TABLETTING TOOL

Description

[0001] The invention relates to a tabletting tool having the features according to the preamble of claim 1.

[0002] To produce tablets, for example, in the pharmaceutical, food, or household sectors, machines and devices are used in which a powdered or granular base material is compressed into tablets. For this purpose, a tableting tool, for example in the form of a die disc, is provided. This die is composed of ring segments and has at least one, usually a plurality of, pressing openings. The powder or granules are poured into the respective pressing opening and compressed there by upper and lower punches moving toward each other in opposite directions, forming a tablet.

[0003] Such a tabletting tool is particularly susceptible to wear due to the abrasive effect of the materials to be pressed. Various measures are known to improve wear resistance. In one proven design, die bushings are inserted into a carrier plate, with at least one pressing opening formed in each of the die bushings. The carrier plate is made of conventional tool steel or stainless steel, while the die bushings are made of hardened steel or hard metal. This allows for a significantly increased service life in the area of ​​the pressing openings. A comparable design is known, for example, from EP 2 377 677 A1, which discloses a tabletting tool according to the preamble of claim 1.

[0004] However, the complexity of the die bushings is high, resulting in considerable costs. Furthermore, wear is not only observed in the immediate area of ​​the die bushings. Various auxiliary tools are provided for filling the press openings and the pressing process, such as filling shoes, tablet scrapers, material scrapers, material removal plows, and suction devices, which partially slide on the upper flat side of the ring segments or are permanently attached with small gaps. This leads to abrasion due to crushed powder and wear. Therefore, in addition to the material of the die bushings, the material of the ring segments must also exhibit appropriate stability.

[0005] In an alternative design, the die bushings are omitted. Instead, the pressing openings are formed directly in the ring segments, as described, for example, in DE 101 59 114 A1. While such a ring segment can be manufactured cost-effectively without the die bushings, there is no mention of a special material selection or special material treatment. Without special measures, such ring segments are subject to considerable wear and must be replaced after a short period of operation.

[0006] The invention is based on the object of developing a generic tableting tool in such a way that high wear resistance is achieved with low manufacturing costs.

[0007] This object is achieved by a tableting tool having the features of claim 1.

[0008] The invention is based primarily on the practical realization that for the tabletting tools in question, in which the pressing openings are formed directly in the ring segment, surface hardening with a shallow hardening depth of less than a tenth of a millimeter, which is often used in other wear-intensive areas, is insufficient. The pressing process not only generates friction but also strong pressure as a result of the pressing of the upper and lower punches onto the material being pressed. This pressure acts on the peripheral wall of the respective pressing opening, comparable to hydrostatic pressure, transverse to the direction of the pressing force.

[0009] It was recognized that under such a load, a thin hardening zone is not well supported by the comparatively soft base material. The resulting pressure leads to elastic or possibly plastic deformation, resulting in small cracks in the thinly hardened peripheral wall of the press openings. Such cracks greatly increase friction during tablet ejection. They can also lead to small breakouts in the hardening zone, thus promoting further wear in the press opening.

[0010] According to the invention, the ring segment is made of steel and is hardened to a specific minimum hardness depth at least in the area of ​​the peripheral wall of the press opening. This minimum hardness depth is measured against specific reference values. A first reference value for the hardness depth is equal to 2 mm. The determination of a second reference value is based on a smallest opening width determined transversely to the central axis of the press opening, whereby the second reference value for the hardness depth is equal to 0.3 times the smallest opening width. The hardening depth provided according to the invention is at least equal to the smaller of the two reference values. It has been shown that, particularly with comparatively large press openings, the hardening depth should be at least equal to the first reference value of 2 mm in order to achieve the desired effect.However, for comparatively small press openings, where 0.3 times the smallest opening width is smaller than the aforementioned 2 mm, a lower hardening depth, at least equal to the second limit, may be sufficient. In any case, this reliably avoids the aforementioned disadvantages. The peripheral wall of the press openings is securely supported by a sufficiently thick hardening zone. Even under high hydrostatic pressure, the deformation of the press openings remains within limits. The surface remains intact and free of cracks, ensuring smooth pressing over time. Combined with the surface's resistance to abrasion achieved through hardening, this results in a long service life. The cost of hardening is manageable.Since the effort of die bushings is dispensed with, the overall design is simple and cost-effective, which nevertheless ensures high operational reliability for a comparatively long service life, even under high operating loads.

[0011] It may be expedient to limit the hardening to the area of ​​the peripheral wall of the press openings. Preferably, the ring segment is also hardened in the area of ​​at least one flat side to a second hardening depth, wherein the second hardening depth is at least equal to the smaller of the two reference hardening depth values. This also results not only in high resistance to abrasion, but also in good support against high local loads. Expediently, hardening takes place not only in the area of ​​one flat side, but also in the area of ​​an opposite second flat side to a third hardening depth, wherein the third hardening depth is at least equal to the smaller of the two reference hardening depth values. This allows the ring segment to be used on both sides. In addition, at least approximately symmetrical hardening conditions are created, which reduce hardening distortion to a minimum.

[0012] For the effect according to the invention, a minimum hardness depth determined according to the above requirements may be sufficient. In a preferred embodiment, the ring segment is hardened through its entire thickness, thereby achieving particularly high resistance. The degree of hardness to be achieved can be adjusted within wide limits as required. However, a hardness of at least 56 and in particular at least 60 Rockwell (HRC) has proven advantageous.

[0013] In this case, the aim is to machine the ring segment, including its at least one press opening, to its finished size, followed by the hardening process. In an advantageous development of the invention, the ring segment is hardened in its finished size state and, after hardening, has not undergone any subsequent processing affecting dimensional and / or shape accuracy. The structural transformation of the steel during hardening can be controlled so that no significant distortion occurs. To this end, the hardening temperature levels, the cooling levels, and the corresponding holding times must be selected so that the hardening stresses in the structure are reduced. This can ensure that no further processing relating to shape and dimensional accuracy is required following hardening. For this purpose in particular, a carbide-forming steel with the ability to precipitate secondary carbides is preferably used.

[0014] Embodiments of the invention are described in more detail below with reference to the drawings. They show: Fig. 1 a rotor segment of a rotary tabletting machine with a tabletting tool designed according to the invention in the form of a die plate composed of ring segments, Fig. 2 in an enlarged sectional view the ring segment made of through-hardened steel according to Fig. 1 during the pressing process with one immersed upper and one lower punch, Fig. 3 in a cross-sectional view a variant of the ring segment according to Fig. 2 with hardening zones in the area of ​​the peripheral walls of the press openings and the flat sides, and Fig. 4 in a schematic diagram showing a typical temperature curve over time to achieve low-distortion hardening,

[0015] Fig. 1 shows a perspective view of a rotor segment 12 of a rotary tabletting machine for producing tablets from powdered or granular materials in any application. Such application areas can be, in particular, in the pharmaceutical, food, or household sectors. Upper punch guides 13 and lower punch guides 14 for Fig. 2 The tableting punches 3, 4 shown are formed into the rotor segment 12. At least one tabletting tool 1 is attached to the rotor segment 12, which in the illustrated embodiment is designed as a ring segment 5 of a circular die plate 11 and has a flat side 7 pointing upwards in the assembled state. The die plate 11 is provided with a number of pressing openings 2 corresponding to the number of upper punch guides 13 and lower punch guides 14 and is located in the vertical direction determined by the direction of gravity between the upper punch guides 13 and the lower punch guides 14. One upper punch guide 13, one lower punch guide 14 and one pressing opening 2 each are aligned with one another in the vertical direction on a common, in Fig. 3 shown central axis 16.

[0016] A rotor of the rotary tabletting machine (not shown in detail here) is formed from several rotor segments 12, arranged rotationally symmetrically to a rotational axis 15, while the individual segments 10 form a die plate 11 rotating around the rotational axis 15. The die plate 11 is firmly connected, for example, by clamping or in some other way, to the rotor or its rotor segment 12. The resulting structural unit rotates during operation about the rotational axis 15, which is parallel to the direction of the weight force.

[0017] Fig. 2 in an enlarged sectional view of the tabletting tool 1 according to Fig. 1 , which is shown in cross-section in the area of ​​a single press opening 2. The press opening 2 extends vertically and parallel to the rotation axis 15 ( Fig. 1 ) extending central axis 16 and has a smallest opening width d transverse to the central axis 16 as well as a peripheral wall 6 running around this central axis 16. In the exemplary embodiment shown, the press openings 2 are cylindrical with a circular cross-section for the production of circular tablets, wherein the smallest opening width d corresponds to the diameter of the circular cross-section. Of course, different cross-sectional shapes, for example elongated ("oblong"), are also conceivable within the scope of the invention, in which case the smallest opening width d is to be determined in the direction of the narrow sides. In other words, the smallest opening width d is equal to the dimension of the minor axis of the opening cross-section. The press openings 2 are formed with their circumferential peripheral walls 6 directly in the ring segment 5.This means that no die bushings or the like are used, but that the peripheral walls 6 of the press openings 2 are formed by the material of the ring segment 5.

[0018] A tabletting punch 3 designed as an upper punch is inserted into the press opening 2 from above, and a tabletting punch 4 designed as a lower punch is inserted from below. Both tabletting punches 3, 4 have a pressing surface 17 at their mutually facing free ends, which lie transversely to the central axis 16 and face each other.

[0019] The function of the rotary tabletting machine results from the combination of Fig. 1 and 2Accordingly, the lower tabletting punch 4 is first inserted from below, relative to the direction of the weight force, in such a way that its pressing surface 17 protrudes into the press opening 2 as its lower boundary. In this state, the press opening 2 is filled from above with the powder or granules to be compressed in the desired quantity.

[0020] Subsequently, in the opposite direction, i.e. in the direction of gravity from above, the upper tabletting punch 3 with its formed pressing surface 17 is introduced into the press opening 2, wherein the two pressing surfaces 17 of the two tabletting punches 3, 4 face each other. The pressing surfaces 17 are each delimited by a circumferential edge which lies sealingly against a peripheral wall 6 of the press opening 2. This creates a completely closed pressing chamber delimited by the two pressing surfaces 17 and the peripheral wall 6 of the press opening 2. In this state, the upper tabletting punch 3 is lowered under the raising and counterpressure of the lower tabletting punch 4, whereby the powder or granulate located in the press chamber or in the press opening 2 is compressed into a tablet (not shown). The tablet produced in this way is then ejected from the press opening 2 by means of the two tabletting punches 3, 4 and sent for further processing orPackaging supplied.

[0021] The movement control or drive of the two tableting punches 3, 4 is carried out by the Fig. 1 The rotor, shown in sections, is rotated together with the tableting tool 1 and the tabletting punches 3, 4 about the rotation axis 15. Not shown, spatially fixed cam elements, with respect to which the tabletting punches 3, 4 perform a relative movement, act on the ends of the tabletting punches 3, 4 opposite the pressing surfaces 17 and thus generate the stroke of the tabletting punches 3, 4.

[0022] The compaction of the powder or granules into a tablet creates a pressure in the interior of the press opening that is comparable to hydrostatic pressure and that acts on the peripheral wall of the press opening. As a result of the forced guidance of the tabletting punches 3, 4 described above, the pressing force and pressure build up depending on the fill quantity in the respective press opening. The greater the fill quantity, the greater the resulting pressing pressure. In practical operation, the fill quantity and pressing pressure can be adjusted to a desired level. However, occasionally parts or entire tablets stick to the tabletting punches 3, 4 and thus lead to a greatly increased pressing force, even double the force, which in turn can cause damage to the tools or to excessively thin hardened layers on the segments due to overloading.

[0023] For filling the press cavities 2 with the powder or granules to be compressed, for removing the compressed tablets, for removing excess powder or granules, or for other purposes, various auxiliary tools (not shown) are provided. These slide along the flat side 7 of the tabletting tool 1, which, when assembled, faces upwards and is designed as a functional surface. Such auxiliary tools can be filling shoes, tablet scrapers, material scrapers, material removal plows, suction devices, or the like. Opposite the flat side 7 mentioned is another flat side 8 of the ring segment 5, which faces downwards here. The further, second flat side is also designed as a flat functional surface. This allows the ring segment 5 to be installed and used upside down, with the second flat side 8 then facing upwards and interacting with the auxiliary tools mentioned.

[0024] The interaction of the auxiliary tools mentioned and also of the filling material with the tabletting tool 1 puts stress on its surface on the facing flat side 7, 8. The pressing process in the press openings 2 described above puts stress on their peripheral walls 6 in particular. In order to counteract these and other stresses with increased wear resistance, the ring segment 5 according to Fig. 2 Made of a carbide-forming steel with the ability to precipitate secondary carbides after heat treatment to achieve a hard and thus wear-resistant microstructure. The ring segment 5 was first machined to its final size, which included the production of the press openings 2. Only then was the ring segment 5 hardened to a hardness of at least 56 HRC and in particular to at least 60 HRC (Rockwell hardness). In the exemplary embodiment according to Fig. 2 The ring segment was hardened in its entirety. The otherwise expected hardening distortion was counteracted by the above-mentioned material in combination with a temperature profile during hardening, as described in Fig. 4 is shown. There, the course of the temperature T over time t is shown schematically, with the help of which, on the one hand, a through-hardening of the steel extending through the entire thickness of the ring segment 5 was achieved, while on the other hand, the ring segment prepared to the finished size retained its shape and dimensions with sufficient dimensional stability even after hardening, so that in this respect no further reworking is required after hardening and none was carried out.

[0025] Fig. 3 shows a cross-sectional view of a variant of the ring segment 5 according to Fig. 2 with hardening zones 9 in the area of ​​the peripheral walls 6 of the press openings 2 and the two opposite flat sides 7, 8. The ring segment 5 was therefore not hardened through. Rather, the hardening was limited to the area of ​​the peripheral walls 6 of the press opening 2 and to the area of ​​the upper and lower flat sides 7, 8. However, the hardening depth h achieved in the area of ​​the peripheral wall 6 of the press opening 2 must have reached a certain minimum value. Two reference values ​​are used to determine this minimum value. A first reference value for the hardening depth h is equal to 2 mm. A second reference value for the hardening depth h is equal to 0.3 times the smallest opening width d. The hardening depth h in the area of ​​the peripheral wall 6 of the press opening 2 is at least equal to the smaller of the two reference values. For example, if the smallest opening width d is 12 mm, the second reference value is 0.3 x 12 mm = 3.6 mm.The first reference value is 2 mm and thus smaller than the second reference value. A hardening depth h at the level of the first reference value of at least 2 mm is therefore sufficient. In the case of a smaller press opening with a smallest opening width d of, for example, 5 mm, the second reference value is 0.3 x 5 mm = 1.5 mm and thus smaller than the first reference value of 2 mm. In such a case, according to the invention, it may be sufficient for the hardening depth h in the region of the peripheral wall 6 of the press opening 2 to be at least 1.5 mm.

[0026] The flat side 7 and optionally also the opposite flat side 8 are hardened and have a second hardening depth h 2 and a third hardening depth h 3 respectively. The second hardening depth h 2 and the third hardening depth h 3 are determined analogously to the hardening depth h in the area of ​​the peripheral wall 6 of the press opening 2 and are at least equal to the smaller of the two above-mentioned reference values, i.e. in the two above-mentioned examples they are at least 2.0 mm and at least 1.5 mm respectively. These are minimum values, so that larger hardening depths h, h 2 , h 3 are also possible. This also includes the option that the actual hardening depths h, h 2 , h 3 can deviate from one another and thus be different. In the remaining features and reference symbols, the exemplary embodiment according to Fig. 3 with the one after Fig. 2 agree.

Claims

1. Tabletting tool (1) comprising at least one press opening (2) for receiving tabletting punches (3, 4) and for compressing powdered or granular substances to form a tablet, wherein the tabletting tool is composed of ring segments (5), wherein the press opening (2) extends along a centre axis (16) and has a smallest opening width (d) transversely to the centre axis (16), and wherein an encircling circumferential wall (6) of the press opening (2) is formed directly in a ring segment (5), characterized in that the ring segment (5) consists of steel and is hardened at least in the region of the circumferential wall (6) of the press opening (2) with a hardening depth (h), wherein a first reference value for the hardening depth (h) is equal to 2 mm, wherein a second reference value for the hardnening depth (h) is equal to 0.3 times the smallest opening width (d), and wherein the hardening depth (h) is at least equal to the smaller of the two reference values.

2. Tabletting tool according to claim 1, characterized in that the ring segment (5) has at least one flat side (7) and is hardened in the region of the flat side (7) with a second hardening depth (h2), wherein the second hardening depth (h2) is at least equal to the smaller of the two reference values for the hardening depth (h).

3. Tabletting tool according to claim 2, characterized in that the ring segment (5) has a second flat side (8) situated opposite the flat side (7) and is hardened in the region of the second flat side (8) with a third hardening depth (h3), wherein the third hardening depth (h3) is at least equal to the smaller of the two reference values for the hardening depth (h).

4. Tabletting tool according to one of claims 1 to 3, characterized in that the ring segment (5) is hardened through.

5. Tabletting tool according to one of claims 1 to 4, characterized in that the hardness of the ring segment (5) in its hardened region is at least 56 HRC.

6. Tabletting tool according to one of claims 1 to 5, characterized in that the steel of the ring segment (5) is a carbide-forming steel with the ability to cause precipitation of secondary carbides.

7. Tabletting tool according to one of claims 1 to 6, characterized in that the ring segment (5) is hardened in its final dimensions and, after the hardening, has not undergone any reworking relating to accuracy in terms of dimensions and / or shape.