Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR MANUFACTURING WOOD POLES
TECHNICAL SCOPE
The invention relates to a method for manufacturing wood
poles consisting of a number of sections which are glued toge-ther
along abutting side surfaces so that a tubular pole with central
cavity is formed. Poles of this type can be used primarily as
power line poles but also as rnasts of various types, columns for
buildings, bridges etc.
STATE OF THE ARI'
For many years power lines have been constructed using
natural poles made from pressure-impregnated pine. Because of
developments in modern forestry however there has been a drastic
reduction in the availability of full-grown timber and hence also
of natural poles having the requisite dimensions. Because of -this
poles of glued -timber have been developed which are designed to
replace natural poles. Examples of such designs are shown in
DE 665 210, GB 745 540, FR 2 348 345 and WO ?30/02709.
In spite of the urgent demand for glued poles and in
spite oE the fact that a plurality of glued pole designs have
been produced in past years, the tubular glued timber pole has not
as yet however been widely employed for power lines and simi]ar
demanding applications. One reason for this is tha-t fro-m the
production viewpoint these poles give rise to a number of problems
which have not been satisfactorily solved using available tech-
niques. These problems concern both the jointing and the gluing
of the individual sections, also the requi,site impregnation of the
glued construction,
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DESCRIPTION OF THE INVENTION
According to one aspect of the inven-tion a method for
manufacturing wood poles as of -the type cornprising a number of
sections glued together along abutting side Eaces so as -to form
a tubular pole with a central cavity comprises:
the steps of providing a number of sections having a
trapezoidal shape, each section having side faces abuttable with
side faces of other sections, providing the side faces with glue
to provlde glue-bearing side faces, and bringing the glue-bearing
side faces into intimate contact with each other to provide a
tube in which the sections define a central cavity, placing seal-
ing means at both ends of the tube for sealing the ends of the
tube, pumping air out of the central cavity through one or both
of the sealing means to provide a vacuum in the central cavity
in comparison to the external pressure, so that contact pressure
between abutting side faces increases, and maintaining the vacuum
until glued joints are formed to hold the sections together.
Sealing devices may be arranged between the central cav-
ity and the glued joints to prevent communication between the
central cavity and the glued joints wlile -the glue is curing.
The abuttable side faces may be provided with circular
tongues and grooves.
The number of sections is preferably more than 10.
Each of the sections may be made up of 2-~ pieces of
timber layers~ which are glued together with the sapwood facing
a base of the -trapezoidal shape.
The tubular pole may be subjected to an external posi--
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tive pressure as compared with surrounding pressure, whereby the
contact pressure between abutting side faces is further increased.
The tube may be hea-ted during gluing of the sections
together by hot air in the cen-tral cavity or by hot air ex-ternally
of the tube.
According to another aspect of the invention a method
for manufacturing wood poles comprising sections glued together
along abutting side surfaces so as to form a tubular pole with a
central cavity comprises:
the steps of providing a number of sections having a
txapezoidal shape, each section having side faces abuttable with
side faces of other sections, gluing the sections together along
the side faces to provide a tube with a central cavity, placing
sealing means a-t both ends of the tube for sealing the ends of the
tube, pumping air out of the central cavity through one or both
of the sealing means to generate a reduced pressure in the tube,
whereby contact pressure between abutting side surfaces increases,
and maintaining the reduced pressure until glued joints are formed
to hold the sections together.
Further characteristics and advantages of the invention
are outlined in the patent claims and are illustrated by the
following description of a preferred embodiment.
~RIEF DESCRIPTION OF DIAGRAMS
In the following description of a preferred embodiment
reference will be made to the appended drawings in which
Figure 1 is a perspective view of a section of the type
from which the pole is to be manufactured in accordance with the
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invention.
Figure 2 is a perspective view which illustrates pole
manufacture.
Figure 3 illustrates the same feature as Figure 2, in
side elevation.
Figure 4 is a section on the line IV-IV in Figure 3.
Figure 5 is a section on the line V-V in Figure 3.
Figure 6 illustrates the conditions prevailing in the
glued joint.
DESCRIPTION OF PREFERRED EMBODIMENT
With reference initially to Figure 1 a section Eor manu-
facture of the pole in accordance with the invention is generally
designa-ted as 1. The section 1 has a profile shaped like an
isosceles parallel trapezoid and is made up of three glued lamin-
ations 2, 3 and 4. The base surface of the section is designated
as 5, its top surfaces as 6 and its two side surfaces as 7 and 8.
The two side surfaces 7 and 8 are provided with tongues and
grooves in the form of grooves
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9 and tongues 10. During assembly the sections 1 are arranged so
that the side faces 7 on adjacent sections are placed against each
other, whereby the tongues 10 fit into the grooves 9. lhe base
surfaces 5 form the outside and the top surfaces 6 form the inside
of the finished pole. The tongue and groove 9, 10 are parallel with
the edge lines 11, 12 between the side surfaces 7, 8 and the top
surface 6. In accordance with the embodiment illustrated tbe section
1 is a~solutely uniform, i.e. has the same cross sectional area
along its entire length, so that the tongue and groove 99 10 are
also parallel with the lower edge lines 13, 1~, but it is also
possible to plalte the base surface 5 so that the section 1 tapers.
This has been indicated by the dashed line 13' which in this case
is not parallel with the tongue and groove 9, 10. The three lamina-
tions 2, 3, and 4 are further sawn and laid in such a way that the
sapwood faces towards the base surfaces 5, i.e. towards the outside
in the finished pole. The laminations 2, 3 and 4 are furthermore
composed appropriately, in a manner which forms part of the state
of the art, of finger-jointed sections, so that the desired length
can always be obtained. Fig. 1 shows also that the tongue and groove
9, 10 is placed considerably closer to the edge lines 11, 12 than to
the edge lines 13, 14 so that the base surface 5 can be planed down,
if so required, without cutting the tongue and groove at the narrow-
est end.
About 2mm from the edge line 12 the side surface 8 is also provided
with a small projection in the form of a "mini-tongue" 30 t~hich
extends along the entire length of section 1. The mini-tongue 30 is
about 1mm wide and ~ to 1mm in height. Its function is to provide
a seal for the glue in the glued joints 31, Fig. 6, so that the
glued joint cannot communicate with the cavity 23. In Fig. 6 the
thickness of the glued joint 31 has been exaggerated for the sa~e
of clarity.
During jointing the side surfaces 7 and 8 are provided with glue
and are then pla-ced in a fixture 15; Fig. 2 and Fig. 3, with semi-
circular-shaped support 16~ First of all a numher of sections 1 are
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placed in this support 16, the sections being orientated with
respect to each other in the desired manner by means of the rQund
tongues and grooves 9, 10. Then a vertical ring 17 is placed at
both ends, after which the layer is completed by adding further
sections 1. Some straps 18 are then wound around the whole assembly
and tightened so that the side faces 7, 8 are pressed firmly against
each other. The two ends of the tube 19 thus formed are cut off so
that the end faces are absolutely even~ after which the ends are
sealed by a pair of covers 20 and 21.
The covers 20, 21 consist of plates 22, the outsides of which are
domed so that they can withstand an external overpressure relative
to the central cavity 23 of the tube 19. On the inside the covers
20, 21 are~ absolutely flush and provided with a ringshaped fairly
~ide rubber packing 24. One cover 20 is provided with an extraction
pipe 25 which is connected with the cavity 23, whilst the other
cover 21 is provided in a corresponding manner with a manometer 26
for measuring the pressure in the cavity 23. Thus when the covers
20, 21 with packings 24 have been placed against both ends of the
tube 19 and are pressed against the ends at a certain pressure, the
air in the cavity 23 is pumped out through the pipeline 25. Until
the vacuum produced in the cavity 23 is so great that the covers
20, 21 are sucked firmly in place1 the covers 20, 21 can be held
in position manually. The pumping out of the air then continues
until the pressure in the cavity 23 has dropped to the desired level,
appropriately to about 0.1 kplcm2. Subsequently this same pressure
difference is maintained between the pressure in the cavity 23 and
the surrounding pressure until the glued joints 31 in the tube 19
have become fixed.
During the assembly of the sections the mini-tongues 30 are pressed
against the opposing side face 7 and to some extent are also pressed
into this. Hence the tongues 30 function as a seal which effec~ively
cuts off the glue in the glued joint 31 from the cavity 23. When the
air is pumped out of the cavity 23, the glue in the glued joints 31
is consequently not sucked into the cacity 23 and the glue does not
start to bail because of the pressure reduction in the cavity 23.
When the glue in the glued joints 31 has hardened so that the joints
have become fixed, the straps 1~ are removed together with the
covers 20, 21 and the supporting rings 17. For this purpose the
latter can be provided with a pair of clamps 27. The pole 19 can
then be transferred to store for su~sequest curing. Finally the pole
19 is impregnated with creosote oil both from the outside and from
the inside in a known manner. As the sapwood faces the outside of
the pole and the grain is orientated in the manner indicated in
the diagrams, this greatly iacilitates the penetration of the impreg.
nation agent.
To increase the gluing pressure it is feasible and possible in
accordance with the invention to subject the outside of the pole
l9 to an overpressure, whilst at the same time a vacuum is produced
in the cavity 23. The ent~re structure illustrated in Fig. 2 and
Fig. 3 is tl1en placed in a pressure vessel in which a positive
pressure is brought about by means of compressors, whilst the air
is simul~aneously pumped out through the pipe 25. To shorten the
gluing time it is also possible to heat up the residual air in the
cavity 23. For this purpose a further connecting pipe 28 can be pro-
vided so that hot air is made to circulate through the cavity 23
so that the pole is heated up from the inside before the air is
pumped out. Even whilst the vacuum is maintained in the cavity 23,
it is possible to allow certain quantities of hot air to circulate
within the cavity. I~ a positive pressure is also applied to the
outside, it is possible in the same way to heat the air in the
pressure vessel so as to obtain a temp~rature rise also from the
outside with a view to shortening the gluing time. Whilst the glue
is curing, the pressure in the cavity is checked continuously so
that it is maintained at the desired level~
The gluing pressure ~or vacuum gluing in accordance with the inven-
tion9 possibly combi~ed with positive pressure treatment~ ls cal-
culated as follows.
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t . D _ r where
2 . m
m = wa]l thickness, cm
t - vacuum ~ possible overpressure, kp/cm
D = external diameter of tubular pole, cm
T = gluing prcssure, kp/cm2, in glued joint 31
The dimensions of the pole can be varied wi-thin wide limits. For
practical reasons the upper limit can be taken as 40 m,whilsta lower economic
limit is about 0.5 m. Ihe external diameter can also be varied within wide
limits. For efficient handling only a restricted number of dimensions for the
sections 1 should be employed. But even with a very restricted number of
section sizes the external diameter can be varied between circa 350 and 1 300 mm,
which gives a wall thickness range between circa 50 and circa 225 mm.
For manufacturing it is best to use a glue which is made and marketed
by the Norwegian company Dyno A/S under the tradename Dynosol S 204, together
with the hardener recommended for this Dynosol H 627 which requires a gluing
pressure of circa 2.0 kp/cm2. With the method in accordance with the invention
this gluing pressure can be achieved for all the dimensions encountered in
prac~ice without it being necessary to apply a positive pressure.
If the vacuum amounts ~o 0.9 kp/cm2 ~0.1 atmospheres gauge) in an
assumed example where D = 48 cm and m = 9 cm the following gluing pressure is
obtained:
D = 0 9 48 = 2.4 kp/cm2
2 . 9
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