Die table for rotary tablet presses and rotary tablet press

The invention relates to a die table (10), for a rotary tablet press, comprising a rotating rotor (1) formed from the die table (10), a punch guide (5) for the upper punch (7) and a punch guide (3) for the lower punch (4). The die table (10) comprises several exchangeable dies (11) arranged concentrically around the rotational axis of the rotor (1) and aligned with the upper and lower punches (7, 4). According to the invention, the short set-up times for changing the press to other die shapes may be achieved, whereby the die table (10) comprise at least two recesses (12) and an insert piece (20) is exchangeably inserted in each of the recesses (12) which comprises several dies (11).

The invention relates to a die table for a rotary tablet press which has a rotatable rotor which is formed by the die table, by a ram guide for upper rams and by a ram guide for lower rams, comprising a plurality of exchangeable dies which are arranged concentrically around the rotational axis of the rotor and are aligned with respect to the upper and lower rams in the respective ram guides. The invention also relates to corresponding rotary tablet presses.

Rotary tablet presses comprise rotors which can also be designed as exchangeable rotors and comprise, in addition to a die table, a guide for the upper rams and a guide for the lower rams. The upper and lower rams which are arranged in the ram guides are aligned axially parallel with respect to dies or die bores which are formed in the die table and in which the powder supplied to the rotary tablet press is shaped into a pellet by means of the ram. The ejection of the pellet is generally carried out by means of the lower ram, upward to the upper side of the die table. The cross section and the design of a die together with the stroke of the ram determine the contour of the pellet which is to be produced. Depending on the contour of the pellet and the composition of the powder which is to be compressed, the wear to the dies varies in intensity.

A die table usually contains a plurality of through bores, with each individual through bore either forming a die itself or forming a holding bore for a sleeve-shaped, exchangeable die (die sleeve). The number of rams used therefore corresponds to the number of dies or die sleeves which, in the event of servicing work or installation work, must be dismounted, serviced and/or mounted, with the exchangeable die sleeves usually being secured in the respective die holding bores in the die table by locking means which are screwed into radial bores. The maintenance effort for die tables with exchangeable die sleeves is correspondingly high.

DE 101 59 114 U1 discloses a rotor for a rotary tablet press in which the die table is composed of a plurality of table segments, with the assembled table segments forming the die table which is fastened in an exchangeable manner to the rotor. Formed in each table segment are a corresponding number of dies which are formed as die bores, so that therefore in the event of wear, it is no longer necessary to replace individual dies, but rather the entire die table is dismounted in segments and replaced with another segment-shaped die table. In the case of the die table which is composed of table segments, although the assembly effort is greater than in the case of conventional die tables which provide a separate bore for each individual die sleeve, the production costs for a corresponding die table are however disproportionately higher. At the same time, during the assembly of the individual ring segments to form the die table, great demands are made on the positional accuracy of the ring table segments relative to one another, since in the event of positional deviations, the upper surface of the die table has uneven portions, which excessively quickly destroy scrapers, sealing lips and other auxiliary means, for supplying the powder and discharging pressing dust or the like, used in the operation of the rotary tablet press.

It is an object of the invention to create a die table which, with short fitting times, can be re-tooled with dies having other contours for the pellets or with new dies for servicing and cleaning purposes.

Said object is achieved according to the invention in that the die table has at least two cutouts, and an insert piece, which comprises a plurality of dies, can be or is inserted in an exchangeable manner into each of said cutouts. With the solution according to the invention, therefore, the die table is not dismantled into ring segments but rather the die table is provided with cutouts where, in conventional tables, the individual bores for holding the die sleeves are seated, with said cutouts subsequently being filled by means of insert pieces in which the dies are formed and which form the support bodies for the dies. The exchange of the insert pieces is significantly easier then the exchange of ring segments, since the latter must be fixed with fitting accuracy to the rotor and have a considerably higher weight then small-format insert pieces. It is self-evident that the insert pieces should end in each case flush with the upper side of the die table in order to avoid wear edges for scrapers or the like.

In one preferred embodiment, the die table has two to nine cutouts, in particular three to five cutouts for insert pieces. Here, each insert piece can comprise five to fifteen dies or form the support for five to fifteen dies. It is particularly advantageous if the cutouts extend in the shape of a circular arc and/or are of substantially kidney-shaped design. It is self-evident that the insert pieces are of correspondingly complementary design such that they can be inserted into the cutouts. Particularly favorable fixing of each insert piece is given if each cutout has a peripherally closed edge. It is particularly advantageous if the cutouts are provided in the die table (only) adjacent to the upper side of the die table with a fitting surface for the insertion of the insert pieces with fitting accuracy. Here, the fitting surface can preferably be formed only by the upper peripheral edge of the cutouts. The fitting surfaces ensure the positional accuracy and axial parallelism of the central axes of the dies with respect to the axes of the guides in the ram guide rings, and at the same time prevent pressing dust or powder from accumulating in the seams between the peripheral edge of the insert pieces and the delimitations of the cutouts. By delimiting the fitting surface to a partial section of the depth of the cutouts, the production costs for the die table with cutouts for the insertion of the insert pieces with fitting accuracy can be further reduced. In the case in particular of an embodiment of a die table having cutouts with a fitting surface only in the upper region, the cutouts can increase in size, and/or widen beneath the fitting surface, toward the underside of the die table, and therefore toward the lower ram guide side.

The insert pieces which can be placed into the cutouts are preferably composed of substantially circular-arc-shaped and/or kidney-shaped ring segments. In one advantageous embodiment, each insert piece can be directly provided with a plurality of through bores which form the dies. In this embodiment, the dies are therefore formed directly in the insert pieces. It is then possible for the insert pieces to use a wear-resistant material which is suitable for dies, such as hardened steel, carbide or ceramic, with the material of the die table in any case remaining at transition webs between two cutouts. Since substantially only the cutouts in the die table are filled by means of the insert pieces, it is possible without cost disadvantages to use even high-quality material for the insert pieces, while the die table itself is composed of more cost-effective material. According to an alternative advantageous embodiment, the die table can be provided on the upper side with a concentrically encircling groove, with the groove base being composed substantially of the cutouts and radial webs which are arranged between said cutouts. In this embodiment, insert pieces can be used which directly adjoin one another at the upper side of the die table, so that a concentric strip is formed within the upper side of the die table by means of the insert pieces.

It is also preferably possible for the insert pieces to have a side face at the inside of the arc and a side face at the outside of the arc, with an assembly web being formed at least on the side face at the inside of the arc. The assembly web is expediently arranged centrally between an upper side and a lower side of the insert pieces. This has the advantage that the insert pieces can, after a rotation through 180°, that is to say after exchanging the upper and lower sides with one another, be re-mounted on the die table, thereby approximately doubling the overall service life of the dies in the insert pieces, with in turn extremely short fitting times.

Fastening means or centering means preferably serve for mounting the insert pieces on the die table, which fastening means or centering means can particularly advantageously extend through the assembly web and be fixed or screwed to the die table. It is particularly advantageous if the insert pieces are fastened to the lower side of the die table, since no scrapers or the like run past on the lower side of the die table and, in addition, the greater forces during the pressing process are applied by the lower rams, by means of which the pellets are ejected upward at the end of the pressing process.

It is alternatively or additionally possible for the die table to have radial bores or transverse bores which open out into the cutouts. This offers the particular advantage that, in order to lock the insert pieces, a small number of locking means such as locking pins or locking screws can be screwed or inserted into the radial bores or transverse bores in the die table proceeding from the peripheral edge of the die table. If appropriate, 2 to 4 locking means are sufficient for locking an insert piece.

It is alternatively or additionally possible for the insert pieces to be fastened relative to the die table by means of bar elements which are buttressed on the rotor. The bar elements can in particular engage in recesses on the lower ram guide.

FIGS. 1 and 2show a rotor1, which is rotatable about the rotational axis of a rotary tablet press (not illustrated in any more detail), in a schematic and highly simplified form. The rotor1comprises a lower ram guide ring2with numerous ram guide bores3, arranged concentrically around the rotational axis of the rotor1, for lower rams4, a further, upper ram guide ring5with numerous guide bores6for upper rams7, and a die table10which is mounted in an exchangeable manner in a way known per se for example at the transition between the lower ram guide ring2and the upper ram guide ring5. It can be clearly seen fromFIG. 1that the lower ram4and the upper ram7in their respective guide bores3and6are aligned so as to be flush with one another, so that the ram shafts, which move up and down in a sliding fashion, of the rams4,7dip with their pressing heads8and9into a die11in which a pellet is pressed by means of the rams4,7. The stroke movement of the rams4,7is effected by means of slide rails (not illustrated) which serve as control cams and along which the rams slide with their ends as the rotor1rotates. InFIG. 2, however, all of the rams4,7are illustrated in the initial position.

Each die11, which can be composed in particular of a die bore, is a constituent part of an insert piece20which has an upper side21, a lower side22, an outer side face23and an inner side face24, with an assembly web25being integrally formed on the inner side face24centrally between the upper and lower sides21,22, by means of which assembly web25the insert piece20is fixed by means of a bar element30to the ram guide ring2for the lower ram3, as will be explained below.

It can be seen in particular fromFIGS. 2 and 3that each insert piece20extends in the shape of a circular arc over approximately 90° here and comprises in each case a plurality (nine in the exemplary embodiment shown) of dies11. Each insert piece20having the plurality of dies11is inserted here in an associated cutout12within the die table10, with the four cutouts12here extending continuously between the upper side13, which faces toward the upper ram guide ring5, of the die table10and the lower side14, which faces toward the lower ram guide ring2, of the die table10. The insert pieces20having the plurality of dies11are inserted into the cutouts12in such a way that, as shown in particular inFIGS. 1 and 2, the upper side21of the insert pieces20ends flush and plane-parallel with the upper side13of the die table10, while the insert pieces20at the same time project far beyond the lower side14of the die table10and bear a really with the centrally integrally formed assembly web25against the lower side14of the die table10, such that the forces which are applied by means of the lower ram3to the insert pieces20when pressing a pellet out of the die11are absorbed by means of the assembly web25and dissipated into the die table10and its fastening to the rotor1.

In the exemplary embodiment shown, the cutouts20extend in each case as circular-arc-shaped curved groove strips, with a peripherally closed edge15, on the upper side13of the die table10, and the complementarily-formed insert pieces20are likewise composed of circular-arc-shaped curved, web-shaped or strip-shaped ring segments, with arc-shaped side faces23,24and rounded ends28, which are inserted from below into the cutouts12. Here,FIG. 1shows that that partial section12A of the cutout12which adjoins the upper side13of the die table10has a smaller free cross section than the lower section12B which extends to the lower side14, since the cutouts12widen downward by means of a step. The upper partial section12A is machined as a fitting surface into which the insert piece20dips with fitting accuracy with the edge face of the peripheral edge29which directly adjoins in each case the lower side22or upper side21.

The design of the die table10according to the invention having insert pieces20, with each insert piece20being provided with a plurality of dies11, offers the advantage that, by exchanging one insert piece20, a plurality of dies are immediately exchanged in order to replace the total, in the exemplary embodiment shown, of four insert pieces20in the four cutouts12with other insert pieces20. The design of the insert pieces20with a symmetrical construction relative to the assembly limb25offers the further advantage that the insert pieces20can be rotated through 180° and can then be inserted into the cutouts12again.

The centering of the insert pieces20in the cutouts12takes place by means of combined centering and locking bolts31which extend through centering bores26in the assembly limb25and if appropriate also in the bar elements30, and are screwed into blind holes27which lie parallel with respect to the bore axes of the dies11. The bar elements30can be buttressed on the rotor in a suitable way, for example in recesses33in the lower ram guide ring2, in order to assist the support of the insert pieces20. It is possible for in particular approximately 4 to 6 bar elements30to be provided for each insert piece20.

As additional locking for the insert pieces20, the die table10is provided with radial bores38shown inFIG. 3, which radial bores38open out into the cutouts12, and with radial bores39which extend into an intermediate web16between two cutouts12. Locking pins can be screwed into the radial bores38and39, with the locking pins which are screwed into the radial bores38extending into corresponding transverse bores in the insert pieces20, while the locking pins which are screwed into the radial bores39extend for example into positioning notches at the peripheral edge of two adjacent insert pieces20in order to ensure their flush positioning with respect to one another and with respect to the die table upper side13.

To a person skilled in the art, numerous modifications can be envisaged from the preceding description which should fall within the scope of protection of the dependent claims. An exemplary embodiment with four insert pieces lends itself to use in particular with a total of thirty-six dies or die bores. With fewer dies, it would also be possible to use only three insert pieces; with a considerably higher number of dies, it would also be possible to use five or six insert pieces and a corresponding number of cutouts. The edges, which adjoin one another, of the insert pieces could also engage into one another, for which purpose the die table is then provided with a concentrically encircling groove so that the surfaces of the insert pieces again end flush with the upper side of the die table. Instead of insert pieces with integral dies formed by through bores, the insert pieces could also be provided with individual exchangeable inserts such as die sleeves or the like. The assembly web could (additionally) also be formed on the outer side face in order to introduce the forces applied by the lower rams into the die table at both sides of the cutouts. It would also be possible for magnets, in particular supermagnets such as neodymium magnets or the like, to be fastened as assembly aids within the cutouts in the die table and/or on the insert pieces, in order to hold the insert pieces in the assembly position within the cutouts while the fastening means for the insert pieces are mounted and tightened. The servicing personnel carrying out the change of the insert pieces then has both hands free for mounting and tightening the fastening means, since the insert pieces are held within the cutouts in a simple way.