Patent Publication Number: US-9839950-B2

Title: Dummy block for extrusion press

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of provisional U.S. Application No. 62/001,958 filed on May 22, 2014, the content of which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present invention relates generally to extrusion and in particular, to a dummy block for an extrusion press. 
     BACKGROUND 
     Metal extrusion presses are known in the art, and are used for forming extruded metal products having cross-sectional shapes that generally conform to the shape of the extrusion dies used. A typical metal extrusion press comprises a generally cylindrical container having an outer mantle and an inner tubular liner. The container serves as a temperature controlled enclosure for a billet during extrusion. An extrusion ram is positioned adjacent one end of the container. The end of the extrusion ram abuts a dummy block, which in turn abuts the billet allowing the billet to be advanced through the container. An extrusion die is positioned adjacent the opposite end of the container. 
     During operation, once the billet is heated to a desired extrusion temperature (typically 800-900° F. for aluminum), it is delivered to the extrusion press. The extrusion ram and dummy block are then advanced, so as to push the billet through the container and towards the extrusion die. Under the pressure exerted by the advancing extrusion ram and dummy block, the billet is extruded through the profile provided in the extrusion die until all or most of the billet material is pushed out of the container, resulting in the extruded product. 
     Dummy blocks for extrusion presses have been previously described. For example, U.S. Pat. No. 5,918,498 to Robbins discloses a dummy block having a dummy block base, a connector for connecting the dummy block base to a stem of an extruder, a replaceable wear ring connected to a forward circumferential portion of the dummy block base, a device for releasably securing the wear ring to the dummy block base, and a device for expanding the ring to engage an inside wall of a container of an extrusion press during extrusion. The wear ring is a metal collar having a conical interior surface converging towards the dummy block base. The device for expanding the ring comprises a metal plunger having a plunger head with a conical surface for engaging the collar conical surface to expand the collar as the plunger head is forced into the collar during extrusion. The converging surfaces of the collar and the plunger head extend a sufficient distance to permit telescoping of the plunger head into the collar to an extent whereby the collar is expanded to engage the inside wall of the container. 
     Improvements are generally desired. It is therefore an object at least to provide a novel dummy block for an extrusion press. 
     SUMMARY 
     In one aspect, there is provided a dummy block for a metal extrusion press comprising: a base having a first surface; an expandable collar seated against the base; a moveable plunger coupled to the base and accommodated by the collar, the plunger having a second surface configured to abut against the first surface of the base; and an outer connecting ring coupling the collar to the base, the connecting ring comprising at least one feature engaging the base and a plurality of fingers engaging the collar. 
     In one embodiment, each finger is received by a corresponding recess of the collar. 
     The at least one feature may be an inwardly extending circumferential rib. The circumferential rib may be received by a groove on an outer surface of the base. 
     The plunger may comprise a convex face configured to abut against a billet during use. 
     The base may comprise a recess configured to receive a portion of a stud. The stud may comprise an internal conduit that is configured to convey fluid into the recess for cooling the dummy block. 
     The connecting ring may comprise a cut extending therethrough. 
     The dummy block may be used in a metal extrusion press for carrying out metal extrusion. 
     There is also provided an extrusion press comprising the dummy block. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described more fully with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic perspective view of a metal extrusion press; 
         FIG. 2  is a perspective view of a dummy block forming part of the metal extrusion press of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of the dummy block of  FIG. 2 ; 
         FIG. 4  is a side sectional view of the dummy block of  FIG. 2 , taken along the indicated section line; and 
         FIG. 5  is an enlarged fragmentary view of the dummy block of  FIG. 4  identified by reference numeral  5 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a simplified illustration of an extrusion press for use in metal extrusion. The extrusion press comprises a container  20  having an outer mantle  22  that surrounds an inner tubular liner  24 . The container  20  serves as a temperature controlled enclosure for a billet  26  during extrusion of the billet. An extrusion ram  28  is positioned adjacent one end of the container  20 . The distal end of the extrusion ram  28  has a dummy block  30  coupled thereto, which is configured to abut the billet  26  for advancing the billet through the container  20 . An extrusion die  32  is positioned adjacent a die end  34  of the container  20 . 
     During operation, once the billet  26  is heated to a desired extrusion temperature (typically 800-900° F. for aluminum), it is delivered to the extrusion press. The extrusion ram  28  with the dummy block  30  coupled thereto are then advanced, so as to push the billet  26  through the container  20  and towards the extrusion die  32 . Under the pressure exerted by the advancing extrusion ram  28  and dummy block  30 , the billet  26  is extruded through the profile provided in the extrusion die  32  until all or most of the billet material is pushed out of the container  20 , resulting in the extruded product  36 . 
     The dummy block  30  may be better seen in  FIGS. 2 to 5 . Dummy block  30  comprises a dummy block base  40 , a replaceable collar  42  seated against the dummy block base  40  and coupled thereto by an outer connecting ring  44 , and a moveable plunger  46  positioned forward of the dummy block base  40  and within the collar  42 . The moveable plunger  46  is configured to move rearwardly when the dummy block  30  abuts a billet  26  during use, which in turn causes the collar  42  to expand. 
     The dummy block base  40  comprises a generally cylindrical body having a planar forward surface  48 . The dummy block base  40  also comprises a center bore  50  extending from the planar forward surface  48  to a central recess  52 . The dummy block base  40  has a plurality of threads  54  formed on an interior surface defining the central recess  52 , and which are configured to engage complimentary outer threads  56  formed on an exterior surface of a stem  58  of a stud  60  or other elongate projection. The stud  60  or other elongate projection is mounted on a forward end of the extrusion ram  28 , and comprises an internal conduit  62  that is configured to convey cooling fluid from a cooling fluid source into the central recess  52 . In this embodiment, the cooling fluid is air. The stem  58  has a central recess  64  for accommodating a spring  66  that is configured to provide a biasing force urging the moveable plunger  46  away from the from the planar forward surface  48  of the dummy block base  40 . The dummy block base  40  also has a circumferential groove  68  formed on an outer surface thereof for engaging the outer connecting ring  44 . 
     The replaceable collar  42  comprises a generally annular body having a first conical inner surface  70 , and a second conical inner surface  72  adjacent the first conical inner surface  70 . The first and second conical inner surfaces  70  and  72  are inclined relative to the center axis  74  of the dummy block  30 , such that the first conical inner surface  70  and the second conical inner surface  72  each define a first angle and a second angle, respectively, with the center axis  74 . The collar  42  has a plurality of recesses  76  formed on an outer surface thereof for engaging the connecting ring  44 . In this embodiment, the collar  42  has five (5) recesses  76 . 
     The plunger  46  has a convex forward face  78  that is configured to abut the billet  26 . The plunger  46  also has a first conical outer surface  80  adjacent the convex face  78 , and a second conical outer surface  82  adjacent the first conical outer surface  80 . The first and second conical outer surfaces  80  and  82  are inclined relative to the center axis  74  of the dummy block  30 , such that the first conical outer surface  80  and the second conical outer surface  82  each define a third angle and a fourth angle, respectively, with the center axis  74 . The plunger also has a planar rear surface  84  that is configured to abut against the forward surface  48  of the dummy block base  40 . Extending rearwardly from the rear surface  84  is a post  86  that is shaped to extend through the center bore  50  and into the central recess  52  of the dummy block base  40 . A connector  88  is fastened to a distal end of the post  86  within the central recess  52  for coupling the moveable plunger  46  to the dummy block base  40 , and for providing a surface against which the spring  66  abuts. As shown in  FIG. 5 , the plunger  46  is shaped such that the planar rear surface  84  and the planar forward surface  48  are spaced by a distance “d” when the moveable plunger  46  is not pressed against the dummy block base  40 . 
     The third angle defined by first conical outer surface  80  and the center axis  74  is slightly greater than the first angle defined by the first conical inner surface  70  and the center axis  74 , so as to ensure that the plunger  46  and the collar  42  do not become jammed during use. In the embodiment shown, the difference between the third angle and the first angle is about 1.5 degrees. As will be understood, if the angle of inclination of the first conical outer surface  80  were the same as, or less than, the angle of inclination of the first conical inner surface  70 , these surfaces would jam as the plunger moves rearwardly into the collar  42  such that when the dummy block is removed from the container, the spring  66  would not have sufficient force to return the plunger  46  to its initial position. 
     The connecting ring  44  has a generally annular shape, and has a cut  92  therethrough for allowing the connecting ring  44  to be expanded during assembly and disassembly of the dummy block  30 , and for allowing the connecting ring  44  to expand as needed during use. The connecting ring  44  comprises an inwardly extending rib  94  that is configured to engage the circumferential groove  68  of the dummy block base  40 . The connecting ring  44  also comprises a plurality of inwardly extending fingers  98 , with each finger  98  being shaped to engage a respective recess  76  on the outer surface of the collar  42 . In this embodiment, the connecting ring  44  comprises five (5) inwardly extending fingers  98 . 
     During use, the extrusion ram  28  with the assembled dummy block  30  mounted thereon is advanced through a container  20  to force the billet  26  through the extrusion die  32 . A forward force is applied by the extrusion ram  28  to the billet  26  via the dummy block  30 . In return, an opposing force is applied by the billet  26  to the dummy block  30 , which causes the plunger  46  to move rearward toward the dummy block base  40 . During this rearward motion, the plunger  46  applies pressure against the first conical inner surface  70  and the second conical inner surface  72  of the collar  42 , causing the collar  42  to expand outwardly to accommodate the plunger  46 . The connecting ring  44  in turn expands circumferentially from the axial cut  92  to accommodate the expanding collar  42 . The plunger  46  continues to move rearwardly toward the dummy block base  40  and to expand the collar  42  until the planar rear surface  84  of the plunger  46  abuts against the planar forward surface  48  of the dummy block base  40 . With the dummy block base  40  and plunger  46  abutting in this manner, the force applied by the extrusion ram  28  can be transferred directly through the core of the dummy block  30  to the billet. At the end of the stroke, the extrusion ram  28  with the dummy block  30  mounted thereon is returned to its starting position in the container  20  to receive the next billet. With the opposing force previously applied by the billet  26  now removed, the spring  66  pushes the plunger  46  forward to its initial position, which in turn causes both the collar  42  and the connecting ring  44  to contract to their original sizes. 
     As will be appreciated, the configuration of the dummy block  30 , and in particular the coupling of the dummy block base  40  and the collar  42  by the connecting ring  44 , eliminates the need for bulky features that would otherwise be needed for a conventional bayonet-style connection. As a result, the contact area between the dummy block base  40  and the plunger  46  (sometimes referred to as “pad area”) is advantageously increased, which allows a greater amount of the force applied by the extrusion ram  28  to be transferred through the core of the dummy block  30  to the billet  26 , as compared to conventional dummy blocks having bayonet-style connections. 
     Additionally, and as will be appreciated, the “crown”-shaped configuration of the fingers  98  of the connecting ring  44  advantageously provide a greater cross-sectional area between the connecting ring  44  and the plunger  46 , which in turn increases the column strength of the dummy block  30  and allows the dummy block  30  to withstand greater force applied by the extrusion ram  28  during operation without deforming, as compared to conventional dummy blocks. 
     Further, and as will be appreciated, the “crown”-shaped configuration of the fingers  98  of the connecting ring  44  advantageously allow the feature(s) engaging the collar  42  to have increased thickness in the axial direction for increasing the axial strength of the connecting ring  44 , while allowing the connecting ring  44  to remain flexible in the circumferential direction for assembly and disassembly of the dummy block  30 . 
     These features advantageously enable the dummy block  30  to be operated at higher extrusion pressures than conventional dummy blocks. 
     Although in the embodiment described above, the connecting ring  44  has five (5) fingers and the collar  42  has five (5) corresponding recesses, the number of fingers and corresponding recesses are not limited to five (5) and, in other embodiments, fewer or more fingers and corresponding recesses may alternatively be used while providing increased column strength of the dummy block and while allowing the connecting ring to remain flexible for assembly and disassembly of the dummy block. 
     Although embodiments have been described above with reference to the accompanying drawings, those of skill in the art will appreciate that variations and modifications may be made without departing from the scope thereof as defined by the appended claims.