Note: Descriptions are shown in the official language in which they were submitted.
CA 02314306 2002-02-04
METHOD OF MANUFACTURING COMPOSITE WOOD FLOORING
Background Of The Invention
This invention relates to an improved laminated wood flooring for truck
trailers and containers. Fiber reinforced polymer composite materials are used
in
conjunction with edge-glued laminated wood members to provide improved
mechanical
properties, moisture protection, fatigue resistance and light weight to the
resulting
composite boards for use in flooring of vehicular trailers.
Conventional wood flooring for over-the-road truck trailers and containers
lis normally manufactured with hardwoods such as oak, maple, birch, beech,
etc. The
green lumber used as a started material in such manufacture is suitably dried
in special
drying chambers under controlled conditions. The dried lumber is then sawed
into strips
of rectangular cross-section and defective portions are eliminated by cross
cutting the
;strips. During the cross cutting process, "hooks" are formed at the ends of
the lumber
strips. The relatively defect-free lumber strips are coated on their vertical
sides or
edges with an adhesive such as urea-melamine formaldehyde or polyvinyl
acetate. The
uncured edge-glued lumber strips are then assembled on a conveyor by placing
them
;;ide to side and behind other strips, which were previously assembled.
Applying heat
and edge pressure to large sections of the assembled lumber strips cures the
adhesive
i;hus forming a unitary panel. During the assembly of the lumber strips, "hook
joints" are
formed at each end of every lumber strip. These joints are simple mechanical
couplings
between the mating hook ends of opposing lumber strips without significant
adhesive
bonding at the joint itself. Often times, due to imperfect assembly, a readily
visible gap
is formed at the hook joints, which can be seen from the top and bottom
surfaces of the
finished laminated wood floor.
7-~9-2000 11:35AM FROM OHLANDT.GREELEY 2033276d01 P.9
323.5489 USQ1
The cured laminated wood is cut to a desired length (up to about 60 feet)
and width (about 6 to 18 inches) to form boards. The boards are then planed to
a
desired thickness and shiplaps and crusher beads are machined on its sides. A
shiplap
is a rectangular projecting lip running along the length on each side of a
floor board.
The crusher bead is a small semi-circular projection running along the length
on each
side of a board and placed over or below a lip. When the floor boards are
assembled in
a trailer such that the side edges of con-esponding boards are squeezed
together, the
shiplaps of adjacent boards overlap to form a seam. The crusher beads provide
spacing between adjacent boards and help in preventing buckling of the boards
due to
expansion on absorption of water. A wood putty is applied at the hook joints
on the top
and bottom surfaces of the boards to fill any resident gaps. Finally, the
underside of the
floor boards is coated with a polymeric substance termed as "undercoating" to
provide
moisture protection. The finished floor boards are assembled into a kit of
about eight
boards for installation in trailers. Normally. a kit consists of two boards
with special
shiplaps so that they will fit along the road and curb sides of a trailer. The
other boards
may be identical in design and they are placed between the road and curb side
boards.
In some trailers, a metallic component such as a hat-channel may be placed
between
any two adjacent boards. The metallic component becomes part of the floor
area. The
boards adjacent to the hat-channel have shiplaps designed to mate with the
flanges of
the metallic component. All the boards are supported by thin-walled cross-
members of
I, C or hat sections, each having an upper flange, which span the width of the
trailer and
are spaced along the length of the trailer. Each floor board is secured to the
cross-
members by screws extending through the thickness of the board and the upper
flanges
of the cross-members.
hardwood-based laminated wood flooring is popularly used in truck trailers
since it offers many advantages. The surface characteristics of hardwoods such
as
high wear resistance and slip resistance are most desirable. The strength and
stiffness
of the flooring is important for efficient and safe transfer of the applied
loads to the
cross-members of the trailer. The shock resistance of wood is useful to
withstand any
sudden dropping of heavy cargo on the floor. Nail holding capability and
ability to
absorb small amounts . of water, oil or grease without significantly affecting
slip
resistance are yet additional favorable properties of hardwood flooring.
CA 02314306 2000-07-19
7-19-2000 11:36AM FROM OHLANDT,GREELEY 2033276d01 P.10
_ g _ 323.5489 USQ1
Although the conventional wood flooring has many desirable features, it
also suffers from certain disadvantages. For example, water from the roads is
known to
leak into trailers through the gaps of the hook joints that exist in the
flooring. The
reasons fot the water leaks are believed to be the capillary action of the
gaps and the
tendency of the end grain of wood to absorb and store water. Although the
undercoating is supposed to provide a barrier to the path of water, it may not
properly
cover larger gaps thus exposing them to moisture. Wetting and drying cycles
can
degrade the undercoating leading to its cracking and peeling away from the
wood.
Bending. of the floor between two adjacent cross-members due to any applied
load on
the top of the floor also has a tendency to open the hook joints and enlarge
the gaps.
A lift truck is often used on the trailer floor to load and unload cargo. The
dynamic action of a moving lift truck placing heavy cargo on the trailer floor
creates
severe stress concentration in the flooring and some of the cross-members. A
very
large amount of the weight of the lift truck and that of the cargo is
transferred to the
flooring through the wheels of the front axle of the lift truck due to the
momentary raising
of the rear axle when the lift truck is dynamically placing a heavy cargo on
the floor.
The effect of repeated lift truck operation on the conventional wood floor
causes
considerable fatigue damage including: delamination of the edge glued lumber
strips
near the hook joints leading to the "pop-out" of the lumber strips; crack
initiation and
propagation in wood on the underside of the floor due to tensile stresses; and
cracking
of edge glue lines due to shearing, transverse bending and twisting of the
floor. The
combination of moisture attack and fatigue damage to the wood floor affects
its
performance thus necess'rtati~g its repair or replacement. In some cases,
catastrophic
structural failure of the trailer floor system may occur leading to the
unacceptable injury
to working personnel and damage to machinery.
To alleviate the above-mentioned problems, novel fiber reinforced
composite wood flooring was designed, tested and refined to be an improvement
over
conventional wood flooring. This new composite wood flooring consists of
conventional
laminated wood member with an underlay of fiber reinforced plastic (FRP)
bonded to
the wood member. The top surface of the composite wood flooring is essentially
the
same as that of the conventional wood flooring. Since the FRP is impervious to
the
passage of 'water, it completely seals the bottom of the wood member and
solves the
problem of leaky hook joints. The fiber reinforcement improves the mechanical
CA 02314306 2000-07-19
7-19-2000 11_37AM FROM ONLANDT.GREELEY 2033276d01 P.11
323.5489 USQ1
properties of the flooring and therefore the thickness of the laminated wood
can be
reduced: Thus, thinner and lighter composite wood flooring can be produced
with
equivalent strength when compared to thicker conventional wood flooring. Since
the
reinforC2ment provides an excellent barrier to the "pop-out" of lumber strips,
the fatigue
resistance of the composite wood flooring can be improved over that of the
conventional
wood flooring.
Technologists are constantly trying to find ways to improve the mechanical
properties. reduce weight and improve moisture resistance of wood flooring.
Fouquet.
U.S. Patent No. 5,143,418 describes the use of composite plywood panels as
flooring in
truck trailers. The plywood was composed of veneers of wood with a majority of
the
veneers oriented with the wood grain along the longitudinal direction while
the remaining
veneers were oriented with the wood grain along the transverse direction. The
top and
bottom surfaces of the plywood panels were overlaid with resin impregnated
cellulose
sheets for providing moisture and slip resistance. Clearly, Fouquet has not
considered
a floor design involving the FRP to provide higher strength and moisture
protection.
Another area of related art is the use of FRP to improve the mechanical
properties of structural wood members. such as beams, columns and trusses.
Theakston (Canadian Agricultural Engineering, January 1965, Pages 17-19) has
discussed the use of glass fibers and epoxy resin to reinforce laminated
timber beams
and arches. Triantafillou and Deskovic (Journal of Structural Engineering,
Vol. 118, No.
5, May 1992, Pages 1270-1284) have published test results on the reinforcem~nt
of
structural wood beams by adhesively bonding prestressed carbon fiber based FRP
panels using epoxy adhesive. Thus the concept of reinforcing structural wood
members
(especially beams) with FRP has been known for several decades. Tingley, U.S.
Patent
No. 5.362,545 describes the use of a resorcinol adhesive to bond certain
special
composite panels to glue-laminated wood beams (Glulams)_ The special composite
panels containing aramid (Kevlar~) fiber reinforcement are abraded by sanding
prior to
bonding. The sanding process makes the panel "hair up" due to Kevlar and helps
to
obtain improved bonding with wood. The Tingley patent teaches the utility of
Kevlar in
FRP panels to improve the bond strength of the FRP to wood while using a
resorcinol
adhesive.
CA 02314306 2000-07-19
7-19-2000 11:37AM FROM OHLANDT.GREELEY 2033276d01 P.12
_ 5 _ 323.5489 USQ1
Th~ above-referenced patents and publications have not addressed the
construction and related benefits of reinforced laminated wood flooring for
use in truck
trailers. The advantages of reinforcing the bottom side and disadvantages of
reinforcing
the top side of the laminated wood boards are not disclosed in these
references. The
publications do not discuss the remedies for the problems associated with the
conventional wood flooring such as water leakage through the hook joints and
fatigue
damage due to lift truck trafFc on the floor. There is no discussion in the
publications
regarding the type of reinforcements and resins that are suited for the
fabrication of
reinforced Composite wood flooring. For example, the question of whether fiber
reinforcement along the width (transverse) direction of the floor is
advantageous is hot
addressed in these publications. A reinforced composite wood flooring
construction
such as that provided by the present invention which is suitable for lift
truck movement
and also for carrying cargo in a trailer has never before been invented.
Methods of manufacturing the reinforced composite wood boards to
construct the improved flooring have never been considered before. The
manufacturing
process needs to be able to produce the composite wood boards at a fairly high
speed
to meet the demands of volume and cost effectiveness. The conventional
laminated
wood boards are typically manufactured at a rate of about 1500 to 2000 sq
ft/hr using
one set of machinery. To be competitive, composite wood boards need to be
produced
at a similar production rate. Since dissimilar materials with mismatch of
physical
properties are bonded together to manufacture composite wood boards,
precaution has
to be taken to ensure the flatness of the board after the bonding is
completed. The
adhesive used to bond the FRP and wood member should not excessively leak
under
the bonding pressure. Squeeze-out of adhesive can contaminate the surfaces of
the
substrates requiring additional clean-up operation. The bond between the FRP
and
wood member needs to be strong enough to resist the stress concentration
around the
hook,joints and also be fatigue and moisture resistant.
Summary Of The Invention
Unlike the FRP-wood structural beams, the reinforced composite wood
flooring of the present invention is designed to provide several desirable
features. The
composite wood floor consists of a plurality of composite wood boards. The top
side of
each of the composite wood boards is composed of a laminated wood member with
a
CA 02314306 2000-07-19
7-19-2000 1 1 :38AM FROM OhiLANDT, GREELEY 2033276d01 P. 13
_ 6 _ 323.5489 USQ1
construction similar to that of conventional wood boards of trailer flooring.
This provides
a high coefficient of friction and slip resistance, thereby facilitating the
safe movement of
man and machine. The surface of wood can also absorb small amounts of water
that
may spill over it. Any oil or grease that spills on the wood surface can be
wiped off and
the left over slick is absorbed by the pores of wood as in the conventional
wood flooring.
On the contrary, even an extremely thin coating of oil on FRP can render it
dangerously
slippery and therefore, FRP is not laid on the top side of the composite wood
board. An
FRP is bonded to the bottom side of the laminated wood member to provide
protection
to wood from the outside environment. The FRP underlay of the composite wood
flooring eliminates the need for a polymeric undercoating and for puttying of
hook joints
that is required in the conventional wood flooring. In fact, the need for hook
joints
themselves can be eliminated; that is, the lumber strips can be joined at butt
ends
thereof or by finger or lap and gap joints. However, the use of hook joints is
preferred.
The gaps in the hook joints are completely sealed by the FRP, thus preventing
water
leakage into the trailer through the flooring.
Preferably, the FRP is fabricated with glass fibers and an epoxy resin.
Other reinforcements such as carbon and aramid fibers and other thermosetting
resins
such as vinyl ester, polyester, phenolic resins and the like and other
thermoplastic
a0 resins such as' polypropylene and polyamide resins and the like can also be
used to
fabricate the FRP. The glass fiber reinforcement provides an economical means
of
,increasing the strength of the flooring in the longitudinal and transverse
directions. The
epoxy resin binds the glass fibers together and protects the fibers from
adverse
environment. The reinforcing fibers resist the pop-out of the lumber strips of
composite
wood floor in trailers when subjected to the fatigue loads of heavy lift
trucks. The
transverse reinforcement resists the splitting of the FRP and delamination of
edge-glue
lines in laminated wood during the application of shearing, twisting and
transverse
bending loads on the floor. Thus, our design of the composite wood floor
provides
improvements in the prevention of moisture leakage through hook joints.
maintains the
desirable surface Characteristics of the wood on the top surface and also
provides
significant improvements in fatigue resistance at lower weight.
The manufacture of the composite wood boards can be accomplished by
means of a suitable process wherein the fiber reinforced plastic is bonded to
the surface
of laminated wood member. in a wet process, the fiber reinforcement is
saturated with
CA 02314306 2000-07-19
7-19-2000 11:38AM FROM OHLANDT.GREELEY 2033276d01 P.ld
_ 7 _ . 323.5489 USQ1
a reactive liquid polymeric resin. The resin-wetted reinforcement is placed in
contact
with the surface of the laminated wood and the resin is cured under heat and
pressure.
A hotpress can be used to apply heat and pressure on the resin-wetted
reinforcement
while it is still in contact with the laminated wood. The composite wood board
can also
be manufactured by adapting the puttrusion process, which normally involves
the pulling
of resin-wetted reinforcement through a stationary heated die where the FRP is
shaped
and the resin is cured. The laminated wood and the resin-wetted reinforcement
can be
pulped together through a heated die to produce composite wood board. In the
wet
processes as described above, it is possible to use the same resin to bind the
fibers
together or form the matrix of the FRP and also to bond the fibers to the wood
member.
In the above-mentioned processes, which uses liquid resins several
s
practicai problems are encountered. The simultaneous application of heat and
pressure
to consolidate and cure the resin-wetted reinforcement leads to squeeze-out of
the
resin. The applied temperature reduces the viscosity of the resin further
compounding
the sc7ueeze-out of resin. The squeeze-out of the resin can occur at the sides
of the ,
layer of the wetted reinforcement or through the hook joints of the wood
member, since
gaps are present at many of these joints. The composite board formed with the
squeeze..out of resin needs a significant degree of subsequent machining to
provide the
required dimensions and shape of shiplaps along the longitudinal edges.
Further, the
FRP layer, which is formed under heat and bonded to a wovd member under heat
tends
to shrink as it cools down. Due to unsymmetrical construction of the composite
board
with FRP bonded to one surFaee of a wood member and difference in the thermal
expansion coefficients of wood and FRP, the composite wood board formed by
heating
the . resin wetted reinforcements tends to warp on cooling. Typically, the
composifie
board develops a bowed shape along the length of the board. For truck-
trailers, the
floor boards need to be substantially flat for easy installation and use.
In order to overcome the problems of squeeze-out of the resin and
warping of the boards due to heating of the FRP for curing the resin, it is
better to
adhesively bond a prefabricated FRP sheet to the wood member with minimal
application of heat to the FRP and wood. A suitable prefabricated FRP sheet
can be
bonded to laminated wood using thermosetting or thermoplastic adhesives.
Thermosetting adhesives include epoxy. polyurethane, phenol-resorcinol
formaldehyde,
urea-melamine formaldehyde, etc. Thermoplastic adhesives include hotmelts such
as
CA 02314306 2000-07-19
7-19-2000 11_39AM FROM OHLANDT.GREELEY 2033276d01 P.15
-- _ g - ' , 323.5489 USQ1
ethylene vinyl acetate polymers (EVA), polyamide, etc. Experiments have shown
that
thermosetting liquid adhesives can be used to fabricate composite wood floor.
However, squeeze-out of the adhesive through the hook joints of the wood
member
continues to be a problem when heat and pressure are applied. Further,
application of
excessive amount of heat through the FRP to quickly cure the adhesive leads to
warping of the board as mentioned before. Even though the use of thermoplastic
hotmelt adhesives such as EVA in bulk form or films eliminate squeeze-out,
they do not
lead to sufficient bond strength to resist the pop-out of the lumber strips at
the hook
joints. Thermoplastic hotmelt adhesives with relatively high strength can
provide the
required performance. After several experiments and extensive testing,
reactive
hotmelt adhesive has. been determined to be the best choice to band
prefabricated FRP
to wood members to manufacture composite wood boards. This method offers high
speed of production with minimal application of heat and good bonding of the
FRP to
wood members to resist the opening of the hook joints under load along with
tittle or no
squeeze-out of the adhesive during production.
Reactive hotmelt adhesives b~have like a typical non-reactive hotmelt
adhesive during processing or bonding, but subsequently undergo chemical
reactions
with moisture to transform into a cross-linked thermosetting adhesive. By
means of
cross=linking, the molecular weight of the adhesive increases thus providing
higher bond
strength and hygrothermal resistance. Reactive hotmelt adhesives are solvent
free
solids at room temperature. They are melted by heating and then applied on the
bondable surface of the substrates by means a roller coater. Typically, only
one
substrate needs to be 'coated in order to bond to another uncoated substrate.
However,
both substrates may be coated, if required. After coating one or both
substrates with
the reactive hotmelt adhesive, the substrates are joined and pressed together
by a
platen press or by means of rollers. The joined and pressed parts are allowed
to cure
for 1 to 7 days before. use.
Reactive hotmelt adhesives are highly suited to the bonding of
prefabricated FRP sheets to wood members for manufacturing composite filooring
for
trailers. The adhesive is the only component that needs to be heated to about
200°F to
350°F for the bonding process. The bonding surfaces of the wood board
and FRP need
to be warmed up to about 60°F to 200°F, if required. Since the
FRP is not substantially
heated for curing its polymer, the quantity of heat required for the bonding
process is
CA 02314306 2000-07-19
7-19-2000 11:d0AM FROM OHLANDT.GREELEY 2033276d01 P.16
- g _ ' 323.5489 USQ1
minimized. This leads to the production of substantially flat boards with
little or no
warping after bonding. Since the reactive hotmelt is used and applied as a
traditional
hotmelt, it leads to high manufacturing speed. The cross-linking of the
reactive hotmelt
provides higher hygrothermal resistance and therefore, the composite floor can
perform
well under the harsh environment of the roadways. Since the reactive hotmelt
has a
fairly high strain to failure, it develops high peel strength, which is
particularly important
to reinforcing the hook joints of the wood member. When a typical b~rttle
adhesive with
a low strain to-failure is used in this application, it leads to debonding of
the FRP from
the wood board at the regions of high stress surrounding the hook joints under
an
applied load on the floor board. These debonds can grow due to fatigue loads
of lift
truck on the floor of a trailer, leading to large-scale failure. However, the
reactive
hotmelt has been shown to work very well under fatigue loading in our testing
and
experiments. Due to a number of advantages as stated above, both in processing
and
performance of composite wood flooring, reactive hotmelt has been determined
to be
the preferred adhesive for this application. The use of a reactive hotmelt for
bonding
prefabricated FRP to wood members with hook joints, in order to improve its
strength,
stiffness, fatigue resistance and water proofing ability for use in vehicular
trailer flooring
has never been published before. Any suitable reactive hotmelt adhesive may be
employed in the process of this invention.
2D
The FRP sheet can be produced by pultrusion and continuous lamination
processes. In the pultrusion process, the resin-wetted reinforcements are
pulled under
tension through a stationary heated die where the FRP is shaped and cured. In
continuous lamination process, reinforcements are wetted with a polymeric
resin. The
wetted reinforcements are aligned in a die and then cured in an oven. Typical
reinforcements' used for the pultrusion process include continuous rovings,
stitched.
woven or knitted fabrics and continuous strand mats. In the Continuous
lamination
process, chopped strands and chopped strand mats can be used in addition to
the
above-mentioned reinforcements. Preferred reinforcements for our prefabricated
FRP
are continuous rvvings in the longitudinal direction of the FRP sheet and
fabrics for
transverse reinforcement. The fabrics may also be designed to provide
bidirectional
structural properties.
The FRP is sanded or abraded on at least one major surface in order to
provide a clean surface and uniform thickness to the FRP sheet for bonding to
the wood
CA 02314306 2000-07-19
7-19-2000 11=dOAM FROM OHLANDT.GREELEY 2033276d01 P.17
- 10 - 323.5489 USQ1
member. The wood member is prepared by planing the major surfaces. Since
planing
produces .a lesser degree of flatness than sanding, the planed board can be
sanded at
least on one surface to which the FRP is eventually bonded. The planed or
sanded
surface of the wood board is coated with a reactive hotmelt. Preferably, bath
the FRP
and wood member are coated on their major surfaces with the adhesive. This
provides
improved bonds between the FRP and wood. Alternatively, only one of the two
substrates may be coated with the reactive hotmelt. By coating on both
surfaces, the
chances of skipping any low spots on the FRP or wood would not be a sign~cant
problem during production. After the substrates are coated. they are joined
together so
that the edges of the FRP are laid within a predetermined distance from the
edges of
the wood member. The joined parts are pressed together by a series of rollers.
Simultaneously, the parts are cooled by means of forced air. The process of
coating
the substrates and joining them is conducted in a continuous fashion to obtain
a
relatively high manufacturing speed.
The present invention provides a novel process for manufacturing
composite wood flooring for use in truck trailers that is subjected to lift
truck loads on
the top side and water spray on the bottom side. The composite wood flooring
consists
of a plurality of composite boards each of which is composed of a wood member
with a
fiber reinforced polymer adhesively bonded to the bottom side of the wood
member
using reactive hotmelt adhesive. Since the top side of the composite wood
flooring is
composed of wood, many desirable features of wood such as slip resistance,
abrasion
resistance and nailing capability are preserved. The underlayer of the
composite wood
flooring provides improved fatigue strength and moisture protection to wood.
Since the
mechanical properties of the reinforced composite wood flooring are superior
to those of
the conventional wood flooring, the thickness of the composite wood floor can
be
reduced leading to lower floor weight in a trailer. Alternatively, the load
carrying
capacity of the trailer can be increased with a suitable composite floor while
having little
or no increase in the weight of the trailer.
The process of this invention particularly comprises a process of
manufacturing a composite wood board for use with a plurality of such
composite wood
boards in a floor system of a vehicular trailer or container, wherein each
composite
board comprises a unitary wood member with an exposed wood top surface and a
bottom surface substantially bonded to a continuous planar layer of fiber
reinforced
CA 02314306 2000-07-19
7-19-2000 11_dIAM FROM OHLANDT.GREELEY 2033276d01 P_18
- 11 - 323_54$9 USQ1
polymer rendering the bottom surface substantially non-exposed, the process
comprising th~ steps of:
providing the wood member as a side-to-side or edge bonded plurality of
wood segments in an approximately planar arrangement with a substantial
majority of the wood segments having shaped coupling portions at ends thereof,
which ends are engaged to form several randomly placed end joints in the wood
member;
machining the bonded wood segments to produce a planar wood member
with two opposing major surtaces and first and second side surfaces, said wood
member having a length, width, thickness and longitudinal and transverse axes;
providing a planar layer of fiber reinforced polymer having two major
1S surfaces and a length, width, thickness and longitudinal and lateral axes,
said
planar layer of fiber reinforced polymer comprising a thermosetting or a
thermoplastic polymer and reinforcing fibers, with at least about 70% of the
fibers
of said fiber reinforced polymer extending in a direction substantially
parallel to
the longitudinal axis of the planar layer of fiber reinforced polymer;
altering at least one major surface of the planar layer of fiber reinforced
polymer by sanding or abrasion to provide a uniform thickness and clean
bonding
surface to the planar layer of fiber reinforced polymer;
substantially aligning the longitudinal axis of the planar layer of fiber
reinforced polymer with the longitudinal axis of the wood member and
substantially continuously coating one or both of the machined major surface
of
the wood member and the altered major surface of the planar layer of fiber
reinforced polymer with a reactive hotmelt adhesive, followed by joining of
the
planar layer of fiber reinforced polymer to the wood membes and pressing of
the
joined surfaces together, causing substantially no squeeze-out of the adhesive
through the end joints of the wood segments and causing substantially no heat
related distortion of the wood member: and
CA 02314306 2000-07-19
7-19-2000 11:d1AM FROM OHLANDT.GREELEY 2033276401 P.19
- 12 - 323.5489 USQ1
curing the adhesive under ambient conditions to bond the planar layer of
fiber reinforced polymer to the wood member to produce a composite wood
board;
whereby said substantially continuous planar layer of the fiber reinforced
polymer bonded to the bottom surface of the wood member of the composite
board resists pop-out of the wood segments at the coupling portions at the
ends
of the wood segments and improves one or more of the flexural modulus,
strength and load carrying capacity of the composite wood board.
Brlef Description Of The Drawings
Fig. 1 is a perspective view of a van trailer showing the composite wood
flooring installed on cross-members with an I-section.
Fig. 2 is a longitudinal sectional view of a composite wood floor board
fastened to cross-members of an I-section.
Fig. 3 is the end view of the shiplap assembly of two adjacent composite
wood floor boards on an 1-beam cross-member.
Fig. 4a is a perspective view of laminated wood with several randomly
arranged hook joints.
Fig. 4b is a perspective view of finro opposing hooked ends of lumber
5tdps.
Fig. 4c is a perspective view of a perfect hook joint with little or no gap.
Fig. 4d is a perspective view of an imperfect hook joint with a significant
gap.
Fig. 5 is a perspective view of a conventional laminated wood floor board
with shiplaps and crusher beads.
CA 02314306 2000-07-19
7-19-2000 11:d2AM FROM OHLANDT,GREELEY 2033276d01 P.20
, - 13 - " 323.5489 USQ1
Fig. 6 is a perspective view of a reinforced composite wood floor board
with shiplaps and crusher beads.
Fig. 7 is a sectional view of a reinforced composite wood floor board of a
first embodiment of the invention.
Fig. 8 is a secttonal view of a reinforced composite wood floor board of a
second embodiment of the invention.
Fig. 9a is a sectional view of a lap joint between two lumber strips.
Fig. 9b is a sectional view of a finger joint between two lumber strips.
Fig. 9c is a sectional view of a butt joint between two lumber strips.
Fig. 9d is a sectional view of a scarf joint between two lumber strips.
Fig. 'i0a is a sectional view of a reinforced composite wood floor board
with two shiplap edges having bottom cuts.
Fig. 10b is a sectional view of a reinforced composite wood floor board
with a shiplap edge having a shallow bottom cut.
Detailed Description Of The Preferred Embodiment
The reinforced composite wood flooring of the present invention Is an
improvement over conventional wood flooring of truck trailers in that it
provides both
moisture proofing and reinforcement to such flooring. In order to understand
the
benefits provided by the composite wood flooring, it is first necessary to
understand the
construction of convcntional laminated wood flooring.
Convcntional wood flooring 11 for over-the-road truck trailers 12 such as
that shown in Fig. 1 is normally manufactured with hardwoods such as ash,
aspen, elm,
CA 02314306 2000-07-19
7-19-2000 11-d2AM FROM OHLANDT,GREELEY 2033276d01 P.21
- 14 - 323.5489 USQ1
yellow-poplar, and preferably oak, maple, birch, beech and the like, although
softwoods
such as Douglas fir and spruce could be employed. The green lumber used as a
starting maternal in such manufacture is suitably dried in special drying
chambers under
controlled conditions. The dried lumber is then sawed into strips 21 of
rectangular
cross-section and. defective portions are eliminated by cross cutting the
strips. During
the cross-cutting process, "hooks" 24 are formed at the ends of the lumber
strips (see
Fig. 4b). The relatively defect-free lumber strips are coated on their
vertical sides or
edges 25 with an adhesive such as urea-melamine formaldehyde or polyvinyl
acetate.
The uncured edge-glued lumber strips are then assembled on a conveyor by
placing
them side to side and behind other strips which were previously assembled
forming glue
lines 22 between adjacent strips 21. The adhesive is cured by applying heat
and edge
pressure to large sections of the assembled lumber strips thus forming a
unitary panel
of laminated wood 20 such as that shown in Fig. 4a. During the assembly of the
lumber
strips, "hook joints" Z3 are formed at each end of every strip (see Fig. 4c).
These joints
are simple mechanical couplings with no significant adhesive bonding. Often
times, due
to imperfect assembly, a readily visible gap 26 is formed at the hvvk joints
which can be
seen from the top and bottom surfaces of the completed laminated wood floor
(see Fig.
4d).
The cured laminated wood 20 is cut to a desired length (up to about 60
feet) and width (about 6 to 18 inches) and then machined to form several
laminated
wood boards 16 (see Fig. 5). Each laminated wood board 16 is planed to a
desired
thickness and shiplaps 18 and crusher beads 19 are machined on its sides. A
shiplap
18 is a rectangular projecting lip running along the length on each side of a
floor board.
The crusher bead 19 is a small semi-circular projection running along the
length on
each side of a board and placed above or below a shiplap 18. When the floor
boards
are assembled in a trailer such that the side edges of corresponding boards
are
squeezed together, the shiplaps 18 of adjacent boards overlap to form a seam.
The
crusher bead 19 provides spacing between adjacent boards and help in
preventing
buckling of the boards when they expand on absorbing moisture. A wood putty is
applied at the hook joints 23 on the top and bottom surfaces of the boards to
fill any
resident gaps. Finally, the underside of the floor boards are coated with a
polymeric
substance termed as "undercoating" 27 (Fig. 5) to provide moisture protection.
The
finished floor boards are assembled into a kit of about eight boards for
installation in
. trailers. Normally, a kit consists of two boards with special shiplaps so
that they will fit
CA 02314306 2000-07-19
7-19-2000 11_d3AM FROM OHLANDT,GREELEY 2033276401 P.22
- 15 - 323_5489 USQ1
along the road and curb sides 15, which are usually metallic components of the
trailer
12. The other boards may be identical in design and they are placed between
the road
and Curb side boards. In some trailers, a metallic component such as a hat-
channel
may be placed between any two ~djacent boards. The metallic component becomes
S part of the floor area. The boards adjacent to the hat-channel have side
edge profiles
designed to mate with the flanges of the hat-channel. Alt the boards are
supported by
thin-walled cross-members 14 of I, C or hat sections, each having an upper
flange,
which span the width of the trailer and are spaced along the length of the
trailer. Each
floor board is secured to the cross-members by screws 13 extending through the
thickness of the board and the flanges of the cross-members (See Figures 1-3).
The reinforced composite wood floor board 28 improves the above
described construction of conventional wood floor board 16 by reinforcing and
moistur~
proofing a laminated wood member 16 with a layer of fiber reinforced plastic
(FRP) 17
(as representatively shown in Figure 6). Two basic designs of the composite
wood floor
board 28 of the invention with laminated wood member 16 on top and FRP 17 on
the
bottom are presented below. These designs differ from one another in the width
of the
FRP as related to the face width of the wood member.
As shown in Fig. 7, the reinforced composite wood floor board Z8 consists
of a laminated wood member 16 with an underlayer of FRP 17. The shiplaps 18
and
crusher beads 19 are incorporated on the sides of the reinforced composite
wood floor
board 28 similarly to these in a conventional laminated wood floor board (Fig.
5). The
finished width of the FRP 17 is nearly equal to the face width of the wood
member 16.
During manufacturing, the starting width of the FRP is selected to be equal or
slightly
wider than the face width of the board. After bonding the FRP to the board,
the corners
are machined so that the FRP does not overhang the face width of the board.
The embodiment of Fig. 8 differs slightly from that of Fig. 7. in this case.
the FRP 17 has a narrower width than the face width of the wood member 1.6. At
each
of the lateral sides of the board, the edge of the FRP is at least 1/64"
inside the edge of
the wood member. By bonding the FRP to the wood member at the correct location
relative to the edges of the board, final machining of the lateral sides of
the composite
floor board is avoided.
Y
CA 02314306 2000-07-19
7-19-2000 11:d3AM FROM OHLANDT.GREELEY 2033276d01 P.23
- 1 s - ' 323.5489 USQ 1
A laminated wood member 16 with shiplaps 18 and crusher beads 19 is
fabricated by the process set forth above for producing conventional laminated
wood
floor boards. ,However, the wood member is not coated with an undercoating and
the
hook joints are not coated with a wood putty. If required, each hook joint at
the ends of
'the lumber strips is substituted with a tap joint 29 or a finger joint 30 or
a butt joint 31 or
a start joint 32 as illustrated In Figures 9a to 9d. In addition to using a
wood member
with edge profiles to produce a composite board as shown in Fig. s, other
types of
profiles are used to produce composite boards as shown in Figs. 10a and 10b.
The FRP is fabricated with continuous fibers in the form of continuous
rovings and fabrics. About 70% to about 100% of the fiber reinforcement are
aligned
along the longitudinal direction while the remaining fibers are aligned along
the lateral
direction of the FRP. The reinforcing fibers are glass, carbon or aramid
fibers or '
mixtures thereof. Glass fiber is more economical than carbon and aramid
fibers, but
provides lower weight savings and flexural modulus than the other fibers. For
higher
performance, carbon fiber is better suited to reinforce wood. Mixtures of
glass and
carbon .fibers can also be used to improve performance at moderate costs.
Epoxy resin is the preferred matrix' for the fabrication of the FRP. Other
thermoset and thermoplastic polymers such as vinyl ester, phenolic, polyester,
polypropylene and polyamide can be used to fabricate the FRP. The method of
fabrication of the FRP is dictated by the type of polymer selected.
Conventional
pultrusion and continuous lamination processes are better suited for
thermosetting
resins. Typically, in these processes the reinf4rcing fibers are placed under
tension and
wetted with a reactive liquid resin, which is subsequently cured around the
fibers. To
fabricate the FRP with a thermoplastic polymer, the fibers are coated with the
polymer
and then the coated fibers are consolidated under heat and pressure followed
by
cooling: Alternatively, co-mingled fibers of reinforcement and thermoplastic
polymer
can be used to form the FRP. Irrespective of the fabrication process of the
FRP, the
FRP for composite wood flooring is preferably designed to have 70°le to
100% of the
continuous fibers aligned along the longitudinal direction while the remaining
fibers are
aligned along the lateral direction of the FRP. The FRP sheet is preferably
sanded or
abraded on at least one side to render it flat and clean for bonding to the
wood member.
CA 02314306 2000-07-19
7-19-2000 ll:ddAM FROM OHLANDT.GREELEY 2033276d01 P.2d
- 1 T - ~ 323.5489 USQ 1
The laminated wood member with shiplaps and other edge details is
sanded or abraded on one side to develop a flatter surtace than that provided
by
planing. Alternatively, a knife-planed surface of the wood member can be used
for
bonding to the FRP. A reactive hotmelt adhesive is coated on the sanded or
planed
surface of the board. Preferably. the sanded surface of the FRP is also coated
with the
reactive hotmelt. Commercially available hotmelt roller coaters are used to
coat the
substrates with the reactive hotmelt. Typical weight of coating on any one
substrate is
about 5 to 20 gms/sq ft. The reactive hotmelt is applied on the substrates in
a molten
state at a temperature generally in the range of about 200°F to
350°F.
Prior to bonding, the edges of the FRP are aligned with respect to the
edges of the wood member. To~manufacture a composite floor board of Embodiment
I,
the width of the FRP is selected to be equal or wider than the face width of
the wood
member. After bonding the FRP to the wood member, the FRP is either in line
with or
19 overhanging the edges of the wood member. In case of an overhanging FRP on
the
wood member. a secondary machining operation is employed to trim the FRP and
wood. Since.glass and carbon fibers are hard to machine than wood, a softer
fiber such
as polyester or cellulose is employed at the edges of the FRP during its
fabrication. To
manufacture a composite floor board of Embodiment II, the width of the FRP is
selected
to be at least 1/16" less than the face width of the wood member, The edges of
the
FRP are aligned with respect to the edges of the wood member such that there
is no
overhang of the FRP over the edges of the wood member.
The, coated surface of the FRP is mated with the coated surface of the
wood member while maintaining proper alignment of the edges of the board and
FRP.
The joining of 'the FRP and wood member is done while the reactive hotmelt
coating is
in a tacky state. In case of a short open time of the reactive hotmelt. to
maintain the
tacky state of the coating, radiant heat is applied on the bonding surface of
the FRP and
wood member before or after the coating step. After the joining of the FRP and
wood
board, a series of rollers are used to apply pressure on the substrates.
Cooled air is
blown aver the substrates while pressure is applied to remove residual heat of
the
substrates and develop green strength of the bond. Quick development of green
strength helps to hold the FRP flat against the wood board and prevents
debonding at
the edges.
CA 02314306 2000-07-19
CA 02314306 2002-10-29
- 18 - 323.5489 USQ 1
To manufacture the composite floor boards in a continuous fashion, a
series of wood members of desired length and edge profiles are run one behind
the
other. The FRP is drawn from a roll of material and continuously joined to the
boards
as the boards pass below the roll. After joining the FRP and wood members, the
FRP is
cut between the ends of two boards next to each other. The cutting of the FRP
is done
by means of an automatic cut-off saw without stopping the flow of the boards.
A 10 foot long composite wood floor kit consisting of eight composite
boards was fabricated by bonding a glass/epoxy FRP to each of the eight
laminated
wood members using commercially available polyurethane reactive hotmelt,
namely
PUR-FECT LOK 34-9028* of National Starch and Chemical Company, The laminated
wood was made of red and white oak strips which were edge-glued using urea-
melamine formaldehyde adhesive. The fiber reinforcement of the FRP was
composed
of about 50 oz/sq yd of continuous glass rovings in the longitudinal direction
of the FRP.
A fabric weighing about 4 ozlsq yd of glass fibers oriented in the weft
direction was used
for transverse reinforcement. Wood members having a rectangular cross-section
and
without any shiplaps were used: The planed surface of the wood members and the
sanded surface of the FRP sheets were coated with a reactive hotmelt. Upon
joining
and pressing of the substrates with rollers, the composite boards were allowed
to cure
at ambient conditions for five days. The boards were then machined to provide
the
required shiplap profiles and crusher beads at the longitudinal edges. The
finished
thickness of the reinforced composite wood floor was about 1.125 inches.
Eight composite floor boards were installed in a partial section of a trailer.
The floor was supported by several 1-beam crass-members running along the full
width
of the trailer and regularly spaced at 12 inches along the length of the
trailer section.
The cross-members with a section of 4 inches by 2.25 inches were made of steel
with a
yield strength of 80 ksi and weighing about 3.2 Ibs/foot. Each floor board was
secured
to each cross-member in the test section by three screws running through the
thickness
of the boards and the top flange of the cross-member. A lift truck load
simulator with
two loading wheels was stationed on the floor. The simulator was loaded with
dead
weights so that a force of about 17,000 Ibs could be applied on the floor
through the
loading wheels. The loading wheels were stationed on the third and sixth
boards in the
eight board configuration of the floor. To subject the floor to fatigue
loading, the
simulator was moved back and forth on the floor. The simulator was allowed to
* Trade-mark
7-19-2000 11-dSAM FROM OHLANDT.GREELEY 2033276d01 P.26
- 19 - 323.5489 USQ1
complete 5,000 fatigue loading cycles, wherein during each cycle the simulator
moved
forward in one direction and then returned back to its starting line on the
floor. At the
end of 5,000 fatigue loading cycles, the reinforced composite floor
experienced little or
no significant damage. The loading wheels were repositioned on the first and
fourth
board and the fatigue test was redone for another 5000 cycles_ Since the
damage to
the composite floor boards was not significant, the fatigue test was continued
at 20,000
Ibs of loading on the same set of floor boards. The loading wheels were
positioned in
two different locations as described above and an additional 10,000 fatigue
load cycles
were applied. There was no catastrophic damage to the floor boards and cross-
members at any time during the test.
A conventional hardwood floor with a nominal thickness of 1 _38"
supported by standard cross-members at 12~ spacing is rated for 17,000 Ibs by
the
trailer industry. During fatigue testing, the conventional hardwood floor
typically
undergoes cracking of some wood segments and opening of some hook joints at
the
bottom side of the filoor. The mechanical properties of conventional hardwood
flooring
show a large variation due to the random location of joints and variation of
properties of
the wood segments.
Compared to the conventional floor boards, the composite floor boards
show superior performance with little or no opening of the joints of the wood
segments
at the bottom side of the floor. The composite floor boards show significantly
lower
variation of mechanical properties due to the strengthening of the hook joints
and better
distribution of load to the tensile bottom side of the floor. The thinner
composite floor of
this experiment weighed about 4.8 Ibs/sq ft, while the thicker conventional
oak floor
weighed about 5_4 Ibs/sq ft. Thus, the composite floor provides weight saving
over the
conventional hardwood floor while providing similar load capacity. By using
carbon
fibers or mixtures of carbon and glass fibers in a continuous roving form
along the
longitudinal direction of the FRP, additional weight saving and even higher
performance
can be obtained.
Since the undersid~ of the trailer flooring is subj~cted to water spray in
service, the environmental durability and aged properties of the floor is of
importance to
the long term performance of the floor. To determine the weathering
characteristics of
the floor boards the following accelerated environmental test was conducted.
Samples
CA 02314306 2000-07-19
7-19-2000 11:d6AM FROM ONLANDT.GREELEY 2033276d01 P.27
- 20 - ~ . 323.5489 USQ1
of composite floor boards with a thickness of 1" and conventional laminated
oak floor
boards with a thickness of 1.31" were tested. The sample boards with a length
of about
three feet and width of about 12" were fastened with screws to steel frames
built with
cross-members used in trailers to support the floor. The attachment of the
boards to
frames simulated a section of a single floor board of a trailer. The boards,
which were
attached to the frames were degraded by immersing them in water for seven days
and
then drying them in a kiln at about 140°F to 160°F for two days.
The soaking and drying
cycle was repeated once more. Finally, the boards were removed from the frames
and
subjected to bend test to determine the loss of ultimate failure load. It was
found that
the conventional oak floor suffered a loss of ultimate failure load from 5200
Ibs for the
virgin boards to 3980 Ibs for the degraded boards. On the other hand, the
composite
floor boards fabricated with glass/epoxy FRP and reactive hotmelt adhesive
suffered a
loss of ultimate failure load from 5920 Ibs for the virgin boards to 4690 1bs
for the
degraded boards. Further, conventional wood floor boards failed in a
relatively brittle
mode. The composite wood floor boards failed in a ductile fashion with little
or no
debonding of the FRP and without opening of the hook joints at the bottom
side. The
ductile failure mode and integrity of the composite boards provides higher
performance
to trailer floor.
With the foregoing description of the invention, those skilled in the art will
appreciate that modifications may be made to the invention without departing
from the
spirit thereof.. Therefore, it is not intended that the scope of the invention
be limited to
the specific embodiments illustrated and described.
CA 02314306 2000-07-19
