Abstract:
There is disclosed a reinforced extruded composite structural member and a method of forming the same. The structural may member comprise a solidified composite mixture of a fibrous material and a resin, and a reinforcing member embedded therein. The reinforcing member may have a known tensile strength, and at least one physical characteristic adapted to promote bonding of the reinforcing member with the surrounding fibrous material.

Description:
[0001]     This application claims the benefit of U.S. Provisional Application No. 60/474,518 filed on May 30, 2003, the contents of which are incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to reinforced composite structural members and methods of making the same.  
       BACKGROUND OF THE INVENTION  
       [0003]     Structural members such as beams and joists made from composite materials are known. The composite material may be made, for example, from a mixture of (1) a natural fiber and (2) a resin. The natural fiber may be wood fiber, or another type of natural fibrous material, available in various processed forms such as flakes, strands, particles and chips. As used in this specification, the term “resin” refers to a polymer having an indefinite and high molecular weight, and a characteristic softening or melting range, exhibiting a tendency to flow when heated and subjected to stress. A composite mixture of wood fibers and resins is often referred to as “composite wood”. Examples of composite wood materials are described in U.S. Pat. No. 3,888,810 to Shinomura, the contents of which are hereby incorporated by reference.  
         [0004]     Structural members, such as joists, beams and sections of decking or walkways, can be formed from composite wood materials by extrusion and pultrusion techniques. Examples of some techniques that can be employed are disclosed in U.S. Pat. No. 5,783,125 to Bastone et al., U.S. Pat. No. 5,096,406 to Brooks et al., U.S. Pat. No. 5,096,645 to Fink and U.S. Pat. No. 5,234,652 to Woodhams et al., the contents of all of which are hereby incorporated by reference.  
         [0005]     There has, however, been a desire to improve the strength and performance characteristics of composite structural members, particularly for structural members such as beams and joists as referenced in U.S. Pat. No. 6,015,611 to Deaner et al., the contents of which is also hereby incorporated by reference.  
         [0006]     Certain techniques for strengthening and reinforcing extruded structures are known, as described for example in U.S. Pat. No. 5,792,529 to May, and U.S. Pat. No. 3,993,726 to Moyer. However, the application of these techniques to composite materials made from natural fiber and resin may not be straightforward. For example, in comparison to pure thermoplastic and synthetic materials, the viscosity of a composite wood mixture prior to extrusion may be relatively high due to the presence of natural fibers, and therefore the composite wood mixture may not easily flow around and bond to a reinforcing member. Also, a relatively high-viscosity composite wood mixture may tend to misalign a flexible reinforcing member, having a detrimental effect on the structural properties of the embedded reinforcing member.  
         [0007]     Therefore, there is a need for an improved method of forming a reinforced composite structural member, and in particular those composite structural members including natural fibers such as wood fibers.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention discloses a reinforced composite structural member having a continuous reinforcing member embedded therein. In an aspect of the invention, there is provided a reinforced composite structural member, comprising: 
        a solidified composite mixture of a fibrous material and a resin;     a reinforcing member embedded therein, said reinforcing member having at least one physical characteristic for promoting bonding of said reinforcing member with said mixture of a fibrous material and a resin.        
 
         [0011]     In an embodiment, the reinforced composite structural member may be formed by extrusion.  
         [0012]     In an embodiment, the physical characteristic comprises an increased bondable outer surface in comparison to a reinforcing member of a substantially similar shape and size having a substantially smooth outer surface.  
         [0013]     In an embodiment, the reinforcing member may comprise, for example, a strip. The strip may have a plurality of flow-through apertures provided along its length. The flow-through apertures may be adapted to allow the composite material to flow therein and solidify, thereby providing an increased bondable surface area and helping to secure the reinforcing member within the extruded composite structural member.  
         [0014]     In another embodiment, the reinforcing member may also comprise a braided cable or tow which provides a sufficiently coarse outer surface for facilitating secure bonding within the composite mixture. The coarse outer surface may provide an increased bondable surface area to secure the reinforcing member within the extruded composite structural member.  
         [0015]     The reinforcing member may be delivered in a flexible format, allowing a sufficiently long length of the reinforcing member to be supplied, for example, on a supply reel in order to make a continuous extrusion run possible.  
         [0016]     The outer surface of the reinforcing member may be heated just as the reinforcing member is introduced into the extrusion apparatus. Bonding between the reinforcing member and the composite mixture preferably occurs immediately adjacent the extrusion apparatus outlet.  
         [0017]     Suitably sized and shaped guide channels may be used to guide the reinforcing member and properly align the reinforcing member for embedding in the extruded composite structure.  
         [0018]     The reinforcing member may be treated with a suitable resin that is the same as, or compatible with, a suitable resin used in the composite mixture. Suitable resins may comprise, for example, low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene, PVC, or another polymeric material, such as those referred to in U.S. Pat. No. 5,783,125 to Bastone et al., the contents of which are also hereby incorporated by reference, or in U.S. Pat. No. 6,015,611 referred to above.  
         [0019]     Suitable resin bonding pairs for the reinforcing member and the composite mixture include, for example, LDPE and LDPE, HDPE and HDPE, polypropylene and polypropylene. Although bonding pairs may be chosen from the same type, this is not strictly necessary. Certain thermoplastic materials may bond to other such materials not of the same type.  
         [0020]     In another aspect of the invention, there is provided a method of forming a reinforced composite structural member, comprising: 
        (i) providing a composite mixture comprising a fibrous material and a resin;     (ii) providing a length of a reinforcing member having at least one physical characteristic for promoting bonding of said reinforcing member with said composite mixture;     (i) embedding said reinforcing member into said composite mixture prior to forming said composite structural member.        
 
         [0024]     These and other aspects of the invention will become apparent through the illustrative figures and accompanying description provided below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     In the figures which illustrate example embodiments of the present invention:  
         [0026]      FIG. 1  is a schematic block diagram of an exemplary processing line for processing a composite structural member.  
         [0027]      FIG. 2   a  is a detailed perspective view of an extrusion apparatus for practicing the method in accordance with an exemplary embodiment of the invention.  
         [0028]      FIG. 2   b  is the extrusion apparatus of  FIG. 2   a  showing an extruded segment of a reinforced composite structural member made in accordance with an exemplary embodiment of the invention.  
         [0029]      FIG. 2   c  is a cross-sectional view of the extrusion apparatus of  FIGS. 2   a  and  2   b  showing paths for introducing reinforcing members.  
         [0030]      FIG. 2   d  is a detail of a portion of the extrusion apparatus of  FIG. 2   c.    
         [0031]      FIG. 3   a  is a cross-sectional view of the reinforced composite structural member formed by the extrusion apparatus of  FIGS. 2   a  to  2   d.    
         [0032]      FIG. 3   b  is a cross-sectional view of another embodiment of a reinforced composite structural member which may be formed in a substantially similar extrusion apparatus. 
     
    
     DETAILED DESCRIPTION  
       [0033]     Referring to  FIG. 1 , a portion of a processing line  100  for making an extruded product is shown. In this illustrative example, the processing line  100  includes an extruder  110  having a mouth  112  for receiving raw materials. The raw materials may be provided, for example, in a pelletized or granular form suitable for storage and transportation. Machines located upstream from the extruder  110  which may form such pelletized or granular raw materials are not shown, but will be familiar to those skilled in the art. Such upstream machines possibly may be located at a completely different location, such as at a supplier&#39;s premises.  
         [0034]     Attached to an end of the extruder  110  is an extrusion apparatus  115 . An extrusion screw  210  (see  FIG. 2   c ) is provided within the extruder  110  to apply suitable pressure on a composite mixture  111  formed from the raw materials therein.  
         [0035]     The raw materials fed into mouth  112  may comprise, for example, any suitable combination of a resin (or resins) and natural fibers (e.g. wood fiber materials). In an embodiment, a suitable ratio for a mixture of HDPE to wood fiber material may be in the range of approximately 50:50 by weight, to 35:65 by weight.  
         [0036]     In operation, with the application of an appropriate amount of heat, pressure and agitation within the extruder  110 , a composite mixture  111  may be formed which has a suitable viscosity for extrusion through the extrusion apparatus  115 . For example, for the mixture of HDPE and wood fiber described above, a suitable pressure is preferably in the order of 2000 PSI+400 PSI, and a suitable melting temperature is preferably in the order of between 150°-190° C. Various other ranges of pressure and temperature may be used for different combinations of resins and natural fiber materials.  
         [0037]      FIG. 1  shows an extruded composite structural member  118  emerging from the extrusion apparatus  115 . The extruded composite structural member  118  may then undergo further processing. For example, the processing line  100  may further include a calibration/cooling machine  120  which receives the extruded composite structural member  118  from the extrusion apparatus  115 . The calibration/cooling machine  120  may be used, for example, to maintain the form of the extruded composite structural member  118  as the structural member  118  cools down and solidifies. Once cooled and solidified, the extruded composite structural member  118  may emerge from the calibration/cooling machine  120  and be pulled by a puller  122 . The puller  122  may be provided with belts  124 ,  126  mounted on rollers which grip the composite structural member  118  from opposite sides. The extruded composite structural member  118  may then emerge from the puller  122  and continue on to a finishing and cutting machine (not shown) further down the processing line  100 .  
         [0038]     Referring to  FIG. 2   a , shown is a perspective view of the extrusion apparatus  115  of  FIG. 1 . As shown, the extrusion apparatus  115  includes a first opening  132   a  for receiving, along a path A, a first reinforcing member  130   a  therein. Shown in a hidden view is a second opening  132   b  located on an opposite side of the extrusion apparatus  115 . The second opening  132   b  receives, along a path B, a second reinforcing member  130   b  therein. In the discussion below, the description of the opening  132   a  and reinforcing member  130   a  should be understood to apply equally to opening  132   b  and reinforcing member  130   b , in a corresponding manner.  
         [0039]     In an embodiment, the reinforcing member  130   a  may be in the form of a flexible strip or tape. The reinforcing member  130   a  may be provided with a plurality of flow-through apertures  133  along the length of the reinforcing member  130   a . In  FIG. 2 , the flow-through apertures  133  are exaggerated in size for the purposes of illustration. As will be explained in detail below, these flow-through apertures  133  are adapted to allow the composite mixture  111  to flow and to solidify therein. This will help to secure the reinforcing member  132   a  within the extruded composite structural member  118 . It will be understood that, generally, the plurality of flow-through apertures  133  increases the area of the bondable outer surface of the reinforcing member  130   a  (in comparison to a reinforcing member of a substantially similar shape and size not having said flow-through apertures  133 ). Also, the flow-through apertures  133  may provide a “peg-in-hole” anchoring effect, to secure the reinforcing member in the composite structural member a lengthwise direction.  
         [0040]     The flow-through apertures  133  may be provided at regular or random intervals, and in a variety of shapes, sizes, and patterns. The flow-through apertures  133  should be sufficiently large to permit the composite mixture  111  to flow through into them, but should not be so numerous, or placed so close together as to render the reinforcing member  130   a  ineffective for bearing a significant tensile load. The possibility of nails or screws being driven through the reinforcing member  130   a  should be taken into account in determining the pattern and size of the flow-through apertures  133 .  
         [0041]     Suitable materials for the reinforcing member  130   a  may include, for example, carbon composites, steel, aluminum, and other metal, glass and polymer based materials. Generally speaking, the material chosen for the reinforcing member  130   a  can be selected to provide a desired tensile strength, but can also accommodate a nail, screw or other fastener that may be driven into the reinforced composite structural member  118 . The material selected should also provide sufficient tensile strength, even if flow-through apertures  133  are provided. Furthermore, the material can be selected to allow the reinforcing member  130   a  to be sufficiently flexible such that a sufficiently long length of the reinforcing member  130   a  may be provided on a supply reel (not shown). This will facilitate a sufficiently long, continuous run through the extruder  110  to form the extruded composite structural member  118 .  
         [0042]     In other embodiments, the reinforcing member may take another form that can be accommodated within the profile of the extruded composite structural member  118 . For example, in one such embodiment, the reinforcing member  130   a  ( FIG. 3   b ) may be made of fibers braided into the form of a cable or tow. Instead of a plurality of flow-through apertures  133 , as shown in  FIG. 2   a , the braided cable or tow may provide a coarse or uneven outer surface.  
         [0043]     It will be understood that such a coarse or uneven outer surface will provide an increased bondable outer surface on said reinforcing member  130   a , in comparison to a reinforcing member of a substantially similar shape and size having a substantially smooth outer surface. Furthermore, such a coarse or uneven outer surface will provide greater frictional force between the reinforcing member  130   a  and the composite mixture  111 . The cable or tow also provides a greater cross-sectional area for bearing tensile strength.  
         [0044]     Still referring to  FIG. 2   a , the extrusion apparatus  115  includes an extrusion outlet  117  suitably shaped to form a desired cross-sectional profile of the extruded composite structural member  118 . For example, in order to form a number of voids or channels within the profile of the extruded composite structural member  118 , a plurality of channel shaping elements  134   a - 134   d  may be suitably positioned within the extrusion outlet  117 . The channel shaping elements  134   a - 134   d  may be suspended at the mouth of outlet  117  by suitably placed braces or webs (not shown) further within the extrusion outlet  117 . Preferably, such braces or webs should have a minimal profile, in the direction of flow of the composite mixture  111 , so as to minimize any disruption of flow of the composite mixture  111  into extrusion outlet  117 .  
         [0045]     Now referring to  FIG. 2   b , shown is another view of the extrusion apparatus  115  of  FIG. 2   a . As shown in  FIG. 2   b , a segment of the extruded composite structural member  118  has emerged from the extrusion outlet  117 . Channels  206   a - 206   d  have been formed by the channel shaping elements  134   a - 134   d , respectively. Furthermore, the reinforcing members  130   a  and  130   b  have passed through the extrusion outlet  117  to become embedded within the extruded composite structural member  118 . The general direction of flow of the emerging extruded composite structural member  118  is indicated by arrow C.  
         [0046]     Referring to  FIG. 2   c , the extrusion apparatus  115  of  FIGS. 2   a  and  2   b , and a segment of the extruded composite structural member  118 , are shown in a cross-sectional view. As shown, the first reinforcing member  130   a  follows a path through opening  132   a  into extrusion apparatus  115  and then in between the channel shaping element  134   a  and an extrusion apparatus wall  131   a . Similarly, reinforcing member  130   b  follows a path through opening  132   b  into extrusion apparatus  115 , and then in between the channel shaping element  134   d  and extrusion apparatus wall  131   b.    
         [0047]     Still referring to  FIG. 2   c , an extrusion screw  210  provides the necessary pressure on composite mixture  111  to extrude the mixture  111  through the extrusion outlet  117 . Within the extrusion apparatus  115 , the composite mixture  111  should have a suitable viscosity, and sufficient momentum in the general direction of arrow C, such that the reinforcing members  130   a  and  130   b  are pulled into and through the extrusion apparatus  115 .  
         [0048]     In an embodiment, the openings  132   a ,  132   b  of the extrusion apparatus  115  may lead into suitably configured guide channels  212   a ,  212   b  which may guide the reinforcing members  130   a ,  130   b  into the extrusion apparatus  115 , near the extrusion outlet  117 , for bonding to the composite mixture  111 . As shown in  FIG. 2   c , the guide channel  212   a  is appropriately sized and shaped to allow reinforcing member  130   a  to pass through the extrusion apparatus  115  and be aligned for accurate placement within the extruded composite member  118 . Similarly, guide channel  212   b  is appropriately sized and positioned to allow reinforcing member  130   b  to pass through the extrusion apparatus  115  and be aligned for accurate placement within the extruded composite member  118 . The size, shape and length of the guide channels  212   a ,  212   b  will be determined by the outer dimensions of the reinforcing member  130   a ,  130   b  and also by the intended placement location in the profile of the extruded composite member  118 .  
         [0049]     Now referring to  FIG. 2   d , and referring back to  FIG. 2   c , in an embodiment, the guide channel  212   b  may be provided with a lining  213 . The lining may provide guide channel  212   b  with different properties. For example, the lining  213  may provide a degree of thermal regulation, allowing the reinforcing member  130   b  to be regulated substantially independently of the composite mixture  111 . As another example, the lining  213  may provide a sufficiently smooth and hard surface which provides a sufficiently smooth entry for reinforcing members  130   a ,  130   b  which may have a coarse or uneven outer surface.  
         [0050]     In an embodiment, a suitable temperature gauge  214  may be employed to monitor the temperature of the guide channel  212   b  for more accurate process control, although care should be taken in unobtrusively placing the gauge  214  so as not to hinder movement of the reinforcing member  130   b.    
         [0051]     If desired, a heating element  215  may be provided along the guide channel  212   b  in order to preheat the surface of the reinforcing member  130   b  prior to its exit from the guide channel  212   b.    
         [0052]     There should not be any back-flow of the composite mixture  111  into guide channel  212   b , especially if the exit of the guide channel  212   b  is suitably sized and shaped for the reinforcing member  130   b . Also, the movement of composite mixture  111  in the general direction of arrow C should minimize any such back-flow problems.  
         [0053]     Still referring to  FIG. 2   d , as shown, the reinforcing member  130   b  may be guided into the opening  132   b  by a pair of opposing rollers  220   a  and  220   b . The rollers  220   a ,  220   b  may be made of a suitably strong and heat resistant material, such as tungsten carbide or ceramic, for example. The direction of rotation of each roller  220   a  and  220   b  is indicated by arrow D and arrow E, respectively. The rollers  220   a  and  220   b  may be initially used in a driving manner to assist in threading the reinforcing member  130   b  into the guide channel  212   b  and through the extrusion apparatus  115 . Once the extrusion process is under way, however, the rollers  220   a ,  220   b  may then become suitably biased against such rotation to regulate tension on the reinforcing member  130   b  as it is pulled into the extrusion apparatus  113 . (In another embodiment, the two functions, driving and tensioning, may be performed by two separate sets of rollers.) Depending on the type of the material used, and the material&#39;s flexibility, appropriate tensioning of the reinforcing member fiber  103   b  may help to impart a desired strength characteristic in the finished product.  
         [0054]     The rate of introduction of reinforcing member  130   b  into the extrusion apparatus  115  will be determined by the rate of formation of the extruded composite structural member  118  through the extrusion apparatus  115 . Consequently, the rate of introduction of the reinforcing member  130   b  should be carefully matched with the rate of formation of the extruded composite structural member  118  in order to obtain substantially uniform product characteristics along substantially the entire length formed in a processing run.  
         [0055]     In the vicinity of the exit of guide channel  212   b , the composite mixture  111  flows into a funnel shaped entrance to gap  225 . Sufficient pressure is present in this region such that the composite mixture  111  flows around and makes substantial contact with the reinforcing member  130   b  as it emerges from the guide channel  212   b . Any flow-through apertures  133  provided on the reinforcing member  130   b  are filled by the composite mixture  111 .  
         [0056]     In another embodiment, the reinforcing member  130   b  may be coated or treated with a resin, selected to be compatible with the resin used in the composite mixture  111 , such that a solid bond may be formed between the reinforcing member  130   b  and the composite mixture  111 . Advantageously, preparation of the composite mixture  111  and preparation of the reinforcing member  130   b  for bonding can proceed substantially independently, up to the point that reinforcing member  130   b  is extruded together with composite mixture  111  through the extrusion apparatus  115 .  
         [0057]     Referring to  FIGS. 3   a  and  3   b , shown are cross-sectional views of an extruded composite structural member  118  formed by the method and apparatus shown and described above. The reinforcing members  130   a  and  130   b  are placed within the composite structural member  118  and bonded to the surrounding composite material to provide assistance in bearing tensile forces under a load A or a load B, as the case may be.  
         [0058]     As shown in  FIG. 3   a , in the case of a reinforcing member  130   a ,  130   b  provided with flow through apertures, such flow-through apertures  133  may be filled in by the composite mixture. This may help to keep to reinforcing member  130   a ,  130   b  firmly in position within the composite matrix.  
         [0059]     As shown in  FIG. 3   b , in an alternative embodiment, the reinforcing members  130   a ,  130   b  may comprise braided cables or tows having a coarse outer surface. As explained earlier, such a coarse surface may provide an effectively greater surface area for bonding to the surrounding composite mixture  111 , and may also provide a greater frictional force between the reinforcing members  130   a ,  130   b  and the surrounding matrix of the extruded composite structural member  118 . Also, the braided cable or tow shape provides a greater cross-sectional area for bearing tensile stresses.  
         [0060]     Still referring to  FIGS. 3   a  and  3   b , if the extruded composite structural member  118  is bearing load A on side  300   b , between two fixed supports (not shown) supporting side  300   a , then reinforcing member fiber  130   a  will be in tension. Similarly, if load B is applied to side  300   a , say between two fixed supports (not shown) supporting side  300   b , then reinforcing member fiber  130   b  will be in tension. By having the symmetrical arrangements shown, it will be understood that the extruded composite structural member  118  provides virtually the same structural loading characteristics regardless of which side,  300   a  or  300   b , is bearing a load.  
         [0061]     While certain illustrative embodiments of the present invention has been shown and described, various modifications will be apparent to those skilled in the art. For example, while an extrusion process has been described, it will be appreciated that various aspects of this invention may be adapted to pultrusion and injection molding techniques. As well, while the illustrative extruded composite structural member is shown and described as having a plurality of channels, it will be understood that the teachings of the present invention are equally applicable to strengthening an extruded composite structural member with just one channel, or without such channels (i.e. a member having a solid cross-section). Also, the shape of the internal channels may vary. While the extruded composite structural member is shown as having a generally rectangular shape, it will be understood that various other shapes may also be used. As well, while the reinforcing member is shown as being embedded substantially along the entire length of a composite structural member, it will be appreciated that only a portion of a length of a composite structural member may be reinforced in this manner, if appropriate to do so.  
         [0062]     Therefore, the invention is defined in the following claims.