WO1997014551A1

WO1997014551A1 - Tabletting machine

Info

Publication number: WO1997014551A1
Application number: PCT/IB1996/001057
Authority: WO
Inventors: Roveno Bonora
Original assignee: I.M.A. Industria Macchine Automatiche S.P.A.
Priority date: 1995-10-19
Filing date: 1996-10-08
Publication date: 1997-04-24
Also published as: ITBO950499A1; IT1279665B1; ITBO950499A0

Abstract

A machine for production of tablets from granular or powder material includes a turret (1), a ring-like plate (5) with die holes (2), and pairs of punches (20, 30) that enter the die holes to form tablets when lower and upper working heads (21, 31) of these punches (20, 30) approach to each other according to predetermined sequences. Each lower punch (20) has a ring-like gasket (10) in the region of the working head (21) and when the lower punch (20) moves upwards the gasket goes in abutment against the ring-like plate (5) so as to make tight the touch region between the lower punch (20) and the related die hole (2). This ring-like gasket (10) allows creation of depression inside a compression chamber (7) formed in the related die hole (2) so as to facilitate introduction of a portion of material to be compressed therein.

Description

TABLETTING MACHINE

TECHNICAL FIELD

The present invention relates to production of aggregates by compression of powder or granular material. In particular, the present invention relates to a rotary tabletting machine, which is equipped with pairs of counterfacing punches .

BACKGROUND ART

It is known that tablets are produced from powder material by rotary compression machine, which usually includes a rotating turret, means for batching and positioning the material to be compressed, compression means, and means for ejection of the produced tablets . Examples of such compression machines are described in the US-A-2, 989,781, US-A-3, 677, 673, US- A-3, 999,922 and US-A-4, 108, 338.

Another known rotating machine for making tablets is disclosed in the US-A-4, 943, 227, to the same Applicant.

This lastly mentioned machine includes a turret, that rotates in a predetermined direction, and fitted with a ring-like plate set around it in an vertical intermediate position.

This plate is has a plurality of regularly spaced apart die holes, defined by internal parts of through holes which have their axes parallel to the rotation axis of the turret.

The through holes are situated in the region of an outlet of feeding radial channels which originate from the bottom of a supply chamber.

The supply chamber is made inside the turret and contains the granular or powder material to be compressed.

For each die hole of the ring-like plate there is provided a pair of counterfacing punches, which are slidably guided so that they can slide along a direction parallel to the turret axis. Each punch features a working head.

These working heads enter the holes made in the ring-like plate at opposite sides thereof. Thus the holes provide a guiding action on the heads of the punches.

An improved rotary tabletting machine is disclosed in the O-A-9515846, in the name of the same Applicant.

The means for driving and guiding the punches of the machine of this publication include fixed groove cams, with a pair of rollers sliding therein and connected to the upper part of the punches. The groove cams are shaped in such a way as to impart the punches vertical movements in mutual time relation with one another.

This allows the punches to separate a portion of material to be compressed inside the respective die hole. Afterwards, compression of the same material is performed to obtain a tablet, which is later ejected.

Each die hole of the ring-like plate is fed with the material to be compressed which is delivered from the supply chamber, via the respective radial channel, due to centrifugal force, that acts on the material as a result of the turret rotation.

At this point, the upper punch is driven upwards, while the lower punch remains motionless in order to further facilitate introduction of the material inside each die hole. This upward movement creates a depression condition inside the die hole, thus facilitating filling thereof .

The compression procedure includes a sequence of working steps performed by suitable reciprocal movements of each pair of punches, so that very- compact and stable tablets are produced as rapidly as possible.

A possible example compression procedure is described in the WO-A-9515847 of the same Applicant.

This publication is concerned with a method for the production of tablets, which method includes an initial step which the material is gradually compacted, a releasing step in which compressing thrust is removed, and afterwards, a precompression step, a precompression thrust maintenance step, a releasing step, a main compression step and an ejection step in which the tablet obtained is ejected.

It is to be noted that, during the main compression step, a load applied to the material is bigger with respect to the load applied thereto in the compacting and precompression steps.

All the above mentioned steps are performed by repeated reciprocal approaching and separation movements of the counterfacing working heads of the pairs of punches, inside the related die hole of the ring-like plate.

In this machine, it is critical that couplings between the punches and the related housings be as air-tight as possible to obtain good depression mside the die holes during the step in which they are filled with the material to be compressed. This is obtained, for example, by reducing considerably clearance of these couplings.

Naturally, reducing the clearance always causes a considerable increase of time and costs of parts processing, particularly when the round profiles of the punches and their housings are not symmetrical with specific reference to a curved profile.

For instance, with a perfectly circular punch profile it is easier to reduce clearance since small rotation due to positioning of the punches with respect to the die holes are possible.

Conversely, when the cross profile of the punches is oblong, a clearance must be kept to compensate for small unavoidable rotary displacement of the punches with respect to the respective die holes, this resulting in reduction of the depression effect.

Good depression is yet more important when the powder to be compressed is little smooth, since its mobility inside the feeding radial channel is limited and powder tend to stick to the walls of the radial channels and of the compression holes.

In some cases, this could provoke the seizure of the punches, if they slide too close to the related hole wall. DISCLOSURE OF THE INVENTION

The object of the present invention is to improve the above mentioned tabletting machine so as to maintain the effect of tightness between the working heads and related die holes of the ring-like plate without substantial reduction of the clearance left between the punches and the walls of the holes. Another object of the present invention is to propose an improvement that does not complicate construction, installation and maintenance of the subject machine.

The above mentioned objects are obtained, in accordance with the invention, by a machine for compression of powder or granular material including: a rotary turret having vertical rotation axis; at least one ring-like plate, rigidly fastened to the said turret and provided with a plurality of die holes, formed by through holes having their axes parallel to the rotation axis of said turret; a pair of punches, lower and upper respectively, provided for each die hole of the ring¬ like plate, said punches being slidably guided to enter said die holes in a direction parallel to the turret rotation axis and in reciprocal time relation, in order to perform a working sequence for production of tablets, beginning from a predetermined amount of material to be compressed; working heads, lower and upper respectively, connected to each pair of said punches so that said working heads faces each other and define a compression chamber inside the die hole, with a clearance left between the working heads and the related die hole; at least one radial channel, provided for each die hole, for feeding continuously material to be compressed to the related chamber.

According to the invention, the machine features sealing means, aimed at preventing inflow of air to said chamber from outside, thus creating a depression inside said chamber as a result of related movements of said punches.

BRIEF DESCRIPTION OF DRAWINGS

The characteristics of the invention will be better understood from the following description, with particular reference to the attached drawing, in which:

- Figure 1 shows a schematic lateral section of a part of the tabletting machine improved in accordance with the present invention.

BEST MODES OF CARRYING OUT THE INVENTION

With reference to this figure, number 1 indicates a rotary turret that belongs to a rotating tabletting machine, for example of the type described in the above mentioned publications US-A-4.943.227, WO-A-9515846 and WO-A-9515847.

A ring-like plate 5 is fastened around the turret and has a plurality of die holes 2, regularly spaced apart and defined by through holes which have their axes parallel to the rotation axis of the turret 1.

The section of the die holes 2 corresponds to the section of the tablets to be produced.

These sections can be round and perfectly circular, to obtain circular tablets, or they may be not circular, e.g. to obtain oblong tablets. Generally, the section of the die holes can be any, with a curved profile.

For each die hole 2 there is provided a pair of punches 20,30, lower and upper respectively, arranged all around the turret 1 and guided slidably along an axis parallel to the rotation axis of the same turret 1.

The punches feature working heads 21 and 31, lower and upper respectively, that, in operation, fit into the die holes 2 from above and below.

The free ends 21a, 31a of the working heads 21,31 of each punch pair delimit, inside the die hole 2, a compression chamber 7, whose volume depends on the distance between the heads and whose position changes due to the related movements of the punches 20,30.

This compression chamber 7 is cyclically fed with a proper batch of material to be compressed.

Each chamber 7 is fed via a radial channel 4 which is made in the turret 1. The channels depart from a supplay chamber, not shown in the figure, containing the material to be compressed and lead to the respective die holes 2.

Each compression chamber 7 can also change its position inside the die hole 2, during the tablet production step.

Sections of the die hole 2 and working head 21 are not perfectly identical, but they are made in such a way that there is left a clearance, as limited as possible, in relation to constructive tolerances.

The lower working head 21 has also a ring-like gasket 10, generally made of rubber or another similar material, located around the end 21b, where the working head is connected to the punch 20.

The gasket 10 striks against the lower surface 5a of the ring-like plate 5, to prevent air from flowing into the chamber 7 through the above mentioned clearance between the lower working head 21 and the hole 2.

Consequently, the gasket guarantees the tightness at the bottom of the related chamber.

Production of tablets using the present compression machine can be carried out, for example, according to the previously mentioned method described in the publication WO-A-9515846, or according to the operation of the machine described in the above mentioned publication US-A-4.943.227.

As has already been said, tablets are produced by a predetermined sequence of reciprocal approaching and separation movements of the counterfacing working heads 21,31 of the pairs of punches 20,30, inside the die holes 2.

As far as the present invention is concerned, it is particularly interesting to describe the step in which the chamber 7 is filled with the material coming from the radial channel 4.

In order to perform this step, the working heads 21,31 are displaced so as to locate the chamber 7 in the region of the outlet of the radial channel 4 of the die hole 2.

Filling of the chamber occurs due to the centrifugal force acting on the material present in the channel 4 and produced by rotation of the turret 1.

In this situation, the ring-like gasket 10 abuts on the lower surface 5a of the ring-like plate 5, all around the lower working head 21.

During the above mentioned chamber filling step, the lower punch 20 is maintained steady, while the upper punch 30, and therefore the related upper head 31, is moved slightly in the direction indicated by the arrow V in Fig. 1, so as to increase temporarily the dimension of the chamber 7.

In this way, a depression is created inside the chamber, and the flow of material from the radial channel 4 into the chamber is facilitated. Creation of the above mentioned depression is possible due to the ring-like gasket 10 that prevents the inflow of the air to the chamber 7.

Possible inflow of the air through the clearance left between the upper head 31 and the ring-like plate 5 is prevented by material gathered therein. Afterwards, the punches 20,30 perform the necessary steps for compression of the material and production of tablets, according to the compression method that has been adopted. During filling of the compression chamber 7, the ring-like gasket 10, connected with the lower working head 21 of the punch 20, allows to combine profitably the action of the centrifugal force with the force produced by the depression inside the chamber 7.

This assures a correct filling of the chamber 7 and more precise batching of the material to be compressed.

Therefore, by using this gasket tablets are produced in a simple and reliable way, no matter of their shape and section, using the same compression machine. Only the ring-like plate 5 and the working heads 21,31 of the punches 20,30 need to be changed for each tablet size. Another advantage of the present invention derives from the possibility to use the same machine configuration also for compression of little smooth powders, with the same filling efficiency.

A further advantage of the present invention lies in the fact that bigger tolerance while working the heads and the ring-like plate are allowed without jeopardising the production quality and efficiency of the compression machine.

It is to be understood that what above has been described as a pure example, non limitative, therefore all possible constructive variations are included in the scope of the present technical solution, as described above and claimed hereinafter.

Claims

________

1 . Machine for compression of powder or granular material including: a rotary turret (1) having vertical rotation axis; at least one ring-like plate (5) , rigidly fastened to the said turret (1) and provided with a plurality of die holes (2) , formed by through holes having their axes parallel to the rotation axis of said turret (1) ; a pair of punches (20,30) , lower and upper respectively, provided for each die hole (2) of the ring-like plate (5) , said punches being slidably guided to enter said die holes (2) in a direction parallel to the turret rotation axis and in reciprocal time relation, in order to perform a working sequence for production of tablets, beginning from a predetermined amount of material to be compressed; working heads (21,31), lower and upper respectively, connected to each pair of said punches (20,30) so that said working heads faces each other and define a compression chamber (7) inside the die hole (2) , with a clearance left between the working heads and the related die hole (2) ; at least one radial channel (4) , provided for each die hole (2) , for feeding continuously material to be compressed to the related chamber (7) ; said machine being characterised in that it features sealing means (10) , aimed at preventing inflow of air to said chamber (7) from outside, thus creating a depression inside said chamber (7) as a result of related movements of said punches (20,30) .

2. Machine according to claim 1, characterised in that said sealing means (10) is connected to said lower working head (21) .

3. Machine according to claim 1, characterised in that said sealing means (10) includes a ring-like gasket which is positioned in the region of the end

(21b) of said lower working head (21) , and is fastened to said lower punch (20) so that it is borught by the same lower punch (20) , while sliding upwards, to abut against the lower surface (5a) of said ring-like plate (5) .