Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ACRGROUND OF ~E INVENTION
FIELD OF THE INVENTION
This invent~on relates to tubular poles which have
been cor.structed from laminated wood veneer and the method of
their manufacture. ;
DESCRIPTION OF T~E PRIOR ART
Solid wooden poles have been widely used as
utility poles ~or many decades. ~owever, as the old ~rowth
large diameter soft woods are gradually disappearing, the
ava~lability of suitable long solid wooden poles is becomln~
more scarce and the cost of same has increased dramatically.
Indeed, man-made laminated wood and composite wood materials
have been constructed and successfully used as substitutes
16 ~or solid wood utility poles as reported in, for example,
"Proceeding~ of the 6th Wood Pole Institute", 1965, page 65
- Bob McKa~n, and at page 69 of the same publication - ~d
Hockaday, and in the 1981 proceedings of the American Wood-
;, .~
Preservers Association entitled "Compole - The Composite Wood
Material Utility Pole".
~hile solid or hollow laminated wood poles as well
as wood chip composite poles are known in the art, at least
hitherto it has not been possible to successfully produce ~ ~
tubular poles of laminated wood construction. In Unlted ~ -
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States Patent 1,058,701 issued April 8, 1913 - Mutter, and
in United States Patent 2,543,901 - Dunne, which issued on
March 6, 1951, hollow tubular laminated poles constructed
from wood veneer are disclosed. Tn these prior art forms of
construotion, the tubular laminated wood veneer pole so
produced includes reverse spiraled wood veneer which
extending the length of the pole, no doubt to impart
additional strength to the side wall of the pole since the
use of an expansible fluid bag internally of the pole is
re~uired to impart sufficient outward pressure to achieve
proper adhesion of the adhesive between the laminates.
Needless to say, tubular poles constructed in the manner are
labor intensive, as well as being slow and difficult to
produce on a commercial scale and at a reasonable cost.
1 have found that laminated wood veneer poles
which have been constructed in accordance with my invention
are easy and faster to produce, and involve limited labor
requirements, when compared to the aforesaid pole
construotions of Mutter and Dunne.
Further, from an eng{neer~ng standpo$nt, the poles
constructed in accordance with the present invention exhibit
greater resistance to external loads imparted thereon over
the principal stress axis (the longitudinal axls of the
pole~. It should be noted that the tensile and compression
strengths of wood markedly decrease with increasing the grain
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angle to e~ternal load dtrection from O to 90 degrees. The
effect of ~rain angle on tensile and compression strengths
,~ can be e~pressed by the following formula - known as
Hankinson's formula.
al3 - __ a~ o, _
a" sinn~ + a~, coonl3
" ~' ':.
Where ~ and $ are the strength parallel and perpendicular
to gra~n directions, respectively, is the angle between the
load direction and grain direction, i8 the strength at
the grain angle , and n is the constant (e.g. 1.5 to 2 for
tensile strength and 2.5 for compression strength).
Although it is obvious that it is much easier to
treat veneer sheets with a presensitive made-up laminated
pole, the use of preservatives is of great environment
concern. It ls not easy to dispose of the heavily
preservative-treated veneer sheets which are pre-treated
prior to the course of pole manufacture. On the other hand,
it is not easy to treat, after fabrication, the laminated
veneçr pole with a preservative. This is because the veneer
~n the laminated pole is normally coated with an ex.terior
adhesive between the veneer layers, and the adhesive
therebetween forms a continuous lmpermeable film after
curin~.
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I have found that the preservative treatability of
; made-up laminated veneer poles or laminated veneer pole
sections can be dramatically improved if the adhesive used
between the layers of veneer does not form a continuous film
after curing thereby enabling the preservative to pass
therethrough. Improved permeability can also be
accomplished, w~thout impairing the performance in terms of
strength properties, by mechanically perforating in the pole
or pole section prior to treating same with a preservative.
Moreover, not only does my tubular pole possess
similar characteristics of solid wooden utility poles, but it
also has several advantages thereover. Natural defects such
as knots, holes and slop of grain common in solid wooden
poles are randomly found in my pole constructlon and thus are
advantageously dispersed among many piles of veneer.
Further, my tubular poles can be readily engineered as to
slze and propertie~ ln order to con~orm with the re~uirements
of various end use appllcations.
When compared to polygonal laminated wood poles,
tubular or rGund poles are easier to climb and, when
constructed in two pole half sections glued together, which
is one preferred form of construction, the likelihood of
glue-line failure is reduced. Polygonal wood chip composite
poles suffer the same shortcomings; and being harder, are
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more d~fficult to climb. They are also heavier, and more
difficult to handle.
SU~MARY OF TKE INV~NTION
The novel tubular pole of my invention is
constructed from two or more co-linear, elongate and
transversely curved, laminated wood veneer pole sections
which are ~oined together along their abutting edges to ~orm
the pole. Two pole sections are prefexred, as this results
0 in only two glue lines being exposed to the environment. It
will be appreciated, however, that three and possibly four
pole sections can be used although the prospect of failure at
the ~oints given the increased number of glue lines, can
result. Where three or ~ore pole sections are used in the
assembly, they can all be identical or substantially alike,
and certain portions of a pole section can be made larger
than the remainder when measured along the transverse
curvature whlch each pole section describes.
In constructing a pole section, a predetermined
number of layers of wood veneer coated w~th an uncured
adhes~ve i8 'llayed-upll on a support plate, with the wood
grain of the veneer in each layer or~entated in the
longitud~nal direction of the pole sectlon to be formed
therefrom.
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Optionally, and in order to improve the depth
penetration for a preservative applied to a pole or pole
section a~ter fabrication, the adhesive between the layers o
veneer may be coated in such a way that the cured adhesive
will not form a continuous film and which thus enables the
preservative to pass from one veneer layer to the next
through the voids in the discontinuous film of adhesive.
This may be achieved, for example, by using a foam adhesive
having abundant bubbles. The bubbles will collapse and leave
a discontinuous film after the veneer lay-up is pressed and
the adhesive is cured. Alternatively, the adhesive may ~e
applied to the veneer in random spacing, such as in strips or
s~nuously in order to permit migration of preservative
between Joined together layers of veneer. All or ~ust the
lnterlor layers of veneer may also be incised or perforated
prior to molding, again to promote penetration of the veneer
layers by a wood preservative.
once the laying up has been completed, it or it
and its supportlng plate is transversely curved in a press
which simultaneously effects curin~ of the adhesive. The
longitudinal edges of the curved and cured (now molded) lay-
up, are then trimmed so that the requisite number of pole
sections, each functioning a longitudinal pole segmen~, as
required to create the tubular pole, can be ~oined together
at their abutting trimmed edges.
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T~e number of layers of wood veneer in each lay-up
is predetermined as it represents the wall thickness of the
mclded pole section. The support plate on which the layerfi
of wood veneer are initially layed up, in addition to being
used as a carrier or vehicle for positioning the lay-up in
the molding press, can also usefully serve as a sliding
interface between the female pres~ face and the layer of
veneer abutting it and which, once molded, becomes the large
~0 radius side of the transversely curved pole section. The
bendable support plate which assists in positioning the lay-
up above the female mold during pressing, al~o assists in
mlnimlzing cracking or splintering of the veneer in each
layer during curve mold~ng, particularly with respect to
those veneer layers undergoing large radius curvature where
relative sliding mot~on between ad~acent layers is most
acute. Thin metal sheet, wlre mesh or a substitute such as
Teflon ~a trade mark), has been found to be suitable as a
support plate.
The need for bending the carrier plate with the
lay-up in the press may be dispensed with, provided the
molds, and particularly the upper edyes of the female mold
are rounded in order to facilitate ease of entry and minimize
cracking or splinterlng of the layer of wood veneer in
contact with it.
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,: ,, , .:As the tubular pole may be of substantial length,
two or more lengths of wood veneer sheet which are of
substantially the same thickness can be arranged in end-to-
end relationship in any given layer. These sheets can either
be joined together prior to lay-up, or physically joined
during the curving and curing press operation. The ~oints
themselves can be any one of scarf, lap and butt joints, and
when ~oints are required, the ~oints in any given layer can
be offset to those appearing in the remaining layers in
order to reduce the likelihood of stress failure during field
use. Additionally, and in instances where the fabricated
pole is of a substantial extent, each pole section may be
made up of two or more pole section lengths which have been
joined together in end-to-end relationship. In ~uch a case,
the joints between two lengths in a given pole section should
be off~et relative to any similar Joints in the corresponding
pole section.
Where two pole section~ are employed in the pole
assembly, as indicated above, they are preferably
substant$ally alike meaning they are effectively trimmed 80
that two pole sections can be joined ~ogether into a tubular
pole. Where t~ree pole sections are utilized in making up
the tubular pole, alike pole sectlons can again be
advantageously employed. If two or more pole sections used
in forming the tubular pole have butt joints, the trimmed
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pole sections can be identical, and can otherwise be
substantially alike if scarf, tongue and groove, splined or
other types of joints as known in the art are employed.
The number of layers utilized in the lay-up
depends on the density of the formed pole and the wall
thickness of the pole section to be formed and necessarily
the spacing between the press faces. ~he radius of
curvature of the female face determines the outer diameter of
the pole, and the male press face radius determines the inner
diameter of the pole; the difference therebetween determ$ning
the thickness of the pole wall. These press face~ can be
either uniformly transversely curved along their longitudinal
extent at a constant spacing for the purpose of producing an
uniform curvature, or tapered along their longitudinal extent
if it is desired to produce tapered pole sections and a
resultant tapered tubular pole.
The uncured resin used in coating the layers of
wood veneer is preferably a pressure or a pressure and
temperature curing exterior grade wood adhesive such as
phenol-formaldehyde resin, resorcinol-phenol-for~aldehyde
resin and isocyanat. Any suitable glue to best suit a given
application, can be e~ployed when ~oinin~ pole sections
together. These joints can be further reinforced using
other suitable ~eans such as strapplng or the like, as $s
known ln the art.
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The assem~led pole itself may be made from the
same or different wood species. Sapwood or heartwood may be
utilized as desired, in order to facilitate preservation
uptake. It w~ll also be apparent that the pole can be
treated with preservative to improve its durability or a
softening agent to improve its cllmbability.
The bottom portion of the pole may also be
specially treated or overlaid to increase its durability, or
to reinforce same in order to impart to it improved
performance in terms of strength. In this respect, by
relatively minor changes to the lay-up technique and the
spacing between the male and female faces of the press, the
wall thickness of the pole can be varied along its length,
such as making it thinner at the top o~ the pole and thicker
at the pole bottom. Further, different wood species can be
grafted into eaFh layer in strateyic locations along each
pole section, if thls type of wood species is regarded as an
attr~bute in the overall pole construction.
BRI~F DESCRIPTION OF T~E D~AWINGS
In the accompanying drawings which lllustrate one
working embodiment of my invention:
~igure 1 ~llustrates a cut-away view of an
elongate male press component as used when constructing
circular pole half sections;
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Figure 2 illustrates a cut-away view of the
corresponding female press component used in producing a half
section with a molded half section therein; and
Figure 3 i5 a sectional view taken lonsitudinally
of the molded layers of wood veneer in a pole section and
which illustrates the offsetting of veneer sheet ~oints in
each layer from the sheet joints in the remaining layers; and
Figure 4 is a cut-away view of a laminated wood
veneer pole when constructed from two alike half sections.
DETAIL~D DESCRIPTION OF T~ DRAWINGS
With reference to Figures 1 and 2, the elon~ate
male press component 1 and elongate female press component 2
as illustrated i8 used for forming longitudinal wood veneer
pole half sections 4 which are made from a lay-up of
laminated wood veneer. As depicted, the press components are
designed for press~ng a lay-up of a half pole section having
a uniform thickness throughout its length. The pole half
section may have a un~form radius along its length, or it may
be tapered along its length.
With reference to Figure 1, the male press
component 1, at one end has a radius of curvature rl from
point 10 and at its other end, a radius of curvature r2 taken
from point 11. If the pole section to be formed is of
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uniform radius along its length, r1 equals r2. However, if
the pole is to be tapered, r2 is made greater than rl.
The female press component 2, at one end, has a
radius of curvature R1 from point 10 as illustrated, and at -~
its other end, a radius R2 from point 11 as illustrated.
Again, for c1rcular poles R1 is equal to R2: but where the
pole is to be tapered, R2 i8 made greater than R1. Thus,
for a pole section of uniform thickness, the spacing between
press face 20 of male press component 1 and press face 22 of
female press co~ponent 2 is uniform along the length of these
components; the spacing therebetween being represented by the
thickness o~ the laminated wood veneer 4 and its carry plate
3 as seen 1n situ in Pigure 2.
IS it is desired to laminate pole half sections
which are thicker at one end than the other, the spacing
between face 20 and face 22 of press components 1 and 2 is
not uniform, but rather the ~pacing therebetween increasec
toward the end which is to become the thick end of the :
finished pole. ~: :
The upper portion of male press component has a -: -
diameter 2r1 which corresponds to the 2r1 diameter of the
laminated pole section 4 shown in Figure 2. It will be
observed that the axis of revolution taken through points 10
and 11 lies below the back~ng face 30 of male component 1,
and also below the upper longitudinal edges 32 of laminated -~
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pole section 4. The distance therebetween represents the
amount of the laminated wood which may be cut off or trimmed
from the formed pole half section.
Carry plate 3 undergoes deformation with the wood -
veneer laminate and in addition to supporting the lay-up
during its posltioning in the press, serves to avoid breakage
or splitting of the layers of wood veneer and particularly,
those layers adjacent plate 3 which otherwise can occur as
the lay-up ic pressed into female component 2. As indicated
above, the grain of wood in each layer is or~entated
longitudinally of the pole half section.
Typically, tubular pole half sections of uniform
inner and outer radii along their length can be malded in a
press, where the radius rl e~uals r2 and R1 equals R2 which
renders a wall thickness of R1 ~ r1 minus the thicXness of
the carrier plate 3.
.: .
The longitudinal cross-sect10n v~ew of the pole
wall 18 seen in Figure 3 as laminate 4 overlying carrier
plate 3. Scarf joints 40 interconnect adjacent veneer sheets
in each layer, and these joints are offset relative to the
joints of sheets found in other layers of the la~inate. As
ment~oned previously, the woo~ grain in ea~h layer of ~eneer
is aligned and extends in the same direction of the pole or
pole section.
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The assembled pole 50 as seen in F~gure 4 is of
- uniform thickness and has the same inner and outer diameter
along its length. The pole i8 formed from two alike pole
sections 51 and 52. Pole sections 51 and 52 have been formed
in a press as above described, and have had their edges
trimmed 80 that each pole section describes an arc of 180
such that they are thereafter joined together along butt
~oint 56 and glue line 53.
~0 Optionally, and if desired, the glue ~oints can be
supported or strengthened using strapping rings 55 positioned
thereabout in a manner as is well-known in the art. Fur'her,
and as indicated above, the connecting ~oint can be any
sultable type of joint such as a butt, scarf, tongue and
groove or spline, as i8 known in the art, and thus two pole
sections can be the same s~ze, or of slightly dif~erent size.
As indicated above, the adhesive film bstween the
layers o~ veneer may be discontinuous, or the adhesive can be
randomly applied so as to permit a wood preservative to pass
through ad~acent layers of veneer of the molded pole or pole
section. In order to also promote the migration of
preservative into the interlor of the molded pole or pole
section, the molded veneer can also be incised or its
interior veneer layers perforated.
