Note: Descriptions are shown in the official language in which they were submitted.
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1 FIELD OF THE INVENTION
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The present invention relates to a twin wire
~ormer that is used as a former (i.e. having a formation
forming section) in a paper making machine.
S
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side cross-sectional view showing
one preferred embodiment of a twin wire former according
to the present invention.
FIG. 2 is a perspective view illustrating that
fiber distribution is improved by the present invention.
FIG. 3 is a side cross-sectional view of a prior
art Bel-Baie former.
FIG. 4 is a side cross-sectional view of a prior
art hybrid former.
DESCRIPTION OF THE RELATED ART
What determines the nature of a paper sheet is
mostly the performance of a paper making machine from an
initial portion thereof to a former. With respect to the
performance required for this former, it is required that
retention of raw material is good, that a paper sheet
having a large strength can be formed, that only small
differences in quality exists such as printability or the
like between the front and back surfaces of the paper
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1 sheet, that a paper sheet having a large surface strength
can be formed, that high speed operation is possible, and
that the former can be operated consistently, etc. While
various types of formers have been invented in order to
fulfill these requirements, any one of them has not
fulfilled all the requirements. In the case of the Bel-
Baie former in the prior art as shown in FIG. 3, although
these requirements were almost fulfilled, there were
difficulties in the retention of fine raw material and in
the coupling strength in a thicknesswise direction of
paper sheets formed thereby.
According to research and investigation, it has
been known that after a raw material liquid has been
sandwiched between two wires, if dewatering is carried out
while scrubbing the wire with a fixed body, then a lot of
fine raw material would flow therefrom, that is, retention
is lowered. If one employs the construction such that the
number of fixed bodies for scrubbing the wire such as shoe
blades a, suction boxes b and the like in FIG. 3 are
reduced and the number of dewatering means comprising a
rotary body such as a suction couch roll c and the like
are increased in order to improve the retention, then
while the retention is improved, the formation is
deteriorated.
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1 With regard to the strength in the thicknesswise
direction of a paper sheet, if a paper raw material liquid
is sandwiched between two wires d and e and dewatering is
effected from the both surfaces to form a fiber mat, then
a paper sheet having a structure in which the coupling
strength in the thicknesswise direction is low as compared
to the case where dewatering is effected from oniy one
surface to form a fiber mat, is formed. In order to
reduce differences between the top and bottom surfaces of
a paper sheet, it is necessary to dewater at both surfaces
to form a mat, and for that purpose, considerably
asymmetric both-surface dewatering would suffice. In the
case of the asymmetric both-surface dewatering, lowering
of the coupling strength in the thicknesswise direction
can be also suppressed to a little extent.
In the above-mentioned type of formers, many
formers in which a top wire unit is provided at a rear
portion of a long wire, are known. One example of the
formers is illustrated in FIG. 4. However, in such type
of former as shown in FIG. 4, that is, in the former of
the type that a long wire f and a twin wire former g in
the prior art are joined together (hybrid former), when
carrying out high speed operation, a raw material liquid
is subjected to an excessive influence by pulse pressure
produced by dewatering elements such as foils or the like
lZ51~'7~
1 provided in the portion of the long wire f, resulting in
the destruction of the texture of the paper. Therefore,
the former was not always suitable for high speed
operation. It is to be noted that h in FIGS. 3 and 4
represents a headbox, i in FIG. 3 represents a water
deflector, and j represents a vacuum deflector.
SUMMARY OF_THE INVENTION
It is therefore one object of the present
invention to resolve the difficulties in the prior art
twin wire formers with respect to the retention to fine
raw material and the coupling strength in the
thicknesswise direction of a paper sheet, without an
accompanying problem of the texture is being deteriorated
or that the former is not suitable for high speed
operation being presented.
To that end, according to the present invention,
in a twin wire former the top wire is partly provided with
a portion in which a water-impermeable belt is made to
travel along the inside of the loop, so that dewatering in
this portion is effected only on one side, i.e. the bottom
wire side, and in this portion a wrapping angle for the
wire is varied by adjusting the positions of a plurality
of rolls or shoes to improve the formation. Thereafter,
dewatering on the side where dewatering has been
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1 suppressed by the above-mentioned belt is also effected,
and this construction is employed as a measure for
resolving the problems.
The present invention will be explained below
with reference to its preferred embodiment illustrated in
the accompanying drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows the preferred embodiment of the
present invention in which raw material ejected from a
headbox 36 is sandwiched between a bottom wire 33 and a
top wire 34. However, initially, upward dewatering is not
effected because a water-impermeable belt 35 is traveling
along the top wire 34. In addition, a breast roll l is
supported in a vertically adjustable manner.
Reference numeral 2 designates forming boards,
and numeral 3 designates open rolls which enable
adjustment of a wrapping angle of the bottom wire by
adjustment of their vertical positions. Reference numeral
4 designates deflectors which prevent white water removed
at the portion of the forming boards 2 from striking
against the open rolls so as to not be brought again into
inlet nips between the bottom wire 33 and the open rolls
3. The deflector 4 can be adjusted with respect to the
engagement thereof with the wire in accordance with the
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1 vertical position adjustment of the breast roll 1 or the
open rolls 3. The forming boards 2 are also adjustable.
It is assumed that multiple open rolls 3 and the
deflectors 4 are provided. A roll 5 is an open roll
similar to the open rolls 3 or a suction roll, but its
position is fixed.
Reference numeral 6 designates an optional
suction box. In addition, while reference numeral 7
designates a suction box, its surface is curved, and it
ensures that a fiber mat leaves the top wire 34 and
travels on the bottom wire 33. Numeral 8 designates a
suction couch roll, numeral 9 designates a turning roll,
numeral 10 designates a return wire roll, numeral 11
designates a wire guide roll, and numeral 12 designates a
stretch roll.
A wet paper sheet is transferred by a suction
roll 37 to a felt 38 and is carried to a press. A top
breast roll 13 is vertically adjustable similarly to the
breast roll 1, and so it is possible to gradually pinch a
jet by reducing a converging angle between the top wire 34
and the bottom wire 33. Reference numeral 15 designates a
beam extending in the widthwise direction over the entire
width, and it is possible to detachably mount a shoe 14 to
the beam 15. The extent to which the top wire 34 is
pressed downwards via the belt 35 can be adjusted by
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1 employing shoes having different thickness or different
configurations. Reference numeral 16 designates a shower
which feeds lubricant water between the shoes 14 and the
belt 35. While the sets of shoes 14 and the shower 16 can
be provided respectively behind the rolls 3, the same
function performed thereby can be achieved by a roll 17
that is vertically adjustable in position. Or else, as
different means, a set of shoes 18 and a pressurizing tube
21 could be employed.
More particularly, the shoe 18 is mounted on a
beam 19 extending over the entire width so as to be
rotatable about a fulcrum, and the extent to which the top
wire 34 is depressed is adjusted by regulating the
pressure in the pressurizing tube 21. In order to apply a
strong wedge pressure to the raw material sandwiched
between both the top and bottom wires, it is also possible
to place the shoe 18 above the deflector 4. Or else, as
an alternative method, it is also possible that the lower
surface of the beam 22 extending over the entire width is
used as a shoe and that the amount of depression of the
top wire 34 is adjusted by vertically moving this portion.
A roll 23 is supported so as to be vertically
adjustable in position, and thereby a wrapping angle of
the belt 35 around the roll 5 can be adjusted. Reference
2S numeral 24 designates a stretch roll for the belt 35,
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1251~7~
1 numeral 25 designates a guide roll, and numeral 26
designates support rolls for the belt, the rolls being
able to simultaneously support the wire 34. Reference
numerals 27 and 29, respectively, designate casings for
collecting white water extracted on the top wire side, the
casings being able to employ a vacuum in combination.
Reference numeral 28 designates a wire roll, but it could
be an open roll. Numeral 30 designates a stretch roll for
the top wire, numeral 31 designates a wire roll, and
numeral 32 designates a guide roll.
Now, describing an operation with respect to the
preferred embodiment constructed in the above-described
manner, based on the adjustment of the positions in the
vertical direction of the breast roll 1, the top breast
roll 13 and the first open roll 3, a raw material jut
ejected from the headbox 36 is gradually sandwiched
between two wires 33 and 34. Furthermore, the wrapping
angle of the both wires 33 and 34 about the open roll 3 is
based upon the position of the adjustable open roll 3. In
addition, by adjusting the positions of the shoes 14 and
18, the roll 17, the beam 22 and the like in the direction
of the wires, the wrapping angles of the both wires 33 and
34 around these members can be varied, and at the same
time the wrapping angles of the both wires 33 and 34
around the open roll 3 and the roll 5 can be adjusted.
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1 At such locations where a wrapping angle exists,
due to tension in the wire 33 or in the wire 34 and belt
35 positioned outside of the arc, a pressing pressure acts
upon the raw material liquid placed between the two wires,
and so, dewatering is effected. In order for the raw
material liquid sandwiched between the two wires to pass
through the dewatering section in the direction of
traveling, it must move from a low pressure side to a high
pressure side, and so, it passes while the energy
associated with the velocity of the belts is converted to
pressure. In other words, the raw material liquid enters
the dewatering section while the traveling velocity is
reduced and while a dynamic pressure is converted into a
static pressure. In the case where the dewatering section
is long, the once decelerated raw material liquid is again
accelerated by the wires traveling nearly at the same
velocity to the same velocity, but in the case where the
wrapping angles of the respective dewatering sections are
small as shown in FIG. 1, the raw material which has
passed a high pressure portion would travel at the wire
velocity in a large proportion due to the conversion of a
static pressure to dynamic pressure. In any event, each
time the raw material passes through the locations of the
plurality of rolls 3, the roll ~, the shoes 14 and 18, the
roll 17, the beam 22 and the like, dewatering is effected
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1 at the respective locations, and acceleration and
deceleration in the traveling direction are appropriately
applied to the raw material liquid.
The explanation for the fact that if such
acceleration and deceleration are applied appropriately,
then dispersion of fibers is improved, is set forth in
Laid-Open Japanese Patent Specification No. 57-89694
published June 4, 1982 and relating to a headbox, and it
can be easily confirmed through a simple experiment as
illustrated in FIG. 2. That is, paper making raw material
41 is enclosed in a transparent bag 40 made of plastics
and is placed on a table, then a roll-like body 42 such as
a rod or the like is pressed against it and moved up and
down to move the raw material 41 is to the left and to the
right. While this roll-like body 42 is held in the state
of lightly pressing the bag 40, the rod-like body 42 is
moved to the left and to the right by rolling it along the
surface of the bat 40, and thereby the raw material 41 in
the bag 40 is moved to the left and the right. If such
movement is repeated, dispersion of the raw material 41 in
the bag 40 becomes uniform.
In the arrangement as shown in FIG. 1, the
movement of the raw material for improving dispersion of
fibers is similar to the above-described experiment, and
is effected under an adjustable condition. During the
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1 period in which the raw material has been ejected from the
headbox 36 until it reaches the roll 5, since the raw
material is dewatered only on~he side of the bottom wire
33, the number of repetitions of acceleration and
deceleration for improving dispersion of fibers is
increased. In addition, in the interval where the belt 35
is traveling along the top wire 34, since dewatering is
effected downwards only, the dewatering is asymmetric
although the upward dewatering in which the extracted
water is collected in the casings 27 and 29 exists.
Therefore, a reduction in the coupling strength
in the thicknesswise direction also can be suppressed. In
the initial portion of the former where the amount of
dewatering is large, since dewatering is effected on the
rollers and the wires are not scrubbed by a fixed body,
retention is high (although the shoes 14 and 18 and the
beam 22 scrub the belt 35, since the belt 35 is traveling
at the same velocity as the wire, the wires are not
scrubbed by a fixed body). Dewatering of raw material in
a liquid state is not effected on a free surface thereof,
but it is effected entirely in the state where the raw
material is sandwiched between two wires, the state being
adjustable, and so, even upon high speed operation no
problem arises.
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1 After the downward dewatering has proceeded, the
consistency of the raw material has been raised. In order
to improve the dispersion, it becomes necessary to carry
out abrupt acceleration and deceleration with a stronger
pressure variation. In such a case, the set consisting of
the shower 16, the shoe 18 and the tube 21 or consisting
of the shower 16 and the beam 22 could be provided above
the deflector 4. In this case, since the amount of
downward dewatering has been reduced, reduction in the
retention is not influenced so much.
As to the open roll 3, if a perforated cell such
as a suction roll around which a wire is wound, is used
therefor, then the dewatering effected at the portion of
the roll 3 on the side of the bottom wire 33 is
accompanied by a flow tending to move the raw material
between the two wires 33 and 34 towards the holes of the
cell. Since multiple open rolls 3 are provided, at the
location of the next roll, the raw material is moved in a
different direction. Such reciprocating movement of the
raw material along a plane is effected for uniformly
dispersing fibers similarly to the accelerating and
decelerating flow as described previously. In the former
having the arrangement shown in FIG. 1, an effect of
improving the formation of paper due to such actions is
also provided.
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1 As explained above, the present invention can
achieve excellent effects in that since formation forming
on a free surface is not effected, the former is suitable
for high speed operation. Also, since adjustable
asymmetric dewatering is effected, only small differences
exist between the top and bottom sides of the paper sheet,
balance for maintaining the lowering of the coupling
strength in the thicknesswise direction minimum can be
established and also improvement in the formation can be
achieved. Moreover, since dewatering is effected mainly
by rotary rolls or a belt, a reduction in retention does
not occur, and since surface both dewatering is also
effected, a surface strength is also high.
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