Reinforced composite structural members and methods of making the same

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

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

This invention relates to reinforced composite structural members and methods of making the same.

BACKGROUND OF THE INVENTION

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.

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.

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.

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.

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

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.

In an embodiment, the reinforced composite structural member may be formed by extrusion.

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.

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.

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.

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.

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.

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.

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.

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.

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.

These and other aspects of the invention will become apparent through the illustrative figures and accompanying description provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures which illustrate example embodiments of the present invention:

FIG. 1 is a schematic block diagram of an exemplary processing line for processing a composite structural member.

FIG. 2a is a detailed perspective view of an extrusion apparatus for practicing the method in accordance with an exemplary embodiment of the invention.

FIG. 2b is the extrusion apparatus of FIG. 2a showing an extruded segment of a reinforced composite structural member made in accordance with an exemplary embodiment of the invention.

FIG. 2c is a cross-sectional view of the extrusion apparatus of FIGS. 2a and 2b showing paths for introducing reinforcing members.

FIG. 2d is a detail of a portion of the extrusion apparatus of FIG. 2c.

FIG. 3a is a cross-sectional view of the reinforced composite structural member formed by the extrusion apparatus of FIGS. 2a to 2d.

FIG. 3b 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

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's premises.

Attached to an end of the extruder 110 is an extrusion apparatus 115. An extrusion screw 210 (see FIG. 2c) is provided within the extruder 110 to apply suitable pressure on a composite mixture 111 formed from the raw materials therein.

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.

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.

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.

Referring to FIG. 2a, shown is a perspective view of the extrusion apparatus 115 of FIG. 1. As shown, the extrusion apparatus 115 includes a first opening 132a for receiving, along a path A, a first reinforcing member 130a therein. Shown in a hidden view is a second opening 132b located on an opposite side of the extrusion apparatus 115. The second opening 132b receives, along a path B, a second reinforcing member 130b therein. In the discussion below, the description of the opening 132a and reinforcing member 130a should be understood to apply equally to opening 132b and reinforcing member 130b, in a corresponding manner.

In an embodiment, the reinforcing member 130a may be in the form of a flexible strip or tape. The reinforcing member 130a may be provided with a plurality of flow-through apertures 133 along the length of the reinforcing member 130a. 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 132a 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 130a (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.

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 130a ineffective for bearing a significant tensile load. The possibility of nails or screws being driven through the reinforcing member 130a should be taken into account in determining the pattern and size of the flow-through apertures 133.

Suitable materials for the reinforcing member 130a 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 130a 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 130a to be sufficiently flexible such that a sufficiently long length of the reinforcing member 130a 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.

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 130a (FIG. 3b) 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. 2a, the braided cable or tow may provide a coarse or uneven outer surface.

It will be understood that such a coarse or uneven outer surface will provide an increased bondable outer surface on said reinforcing member 130a, 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 130a and the composite mixture 111. The cable or tow also provides a greater cross-sectional area for bearing tensile strength.

Still referring to FIG. 2a, 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 134a-134d may be suitably positioned within the extrusion outlet 117. The channel shaping elements 134a-134d 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.

Now referring to FIG. 2b, shown is another view of the extrusion apparatus 115 of FIG. 2a. As shown in FIG. 2b, a segment of the extruded composite structural member 118 has emerged from the extrusion outlet 117. Channels 206a-206d have been formed by the channel shaping elements 134a-134d, respectively. Furthermore, the reinforcing members 130a and 130b 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.

Referring to FIG. 2c, the extrusion apparatus 115 of FIGS. 2a and 2b, and a segment of the extruded composite structural member 118, are shown in a cross-sectional view. As shown, the first reinforcing member 130a follows a path through opening 132a into extrusion apparatus 115 and then in between the channel shaping element 134a and an extrusion apparatus wall 131a. Similarly, reinforcing member 130b follows a path through opening 132b into extrusion apparatus 115, and then in between the channel shaping element 134d and extrusion apparatus wall 131b.

Still referring to FIG. 2c, 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 130a and 130b are pulled into and through the extrusion apparatus 115.

In an embodiment, the openings 132a, 132b of the extrusion apparatus 115 may lead into suitably configured guide channels 212a, 212b which may guide the reinforcing members 130a, 130b into the extrusion apparatus 115, near the extrusion outlet 117, for bonding to the composite mixture 111. As shown in FIG. 2c, the guide channel 212a is appropriately sized and shaped to allow reinforcing member 130a to pass through the extrusion apparatus 115 and be aligned for accurate placement within the extruded composite member 118. Similarly, guide channel 212b is appropriately sized and positioned to allow reinforcing member 130b 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 212a, 212b will be determined by the outer dimensions of the reinforcing member 130a, 130b and also by the intended placement location in the profile of the extruded composite member 118.

Now referring to FIG. 2d, and referring back to FIG. 2c, in an embodiment, the guide channel 212b may be provided with a lining 213. The lining may provide guide channel 212b with different properties. For example, the lining 213 may provide a degree of thermal regulation, allowing the reinforcing member 130b 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 130a, 130b which may have a coarse or uneven outer surface.

In an embodiment, a suitable temperature gauge 214 may be employed to monitor the temperature of the guide channel 212b 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 130b.

If desired, a heating element 215 may be provided along the guide channel 212b in order to preheat the surface of the reinforcing member 130b prior to its exit from the guide channel 212b.

There should not be any back-flow of the composite mixture 111 into guide channel 212b, especially if the exit of the guide channel 212b is suitably sized and shaped for the reinforcing member 130b. Also, the movement of composite mixture 111 in the general direction of arrow C should minimize any such back-flow problems.

Still referring to FIG. 2d, as shown, the reinforcing member 130b may be guided into the opening 132b by a pair of opposing rollers 220a and 220b. The rollers 220a, 220b 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 220a and 220b is indicated by arrow D and arrow E, respectively. The rollers 220a and 220b may be initially used in a driving manner to assist in threading the reinforcing member 130b into the guide channel 212b and through the extrusion apparatus 115. Once the extrusion process is under way, however, the rollers 220a, 220b may then become suitably biased against such rotation to regulate tension on the reinforcing member 130b 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's flexibility, appropriate tensioning of the reinforcing member fiber 103b may help to impart a desired strength characteristic in the finished product.

The rate of introduction of reinforcing member 130b 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 130b 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.

In the vicinity of the exit of guide channel 212b, 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 130b as it emerges from the guide channel 212b. Any flow-through apertures 133 provided on the reinforcing member 130b are filled by the composite mixture 111.

In another embodiment, the reinforcing member 130b 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 130b and the composite mixture 111. Advantageously, preparation of the composite mixture 111 and preparation of the reinforcing member 130b for bonding can proceed substantially independently, up to the point that reinforcing member 130b is extruded together with composite mixture 111 through the extrusion apparatus 115.

Referring to FIGS. 3a and 3b, 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 130a and 130b 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.

As shown in FIG. 3a, in the case of a reinforcing member 130a, 130b 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 130a, 130b firmly in position within the composite matrix.

As shown in FIG. 3b, in an alternative embodiment, the reinforcing members 130a, 130b 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 130a, 130b 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.

Still referring to FIGS. 3a and 3b, if the extruded composite structural member 118 is bearing load A on side 300b, between two fixed supports (not shown) supporting side 300a, then reinforcing member fiber 130a will be in tension. Similarly, if load B is applied to side 300a, say between two fixed supports (not shown) supporting side 300b, then reinforcing member fiber 130b 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, 300a or 300b, is bearing a load.

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.

Therefore, the invention is defined in the following claims.

Claims

1. 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.

2. The reinforced composite structural member of claim 1, wherein said composite structural member is formed by extrusion.

3. The reinforced composite structural member of claim 1, wherein said 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.

4. The reinforced composite structural member recited in claim 1, wherein said physical characteristic comprises a plurality of flow-through apertures.

5. The reinforced composite structural member recited in claim 4, wherein said reinforcing member is in the form of a strip, and said flow-through apertures are provided along the entire length of said strip.

6. The reinforced composite structural member recited in claim 1, wherein said physical characteristic comprises a resin compatibly bondable with said resin in said composite mixture.

7. The reinforced composite structural member recited in claim 1, wherein said physical characteristic comprises a coarse outer surface.

8. The reinforced composite structural member recited in claim 7, wherein said reinforcing member is a braided cable having said coarse outer surface.

9. The reinforced composite structural member recited in claim 8, wherein said reinforcing member includes a resin compatibly bondable with said resin in said composite mixture.

10. The reinforced composite structural member recited in claim 1, wherein said fibrous material is a natural fiber.

11. The reinforced composite structural member recited in claim 1, wherein said fibrous material is wood fiber.

12. The reinforced composite structural member recited in claim 1, wherein said reinforcing member includes an anchoring feature to secure said reinforcing member in said composite structural member in a lengthwise direction.

13. 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;

(iii) embedding said reinforcing member into said composite mixture prior to forming said composite structural member.

14. The method recited in claim 13, wherein (iii) is performed during extrusion of said composite mixture.

15. The method recited in claim 13, wherein said 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.

16. The method recited in claim 13, further comprising, prior to (iii), applying sufficient heat, pressure and agitation to said composite mixture to bring said resin to its melting point, and said composite mixture of said natural fiber and said resin to a flowing, extrudable state.

17. The method recited in claim 16, wherein said characteristic comprises providing on said reinforcing member a resin compatibly bondable with said resin in said composite mixture.

18. The method recited in claim 13, further comprising thermally regulating said reinforcing member strip independently of said composite mixture, up to the point of said embedding in (iii).

19. The method recited in claim 13, wherein in (ii) said providing a length of a reinforcing member with at least one physical characteristic for increasing the area of the bondable outer surface of said reinforcing member comprises providing a plurality of flow-through apertures on said reinforcing member.

20. The method recited in claim 19, further comprising providing on said reinforcing member a resin compatibly bondable with said resin in said composite mixture.

21. The method recited in claim 13, wherein in (ii) said providing a length of a reinforcing member with at least one physical characteristic for increasing the area of the bondable outer surface of said reinforcing member comprises providing a coarse outer surface.

22. The method recited in claim 21, further comprising providing on said reinforcing member a resin compatibly bondable with said resin in said composite mixture.

23. The method recited in claim 22, further comprising heating the outer surface of said reinforcing member as said reinforcing member is embedded in (iii).

24. The method recited in claim 13, wherein said reinforcing member is provided in a flexible format, allowing a sufficiently long length of said reinforcing member to be supplied on a reel.

25. The method recited in claim 14, further comprising providing guiding said reinforcing member into an extrusion apparatus and immediately adjacent to an extrusion apparatus outlet for proper alignment within said reinforced composite structural member.

26. The method recited in claim 13, wherein said fibrous material is a natural fiber.

27. The method recited in claim 13, wherein said fibrous material is wood fiber.