Note: Descriptions are shown in the official language in which they were submitted.
~67g~
BACKGROUND OF THE INVENTION
. .
The present invention relates to a method and apparatus
for drying a sheet of veneer and contemplates providing
a rationalized drying technique which minimizes or practically
eliminates splitting in a veneer sheet which conventionally
resulted from such trea-tment~
Traditionally, a process for producing plywood includes
a step of drying veneer sheets with a drier. When dried,
however, veneer sheets crack concentrically at irregularly
distributed spots and become very poor in quality even
though they may have been of favorable quality before
the drying step. Cracked parts of veneer sheets must be
cut off and wasted with the resultant decrease in the yield
and this critically reduces the output from veneer sheets.
To cope with this problem, there has been proposed
and put to practical use, though in a minor part of
the industry, a process by which a veneer sheet is first
formed with numerous short slits to be tenderized and then
allowed to go on the drying step (referred to as the
"Y process" hereinafter). Compared with the process without
tenderizing (referred to as the "X process" hereinafter~,
the Y process somewhat decreases the tendency of veneer
sheets to split concentrically during drying and has given
an acceptable result so far. However, such a technique is
not fully acceptable in that it still fails to entirely
- eliminate splits attributable to the drying step.
It is apparent that the splits in a veneer sheet
caused by drying and commonly observed in the conventional
~ .
, . . .
b;7~2
processes result from contraction of the veneer sheet when
subjected to such treatment. Where the conveying members
within a drier comprises upper and lower nets as in a net
drier for example, they obstruct the contraction of a veneer
sheet which should be allowed gradually in the course of
the drying step and allow stresses to develop within
the veneer sheet. The veneer sheet breaks or cracks in
locations where the stresses are the most concentrated.
With this in view, the Y process employing tenderizing
process is designed to avoid cracks by decentralizing
the stresses in the veneer sheet by means of numerous short
slits and thereby reduce the tendency of splitting as
a whole. Extended studies which we made to determine
the benifit of tenderized veneer sheets showed that the range
of elasticity in which a veneer sheet stretches without
splitting when pulled in a direction perpendicular to its
grain is larger in tenderized sheets than in non-tenderized
sheets.
SU~ARY OF TH~ TNV~N~ION
The present invention has been achieved on the basis
of the above-mentioned finding. An object of the present
invention is to improve the quality and yield from ven~er
. .
sheets by precluding or minimizing splits attributable to
drying. This will eliminate the discussed problems
originating from the drying step in the plywood industry,
which has suffered from a sh~rtage in the supply of logs.
Another object of the present invention is to establish
the basis for automatic operation in drying and other
procedures subsequent to drying by giving a favorable
elastic property to veneer sheets.
~67~
In order to accompllsh the above objec-ts, and
in accordance with the broad concept of one aspect of
the present inven-ti.on, there is provided and claimed
herein a method of drying a veneer shee-t comprising the
steps of tenderizing a veneer sheet by forming numerous
small splits in the veneer sheet to increase the range
of elasticity in a direction perpendicular to the
veneer grain; compressing -the veneer sheet across the
veneer grain in the plane in which the veneer sheet
extends; and heating the veneer sheet to dry same, the
tenderizing step being performed prior to or during the
heating step, and the compressing step being performed
during the heating step.
Also, and in accordance with the broad concept
of another aspect of the invention, there is provided
and claimed herein an apparatus for drying a veneer
sheet comprising a deceleration transfer section having
speed-reducing mechanisms and extending from one point of
the transfer path for conveyi.ng the veneer sheet over
to another point downstream of the first point; a
-- tenderizing device for forming numerous small splits on
the veneer sheet and located in a suitable position in
an upstream portion inclusive of the deceleration
section with respect to an intended direction of transfer;
and heating means facing at least that part of the
transfer path which covers the deceleration section.
In accordance also with the broad concept of
a further aspect of the invention, there is provided and
claimed herein an apparatus for drying a veneer sheet
comprising a plurality of rollers having a decelerating
section to sucessively decrease roller speed toward a
- downstream side, each roller having-in a peripheral
surface thereof at least one annular recess; elongated
elements passed over said rollers while holding a veneer
sheet therebetween so as to define a zigzag transfer path,
- 3
, .. , .. ,~ . ,.
.:,
7~
each of elonga-ted elements located be-tween the veneer
sheet and the rela-ted element being received in the
annular recess, the rollers being heated.
The inven-ti.on w:ill now be described with
S reference to the following description of preferred
embodiments thereof, the description.having reference
to the appended drawings wherein:
3~
~4~i74~
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plot explanatory of the present invention
in comparison with prior art;
FIGS. 2 and 3 show the tenderizing device in plan and
front elevation, respectively;
FIGS. 4 and 5 are perspective views of tenderized
veneer sheets;
FIG. 6 are enlarged views of splits formed on other
tenderized veneer sheets;
FIG. 7 illustrates a preferred embodiment of the present
invention;
FIGS. 8 - 10 show another preferred embodiment of
the present invention in side elevation, fragmentary
front elevation and fragmentary section, respectively;
FIG. 11 is a partly cut away plan view of FIG. 3;
` FIG. 12 is a side elevation of the tenderizing device
shown in FIG. 11;
FIG. 13 is a fragmentary enlarged side elevation of
the tenderizing device;
FIG. 14 shows a modification to the embodiment of FIG. 3;
FIG. 15 shows in side elevation another modification;
FIG. 16 is a side elevation of an alternative arrange-
ment to the device of FIG. 15;
FIG. 17 is a fragmentary enlarged side elevation
showing modified extensible members;
FIGS. 18(A) - 18(;C) are sections along line XVIII - XVIII
: of FIG. 17 and showing various examples of the extensible
members; and
FIGS. 19 and 20 illustrate in side elevation a further
modification of FIG. 3.
- 4 -
7fl~;~
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
_ _ _
A basic process according to the present invention will
be described with reference -to FIG. 1. Lines in FIG. 1
demonstrate for comparison the X and Y processes typifying
the know drying processes and the Z process embodied by
the present invention. The reference level "100" on
the ordinate indicates the free length of a veneer
sheet just cut from a log by a known veneer lathe in
a direction perpendicular to its grain (the veneer
sheet having cracks at its back but not on its front or
no secondary cracks). The X process includes drying P
along, the Y process includes tenderizing Q and drying P,
and the Z process of the invention includes tenderizing Q,
compressing R and drying P. In these processes, the reference
character A denotes a non-processed veneer sheet having
only back cracks, B a tenderized veneer sheet having
numerous short slits, C a compressed veneer sheet and D
a dried veneer sheet. The length of veneer sheets vary
as illustrated when treated by the three different
processes X, Y and Z. Now, what has primary importance
to promote understanding of the present invention is whether
the changes in length can occur within the ranges of
elasticity for the veneer sheets. For instance, with the prior
art process X, a veneer sheet undergoing the drying step
tends to shrink by 5% (average value) despite the elasticity
range of substantially 1% of the veneer sheet A as determined
by experiments. Stated another way, the veneer sheet A tends
to shrink 4% beyond the elasticity range and is therefore
~67~
quite liable to crack during the drying step. According
to the other prior art process Y, the veneer sheet A is
tenderized by numerous short slits before being dried
to obtain an expansion rate of 2% while the elasticity range
S will then have extended to substnatially 3.5% as discussed.
Therefore, the subsequent drying step P causes the veneer
sheet A to shrink by 5~ which exceeds the elasticity range
by 1.5~. This is less serious than in the process X but
still involves the possibility of cracking. It will
therefore be seen that the conventional processes commonly
fail to free veneer sheets from the possibility of spl tting
due to drying and that splits always appear when they are
retained strongly as by securing opposite ends thereof
perpendicularly to the grain. In this respect, the technique
for reducing the retaining load on veneer sheets has just
been the technique for preventing splits during drying
in various types of known driers. Indeed, this will be
understood from the fact that net driers, roll driers and
other predominant driers now in use are commonly of the hot
air circulation type which blows hot air onto the veneer
sheets to avoid strong restraint thereon.
Meanwhile, the Z process of the present invention
includes the compression of R between the tenderizing
step Q and the drying step P as shown in FIG. 1. More
specifically, veneer sheet A in the illustrated example
has its proportion stretched by the tenderizing step Q,
reduced by the compression step R to give a compressed
veneer sheet ~, and followed by the drying step P.
74Z
The veneer sheet maintaining an elasticity range of 3.5%
undergoes a 2~ compression and then drying at which point
it starts shrinking. Then, the compression in the veneer
sheet is released when 2~ of the 5% contraction has been
completed while the remaining 3% of contraction is accommodated
by the potential 3.5% of elasticity range of the veneer
sheet provided by the tenderizing step. The process Z
can thus practically eliminate the possibility of splitting
during the drying step by confining the contraction to
within the range of elasticity. The splitting can be
avoided even though the drier may exert a relatively heavy
restraining load on the veneer sheet. Additionally,
the process Z opens up the road to the practical use of
; driers of the type which brings veneer sheets into direct
contact with heated plates and efficiently dries them
with relatively intense restraining force.
Such prevention of splits obtainable with the present
invention is derived from the effectlve combination of
tenderizing and compressing with drying as in the Z process~
Basic prerequisites concerning this combination are that
tenderizing takes place during or before drying and that
compression occurs during *rying. With this principle,
the short range of elasticity relative to the amount of
contraction is compensated for by the tenderizing and
compressing steps and, hence, splits which would otherwise
occur can be avoided when the contraction exceeds
the elasticity range. Tenderizing if done without any
assistance would greatly reduce the elasticity range as
-- 7 --
67~
already stated. Compression when employed alone would be
needed in an excessively large amount and, in view of
the difficulty presented in compressing various types of
veneer sheets with differing contraction rates, a wide range
of compression force would be required to accommodate all
of them. Thls degree of compression tends to damage veneer
sheets and such tendency can not readily be prevented.
The combination according to the present invention permits
the two different kinds of process to mutually reduce their
necessary degree of treatment to such an extent that
the individual processings, particularly the compression,
can be performed with ease. Thus, the present invention
prevents the splitting of veneer sheets easily and
effectively. Another advantage is derived from the inherent
combination of the elasticity range provided by tënderizing
and that provided by compression. Since the elasticity
range as a whole is freely selectable because of the combina-
tion of the determined elasticity range (Frovided by com-
pression) and the free one (provided by tenderizing), it can
accommodate any irregularity in the compression distribution
of veneer sheets and, therefore, can also accommodate with
ease any contraction which may differ from one location
to another on a veneer sheet. With this advantage,
the contraction of veneer sheets can be easily accommodated
over a wide range to favorably fit the properties of
the veneer sheets. For example, the Z process shown in FIG.
1 achieves the desired effect without any adjustment even
though the contraction rate may rage from 2% to 5.5%.
~i79~Z
In accordance with the present invention, a veneer sheet
may be tenderized and then compressed, or compressed and
then tenderized, or tenderized and compressed at the same
time. However, the process wherein tenderizing precedes
compression is more desirable than other procedures since,
where tenderizing stretches a veneer sheet as in Z process
of FIG. 1 for example, at least the stretched proportion of
the veneer sheet can be compressed with ease. Preferred
examples of the entire process employing such a favorable
order of tenderizing and compressing are a process wherein
` tenderizing occurs before drying and then compression occurs
during drying and a process wherein tenderizing occurs during
the drying process and then compression takes place.
In a case where the tendering and compressing take place
in the opposite order or in an overlapped manner, they will
proceed in the course of drying since the compression must
occur during drying in any case. Compared with the ideal
order, such alternative sequences present difficulty in
the compression for compressing a veneer sheet in a direc-
tion perpendicular to its grain or maintaining the compressed
state of the veneer sheet. Nevertheless, the alternative
processes can be readily designed in view of the fact that
the necessary amount of compression is far smaller than
in the process employing compression~along.
The elastic property of veneer sheets will be discussed
in greater detail in combination with a desirable manner of
tenderizing with reference to FIGS. 2-6.
It appears that the elastic property of veneer sheets
originates from various kinds of cracks distributed therein.
When pulled by hands, a veneer sheet has such cracks enlarged
sufficient to pass visible light rays therethrough.
Particularly, an increased number of trans~,itted light rays
are visible when a suitable degree of tenderizing is applied
to a non-processed veneer sheet having cracks only on its
back. This is sufficient to-provide that tenderizing
increases the range of elasticity. Further observation will
show that the elasticity results from bending actions of,
for example, narrow elongate portions of wood finely divided
by the numerous cracks. FIG. 4 depicts a tenderized
veneer sheet formed with splits or slits 2 regardless
of its grain 1 (indicating the direction of the grain) by,
for example, a roller having a number of piercing elements
in the form of cutting edges. FIG. 5 shows another tenderized
veneer sheet whose slits 2 extend substantially along
the grain without damaging the fibers. The tendency of
elasticity concerned here is enhanced more stably in
the veneer sheet of FIG. 5 having the fikers unbroken than
in the veneer sheet of FIG. 4 having the fibers cut
apart. However, the veneer sheet of FIG. 5 tends to permit
the slits or splits provided or enlarged by tenderizing
to run together and ~urn into large cracks. In this respect,
the veneer sheet of FIG. 4 is desirable because artificial
distribution of slits is easy. A veneer sheet tenderized
in any of the two illustrated manners has been proved
to gain far more elasticity than any non-tenderized veneer
-- 10 --
742
sheets. The present invention proposes a process and
apparatus which, as will be descriebed hereinafter, has
combined advantages of the two tenderizing methods to give
veneer sheets a particularly favorable enlarged range
of elasticity.
The process of the present lnvention includes primary
tenderizing and secondary ~enderizing which may occur
simultaneously with, or after the primary tenderizing.
For the pr~E~y tQnderiæing, a veneer sheet is formed with
preferably distributed pierced flaws by piercing elements
or cutting edge elements on the periphery of a roller or
suitable means is employed to form small flaws (or short
slits) from which splits can start. In the secondary
tenderizing, sp~ts tending to extend along the fibers
of the veneer sheet are formed as by an apparatus shown
in FIGS. 2 and 3. This process employing two simultaneous
or successive stages of tenderizing suppresses irregular
communication of adjacent splits and permits the splits
to be distributed in the manner shown not in FIG. 6(b)
but in FIG. 6(a).
Naturally, it is preferable for the splits to run
to the pattern of FIG. 6(a) than to that of FIG. 6(b)
and most preferable if they extend along the grain of
the wood. This most preferable pattern will also increase
the elasticity range to a signiticant degree.
Referring to FIGS. 2 and 3, there is shown a tenderizing
apparatus which has been newly developed in connection with
the present invention. The apparatus includes a roller
74Z
8 whose outer periphery is covered with a layer of elastic
material such as rubber, and a small diameter roller 6
having a number of recesses 7 adapted to guide elongated
coil springs 4 therein. In operation, the rollers 6 and
8 rotating as indicated by arrows nip a veneer sheet 3
therebetween and feed it in the direction also indicated
by the arrow. Then pressurizing means tnot shown) associated
with the roller 6 or 8 applies a pressure to the moving
veneer sheet 3 while the elongated coil springs 4 move as
indicated by the arrow in contact with the periphery of
the roller 6 with a relatively small radius of curvature
to be opened individually, thereby making the veneer sheet 3
tenderized. More speci~ically, this tenderizing device
~ employs an improved version of Elemendorf's tenderizing
; 15 system, that is, it utillzes in combination with Elemendorf's
principle the opening actions of outer portions of
the adjacent turns of each coil spring 4 relative to each
other which occur when the coil springs are guided within
curvature. The device therefore stretches the veneer sheet
3 from opposite sides thereof while forming or enlarging
splits by bending, tenderizing the veneer sheet with
- favorably small pitches. The tenderizing device additionally
includes guide members 5 and 5' for the veneer sheet and
a conveyor 9 for feeding the veneer sheet.
It should be borne in mind that the "tenderizing"
implies herein is not only forming or enlarging numerous
small splits which can stretch a veneer sheet. Even if
a processed veneer sheet does not show any expansion,
it suffices that the veneer sheet bears numerous small
- 12 -
splits ~inclusive of pierced flaws and flaws formed by a knife-
like tool) to have its range of elasticity increased
in a direction perpendicular to the direction of the grain.
Now, compression of a veneer sheet will be described
in connection with a system for carrying out the discussed
process according to the present invention.
Referring to FIG. 7, a veneer sheet processing system
is shown to include a tenderi~ing device whose major part
consists of an anvil roller 15 and a tenderizing roller
16 having a number of cutting edge elements thereon. This
tenderizer is followed by a transfer path defined by
numerous roller pairs such as 17, 17' and 17" and guide
plates 18 each intervening between adjacent roller pairs.
While it is not always necessary to connect the transfer
path with the tenderizer 15, 16 by a conveyor, they need
be connected together essentially ln the same way as
the conveyor connection so that a non-processed veneer sheet
can be tenderized in advance by the tenderizer. The transfer
path extending substantially as far as the tenderizer 15, 16
includes a deceleration section which covers an upstream
length of the transfer path. This deceleration section
has a drive source 19 and speed-reducing mechanisms 20
and 21 operating such that the second roller pair 17'
rotates at a speed lower than that of the first roller pair
17 and the third roller pair 17" at a speed lower than
that of the second. Accordingly, the veneer sheet
travelling through this particular section of the transfer
path will be compressed by the transfer roller pairs.
- 13 -
In the rest of the transfer path, a fourth roller pair and
onward will operate at the same speed as the third roller
pair 17" and convey the veneer sheet while maintaining
the compressed state. In the meantime, hot air is circulated
through the space enclosed by heat insulating walls 22
so as to dry the veneer sheet under compression. Denoted
by the re~erence numerals 10 and 11 are a log and a cutting
knife, respectively. This cutting station may be connected
to the tenderizer 15, 16 either directly or through any
known processing step. In this way, where compression is
applied to a veneer sheet which is being transferred,
a deceleration transfer passage using speed-reducers is
defined from a certain point on the transfer path over to
a certain downstream point. Then, as clearly understood
lS from FIG. 7, a veneer sheet is compressed by the first roller
pair 17 to the third roller pair ~7" progressively and
maintains a certain degrRe Qf its compressed state even
after having moved past the third pair of rollers. This
permits the compression of the veneer sheet until the com-
pression stress in the veneer sheet reaches zero due todrying. In this case, the drying step P using heating
means proceeds in combination with the compressing step
R and the tenderizing step Q takes place in a position sub-
stantially upstream of the drying and compressing station
in the transfer path. Naturally, the tenderizer may be
located in the space dbfined by the walls 22 in order to
tenderize a veneer sheet during drying. In any case,
~he tenderizer is preferably located within the deceleration
- 14 -
.
i'79~
section of the transfer path or in a position upstream of
the deceleration section to promote easy compression and,
therefore, simplification of the mechanical arrangement.
It will be appreciated from the above that, of systems
using the aforementioned process a system for continuously
processing a veneer sheet basically includes a transfer
path conveying the veneer sheet, a deceleration section
covering a certain upstream length of the transfer path and
using deceleration mechanisms, a tenderizer located in
a suitable upstream position inclusive of the deceleration
section, and suitable heating means facing the transfer
path inclusive of the deceleration section. The guide
plates 18 employed in combination with roller pairs in FIG.
7 may be replaced by piano wires or like similar elongated
elements extending along the lower surface or the lower
and upper surfaces of a veneer sheet so long as they define
the transfer path together with -~he rolle-r pairs. Such guide
means cah be in practice omitted depending on the spacing
between adjacent ones of the roller pairs. Furthermore,
the deceleration section of the txansfer path need not
always be defined in an inlet portion of the transfer path
as illustrated~ Rather, it is preferable for the decelera-
~ion section to extend from a position where the moisture
content of a veneer sheet becomes substnatially 30~ and
~5 causes it to shrink noticeably over to a position down-
stream of the first position~
FIG. 8 shows in side elevation another veneer sheet
processing system representing a preferred drying device.
FIG. 9 shows this system in fragmentary front elevation
and FIG. 10 in a section along line X - X of FIG. 8.
The illustrated arrangement is concerned with a drying
device of heat plate type for carrying out the afore-
mentioned process according to the present invention.
This type of drying device has been impracticable because
it restrains a veneer sheet with relatively large strength
and thereby causes noticeable cracks in the veneer sheet
during drying. The present invention readily makes it
practicable by applying the drying principle discussed and
further improving it to promote drying of a veneer sheet
in the course of the transfer.
Referring to FIGS. 8 - 10, the system includes two sets
of multiple elongated elements 24 and 25, such as coil springs
which are passed over a plurality of rollers 26a-26h to
define a zigzag transfer path while sandwiching a veneer
sheet 23 therebetween. Each of the rollers 26a-26h has
on its periphery multiple annular chan-nels in which those
elongated members closer to the roller than the veneer
sheet 23 are received to become entirely hidden thereln.
For example, as partly shown in FIG. 10, the roller 26a
; is formed with annular channels 27a and the roller
26b is formed with annular channels 27b. The veneer sheet
23 is thus directly engaged with the peripheral surfaces
of the individual rollers. The rollers 26a-26h are
individually heated by steam or the like from the inside and
connected through speed-reducing mechanisms 28a-28h with
a drive source 29. The rotational speed progressively
decreases from the most upstream roller over to the most
- 16 -
7~
downstream roller with respect to the intended direction
of transfer thereby defining a deceleration transfer
section. The reference numeral 30 denotes rollers for turning
the running directions of the elongated elements 24 and 25.
In operation, the rollers 26a-26h are driven in
the directions indicated by the arrows to transfer the veneer
sheet 23 while heating the veneer sheet. At the same time,
the rollers rotating at successively decreased speeds
compress the veneer sheet at the respective shift points
from one roller to another. Accordingly, splits due to
drying can be reasonably suppressed by the simultaneous
drying and compression even without a tenderizer. More
effective prevention of splits is achievable ~y so controlling
the speed-reducer mechanisms 28a-28h as to carry out decelera-
tion transfer matching with the contraction of various parts
of the veneer sheet. Additionally, the illustrated system
conveys the veneer sheet 23 in a desirable manner. Since
the elongated elements guide the veneer sheet from one
roller to another holding it therebetween, the system
overcomes possible defects in the veneer sheet such as rotten
spots and knotholes in smoothly conveying ~he veneer s~e~t
without any dislocation or lifting from the heated rollers.
This also holds when the veneer sheet has a relatively
narrow width. The system is therefore free from jamming
of the veneer sheet and like troubles and favourable from
the viewpoint of practical use.
To conform with the drying principle of the invention,
the tenderizer will be located in a suitable position
which is basically in or ahead of the drying station.
- 17 -
~4~i7~
Preferablyr it may occupy a position within the deceleration
section or a suitable position ahead of the deceleration
section such as one independent of the deceleration section
to introduce a veneer sheet therefrom in the manner shown in
FIG. 8. In practice, though not shown, the tenderizer may
be positioned in the vicinity of the inlet of the system
shown in FIG. 8 or immediately past of a veneer lathe
located in a further upstream position or may be replaced
by a veneer lathe of the type which tenderizes a veneer
sheet while cutting it off from a log. When located
in the drying station, the tenderizer may take the form
of a tenderizing roller with piercing elements and afforded
by the roller 26a of FIG. 8. Alternatively, the tenderizer
in the drying station may utilize the speed-reducer mechanisms
28a and 28b and cause the latter 28b to rotate at a higher
speed than the former 28a so that their associated rollers
28b and 28a slightly pull a veneer sheet therebetween to
enlarge splits in the veneer sheet.
Meanwhile, it lS not a prerequisite to employ all of
the rollers 26a-26h in FIG. 8 for constituting the decelera-
tion section. For example, some of the speed-reducers shown
may be omltted in order to define the deceleration section
by a suitable number of the speed-reducers and their
associated rollers. The deceleration section will become
particularly effective when designed to cover the region
from a position where the moisture content of a veneer
sheet is substantially 30% to a certain downstream position.
The individual speed-reducers may be driven at a variable
- 18 -
speed reduction ratio to cope with varlous ~oistu~e c~ntents
and various degrees of contraction of the ve~eex sheets. The
compression ma~ be pex~ormed in re~ation ~with the conditio~ of
a veneer sheet processed by a tenderizer wi-th a vie~ to pro-
viding optimum compression. To simpli~y the system, the rollers
may ha~e their diameters varied to co~stitute a substantial
speed-reducing mechanism.
This syste~ not only achieves the advantages inherent
in the basic process discussed but operates with excellent
efficiency because a veneer sheet directly contacts heated
roller surfaces to be dried while having its opposite surfaces
turned over repeatedly~ The xesult is a d~ying step which con-
sumes only a short period of time and a low cost. Moreover,
due to the smooth transfer of a veneer sheet, a desired length
of heating plate can be obtained merely by installing numerous
additional rollers of small diameters. The transfer of a
veneer sheet from one roller to another occurs smoothly.
It is preferable that the spacing between each two
adjacent elongated elements 24 or 25 be substantially 150 times
the veneer thickness or less. If it exceeds150 times, the veneer
sheet floats from the rollers at intermediate areas between the
elongated elements 24 or 25 with the result that drying
efficiency is reduced. However, if the elongated elements are
replaced with belt-like members, the spacing therebetween may
be broader, depending upon the belt width. At any rate, the
veneer thickness determines the required areas where the sheet
is held from the outside.
As viewed in Fig. 9, -the elongated elements 24 and
25 will be installed in numbers matching the width of the veneer
sheet 23. Coil springs are preferable as the elongated
elements because they will desirably transfer a veneer sheet
even in the deceleration section without slipping on the veneer
19 ~
~ 467~
sheet or in the annuIar channe].s on the roLlexs.. ~h.ere coil
springs or the like constitute. the e1Qngated elem.~.ts, the
two vertical se~ies of rollers in Fig. 8 ~.ay be spaced a little
distance from each othex to make the trans-~er of a veneer sheet
from one roller to another, smoother~
..... ,~,
. \ .
- l9a -
4~
Next, the tenderizer of FIGS. 2 and 3 will be described
in more detail.
Refarring to FIGS. 11-13, a tenderizing device
according to the present invention includes a plurality
of parallel extensible members 4 or flexibe bellows like
coil springs. These e~tensible members of coil springs 4
extend perpendicular to the axis of a roller 8 so that
a path for conveying a ven-eer sheet 3 is defined between
the coil springs 4 and roller 8. The roller 8 has its
outer periphery covered with an elastic layer made of rubber
for example and is driven for rotation to transfer the veneer
sheet 3. A roller or like sylindrical pressing member 6
is located at the back of the coil spring 4 and presses them
towards the roller 8 whereby the coil springs 4 moving
with the veneer sheet 3 are pressed against the surface
of the veneer sheet.
With this device, the presser roller 6 causes the coil
springs 4 to bend towards the roller 8 to-gether with
the veneer sheet 3 and thereby enlarges the spacing between
the adjacent turns of each coil spring. More specifically,
those portions of the coil springs 4 engaged with the veneer
sheet 3 stretch in their lengthwise direction. This locally
subjects the veneer sheet 3 to a tensile force with the result
that small splits 2 are formad in the veneer sheet. Such
splits 2 will be formed successively in the veneer sheet
in accordance with the rotation of the roller 8. It will
be noted that, since the magnitude of the tensile force
acting on the veneer sheet depends on the opening degree
- 20 -
~6742
of the adjacent turns of the coil springs in the bent posi-
tion, the splits 2 can be provided to the veneer sheet
substantially regardless of various conditions such as
thickness, strength and transfer speed of the veneer sheet
as well as presence/absence of cracks at the back of
the veneer sheet and orientation of the back cracks if
present. Meanwhile, the elastic layer on the roller 8
assists in forming and enlarging the splits 2 from
the side of the veneer sheet 3 opposite to the coil springs
-
4 due to its local variation in speed which results fromdeformation. This, however, does not help enlarge the splits
beyond a necessary degree because the extension of the splits
2 is regulated by the coil springs 4. For this reason
and slnce the splitting caused by tension does not accompany
a cut across the grain of the veneer sheet, the illustrated
device offers quite an effective and adequate tendering effect
inclusive of extension without detriment to the strength
of a veneer sheet.
The coil springs are an example of the extensible
members 4 which is the most preferable in forming minute
splits, increasing the applicable range of the device and
promoting easy maintenance. FIG. 17 illustrates an alterna-
tive example of the extensible members which comp~ises
a number of blocks 4b arranged along the lengthwise direc-
tion of the extensible members in an intimately engagedor slightly spaced relation. The blocks 4b are connected
together by a belt 4a of a relatively hard material at their
one side. Each block 4b may have a section shown in FIG. 18a
~4~2
or 18b; the blocks 4b and belt 4a may even be formed integrally
o~ a hard resln or hard rubber for instance as shown in FIG.
18c with the blocks arranged into a comb like configuration.
Any other arrangements may be employed for the extensible
members 4 insofar as they have those portions pressingly
engagable with a veneer sheet aligned in the lengthwise
direction and the spacing between said adjacent engagable
portions can be increased by bending of the extensible
members as discussed. It will be recalled that the magnitude
of the tension or the dimension of the small splits depends
on the opening degree of the neighboring portions of
the extensible members in the bent positions. It is thus
preferable to select the spacing of the adjacent engaging
portions, the length ~thickness) of each engaglng portion
lS and the like according to a specific application and in
consideration of the bending degree attributable to the presser
roller. Preferably, the extensible members are located
at suitable spacings as shown in FIG. 11 in order to
avoid interference between ad~acent extensible members
and that between neighboring splits. Where the extensible
members are endless, the whole device will become favorably
small in size. Coil springs are usually formed of iron or
an alloy of iron, but such a metal reacts the sap and
the like of veneer sheets to change -the color of the veneer
sheets into brown. Hence, where the device is operated
for tenderizing a fresh veneer sheet, it is preferable to
use coil springs whose outer surfaces carry rubber layers
or plated layers provided such covering layers do not prevent
- 22 -
z
resilient actions of the coil springs. If desired, the coil
springs may be bodily made of stainless steel which is
inactive to the sap. In any case, a greater effect is
achievable by selecting coil springs in consideration of
the conditions of a veneer sheet to be processed, intended
application of the processed veneer sheet etc.
Concerning the presser member, it should preferably be
a rigid member to positively bend the extensible members
and its curvature should be suitably determined because
the curvature would affect the opening degree of the engaging
portions of the extensible members. However, the curvature
is not limited to a constant one as that of the presser
roller. If use is made of a freely rotatable pressure
roller having a polygonal or~elliptic cross-section for
example, splits in a veneer sheet can be conditioned in
a desired manner by the adjustable magnitude and acting
point of the tension. Furthermore, the freely rotatable
presser roller may be replaced by a non-rotatable pressing
member. Generally, the veneer sheet 3 is conveyed by
the rotation of the roller 8. Where another member is
installed in the device for moving the veneer sheet 3,
the roller 8 will need no drive mechanisms and be only
free to rotate.
Meandering and li~e actions of the extensible members
4 would cause the extensible members to interfere with each
other and excessively press the veneer sheet. To prevent
this, the presser member 6 may have radially outward flanges
61 of a radial dimension less than the thickness of
the extensible members and serving to guide and stop
- 23 -
7~
the extenslble members 4 as depicted in FIG. 14.
Alternatively, annular recesses (not shown) may be formed
on the presser member 6 to serve the same purposes. If
necessary, a supporting member (not shown) may be located
at the back of the presser membex 6 in order to avoid
flexing of the presser member attributable to its pressing
action.
It may occur that, when the extensible members 4 are
released from the bending force to have their adjacent
engaging portions closed again, they nip fine fibers of
the veneer sheet between their adjacent turns and carry
the veneer sheet therewith along their running direction.
This can be avoided if as shown in FIG. 13 the presser
member 6 and extensible members 4 are so located that
the adjacent turns of each extensible member close at
a position downstream of the presser member 6 with respect
to the direction of veneer sheet conveyance and where
the veneer sheet will have become fully released from
the extensible members. The problem can also be settled
by locating a separating member 13 in a position downstream
of the presser member 6 as indicated in FIG. 14. Additionally,
it is permissible to design the presser member 6 and roller
8 to be movable away from each other under a predetermined
level of pressure with a view to coping with unusual pressure
forces which may result from overlapping or the like of
a veneer sheet.
Second and third embodiments of the present invention
are illustrated in FIGS. 15 and 16. Each of these embodiments
24 -
7~2
includes, in addition to the various component parts of
the first embodiment, a piercing rolier 14 in the transfer
path of a veneer sheet upstream of the presser member 6.
The roller 12 has numerous short piercing elements 13 on
its outer periphery and opposes the roller 2 in such a manner
as to cut into the veneer sheet 3 while pressing the same.
With this alternative design, the piercing elements
12 on the roller 14 form numerous cuts (not shown) in
the veneer sheet 3 with the rotation of the roller 8.
Then the presser roller 6 urges the extensible members 4
towards the roller 8 together with the veneer sheet 3 whereby
the turns of the members 4 are opened in contact with the veneer
sheet as stated to exert local tension to the veneer sheet.
Since cuts provided by roller 14 are now present in
the veneer sheet 3, the tension concentrates on the relatively
weak cuts and s~ccessively forms splits each starting from
the cut.
Thus, splits in the veneer sheet start from individual
cuts provided by the roller 14 and therefore can be formed
easily and positively. The cuts in the veneer sheet serve
only to cause the tension originating from bending of
the extensible members 4 to concentrate to each local
portion while the splits or slits are formed strictly by
the tension. For this reason and because the extensible
members 4 regurate the extension of the splits, growth of
the splits beyond a given limit is prevented. Where
the cuts in the veneer sheet have irregular distributions in
- 25 -
i74~
sizel depth etc., a traditional tenderizing device merely
added with the piercing roller applicable to the present
invention or like roller will further promote such irregular
distributions and thereby bring about various problems
such as fall in the strength of the veneer sheet and
breakage of the veneer sheet. The device of the invention
is free from this kind of drawback and offers a far more
improved tenderizing and extending effect.
By suitably locating the piercing elements 12 on
the roller 14, for example in a zigzag pattern, splits
neighboring each other along the grain of a veneer sheet
are prevented frcm communicating with each other in a more
positive way. This suggests the possibility for increased
degrees of tenderness and extension of a veneer sheet
without an accompanying fall in the strength, breaXage
or the like. Designed only to form cuts in a veneer sheet,
the short piercing elements on the roller 14 can be arranged
densely enough to effectively and adequa-tely form splits
even in very thin veneer sheets (thickness usually ranging
from 0.~ mm to 1 mm) which conventional tenderizing devices
have been incapable of processing.
Each piercing element 12 may be in any desired shape
such as a needle shape, a cone, a pyramid or a wedge shape
- as long as it definitely forms cuts in a veneer sheet
without unnecessarily cutting of the grains. Also, its
height and others on the roller 14 may be suitably determined
according to a specific application. It is preferable,
for preventing the veneer sheet from being conveyed round
- 26 -
ii7~
the circumference of the roller 14 which has cut into
the veneer sheet, to so locate the extensible members 4
as to guide the veneer sheet towards the roller 8 in
the transfer path downstream of the roller 14 as viewed
in FIG. 15 or, as shown in FIG. 16, to position a guide
in the transfer path downstream of the roller 14 in
the same way. Meanwhile, the extensible members 4 may
extend somewhat longer along the outer periphery of the roller
8 as viewed in FIG. 15 in a position upstream of the presser
roller 6 or the presser roller 6 and roller 14. Then
the resultant transfer path will promote very accurate
transfer of a veneer sheet and create a precautionary
measure against the meandering of the veneer sheet wh`ic~
might occur due to the formation of splits or cuts.
A further tenderizing device according to the present
invention is shown in FIG. 19 and which has a combined
presser and piercing roller 12. This roller 14 is intended
to press the extensible members 4 and cut into a veneer
sheet simultaneously. For this purpose, ~he roller 12
- 20 is positioned on the side of the extensible members 4
opposite to the roller 8 in such a manner as to force
the extensible members towards the roller 8 and press and
cut into the veneer sheet through the gaps between neighboring
~- parallel extensible members. Short piercing elements 12
may be formed on the periphery of each of multiple flanges 6'
which are arranged at equally spaced axial locations on
the roller 14 (see FIG. 19). Alternatively, such piercing
elements 12 may be directly studded on the roller 14 lsee
FIG. 20). The roller 14 which is freely rotatable allows
its elements 12 to engage the veneer sheet 3 before
- 27 -
t7~2
the extensible members 4 are bent to cause splitting of
the veneer sheet. Accordingly, numerous splits or slits
will be formed successively starting from the cuts provided
by the elements 12. While achieving substantially the same
effect as the device shown in FIGS. 15 and 16, the device
according to this embodiment simplifies the mechanism and
therefore offers additional effects because it allots
the function of forming cuts and that of forming splits
to a single common roller. The piercing elements 12
press and cut into the veneer sheet through between
the parallel extensible members 4. Due to this arrangement
and if the elements 12 are rigid as in the case of FIGS. 19
and 20, the roller 12 can allow the flang~s 6' or the elements
6' to also serve as a guide for avoiding meandering of
the members 4.
In summary, a tenderizing device according to the present
invention forms numerous small splits effectively and
adequately regardless of the physical properties, thickness
and cracks on the back of a veneer sheet, orientation of
the back cracks, transfer speed of a veneer sheet and other
conditions which have obstructed versatile application of
conventional devices. The device of the invention thus
offers a marked tenderizing and extending effect and greatly
contributes to the progress of the art of plywood production.
- 28 -
