Punch for a rotary press

A compression punch for a rotary press, with a punch shaft that has a punch head at its one end and means for accommodating a separate punch insert at the other end, and with fastening means for detachably fastening the punch insert on the punch shaft, wherein the punch head and the punch shaft have an axial through bore, the axial through bore accommodates a drawbar that has a tensioning head at the end turned away from the punch head, said tensioning head having at least one connection portion, the punch insert has a recess at the end facing the punch shaft which is realized to be detachably connectable with the connection portion, and that tensioning means are arranged in the axial through bore, by which the drawbar can be tensioned in the direction of the punch head.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

BACKGROUND OF THE INVENTION

As is well known, a rotary press contains a plurality of upper and lower punches, which are guided in suitable guide bores of punch guidings and which co-operate with bores in a die plate. The individual punches feature a shaft, as well as a head at one end, which co-operates with compression rollers of the press. At the end turned away from the punch head is arranged a punch insert, which is realised separately and adapted to be connected with the shaft via suitable fastening means. The connection takes place with the aid of screws or pins. However, it is also known to realise compression punches in one single piece.

The known punch constructions have several disadvantages. Installation and disassembly of the punch inserts is sumptuous, and time-consuming in particular. Replacement of the punch inserts is not possible within the rotary press. The fastening of the punch inserts is susceptible to troubles and subject to high wear. Problems arise also with respect to the centring and alignment of the punch inserts, with compression moulds that are not round in particular. Finally, even the aptitude for cleaning of the known compression punches is bad, in particular if they must remain in the press (CIP=Cleaning in Place). A reason is the existence of threads, corners and seams.

The present invention is therefore based on the objective to provide a compression punch for a rotary press which ensures uncomplicated installation and disassembly of the punch insert and which permits cleaning inside the press.

BRIEF SUMMARY OF THE INVENTION

In the compression punch according to the present invention, the punch head and the punch shaft have an axial through bore, wherein the axial through bore accommodates a drawbar that has a tensioning head with at least one connection portion on that end which is turned away from the punch head. The connection portion is adapted to be brought into connection with a facing recess of the punch insert. Tensioning means are arranged in the axial through bore, by which the drawbar can be tensioned in the direction of the punch head.

In the installation, the punch insert is connected with the facing end of the drawbar, i.e. with the tensioning head. Subsequently, the drawbar is actuated in order to pull the punch insert axially against the punch shaft. According to one embodiment of the present invention, this may happen in that the drawbar has a thread, onto which a tensioning nut is screwed at the punch head side, said tensioning nut being supported by a shoulder in the axial through bore. By turning the tensioning nut, the drawbar is subjected to tensile stress, and so it can draw the punch insert against the punch shaft. Alternatively, the tensioning head may have at least one radial projection which permits insertion of the tensioning head into the recess in the one rotational position of the punch insert with respect to the drawbar, and grasps behind an undercut in the other rotational position. Instead of by a tensioning nut, the tensile stress may also be applied by a spring, which biases the drawbar into the direction of the punch head.

The connection of a punch insert with the punch shaft according to the invention makes it possible that there are only smooth surfaces of punch shaft and punch insert towards the outside. Through this results a good washability of the entire punch, because neither punch shaft nor punch insert have threads, seams or other unfavourable geometries on the outer side. Installation and disassembly of the punch insert is possible within an extremely short period of time, in fact also within the rotary press, even in an automatic way. As is well known, during their movement in the rotary press, the punches are held by cam sections in certain paths. In these stages it may then be manipulated on the punches in order to install or to remove the punch insert.

Because the punch insert is directed towards the die bore when it is installed, the tolerances of punch shaft, die bores and punch guiding may be chosen to be large. This permits significant savings in the production of the punches, dies and segments for the die plate and the punch guiding.

Near to the end of the punch insert, the outer contour of the punch insert is congruent with the outer contour of the punch shaft, so that there are no stepped transitions. The close fit of the punch insert on the facing end of the punch shaft takes preferably place via even surfaces. By way of these surfaces, a frictional fit may be achieved also, which prevents a relative rotation of the punch insert with respect to the punch shaft. Alternatively, a position pin may be provided, which is incorporated in the punch shaft and co-operates with a facing bore in the punch insert.

DETAILED DESCRIPTION OF THE INVENTION

A compression punch10with a punch head12and a punch shaft14is shown inFIG. 1. Punch head12and punch shaft14have a radial through bore16. On the end facing the punch head12, the through bore16has a bore portion18with a greater diameter. The through bore16accommodates a drawbar20, which has a tensioning head22on its lower end. On the upper end, the drawbar20is provided with a thread, onto which a nut24is screwed up. The nut24serves as abutment for a helical spring26that is supported on a disk28. The disk28is supported on the facing shoulder of the bore portion18. An elastomer seal30is arranged below the disk28. It has the purpose to prevent liquid or dust from reaching the direction of the through bore18from out the punch head12.

A punch insert32is connected with the shaft14in that the tensioning head22engaging into a recess34of the punch insert32is biased against the facing end of the shaft14. A position pin36sits in an axis parallel blind bore of the shaft14. It co-operates with a hole50on the facing end of the punch insert32. A flat seal40, made of plastic material, sits between the tensioning head22and the facing end of the punch shaft14.

Near to the punch shaft14, the perimeter contour of the punch insert32is congruent with that one of the punch shaft14, and punch shaft14and punch insert32sit close against each other via even surfaces that stand vertically to the axis of the punch10. Due to this, there is no stepped transition towards the outside, and also no seam into which contaminations might intrude. A pressing tool42is formed in one piece with the punch insert32.

The installation of the punch insert32emerges more clearly from theFIGS. 3 and 4. As emerges fromFIG. 4, the tensioning head22has diametrically opposing projections44. In the recess34, the punch insert32has axis parallel grooves46that are diametrically opposed. They are adapted to accommodate the radial projections44when the punch insert is set against the shaft14and the tensioning head22submerges into the recess34. Shoulders extending transversely to the axis are formed at the end of the grooves48by a clearance boring48, which forms an undercut in the recess34. A hole50is formed into the punch insert32eccentrically to the recess50, which is formed as a long hole in the radial direction. In the perimeter direction, it is suited to accommodate the position pin36matingly.

In the installation of the punch insert32on the punch10, the punch insert is held in such a rotational position that the radial projections44are directed towards the grooves46. Then, the punch insert32is pushed forward against the shaft14until the position pin36hits the facing even surface of the punch insert32. The punch insert32is subsequently turned about approximately 45°, by which operation the radial projections44or noses grasp behind the shoulders formed by the clearance bore. The rotation is performed for so long until the position pin36is situated over the hole50. Subsequently, the drawbar20is drawn tight, so that the punch insert is tensioned against the shaft14of the punch10according toFIG. 1. In order to perform the described installation, a force is exerted on the drawbar20according to the arrow F inFIG. 1, so that it juts out sufficiently over the end of the shaft14under compression of the spring26, so that the described installation of the punch insert32can be performed. For instance, this path corresponds to the path S inFIG. 1. After the installation, the force F is released, so that the spring26can exert its tensioning force on the punch insert32.

A punch10acan be recognised inFIG. 2, which is essentially similar to the punch10inFIG. 1. It accommodates a drawbar20ain a corresponding through bore, the through bore having an enlarged bore section18anear to the punch head12. A tensioning nut52is screwed up onto a thread of the drawbar20a, so that a tensile force in the direction of the punch head12can be exerted on the drawbar20ain order to tension a punch insert32aagainst the punch shaft14a. The connection of the tensioning head22awith the punch insert32amay take place in the same way as has been described forFIG. 1. The tensioning nut52is axially secured in the bore portion18aby a locking ring54.

FIG. 5shows the lower end of a shaft14bof a compression punch not shown in more detail, on which a punch insert32ais fastened in a way like that described in the context ofFIG. 1 to 3. Therefore, it will not be dwelled further on this connection. The particular feature of the punch insert32aafterFIG. 5is that the punch insert32ahas four compression portions56. In the operation, the compression portions co-operate simultaneously with four die bores.

Referring now toFIG. 6, as is well known, a rotary press contains a plurality of upper punches60and lower punches62, which are guided in suitable guide bores64of punch guidings66and which co-operate with bores70in a die plate72. Compression rollers68compress the punches together to form the tablet.