GB2163093A - Spreader mechanism for a powder compacting press - Google Patents

Abstract

A spreader mechanism for feeding material to a powder compacting press, in particular to a rotary tablet press (2), comprises a driven hub (23) having radially projecting blades (24). The spreader mechanism is positioned in the region of an outlet of a powder container or of a filler device arranged after the container. The blades (24) of the spreader mechanism are each rotatably journalled about an axis which is substantially radial with respect to the hub (23), for varying the angle of incidence or pitch of the blades (24). The spreader mechanism may thereby be adjusted to the dissimilar properties of the different powders. The pivotable blades (24) may be coupled to a gear within the hub (23) comprising vertically adjustable roller track (25) on which run rollers (29,30) coupled to the blades (24) via cranked levers (31,32) or eccentrics. A joint adjustment of the blades (24) is possible thereby. <IMAGE>

Description

SPECIFICATION Spreader mechanism for a powder compacting press The invention relates to an agitator or spreader mechanism for a pulverulent material for a powder compacting press, in particular for a rotary tablet press comprising a boss with radially projecting vanes which is situated in the area of the outlet of a powder container or of a filling device for filling dies of a die plate which are being moved past.

Presses of this kind are used in the pharmaceutical industry, in the production of confectionary, as well as for investment or other pressing of electronic components. The powders utilised in each case have different properties. Many of the powders or granulates which are to be pressed are thus particularly flowable, but many tend to cohere and clog the machine. This different flowability may lead to irregularities upon charging the dies.

Costly and protracted conditioning methods were developed as a result, to affect the flowability of the different powders in such manner that a pressing action becomes possible. The agitator or spreader devices utilised within the framework of the powder compacting press serve the purpose of conveying the powder into the bores of the dies.

The invention has as its object to devise a spreader mechanism for a powder compacting press of the kind described in the foregoing, which enables powders of different flowability to be pressed without special preparation of the powder.

This is accomplished by the fact that the vanes are rotatably journalled around a spindle which is substantially radial with respect to the hub for the purpose of varying the angle of the incidence of pitch of the vanes. The spreader mechanism may thereby be adjusted to the different properties of the powders. Powders having a poorflowability are accelerated and kept in motion in the area of the container outlet by means of the vaned wheel having the angles of vane incidence adapted correspondingly. Powders having too great a flowability may be decelerated. The outflow of the powder may thus be adjusted in such a manner that the dies may be filled completely and uniformly with powder. Disregarding powder compacting presses and their stirrer mechanisms, it is known in the case of propellers that the propeller blades may be constructed to be pivotable.Because of the entirely different technical field, the problem specification and action of propellers are not comparable to those of the stirrer mechanisms utilised in powder compacting presses for conveying powder, although structural features appear in the object of the application which are known in marine construction. In the case of stirrer or spreader mechanisms, it is appropriate if the pivotable blades are connected in known manner to a gear within the boss, for example by means of a rollers track installed in co-rotatory but vertically displaceable manner, on which run roller coupled to the blades via cranked levers or eccentrics, for joint alteration of the angle of incidence of the blades. The most effective angular displacement may then be per formed from the outside during operation, based on experimentation.It is appropriate if the roller track is provided as known with two plates posi tioned mutually parallel, and the rollers of the cranked levers or eccentrics run between the plates. Furthermore, the roller track may be pro vided in its area adjacently situated to the axis of rotation of the die plate with an undulant raised portion or depression for the deflection of the cranked levers or eccentrics and for local variation of the pitch of the blades.

In another embodiment of the invention each blade is made separately adjustable in respect of its angle of incidence and a linkage control system is provided for continuous variation of the pitch, for example in accordance with a sinusoidal function. The blades thus move during a revolution and vary their pitch between two limiting angles (amplitudes) which may be preselected. To maintain a constant gap or a scraper-like contact of the lead ing edges of the blades on the die plate notwithstanding the pitch of the blades, the bladed wheel or impeller is mounted in vertically variable manner on its axis of rotation. A trowel or smoothing action by the blades is thereby assured at any angle of incidence.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows an illustration in principle of a circular tablet press in partial cross-section, Figure 2 shows a bladed wheel of a spreader mechanism, Figure 3 shows a filler device constructed as a filler 'shoe' with blades above a die plate, Figure 4 shows a modified embodiment of a bladed wheel, Figure 5 shows a development of the bladed wheel according to Figure 4 above a die plate, and Figure 6 shows a blade in the case of two different angles of incidence and of convex modified vertical position of the bladed wheel, for assuring the smoothing action.

A rotary tablet press according to figure 1 comprises a fixed vertical column 1 around which a die plate 2 is rotatably journalled. Exchangeable dies 3 comprising bores whose diameter corresponds to the tablet diameter, are inset in the die plate 2. For example, eight dies 3 may be provided at equal angular intervals along a graduated circle in the die plate 2. Press plungers 4, 5 and 6, 7 respectively are movably installed in axial direction, above and below each die bore, in each case. The plungers are moved apart (plungers 4, 5) by means of stationary guides 8, 9, and are pressed against each other (plungers 6, 7) by thrust rollers 10, 11.

The charging of the dies 3 is performed in the area of the press plungers 4, 5. A stationary funnel 12 contains the powder which is to be pressed.

The funnel or hopper is followed by a filling device constructed as a filler shoe 13 which extends inwards radially as far as over the die opening. The powder is picked up in the filler shoe 13 by a horizontal bladed wheel 14 and conveyed in the direc tion of the graduated die circle 15 (figure 3). Drive is provided to the bladed wheel 14 via a hollow shaft 15 by a controllable electric motor 16. The die plate 2 is firmly connected to a flange-like guide 17, 18 for the upper plungers 4, 6 and the lower plungers~5, -7 in each case, and is rotatably jour nalled on the central column or post 1. The guide 18 carries a ring gear 19 meshing with a pinion 20.

The latter is driven by an electric motor 21 in the pedestal box 22.

The bladed wheel 14 has available, for example, four, six or eight blades 24 positioned radially on a hub 23. Figure 1 shows four blades, and figures 3 and 4 show six blades 24. The blades are pivotally mounted around a substantially radial axis. The radial axes may also slope with respect to the post The blades are obliquely set in the example shown in figure 1, and push the powder into the die open ing. The directions of rotation of the bladed wheel 14 and die plate 2 may be equidirectional but also contradirectional (arrows in figure 3 for contradi rectional operation). After a die bore is filled, the bottom plunger 5 is raised a little so that the surplus of powder issuing from the die bore at the top may be scraped off by the case rim of the filler shoe upon leaving the filler shoe. The rotation of the die plate 2 occurs continuously.The press plungers of the filled die reach the positions 6 and 7 at which they impinge against the press rollers 10, 11. A tablet is pressed at the same time. The -plunger 6 is then raised and withdrawn from the opening. The plunger 7 lifts the tablet-out of the bore of the die 3, so that a stripper bar may intercept the tablets and convey these away from the die plate.

The term "tablet" is understood in this context as denoting a medicine or a sweet, but the product might also be for example a plastics material case, e.g. for electronic components.

The cross-section according to figure 2 shows the mechanism internal to the hub 23, for displace ment of the blades 24. Whereas the hollow shaft 15 and thus the hub 23 are driven, a roller track 25 comprising two parallel plates, as well as a central push rod 26, are stationary within the hub 23. Roll ers 29, 30 which are coupled to the blades 24 via cranked levers 31, 32 or by eccentrics, run between the plates 27, 28 forming the roller track 25. The angle of incidence of the blades 24 is altered upon raising or lowering the push rod. If use is made of one plate 27 only, an initial spring loading is needed, which thrusts the rollers on to the plate.

Figure 3 shows a plan view of a filler shoe 13, with the funnel or hopper 12 removed. The die plate 2 runs past in rotation under the filler shoe 13. Within the filler shoe 13, the bladed wheel 14 assures uniform charging of the dies 3 after setting up the angle of blade incidence matched to the flowability of the powder.

With a control system according to figure 4 for the blade angles, the blades 24 are positioned obliquely only in the area of overlap with the grad uated die circle 15. This is secured by the fact that the two plates 27, 28 in figure 2 are not made planar, but have a raised portion (or depression) in the area of the graduated circle 15 having the effect of a link motion.

The development according to figure 5 shows the horizontal position of the blades 24 below the hopper or funnel 12, and the trowel-like oblique position above the die 3 which is to be filled. Furthermore, the path of the rollers 29, 30 between the undulant plates is entered in pecked lines.

Let it be said the more than one bladed wheel may be placed within a filler shoe of larger structure. In an example of embodiment, three intermeshing bladed wheels had their axes of rotation situated on a divided circle concentrical with respectto the graduated circle 15.

If it is desirable that the powder be scraped in, in the manner of a spatula, with a constant distance from the die plate irrespective of the angular setting of the blades, the axes of rotation of the blades 24 are situated as low as possible on the hub 23 and the bladed wheel is constructed to be vertically displaceable.

In figure 6, a part of a hub 23' is illustrated at a distance h1 from the die plate 2, on which a blade 24' rests in the manner of a spatula or trowel. After displacement via the push rod 26 (figure 2) this results in a steeper angle of incidence of the blade 24'. The boss 23' has to be raised accordingly, to render this possible. The distance h2 between the hub and the die plate allows this oblique positioning.

The oblique positioning of the blades is so illustrated in the figures that an acute angle results with respect to the direction of operation of the bladed wheel. In special cases, for example in the case of excessive flowability, the blades may also be set at an obtuse angle to the direction of rotation. The bladed wheel may then well loosen the bulk material, but operates against the departure of the flow of powder.

So that the powder, which may if appropriate emerge laterally from the filler shoe, cannot drop off the die plate under the action of ce#ntrifugal forces for example, an edge bar 33 is provided (figure 1). After one revolution of the die plate, the powder reaches the range of operation of the bladed wheel, again. The diameter of the die plate was selected so great that the bladed wheel is wholly positioned within the plate rim.

An adaptation of the pressing operation to the physical properties of the powder may be obtained by turning the rotational speeds of the die plate and of the bladed wheel as well as by adjustment of the angle of incidence of the blades of the bladed wheel. This optimisation results in a satisfactory final product with maximum efficiency of the press.

Claims (8)

1. A spreader mechanism for a pulverulent material for a powder compacting press, in particular for a rotary tablet press, comprising a hub having radially projecting blades which is situated in the area of the outlet of a powder container or of a filler device following the container for charging dies of a die plate which are being moved past, characterised in that the blades are rotatably jour nalled around substantially radial spindles with respect to the hub for varying the pitch of the blades.

2. A spreader mechanism according to Claim 1, characterised in that the pivotable blades are coupled to a gear within the hub, for example comprising at least one roller track which is corotatorily arranged but is vertically adjustable, on which run rollers coupled to the blades via cranked levers or eccentrics, for joint adjustment of the pitch of the blades.

3. A spreader mechanism according to Claim 2, characterised in that the roller track comprises two plates arranged mutually parallel and that the rollers of the cranked levers or eccentrics run between the plates.

4. A spreader mechanism according to Claim 2, characterised in that the roller track has an undulant raised portion or depression situated in its area closest to the axis of rotation of the die plate, for deflection of the cranked levers or eccentrics, and for localised variation of the angle of incidence of the blades.

5. A spreader mechanism according to Claim 1, characterised in that each blade is constructed to be separately adjustable in respect of its pitch, and that a linkage control or the like is provided for continuous variation of the pitch, for example in accordance with a sinusoidal function.

6. A spreader mechanism according to claim 1 or 2, characterised in that the bladed wheel is installed in vertically variable manner on its axis of rotation for maintaining a constant gap or a scraper-like contact of the leading edges of the blades on the die plate notwithstanding the angle of incidence of the blades.

7. A spreader mechanism for a powder compacting press, substantially as herein described with reference to the accompanying drawings.

8. A powder compacting press equipped with a spreader according to any preceding claim.