EP0062139A2

EP0062139A2 - Elongate structural members comprised of composite wood material

Info

Publication number: EP0062139A2
Application number: EP82100664A
Authority: EP
Inventors: Anders E. Lund; Gordon P. Krueger; Roy D. Adams
Original assignee: Michigan Technological University; University of Michigan
Current assignee: Michigan Technological University; University of Michigan
Priority date: 1981-04-03
Filing date: 1982-01-30
Publication date: 1982-10-13
Also published as: FI71603C; EP0062139B1; NO820638L; FI820675L; EP0062139A3; DE3264351D1; ATE14032T1; FI71603B

Abstract

An elongate structural member has a longitudinal axis and is comprised of a plurality of elongate panels having lateral edges, the panels being arranged to form an elongate central cavity with lateral edges of adjacent panels being fixedly joined together. The elongate panels are each comprised of a plurality of wood particles intermixed with a suitable binder and compressed to form a densified product. A rigid foam material is provided filling at least a portion of the elongate central cavity for reinforcing the elongate structure, the rigid foam material also being bonded to the inwardly facing surfaces to further reinforce the elongate structure.

Description

The present invention relates to the construction of elongate structural members such as utility poles, pilings, cross-ties and cross-arms from composite wood material. Such structural members can possess strength properties as good as or better than similar structures comprised of high grade solid wood and can be manufactured at a cost making them competitive with such solid wood structures.
While comminuted wood materials have been found to be useful in other applications such as in the construction of panels or other planar structural wood products, the prior art does not suggest a suitable or -commercially viable means for_producing a high strength elongate structural member from such wood material.
According to the present invention there is provided an elongate structural member comprising a plurality of elongate panels each being comprised of a plurality of wood particles intermixed with a suitable binder and compressed to form a densified product and arranged to form an elongate structure, characterised by said panels having inwardly facing surfaces defining an elongate central cavity, the lateral edges of adjacent panels being fixedly joined together and means for reinforcing said elongate structure, said reinforcing means comprising a rigid foam material filling at least a portion of said elongate central cavity, said rigid foam material being bonded to said inwardly facing surfaces.
In one embodiment of the invention the rigid foam material comprises rigid polyurethane foam.
The invention will now be particularly described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 is an elevation view of an elongate structural member according to the present invention;
Figure 2 is a cross section view taken along line 2-2 in Figure 1;
Figure 3 is a cross sectional view of the elongate structural member shown in Figure 1;
Figure 4 is an enlarged partial cross-section perspective view of the composite wood material comprising the elongate structural member of Figure 1 ;
Figure 5 is a perspective view showing an alternative embodiment of an elongate structural member embodying the invention.

The example illustrated in Figure 1 is an elongate structural member 10 comprised of composite wood material and defining an elongate hollow tapered pole of the type used as a utility pole, piling, or in another similar application.
The elongate structural member 10 is constructed of a plurality of elongate composite panels or boards 14, the panels 14 being comprised of composite wood material. In the construction shown in Figures 1-3, the panels 14 are illustrated as each being comprised of a plurality of planar layers 18 of composite wood material laminated together, the layers 18 being secured together by an interface adhesive 19. The panels 14 so formed are miter cut or otherwise cut to shape and combined to form a composite wood pole. In the illustrated construction, the respective elongate lateral edges 20 of the panels 14 are joined together by an interface adhesive to thereby join the panels 14 in an octagonal shape as illustrated in Figure 2.
As shown in Figure 3 the panels 14 may be comprised of a plurality of planar composite wood material layers 18 of successively increasing lengths such that the thickness of each of the panels 14 tapers from the base portion of the pole 14 toward the upper end of the pole, the portions of the elongate panels 14 at the base portion of the illustrated pole 10 having a thickness of three layers 18 of composite material and the upper portions of the panels 14 being comprised of a single layer 18 of composite wood material. In other embodiments of the invention the panels 14 can comprise a single layer 18 of composite wood material, those panels being tapered in thickness such that when assembled they can form a pole as illustrated in Figure 1.
Referring more specifically to the material composition of the panels 14, in a preferred embodiment of the invention, they are comprised of composite wood material formed from wood flakes 22 (figure 4) intermixed with a suitable binder material and compressed in a suitable press. In particular the compressed product is formed by constructing a loosely felted mat of wood flakes 22, the wood flakes having been mixed with a binder material. More particularly the mat is formed by disposing generally planar wood flakes 22 such that the planes of the flakes 22 are generally parallel to the major plane of the mat and with substantially all of the flakes being aligned as illustrated in Figure 4 such that the longitudinal axis of the flakes 22 are mutually parallel and parallel to the longitudinal axis of the elongate structural component to be formed. The mat is then compressed to form the dense elongate planar layers 18, the mat being compressed in generally the same manner and using the same operating conditions as are used in the manufacture of conventional particleboard.
In a preferred form of the invention, at lease 90% of the wood flakes 22 are to be aligned in the planar layers 18 so as to be parallel to the longitudinal axis of the elongate panel 14 or the layer 18 being formed. The planar flakes 22 also lie in planes which are parallel to the major plane of the layer comprised of those flakes. The flakes 22 each have a grain direction extending generally parallel to the longitudinal axis of the flakes. Alignment of the flakes 22 also results in alignment of the wood grain of the flakes with the longitudinal axis of the structural member of pole 10 in a manner similar to a solid wood pole. In fact, the pole 10 may have a more uniform grain direction than that of a solid wood pole since conventional poles will normally have innate grain inconsistencies and knots.
Wood flakes 22 of the type forming the layers 18 are conveniently formed using a conventional ring flaker or a round wood flaker to commutate small logs, branches, or rough pulp wood and form suitably shaped flakes 22. In the production of the elongate panels 14, it is preferred that the wood flakes 22 have a length of from 0.5 to 3.5 inches (1.27 to 8.89 cms) ) a width of 0.1 to 0.5 inches (0.25 to 1.27 cms) and a thickness of .01 to .05 inches (0.025 to 0.127 cms). Additionally, it is preferred that the ratio of the average length of the flakes to the average width of the flakes be from about 4:1 to about 10:1. An example of a convenient flake geometry is the use of flakes having a length of a.pproximately 1.6 inches (4.06 cms), a thickness of approximately .02 inches (0.05 tms) and a width of 0.2 to 0.5 inches (0.5 to 1.27 cms).
A convenient binder for use in the manufacture of the panels 14 can comprise phenol-formaldehyde or an isocyanate adhesive. In one preferred form of the invention the binder may comprise an organic polyisocyanate having at least two active isocyanate groups per molecule. It has been found that an 8% resin solids composition of such binder, based on oven-dry flake weight gives satisfactory strength properties to the resulting elongate structure. To maximize coverage of the flakes, the binder may be applied by spraying droplets of the binder in liquid form on to the flakes.
To preserve the elongate structural members from decay due to decay fungi and insects it is also desirable to further include a suitable fungicide in the composite wood mat. The wood flakes may also be treated or mixed with a suitable biocide such as pentachlorophenol, creosote, chromated copper arsenate and ammoniacal copper arsenate.
While the elongate pole 10 is shown as having an octagonal cross-sectional configuration, it should be understood that the pole could alternatively have other cross-sectional configurations such as a circular or a hexagonal cross-sectional configuration.
While the respective panels 14 of the elongate pole 10 are conveniently fixedly joined together at their elongate lateral edges 20 by any high strength adhesive such as resorcinol-formaldehyde, and isocyanate adhesive, or other adhesive suitable for bonding wood products, it is contemplated that the panels 14 could also be joined to gether by splines or by a combination of splines and an adhesive.
The pole 10 also includes means for providing structural reinforcement for the panels 14 forming the pole and for further bonding the panels 14 together. This means includes a foam material 24 poured or injected into the central elongate cavity 26 formed by the panels, the foam material 24 filling at least a portion of the elongate cavity 26. In a preferred formof the invention, the foam material 24 can conveniently comprise a foam-in-place rigid polyurethane foam which can be poured into the elongate central cavity 26 as a pourable liquid and which will then foam so as to form a rigid core filling the pole. The rigidity of the polyurethane foam core provides structural support for the elongate structure formed by the panels 14, and thepolyurethane foam will also form an adhesive bond with the inner planar surfaces 28 of the panels 14 and will thus act as an additional means for bonding the panels 14 together and for preventing them from separating. An example of a suitable polyurethane foam is BAYTHERM 851 produced by Mobay Chemical Corporation of Pittsburgh, Pennsylvania. As is conventional, the polyurethane foam is made by mixing two liquid components, whereupon the liquid material foams and cures at room temperature to form a rigid foam 24. While the density of the resultant rigid polyurethane foam can be varied in a conventional manner by varying the quantities of the two components combined, it has been found that a suitable density is 2 Ibs/ft 3 (32kg/m³). On the other hand, the rigidity of the foam and the reinforcing strength of the foam can be increased by increasing the density of the foam used. For example, a pole having increased strength may be produced by employing foam having a density of 5 lbs/ft³ (80kg/m³), but the expense of the pole increases due to the increase in the amount of foam material used.
One of the features of the employment of polyurethane foam material in the elongate cavity 26 is . that it has a. closed cell structure and thereby does not readily absorb moisture and provides an effective barrier to movement of moisture in the pole interior.
While the rigid foam material 24 has been described as comprising polyurethane, in other embodiments, the foam material could comprise other suitable foam-in-place materials. It is preferred, however, that the material have the properties of inhibiting the movement of moisture into the pole, and that it so form a bond with the panels to thereby provide structural rigidity or reinforcement to the pole. It is also preferred that the foam material be a rigid foam rather than a flexible foam so that the rigid foam provides structural support for the pole. In a preferred form of the invention it is also desirable that the foam material selected have the property of curing at room temperature. Though other foam materials can be used, manufacturing costs can be reduced if heating of the foam material to effect curing can be avoided. In other alternative forms, filler materials such as wood chips, saw dust, wood strands or the like could also be mixed into the liquid material poured into the cavity 26 to form the rigid foam.
While in the illustrated embodiment the foam material could fill only the upper and lower ends of the elongate central cavity, in other arrangements the foam material could fill the entire central elongate cavity 26. In the illustrated construction, foam material 24 in the lower end of the pole 10 will be particularly effective for inhibiting movement of moisture into the pole. The foam material 24 in the upper end of the pole 10 provides reinforcement of that end of the pole which is intended to support utility pole cross-arms or the like.
Illustrated in Figure 5 is an alternative embodiment of an elongate structural member embodying the invention. The elongate structural member 40 shown there comprises a hollow elongate cross-arm of the type commonly employed with utility poles and used to support telephone lines or power lines. More particularly, the cross-arm 40 is comprised of four planar elongate panels 42 each comprised of composite wood material produced in the manner described above and having a construction as shown in Figure 4. The elongate panels 42 are fixedly joined together at their interfaces 44 by a suitable adhesive of the type previously described. It should be understood that the panels 42 could also be secured together by other suitable joining means.
As in the case of the elongate hollow pole shown in Figures 1 - 3, the elongate panels 42 of the cross-arms 40 are comprised of elongate wood flakes 22 aligned such that substantially all of the flakes are positioned with their longitudinal axes parallel to the longitudinal axis of the elongate panels 42 and with the generally planar flakes 22 oriented so as to define pla.nes substantially parallel to the major plane of the elongate panel defined by the flakes.
As in the case of the elongate pole 10, means are also provided for filling at least a portion of the elongate central cavity 46 of the cross-arm, the means for filling also functioning to provide structural reinforcement or support for the elongate panels 42 forming the cross-arm and to provide means for further bonding the panels 42 together. The means for filling includes a rigid foam material 48 which can be poured or injected into the central elongate cavity 46 defined by the elongate panels. It is preferred that the foam material 48 have the property of forming an adhesive bond with the internal surfaces 50 of the panels as previously described so that. the internal foam material 48 will bond the panels together. As previously described, one preferred foam material having this property and also providing structural rigidity is a rigid polyurethane foam.
The rigid foam material is placed in the cross-arm by positioning the cross-arm vertically, whereupon the polyurethane foam can be poured in its liquid state into the cross-arm. This material will then foam-in-place to fill the elongate central cavity of the cross-arm and will cure to form a rigid core for the cross-arm. The polyurethane could also be injected into the cavity 46 using a conventional foam injection nozzle arrangement.

Claims

1. An elongate structural member comprising a plurality of elongate panels each being comprised of a plurality of wood particles intermixed with a suitable binder and compressed to form a densified product and arranged to form an elongate structure, characterised by said panels having inwardly facing surfaces defining an elongate central cavity, the lateral edges of adjacent panels being fixedly joined together, and means for reinforcing said elongate structure, said reinforcing means comprising a rigid foam material filling at least a portion of said elongate central cavity, said rigid foam material being bonded to said inwardly facing surfaces.

2. An elongate structural member according to claim 1 characterised in that said rigid foam material comprises rigid polyurethane foam.

3. An elongate structural member according to claim lor claim 2 characterised by said wood particles forming said elongate panels comprising elongate flakes each having a longitudinal axis, the grain direction of said wood flakes being aligned substantially parallel with said longitudinal axes of said wood flakes, and wherein at least 90% of said wood flakes are aligned with their longitudinal axes parallel to the longitudinal axis of the elongate member.

4. An elongate structural member according to any preceding claim characterised in that each of said panels has a major plane, and said wood flakes in said panel are planar and define planes parallel to said major plane of said panel.

5. An elongate structural member according to any preceding claim characterised in that said wood flakes have an average length of 0.5 inches to 3.5 inches (1.27 to 8.89 cms), an average width of 0.1 to 0.5 inches (0.254 to 1.27 cms) and an average thickness of 0.01 to 0.05 inches (0.025 to 0.127 cms).

6. An elongate structural member according to any preceding claim characterised in that said elongate panels are planar and each have lateral edges, and the lateral . edges of the elongate planar panels are adhesively bonded together in abutting relationship.

7. An elongate structural member according to any preceding claim characterised in that said binder comprises an organic polyisocyanate having at least two active isocyanate groups per molecule.

8. An elongate structural member according to any preceding claim characterised in that each of said elongate planar panels is comprised of a plurality of planar layers of composite wood material laminated together, each planar layer being comprised of elongate wood flakes intermixed with a binder and compressed.

9. A method for forming an elongate structural member comprising the steps of forming a plurality of elongate planar panels, each of the panels being comprised of wood flakes mixed with a binder and compressed to form a densified product, characterised by each of the panels having a major plane and a longitudinal axis and the wood flakes comprising each such panel being planar and lying in planes parallel to the major plane of that panel, and the wood flakes having a longitudinal axis, the grain direction of the wood flakes being parallel to the longitudinal axis of the flakes, and the longitudinal axis of the flakes being parallel to the longitudinal axis of the panel, fixedly joining said panels together to form an elongate composite member having an elongate central cavity, said panels being joined together with the lateral edges of each of said panels being bonded to a lateral edge of an adjacent panel, and filling at least a portion of said central cavity with a rigid foam material.

10. A method according to claim 9 characterised in that said step of filling said central elongate chamber with foam material comprises the step of introducing a foam-in-place polyurethane foam into said central elongate chamber and causing said foam to fill said chamber and to bond said panels.