METHOD OF CLEANING A SURFACE OF A CAM OF A TABLET PRESS
BACKGROUND OF THE INVENTION
This invention relates to a method of cleaning a surface of a cam of a tablet press, and to a cleaning tool for use in the method.
It is well known to manufacture tablets, such as for example pharmaceutical tablets and food products such as sweets, from a loose material such as a powder, by compression or compaction of the powder between two opposing punches or plungers in a die or cavity. In a common form of tablet press, a plurality of upper and lower punches are carried by upper and lower punch guide hole plates, in a circular arrangement, and are operated upon by cams which, in turn, lift and lower the punches. One problem with
this type of tablet press is that it is often difficult to clean the cams.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a method of cleaning a surface of a cam of a tablet press, in which tablet press the cam is adapted to operate on a plurality of punches which press the tablets, each punch having a punch shaft and a punch head attached thereto, which method includes the steps of:
(i) removing the punches from the tablet press;
(ii) replacing at least one of the punches with a cleaning tool having a tool shaft similar to the punch shaft of the punch and a tool head attached to the tool shaft, the tool head being adapted to clean the surface of the cam; and (iii) rotating the tablet press to allow the cleaning tool to clean the surface of the cam.
In step (iii), the tablet press is preferably rotated through one full revolution. Thereafter, the cleaning tool may be removed and cleaned and steps (ii) and (iii) then repeated one or more times, if necessary.
According to a second aspect of the invention there is provided a cleamng tool for cleaning a surface of a cam of a tablet press in which tablet press the cam is adapted to operate on a plurality of punches which press the tablets, each punch having a punch shaft and a punch head attached thereto, which cleaning tool comprises a tool shaft similar to the punch shaft of the punch and a tool head attached to the tool shaft, the tool head being adapted
to clean a surface of the cam.
The tool head may comprise a holder and a cleaning element located in the holder. For example, the holder may comprise a head section having a slot therein and the cleaning element may comprise a felt insert or a brush insert adapted to be received and held in the slot. In this case, the head section is preferably smaller than the equivalent punch head and the cleaning element is preferably of approximately the same size as or larger than the equivalent punch head, to ensure good cleaning of the surface of the cam.
Alternatively, the tool head may, in its entirety, be designed as a cleaning element. For example, the tool head may be made of a cleamng material such as felt or of a plastics material and carrying a plurality of bristles. In this case, the tool head is preferably of approximately the same size as or larger than the equivalent punch head to ensure good cleaning. The tool shaft may also be made of felt or of a plastics material respectively.
The cleamng tool of the invention may be used to clean any type of cam, whether an upper cam or a lower cam, and including a lifting cam, a carry over cam, a lowering cam, an ejection cam, a fill cam, and a weight adjustment cam.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a front view of a section of a tablet press;
Figure 2 is an exploded view of an upper cam of the tablet press of
Figure 1;
Figure 3 is an exploded view of a lower cam of the tablet press of
Figure 1 ; and
Figures 4 to 6 are a side view, front view and top view of a cleaning tool for cleaning the cams of Figures 2 and 3.
DESCRIPTION OF EMBODIMENTS
The crux of the invention is a method of cleaning a surface of a cam of a tablet press, in which tablet press the cam is adapted to operate on a plurality of punches which press the tablets, each punch having a punch shaft and a punch head attached thereto. The punch head is held by and/or operated on by the cam.
In terms of the method, firstly the punches are removed from the tablet press. Generally, the punches will be carried by a tablet press turret including a plate having upper punch guide holes and a plate having lower punch guide holes and located therebetween, a plate including a plurality of cavities or dies.
Thereafter, at least one of the punches is replaced with a cleaning tool having a tool shaft and a tool head attached to the tool shaft.
The tool shaft is similar to the punch shaft of the punch so that the cleaning tool can be carried by the tablet press turret in the same manner as a punch. However the end of the punch shaft remote from the punch head is generally shaped for compression of the material to be tab letted in a die. This is not necessary for the tool shaft as the cleaning tool is not designed to clean or
even enter the die.
The tool head is adapted to clean a surface of the cam over which it passes.
Thereafter the turret press is rotated, preferably through at least one full revolution to allow the cleaning tool to clean the surface of the cam.
Thereafter, the cleaning tool may be removed and cleaned and the cleaning steps repeated, if necessary.
Referring to Figure 1 , there is shown a tablet press 10 including an upper cam 12, a lower cam 14, an upper punch 16, a lower punch 18 and between them a die 20. Each of the upper punch 16 and lower punch 18 include a punch shaft 22 and a punch head 24. In use, the lower punch 18 is lifted until an end 26 of the lower punch is located in the die 20, whereafter the die 20 is filled with a powder or granular material. Thereafter, the upper punch 16 is lowered to compact the powdered granular material in the die 20 between the end 26 of the lower punch 18 and an end 28 of the upper punch 16, to form a tablet.
In a further stage, the formed tablet is ejected from the die 20.
Referring to Figure 2, the upper cam 12 is shown in more detail. The upper cam 12 includes a lifting cam 30 designed to lift the upper punches 16 out of the dies 20, a carry over cam 32, and a lowering cam 34 designed to lower the upper punches 16 into the dies 20.
Referring to Figure 3 the lower cam 14 is shown in more detail. The lower cam 14 includes an ejection cam 36 at which stage the formed tablets are ejected from the dies 20, a fill cam 38 at which stage the dies 20 are filled with the powder or granular material, and a weight adjustment cam 40 at which stage it is ensured that there is the right quantity of powder or granular material in the dies 20.
Referring to Figures 4 to 6 there is shown a cleaning tool 42 for the cams 12, 14, which consists of a tool shaft 44 similar in size and shape to the punch shaft 22 of the upper punch 16 or the lower punch 18, (except for the ends 26, 28), and a tool head 46. In the cleaning tool 42 as illustrated, the tool head 46 includes a head section 48 having a slot 50 therein, and a solid felt insert 52 located and held in the slot 50.
In use, as described above, the cleaning tool 42 replaces either one of the upper punches 16 or one of the lower punches 18. Thereafter the tablet press 10 is rotated to allow the cleaning tool 42 to pass through the various sections of the upper cam 12 or the lower cam 14 and thus to clean the surfaces, particularly the inaccessible surfaces of the various sections of either the upper cam 12 or the lower cam 14. For example, referring to the lifting cam 30 in Figure 2, it can be seen that the cleaning tool 42 is useful for cleaning the area 54 of the cam 30.
In the cleaning tool 42 as illustrated, the head section 48 is approximately 2mm smaller than the punch head 24 of either the upper punch 16 or the lower punch 18, which ensures good clearance as the cleaning tool 42 passes through the cams 12, 14 in the tablet press 10. The head section 48 includes a 5mm wide slot 50, which accommodates a felt insert 52 which is
2mm larger than the size of the punch head 24 of either the upper punch 16 or the lower punch 18. As stated above, as the cleamng tool 42 passes through the cams 12, 14, the felt insert 52 wipes all the cam surfaces, removing old grease and remaining product.
As the cams 12, 14 are not often removed from the tablet press 10, the cleaning tool of the invention offers the opportunity to clean inaccessible areas of the cams 12, 14 while still in situ, reducing clean down times while maintaining a high standard of GMP (Good Manufacturing Practices). As grease and remnants of product granule act as a mild grounding paste, removing this from the cams 12, 14 with the cleaning tool 42, results in the life of the punch heads 16, 18 and the cams 12, 14 themselves being extended.
The cleaning tool of the invention may be used in place of various types of punches including keyed top punches, top punches and bottom punches which are not keyed, and B configuration and D configuration punches.
Although the cleamng tool 42 is illustrated with a felt insert 52, it is also possible to manufacture the cleaning tool 42 with a solid felt head, and shaft or from a plastics material with the head incorporating a plurality of bristles.