Abstract:
A polymer molding system and method of operation produces synthetic article of manufacture that simulate natural building materials such as wooden shakes and stone roofing tiles. The system preferably feeds at least two dye compounds and a polymer filler material into an extruder for heating into a ribbon. The ribbon is heated as it travels through the extruder and through an outlet end where a slicing unit cuts the ribbon into a plurality of preforms at a pre-defined rate. Because the dye compounds are not homogeneously mixed with one another, the ribbon and hence the preforms are generally of at least two colors. Each preform is individually fed into a press that stamps and partially cools the preform into the simulated article of manufacture shape that also accentuates the varying colors. Preferably, the stamped article is then flexed or cupped between a carriage and a dead weight prior to crystallization and where it then cools and crystallizes to a final shape. This cupped shape of the article of manufacture is generally straightened out under stress when the article is installed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     The instant application claims priority to U.S. Provisional Patent Application Ser. No. 60/747,578, filed May 18, 2006, the entire specification of which is expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to a polymer molding system and more particularly to a plastic extruding and stamping system for producing a synthetic article of manufacture that simulates building products made of naturally occurring materials.  
       BACKGROUND OF THE INVENTION  
       [0003]     Natural slate and cedar have long been common roofing materials because of their ability to protect the underlying structure from the weather while appearing aesthetically pleasing. Unfortunately, slate or any stone is relatively heavy and expensive to manufacture and install. Due to the weight of stone, special preparations must also be done to support the additional weight when compared to conventional construction. Yet further, stone or slate is known to be brittle and therefore cannot withstand appreciable amounts of weight when lying upon the roof. Maintenance of slate roofs or replacement of broken tiles or shingles is therefore known to be cumbersome and expensive. In regards to the use of wood or cedar as shingles, such material is not naturally resistant to fire and like stone, is time consuming and expensive to install.  
         [0004]     As an alternative material, shingles made generally of plastic and manufactured in an attempt to resemble stone or wood are known in the industry. Two such shingles are taught in U.S. Pat. No. 6,025,052, issued Jul. 15, 2000 and U.S. Pat. No. 4,307,552, issued Dec. 29, 1981, both being incorporated herein by reference in their entirety. Unfortunately, known simulated shingles are uniform in color (i.e. dark grey) and a single shingle does not very in color as the naturally occurring stone or wood would, thus it&#39;s authenticity from a casual observer is placed in question. Moreover, known molds of a press are machined in an attempt give the finished product the dimensional appearance of slate or cedar. Unfortunately, this appearance is still very different than the detail of the naturally occurring material.  
         [0005]     The manufacturing process of these simulated natural occurring shingles or any other similar articles of manufacture utilizing plastic as the material, typically delivers a pellet form of the plastic to an extruder that then heats the plastic into a pliable form. Prescribed quantities of the heated plastic is placed in a press for shaping of the shingle in a planar form. Unfortunately, the finished, planar, product is relatively stiff and any inconsistencies or variances in the roof underlayment can lead to a shingle that does not lye flat to the roof (i.e. the exposed leading edge of the shingle is spaced from the underlying shingle). Yet further, some plastic tiles may warp under the harsh exposure and heat from lying upon a roof. This exposure could cause the leading edge of the tile to warp and lift away from the underlying tile causing an unwanted “ruffled-feather” appearance.  
         [0006]     Moreover, known presses typically have hydraulic rams that push down from above, thus moving an upper platen carrying the first half of a mold against a stationary lower platen carrying the second half of the mold. Should the hydraulic ram fail, it is plausible that the press fails in a compressed position in part due to gravitational forces making repairs more difficult and leading to safety concerns.  
       SUMMARY OF THE INVENTION  
       [0007]     A polymer molding system and method of operation produces synthetic article of manufacture that simulate natural building materials such as wooden shakes and stone roofing tiles. The system preferably feeds at least two dye compounds and a polymer filling material into an extruder for heating into a ribbon. The ribbon is heated as it travels through the extruder and through an outlet end where a slicing unit cuts the ribbon into a plurality of preforms at a predefined rate. Because the dye compounds are not homogeneously mixed with one another, the ribbon and hence the preforms are generally of at least two distinct colors. Each preform is individually fed into a press that stamps and partially cools the preform into the simulated article of manufacture shape that also accentuates the varying colors. Preferably, the stamped article is then flexed or cupped between a carriage and a dead weight prior to crystallization and where it then cools and crystallizes to a final shape. This cupped shape of the article of manufacture is generally straightened out under stress when the article is installed.  
         [0008]     Preferably, the article of manufacture is a roofing tile that resembles in color, shape and texture a stone tile such as slate. The press has a stationary first platen and a moving second platen that preferably moves vertically from a lower open position and upward to a pressed or closed position. Both platens preferably carry cooling channels for partially cooling the article of manufacture. A mold of the press has a first half portion carried by the first platen and a second half portion carried by the second platen. The second half portion is preferable cast from a building material (e.g. slate tile) to enhance authenticity and appearance.  
         [0009]     Objects, features and advantages of this invention include a system that produces economical, light weight and easy to install articles of manufacture that closely simulate natural building materials such as stone roofing tiles and wooden shakes. Other advantages include a process that produces an improved synthetic roofing tile that resists warpage as a result of exposure to harsh environmental conditions and a system that enhances safety, is robust, relatively simple in design and durable. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0011]      FIG. 1  is a schematic of a polymer molding system of the present invention;  
         [0012]      FIG. 2  is a perspective end view of an extruder of the polymer molding system;  
         [0013]      FIG. 3  is a perspective view of a press in an open position of the polymer molding system;  
         [0014]      FIG. 4  is a perspective view of the press in a closed position;  
         [0015]      FIG. 5 a  perspective view of a carriage of the polymer molding system;  
         [0016]      FIG. 6  is a top view of an article of manufacture produced by the polymer molding system;  
         [0017]      FIG. 7  is a side view of the article of manufacture; and  
         [0018]      FIG. 8  is a cross section of the article of manufacture taken from line  8 - 8  of  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]     Referring to  FIGS. 1 and 6 , a polymer molding system  20  and method for the continuous extrusion and stamping of a polymeric material, of the present invention, produces a generally synthetic article of manufacture  21 . The article of manufacture  21  is preferably a roofing shingle or tile made of a polymer such as plastic and designed to simulate natural stone both in color variations, shape and texture. This simulated stone is preferably slate that is commonly used for roofing tile. Another natural building material commonly used on roofs and exterior walls are wooden or cedar shakes which may also be generally copied via the system  20  and as the article of manufacture  21  of the present invention.  
         [0020]     The system  20  preferably has a first or main hopper  22  that feeds pellets of a polymeric, filler, material into an inlet end  30  of a stationary extruder  24  at a prescribed rate. Preferably, the inlet end  30  is a gravity fed receiving chute that receives the pellets from above. Also fed into the chute  30  of the extruder  24  at a prescribed rate and/or periodic frequency is at least one dye compound. As illustrated, the system  20  preferably has a first dye hopper  26  and a second dye hopper  28  that feeds selected dye compounds into the receiving chute  30  of the extruder  24  preferably located below. Because the dye compounds are generally not mixed homogenously with one-another, the resulting article of manufacture  21  displays a novel plurality of distinctive colors.  
         [0021]     The compounded polymeric material and dye compounds flowing controllably through the extruder  24  are heated to generally melt the raw pellets, or filler, and form a ribbon  32  of polymeric material having a desired cross sectional shape. The elongated ribbon  32  is substantially linear and horizontal. Discrete lengths of extruded material are cut from the continuously formed ribbon  32  by a slicing unit  34  and as the heated ribbon  32  exits an outlet end  35  of the extruder  24  (see  FIGS. 1 and 2 ). Each cut length of the ribbon  32  forms a preform  36  having a prescribed volume and density preferably for the formation of the article of manufacture or roofing tile  21 . See U.S. Pat. No. 5,266,246, issued Nov. 30, 1993 and incorporated herein by reference in it&#39;s entirety.  
         [0022]     The system  20 , has at least one and preferably a plurality of presses  38  that operate preferably asynchronously to one another for manufacturing efficiency. Each press  38  is preferably manually fed a preform  36  by an operator  40  and while the preform  36  is still in a heated and pliable state. One skilled in the art, however, would now know that feeding of the preforms  36  could also be done by an automated transport.  
         [0023]     Referring to  FIGS. 1 and 3 - 4 , the press  38  has a stationary upper platen  42  and a substantially vertically movable bottom platen  44 . Each platen  42 ,  44  carries a respective half portion  46 ,  48  of a mold  50 . At least one of the two half portions  46 ,  48  of the mold  50  is cast (as opposed to machined) to substantially form the shape and texture of the naturally occurring material (i.e. slate shingle/tile or cedar shake) being simulated. The bottom platen  44  connects to a hydraulic ram unit  52  that moves the bottom platen  44  and mold half portion  48  upward toward the half portion  46  of the mold  50 .  
         [0024]     Both platens  42 ,  44  of the press  38  carry cooling fluid channels  53  that preferably flow chilled water controlled via a cooling control unit  54 . By cooling the platens  42 ,  44 , the platens, in turn, partially and controllably cool the preform  36  and/or article of manufacture  21  during the hydraulic press procedure. Preferably, projecting downward from each corner of the upper platen  42  is a cylindrical guide  56  that extends through holes in the bottom platen  44 . Located generally in the holes and concentrically about each guide  56  is a ball bearing carrying sleeve  60  that reduces frictional forces placed upon the ram unit  52 .  
         [0025]     In operation of the system  20 , a controller  70  controls the volumetric rate of filler material and dye compounds exiting the hoppers  22 ,  26 ,  28  preferably at least in-part through electric screw delivery units  72  of the hoppers (see  FIG. 1 ). In this way, the controller  70  controls the color distribution of the final product and matches the resultant volumetric flow with the processing rate of the extruder  24  (i.e. heat up rate and ribbon travel rate). Preferably, knowing the ribbon  32  travel rate, the controller also controls the reciprocating action of the slicing unit  34 .  
         [0026]     When cut, the operator  40  places the heated preform  36  on top of the half portion  48  of the mold  50  while the press  38  is in an open position  73  (see  FIGS. 2-3 ). The operator  40  then selects an actuator or button  74  to begin the press process. Preferably, while the first press  38  is hydraulically moving upward toward the compressed position  75  (see  FIG. 4 ), the operator grabs a second preform  36  from the extruder  24  and is placing it into a second press  38 , thus the first and second presses  38  operate asynchronously.  
         [0027]     Preferably, the controller  70  controls the temperature of the exiting ribbon  32  to about 400 degrees Fahrenheit and/or preferably within a range of 390 to 410 degrees Fahrenheit. This temperature is generally dependent upon the composition of the filler material of the ribbon  36  and is generally that temperature required to maintain pliability of the preform  36  for the pressing process, while still having a rigid enough consistency to be handled by the operator  40  when moved from an extruder tray  76  to the press  38 .  
         [0028]     The controller  70  also controls the temperature of the platens  42 ,  44  and thus the preformed article of manufacture or tile  21  through the control unit  54 . The preferred exiting temperature of the tile  21  is about 180 degrees Fahrenheit and/or preferably within the range of  160  to 200 degrees Fahrenheit. This temperature is also dependent upon the material. Ideally, the temperature is not so high that the tile deforms upon handling, but is high enough that the tile  21  has yet to crystallize and thus can still be altered in shape while cooling by the external exertion of a force or dead weight  66 .  
         [0029]     For the sake of illustration and example, if the article of manufacture  21  is a simulated/synthetic roofing tile, after exiting the press  38  the partially cooled tile  21  is substantially planar. Prior to full cooling of the tile  21  and thus crystallization of the polymeric material, the tile  21  is cupped or slightly bent utilizing a carriage  62 . The partially cooled tile  21  is stacked in the carriage  62  with other tiles preferably upon a concave bottom  64  of the carriage (see  FIGS. 1 and 5 ). With a plurality of cooling tiles  21  stacked in the carriage  62  the dead weight  66  having a convex bottom face  67  is placed on top of the stacked tiles  21 . Because the convex bottom face  67  substantially conforms in shape to the concave bottom  64  each tile  21  crystallizes as they cool with a substantially consistent radius of curvature.  
         [0030]     Once cooled to room temperature, the curved tile is relatively stiff. When installing on a roof, the cup of the tile  21  is placed face down. This cupping effect alleviates any inconsistencies or variances in the roof underlayment that could otherwise lead to an unwanted finished appearance where the tiles do not lie flat. Moreover, because polymeric tiles may warp (i.e. leading tile edges lifting up and away from the underlying tile) under the harsh exposure and heat from lying upon a roof, the cupped tiles  21  are preferably under stress when installed. This stress counters any affects that could otherwise lead to unsightly warpage by producing a force upon the underlying tile by the leading edge of the overlying tile.  
         [0031]     Referring to  FIGS. 6-8  and more specific to the tile  21 , the tile is preferably made of polypropylene type WPP221-Natural Co-Polymer 2.0-6.0 Melt, 1.0-2.5 Izod. The compound type is preferably PPC1FR&amp;-Natural 0.25-3.5 Melt Flow, Filler Content 47.0-53.0. Color may vary depending upon the final product demands. Each tile  21  has longitudinal first and second edges  80 ,  82  that a are substantially parallel to one another, a lower edge  84  and an upper edge  86 . The tile  21  has a top surface  88  and an opposite bottom surface  90 .  
         [0032]     In one example of a slate simulated tile  21 , the tile is about eighteen inches long and eleven and a half inches wide, or in other words, the longitudinal first and second edges  80 ,  82  are about eighteen inches long and the lower edge  84  is about eleven and a half inches wide. The top and bottom surfaces  88 ,  90  taper toward one-another as they extend from the lower edge  84  to the upper edge  86 . Preferably, the lower edge  84  is about one-quarter inches wide or thick and the upper edge  86  is about one-eighth inches wide or thick. When the tile  21  is fully cooled and prior to installation on the roof, the top surface  88  carries a convex contour as it spans between the edges  84 ,  86 . Similarly, the bottom surface  90  has a concave contour as it spans between the edges  84 ,  86 . For a typical roof application where the tile  21  is approximately eighteen inches long, the contour forms a camber (designated by arrow  92 ) of about 1.25 inches and/or within a range of 1.00 to 1.50 inches. Alternatively, the ratio between the camber  92  and the length of the tile  21  is about six to eight percent.  
         [0033]     The top surface  88  has a reveal portion  94  that extends between side edges  80 ,  82  and spans from the lower edge  84  to about thirty-five to fifty percent the length of the tile  21  (e.g. for a tile that is eighteen inches long, the reveal portion generally extends about 7.5 inches from the lower edge  84 ). The top surface  88  also has a covered portion  96  that spans the remainder of the top surface  88 , from the reveal portion  94  generally to the upper edge  86 .  
         [0034]     Preferably, the top surface  88  is formed by the bottom half portion  48  of the mold  50 . Because the half portion  48  is cast, the reveal portion  94  of the top surface  88  can closely simulate the surface roughness and/or texture of authentic slate. This texture includes chamfered edges common in natural slate. The mold  50  may also create other features in the covered portion  96  including two fastener or nail indentations or pads  98  each having a plurality of grooves  100  that generally decrease the thickness of the tile  21  at the indentations  98  for improving the tile installation process. The covered portion  96  may also carry a plurality of indexing recesses  102  and indexing spacers  104  at each side edge  80 ,  82  for appropriate spacing of the tiles from one another when installed on a roof.  
         [0035]     Preferably, the concave bottom surface  90  of the tile  21  has a plurality of ribs  106  that promote strength of the tile  21  while reducing the volume of material required to form the tile  21 . The ribs  106  preferably extend longitudinally between the lower and upper edges  84 ,  86 .  
         [0036]     When the tile is installed, the nails projecting through the nailing pads  98  of the tile  21  generally flatten the tiles out upon the roof so that the camber range is substantially reduced to zero while the resiliency of the crystallized tile caused the revealed edge  84  to generally exert a downward force upon the underlying tile due to the resiliency of the overlying tile. This biasing force counters any tendency of a tile or shingle from warming upward because of harsh weather environment.  
         [0037]     Although the preferred embodiment of the present invention has been disclosed, various changes and modifications may be made thereto by one skilled in the art without departing from the scope and spirit of the invention as set forth in the appended claims. It is also understood that the terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the scope and spirit of the invention.