Abstract:
An extrusion apparatus which satisfactorily adjusts differences in skin-body flow rates at multiple locations around the die, and allows for the external manipulation of the interior components controlling batch flow, during the production without having to stop manufacturing operations to effect the necessary changes thereat.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the extrusion of honeycomb bodies from plastic batches, and more particularly to an honeycomb extrusion apparatus having an improved control system for batch flowing into an skin-forming region of the die. 
     In an extruder, the batch flow path in the peripheral areas of the die, where the skin of the honeycomb structure is formed, is more complicated and more difficult to control than in the main field of extrusion, where the body of the honeycomb structure is formed. Batch flow control in the peripheral area of the die is important because skin defects (i.e., air checks, cell distortion/deformation, blisters, and the like) can later result in product failure. 
     U.S. Pat. No. 4,710,123 (Ziebig et al.) discloses an apparatus with adjustable means on the outlet side of the die for regulating the flow of the batch in the skin region, and bringing it in conformity with the flow rate of the batch in the main body region. The apparatus can also include a device (i.e., breaker plate) positioned at the inlet side of the die for further batch flow control. 
     U.S. Pat. App. Pub. 2003/0001308 (Shibagaki et al.) discloses an apparatus for controlling the batch in the skin region, the apparatus having an adjusting instrument with a flexible part which can be lowered into the skin region to regulate the flow rate. 
     Although these references address the problem of correlating flow between the skin and body regions, they provide no solution to the observed problem that flow rate differences in the material batch between the skin and body regions vary with die location. A disadvantage of the previous apparatuses is the allowance of only uniform correction of skin-body flow rate difference around the die. Under such circumstances skin-body flow rate differences may be insufficiently corrected at some locations around the die. 
     Therefore there exists a need for an extrusion apparatus which can satisfactorily adjust differences in skin-body flow rates at multiple locations around the die. Furthermore, there also exists a need for an extrusion apparatus which allows for the external manipulation of the interior components controlling batch flow, during the production without having to stop manufacturing operations to effect the necessary changes thereat. 
     SUMMARY OF THE INVENTION 
     In its simplest form, the present invention provides an extrusion apparatus which successfully balances the batch flow at the skin-body regions at multiple locations around the die, to form a honeycomb structure that is free of defects and meets customer standards. 
     The apparatus includes a die having an inlet face comprising peripheral feed holes and central feed holes, and an outlet face comprising interconnected discharge slots forming peripheral and central pins. A cavity is formed in a plurality of peripheral pins at the outlet face and is used for forming an outer skin on the honeycomb body. 
     A skin-forming assembly is positioned in the extrusion apparatus downstream from the die and adjacent the cavity at the outlet face, and includes a segmented flow controller and a mask, both supported on a holder. The flow controller and the mask are independent in movement. The segments of the flow controller are movable in an axial direction to batch flow. 
     A peripheral feed flow device is positioned upstream from the die, and adjacent the inlet face of the die. The peripheral feed flow device comprises a plurality, preferably six to twelve, of segments movable in a radial direction to batch flow. The extrusion apparatus also optionally includes, an extrudate bow corrector adjacent the peripheral feed flow device. 
     Adjustment means external to the extrusion apparatus are provided for controlling the operation of the skin-forming assembly, the peripheral feed flow device, and the extrudate bow corrector (if included), without interruption to the operation of the extrusion apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be further understood by reference to the following drawings, wherein: 
         FIG. 1  is a sectional view of one aspect of the present invention showing a die and an adjustable skin-forming assembly; 
         FIG. 2  is a top view of a peripheral feed hole controller; 
         FIG. 3  is a cross-sectional view of the peripheral feed hole controller of  FIG. 2  along line A—A; and, 
         FIG. 4  is a sectional view of another aspect of the present invention showing a die, a peripheral feed hole and an extrudate bow corrector. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1  therein presented is one aspect of the present invention, wherein a honeycomb extrusion apparatus  10  includes a die  12 , and a skin-forming assembly  14 . The die  12  is composed of peripheral feed holes  16  and central feed holes  18  communicating at one end with an inlet face  20 , and at the other end with a plurality of interconnected peripheral discharge slots  22  and central discharge slots  24 , forming peripheral pins  26  and central pins  28  at an outlet face  30 . A section of the peripheral pins  26  are machined or cut-down to form a cavity  32  having a tapered surface  34 . Cavity  32  at outlet face  30 , is the skin-forming region of die  12 . Beginning with central discharge slots  24  is the body-forming region of die  12 . 
     The skin-forming assembly  14  is positioned downstream or adjacent outlet face  30  of the die  12 , and includes a flow controller  36  and a mask  38 . The flow controller  36  is comprised of a plurality of segments  42 , preferably six to twelve, movably mounted to holding plate  40 . The key role of the flow controller  36  is to meter batch flow out of peripheral discharge slots  22  into cavity  32 . Segments  42  can be adjusted to completely cover discharge slots  22 , and interrupt flow of the batch material into cavity  32 . Accordingly, an advantage of the segmented flow controller  36  is versatility in the amount and location of batch flow in the skin region. 
     Mask  38  is attached peripherally to support  44 , and is movable relative to the batch flow. The key role of mask  38  is to form a gap  48  with tapered surface  34  of cavity  32  for determining the skin thickness. The mask  38  is therefore used to control the width of gap  48 . Again though, control of batch flow in cavity  32  is performed with flow controller  36 . Batch flow varies to different degrees depending on location around the die. The number of segments  42  provided on flow controller  36  is dependent on the size of the die, and the shape/size of the honeycomb product being formed. 
     A feature of the skin-forming assembly  14  is external control adjustment. Specifically, by “external control” is meant that skin-forming assembly  14  can be adjusted from outside the extrusion apparatus to desired settings during the manufacturing operations without interruption of production. Adjustment means are shown at  46   a–b  in the form of bolts. Specifically, bolt  46   a  regulates the movement of segments  42  on flow controller  36 , and bolt  46   b  regulates the movement of the mask  38 . Thus adjustment means  46   a–b  are rotated to cause movement and obtain the desired setting of the flow controller  36  and mask  38 . This rotation is accomplished with a suitable wrench, or possibly by pneumatic or hydraulic means (not shown). Flow controller  36  and mask  38  are movable independent of each other. 
     In another aspect of the present invention there is provided a peripheral feed flow device  50  as shown in  FIGS. 2  (top view) and  3  (cross-sectional view). Peripheral feed flow device  50  is composed of segments  52 , preferably six to twelve, movably mounted on a ring  54 . Segments  52  can be adjusted radially to the flow direction of the material batch by rotation of bolts  56 . 
     The peripheral feed flow device  50  is positioned upstream or adjacent inlet face  20  of the die  12 , as shown in  FIG. 4 , and acts to regulate the batch flow into the peripheral feed holes  16 . Segments  52  can be adjusted to control flow of the batch in one or more of peripheral feed holes  16 , and at one or more locations around die  12 . Consequently, batch flowing into the cavity  32  is also further controlled by peripheral feed flow device  50 . The skin-forming assembly  14  ( FIG. 1 ) and the peripheral feed flow device  50  act in combination to control the batch in the skin region of die  12 . 
     In another aspect, the inventive honeycomb extrusion apparatus optionally includes an extrudate bow corrector  60  ( FIG. 4 ). Such devices for correcting bow in a stream of extruded material are well known in the art, and suitable examples are provided in co-pending U.S. patent application having Ser. No. 09/967,110 now U.S. Pat. No. 6,663,378, issued Dec. 16, 2003, entitled “Apparatus and Method of Correcting Bow in a Honeycomb Extrudate” by Lubberts et al., and co-pending U.S. patent application having Ser. No. 10/370,840 and Publication 2004-0164464, published Aug. 26, 2004, entitled “Device and Method of Correcting Extrudate Bow” by Lubberts et al., both of which are herein incorporated by reference in their entirety. 
     The extrudate bow corrector  60  is positioned upstream of the die  12 , adjacent the peripheral feel flow device  50 , and includes a base  62  having an aperture (not shown) sufficiently large for the batch material to pass therethrough. A plurality of adjustable plates  64  movably mounted to the base are provided, each adjustable plate capable of being moved independently of the others at bolt  68 , such that when the adjustable plates are adjusted to varying positions a correction is simultaneously effected in the direction and magnitude of a bow in a honeycomb extrudate. A cover  66  is also provided on the bow corrector  60 , the cover being equal in size and shape to the base. The cover  66  acts to shield the adjustable plates, and is securely mounted to the base. It mirrors the base in size and shape, and includes an aperture (not shown) of equal or greater diameter to the base aperture. 
     As with the skin-forming assembly  14 , both the peripheral feed flow device  50  and the bow corrector device  60  are adjustable externally to the extrusion apparatus. Again, a suitable wrench or pneumatic or hydraulic means may be used to control the movement of bolts (adjustment means)  56  and  68 , and obtain the desired settings for peripheral feed flow device  50  and bow corrector  60 , respectively. 
     In operation, the batch flowing towards the die first encounters the bow corrector device positioned to correct any degree of bow in the batch. Next, the exterior of the batch encounters the peripheral feed flow device which acts to control the flow of the batch into the peripheral feed holes of the die. At the exit of the peripheral flow device the batch enters the die, where it is extruded. The peripheral area of the batch encounters the skin-forming assembly which controls both the amount of batch coming out of the peripheral discharge slots, and the skin thickness. Control of the various components of the extrusion apparatus is made externally thereto. The resulting extruded structure, exiting the outlet end of the die, is a honeycomb having an integral outer skin is formed thereon. 
     Advantages of the extrusion apparatus in accordance with the present invention include: (1) customizable batch flow control; (2) more precise adjustment of differences in skin-body flow rates at multiple locations around the die; (3) external manipulation of the interior components controlling batch flow; (4) better control of the batch in skin forming area; (5) more precise adjustment of batch flow in the skin-forming area at multiple locations; (6) reduction in preferential flow of dies; (7) reduction in skin defects; (8) reduction in hardware costs; (9) reduction in hardware downtime; (10) increased product output. 
     Although the now preferred embodiments of the invention have been disclosed it will be apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as set forth in the appended claims.