Note: Descriptions are shown in the official language in which they were submitted.
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ORIENTING DISK FOR IMPROVING MAT FORMATION IN
COMPOSITE WOOD PRODUCTS
Technical Field
[0001] The present invention relates to machinery used to produce
composite wood products, and in particular relates to disks used in rotating
disk-type wood strand orienter machinery.
Background
[0002] Composite wood products such as oriented strand board
("OSB"), particleboard and the like are produced from wood particles or
strands. Such strands are generally elongated (longer than they are wide),
and it is desirable to have these strands aligned longitudinally and lying
flat
on the mat when producing OSB. During the manufacturing process,
strands of wood are typically formed into mats with the orientation of the
wood strands controlled by strand-orienting machinery. Generally, the
quality of a composite wood product depends in large part upon how well
aligned the wood strands are in the wood strand mat produced by the
orienter.
[0003] Commonly used strand orienters employ rotating disks. One
type of orienter known in the art is the "Stokes" type of orienter, which is
described in detail in United States Patent No. 3,115,431, which issued on
Dec. 24, 1963 to Stokes et al. This orienter uses a plurality of intermeshed
rotating disks mounted on a plurality of substantially parallel shafts ori-
ented in a plane beneath a supply of wood strands. The wood strands are
permitted to fall down upon the disks, which, while turning, tend to align
the strands longitudinally. The aligned strands fall between the disks to
form a mat of strands on a platform or conveyor beneath the disks. The
mat is accordingly formed of particles aligned generally longitudinally,
although the strands are not perfectly aligned.
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[0004] Another type of orienter known in the art, which also employs orienting
disks, is the
type known as the "Biirkner" orienter. The Burkner orienter is disclosed in
United States Patent No.
4,380,285, which issued on 19 April, 1983. In the Burkner orienter, disks on
adjacent shafts are
arranged in pairs in side-by-side relationship, defining passages for allowing
strands of wood to pass
through to form a mat.
[0005] Over many years, various types and shapes of orienting disks have been
used in
Stokes and Biirkner orienters to orient wood strands. One type of disk
commonly used today is
shown in Figure 1 (the "prior art disk"). This prior art disk has a generally
circular shape, with
protuberances formed along its periphery. Shallow notches are also cut into
the periphery, the
notches having a rear edge extending inwardly towards the center of the disk,
and a forward edge
extending upwardly and forwardly from the bottom of the rear edge, as
described in greater detail
below.
[0006] As discussed earlier, better quality wood composite products can be
formed from
wood strand mats having a high percentage of strands that are aligned
longitudinally as well as lying
flat on the mat, and the improved orienting disk of the present invention
provides better strand
alignment than the prior art disk.
Summary of Invention
[0007] The present invention provides an improved orienting disk for use in a
wood strand
orienter. In one embodiment of the invention the
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orienting disk comprises a plate having a generally circular shape and an
outer periphery. An aperture is formed through the center of the plate for
allowing the plate to be fitted onto a shaft in the wood strand orienter for
rotation in a first direction about a rotation axis. A plurality of fin-shaped
teeth extend outwardly from the periphery of the plate.
[0009] Each one of the teeth has a leading edge extending outwardly
from the periphery of the plate to a tip of the tooth, the leading edge facing
the first direction of rotation when the disk is fitted onto the shaft; and a
trailing edge trailing rearwardly and downwardly from the tip of the tooth
to the periphery of the plate.
[0010] In another embodiment of the invention, the fin-shaped teeth
number between two a.nd eight and are evenly spaced about the periphery
of the plate. In yet another embodiment, there are six fin-shaped teeth, and
each one of the teeth is separated from another by 60° about the
periphery
of the plate.
[0011] The leading and trailing edges can be straight or curved, but in
a preferred embodiment, the leading edge is straight, and the trailing edge
is curved.
[0012] In another preferred embodiment, protuberances are formed
about the periphery of the disk, between the fin-shaped teeth.
Brief Description of Drawings
[0013] In the accompanying drawings which illustrate specific em
bodiments of the invention, but which should not be construed as restrict
ing the spirit or scope of the invention in any way:
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[0014] Figure 1 is side view of a prior art strand-orienting disk used
in a typical rotating disk-type strand orienter.
[0015] Figure 2 is side view of a strand-orienting disk made in
accordance with the preferred embodiment of the invention.
Description
[0016] Throughout the following description, specific details are set
forth in order to provide a more thorough understanding of the invention.
However, the invention may be practised without these particulars. In
other instances, well known elements have not been shown or described in
detail to avoid unnecessarily obscuring the invention. Accordingly, the
specification and drawings are to be regarded in an illustrative, rather than
a restrictive, sense.
[0017] Referring first to Figure 1, a common prior art orienting disk
10 used in both Stokes and Burkner wood strand orienters is a plate 11 of
generally circular shape, with a plurality of protuberances 12 formed along
the circular periphery 14 thereof. "Periphery", as that word is used
throughout this description, refers not to the actual outer edge of plate 11,
but rather to that circular imaginary line (shown partially by dashed line 16
in Figure 1) which bounds the generally circular outer edge of plate 11.
"Periphery" has a similar meaning when the invention is described below.
[0018] In prior art disk 10, a plurality of shallow notches 18 are cut
into plate 11 from periphery 14. Each of notches 18 has a short rear edge
20 extending inwardly towards the center of disk 10, and a longer forward
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edge 22 extending upwardly and forwardly from the bottom of rear edge
20 to periphery 14.
[0019] Disk 10 has an aperture 24 formed through the center thereof
for mounting disk 10 onto a shaft (not shown) in a wood strand orienter in
a manner known in the art. Disk 10 is intended to be rotated in the direc-
tion indicated by arrow 26.
[0020] Figure 2 illustrates one embodiment of the improved orienter
disk of the present invention. In this embodiment, disk 30 is a plate 31
having a generally circular shape and an outer circular periphery 32.
Improved disk 30 also has an aperture 34 for mounting disk 30 onto a shaft
in a wood strand orienter.
[0021] Disk 30 has a plurality of fin-like teeth 36 which extend
outwardly from the periphery 32 of plate 31. Each one of teeth 36 has a
leading edge 37 extending outwardly from periphery 32 of plate 31 to a tip
38 of tooth 36. Leading edges 37 face the direction of rotation of disk 30,
as indicated by arrow 40. Each tooth 36 also a trailing edge 39 trailing
rearwardly and downwardly from tip 38 of tooth 36 to periphery 32 of
plate 31.
[0022] It is not essential to the invention that any particular number of
teeth 36 be employed by disk 30. However, it has been determined that
too great a number will not allow wood strands to be well aligned by disk
30, and accordingly, the inventors believe that a disk 30 having between
two and eight teeth will be most desired. In preferred embodiments, the
teeth 36 are evenly spaced about periphery 32 of plate 31, and in the most
preferred embodiment (shown in Figure 2), disk 30 has six teeth 36, each
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of which is separated from an adjacent tooth by an angle, a, of 60°
about
said periphery of plate :31.
(0023] In one embodiment of the invention, leading edge 37 is
straight and trailing edge 39 is curved, as shown in Figure 2. Further,
protuberances 42 may be formed about periphery 32 of plate 31, between
fin-shaped teeth 36.
[0024] The benefits of the improved orienting disk of the present
invention are illustrated by the following experimental results:
[0025] Tests were carried out on the Alberta Research Council (ARC)
pilot plant Oriented Strand Board (OSB) forming line comparing the
performance of the wood strand orienter using the improved orienting disks
to the performance of the orienter with a standard commercial design of
orienting disk (the prior art disk). Except for the orienting disks, there
were no differences between the orienter set-ups for the comparative tests.
The ARC pilot plant orienting system is typical of commercial OSB strand
orienters except that the ARC pilot plant orienter has four shafts of rotating
disks, whereas commercial orienters typically have about 12 shafts of
rotating disks.
[0026] Tests were carried out using a Stokes type of orienter arrange-
ment and also using a Burkner type of disk arrangement as well. It was
found that results for the two types of orienter disk arrangements were
similar. Only the results of the Stokes type of disk arrangement are
reported here for simplicity.
(0027] The following test variables were included in the study:
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[0028] Disk type: 1) Prior art disk design used in commercial
orienters with small notches on the periphery of
the disk (Figure 1 disk).
2) Improved disk design (Figure 2 disk)
(0029] Disk spacing: 1) A common mill spacing of 2 inches (50
mm) between disks on adjacent orienter
shafts
2) A narrower spacing of 1. S inches (38
mm) between disks on adjacent orienter
shafts
[00301 Disk speed: 1) Constant 30 RPM for all orienter shafts
2) Low acceleration between orienter shafts
(consecutive shaft speeds of 10, 20, 30 and
40 RPM)
3) High acceleration between orienter shafts
(consecutive shaft speeds of 15, 30, 45 and
60 RPM).
[0031] Strand flaw rate: 1) Low flow rate (typical mill flow rate).
2) Medium flow rate (1.5 times typical mill
flow rate)
3) High flow rate (2 times typical mill flow
rate).
[0032] The following conditions were held constant for all tests.
Strands: Screened mill-produced strands to represent typical face
quality strands used throughout the study. Strands were
not recycled.
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Line speed: Constant setting of 30 Hz.
Orienter height above mat: 2 inches (50 mm).
Replicates: Three per test condition.
[0033] In the first test, the improved disk was compared to the prior
art disk using both a normal and narrow disk spacing as defined above.
The following parameters were measured, determined or calculated:
[0034] 1. The average and median orientation angles of
the wood
strands in the wood strand mat.
[0035] 2. The predicted "modulus of elasticity" (MOE)
of the end
product.
[0036] 3. The percentage of strands having an orientation
angle of
less than 20.
(0037] 4. The "% error" - this is an indication of the
smoothness
of the mat, as discussed below.
[0038] 5. The "% overs" - the percentage of wood strands
which
"bridged" the disks, being carried over all of
them to
the end of the orienter without being aligned
and with-
out falling to the strand mat.
[0039] Results of the first tests are summarized in Table 1:
Table 1. Orientation Study Results.
Disk Disk StatisticAverageMedian MOE, % of
Type Spacing Orienta-Orienta-% StrandsErrorOvers
of
lion lion Max. <20.
An- An-
gle, gte,
. .
nor orma Mean
art St. 2.7 3.4 3.7 6.0 3.1 0.74
Dev.
nor arrowcan
art St. 1.9 2.6 3.4 4.9 2.4 I
Dev. .26
m- orma nnean
proved St. I 2.5 I 3.2 4.8 I 5.9 I I
Dev. I 1.7 0.85
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Im- Narrow Mean 28.8 20.2 37.9 40.1 9.6 7.41
Proved I ~ St. Dev.- ~ 2.l ~ 2.8 I 3.1 I 4.8 I 2.2 I 1.04 I
S Twenty seven (27) samples per test cell.
[0040] As expected, the narrower disk spacing gave lower mean and
median orientation angles, a higher predicted modulus of elasticity (MOE)
and a higher incidence of strands with < 20° orientation angle. The
trends
for these measures of orientation were similar for the prior art and im-
proved orienting disk configurations at the same orienter disk spacings.
[0041] Where the improved orienting disk design differed from the
prior art orientation disk design was in smoothness of the mat at the normal
disk spacing. The improved orienting disks produced a much smoother
strand mat than the prior art disks as evidenced by a much lower incidence
of error readings from a laser strand orientation measurement system used
to measure flatness of the resultant mat (10.1% vs 26.0% of instrument
readings) as shown in Table 1. Strands that are not lying sufficiently flat in
the furnish mat do not produce a regular ellipse with the laser orientation
measurement system and cause an error reading in the system. The
incidence of error readings with narrow disk spacing was similar for the
improved (9.6%) and prior art orienting disks (9.7%).
[0042] A smoother strand mat is advantageous for several reasons.
Strands falling onto an uneven, partially formed strand mat will have a
greater probability of becoming less well oriented. Thus the final strand
mat produced from multiple layers of uneven strands will tend to have
poorer overall orientation than one produced from multiple layers of even
strands. An uneven strand mat will have lower bulk density, resulting in a
thicker strand mat, which will require greater press daylight and require
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more time for the press to close to thickness. More strand breakage during
press closing would be expected with an uneven strand mat with many
strands sticking up out of the mat. Broken strands reduce product strength.
It is postulated that the fin-like teeth on the improved orienting disks help
to control the flow of strands down to the mat, resulting in a smoother
strand mat.
[0043] The difference in the % overs (strands bridging the orienter
disks and carried over the orienter) between the improved disks (7.41%)
and prior art disks (8.23%) with narrow disk spacing was significant at the
95% confidence level. It would appear that the improved disks help to
reduce the amount of strands bridging the orienter disks.
[0044] Table 2 contains results of statistical t-tests comparing the
different variables in Table 1 to indicate which ones were statistically
significant:
Table 2. Results of Statistical t-tests comparing test variables.
reenter on tgurattonsarea a Mea-Va ue a ue tattsrica
2
Compared sured Significance'
Prior art Disks/NormalAverage 33.1
Spacing Angle,
'
Median Angle,25.0 18.5 ***
'
vs MOE, % of 32.6 39.9 ***
Max.
% Strands 32.3 43.3 ***
<2O'
Prior art Disks/Narrow% Error 26.0 9.7 ***
Spacing
Overs 3.39 8.23 ***
tmproveo uiskslNOrma~coverage L7.4 L8.8 lVJ
~pacmg nng~~,
Median Angle,20.9 20.2 NS
'
vs MOE, % of 37.0 37.9 NS
Max.
% Strands 39.2 40.1 NS
<20'
Improved Disks/Narrow% Error 10.1 9.6 NS
Spacing
Overs 3.33 7.41 ***
Ynor art UiskslNOrmalAverage s.s.i ~y.w ___
Spacing Angle,
Median Angle,25.0 20.9 ***
'
vs MOE, % of 32.6 37.0 **
Max.
% Strands 32.3 39.2 ***
<20'
Improved Disks/Normal% Error 26.0 10.1 ***
Spacing
Overs 3.39 3.33 NS
r~or ar is s orma verage ng
pacing e,
Median Angle,25.0 20.2 ***
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vs MOE, % of 32.6 37.9 ***
Max.
Strands 32.3 40.1 ***
<20'
Improved Disks/Narrow% Error 26.0 9.6 ***
Spacing
Overs 3.39 7.41 ***
Prior art Disks/NarrowAverage 27.7 28.8
Spacing Angle,
'
Median Angle,18.5 20.2
'
vs MOE, % of 39.9 37.9
Max.
Strands 43.3 40.1
<20'
Improved Disks/Narrow% Error 9.7 9.6 NS
Spacing
Overs 8.23 7.41
' NS = difference not significant; * = difference significant at 95%
confidence level; ** = difference
significant at 99% confidence level; *** = difference significant at 99.9%
confidence level
[0045] Table 3 indicates that strand flow rate had little effect on any
of the parameters measured, with the possible exception of % error. With
narrow disk spacing the improved disks, and possibly the prior art disks,
appeared to show a trend toward a flatter mat (lower % error) as the strand
flow rate increased.
Table 3. Effect of strand flow rate on performance of the different orienter
types'.
is is tran veragea tan MUI:, % of
Type Spac- Flow Orient.Orient.% of StrandsError Overs
ing Rate Angle,Angle, Max. < 20'
' '
Ynor Nor- LOW L.b L4.J JG.O ~
art mal 3.1 3.6 3.7 6.6 3.4 0.50
., .. Me_ ~.~ . .~ ~..~
dium 2.4 3.7 4.8 7.4 2.0 0.86
,. .. n,gn ~~.y .a ~c.~ tea.. ..
2.9 3.1 2.8 4.1 3.7 0.85
YrtorN8I- LOW ~a ty.~ ~o.o
art row 2.0 3.0 4.0 S.6 l.4 1.27
e-
dium 1.0 0.7 2.2 2.0 1.6 1.1
1
.. .. n~gn ti.y ia.~
2.4 3.3 3.9 6.5 2.8 1.26
m- Nor- Low m.v cc.o . . . .
provedmal 2.5 3.5 3.6 6.0 2.1 0.99
- w Me- ta.a io.o ~~..
dium 1.6 1.6 5.7 2.9 1.7 0.85
.g
2.4 3.2 4.2 5.5 1.3 0.67
m- Nar- Low ~a.o ~y.o ~o.~ ~....
provedrow l.6 2.4 2.6 4.0 1.4 0.87
__ Me- ty.~ c ~.
i
dium 1.9 2.1 2.5 4.6 1.3 0.73
.. ri~gn~a.~ i7.~ . t..~ ~.~
2.6 3.2 3.9 5.3 2.8 0.80
. .1
v
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' Nine (9) samples per test cell. The top number given in each cell is the
mean value and the
bottom number is the standard deviation.
[0046] Table 4 indicates that disk speed had little effect on any of the
parameters measured, with the possible exception of % overs, which is the
percentage of strands bridging the orienter disks and carried across the top
of the orienter without falling through the orienter. For both the prior art
disks and improved disks with normal spacing, the % overs appeared to
increase as the orienter disk speed was accelerated from one bank of disks
to the next. With narrow disk spacing there was no apparent trend for the
overs to increase with increasing orienter disk acceleration for either the
prior art disks or the improved disks.
1$ Table 4. Effect of orienter disk speed on performance of the different
orienter types' .
Dts -Disk OrienterAverageMedian MUE, "/o "/o "/"
"/o of
Type Spac- Disk Orient.Orient.of StrandsError Overs
Max.
ing Speed Angle, Angle, <20'
' '
Prior NormalConstant34.5 26.6 30.6 30.3 25.1 2.81
art 2.0 2.8 3.1 5.4 2.5 0.20
" " Low 32.0 23.9 33.4 33.7 25.2 3.1
Accel.2.7 3.2 4.1 6.6 3.7 0.28
" " High 3 .0 4.4 3 .7 .0
Accel.2.9 3.8 3.4 6.1 2.5 0.69
nor arrow onstant
art 2.3 2.7 3.6 5.5 2.2 1.50
ow
Accel.2.2 3.5 4.0 6.3 2.6 1.39
tttgn
Accel.1.1 1.3 2.8 2.3 2.3 0.68
m- orma oastant. . . 4 . . . 4
proved 2.7 3.2 3.2 4.2 1.7 0.30
.. __ LOW . . .u
Accel.3.0 3.9 5.6 7.1 1.5 0.54
.g
Accel.1.7 2.8 4.9 6.3 1.8 0.54
Tm-- tvarrow~onsLan<<i.7
proved 2.0 2.6 2.9 5.7 1.4 0.36
LVYY . .a z.. r...
Accel.2.4 '3.4 4.l 5.8 2.2 1.23
Accel.1.3 1.9 2.3 2.9 2.0 1.34
'
Nine
(9)
samples
per
test
cell.
The
top
number
given
in
each
cell
is
the
mean
value
and
the
bottom
number
is
the
standard
deviation.
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[0047] It will be clear to those skilled in the art from these experi-
mental data that the improved disk improves strand formation in orienters.
[0048] As will be apparent to those skilled in the art in the light of the
foregoing disclosure, many alterations and modifications are possible in the
practice of this invention without departing from the spirit or scope thereof.
Accordingly, the scope of the invention is to be construed in accordance
with the substance defined by the following claims.
