Patent Publication Number: US-7210915-B2

Title: Powder compacting apparatus

Description:
FIELD OF THE INVENTION 
   The present invention relates to a powder compacting apparatus for use to produce consolidated pieces of a powder. 
   BACKGROUND OF THE INVENTION 
   In general, powder compacting apparatuses are used for instance in the conventional metallurgy industries in which a basic iron powder is blended with a copper powder, a graphite powder or the like alloy element to prepare a composition. Usually added to this composition is a lubricant such as zinc stearate, lead stearate or the like, to provide a mixed powder that will then be compacted in a press mold. Powder metallurgy is a process for producing for example such an iron-based compacted powder pieces, and in the atomic power industries the mold is disposed in a glove box so as to produce such pieces as nuclear fuel pellets. 
   Presses widely used in this field comprise each two or more punches for a mold. 
   One of the prior art powder compacting apparatuses is disclosed in the Japan Patent Laying-Open Gazette No. H.9-253896 and shown in “FIG. 1” thereof (—FIG.  7 —herein). This apparatus comprises a punch holder for attaching an upper punch to a top plate, a die plate for holding a die, and a bottom plate to which a lower punch is secured. The upper and lower punches are strongly urged towards each other to compress a powder mixture and compact it into a consolidated piece. 
   Now,  FIG. 7  will be referred to in detail for description of the prior art type of powder compacting apparatuses. 
   This prior art proposes a die device for incorporation into a powder compacting apparatus. The die device comprises an upper punch  113  held in place by an upper holder  112 , that is bolted to the lower face of a top plate  110 . A die  121  fitted downwards in a die plate  123  is fixed therein by a die retainer  122  bolted thereto. A die plate supporter  126  is disposed below and adjacent to the lower face of die plate  123 . A pair of guide posts  114  depend from opposite side ends of the top plate  110 . These posts are loosely extend through corresponding holes formed in the die plate  123 . Beatings secured in the supporter  126  hold the lower end portions of such guide posts  114  in a freely rotating engagement with said supporter. The die  121  has a central bore fitting on the top end of a lower punch  131 , that can reciprocate up and down relative to this die  121 . A lower holder  132  is bolted to a base plate  140  so as to retain thereon the lower punch  131 . A pair of upright guide rods  160  penetrate the opposite side regions of said base plate  140 . 
   In operation, an amount of powder will be placed in the die  121 , and then the top plate  110  will be lowered along the guide posts  114  so that the upper punch  113  descends towards the die  121 . On the other hand, the base plate  140  will be raised along the guide rods  160 , thus driving the lower punch  131  upwardly towards the die  121 . Those upper and lower punches  113  and  131  cooperate with each other to press the powder between them, thereby compacting it into a consolidated piece. 
   When setting this apparatus ready to operate, the upper end of lower punch  131  will be positioned at first to fit in the die  121 . This die will then engage the die plate  123 , before the retainer  122  is placed onto the die and bolted downwards to this die plate. The lower holder  132  restraining the lower punch  131  from sideways movement will be bolted downwards to the base plate  140  so as to fix thereon the lower punch. Subsequently, the lower end of upper punch  113  will be fitted in die  121 , before temporarily lowering the top plate  110 . Next, the upper holder  112  will be positioned correct relative to this plate by upwardly screwing some bolts. As the final step, the top plate  110  will be retracted upwards in order to tightly fasten those bolts for firmly fixing the upper punch  113 . 
   In the powder compacting apparatus summarized above, many bolts are used around the die  121  in order that the retainer  122  urges downwards this die within the die plate  123 . Thus, very intricate and time-consuming works are necessary when mounting and dismounting the die  121 . 
   As also noted above, the upper punch  113  has to preliminarily fit in the die  121  to be aligned therewith. Thus, many further bolts inserted upwards through the upper holder  112  will be allowed to loosely engage with the top plate  110 . Subsequently, the top plate will be lifted to tightly fasten the bolts and firmly secure the upper punch  113  in position. Due to almost impossible visual inspection of the positions of those bolts and bolt holes receiving them, the upper holder  112  is not easy to fix. All the works to bolt this holder  112  may alternatively be done after having raised the top plate  110 . In this case, it will however be more difficult to precisely align the upper punch  113  with the die  121 , also failing to smoothly attach and quickly fasten those bolts. 
   The upper punch  113  should be protected from damage when it is driven into a smooth alignment with the die  121 . For this purpose, a manually operable mold changer may be necessary for slowly raising and lowering the upper punch. Such a mold changer will be located apart from the main body of a powder compacting apparatus. Therefore, a set of dies and relevant members therefor must move fore and aft between such a changer and the apparatus. 
   SUMMARY OF THE INVENTION 
   A powder compacting apparatus ( 1 ) provided herein in view of such problems noted above will comprise a top plate ( 3 ), a die plate ( 9 ) and a bottom plate ( 12 ), combined with each other as follows. The top plate ( 3 ) holds upper punches ( 4 ) in place by means of punch holders ( 5 ), and the die plate ( 9 ) firmly grips a die holder ( 8 ) holding dies ( 7 ) therein. The bottom plate ( 12 ) keeps lower punches ( 11 ) in place by means of clamps ( 32 ) for gripping the punches. An amount of powder fed into each die ( 7 ) will thus be compacted therein to give a consolidated powder piece. Characteristically, the die plate ( 9 ) is composed of an upper part ( 9   a ) and a lower part ( 9   b ). The die holder ( 8 ) is sandwiched by and between the parts ( 9   a,    9   b ), in such a manner that these parts cooperate with each other to secure each die ( 7 ) in position. 
   Also characteristically, an upper retentive plate ( 6 ) is disposed below and attached to the top plate ( 3 ) so that the punch holders ( 5 ) are firmly fitted in and through this retentive plate ( 6 ). Further, an internal sleeve ( 13 ) is disposed around each upper punch ( 4 ) held in the corresponding punch holder ( 5 ). In operation, the internal sleeve ( 13 ) will be inflated uniformly so as to press and strongly grip each upper punch ( 4 ) in the holder ( 5 ), in a centripetal manner. Furthermore, a lower retentive plate ( 10 ) fixed on the bottom plate ( 12 ) does comprise the clamps ( 32 ) and locking bolts ( 33 ) cooperating with them. These bolts ( 33 ) are capable of being fastened such that the clamps ( 32 ) will slide on and along the body of retentive plate ( 10 ). In operation, each lower punch ( 11 ) will immovably be pressed against the body of this plate ( 10 ). 
   The mounting and dismounting of dies in the present apparatus are much easier and much quicker than in the prior art apparatuses, thus saving labor time. Particularly, the upper punches can be aligned with the dies more smoothly in situ, without moving a set of the dies and relevant members to or away from any mold changer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front elevation of a powder compacting apparatus provided in an embodiment of the present invention; 
       FIG. 2  is a side elevation of the apparatus shown in  FIG. 1 ; 
       FIG. 3  is a cross section taken along the line A—A in  FIG. 1 ; 
       FIG. 4  is a front elevation of an upper punch being fixed in position in the apparatus; 
       FIG. 5  is a front elevation of the upper punch having been fixed in position; 
       FIG. 6  is an enlarged cross section of a portion of the punch fixed in position; and 
       FIG. 7  is a vertical cross section of the prior art apparatus. 
   

   THE PREFERRED EMBODIMENTS 
   As shown in  FIGS. 1 and 2 , a powder compacting apparatus  1  of the present invention comprises a top plate  3 , and upper punches  4  held by punch holders  5 . These plate  3  and holders  5  are to be driven up and down along guide shaft  2 . An upper retentive plate  6  serves to fix the punch holders  5  on the top plate  3 . The apparatus further comprises dies  7  that extend vertically and centrally of a die holder  8 , which in turn is locked in position by a die plate  9 . In other words, such a holder  8  and die plate  9  do function to fixedly secure the dies  7 . The apparatus still further comprises a bottom plate  12  that supports thereon a lower retentive plate  10  so as to hold lower punches  11  in position. 
   The guide shafts  2  are arranged at four corner regions of the die plate, surrounding 6 (six) dies  7  as seen in  FIG. 3 . 
   An oil-hydraulic or electric motor (not shown) will drive the top plate  3  to move up and down along the guide shafts  2  holding this plate. The top plate  3  in turn retains the punch holders  5  and pistons  14 , and the number of these pistons is the same as that of dies  7 . 
   Each upper punch  4  is an integral piece comprising a press portion  15  to be forced into the die  7 . As shown in  FIG. 4 , the upper punch  4  farther comprises an annular shoulder  16  and an insert portion  17 , continuing upwards in this order from the press portion  15 . The shoulder  16  of an enlarged diameter will bear against the lower end of punch holder  5 . The insert portion  17  will be received in the punch holder  5  so that its periphery is firmly seized therein. A tapered region  16   a  is formed as a portion of the shoulder  16  continuing to the insert region of a smaller diameter. 
   As also seen in  FIG. 4 , the punch holder  5  is constructed to firmly hold therein the insert portion  17  of upper punch  4 . Thus, the punch holder  5  comprises a lower cylindrical body  18  continuing upwards to a support head  19  made integral therewith. A cylindrical cavity or bore  20  is formed centrally and upwards from a lower tapered end  20   a  of the body  18 , so that the insert portion  17  can be received in this cavity. The upper end region of the periphery of this cavity  20  is formed as a squeezing section  21 , as will be detailed below. A tip end of the head  19  of each punch holder  5  is supported by the lower face of piston  14  that is held in the top plate  3 . 
   Formed between the cavity  20  and the outer peripheral surface of cylindrical body  18  of punch holder is the squeezing section  21  as shown in  FIGS. 4 and 6 . This section  21  comprises a compressed-oil chamber  26  in fluid communication with an oil-feed passage  22  and oil discharge passage  23 . These passages extend from the lower end of said body  18 , and an airtight stopper  24  serving also as an air-breaker is closely fitted in the lower end of said discharge passage  23 . In addition, a screw-type hydraulic element  25  is installed in the lower end region of the oil-feed passage  22  so that hydraulic pressure in the chamber  26  can be raised by operating this screw. 
     FIG. 6  illustrates in detail the squeezing section  21  that is an annular space formed around the cavity  20  of each punch holder  5 . The internal sleeve  13  will be brought into a close contact with the insert portion  17  of upper punch  4  fitted in the cavity  20 , to thereby fix this portion at its normal position. The reference numeral  28  denotes seal rings. A tip end of the insert portion  17  will be pressed towards the head  19  of punch holder  5 , and then rotated a little angle so as to protect the punch  4  from falling out of the cavity  20 . 
   The upper retentive plate  6  bolted up to the top plate  3  has apertures each receiving the lower cylindrical body  18  of each punch holder  5 . The number of such apertures is the same as that of the dies. Each piston  14  seizes the upper end of each holder  5 , preventing it from slipping off. If the upper retentive plate  6  has preliminarily been aligned with the die holder  8 , then clearance adjustment between it and the dies  7  will not be necessary. Also, the tapered regions  16   a  of each upper punch  4  need not be aligned with a tapered inlet  20   a  of the corresponding punch holder  5 . Further, any adjustment in position of the upper punch  4  will not be necessary relative to the internal sleeve  13  fitting thereon. 
   Each die  7  is, as seen in  FIGS. 1 and 7 , a hollow cylindrical piece shown at its upright position in the drawings. A flange  29  integrally protrudes outwards and radially from a middle height of the outer periphery of each die  7 . 
   The die holder  8  has apertures formed therein to receive the flanges  29  of dies, the number thereof being the same as that of the dies  7 . 
   The die plate  9  discussed above is split into an upper part  9   a  and a lower part  9   b , both being guide by the shafts  2  so as to be movable relative to each other. Each part  9   a  and  9   b  has apertures for receiving cylindrical portions of each die  7 , the number of such apertures also being the same as that of the dies. 
   Thus, the lower cylindrical portions of dies  7  fit in the respective apertures of the lower part  9   b  of die plate. Next, the die holder  8  will be laid on this lower part  9   b  so that the apertures of this holder  8  receive the respective flanges  29  of dies  7 . Then, the upper part  9   a  of said die plate is put on the die holder  8 , likewise receiving the upper cylindrical portions of dies  7 . Hooks  30  having their bases attached to the lower part  9   b  will thereafter be actuated oil-hydraulically or pneumatically. By locking the upper part  9   a  in this way, the die holder  8  becomes sandwiched together with the dies  7  by and between those upper and lower parts  9   a  and  9   b.    
   The bottom plate  12  is set on the ground by means of the guide shafts  2  disposed at each corner of this plate. The lower retentive plate  10  is bolted to the upper face of bottom plate  12 . 
   The lower punches  11  held on this retentive plate  10  will be caused to upwardly fit in the respective dies  7  that have been temporarily lowered. Subsequently, clamps  32  will be operated to lock these lower punches  11  in position on said retentive plate  10 . 
   It will be apparent from  FIG. 2  that each clamp  32  has an outer lower portion loosely held in the lower retentive plate  10  so that the clamp can slide in and out. Each clamp  32  has an inner end with a cutout serving as a groove for engagement with the lower punch  11 . A locking bolt  33  screwed inwards from the lateral wall of retentive plate  10  has an inner end bearing against the clamp  32 . 
   The reference numeral  33  denotes connective plates each serving to connect the top plate  3  to the upper part  9   a  of die plate  9 . 
   When bringing the lower punches  11  into operative connection with the respective dies  7 , these dies will be fitted in the respective apertures of the lower part  9   b  of die plate. Next, the die holder  8  will be laid on this lower part  9   b  so that the apertures of this holder receive the respective flanges  29  of the dies. Then, the upper part  9   a  of said die plate is put on the die holder  8  so that they receive the upper cylindrical portions of dies  7 . The hooks  30  connected to the lower part  9   b  will thereafter be actuated to lock the upper part  9   a  of die plate. Now, the dies  7  can be mounted on or dismounted from the apparatus, without using any further bolts other than those noted above. Such an operation that does not involve any intricate or complicated steps can be done more quickly as compared with the prior art apparatus. This feature is advantageous particularly to atomic energy industries in which glove boxes are used to conduct operations necessary to produce nuclear fuel pellets in the shape of compacted pieces of powder. 
   As will be seen in  FIG. 2 , the locking bolts  33  will be screwed inwards into the lower retentive plate  10  so that the clamps  32  engaging with the inner ends of said bolts are caused to slide on this plate  10 . As a result, the lower end of each lower punch  11  is retained in the groove of each clamp  32  and strongly urged towards the retentive plate  10 , not to fluctuate in position to any extent. 
   With the upper retentive plate  6  being bolted to the lower face of to plate  3 , each punch holder  5  supported on the piston  14  in the top plate will be will surely be retained not to fall down as a whole or to rock at its inner end. In this state of the members, the top plate  3  can safely be lowered for the next operation. 
   As for each upper punch  4 , its insert portion  17  will be placed in the corresponding punch holder and twisted for temporary attachment thereto. The punch  4  will then have its tapered region  16   a  caused to slide into an aligned engagement with the tapered region  20   a  of punch holder  5 . Thereafter, the hydraulic element  25  will be operated to raise oil pressure in the compressed-oil chamber  26 . This chamber will thus expand to inflate the internal sleeve  13  inwardly towards cylindrical cavity  20 . As a result, this sleeve will come into a forced contact with the insert portion  17  of upper punch  4 , thereby affording a strong and uniform fastening force each upper punch. 
   In this way, the dies  7  can now be aligned with the upper punches  4  easily and surely, and these punches can be locked in position in a shorter time. The setting of those dies can be done in situ, no longer transporting any die assembly to a foreign mold changer. 
   The embodiment described above is meant to be merely an example of the invention, and it may be modified within the spirit and scope thereof even in application to any industrial fields other then the atomic energy industries.