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| United States Patent |
5,043,122
|
|
Churchland
|
August 27, 1991
|
Composite assembly press and method of use
Abstract
An apparatus for pressing composite assemblies including a continuous belt
press having a pair of endless belts facing one another. The distance
between the belts varies to define therebetween a compression zone wherein
lock-up of the composite assemblies occurs, a parallel bed press zone, and
a transfer zone therebetween. The curvature radius of the compression
zone, which can be positive, negative or zero, is longer than that of the
transfer zone.
| Inventors:
|
Churchland; Mark T. (Vancouver, CA)
|
| Assignee:
|
MacMillan Bloedel Limited (British Columbia, CA)
|
| Appl. No.:
|
456657 |
| Filed:
|
December 29, 1989 |
| Intern'l Class: |
B27N 003/12 |
| Field of Search: |
264/109
425/371
156/580,583.5,62.2
|
References Cited
U.S. Patent Documents
| 3120862 | Feb., 1964 | Burger | 144/281.
|
| 3493021 | Feb., 1970 | Champigny | 144/317.
|
| 3723230 | Mar., 1973 | Troutner | 156/580.
|
| 3792953 | Feb., 1974 | Ahrweiler | 42/371.
|
| 3851685 | Dec., 1974 | Ahrweiler et al. | 144/281.
|
| 3993426 | Nov., 1976 | Ahrweiler et al. | 425/371.
|
| 4043732 | Aug., 1977 | Ahrweiler | 425/371.
|
| 4061819 | Dec., 1977 | Barnes | 428/294.
|
| 4410474 | Oct., 1983 | Ahrweiler | 264/109.
|
| 4456498 | Jun., 1984 | Churchland | 156/275.
|
| 4517148 | May., 1985 | Churchland | 264/112.
|
| 4563237 | Jan., 1986 | Churchland et al. | 156/62.
|
| 4850846 | Jul., 1989 | Walter | 425/337.
|
| Foreign Patent Documents |
| 2008951 | Jul., 1990 | CA.
| |
Primary Examiner: Theisen; Mary Lynn
Attorney, Agent or Firm: Banner, Birch, McKie & Beckett
Claims
What is claimed is:
1. A composite pressing apparatus comprising:
a continuous press for pressing composite assemblies;
wherein said continuous press includes defining means for defining a
parallel bed press zone, a compression zone wherein lock-up of the
composite assemblies occurs, and a transfer zone therebetween, said
transfer zone having a transfer zone curvature radius, and said
compression zone having a compression zone curvature radius; and
wherein said compression zone curvature radius is longer than said transfer
zone curvature radius.
2. The apparatus of claim 1 wherein said compression zone curvature radius
is relatively large whereby said compression zone is relatively flat.
3. The apparatus of claim 1 wherein said defining means includes a
gathering zone upstream of said compression zone.
4. The apparatus of claim 3 wherein said gathering zone has a gathering
zone curvature radius, and said gathering zone curvature radius is shorter
than said compression zone curvature radius.
5. The apparatus of claim 4 wherein said gathering zone curvature radius is
shorter than said transfer zone curvature radius.
6. The apparatus of claim 5 wherein said gathering zone curvature radius is
generally forty feet, said transfer zone curvature radius is generally one
hundred and twelve feet, and said compression zone curvature radius is
generally two hundred and fifty-four feet.
7. The apparatus of claim 3 wherein said gathering zone has a length of
about two feet, said compression zone has a length of eleven feet, and
said transfer zone has a length of three feet.
8. The apparatus of claim 1 wherein said compression zone is eleven feet
long and said transfer zone is three feet long.
9. The apparatus of claim 1 wherein said transfer zone curvature radius is
large enough to avoid damage to the composite assemblies after lock-up
thereof.
10. The apparatus of claim 1 wherein said compression zone is more than
twice as long as said transfer zone.
11. The apparatus of claim 1 wherein said transfer zone at one end thereof
is directly adjacent to said parallel bed zone and at the other end
thereof is directly adjacent the said compression zone.
12. The apparatus of claim 1 wherein said transfer zone curvature radius at
one end thereof is tangent to said parallel bed press zone and at the
other end thereof is tangent to said compression zone curvature radius.
13. The apparatus of claim 1 wherein said compression zone curvature radius
is an infinite radius.
14. The apparatus of claim 13 wherein said transfer zone curvature radius
is a generally one hundred feet.
15. The apparatus of claim 1 wherein said compression zone includes at
least one flat platen.
16. The apparatus of claim 1 wherein said continuous press includes a pair
of continuous belts facing one another through said zones and driven
towards said parallel bed press zone.
17. The apparatus of claim 1 further comprising said continuous press
having a press inlet, and conveying means for conveying the composite
assemblies in a mat to said press inlet.
18. The apparatus of claim 17 wherein said press has a gathering zone
directly adjacent to said compression zone and at said press inlet.
19. The apparatus of claim 18 wherein said gathering zone has a gathering
zone curvature radius and said gathering zone curvature radius is
generally less than one-quarter of said compression zone curvature radius.
20. The apparatus of claim 1 wherein each said curvature radius is formed
by a series of flats adjacent and at slight angles relative to one
another.
21. The apparatus of claim 1 wherein each said curvature radius is formed
by a smooth continuous curve.
22. The apparatus of claim 1 wherein said compression zone has a concave
curvature.
23. A method for compressing composite assemblies, comprising the steps of:
conveying composite assemblies through a continuous belt press compression
lock-up region and thereby causing lock-up of the composite assemblies;
thereafter, conveying the locked-up composite assemblies through a
continuous belt press transfer region whose radius of curvature is shorter
than that of the compression lock-up region; and
thereafter, conveying the composite assemblies through a parallel bed press
region.
Description
BACKGROUND OF THE INVENTION
The present invention relates to belt presses for pressing composite
assemblies and is more particularly an improvement on the technologies
disclosed in U.S. Pat. No. 4,517,148. This and each of the other patents
mentioned in this disclosure are hereby incorporated by reference in their
entireties.
Structural wood products can be manufactured from long relatively thin
strands of wood by coating the strands with an adhesive, arranging the
strands side-by-side in a lengthwise dimension of the lumber product and
subjecting the arranged strands to heat and compression. A high strength
dimensional wood product is thereby formed, and this process is disclosed
for example in U.S. Pat. No. 4,061,819. Belt presses are typically used in
processes for the manufacture of composite wood products, and examples
thereof are shown in U.S. Pat. Nos. 3,120,862; 3,723,230; 3,792,953;
3,851,685; 3,993,426; 4,043,732; 4,850,846; and 4,410,474. The belt
presses include facing endless belts between which the material is
compressed and platens and anti-friction devices which hold the belts in
pressure engagement with the materials conveyed therebetween. The inlet
end of the press belts and the platens over which they run converge
towards one another to form a compressing zone. As the strands enter the
compressing zone they are generally free to move with respect to one
another. However, as the belts converge within this zone the strands have
their positions set, in a "lock-up" position, with respect to one another.
After lock-up further compression of the material results from the further
convergence of the press belts. Since lock-up usually occurs in a curved
area, the material is curved as it is being pressed. After the compressing
zone the lock-up material is passed through a parallel belt zone.
Although the resulting material passing out of the parallel belt zone is
planar, the curvature of the strands at lock-up is "remembered" as an
internal stress therein. Where the end products are thin and planar these
internal stresses do not present a problem. For relatively thick products,
however, such as dimensioned lumber, these internal stresses present a
problem when the thick product is cut longitudinally. When so cut the
internal stresses are released and the two resulting halves bow in
opposite directions. In other words, with single radius infeeds which are
tangent to the parallel belt of the press prestresses in the wood, which
are a function of the infeed radius, occur and when later resawn axially
the prestresses are released and the final product curves. This problem
has been addressed in the past by using a very large compression radius.
Increasing the entire infeed radius may not always be possible, however, as
the large radius may not provide a large enough infeed opening for the
projected point of lock-up. Additionally, the radius at times cannot be
extended sufficiently to open the press opening where there are physical
limitations on the length of the press bed. Also, a long press has been
needed to obtain an opening large enough to "bite" on thick incoming mats.
For example, when a twelve inch product is being compresssed, a
twenty-four to thirty-six inch opening is initially required. It thus
takes a very long press bed in proportion to the extra press depth to gain
a smooth even compression.
In one known press the required shape of the compression radius and the
parallel bed was cut from a steel plate about one-and-a-half inches thick.
Four shaped "ribs" were cut out of an about ten inch deep, one and a half
inch wide and fifteen foot long plate in about thirty inch wide sections
and were bent over the plate. The ribs acted as stiffeners to hold the
shape of the plate. The assembly was welded together, and two such platen
assemblies were mounted facing each other. Roller chains covered the
platens and moving bearing plates covered the rollers. A tensioned and
driven belt provided the traction force and faced directly on the product.
This is a constant radius type of fabricated radiused platen.
An example of another known press, a stepped radius press, is the
commercial press available from Eduard Kuesters of Krefred, West Germany.
It uses a flat platen bent at specific discrete points defined by machined
slots in the back thereof. Each flat section, which is typically eighteen
inches long, is supported with a wedge block and frame. In this press,
roller chain assemblies separate the steel belt which is driven by drums
from the platen and form the friction reducing medium. The effective
radius of the platen area, which can be defined by the intersection of the
perpendicular bisectors of adjacent platen segments, is for example for a
three-quarters of a degree bend between two sections or segments one
hundred and twelve feet. The prestressing can be characterized by the
amount of bow in beams cut from the product. A forty-eight foot long beam
produced by this press and cut from the face of the billet typically has
an often unacceptably large bow of two-and-a-half to four inches.
SUMMARY OF THE INVENTION
Accordingly, it is a principal object of the present invention to provide
an improved composite press assembly which can form thick products without
any significant prestress.
Another object of the present invention is to provide a composite press
assembly having lower production costs and consistent product output.
A further object of the present invention is to provide a composite press
assembly design allowing, for the same amount of prestress, a shorter
press bed thereby saving machinery cost, maintenance cost and floor space.
Directed to achieving these objects, a continuous press for processing
composite assemblies, including a pair of facing endless forming belts
symmetrical about the transport axis, is herein provided. The space
between the belts varies as the composite assemblies are conveyed
therebetween through gathering, compression, transfer and parallel bed
press zones. Lock-up of the composite assemblies occurs in the compression
zone, and the radius of curvature (positive, negative or zero) of the
compression zone is great enough to minimize pre-stressing, especially for
thick products. The curvature radius of the transfer zone is significantly
shorter than that of the compression zone, allowing for a sufficiently
large in-flow opening and for a significantly shorter press bed, but not
so short a radius as to damage the composite product. Although the present
invention relates primarily to presses for long strand composite
materials, its concept can also be applied to any composite which go
through lock-up on compression, such as thick section fiberboard and
particle board.
Other objects and advantages of the present invention will become more
apparent to those persons having ordinary skill in the art to which the
present invention pertains from the foregoing description taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic side view of a first belt press of the present
invention.
FIG. 2 is a diagrammatic side view of a second belt press of the present
invention.
FIG. 3 is a diagrammatic side view of a third belt press of the present
invention.
FIG. 4 is a diagrammatic side view of a fourth belt press of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
Referring to the drawings, a first belt press assembly of the present
invention is illustrated generally at 20 in FIG. 1. Belt press assembly 20
and the other belt presses illustrated in FIGS. 2-4 are shown
diagrammatically since they are of conventional construction except for
the arrangement of their belts and platens. Examples of conventional
presses are discussed and referred to hereabove in the "Background of the
Invention" section of this disclosure.
Belt press 20 includes an upper continuous press belt 22 trained about a
pair of rotating drums, one of drum 24 of which is illustrated, and a
lower continuous press belt 26 trained about a pair of rotary drums
including drum 28. Upper and lower platens 30, 32 apply compressive
pressure on the strand material 34 being moved between and with the belt
22 and 26. The press 20 can incorporate a heating device (not shown) to
heat the material 34 during its passage through the press. An example of a
known mircrowave heating device used in conjunction with continuous
presses is shown in U.S. Pat. No. 4,456,498.
The strands 34 are conveyed to the continuous press such that their ends
overlap. The strands in the lay-up mat are thus in a "card-decking"
orientation, as shown for example in U.S. Pat. No. 3,493,021, on the
infeed conveyor 36. An improved method thereon is disclosed in U.S. Pat.
No. 4,563,237 wherein the elongate members are deposited on the carrier
over a carrier length that is at least as long as about one-and-a-half
times the length of the members and is at least as long as about thirty
times the final thickness of the composite product.
The belts 22, 26 define by the variances in the distances between them a
compression zone, a transfer zone and a parallel bed press zone along the
flow of the strands 34. A key feature of this invention is that the
curvature radius R.sub.C of the compression zone is larger than the radius
R.sub.T of the transfer zone. The inner smaller radius R.sub.T does the
final changing of direction of the final compression after lock-up.
The compression zone wherein lock-up occurs can have any large curvature
radius R.sub.C including infinitely large, that is a flat platen (FIG. 3),
or even a concave platen (FIG. 4) if it is desired to induce prestresses
for whatever reason. As long as the radius R.sub.T of the final
compressing area, that is the transfer zone, is gentle enough to avoid
damaging the product, the desired prestress can be obtained. In other
words, once compression of the strand mat has progressed to a point of
lock-up, prestresses have been defined and as long as the geometry of
further compression (in the transfer zone) is gentle enough to avoid
damage, the final product will be affected. The point at which the product
is damaged depends upon the properties of the product and would be
apparent to one skilled in the art. This damage is by overstressing or
straining the product by bending it too far and then straightening it. The
product is bent curved as it is being compressed to the curvature of the
platen, and then it is bent straight as it passes through the parallel
portion of the press bed resulting in the "remembered" stresses.
What is critical is that there be a flat or nearly flat platen at the point
of lock-up. It is difficult to define exactly when lock-up occurs so the
compression zone must have an extensive area volume. An extensive volume
is also needed if the press height is changed as the height of the mat
changes with changing press height since a different amount is being fed
into the press. In order to have the same press radius effect the same
results of compressing to lock-up under the large radius, a long section
of larger radius is needed because lock-up occurs at different places for
different press depths.
Instead of being a continuous radius the press can comprise a series of
discrete bends which are, for example, approximately eighteen inches
apart. Thus similar to the previously-discussed Kuesters press, the
present press can be constructed as a stepped radius press. An example
thereof is illustrated in FIG. 2 generally at 40, and its dimensions and
geometry are further defined in Table I.
It is seen in Table I that the first two increments are 0.75.degree. each,
which is a much smaller radius than that of the next increments which are
0.333.degree.. A nominal two hundred and fifty-three foot radius results,
as shown in the bottom line of Table I. The angle increments are not
consistent across because the platen lengths are not consistent. The
places at which the bends were placed in the platen could not carry on in
a four hundred and forty-eight millimeter increment for vestigial
structure within the press that could not be changed. However, a radius of
generally two hundred and fifty feet as shown on the bottom line was
maintained. This radius was calculated by taking the perpendicular
bisector of each of the segments, the four hundred and forty-eight
millimeter segment or six hundred and seventy-two millimeter segment of
the press bed for example, and determining the intersections of the
adjacent perpendicular bisectors. This is a close estimate of the true
radius. A one hundred and twelve foot radius R.sub.T is provided because
this is gentle enough bend to not hurt the product, and the critical
compression is done on the larger radius R.sub.C, the two hundred and
fifty foot plus radius.
Referring to the alternative stepped radius design of Table II, the angle
increment is 0.75.degree. four times followed by two 2.degree. increments
and there are then no 0 through -5 sections of this press. The
0.75.degree. increments through the first four sections provide a one
hundred and twelve foot radius throughout and then a fifty foot radius
follows on the very large opening of the press where the strands are fed
in. The press design of Table I is preferred over that of Table II,
however, because the Table I design has the bottom line effective radius.
The designs of both Tables I and II are for product depths of 11.4 inches.
A gathering zone can also be provided at the inlet of the press. Similar to
the gathering zone shown in the '148 patent it has a small radius R.sub.G
on the order of twenty, forth or fifty feet, gathers the strands into the
horn of the press and does no real compression on the strands. In others
words, the gathering radius allows the press to open up and gather the
product and then take it gently to the lock-up point. As an example, the
gathering radius R.sub.G can be only about forty feet while the
compression radius R.sub.C is about two hundred and fifty feet and the
transfer radius R.sub.T about hundred and twelve feet. The gathering zone
will have a length of around two feet, the compression zone of eleven feet
and the transfer zone of three feet.
Compared with the two-and-a-half to four inch bow resulting from the
Kuesters stepped radius press as previously described, the press of FIG. 2
having a two hundred and fifty-four foot effective radius reduces the bow
to between one-half and one inch and more typically one-half inch.
A one hundred and twelve foot radius R.sub.T is a gentle enough bend or
curve to not hurt a wood strand composite product. It also opens the press
up much faster. The critical compression must, however, be at a larger
radius R.sub.C, such as greater than two hundred and fifty feet. When a
single radius over the same press bed length was used, only a one hundred
and fifty foot radius out of the press could be obtained.
In theory, if the press at the lock-up point has an infinite radius, that
is it is a flat platen, the product produced is free from bending
stresses, though there may be other induced stresses from other properties
of the material or the process. A bed press with a flat platen compression
zone is illustrated in FIG. 3 generally at 50. The platen thereof have
transfer radiuses R.sub.T of around one hundred feet.
A concave compression zone type of bed press is shown in FIG. 4 generally
at 60. It is seen therein that the compression radius R.sub.C is three
hundred feet (or, more appropriately, minus three hundred feet) and the
transfer radius R.sub.T is one hundred and twelve feet. The tangent
point(s) bewteen these radiuses marks the end of the compression or
lock-up zone.
This concept works well for strand mats and continuous presses and also for
any composite which goes through "lock-up" on compression. The present
invention works for example for fiber and particle boards made in thick
sections, such as those greater than two inches. For a one-half inch thick
product press bed lengths may not present a constraint because only a
three or four foot of press bed length is needed to obtain the gentle
large radius compression. It is especially when the product is twelve
inches thick that twelve times that length of compression zone is needed
for the same general compression. So practically speaking, the concept of
this invention is more useful in thicker products though it still has
utility in thin products if the structure of the press needs to be changed
to obtain a smooth compression.
This invention can be used for example in making rubber belts by
compressing fiber and a vulcanizable material in a hot press. A relatively
thick, stress-free belt can be produced by compressing with totally flat
platens converging towards the parallel region of the press and then
connected thereto with a single radius of perhaps only a few feet--similar
to going around a corner. Since rubber is still flexible it would not be
hurt and could tolerate such a small radius.
However, for laminating wood strands into thick lumber products a radius
below one hundred feet risks overstressing the product when it is
straightened out. In other words, the radius is a function of the material
and the thickness of the product being compressed. For one-quarter or
one-half inch thick wood board it would only be a few feet. This is
because thin pieces of wood can be bent around a rather small radius
without overstressing the wood. However, for thick sections a gentle
larger radius must be used.
An advantages of this invention is thus that any degree of
prestressing--positive, negative or zero--can be obtained in a finite
continuous press. This invention also allows for a much shorter press to
be used thereby saving machinery and maintenance costs and floor space.
Since very thick products can be made without inducing any significant
prestress, large cross-section, high value products can be made. Thus, a
larger volume of products at the same process speed can be pressed,
product costs are lower, and a straight even density consistent product
can be produced. As previously discussed and as illustrated in the
drawings, the concept of this invention works equally well with true
continuous radiuses as well as actual segmented platens forming a pseudo
or effective radius from a series of flats.
From the foregoing detailed description, it will be evident that there are
a number of changes, adaptations and modifications of the present
invention which come within the province of those skilled in the art.
However, it is intended that all such variations not departing from the
spirit of the invention be considered as within the scope thereof as
limited solely by the claims appended hereto.
TABLE I
__________________________________________________________________________
PRESS SECTION NUMBER
7 6 5 4 3 2 1 0 -1 -2 -3 -4 -5
__________________________________________________________________________
ANGLE INCRE-
0.75
0.75
0.333
0.333
0.333
0.42
0.358
0.216
0.216
0.216
3 3 0
MENT (DEG)
ANGLE TOTAL
0.75
1.5 1.833
2.166
2.499
2.919
3.277
3.493
3.709
3.925
6.925
9.925
9.925
(DEG)
LENGTH OF 448 448 448 448 448 672 290 290 290 290 90 544 360
SECTION (mm)
TOTAL LENGTH
448 896 1344
1792
2240
2912
3202
3492
3782
4072
4162
4706
5066
(mm)
DEPTH CHANGE
5.86
11.73
14.33
16.93
19.53
34.22
16.58
17.67
18.76
19.85
10.85
93.76
62.05
(mm)
TOTAL DEPTH
5.86
17.59
31.92
48.85
68.39
102.61
119.19
136.85
155.61
175.46
186.32
280.08
342.13
(mm)
SECTION LENGTH
447.96
447.85
447.77
447.68
447.57
671.13
289.53
289.46
289.39
289.32
89.34
535.86
354.61
(mm)
TOTAL LENGTH
447.96
895.81
1343.58
1791.26
2238.83
2909.96
3199.49
3488.95
3778.34
4067.66
4157.00
4692.86
5047.47
(mm)
PRESS OPENING
301.29
324.74
353.40
387.27
426.33
494.78
527.93
563.27
600.79
640.49
662.19
849.72
973.82
(mm)
PRESS OPENING
11.86
12.79
13.91
15.25
16.78
19.48
20.78
22.18
23.65
25.22
26.07
33.45
38.34
(INCHES)
RATIO - PRESS
1.04
1.12
1.22
1.34
1.47
1.71
1.82
1.95
2.07
2.21
2.29
2.93
3.36
OPENING TO
FINAL PRODUCT
EFFECTIVE 112.29
112.29
252.90
252.90
252.90
250.64
252.56
252.38
252.38
252.38
11.91
19.87
ERR
RADIUS (FEET)
__________________________________________________________________________
TABLE II
__________________________________________________________________________
PRESS SECTION NUMBER
6 5 4 3 2 1
__________________________________________________________________________
ANGLE INCREMENT (DEG)
0.75
0.75
0.75
0.75
2 2 0 0 0 0
ANGLE TOTAL (DEG)
0.75
1.5 2.25
3 5 7 7 7 7 7
LENGTH OF SECTION (mm)
448 448 448 448 448 547 500 500 500 500
TOTAL LENGTH (mm)
448 896 1344
1792
2240
2787
3287
3787
4287
4787
DEPTH CHANGE (mm)
5.86
11.73
17.59
23.45
39.05
66.66
60.93
60.93
60.93
60.93
TOTAL DEPTH (mm)
5.86
17.59
35.18
58.63
97.67
164.33
225.27
286.20
347.14
408.07
PRESS OPENING (mm)
301.29
324.74
359.92
406.81
484.90
618.23
740.10
861.97
983.84
1105.71
PRESS OPENING (INCHES)
11.86
12.79
14.17
16.02
19.09
24.34
29.14
33.94
38.73
43.53
RATIO - PRESS OPENING
1.04
1.12
1.24
1.40
1.67
2.14
2.56
2.98
3.40
3.82
TO FINAL PRODUCT
EFFECTIVE RADIUS (FEET)
112.29
112.29
112.29
112.29
42.12
42.12
ERR ERR ERR ERR
__________________________________________________________________________
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