Abstract:
A feedblock for supplying a multi-layer stream of polymeric material to an extrusion die is provided wherein the dimension of at least some of the layers of the multi-layer stream can be precisely adjusted and/or controlled. The feedblock includes a primary flow path which is used to create a first layer and two secondary flow paths which are used to create a set of second and third layers. The secondary flow paths are positioned relative to the primary flow path such that the second and third layers are deposited on opposing sides of the primary layer in a sandwich-like configuration. Each of the secondary flow paths include a contoured slot through which a secondary fluid stream of polymeric material is deposited onto a primary stream of polymeric fluid flowing in the primary flow path. The contoured slot is geometrically shaped such that adjusting the position of the contoured slot alters the shape of the secondary fluid stream as it is deposited onto the primary flow path. A set of heaters disposed within the feedblock are positioned on either side of the combined primary and secondary flow paths adjacent to the exit port of the feedblock and are used to heat the secondary streams thereby altering the flow characteristics of the streams which, in turn, causes a corresponding change in the dimensions and profiles of the secondary fluid streams.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a feedblock for an extrusion die, and more particularly to a feedblock for creating a multi-layer polymeric sheet wherein the dimensions of at least some of the layers are adjustable. 
     BACKGROUND ART 
     Extrusion processes generally involve forcing a viscous material through a die typically comprising an inlet, a cavity, and an exit. In many instances, the end-product of the extrusion process is a sheet comprising a single layer of polymeric material. In other instances, however, it is desirable to produce a sheet of formable material having a plurality of distinct layers that comprise different materials having different properties. By using different materials having different properties to create each layer, the resulting multi-layer sheet has the combined properties of all of the layers. For example, it may desirable to create a food wrap bars oxygen so that food stored therein remains fresh. However, materials that act as oxygen barriers are typically structurally weak. Thus, it may be desirable to create a food wrap that acts as an oxygen barrier and that is structurally strong by combining a layer made from a material having the. characteristics of an oxygen barrier with a layer made from a material that is known for its structural integrity and strength. 
     Methods known in the art for creating multi-layer sheets typically involve combining a plurality of polymeric streams wherein each stream comprises a different material and wherein each stream forms a distinct layer of the sheet. More advanced methods for creating multi-layer sheets additionally include ways to control and adjust the dimensions of the co-extruded layers of a multi-layer sheet. Controlling and adjusting the dimensions of the co-extruded layers is useful for a variety of reasons including, for example, to further affect the properties of the resulting multi-layer sheet. More specifically, depending upon the materials used to form the layers, the thickness of the layers may affect the surface finish of the resulting multi-layer sheet causing it to be either clear or opaque. In addition, it is necessary to ensure that the dimensions of the various layers are consistent throughout the sheet to ensure that the properties of the resulting multi-layer sheet are uniform throughout the sheet. Also, it is necessary that the layer widths be equal and precisely positioned so that uniformity is maintained at the edges of the sheet. In addition, dimension control can also be used to control fabrication costs. As an example, a base material may be coated with a layer of resin that shields the base material from UV rays. The protective resin layer must be at least of a minimum thickness in order to achieve adequate UV protection. However, UV protective resins are costly, and therefore it is desirable to use only as much as needed to obtain the required level of UV protection. Accordingly, precise dimensional control over layer thickness is required so that costs are minimized. 
     Murakami U.S. Pat. No. 4,669,965 discloses a multi-layer extrusion die having an integrate that resides within a cavity of the die body and that comprises a set of flat plates disposed on top of one another. To produce a multi-layer sheet, a stream of resin is supplied to a flow inlet disposed in each plate and the stream thereafter flows into a downstream portion of the plate having a wide and flat geometry. As the resin stream enters the downstream portion of the plate it conforms to the wide and flat geometry of the downstream portion thereby causing individual layer-like streams to form in each plate. The layer-like streams then enter into a flow-combining zone where the streams are deposited one on top of the other. The dimensions of the layers, such as the width or thickness of the various layers, are dictated by the geometry of the plates and the flow passages of the die. To create a set of layers having a desired width or thickness, a set of suitably sized plates must be fabricated and inserted into the integrate which is then inserted into the die body. However, to create a new set of layers having a different set of dimensions, a different, properly sized set of plates must be fabricated for insertion into the integrate. 
     Similarly, Blemberg U.S. Pat. No. 5,236,642 discloses an apparatus comprising an encapsulator, a feedblock and a die wherein two melt streams are combined in the encapsulator to produce an encapsulated layer element that is thereafter supplied to the feedblock  62  via an elongate transport pipe. Within the feedblock  62 , the encapsulated layer element is combined with yet another stream and the resulting layered stream thereafter flows into a main channel disposed within the die body. The main channel converges with two auxiliary flow channels that are also disposed within the die body such that the materials flowing in the two auxiliary flow channels combine with the layered stream of the main channel to form a multi-layer sheet. Like Murakami, Blemberg et al. also teaches that the dimensions of the individual layers are a function of the geometry of the flow passages within the feedblock or die. More particularly, Blemberg et al. reduces the variations in the thickness of a layer by passing the layered stream that exits the encapsulator through the elongate transport pipe. According to Blemberg et al., passing the stream through the elongate transport pipe tends to automatically correct any asymmetry, non-concentricity or other non-uniformity which may exist in the combined melt stream as it leaves the encapsulator, thereby resulting in a more uniform melt stream thickness. In addition, Blemberg et al. teaches that the thickness of a set of two layers can be adjusted by altering the flow rates of the two streams that form the individual layers. 
     However, methods that rely upon the geometry of fixed flow channels in a feedblock or die to produce a sheet with layers having a desired set of dimensions are of limited value because the dimensions of the streams, and thus, the layers, cannot be adjusted without changing the geometry of the flow channels. This, in turn, requires the design and fabrication of a different feedblock or die. In addition, methods that rely upon the relative flow rates of the streams to adjust the dimensions of the layers require that new flow rates be established for each stream in order to achieve the new set of desired dimensions. 
     SUMMARY OF THE INVENTION 
     Other advantages of the invention will be apparent to those skilled in the art from the following detailed description taken in conjunction with the drawings and the appended claims. 
     In accordance with one aspect of the present invention, a feedblock includes a first passage defining a first flow path and a second passage defining a second flow path in fluid communication with the first flow path. In addition, a rotatable member having a passage therethrough forms at least a part of the second flow path and terminates at a convergence zone at which the second flow path meets the first flow path. Rotation of the rotatable member changes a size of the convergence zone. 
     Preferably, the rotatable member comprises a hollow spool. Also preferably, the convergence zone is defined by an opening in the rotatable member. Further, the opening in the rotatable member may be contoured or rectangular. 
     Still further in accordance with the preferred embodiment, the feedblock includes an adjustment apparatus coupled to the rotatable member. Also, the adjustment apparatus may include an adjustment lever coupled to the rotatable member and an adjustment screw threaded into a bore carried by the adjustment lever. In addition, the adjustment apparatus may further include indicating apparatus coupled to the rotatable member and operable to indicate a position of the rotatable member. 
     Also, according to the preferred embodiment, the feedblock may additionally include an adapter coupled to the second flow path by which a formable material is supplied to the second flow path. 
     Preferably, the feedblock further includes a third flow passage defining a third flow path that is also in fluid communication with the first flow path and a second rotatable member having a passage therethrough. The passage of the second rotatable member forms at least a part of the third flow path and terminates at a second convergence zone at which the third flow path meets the first flow path. Rotation of the second rotatable member changes a size of the second convergence zone. 
     In addition, to the foregoing, the feedblock may further include a set of heaters disposed within a body of the feedblock and disposed parallel to a portion of the first flow path that is located downstream of the convergence zone. The set of heaters may be controllable to control a viscosity of a formable material flowing through the portion of the first flow path that is located downstream of the convergence zone. 
     In a further embodiment of the present invention, a feedblock may include a primary passage defining a primary flow path, and a plurality of secondary passages, each defining one of a plurality of secondary flow paths that are in fluid communication with the primary flow path. The feedblock may further include a plurality of rotatable members, each rotatable member having a channel therethrough that forms at least a part of one of the secondary flow paths and each of the channels terminating at one of a plurality of convergence zones, wherein each convergence zone is defined by a region in which one of the secondary flow paths meets the primary flow path and wherein rotation of each of the rotatable members changes a size of a corresponding one of the convergence zones. 
    
    
     Other aspects and advantages of the present invention will become apparent upon consideration of the following drawings and detailed description. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 comprises an isometric view of a feedblock according to the present invention wherein the feedblock is positioned to reveal a first side at which an inlet port is disposed, a second side at which a dividing adapter is disposed, and a top of the feedblock; 
     FIG. 2 comprises a cross-sectional view of the feedblock with the dividing adapter and an adjustment assembly removed, wherein the view is taken generally along the lines  2 — 2  of FIG. 1; 
     FIG. 3 comprises an isometric view of a multi-layer sheet created using the feedblock of FIG. 1; 
     FIG. 4 comprises an enlarged isometric view of the dividing adapter of FIG. 1; 
     FIG. 5A comprises a rotated and exploded view of the dividing adapter of FIG. 4; 
     FIG. 5B comprises a side elevational view of a lower portion of the dividing adapter of FIG. 5A; 
     FIG. 5C comprises a side elevational view of a guideblock of the dividing adapter of FIG. 5A; 
     FIG. 5D comprises a cross-sectional view of the guideblock of FIG. 5C taken generally along the lines  5 D— 5 D of FIG. 5C; 
     FIG. 6A comprises an isometric view of the dividing adapter of FIG. 4 rotated to reveal a side of the dividing adapter that is secured to the feedblock of FIG. 1; 
     FIG. 6B comprises a side elevational view of the upper portion of the dividing adapter; 
     FIG. 7A comprises an isometric view of one of the spools utilized in the feedblock of FIG. 1 which is positioned to reveal a shaft that extends from a first axial end of the spool, 
     FIG. 7B comprises an isometric view of the spool of FIG. 7A positioned to reveal a second axial end opposite the first axial end of the spool, 
     FIG. 8 comprises an isometric view of the feedblock of FIG. 1 with a portion of an upper body of the feedblock removed to reveal the spool of FIGS. 7A and 7B wherein the feedblock is positioned to reveal a third side at which an outlet port is disposed and a fourth side at which an adjustment assembly is disposed; 
     FIG. 9 comprises an isometric view of the spool of FIG. 7A rotated to reveal a contoured outlet slot disposed on an outer surface of the spool; 
     FIG. 10A comprises an isometric view of the feedblock of FIG. 1 positioned to reveal an adjustment assembly disposed on the fourth side of the feedblock; 
     FIG. 10B comprises a side elevational view of the spool retainer by which a first end of the spool is rotatably supported wherein the spool retainer is positioned to reveal a surface of the spool retainer that abuts against the feedblock and the spool; 
     FIG. 10C comprises a cross-sectional view taken generally along the lines  10 C— 10 C of FIG. 10B; 
     FIG. 10D comprises a side elevational view of an adjustment screw retainer and a screw guide for enabling rotation of the adjustment lever wherein the adjustment screw retainer is positioned such that the side of the adjustment screw retainer that is disposed adjacent to the side of the feedblock is revealed; 
     FIG. 11 comprises a side elevational view of an adjustment lever of the adjustment assembly; 
     FIG. 12 comprises a side elevational view of the feedblock wherein the feedblock is positioned to show the second side at which the dividing adapter is disposed and further wherein a set of covers are removed from the side of the feedblock to reveal a set of channels and bores disposed therein; and 
     FIG. 13 comprises a side elevational view of the spool  148  to illustrate the positioning of a set of bolts used to secure two halves of the spool together and to further illustrate a set of seal relief areas. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIGS. 1 and 2, a feedblock  10  includes an upper body  14  and a lower body  16 . The upper body  14  and lower body  16  are bolted together by a plurality of threaded bolts  18  that are disposed in aligned, cylindrically shaped bores  20 ,  22  in the upper body  14  and the lower body  16 , respectively. The cylindrically shaped bores  22  disposed in the lower body are threaded to engage and fasten the threaded bolts  18 . To facilitate alignment between the upper body  14  and the lower body  16 , a dowel pin  24  extends through and projects out of a bore  26  disposed in the lower body  16  and extends into a bore  28  disposed in the upper body  14 . A threaded jack bolt  30  is fastened into a threaded bore  32  and is positioned such that an end  34  of the jack bolt  30  abuts against the bottom of the dowel pin  24 . To separate the upper body  14  from the lower body  16 , the jack bolt  30  is rotated causing the jack bolt  30  to extend farther into the threaded bore  32  and causing the jack bolt  30  to apply a force against the bottom of the dowel pin  24 . The force applied to the bottom of the dowel pin  24 , in turn, causes the dowel pin  24  to press against the upper body  14  thereby causing the upper body  14  to separate from the lower body  16 . A through hole  36  extends through the upper body  14  and is disposed such that a rod (not shown) placed into the through hole  36  can be forced against the top of the dowel pin  24 , thereby allowing the dowel pin  24  to be pushed out of the bore  28  in the event that it becomes lodged in the upper body  14 . The ability to separate the upper body  14  from the lower  16  facilitates cleaning of the interior cavities (described hereinafter) of the feedblock  10 . 
     The upper body  14  and lower body  16  include channels  38 ,  40 , respectively, which, when the upper and lower bodies  14  and  16  are assembled together, together form a primary flow path  42  that extends longitudinally through the feedblock  10  from an inlet port  44  disposed on a side  46  of the feedblock  10  to an outlet port  48  (see FIG. 2) disposed on an opposing side  50  of the feedblock  10 . A set of bores  51 , which may be threaded, enables the attachment of an upstream adaptor (not shown) to the side  46  of the feedblock  10  through which a formable material, such as a heated thermoplastic polymer material, may be supplied to the inlet port  44 . Likewise, a set of bores  53  (see also FIG.  10 A), which may also be threaded, enables the attachment of a downstream adaptor (not shown) to the side  50  of the feedblock  10  to which the formable material flowing from the outlet port  48  may be supplied. 
     Referring also to FIG. 3, the formable material supplied to the inlet port  44  flows through the primary flow path  42  and forms a first layer  52  of a multi-layer flow of material  54 . Preferably, (although not necessarily) the multi-layer flow of material  54  includes three layers wherein the first layer  52  is sandwiched between a second layer  56  and a third layer  58 . The dimensions of the layers  52 ,  56  and  58  are referred to hereinafter as the width and height of-the layers  52 ,  56  and  58  and are denoted in FIG. 3 with the letters “w” and “h,” respectively. 
     Referring now to FIGS. 1 and 4, to facilitate the formation of the second and the third layers  56  and  58  (see FIG.  3 ), two secondary flow paths  60 ,  62  (indicated with directional arrows in FIG. 4) are provided, both of which originate at a dividing adapter  64 . Only portions of the secondary flow paths  60 ,  62  are shown in FIG.  4  and the remaining portions of the flow path  60  are shown in FIGS. 7A,  7 B,  8  and  9  and described with reference thereto. The dividing adapter  64  includes an upper portion  66  and a lower portion  68  that are both secured to a side  69  of the feedblock  10  with a set of eight bolts  70  (only four of which are shown in FIG. 1) that extend through bores  141  into further bores  75  (see FIG. 12) in the feedblock  10 . The dividing adapter  64  includes a circular inlet port  72  which, during operation, is coupled to an extruder (not shown) that is mounted to the dividing adapter  64  via the bores  73 . The inlet port  72  is in fluid communication with a main passage  74  which is, in turn, in fluid communication with a set of channels  76  and  78 , respectively, that are disposed in the upper and lower portions  66 ,  68  of the dividing adapter  64 . The secondary flow path  60  begins at the inlet port  72 , then flows into the main passage  74  and into the channel  76 , whereas the secondary flow path  62  begins at the inlet port  72 , then flows into the main passage  74  and into the channel  78 . 
     To control the flow of material from the main passage  74  into the channels  76  and  78 , first and second valve assemblies  80 ,  82  are secured to the upper-and lower portions  66 ,  68 , respectively, of the dividing adapter  64 . Referring also to FIGS. 5A and 5B, the upper and lower portions  66 ,  68  are fastened to one another by a set of threaded bolts  84  that extend through a set of bores  86  disposed in the lower portion  68  and further are threaded into a set of aligned, threaded bores  88  disposed in the upper portion  66 . Each of the upper and lower portions  66 ,  68  includes a semi-circular opening  87 ,  89 , respectively, that is positioned such that when the upper and lower portions  66 ,  68  are aligned with and fastened to one another, the semi-circular openings  87  and  89  together form the circular inlet port  72  (see FIG.  1 ). A groove  147  is disposed in the throat of the semi-circular opening  89  and is dimensioned to accept a soft aluminum wire  91  (FIG. 5B) that, when disposed in the groove  147 , prevents fluid leakage from occurring at the junction where the semi-circular openings  87  and  89  meet. 
     The valve assemblies  80 ,  82  include a valve guideblock  90 ,  92 , respectively, and a retainer  94 ,  96 , respectively. The valve guideblocks  90 ,  92  are secured to the retainers  94 ,  96  and to the upper and lower portions  66 ,  68 , respectively, with a set of bolts  98 ,  100 , respectively. The bolts  98 ,  100  extend through sets of bores  102 ,  104  in the retainers  94 ,  96 , respectively, a set of aligned bores  106 ,  108  in the guideblocks  90 ,  92 , respectively, and into a set of aligned threaded bores  110 ,  112  in the upper and lower portions  66 ,  68 , respectively. Each guideblock  90 ,  92  abuts a planar face  114 ,  116  of the upper and lower portions  66 ,  68 , respectively, and each of the upper and lower portions  66 ,  68  includes a shouldered circular opening  118 ,  120  that leads to the main passage  74  (see FIG.  4 ). Each of the shouldered openings  118 ,  120  aligns with a circular opening  122 ,  124  disposed in the guideblocks  90 ,  92 , respectively. A circular o-ring  126  is disposed between the circular openings  118  and  122  to prevent leakage between the guideblock  90  and the upper portion  66 . Similarly, a circular o-ring  128  is disposed between-the circular openings  120 ,  124  to prevent leakage between the guideblock  92  and the lower portion  68 . The o-rings  126 ,  128  may be replaced by any other suitable sealing apparatus, if desired. 
     Each of the circular openings  122 ,  124  in the guideblocks  90 ,  92  provides access to a channel  125 ,  127  that extends through each of the guideblocks  90 ,  92 , respectively. The openings  122 ,  124  further align with the openings  118  and  120  such that the channels  125  and  127  are also aligned with the main passage  74  of the dividing adapter  64 . Tapered valve stems  130 ,  132  are disposed in the channels  125 ,  127 , respectively, and extend into the main passage  74  of the dividing adapter  64 . Each of the tapered valve stems  130 ,  132  threadably engages a nut  134 ,  136 , respectively, that is captured axially by the retainer  94 ,  96 , respectively, so that rotation of the nut  134 ,  136  causes the valve stem  130 ,  132 , respectively, to extend into or retract out of the main passage  74 . Referring again to FIG. 4, the valve stems  130 ,  132  may be extended to cover an opening  138  located between the main passage  74  and the channel  76  and an opening  140  located between the main passage  74  and the channel  78 , respectively. Thus, the valve assemblies  80 ,  82  control the passage of material from an extruder (not shown) coupled to the inlet port  72  into the channels  76  and  78 . 
     The channels  125 ,  127  are preferably identical and hence only the-channel  127  is shown and described in detail. The channels  125 ,  127  are dimensioned and configured both to enable passage of the tapered valve stems  130 ,  132 , respectively, therethrough, and to prevent the fluid flowing through the main passage  74  from leaking into the guideblocks  90 ,  92 . More particularly, and referring also to FIGS. 5C and 5D, a first portion  129  of the channel  127  is substantially square in cross-section and extends to a point  133  located near the opening  124 . Between the point  133  and the opening  124 , a second portion  249  of the channel  127  is circularly shaped in cross-section and dimensioned such that the tapered valve stem  130  fits snugly therein to prevent leakage of fluid from the main passage  74  into the guideblocks  90 ,  92 . Of course, if differently shaped valve stems are utilized then the openings  118 ,  120 ,  122 ,  124  might alternatively be of a different cross-sectional configuration. 
     Each of the guideblocks  90 ,  92  includes a bore  91 ,  93 , respectively, that aligns with a bore  95 ,  97  disposed in the upper and lower portions  66 ,  68 , respectively. A dowel pin  99 ,  101  extends through each of the aligned bores  91 ,  95  and  93 ,  97 , respectively, to facilitate alignment between each of the guideblocks  90 ,  92  and the upper and lower portions  66 ,  68  respectively. Two set screws  103 ,  105  are disposed in threaded passages  107 ,  109 , respectively, in the guideblocks  90 ,  92 , respectively. To separate the guideblocks  90 ,  92  from the upper and lower portions  66 ,  68 , respectively, the set screws  103 ,  105  are threaded into the passages  107 ,  109 , respectively, causing the set screws  103 ,  105  to press against the planar faces  114 ,  116  of the upper and lower portions  66 ,  68 , respectively. The force applied by the set screws  103 ,  105  against the planar faces  114 ,  116 , respectively, causes the guideblocks  90 ,  92  to separate from the upper and lower portions  66 ,  68 , respectively. Likewise, to enable alignment of the upper portion  66  and the lower portion  68 , two bores are  113  disposed in the upper portion  66  and are aligned with two bores  115  (only one of which is visible in FIG. 5) disposed in the lower portion  68 . Two dowel pins  117  (only of which is visible in FIG. 5) are disposed in the aligned bores  113  and  115 . The bores  113  extend all of the way through the upper portion  66  and both terminate at an opening  119  in the planar face  114 . A pair of jackbolts  111  are inserted into the bores  113  and each abuts against one of the dowel pins  117  disposed in the aligned bores  113  and  115 . When the jackbolts  111  are threaded into the bores  113 , the jackbolts  111  apply forces against the dowel pins  117  to cause the upper portion  66  to separate from the lower portion  68  thereby to permit cleaning of the interior cavities of the dividing adapter  64 . In addition, a threaded tap hole (not shown) into which a screw may be inserted is disposed on a face  121  of each of the dowel pins  117 . In the event that the dowel pins  117  become lodged in the bores  115 , the screw may be partially screwed into the tap hole leaving a portion of the screw outside of the dowel pin so that it may be grasped, thereby to enable extraction of the dowel pins  117  from the bores  115 . 
     Referring now to FIGS. 6A and 6B, each of the upper and lower portions  66 ,  68  of the dividing adapter  64  is molded to include a flat, plate-like surface  142 ,  143 , respectively, at which the upper and lower portions  66 ,  68  of the dividing adapter.  64  are secured to the side  69  of the feedblock  10 . Each of the channels  76 ,  78  (see FIG. 4) terminates at an opening  144 ,  145 , respectively, in the sides  142 ,  143 . As described hereinbefore, the bolts  70  pass through a set of bores  141  in the sides  142 ,  143  that align with a set of bores  75  (see FIG. 12) disposed in the side  69  of the feedblock  10  to secure the upper and lower portions  66 ,  68  thereto. A set of soft brass crush rings  152  and  153  are secured in counter bores  157  and  159 , respectively, (FIG. 4) radially inside the openings  144 ,  145  by button head socket screws  161  and  163  and a set of metal o-rings  131 ,  135  (see FIG. 5A) are disposed in a set of grooves  137 ,  139 , respectively. The soft brass crush rings  152 ,  153  and the metal o-rings  131 ,  135  prevent fluid leakage between the upper and lower portions  66 ,  68 , respectively, of the dividing adapter  64  and the feedblock  10 . 
     As described hereinbefore, the secondary flow path  60  branches from the main passage  74  into the channel  76  whereas the secondary flow path  62  branches from the main passage  74  into the channel  78 . For clarity, and because the set of two secondary flow paths  60  and  62  are mirror images of one another, only the remainder of the secondary flow path  60  is described in detail. 
     Referring also to FIGS. 7A and 7B, the secondary flow path  60  extends through the opening  144  and into a channel  146  disposed within a spool  148 . The soft brass crush ring  152  is disposed such that it is partially disposed in the counter bore  157  (see FIG. 6A) and is partially disposed in a counter bore  150  located in an axial end  149  of the spool  148 . 
     Referring now to FIGS. 2,  7 A,  7 B and  8 , the spool  148  resides within a bore  154  having a substantially circular, cylindrical shape. A set of sealing rings  197 ,  199  (see FIGS. 7A,  7 B and  8 ) are disposed within a set of grooves  201 ,  203 , respectively, to prevent fluid from leaking out of the spool  148  into the chamber  154 . Preferably, although not necessarily, the bore  154  has an inner diameter slightly larger than the outer diameter of the spool  148  to allow rotation of the cylindrical spool  148 . The bore  154  and the primary flow path  42  are positioned relative to one another such that when the spool  148  is inserted into the bore  154 , a portion of the spool  148  extends into the primary flow path  42 . 
     Referring now to FIGS. 2,  7 A,  7 B,  8  and  9 , the channel  146  residing within the cylindrical spool  148  feeds into a contoured channel  156  that extends radially from the interior of the spool  148  to a contoured outlet slot  158  located on an exterior surface  160  of the spool  148 . The contoured outlet slot  158  is positioned on the surface  160  of the portion of the spool  148  that extends into the primary flow path  42  such that molten polymer exiting the contoured outlet slot  158  is deposited in a layer onto the fluidized polymer flowing in the primary flow path  42 . Thus, the secondary flow path  60  extends from the dividing adapter  64  to the channel  146 , the contoured channel  156  in the spool  148  and the outlet slot  158  and converges with the primary flow path  42  at a convergence zone  165  (see FIG. 2) adjacent to the outlet slot  158 . 
     Because of the geometry of the contoured outlet slot  158 , rotation of the spool  148  causes the geometry of the polymeric stream exiting the slot  158  to change shape, thereby enabling adjustment of the width and the height of the secondary polymeric stream as it is being deposited onto the polymeric stream flowing in the primary flow path  42 . Alternatively, the geometry of the outlet slot  158  may be rectangular, in which case only the height and not the width is changed when the spool  148  is rotated. 
     Referring still to FIGS. 7A,  7 B and also to FIG. 10A, an adjustment assembly  160  is provided that rotates the spool  148  thereby to adjust the height and/or width of the second layer  56 . The adjustment assembly  160  includes a spool retainer  162 , an elongate adjustment lever  164 , an adjustment pin  166 , a locking adjustment screw  168  and an adjustment screw retainer  170  upon which is disposed an adjustment screw guide  171 . Referring also to FIGS. 10B and 10C, the spool retainer  162  is secured to the side of the upper body  14  of the feedblock  10  by a set of four bolts  172  that extend through a set of four bores  260  disposed in the spool retainer  162  and that further extend into bores  261  (see FIG. 12) disposed in the side of the feedblock  10 . A set of bores  280  within which a set of dowel pins (not shown) may be disposed align with a set of holes (not shown) in the feedblock  10  to ensure proper placement of the spool retainer  162  when it is being secured to the feedblock  10 . A cylindrical shaft  174  disposed at an axial end  191  of the spool  148  is disposed in a circular bore  176  in the spool retainer  162  and extends through a bore  178  disposed in a first end  158  of the adjustment lever  164 . The shaft  174  extends axially from a stepped axial end  193  of the spool  148 . A circular outer surface  191  of the end  193  has a diameter slightly smaller than the diameter of a circular flange  195  that extends outwardly from the spool retainer  162 . Thus, when the circular, cylindrical shaft  174  extends through the bore  176  in the spool retainer, the annular end  193  of the spool  148  abuts against the spool retainer  162  in a manner such that there is a small annular area of space between the outer surface  191  and the flange  195 . A flexible graphite packing material, such as, for example, the flexible graphite packing made by Palmetto®, may be used to fill this area thereby to create a seal between the stepped axial end  193  of the spool  148  and the flange  195  and, thus, between the spool  148  and the spool retainer  162 . A set of threaded bores  262  may also be provided on both of the axial ends  191 ,  149  of the spool  148  to facilitate removal of the spool  148  from the feedblock  10  for cleaning and/or servicing. 
     Referring still to FIG.  10 A and also to FIGS. 9,  10 D and  11 , the shaft  174  includes a slot  182  that aligns with a slot  184  disposed in the adjustment lever  164 . A key  186  is sized to fit snugly into the aligned slots  182  and  184  such that the shaft  174  is keyed for rotation with the adjustment lever  164 . The adjustment lever  164  is disposed in a generally horizontal position and has a further bore  188  disposed in a second end  190  thereof The adjustment pin  166  includes a first end  192  retained in the further bore  188  and a second end  194  having a threaded hole  196  therethrough. A first end  167  of the adjustment screw  168  is threaded through the hole  196  and a second end  169  of the adjustment screw is threaded through a round nut  175  disposed in a circular recess  269  in a channel  177  in the adjustment screw retainer  170  wherein the screw retainer  170  is secured to the feedblock  10  by a set of screws  173 . The round nut  175  is captured in the circular recess  269  between the face of the feedblock  10  against which the adjustment screw retainer  170  is disposed and a circular opening  270  disposed on the opposing surface of the adjustment screw retainer  170 . Of course, the diameters of both the circular recess  269  and the round nut  175  are larger than the diameter of the circular opening  270  to prevent the round nut from slipping out of the adjustment screw retainer  170  A set of dowel pins  263  that extend through a set of bores  264  in the adjustment screw retainer  170  and that extend into a set of further bores (not shown) disposed in the side of the feedblock  10  are used to ensure that the adjustment screw retainer  170  is disposed on the feedblock  10  at the proper location The adjustment screw guide  171  is secured to the adjustment screw retainer  170  by a plurality of screws  179  that extend into channels  181  that are aligned with threaded bores  183  disposed in the adjustment screw retainer  170  A hole  185  disposed in the adjustment screw guide  171  permits access to the adjustment screw  168  so that the adjustment screw  168  may be rotated by any suitable tool (such as a wrench which may engage a shaped head of the screw  168 ). As described hereinbefore, the adjustment screw  168  is threaded into the round nut  175  and is further threaded into the adjustment pin  194 . Moreover, the adjustment screw  168  includes two separate sets of threads (not shown), each having a different size pitch, wherein the first set of threads is disposed at the portion of the adjustment screw  168  that is threaded into the round nut  175  and the second set of threads is disposed at the portion of the adjustment screw  168  that is threaded into the adjustment pin  194 . The set of threads that engage the round nut  175  are larger in pitch than the set of threads that engage the adjustment pin  194  and the ratio of the pitch sizes of the two different thread sets is selected so that rotating the screw  168  causes the adjustment pin  194  to travel a desired distance either up or down (depending on the direction that the screw  168  is turned). This vertical movement of the adjustment pin  194 , in turn, causes the adjustment lever  164  to rotate thereby also causing the shaft  174  and the spool  148  to rotate. To prevent the adjustment pin  194  from falling off of the adjustment screw  168  due to rotation of the adjustment screw  168 , the set of threads on the adjustment screw  168  that engage the adjustment pin  194  are placed a sufficient distance from the bottom of the adjustment screw  168  and are further configured to prevent rotation of the adjustment screw  168  beyond a point at which the spool  148  is rotated to a position wherein the outlet slot  158  is fully disposed in the convergence zone  165 , i.e., wherein the outlet slot  158  is fully open. 
     The round nut  175  is disposed in the recess  269  of the channel  177  such that the nut  175  is able to rotate which, in turn, permits lateral movement of the adjustment screw  168  and the pin  194 . The lateral movement is required to accommodate the rotation of the adjustment lever  164 . The first end  167  of the adjustment screw  168  is smaller in diameter than the second end  169  of the adjustment screw  168  which lengthens the lateral distance that the adjustment screw  168  may move thereby further accommodating the rotation of the adjustment lever  164 . The adjustment screw guide  171  further includes a set of markings  187  that are spaced in a manner such that the markings  187 , in conjunction with a flange  189  disposed on the screw  168 , indicate the position of the spool  148  as it rotates. More particularly, rotation of the adjustment screw  168  causes the flange  189  to move a corresponding distance either up or down. The distance moved by the flange  189  may be measured with the markings  187  and, because the amount of rotation experienced by the spool  148  corresponds to the distance moved by the flange  189 , the distance may be used to determine the rotational position of the spool  148 . 
     The adjustment lever  164  may be rotated to a vertical position as shown in FIG. 11 thereby to prevent the flow of material from the secondary channel  60  onto the flow of material through the primary flow path  42 . This function is facilitated by a spring-loaded plunger  198  that has threads (not shown) disposed on the exterior surface of the plunger  198  and that has a spring (not shown) residing within the plunger  198 . The spring-loaded plunger  198  is threaded into a bore  200  that extends through the adjustment lever  164 . A pin  202  forms an interference fit in a groove  204  in the end of the spring-loaded plunger  198 . To move the adjustment lever  164  into the vertical position, the adjustment lever  164  is disengaged from the screw  168  by removing the screw  168  from the hole  196  and the adjustment pin  166  is removed from the hole  188  disposed in the adjustment lever  164 . After disengaging the adjustment lever  164  from the screw  168  and removing the adjustment pin  166  from the adjustment lever  164 , the pin  202  is pulled away from the feedblock thereby causing an end (not shown) of the spring loaded plunger  198  to become disengaged from a groove  267  (see FIG. 10B) in the spool retainer  162  which, in turn, allows the adjustment lever  164  to be rotated into the vertical position. To maintain the adjustment lever  164  in this vertical position, the pin  202  is released, thereby causing the end (not shown) of the spring-loaded plunger  198  to extend into a hole  206  (see FIG. 10A) in the spool retainer  162 . Note that, while the pin  202  is engaged in the groove  267 , any movement of the adjustment lever  164  is restricted to the distance that the pin  202  can travel in the groove  267 . Thus, the groove  267  is sized to permit the adjustment lever  164  to move a distance that is sufficient to allow the spool  148  to rotate a distance that is, in turn, large enough to enable the proper positioning of the contoured outlet slot  158  in the convergence zone  165 . 
     As described hereinbefore, the secondary flow path  60  is a mirror image of the secondary flow path  62 . Thus, a spool  214  (see FIG. 2) disposed in the lower body  16  is positioned below the primary flow path  42  thereby allowing the third layer  58  (see FIG. 3) of fluidized polymer to be deposited in a sandwich-like manner onto the first layer  52  flowing in the primary flow path  42  (see FIG.  3 ). An adjustment assembly  216  (see FIG. 10A) identical to the adjustment assembly  160  is secured to the lower body  16  for adjustment of the spool  214  (see FIG. 2) disposed in the lower body  16 . 
     Referring again to FIG. 2, one or more heaters  218  are disposed in a like number of recesses  220  in the upper and lower bodies  14 ,  16  of the feedblock  10 . The heaters  218  are supplied electric power and develop heat which is transferred through the feedblock  10  to the polymer in the primary flow path  42 . As will be understood by one having ordinary skill in the art, to promote thermal transfer, the feedblock  10  may be fabricated from any thermally conductive material, such as, for example, stainless steel. 
     Referring still to FIG. 2, a plurality of thermocouples  226  are inserted into cavities  228  disposed at various locations in the feedblock  10  to measure and control the temperature of the feedblock  10 . As will be understood by one of ordinary skill in the art, the thermocouples  226  and the respective cavities  228  may be disposed at any of a number of locations within the feedblock  10 . 
     To enable fine tuning of the height of the second and third layers  56 ,  58  a first set of further heater elements  222  is disposed in the upper body  14  of the feedblock  10  parallel to the primary flow path  42  and a second set of further heater elements  224  is disposed in the lower body  16  of the feedblock  10  parallel to the primary flow path  42 . The electric power supplied to the pluralities of heaters  222 ,  224  is controlled to control, in turn, the viscosities of the second and third layers  56 ,  58 . The viscosities of the second and third layers  56 ,  58  affect the profiles of the second and third layers  56 ,  58  as such layers exit the feedblock  10  together with the first layer  52 . For example, the viscosity of the second and third layers  56 ,  58  can be controlled using the heaters  222 ,  224  to eliminate any undesired variations or patterns appearing in the surface profiles of these layers  56 ,  58 . To further facilitate control of the viscosity of the second and third layers  56  and  58 , the heater elements  222  and  224  are equipped with built-in thermocouples (not shown). Thus, profile control is afforded in a simple and inexpensive manner. 
     Referring now to FIGS. 1 and 2 and  12 , electrical wires (not shown) associated with each of the electric components such as, for example, the heaters  218 ,  222 ,  224  and the thermocouples  226 , are disposed in a like number of recesses  250 ,  252 ,  253 ,  254 ,  255 ,  256  in the feedblock  10  and a plurality of covers  230  (see FIG. 1) that shield the electrical wires are secured to the sides of the feedblock  10  with a plurality of bolts  257  (see FIGS. 1,  2  and  10 A) secured in a plurality of bores  258 . An additional set of recesses  259  dimensioned to fit extra thermocouples (not shown) are also provided in the event that further temperature monitoring is required. In addition, a case  232  for holding the wires of the electric components is secured to the upper body  14  by a set of screws  266  (see FIG. 1) and a further wire case  233  is secured to the lower body  16 . The recesses  250 ,  253 ,  254  and  252 ,  255 ,  256  provide a pathway by which the electrical wires (not shown) are supplied to the cases  232  and  233 , respectively, thereby providing a single routing point at which power may be supplied to the electric components disposed in each of the upper and lower bodies  14 ,  16 . A set of lifting lugs  234  may be fastened to the wire case  232  with a set of screws  167  (see FIG. 1) to facilitate lifting the entire feedblock  10 , thereby enhancing the portability of the feedblock  10 . 
     The partitioning of the feedblock  10  into a mirror set of upper and lower bodies  14 ,  16  allows for easy cleaning of the interior chambers of the feedblock  10  and the feedblock flow paths  42 ,  60 ,  62 . To further facilitate cleaning of the feedblock  10 , the dividing adapter  64  is comprised of the upper portion  66  and the lower portion  68  as described hereinbefore. Referring again to FIG. 2, and also to FIG. 13, the spools  148 ,  214  are also comprised of two halves that are separable at a partitioning line  236 ,  238  and that are bolted together by a set of bolts  240 ,  242 . A set of jackbolts  244 ,  246  that abut against a set of dowel pins  245 ,  247  is also provided to separate the halves of the spools  148 ,  214 . Note that three of the bolts  240  are omitted from the view of the feedblock  10  presented in FIG.  2 . Further, the spool halves, which are generally solid and not hollow abut against one another at a set of surfaces  265  (see FIG.  2 ). Portions of the surfaces  265  of the one of the spool halves are recessed from the remaining surface of the spool half thereby to form seal relief areas  248 . The seal relief areas  248  lessen the likelihood of fluid leakage between the two halves of the spool  148  by reducing the amount of Surface area of the two spool halves that are in contact. In addition, to facilitate machining of the feedblock  10  and to enable lifting of the feedblock during manufacture, set of tabs  265  (see FIGS. 2 and 10A) are provided in the feedblock  10  by which a lifting device (not shown) may be secured to the feedblock  10  or by which the feedblock  10  may be secured in a given position during manufacture. 
     As described, the feedblock  10  of FIG. 1 may be used to create a three-layer sheet  54  wherein the upper and lower layers  56 ,  58  comprise a first material and wherein the layer  52  disposed therebetween comprises a second material. However, the feedblock  10  may alternatively be configured to produce any one of a number of different coextrusion flow permutations of one, two or three different materials A, B, C. For example, the feedblock  10 , instead of having the dividing adapter  64  wherein a single material is branched to provide two separate layers, may include an adapter (not shown) which has only a single flow path thereby to produce a two layer sheet comprising materials A and B. Alternatively, the feedblock  10  may instead be configured to include a set of two adapters each having a single flow path therein thereby to produce a three-layer sheet comprising materials A, B and C. In addition, the feedblock  10  is not limited to two spools and two secondary flow paths but may instead may be configured to include any number of spools and, thus, any number of secondary flow paths. For example, the upper and lower bodies  14 ,  16  may each include two or more spools configured to deposit layers upon the primary flow path. Thus, the feedblock  10  may include as many spools as are necessary to produce a desired number of layers. 
     Referring now to FIG. 12, for symmetry, the set of bores  261  by which the spool retainer  162  is attached to the side of the feedblock  10  and the set of bores  75  by which the dividing adapter  64  is attached to the feedblock  10  are disposed on both sides of the feedblock  10  thereby to support attachment of the dividing adapter  64  and the adjustment assembly  160  to either side of the feedblock  10 . Of course, both sets of bores  75  and  261  need not be disposed on both sides of the feedblock  10  if such versatility is not required or desired. 
     The foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications within the scope of the invention will be apparent to those skilled in the art.