die opening.
Of course it is also possible to insert the powder just in that very appropriate position in which the filling shoe is already situated right above the die opening. Also in this case it can be advantageous to cover the opening of the die with a mask leaving an area free which really has to be fed.
Very advantageous is also a sucking or wiping device in order to clean the mask when being removed from the die opening from powder residues which stick on the mask. This prevents contamination at a later working step, at which such powder residues sticking on the mask could come into the die opening or into the filling shoe chamber.
Brief description of the drawings An embodiment with different designs is described below in more detail with reference to the drawings. There is shown in:
Fig. 1 sequence of 7 cut representations shown in parts 1A - 1G through a die and a die opening, a feeding procedure for a die opening in several working steps;
Fig. 2 three different mask guiding devices;
Fig. 3 three diagrams illustrating operation of a multi-material filling device with at the same time displacement of the mask between the single feeding steps;
Fig. 4 a powder feeding apparatus with a plurality of feeding stations in two designs and Fig. 5 a cut through a powder feeding apparatus during the over-sliding of a filling shoe over an already partly with powder fed die opening according to the prior art.
Detailed description of certain inventive embodiments As can be seen from Fig. 1 with sub-Fig. 1A-1G a die 1 comprises a die opening 2, in which is arranged at least one punch being movable in upward and downward direction preferably, however, a plurality of such punches 3 - 5. By moving downward of the individual punches above these punches there is created a space in the die opening 2 able to be fed with powder.
A filling shoe which preferably can be driven into two basic positions serves for feeding the die opening 2 with powder 11. The filling shoe 7 is coupled to a powder feeding apparatus 8 particularly coupled to one or more powder hoses 8, through which powder can be filled into an interior filling shoe chamber 10.
In a preferred construction the filling of powder 11a into the filling shoe chamber 10 takes place in a basic position, in which the filling shoe 7 is arranged on the die surface 6 away from the die opening 2. For transferring the filling shoe 7 over the upper side of the die 1, i. e. over the plate of the die respectively the die surface 6 there serves a filling shoe driver preferably having a guide rod arrangement 9 which is coupled to the filling shoe 7. In a very preferred design, part of inversely U-shaped guide rods 9 reach over bolts 9b which laterally protrude from the filling shoe 7 and the filling device 7, respectively.
As can be seen from Fig. 1A, the filling shoe 7 when being in an advanced stage of the process is situated already above the die opening 2, whereby powder 11 falls into the die opening above the down-sunk punches 3 and 4 from the filling shoe chamber 10. Usually the filling shoe 7 with already powder-filled filling shoe chamber 10 and with not yet down-lowered punches 3 - 5 will be driven above the die opening 2.
Only if the filling shoe 7 with its filling shoe chamber 10 is situated above the punches 3, 4 to be lowered, then the punches 3 and 4 will be lowered whereby the powder falls out of the filling shoe chamber 10 into the space or cavity, respectively, which now is created above the down-lowered punches 3 and 4 in the die opening 2. As a result of creating lower pressure above the punches 3 and 4 by down-lowering them, this method is also called suction-filling.
After the die opening 2 has been fed with powder 11, the filling shoe 7 again is moved back into the other basic position as it can be seen from Fig. 1B. In that other basic position the filling shoe chamber 10 of the filling shoe 7 then again will be fed with powder 11a, being the powder 11a introduced via a filling hose 8 out of a hopper, as it also can be seen from Fig. 1C. The powder 11a mostly is another powder 11a than powder 11, which has been filled into the die opening 2 in the preceding cycle of the process.
As can be seen from Fig. 1D, the filling shoe 7 is again moved above the die opening 2 in the following step of the procedure. Together when or before moving the filling shoe 7 above the die opening 2, however, a mask , particularly a stencil or a sheet, will be put over the die surface 6 and the die opening 2. The mask 12, particularly a flexible sheet, comprises at least one mask opening 13, which comes to lie above an area of the die opening 2, whereby in the following into this area the powder 11a should be fed from the filling shoe chamber 10. The mask opening 13 is adapted to the die opening 2 especially in view of the form of the section which has to be fed, it can, however, also be adapted to certain demands in a finely-structured manner, e. g. in order to produce an electrically finely structured conductive circuit on a normally rigid compact.
As can be seen from embodiment shown in Fig. 1D the mask 12 is provided in the form of a sheet which is rolled off over the die surface 6 by a rolling movement in a similar way like a carpet is unrolled. There, the placement of the mask 12 on the die surface 6 and on the die opening 2 can be carried out synchronously to the movement of the filling shoe but it also can be done independently of the movement of the filling shoe.
In particular, it is possible to put on the sheet from another side than the side of the position the filling shoe being filled. Particularly preferred, however, are designs, where the filling shoe is permanently arranged on the mask being therefore not necessary to move the filling shoe over an edge of the mask.
As can be seen from 1E, in a following moment the filling shoe 7 with a heavy powder 11a, for example, is located above the die opening 13 in the mask 12. When being moved into this position there does not occur contamination of the powder which already has been filled into the die opening 2, because the mask 12 is placed between. In a further step the appropriate punch 5 below the opening of the die 13 will be lowered, as a result of which the powder 11a is being sucked or falls from the filling shoe chamber 10 into the area which is created above punch 5.
Then the filling shoe 7 again will be moved into the other basic position i. e. into the position where the filling shoe is fed, as can be seen from Fig. 1G. On that occasion, automatically or apart from it, the mask 12 can be removed from the die opening 2 again.
As can be seen from Fig. 2A - 2C, there are a plurality of different designs for mask guiding devices. Besides stencils and rigid masks flexible masks 12 e.g. sheets are particularly preferred. The thinner the mask the less powder possibly will stand over the basic height of the plate of the die or the die surface 6 after removal of the mask.
As can be seen from Fig. 2A, a particularly simple mask guiding device consists of a guide mechanism, a guiding rail for example. A simple guide mechanism can exist in the form of a mask guide 20 which is spaced at the front side of the filling shoe 7. The mask guide reaches down with its lower end until the die plate 6 (see Fig. 1F) being preferably bent 5 in a slightly arched way to the front, then to the upper side and lastly sloped back in direction of above the filling shoe 7. As a result of this the mask 12 is bent from the die surface 6 in an upward direction and lastly in a backwardly direction tilted above the filling shoe 7. The mask guide 20 10 preferably is fixed on the front side of the housing of the filling shoe 7 with the appropriate fixing and spacing elements 21.
When the filling shoe 7 moves in forward direction, it presses the mask 12 in downward direction by the edge of its front and lower edge and, correspondingly, causes the mask 12 to be retracted when moving in forward direction. When the filling shoe 7 is moved in backward direction away from the die opening 2 into the resting position of the filling shoe and into the position where the filling shoe has to be fed, respectively, the mask 12, however, in the front side slides into the mask guide 20 and through the mask guide 20 into an upper direction, tilted above the filling shoe 7, respectively, being lastly as a result of it lifted off of the die surface 6.
In a particularly preferred design a sucking device 31 can be provided, which on one side or on both sides sucks the remaining powder from the off-lifted mask 12. On the lower side of the mask 12 powder can remain stuck from the opening of the die 2, on the upper side of the mask 12 remaining powder from the filling shoe chamber 10 also can remain stuck. Particularly powder containing carbon would remain stuck on the mask 12 in a stronger way than simple metallic powder.

The mask 12 can be produced out of different sorts of materials to provide flexibility demanded pursuant to the designs of Fig. 2A-2C. Preferably, the mask 12 can be made out of a thin stable synthetic sheet or a thin metal sheet with sufficient flexibility.
As can be seen from Fig. 2B, the mask 12 also can be pulled in an upwardly inclined direction from the front side of the filling shoe 7 by means of a frame which is arranged on the upper side of the filling shoe 7. The device shown consists of a linkage 23 which protrudes from the upper side of the filling shoe in the upward direction, on the upper side of which a roll 24, for example, as a turning device is mounted. From the end of the mask 12 preferably a tensile rope 25 leads over the roll 24 to a spring 26, which is mounted on the upper side of the filling shoe 7 with its other end. Therefore, the spring 26 always pulls the front end of the mask 12 in an upward direction. The mask 12 is, consequently, pulled in an upward direction in an area in front of the filling shoe 7. The longer the distance through which the filling shoe 7 has to be moved in a forwardly or backwardly direction, the higher the linkage 23 which, accordingly, has to be used.
Also, one can imagine any other design, for example using a weight instead of a spring 26. Instead of the roll 24 there also can be used a roller like turning device via which not only a tensile rope but also the mask 12 itself can get turned in its course. Also, e. g. the spring can be arranged directly acting on the front side of the mask 12 from the upper end of the linkage.
As can be seen from design shown in Fig. 2C the mask 12 is not pulled into the upward direction by means of a mask guiding device which is arranged on the filling shoe 7 itself, but via a mechanical frame device 28, which has been mounted rigidly relative to the die 1. The illustrated mechanical device 28 again shows rolls 27 which change the course of a tensile rope, which is tensioned between the mask 12 and a weight 29.
Alternative mask guiding devices also can be constructed as rolls or drums in order to roll up the mask, being it therefore possible to roll out and to roll up the mask 12 like a carpet.
While according to the three embodiments shown in the figure with the aid of the filling shoe 7 the mask 12 is pressed against the die surface 6 or above the die opening 2, respectively, when being moved into the position above the die opening 2. However, the putting of the mask 12 onto the die surface 6 or above the die opening 2, respectively, and the moving or transferring of the filling shoe 7 also can be carried out independently of each other. In particularly preferred designs, however, the single moving steps are coupled synchronously one to each other.
An exemplary design for the movement of the mask 12 and the movement of the filling shoe 7 the one moving independently from the other is outlined by the sequences shown in Fig. 3A-3C.
As can be seen from Fig. 3A in plan view a die 1 again comprises a die surface 6 with a die opening 2 embedded therein. Above the die surface 6 a filling shoe 7 moves forwardly and backwardly. The movement in forward and backward directions of the filling shoe 7 again is done via guide rods 9, which again preferably reaches over bolts 9b which laterally protrude out of the filling shoe 7. According to a particularly preferred design of the mufti-material filler it is possible to move the filling shoe 7 not only in forwardly and backwardly directions but also crosswise to said moving direction above the die surface 6. Instead of separate movements in forwardly and backwardly directions and to the left or to the right, respectively, there is also possible a swivelling movement overlying these movements or independent of them around a swivelling axis 9c, which is situated in the guide rods 9 or in the area of the drive of the guide rods 9, such as is generally known.
The filling shoe 7 which is shown is designed as a multi-material filler and preferably comprises two or more filling hoses 8a, 8b in order to feed the filling shoe chamber 10.
Instead of feeding only one filling shoe chamber 10 also more filling shoe chambers can be designed in the filling shoe 7.
According to the procedural step shown in Fig. 3A the die opening 2 is already partly fed with powder. Before moving the filling shoe 7 over the opening of the die in a further step the mask 12 will be laid over the die opening 2. The mask 12 shown comprises a mask opening 13 in the form of a cylindrical hoop. Such a mask opening 13 can be formed by leaving a filled circle with smaller diameter within a tubular opening in the mask 12. For fixing the inner circle there can be left thin rods, which do not cause problematic interference when the die opening 2 below is being fed evenly.
After moving the filling shoe 7 in a forward direction over the mask opening 13 and the below-lying die opening 2 and after the act of feeding by means of the powder being carried with the filling shoe 7 will again be drawn back to the starting point for being fed. When the filling shoe is at the starting point or during the act of drawing back the mask 12, the mask 12 will be pulled laterally in relation to the movement in the forwardly and backwardly directions of the filling shoe 7 using a mask transferring drive 30. The mask transferring drive 30 is situated on the die 1 or on a frame device as can be seen from Fig. 3B. Effectively, the transfer of the mask happens only when it has been removed from the die opening 2, in order to prevent dragging of powder 11 and 11a situated in the die opening 2, respectively, over the die surface 6.
After lateral transfer of the mask 12 it again will be put over the opening of the die 2, while, now, other additional mask openings 13a lie above the die opening 2. As can be seen from the aforementioned, also these further mask openings 13a for the appropriate purpose lie above areas of the die opening 2, below which appropriately moulded punches will be lowered after the filling shoe 7 has been moved over the die opening 2 or the mask openings 13a, respectively, in order to fill powder from the filling shoe 7 into the appropriate areas of the die opening 2.
As can be seen from Fig. 3A - 3C, the mask openings 13a can have certain desired circumferential shapes. This is important in the production of pressed bodies, which, for example, have lower layers consisting of a solid bearer material and upper or intermediate layers containing materials which are electrically conducting or electrically isolating.
As can be seen from Fig. 4A, a complex powder feeding apparatus 40 can comprise a plurality of filling stations 43, which are used for feeding a single die having a die opening 2. According to the design demonstrated the die is situated in a die slide 41, and can be moved crosswise to the single filling stations 43. After the die opening 2 has been fed completely, the die slide 41 advantageously and in a direct way can move the guided die out of the side of the filling apparatus into a press 44, in which the powder will be pressed into a solid compact, as it is known generally. The feeding of the die opening 2 of course also can be carried out in a direct way within such a powder press by using the mask technology being generally described.

In the filling apparatus 40 shown, with the first filling shoe 7 in a position on the left, a first filling shoe 7 carrying a first powder is moved over the die opening 2, in order to put powder, which is contained in the filling shoe 5 chamber of the filling shoe 7, into the die opening 2. After the filling shoe 7 has been moved back into the basic position the die slide 41 is moved into the appropriate position in front of one of the other filling stations 43. In this position an appropriate filling shoe 7 will be moved 10 from the other filling station 43 above the die opening 2, in order to release powder being in the filling shoe 7 into the opening of the die. In an advantageous way at least one powder hopper with the appropriate different powder will be assigned to each of the filling shoes 7 making it possible to 15 fill the filling shoe for each filling station 43 powder of a different nature and to then fill the die opening 2 with a desired layer structure of powder. When producing a compact with a plurality of layers it is also possible to move the die slide 41 more than one time to a certain filling station 43, if an appropriate powder layer structures is desired.
As can be seen, when using loose filling shoes 7 with coupled filling hose 8, at the most there can be used a unique filling shoe drive for the purpose, the frame 9 of which arranged on the side of the filling shoe can be coupled to the appropriate filling shoe 7 which is to be moved. Together with the transfer of the die slide 41 accordingly the guide rod arrangement 9 for guiding the single filling shoes 7, will be transferred to another of the filling shoes 7 in lateral or parallel direction onto the slide guide 42.
As can be seen from Fig. 4B there also can be constructed any other forms of filling apparatus. Advantageously, there can also be a central die comprising a die opening 2, around which there, in a circular arrangement, there are several filling stations 43 each of which has one filling shoe.

Particularly, such an arrangement can be part of the powder press 44.
While the aforementioned description follows the example of metal powder presses, the basic principle can be taken for any constructions where a pulverized or granulated material is to be filled into a receiving space. Also, in the following there need not be carried out a pressing of the powder in a powder press as an absolute requirement.
As a pulverized or granulated material there can be used the most different sort of material, i. e. besides metal powders also ceramic powders or carbon powders can be used. The aforementioned described procedure particularly also makes possible the production of mixed alloys or complex compacts, where less solid layers are put onto solid layers. It is also possible to produce compacts, for example, comprising a solid material on the outer side and a softer material which also can have greasy attitudes around a central through opening on the inner side in order to receive a rotating shaft. Further application areas are for example the production of fuel cells, i. e. the production of compacts, where very different materials have to be arranged above each other and/or beside each other in the compact which is to be produced while satisfying the requirement for extreme cleanliness of the single areas.

Claims

WHAT IS CLAIMED IS

1. A powder feeding apparatus, especially for powder metallurgical powders, having at least one die having a die surface and at least one die opening within the die surface, one or more punches being shiftable within the die opening in upward and downward directions, a feeding device having a filling shoe moveable above the die surface into at least one position above the die opening in order to feed the die opening and into at least one position which is remote from the die opening, a powder filling device for filling the feeding device with powder, said apparatus comprising at least one mask having at least one mask opening, and a mask guiding device having means for temporarily covering the die opening with the mask such that the mask opening is arranged above a part of the die opening which has to be filled with powder, before or during movement of the filling shoe toward and over the die opening and for removing the mask from the die opening during or after movement of the filling shoe away from the die opening.

2. The powder feeding apparatus according to claim 1 wherein said mask guiding device raises the mask in an upward direction away from the die surface, when the filling shoe is situated away from the die opening.

3. The powder feeding apparatus according to claim 1 comprising a plurality of feeding devices, at least one of the feeding devices having said mask guiding device and whereby the feeding devices are arranged to be driveable separately of each other for feeding the die.

4. The powder feeding apparatus according to claim 1, wherein said mask has a plurality of mask openings and said mask guiding device is operative to place selected mask openings above the die opening.

5. A filling shoe, having a filling shoe guiding device and a powder feeding device, said filling shoe comprising a mask guiding device for putting a mask having at least one mask opening over a die opening before or during movement of the filling shoe over the die opening and for removing the mask from over the die opening after or during movement of the filling shoe away from the die opening.

6. The filling shoe according to claim 5, wherein the mask guiding device comprises a lifting arrangement with a pulling mechanism operative to remove the mask from the die opening when the filling shoe is moved away from the die opening and operative to place the mask on the die opening when the filling shoe is moved toward the die opening.

7. The filling shoe according to claim 5, wherein the mask guiding device comprises a lifting arrangement with a turning device on an upper side of the filling shoe operative to remove the mask from the die opening when the filling shoe is moved away from the die opening and operative to place the mask on the die opening when the filling shoe is moved toward the die opening.

8. The filling shoe according to claim 5, wherein the filling shoe is a mufti-material feeder.

9. The filling shoe according to claim 5, wherein the mask opening is smaller than the die opening and wherein the mask opening has a non-circular shape.

10. The powder feeding apparatus according to claim 1, wherein the mask opening is smaller than the die opening and wherein the mask opening has a non-circular shape.

11. The powder feeding apparatus according to claim 1 comprising a cleaning device for cleaning the mask.

12. The filling shoe according to claim 5, comprising a cleaning device for cleaning the mask.

13. Method for feeding a pulverized or granulated material into a die having a die opening and at least one punch which is moveable in an upward and downward direction, said method comprising:
- providing a powder feeding apparatus having a filling shoe and a mask, said mask having a mask opening;
- positioning said mask over said die such that said mask opening is aligned with the die opening;
- moving said filling shoe into a feeding position above the mask opening and the die opening so that the pulverized or granulated material flows from the filling shoe through said mask opening and said die opening into said die; - moving said filling shoe out of said feeding position; and - removing said mask from said die opening;
wherein said mask opening is aligned with said die opening, before or during movement of the filling shoe into said feeding position, and said mask is removed from said die opening during or after said movement of said filling shoe out of said feeding position.

14. The method according to claim 13, wherein the mask is positioned above the die and said mask opening is aligned with said die opening by rolling the mask onto a die surface.

15. The method according to claim 13, wherein the mask is positioned above the die and said mask opening is aligned with said die opening by sliding said mask over a die surface.

16. The method according to claim 13, wherein the mask is positioned above the die and said mask opening is aligned with said die opening synchronously with movement of the filling device.

17. The Method according to claim 13, wherein the mask is removed from the die opening during or after movement of the filling shoe away from the die opening.