Abstract:
A rotary tablet press comprises a housing and a rotary die table having dies arranged circumferentially. Each die is associated with a punch having an end receivable in the die and being arranged for compression of a powder or granular material in the die by reciprocation of the punch by rotation of the die table. The rotary tablet press comprises a feeding device and a tablet discharge device. Each die opening and its corresponding punch end are enclosed in a compression chamber comprising a dust extraction nozzle. The compression chamber communicates with the surroundings of the tablet press through a non-return valve arranged to prevent outflow from the compression chamber to the surroundings of the tablet press.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a rotary tablet press comprising a housing, a rotary die table having a number of dies arranged circumferentially, each die being associated with at least a first punch having a first end receivable in the die through an opening of the die and arranged for compression of a powder or granular material in the die by reciprocation of the punch, at least a cam for cooperation with a second end of the punches in order to effect axial displacement of the punches by rotation of the die table, a feeding device for the supply of material to be compressed into the dies, and a tablet discharge device for removal of compressed material in the form of tablets, wherein each die opening and its corresponding first punch end are enclosed in a compression chamber, said compression chamber comprising at least one dust extraction nozzle communicating with a dust extraction tube located outside the compression chamber. 
         [0002]    US 2004/0207107 A1 (assigned to Courtoy N V) describes a rotary tablet press having dust extraction nozzles placed in appropriate positions in the compression chamber to prevent build-up of dust in the compression chamber. The suction system may advantageously be designed to constantly keep a certain under pressure in the compression chamber in order to prevent any leakage from the chamber. 
         [0003]    Furthermore, it is well-known practice to provide the compression chamber of a rotary tablet press with a chimney-like, vertical air intake duct extending from an upper wall of the compression chamber to an intake opening at an area at the top of the rotary tablet press. Through this duct, air from the surroundings of the rotary tablet press may enter the compression chamber in order to replace air removed by means of dust extraction nozzles. The intake opening of the duct may be covered by means of a simple filter or a HEPA filter, if necessary. Such a filter may both ensure that the air entering the compression chamber is clean and that no powder or dust leaks from the compression chamber. However, such filters have the disadvantage that they become clogged during use, and therefore they must be monitored and replaced when necessary. 
         [0004]    In another known application, the compression chamber is comprised by a compression unit detachably mounted in the housing of the rotary tablet press, and the compression unit is located in a compression section delimited by an upper partition wall and a lower partition wall of the housing of the rotary tablet press. A vertical air intake duct similar to the above explained projects from the upper side of the upper partition wall in order to enable air to enter the compression section from the surroundings of the tablet press. Thereby, air may by suction enter the compression chamber from the compression section through a hole in the wall of the compression chamber, or the compression chamber may be connected with the vertical air intake duct by means of a rigid or flexible pipe or tube connection extending through the compression section. 
       SUMMARY OF THE INVENTION 
       [0005]    An object of the present invention is to provide a rotary tablet press, whereby air intake to the compression chamber is enabled without the risk of dust leakage to the surroundings and without the above-mentioned disadvantages. 
         [0006]    In view of this object, said compression chamber communicates with the surroundings of the tablet press through a non-return valve arranged to prevent outflow from the compression chamber to the surroundings of the tablet press. A non-return valve may allow air to enter the compression chamber and prevent dust from leaving the compression chamber; the valve may be of simple construction and does not need replacement on a regular basis. 
         [0007]    The valve may comprise a valve flap and a valve seat facing the inside of the compression chamber, and the valve flap may be biased against the valve seat. 
         [0008]    The valve seat may be concave and the valve flap may be made of flexible material. Thereby, the effective contact area between the valve flap and the valve seat in which the contacting surfaces have to be brought out of contact in order to open the valve is reduced, thereby reducing the under pressure necessary to open the valve. This is because in this embodiment, only the peripheral part of the valve flap has to be lifted from the valve seat in order to open the valve. 
         [0009]    In an embodiment, the valve flap is fixed on a shaft that is mounted axially displaceable in a central hole in the valve seat, and the shaft is spring loaded to press the valve flap against the valve seat. If a relatively weak spring is used, only very little under pressure is needed to open the valve, even if the valve flap is made of a more rigid material. 
         [0010]    In an embodiment, the valve seat is circular and is provided with a plurality of through holes along its periphery. The circular parts are easy to manufacture with tight tolerances, which allow for a good closing of the valve flap against the valve seat and hence a good sealing action. 
         [0011]    In an embodiment, the compression chamber is delimited by a top wall in which the non-return valve is located, and the non-return valve communicates with the surroundings of the tablet press through a vertical air intake duct. Thereby, very little under pressure is needed to open the valve. 
         [0012]    In an embodiment, the compression chamber is comprised by a compression unit detachably mounted in the housing of the rotary tablet press, and the non-return valve is located in wall of the compression unit. 
         [0013]    In an embodiment, the compression unit is located in a compression section delimited by a upper partition wall and a lower partition wall of the housing of the rotary tablet press, and a vertical air intake duct projects from the upper side of the upper partition wall in order to enable air to enter the compression section from the surroundings of the tablet press. Thereby, very little under pressure is needed to open the valve. 
         [0014]    In an embodiment, the non-return valve is detachably connected with the vertical air intake duct by means of a vertically arranged connection piece. The connection piece allows for a detachment of the intake duct from the valve. Therefore, the compression unit will stay detachably connected in the housing. 
         [0015]    In an embodiment, the non-return valve is detachably connected with the vertical air intake duct by means of a flexible tube. Thereby, the air intake duct need not necessarily be in line with the valve, which is sometimes, due to other dimensional constraints, not possible. The flexible tube allows more freedom to place the air intake duct or the valve. 
         [0016]    In another embodiment, said compression chamber communicates with the surroundings of the tablet press through a pressure controlled valve adapted to open, when the pressure inside the compression chamber is smaller than the pressure at the surroundings of the tablet press, and adapted to close, when the pressure inside the compression chamber is larger than the pressure at the surroundings of the tablet press. In this way, the valve will prevent outflow of air from the compression chamber to the surroundings, and thereby it will be prevented that dust leaks from the compression chamber. 
         [0017]    In an embodiment, the pressure-controlled valve comprises a valve element that is biased against a valve seat. 
         [0018]    In an embodiment, the pressure-controlled valve is controlled by a computer on the basis of a signal provided by a pressure transducer. An actuated valve allows for a stronger valve, made of stronger, more rigid material that can be pressed with higher forces against the valve seat. Hence, it is possible to obtain a better sealing action. 
         [0019]    In an embodiment, the compression chamber is delimited by a top wall in which the non-return valve is located, and the non-return valve communicates with the surroundings of the tablet press through a vertical air intake duct. 
         [0020]    In an embodiment, the compression chamber is comprised by a compression unit detachably mounted in the housing of the rotary tablet press, and the non-return valve is located in wall of the compression unit. 
         [0021]    In an embodiment, the compression unit is located in a compression section delimited by a upper partition wall and a lower partition wall of the housing of the rotary tablet press, and a vertical air intake duct projects from the upper side of the upper partition wall in order to enable air to enter the compression section from the surroundings of the tablet press. 
         [0022]    In an embodiment, the non-return valve is detachably connected with the vertical air intake duct by means of a vertically arranged connection piece. 
         [0023]    In an embodiment, the non-return valve is detachably connected with the vertical air intake duct by means of a flexible tube. 
         [0024]    In yet another embodiment, said compression chamber communicating with the surroundings of the tablet press through a valve comprising a valve flap made of a material that is impervious to dust and a valve seat facing the inside of the compression chamber, and the valve flap being biased against the valve seat. 
         [0025]    In an embodiment, the valve flap is made of a filter material. This will allow an air intake at very low under pressure, smaller than that needed to lift the valve flap from the valve seat. 
         [0026]    In an embodiment, the compression chamber is delimited by a top wall in which the non-return valve is located, and the non-return valve communicates with the surroundings of the tablet press through a vertical air intake duct. 
         [0027]    In an embodiment, the compression chamber is comprised by a compression unit detachably mounted in the housing of the rotary tablet press, and the non-return valve is located in wall of the compression unit. 
         [0028]    In an embodiment, the compression unit is located in a compression section delimited by a upper partition wall and a lower partition wall of the housing of the rotary tablet press, and a vertical air intake duct projects from the upper side of the upper partition wall in order to enable air to enter the compression section from the surroundings of the tablet press. 
         [0029]    In an embodiment, the non-return valve is detachably connected with the vertical air intake duct by means of a flexible tube. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The invention will now be explained in more detail below by means of examples of embodiments with reference to the schematic drawing, in which 
           [0031]      FIG. 1  is a perspective view of a rotary tablet press according to the invention, the cover of the housing being partly removed, 
           [0032]      FIG. 2  is view similar to that of  FIG. 1  of another embodiment of the rotary tablet press according to the invention, 
           [0033]      FIG. 3  is a perspective view showing a section through the compression unit of the rotary tablet press shown in  FIG. 1 , 
           [0034]      FIG. 4  is a perspective view of the compression unit shown in  FIG. 3 , 
           [0035]      FIG. 5  is a perspective view of the compression unit shown in  FIG. 4 , seen from behind, 
           [0036]      FIG. 6 to 8  show very schematic three different embodiments of a rotary tablet press of the type shown in  FIG. 1 , 
           [0037]      FIG. 9  is a perspective view of a valve of the rotary tablet press according to the invention, 
           [0038]      FIG. 10  is an axial section through the valve of  FIG. 9 , shown in closed state, and 
           [0039]      FIG. 11  is an axial section through the valve of  FIG. 9 , shown in open state. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]      FIG. 1  shows a rotary tablet press  1  for compression of a feedstock in the form of powder or granular material into tablets, compacts or the like. The press shown is of a type suitable for use in the pharmaceutical industry, but the press according to the invention may as well be a so-called industrial press employed in the production of a variety of different products, such as vitamins, pet food, detergents, explosives, ceramics, batteries, balls, bearings, nuclear fuels, etc. 
         [0041]    The rotary tablet press  1  has a press housing  2  comprising an internal frame  3 , which supports various components located in the housing  2 , and an outer lining  4 , which is shown only at a lower section  5  of the press. The press housing  2  is composed of three sections, which are located on top of each other and are separated by means of partition walls. The lower section, designated the drive section  5 , is separated from a central section, designated the compression section  6 , by a lower partition wall  7 , and the compression section  6  is separated from an upper section, designated the accessory section  8 , by an upper partition wall  9 . 
         [0042]    The drive section  5  comprises a not shown electrical drive motor driving a not-shown vertical drive shaft projecting up through a central opening in the lower partition wall  7  and having at its upper end a coupling part for detachable connection with a rotary turret  12  located in a casing  13  of a compression unit  14  which is arranged detachably in the compression section  6  of the press housing  2 , see also  FIGS. 3 to 5 . The chamber comprised by the compression unit  14  is designated the compression chamber  29 . 
         [0043]    Referring to  FIGS. 3 to 5 , the rotary turret  12  comprises a die table  15  having a number of dies arranged evenly distributed along its circumference, each die  16  having the form of a bore arranged with its axis parallel to the vertical rotational axis of the turret  12 . On either side of the die table  15  are arranged top and bottom punches  17 ,  18 , respectively, in corresponding guides  19 ,  20  accommodated in the turret  12  so that a first end  21 ,  22  of each punch  17 ,  18  is able to enter a corresponding die  16  by displacement of the punch in its guide  19 ,  20  in order to compress material in the die. The punches  17 ,  18  may be sealed against their guides  19 ,  20  at the end of these facing the die table  15  by means of not shown lip seals. For use with toxic products, a bellows seal, for instance of silicone, may be employed. 
         [0044]    A second end  23 ,  24  of each punch  17 ,  18  is in a well-known manner co-operating with top and bottom cams, respectively, arranged stationary in relation to the press housing  2  in order to effect axial displacement of the punches by rotation of the turret  12 . Only the top cams  25  are visible, see  FIGS. 1 and 2 . The cams only extend along part of the circumference of the turret, and at that circumferential position where the final compression of the material in the die is to be performed, top and bottom precompression rollers  32 ,  46  and top and bottom main compression rollers (of which only the top roller  33  is shown), respectively, take over the displacement of the punches  17 ,  18 . 
         [0045]    The casing  13  of the compression unit  14  comprises a top wall  39 , a bottom wall  40  and more transparent side walls  41 . A number of the side walls  41  may be detached from the compression unit  14  in order to gain access to the internal components of the unit for exchange of components at change-over between batches of different products, for cleaning or for maintenance, see also  FIG. 5 , in which the side wall at the left side of the compression unit has been removed. The top and bottom walls  39 ,  40  are substantially plane, each having a central circular opening  42 ,  43  sealed rotatably against the periphery of the turret  12  by means of a not shown seal, such as a lip seal. 
         [0046]    The compression unit  14  is provided with a feeding device in the form of a not shown, well-known double rotary feeder with two rotary paddles located in a feeder housing and driven by means of separate drive motors located in the accessory section  8  of the press housing  2  and providing for independent speed setting of the paddles. The feeding device has been removed in the figures for the sake of simplicity. 
         [0047]    The feeder housing has a feedstock inlet that opens through the top wall  39  of the casing  13  of the compression unit  14  and is provided with a first coupling half  56  for connection with a corresponding, not shown, second coupling half provided on a lower end of a similarly not shown supply channel in the press housing  2 . Said first and second coupling halves may be provided with closing mechanisms, and for operation with toxic products they may constitute a so-called split valve, such as a split butterfly valve. 
         [0048]    The compression unit  14  is further provided with a not shown tablet chute protruding from the casing  13  for conducting away compressed material in the form of tablets from the dies  16 . 
         [0049]    Further, the compression unit  14  is provided with a dust extraction coupling half  67 , see  FIG. 5 , for connection with a corresponding, not shown, coupling half that is located in the press housing  2  and connected to a not shown, well-known, suction system. The dust extraction coupling half  67  is by means of tubing  68  connected with dust extraction nozzles  69 ,  70  placed in appropriate positions inside the casing  13  of the compression unit  14  in order to prevent build-Lip of dust in the casing. The suction system may advantageously be designed to constantly keep a certain under pressure in the casing  13  of the compression unit  14  to prevent any leakage from the casing. The under pressure may advantageously be monitored and controlled to maintain a certain value. The dust extraction coupling half  67  on the unit  14  may together with the corresponding coupling half in the press housing  2  constitute a split valve of the above-described type. 
         [0050]    In order to both allow air to enter the compression chamber and prevent dust from leaving the compression chamber, a non-return valve  10  is arranged in the top wall  39  of the casing  13  of the compression unit  14 . Air may reach the non-return valve  10  from the surroundings of the rotary tablet press through a vertical air intake duct  11  extending from the upper partition wall  9  of the housing  2  to an intake opening  26  at an area at the top of the rotary tablet press. The non-return valve  10  may be connected with the vertical air intake duct  11  by means of a connection piece  27  that is slidably connected with the vertical air intake duct  11 , see  FIGS. 1 and 6 .  FIG. 8  shows another embodiment, whereby the non-return valve  10  is connected with the vertical air intake duct  11  by means of a flexible tube  28 . In this embodiment, as is seen in the figure, the vertical air intake duct  11  is not aligned with the non-return valve  10 .  FIG. 7  shows yet another embodiment, whereby the non-return valve  10  is not connected directly with the vertical air intake duct  11 , but may receive air through the vertical air intake duct  11  from the surroundings via the compression section  6 . 
         [0051]    The non-return valve  10  is shown in detail in the  FIGS. 9 to 11 . The non-return valve  10  comprises a substantially cylindrical housing  34  with an outer mounting collar  35  at a lower end, an inner, circular, disc-formed valve seat  36  formed integrally with the housing  34  and facing the inside of the compression chamber  29 , and a thin, flexible, circular, disc-formed valve element  37  biased against the valve seat  36  by means of a compression spring  38  arranged around a shaft  44  that is mounted axially displaceable in a central hole  45  in the valve seat  36 . The valve seat  36  has a backside  47  and a front side  54 . The compression spring  38  located around the shaft  44  is compressed between the backside  47  of the valve seat  36  and a first end stop  48  fixed on a top end  49  of the shaft  44 . A second end stop  50  is fixed on a bottom end  51  of the shaft  44  and abuts the disc-formed valve element  37 . An intermediate washer  52  may be located between a central part of the disc-formed valve element  37  and the valve seat  36 . Along its periphery, the valve seat  36  is provided with a plurality of through holes  53 , through which air may enter from the backside  47  of the valve seat  36  to the front side  54  of the valve seat  36 , when the disc-formed valve element  37  is flexed away from the valve seat  36 , as shown in  FIG. 11 . It is preferred that the front side  54  of the valve seat  36  is concave, as shown in  FIGS. 10 and 11 , in order to provide better abutment between the disc-formed valve element  37  and the valve seat  36 ; this is, however, not necessary. In the open position of the non-return valve, as shown in  FIG. 11 , the compression spring  38  is not even compressed more than in the closed position shown in  FIG. 10 ; however, the compression spring  38  may be compressed further than shown in order to open the non-return valve  10  even more. 
         [0052]    The flexible, disc-formed valve element  37  may have the form of a valve flap made of a filter material that is impervious to dust in a suitable degree. 
         [0053]    According to the present invention, another type of pressure controlled valve  10  may also be applied, whereby the valve is adapted to open, when the pressure inside the compression chamber  29  is smaller than the pressure at the surroundings of the tablet press, and adapted to close, when the pressure inside the compression chamber is larger than the pressure at the surroundings of the tablet press. Such a pressure controlled valve may be controlled by a computer on the basis of a signal provided by a pressure transducer registering the pressure in the compression chamber  29  and on the basis of a pressure transducer registering the pressure at the surroundings. The pressure controlled valve may be actuated electrically. The pressure controlled valve may also be controlled fully mechanically and/or pneumatically. 
         [0054]    In order to clean the interior of the compression unit  14  between batches of different products or in order to exchange the unit for another type of unit, the rotary tablet press  1  shown in  FIG. 1  is equipped with a handling system for removal of the unit from the press and for placement of another unit in the press. 
         [0055]      FIG. 2  shows another embodiment of the rotary tablet press according to the invention, whereby the housing does not comprise a detachable compression unit in the compression section  6 . Instead, the compression chamber  29  is comprised between a bottom wall  30  and a top wall  31  arranged in a well-known manner fixed in the housing and situated in the compression section  6  between the lower partition wall  7  and the upper partition wall  9 . The non-return valve and/or pressure controlled valve  10  is arranged in the top wall  31 , as shown in  FIG. 2 , in the same way as it is arranged in the top wall  39  of the casing  13  of the compression unit  14  in the embodiment shown in  FIG. 1 . Furthermore, the rotary tablet press shown in  FIG. 2  is, in the same way as the rotary tablet press shown in  FIG. 1 , provided with a feeding device, a tablet chute and dust extraction nozzles  69 ,  70  connected with a dust extraction coupling half  67 . These devices are, however, for the sake of simplicity, not shown. 
         [0056]    The invention has in the above been explained by means of a tablet press having a single feeding device and a single tablet discharge device; however, the tablet press according to the invention may have several tablet discharge devices and and/or several feeding devices arranged in combination with a single die table.