Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02238353 1998-OS-22
47865-8
WOOD TREATMENT PROCESS TO PREVENT
SPLITTING AND CHECKING DURING DRYING
FIELD OF THE INVENTION
This invention relates generally to a process for
treating wood, and more particularly, to a treatment
process to reduce the tendency of a wood pole to split
and check during subsequent drying by passing an electric
current through the wood.
BACKGROUND OF THE INVENTION
In the following description, the term "pole" is
defined as an elongate portion of a tree trunk or tree
branch that is created by making cuts across the full
cross-section of the tree or branch at both ends. The
pole thus includes bark, phloem tissue, xylem tissue, and
heartwood as will be more fully explained.
Pine and spruce poles tend to split and check during
air drying or seasoning which make the poles unsuitable
for carving and turning on a lathe to create walking
sticks. Green wood poles cut from the trunk or branch of
live pine or spruce trees have been found to check and
split during air seasoning. Dead wood poles, defined as
poles cut from the trunk or branch of dead, still
standing trees whose sap has stopped flowing, have less
water content than green wood, but are also prone to
checking when air dried. Cracking and checking is caused
by the outer surface of the pole drying faster than the
interior wood of the pole.
A currently marketed chemical treatment for the
control of shrinkage and swelling of wood is a member of
a whole family of polyethylene glycols. Polyethylene
glycol is best used on green wood as soon as possible
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after the wood has been cut. The wood is soaked in the
Polyethylene glycol till the chemical is absorbed
throughout the wood. Wood stabilized with polyethylene
glycol is left impregnated with the chemical.
SUMMARY OF THE INVENTION
There is a need for a chemical-free, inexpensive
method of stabilizing wood pieces, such as pine or spruce
poles, to permit drying of the pieces without splitting
or checking which reduces the quality of the wood or
renders it unusable.
Broadly stated the present invention is directed to
a treatment method in which electrodes are driven into
the center of each end of the pole. Wire conductors are
connected to the electrodes and an electric current is
passed through the length of the pole prior to the pole
being subjected to air drying.
Accordingly, the present invention provides a method
for treating an elongate wood piece to be dried, the wood
piece being a complete cross-section through a tree trunk
or branch and including bark, phloem tissue, xylem tissue
and heartwood, comprising the steps of:
a) passing an electric current through the length of
the wood piece for a pre-determined period; and
b) removing the bark layer before or after step a)
whereby the tendency for the wood piece to split or check
during subsequent drying is reduced.
In a further aspect, the present invention provides
a method for drying an elongate wood piece, the wood
piece being a complete cross-section through a tree trunk
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or branch and including bark, phloem tissue, xylem tissue
and heartwood, comprising the steps of:
a) treating the wood piece by passing an electric
current through the length of the wood piece for a pre-
y determined period to reduce the tendency of the wood
piece to split or check;
b) removing the bark before or after step a); and
c) storing the wood piece in an environment for drying
of the wood.
Preferably, the passage of electric current through
the length of the wood piece is achieved by inserting
electrodes into opposite ends of the wood piece, placing
the wood piece on an insulating surface, and connecting
the electrodes to a power source to deliver current
through the wood piece.
The electric current of the above methods is applied
for a period dependent on the moisture content and size
of the wood piece.
BRIEF DESCRIPTION OF THE DRAWINGS
Aspects of the present invention are illustrated,
merely by way of example, in the accompanying drawings in
which:
Figure 1 is a view of a piece of wood undergoing the
treatment process of the present invention;
Figure 2 is a detail view of the structure of a wood
pole; and
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Figure 3 is a detail view of the end of the wood
piece of Figure 1 showing the preferred positioning of
the electrode for passing electric current through the
wood piece.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The method of the present invention is particularly
suited for treatment and drying of wood pieces such as
pine or spruce poles to be made into walking sticks by
hand carving or turning on a lathe. The poles are full
cut sections through the trunk of a tree or the branch of
a larger tree and include an outer bark layer, the phloem
tissue, the xylem tissue and the heartwood. The poles
are preferably cut into about six foot lengths and
generally taper from a diameter in the range of
approximately two to three inches at the base to a
diameter in the range of approximately one to two inches
at the tip. Before carving can begin, it necessary to
dry the poles, generally by air drying. The treatment
method of the present invention is used prior to drying
to treat the poles to reduce their tendency to split and
check during drying which renders the poles useless for
carving. The treatment method of the present invention
has been used on pine and spruce poles cut from the trunk
of still standing trees that have died naturally in which
the trunk has not split and checked with age. Also, the
treatment method has been used on green wood poles cut
from the trunks of newly felled live trees.
Referring to Figure 1, there is shown a pole 10
which is set up to be treated according to the method of
the present invention. The method involves passing an
electric current through the length of the pole 10 for a
pre-determined period. Immediately before or after the
applying the electric current, the bark is removed from
the pole. Applicant has discovered that this treatment
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significantly reduces the tendency for the pole to split
or check during subsequent air drying.
Passing an electric current through the length of
the pole 10 is accomplished by inserting electrodes 14
into opposite ends of the pole. Electrodes 14 are made
from a conducting material and have a sharpened tip to
facilitate insertion of the electrodes into the ends of
the pole 10 to a depth sufficient to hold the electrodes
in place. The electrode end opposite the tip is
preferably formed with a flattened head 16 to provide a
surface for hammering the electrode into place. The
electrodes are intended to be reusable. A common nail is
appropriate for use as an electrode.
As best shown in Figure 3, the electrodes are
preferably positioned in the centre or heartwood 30 of
the wood pole 10. The desirability of this positioning
will be explained in more detail below. Figure 2 is a
detail view of the structure of a typical pole cut from a
tree trunk or branch with broken away sections to show
the central heartwood 30 surrounded by xylem tissue 32
and a relatively narrow zone of outer phloem tissue 34
covered by a cork or bark layer 12.
Insulated wire conductors 18 are removably
connectable to electrodes 14 by clips 20. Wire
conductors 18 are connected to a power source 22 for
generating a current. As best shown in Figure 1, when
electrodes 14, wire conductors 18, power source 22 and
pole 10 are connected together in the manner described
above a circuit is created that acts to deliver electric
current through the length of pole 10.
Preferably, prior to completing the electrical
circuit, pole 10 is placed on an insulating surface to
avoid risk of electrical shock. In the Figures, the
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insulating surface comprises a plurality of brackets 25
made from a non-conducting material such as rubber to
support the length of pole 10, however, other
arrangements such as a rubber sheet will be readily
apparent to those wishing to practice the method of the
present invention.
Immediately prior to or immediately after passing
electric current through the wood pole, water impermeable
bark 12 (cork) is removed from the pole.
For power supply 22, applicant has used a standard
household electrical outlet supplying alternating current
at 15 amps, 120 volts and 60 Hz. and a single wave
rectifier to convert the household power supply to 120
volts direct current. Applicant has also used a 15 amp
12 volt battery charger and a 55 amp 12 volt battery
charger have also been used successfully as power sources
in the treatment method of the present invention. A
battery is particularly useful where commercial power is
unavailable. Testing by the applicant indicates that the
treatment method of the present invention works equally
well with either alternating or direct current.
Applicant has also used as a direct current power
source, a radio receiver tuned to static (white noise)
connected to a 40 Hz to 15 kHz audio amplifier rated at 8
ohms and 60 watts at full volume to modify the electric
current delivered through the pole. The electrical leads
from the power outlet of the amplifier that are normally
connected to a speaker were connected to each end of the
pole.
The specific examples given above are by way of
example only and are not meant to limit the power sources
that can be used with the method of the present
invention. It is anticipated that direct current at
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other voltages and amperages, and alternating current at
other frequencies, voltages and amperages will also be
effective in the treatment method of the present
invention.
S Preferably, the treatment method of the present
application involves application of the current only once
and for a period of time dependent primarily on the
moisture content and dimensions (length and diameter) of
the pole being treated. In testing, applicant has
determined that a green pine pole, heavy with sap must be
subjected to an electric current for a longer period of
time than a dead pine pole. Dead wood pine poles cut
down in the summer and fall when sap is not running have
been treated with an electric current for as little as
about one and a half hours and up to about six hours
without splitting or checking taking place along the
length of the pole during subsequent drying. Applicant
has determined that green pine poles generally require a
treatment of from about four hours to about twelve hours.
It is impossible to provide an exact period for treatment
according to the method of the present invention given
all the variables involved including the moisture content
and dimensions of the wood. The mineral content of the
wood, the wood species and the time of the year the tree
is cut down also effects the amount of electrically
conductive sugars and salts the pole contains. The times
given above have worked for treatment of pine poles cut
down in the summer and fall. It will be readily apparent
to a person skilled in the art that additional testing
will be necessary to determine appropriate times of year
for harvesting and resulting treatment times for other
types, moisture contents and dimensions of wood poles.
By way of example, six foot long, green wood spruce
poles cut in the fall and winter and treated with
electric current in the range of about four hours to
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about twelve hours have been successfully dried without
splitting or checking.
After being subjected to an electric current, poles
are then placed in an appropriate environment for air
5 drying. This can include placing the treated poles
outdoors in a location protected from precipitation to
be air seasoned. The poles may also be placed indoors,
in a well ventilated area, to be air dried until the
poles are dried to a suitable moisture content to be
10 further processed, for example, by carving.
The precise reasons for the effectiveness of the
treatment method of the present invention are not known,
however, applicant theorizes that the method works for
the following reasons:
In a living tree, mineral salts are in the form of
electrically charged ions. Once absorbed, the ions travel
in the water in the xylem tissue and pass to the growing
points of the plants where they are used for growth. The
ions may also pass laterally from the xylem to the
phloem. The electric current that is passed through the
length of the pole in the method of the present invention
causes mineral salt ions within the pole to migrate
radially from the heartwood 30 and the xylem tissue 32
(sap wood) to the phloem layer 34. The effect of the
electrical treatment is to leave the phloem tissue 34
with a higher concentration of mineral salts than the
heartwood 30 and the xylem 32.
Removal of the bark (cork) layer 12 from the pole
exposes the phloem layer 34 directly to the air for
faster evaporation of water directly from the phloem
layer. The exposed permeable phloem cells retain a
higher concentration of mineral salts than the heartwood
and the xylem due to the treatment of the present
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invention. As the water evaporates from the exposed
surface of the phloem, the water molecules of the weaker
salt solution in the cells of the heartwood and the xylem
pass radially through the cambium to the stronger mineral
salt solution in cells of the phloem. The exposed phloem
in turn transpires water to the surrounding atmosphere
during air seasoning. Through osmotic action, the water
molecules pass from the interior of the pole to the outer
phloem and from the exposed surface of the phloem by
evaporation to the surrounding atmosphere. This osmotic
action continues to take place during air seasoning. The
moisture content of the dried pole is dependent on the
prevailing atmospheric humidity. Splitting and checking
no longer take place due to the outer surface of the pole
drying faster than the interior.
Although the present invention has been described in
some detail by way of example for purposes of clarity and
understanding, it will be apparent that certain changes
and modifications may be practised within the scope of
the appended claims.
