Note: Descriptions are shown in the official language in which they were submitted.
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HIGH STRENGTH COMPOSITE PRODUCTS
AND METHOD OF MAKING SAME
Field of the Invention
The present invention relates to high strength composite products.
More particularly the present invention relates to a high strength composite
product made from wood elements substantially free of surface and internal
damage and to a method of producing the composite product.
Background of the Present Invention
One of the more important properties of any structural product
such as panels or lumber products is the modulus of elasticity (MOE).
Obviously other properties such as modulus of rupture (MOR), tensile strength,
compression strength, etc., also are factors but the MOE for many applications
is the critical characteristic.
Composite wood products having high strength in particular a high
MOE have been sought after for many years. The Barnes U.S. re-issue patent
30,636 issued June 2, 1981 (a re-issue of U.S. Patent 4,061,819 issued
December
6, 1977) is believed to be the first recognition that the strength of
composite
product could be significantly increased. This patent teaches that strength is
density dependent, i.e. the higher density generally the higher the strength
of the
product for the same starting materials and that by changing the starting
materials, particularly by increasing the length of the strands used, the
strength
to density ratio could be significantly improved. This system utilized wood
elements in particular strands having lengths of at least 12 inches, width of
0.05
to 0.25 inches and thickness of 0.05 inches to 0.5 inches formed by slicing
and
then clipping. The widths and thicknesses specified in this patent are the
opposite to what one would normally define as width and thickness in a
waferizing operation or in producing a clipped veneer strand, i.e. normally
the
thickness is determined by the thickness of the veneer and the width is
determined by the spacing between adjacent clips whereas with the Barnes
patent the width of the strand is the thickness of the veneer and the
thickness
of the strand is the spacing between clips.
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In any event the strength characteristics of the products produced
using the Barnes teachings produced wood products having MOE's in the order
of up to about 2.2 mm psi at a wood density over 35 lbs./cubic foot using
strands 24
inches long.
The Holman patent 4,255,477 issued March 10, 1981 also relates
to panel or strand lumber products having improved strength. This patent
teaches the use of wood elements, in particular 'boat shaped wood strips'
having
lengths in the order of 8 to 12 inches and according to his examples was able
to
successfully produce a board product having an MOE of l.7mm psi at a board
density of -about 48 (wood density probably around 44 lbs/cubic ft.) and a
second product having an MOE of l.6mm psi at a slightly higher density.
Holman attributes his 'high' strength products to the use of a variety of
particularly shaped and sized elements that are substantially boat shaped in
axial
cross section and had lengths up to about 12 inches.
More recent patents of Barnes namely U.S. Patent 4,610,913 and
4,751,131 issued September 9, 1986 and June 14, 1988 describe a high strength
panel product and a high strength lumber product respectively made from long
wafers (lengths 6 to 12 inches and longer). Prior to these teachings, panels
or
lumber products made of wafers always employed short wafers in the order of
up to 4 inches in length and the art clearly taught that extending the length
of
the wafer brought no significant benefits in increased strength and thus for
many
years, until the more recent teachings of Barnes, it was believed that if
wafers
were used to produce composite wood products extending the length of the
wafer beyond about 3 inches was of no merit.
The latest Barnes patents teach that as the wafer length is
increased the MOE to density ratio for a panel' product can be increased
significantly and with a wood density in the order of about-35 Ibs/cubic ft.
panels having MOE's in the order of l.6mm psi could be obtained using wafers
over about 12 inches in length and that with higher wood densities and longer
lengths the MOE could be further increased.
The lumber product described in U.S. patent 4,751,131 produced
a lumber product having a wood density in the range of about 35-40 psi using
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wafers over 8 inches long having MOE's in the range of about 1.6 to l.7mm psi
which was significantly higher than the MOE's for composite lumber products
produced in the prior art.
Laminated veneer lumber is usually made by peeling veneer from
a log by rotating the log and peeling a ribbon of veneer fiom the surface of
the
log. Generally the resulting veneer is eight foot long measured in the grain
direction, i.e. axially of the log being turned and has a thickness in the
order of
about 0.1 inches. A laminated veneer lumber is produced by laying up a
plurality of layers of such veneer with the grain extending substantially
parallel
on each of the layers and securing the layers together under heat and pressure
using an adhesive such as a phenol formaldehyde. The veneer sheets, when they
are peeled, generally have checks (lathe checks) extending in the grain
direction.
These checks are formed by the peeling operating itself.
Laminated veneer products made as above described generally
have MOE's up to about 2.lmm psi at wood densities in the range of about 35
lbs/cubic foot. Repairing of the lathe checks by addition of extra resin has
been
attempted but no one has reported that this contributed significantly to
increasing the MOE of the laminated veneer product made from such repaired
veneers.
Brief Description of the Present Invention
It is an object of the present invention to provide a composite
wood product having an MOE of at least 2.3mm psi at a wood density of 35
lbs/cubic foot and a method of producing such a product.
The present invention is based on the finding that if the wood
elements, (i.e. the veneer or wafers or strands) used to produce the wood
product are cut in a manner to substantially eliminate surface and internal
damage, the stiffness of the resultant wood composite will be increased
significantly and that by proper sizing and alignment of the wood element
composite products having MOE's of at least -2.3 ~rii -Fsi
at a wood density of 35 lbs/cubic foot could consistently be produced.
Broadly the present invention relates to a consolidated composite
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wood product having modulus of elasticity (MOE) equivalent to a MOE of at
least 2.3mm psi at a wood content density of 35 lbs/cubic foot, comprising
wood
elements formed by slicing wood blocks having the grain of the wood
substantially parallel to the longitudinal axis of the block with a knife
having a
cutting edge extending substantially parallel to the grain, and oriented to be
substantially transverse to the axis of the block or substantially parallel to
the
axis of the block (within 10 degrees of parallel or perpendicular to the
block)
during the cutting, said elements having a thickness in the range of 0.005 to
0.1
inches (preferably 0.01 to 0.05 inches) and a length of at least 8 inches,
said
wood elements having their grain substantially parallel to their longitudinal
axis
and having their said surfaces formed by cutting by said cutting edge and
substantially free from said surface and internal damage, said wood elements
being arranged with their longitudinal axes aligned within + 10 degrees of the
longitudinal axis of said composite wood product and consolidated into said
consolidated composite product having an MOE equivalent to a composite wood
product having a MOE of at least 2.3mm psi at product a wood content density
of 35 lbs/cubic foot.
Preferably said longitudinal axes of said wood elements will be
aligned within + S° of said longitudinal axis of said consolidated
composite
wood product being produced.
Brief Description of the Drawings
Further features, objects and advantages will be evident from the
following detailed description of the preferred embodiments of the present
invention taken into conjunction with the accompanying drawings in which:
Figure 1 is a schematic illustration of one of the cutting action of
the present invention.
Figure 2 shows a typical wood element formed in accordance with
the present invention and used to produce the composite product of the present
invention.
Figure 3 is a schematic of the various steps in the typical
forming of a cca~OSite product.
WO 93/13922 PCT/CA92/00005
~~.~6456
Figure; 4 is a graph indicating the tension of products made with
0.100" veneer produced by a slicing action of the present invention and
product
made with 0.100" standard peeled veneer showing the change in strength with
change in grain angle to the longitudinal axis of the product being tested.
5 Figure: 5 is a graph similar to Figure 6 but illustrating MOR for
sliced and peeled veneers having their grains arranged at different angles to
the
longitudinal axis of the product being tested.
Figure 6 is a graph of MOE for products made with 0.10" thick
sliced elements made in accordance with the present invention and products
made with 0.10" conventional peeled veneer showing the difference in MOE
using conventional veneer and sliced veneer (or wafers) made in accordance
with the present invention.
Figure 7 is a graph of grain angle versus MOE for products made
using the present invention but having different veneer and strand thickness.
Description of the Preferred Embodiments
It has been found that by slicing wood elements from a wood
block without causing surface and internal damage to the wood elements so
produced that the MOE of a consolidated composite product made from such
wood elements may be significantly increased to above that of high grade solid
wood.
As shown in Figure 1, a wood block or log 10 is being sliced by a
knife 12 having a sharpening angle A forming a cutting edge 14.
The angle A designates the bevel angle of the knife 12 and angle
B designates orientation of the cutting edge 14 to the longitudinal axis 16
(grain
direction) of the log or block 10.
If strands are desired, the veneer must be separated into strands,
it is possible to cause; said separation by defecting the veneer as it is
being shred
using a breaker bar (not shown) positioned on the face of the cutting edge but
it is preferred to slice a veneer sheet the size of the exposed face and then
clip
the veneer into strands if strands are required, i.e. veneer or strands.
In forming veneer by the conventional slicing process, a pressure
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bar or roller 20 immediately precedes the cutting knife and is used to control
the cutting operation of the slicer.
The angle A preferably will be maintained quite small (preferably
less than about 25°) and the knife 12 and wood will be relatively moved
in a
S direction with the edge 14 substantially parallel to the longitudinal axis
of the
wood, i.e. the angle B between the edge 14 and the. longitudinal axis of the
wood
(grain of the wood) should not exceed + 15 degrees. The thicker the veneer
being sliced preferably the smaller the angle A.
Similarly, the trajectory of the blade across the face of the wood
10 should be substantially in a straight line for the best possible results
however
using rotating dicer wherein the arc of the wood block relative to the knife
is
about 3 foot radius is satisfactory.
The above description has dealt with relative movement of the
cutting edge 14 and wood in a direction substantially perpendicular to the
grain.
It is also possible to produce a sinular wood element by relatively moving the
cutting edge 14 and wood block substantially axially of the block (in the
direction of the grain) with the cutting blade at about + 10 to 20° to
the
longitudinal axis (to the grain direction) of the wood. In this case only
veneer
sheets are produced. These sheets may be later clipped or broken into strands
as desired using a separate step applied to the separated veneer sheets.
It has been found that wood elements such as the element 22
shown in Figure 2 and produced by slicing as above described have their its
major surfaces 24 and 26 substantially free of surface and internal defects
(such
as checking, splitting, tension breaks, etc.) and for the most part the
elements
produced demonstrate an edge grain, i.e. the grain running directly from
surface
24 to surface 26 in a substantially straight line path.
Applicant has found that a veneer for use in the present invention
may be produced by a conventional slicing process used commercially to produce
high grade veneer for decorative purposes. Thus it is believed that any
equivalent slicing action should yield a wood element suitable for the present
invention.
To obtain the required strength characteristics in the composite
WO 93/13922 ~ ~ ~ ~ ~ PCT/CA92/00005
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product it is also necessary that the length L of the wood elements be at
least
8 inches and preferably 12 inches or more and that the thickness not exceed
0.1
inches and preferably be less than 0.05 and may be as thin as 0.005. At very
small thicknesses the cost of may exceed any advantages gained by the
reduction
in thickness. Preferably the average thickness of the elements will be 0.01 to
0.05 inches. The width is not as important but in any event normally will not
be
less than .25 inch. Obviously when a laminated veneer lumber product is being
made size of the elements 22 will be considerably longer, probably in the
order
of about 8 feet and the width will correspond with the trimmed width of the
face
of the block from which the veneer sheet is produced by slicing.
Figure 3 schematically illustrates a typical sequence of process
steps for producing a consolidated wood product. The wood elements 22
(veneer or strands) are first produced by the slicing action in the cutting
station
30 described above. They are then dried as indicated in the station 32,
adhesive
applied in the station 34, a lay-up formed in the station 36 and the lay-up
pressed in station 38 to produce the multi-layered consolidated composite
product 40 which may be formed by laying up the sheets of veneer or layers of
discrete wood strands oriented as above described, i.e. grain at less than ~
10°
to the longitudinal .axis of the consolidated product and preferably less than
S°.
A comparison of the structural properties of composite products
1/2 inch thick formed using wood elements of the present invention with other
wood elements is provided by Table 1 comparing MOR and MOE of products
made from peeled veneers with product made from sliced veneers produced in
accordance with the' present invention.
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TABLE 1
Thickness Species MOE Tensile MOR
(inches) MMpsi Mpsi Mpsi
Peeled 0.020 to Douglas 2.10 12.00 18.00
0.125
Veneers Fir
Sliced 0.10 Douglas 2.68 12.8 18.5
Veneers Fir
0.05 Douglas 2.72
Fir
0.025 Douglas 2.91
Fir
0.025 Aspen 3.09
Products made with peeled veneers made in accordance with the
prior art peeling technique, having a thickness of 0.20 to 0.125, showed
little
difference in Tensile, MOR or MOE strengths for the samples tested regardless
of veneer thickness used.
It will be noticed that the product made with sliced veneers of a
thickness 0.1 inches had essentially the same Tension and MOR as the peeled
veneers yet the MOE was significantly higher. The MOE of the sliced veneer
product increased significantly as the thickness of the veneer was reduced.
Figures 4 to 7 show various strength characteristics at an
equivalent wood content density of 35 lb/cu.ft.
Figure 4 shows the change in tensile strength of composites
produced with different angles of the grain, i.e. the angle of the grain
relative
to the direction of stress application. This figure indicates that for a 0.1
inch
veneer the manner in which the veneer was produced (i.e. sliced or peeled)
made no difference in tensile strength and that in either case the tensile
strength
reduced dramatically with increase in angle.
Similar results were obtained when testing the products for MOR
and comparing peeled and sliced veneers of 0.1 inch thickness (see Figure 5).
There is a major discernible difference between these products in
MOE. The results plotted in Figure 6 show that the product made with sliced
veneer (0.1 inch thickness) had a significantly higher MOE than the one made
212fi45G
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with peeled veneer (0.1 thickness) up to a grain angle to the direction of
stress
applied (i.e. to the longitudinal axis of the specimen being tested) of about
5° and
retained some improvement up to a grain angle of about 10°. Wh ~n the
grain angle
exceeded 10° both products (i.e. peeled veneer or sliced veneer) were
essentially the
same. Thus it will be apparent that to, obtain the benefits of the present
invention
- using wood elements substantially free of surface or internal damage
orientation of
the strands or veneers is extremely important and must be within 10 and most
preferably within 'i° of the longitudinal axis of the product.
Figure 7 shows the difference in strength (MOE) obtainable by changing the
thickness of the sliced veneer. It is apparent that the thinner sliced veneer,
i.e. the
0.025 inch veneer Izad significantly higher MOE at any grain angle than the
product
made with 0.10 in<:h thick veneer. With a veneer at thicknesses of 0.1 the MOE
of
the product was not above 2.3 mm psi at a wood density equivalent to 35
lb/cu.ft
unless the angle of the grain was less than about 5°.
Having described the invention, modifications will be evident to those skilled
in the art without departing from the scope of the invention as defined in the
appended claims.
AMENDED SHF~'
