U.S. patent application number 11/659472 was filed with the patent office on 2007-09-13 for papermaking machine and papermaking method.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES, LTD.. Invention is credited to Shigenari Horie, Hiroshi Iwata, Hideo Nogami, Masahiro Sugihara.
Application Number | 20070209769 11/659472 |
Document ID | / |
Family ID | 36059774 |
Filed Date | 2007-09-13 |
United States Patent
Application |
20070209769 |
Kind Code |
A1 |
Nogami; Hideo ; et
al. |
September 13, 2007 |
Papermaking Machine And Papermaking Method
Abstract
The present invention relates to a papermaking machine and
papermaking method that make paper web by removing moisture while
making a paper stock layer travel, and the object of the invention
is to dehydrate the paper stock layer more efficiently. A
papermaking machine for making continuous paper web by holding a
paper stock suspension 1a jetted from a head box 2 into the shape
of a layer, and removing moisture while making this paper stock
layer 1 travel. The papermaking machine is provided with steam type
heating means 6 and adjustment means 11. The steam type heating
means 6 is provided in a moisture removing part as heating means
for heating the paper stock layer 1 to accelerate the moisture
removal, and supplies steam to the paper stock layer 1 and heats
the paper stock layer 1 by condensation of the steam. The
adjustment means 11 adjusts the supply of the steam performed by
the steam type heating means 6, on the basis of a stock
concentration of the paper stock layer 1 detected when passing
through the steam type heating means 6, so that the paper stock
layer 1 reaches a preset target temperature.
Inventors: |
Nogami; Hideo; (Mihara,
JP) ; Horie; Shigenari; (Hiroshima, JP) ;
Sugihara; Masahiro; (Mihara, JP) ; Iwata;
Hiroshi; (Hiroshima, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Assignee: |
MITSUBISHI HEAVY INDUSTRIES,
LTD.
16-5, KONAN 2-CHOME MINATO-KU
TOKYO
JP
108-8215
|
Family ID: |
36059774 |
Appl. No.: |
11/659472 |
Filed: |
September 16, 2004 |
PCT Filed: |
September 16, 2004 |
PCT NO: |
PCT/JP04/13544 |
371 Date: |
February 6, 2007 |
Current U.S.
Class: |
162/207 ;
162/375 |
Current CPC
Class: |
D21F 1/50 20130101; D21F
9/003 20130101; D21F 1/48 20130101 |
Class at
Publication: |
162/207 ;
162/375 |
International
Class: |
D21F 1/48 20060101
D21F001/48 |
Claims
1-18. (canceled)
19. A papermaking machine for making paper web by holding a paper
stock suspension jetted from a head box into the shape of a layer,
and removing moisture while traveling the paper stock layer,
comprising: steam type heating means, provided in a moisture
removing part as heating means for heating said paper stock layer
to accelerate said moisture removal, for supplying steam to said
paper stock layer and heating said paper stock layer by
condensation of said steam; and adjustment means for adjusting the
supply of said steam performed by said steam type heating means, on
the basis of a stock concentration of said paper stock layer
detected when passing through said steam type heating means, so
that said paper stock layer reaches a preset target temperature;
wherein said moisture removing part is a former which forms a layer
of paper by holding said paper stock suspension jetted from said
head box into the shape of a layer, and removes moisture while
traveling the paper stock layer, or a press part which further
removes moisture by applying pressure to said paper stock layer
formed into the paper layer by said former; said former is
constructed as twin wire formers equipped with wires on both sides
of said paper stock layer; said steam type heating means is
provided with a steam box for guiding the supply of steam to said
paper stock layer, and said steam box is arranged so that the
fringe of its tip opening abuts said wire or is very near said
wire; further comprising a suction box for suctioning steam jetted
from said steam box toward a side opposite to said steam box across
said paper stock layer; and another suction box besides to said
suction box arranged on said side opposite to said steam box across
said paper stock layer and downstream in the traveling direction of
said paper stock layer; wherein suction force of the downstream
suction box is set larger than that of the upstream suction
box.
20. The papermaking machine as set forth in claim 19, wherein the
fringe of the tip opening of said steam box is provided with seal
means for sealing said steam box.
21. The papermaking machine as set forth in claim 20, wherein said
seal means is a seal member which is attached to the fringe of the
tip opening of said steam box and abuts said wire.
22. The papermaking machine as set forth in claim 20, wherein said
seal means is a gas jet device which is provided upstream in the
traveling direction of said paper stock layer relative to the
fringe of the tip opening of said steam box, and suppresses
incursion of wake of said paper stock layer into said steam box by
jetting gas.
23. The papermaking machine as set forth in claim 19, wherein a
downstream end of said suction box in the traveling direction of
said paper stock layer is arranged downstream relative to a
downstream end of said steam box in the traveling direction of said
paper stock layer.
24. The papermaking machine as set forth in claim 19, wherein said
steam box is divided into a plurality of parts in the width
direction of said paper stock layer and said suction box is divided
into a plurality of parts so as to correspond to the divided parts
of said steam box, and wherein a jet of steam and suction of steam
are adjustable for each of the divided parts of said steam box and
said suction box.
25. The papermaking machine as set forth in claim 19, wherein said
steam supplied by said steam type heating means heats said paper
stock layer by acting on said paper stock layer as a collision
jet.
26. The papermaking machine as set forth in claim 19, further
comprising control means for automatically adjusting said
adjustment means.
27. The papermaking machine as set forth in claim 26, further
comprising: stock concentration detecting means, provided in the
vicinity of said steam type heating means, for detecting a stock
concentration of said paper stock layer when passing through said
steam type heating means; wherein said control means controls the
supply of steam performed by said steam type heating means, on the
basis of information detected by said stock concentration detecting
means, so that said paper stock layer is raised to said target
temperature.
28. The papermaking machine as set forth in claim 19, further
comprising: air jet type heating means for blowing high-temperature
air against said paper stock layer and heating said paper stock
layer by a collision jet of said high-temperature air, provided as
heating means for heating said paper stock layer, downstream in the
traveling direction of said paper stock layer relative to a
position at which said steam type heating means is installed.
29. The papermaking machine as set forth in claim 28, wherein said
heating means comprises first heating means for performing heating
on one side of said paper stock layer, and second heating means for
performing heating on the other side of said paper stock layer.
30. A papermaking method of making paper web by holding a paper
stock suspension jetted from a head box into the shape of a layer,
and removing moisture while making the paper stock layer travel,
comprising the steps of: supplying steam to said paper stock layer
at a heating position and heating said paper stock layer by
condensation of said steam, in such a way that said paper stock
layer reaches a preset target temperature; and suctioning and
removing moisture from said paper stock layer.
31. A papermaking machine for making paper web by holding a paper
stock suspension jetted from a head box into the shape of a layer,
and removing moisture while traveling the paper stock layer,
comprising: steam type heating means, provided in a moisture
removing part as heating means for heating said paper stock layer
to accelerate said moisture removal, for supplying steam to said
paper stock layer and heating said paper stock layer by
condensation of said steam; adjustment means for adjusting the
supply of said steam performed by said steam type heating means, on
the basis of a stock concentration of said paper stock layer
detected when passing through said steam type heating means, so
that said paper stock layer reaches a preset target temperature;
and air jet type heating means for blowing high-temperature air
against said paper stock layer and heating said paper stock layer
by a collision jet of said high-temperature air, provided as
heating means for heating said paper stock layer, downstream in the
traveling direction of said paper stock layer relative to a
position at which said steam type heating means is installed.
32. The papermaking machine as set forth in claim 31, wherein said
moisture removing part is a former which forms a layer of paper by
holding said paper stock suspension jetted from said head box into
the shape of a layer, and removes moisture while traveling the
paper stock layer, or a press part which further removes moisture
by applying pressure to said paper stock layer formed into the
paper layer by said former.
33. The papermaking machine as set forth in claim 32, wherein said
former is constructed as twin wire formers equipped with wires on
both sides of said paper stock layer.
34. The papermaking machine as set forth in claim 33, wherein said
steam type heating means is provided with a steam box for guiding
the supply of steam to said paper stock layer, and said steam box
is arranged so that the fringe of its tip opening abuts said wire
or is very near said wire.
35. The papermaking machine as set forth in claim 34, wherein the
fringe of the tip opening of said steam box is provided with seal
means for sealing said steam box.
36. The papermaking machine as set forth in claim 35, wherein said
seal means is a seal member which is attached to the fringe of the
tip opening of said steam box and abuts said wire.
37. The papermaking machine as set forth in claim 35, wherein said
seal means is a gas jet device which is provided upstream in the
traveling direction of said paper stock layer relative to the
fringe of the tip opening of said steam box, and suppresses
incursion of wake of said paper stock layer into said steam box by
jetting gas.
38. The papermaking machine as set forth in claim 34, further
comprising a suction box for suctioning steam jetted from said
steam box toward a side opposite to said steam box across said
paper stock layer.
39. The papermaking machine as set forth in claim 38, wherein a
downstream end of said suction box in the traveling direction of
said paper stock layer is arranged downstream relative to a
downstream end of said steam box in the traveling direction of said
paper stock layer.
40. The papermaking machine as set forth in claim 38, further
comprising another suction box besides to said suction box,
arranged on said side opposite to said steam box across said paper
stock layer and downstream in the traveling direction of said paper
stock layer.
41. The papermaking machine as set forth in claim 39, wherein
suction force of the downstream suction box is set larger than that
of the upstream suction box.
42. The papermaking machine as set forth in claim 38, wherein said
steam box is divided into a plurality of parts in the width
direction of said paper stock layer and said suction box is divided
into a plurality of parts so as to correspond to the divided parts
of said steam box, and wherein a jet of steam and suction of steam
are adjustable for each of the divided parts of said steam box and
said suction box.
43. The papermaking machine as set forth in claim 31, wherein said
steam supplied by said steam type heating means heats said paper
stock layer by acting on said paper stock layer as a collision
jet.
44. The papermaking machine as set forth in claim 31, further
comprising control means for automatically adjusting said
adjustment means.
45. The papermaking machine as set forth in claim 44, further
comprising: stock concentration detecting means, provided in the
vicinity of said steam type heating means, for detecting a stock
concentration of said paper stock layer when passing through said
steam type heating means; wherein said control means controls the
supply of steam performed by said steam type heating means, on the
basis of information detected by said stock concentration detecting
means, so that said paper stock layer is raised to said target
temperature.
46. The papermaking machine as set forth in claim 45, wherein said
heating means comprises first heating means for performing heating
on one side of said paper stock layer, and second heating means for
performing heating on the other side of said paper stock layer.
Description
TECHNICAL FIELD
[0001] The present invention relates to a papermaking machine and
papermaking method that make continuous paper by removing moisture
while making it travel a layer of paper stock.
BACKGROUND ART
[0002] Generally, in papermaking machines, by holding a suspension
of pulp (suspension of paper stock) jetted from a head box into the
shape of a layer by a wire, etc., and removing moisture while
making this paper stock layer (also referred to as wet paper web)
travel, a paper web is made.
[0003] Various methods of dehydration for papermaking machines have
been developed. For example, as shown in FIG. 8(a), patent document
1 discloses a papermaking machine equipped with a steam box 60 for
supplying steam to the upper side of wet paper web 1. The steam box
60 is arranged over a path of travel in the final part of a former
(also referred to as a forming part or paper layer forming
part).
[0004] In such a papermaking machine, steam from a steam generator
10 is supplied to the steam box 60 through a steam conduit. The
steam touches the wet paper web 1 held on a wire 30 and condenses,
whereby heat is transferred to the wet paper 1.
[0005] It is conceivable that in the final part of the former, the
wet paper web 1 will be in a state before completion of
dehydration, that is, a state in which minute interstices have been
formed by dehydration, or a porous state. By suctioning the under
side of the wet paper web 1 through the wire 30 by a suction box
70, steam enters such interstices or pores and permeates into the
wet paper web 1. As a result, the latent heat of the steam is
converted to the sensible heat of water, whereby the wet paper web
1 is raised in temperature and the dehydration rate rises.
[0006] The dehydration rate of the wet paper web 1 traveling
through the former is not uniform. In general, the widthwise
central portion of the wet paper web 1 is lower in dehydration rate
than the widthwise right and left end portions. Hence, as shown in
FIG. 8(b), there has been developed a technique in which, in order
to cause the widthwise central portion of the wet paper web 1 whose
dehydration rate is relatively low to touch more steam than the
widthwise right and left portions, by widthwise dividing the steam
box 60 into a plurality of steam supply chambers 61, and suitably
adjusting valves 11 corresponding to each steam supply chamber 61,
the widthwise central steam chambers 61 are supplied with more
steam than the widthwise right and left steam chambers 61.
[0007] Similarly, patent document 2 discloses a technique in which
by causing steam to touch wet paper, the wet paper is raised in
temperature.
[0008] Patent document 1: Japanese patent laid-open publication No.
Sho 55-137293
[0009] Patent document 2: U.S. Pat. No. 5,149,401
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0010] The inventors have made various investigations and
experiments with respect to a mechanism of raising the dehydration
rate of wet paper web by heating the wet paper web with steam and
found the following facts. That is, there are cases where even if
the supply of steam is increased in order to further raise the
dehydration rate, conversely the dehydration rate will be reduced.
A possible cause is that an increase in the supply of steam
increases the quantity that steam condenses into water.
[0011] However, in the conventional papermaking machine described
above, such a change in the dehydration rate with respect to the
supply of steam is not taken into account and an optimum supply of
steam is not always set. Thus, the problem of performing
dehydration with good efficiency remains unsolved.
Means for Solving the Problems
[0012] The present invention has been made in view of the problem
described above. Accordingly, it is the primary object of the
present invention to provide a papermaking machine and papermaking
method that are capable of dehydrating a layer of paper stock with
better efficiency.
[0013] To achieve the aforementioned object, the papermaking
machine of the present invention as set forth in claim 1 is a
papermaking machine for making paper web by holding a paper stock
suspension jetted from a head box into the shape of a layer, and
removing moisture while traveling the paper stock layer. The
papermaking machine comprises: steam type heating means, provided
in a moisture removing part as heating means for heating the paper
stock layer (wet paper web) to accelerate the moisture removal, for
supplying steam to the paper stock layer and heating the paper
stock layer by condensation of the steam; and adjustment means for
adjusting the supply of the steam performed by the steam type
heating means, on the basis of a stock concentration of the paper
stock layer detected when passing through the steam type heating
means, so that the paper stock layer reaches a preset target
temperature.
[0014] The steam used herein is not limited to saturated steam, but
may be heated steam, wet air, etc. By detecting the above-mentioned
stock concentration of the paper stock layer in real time, the
supply of steam may be adjusted based on the information detected.
In addition, by obtaining a stock concentration of the paper stock
layer beforehand, the supply of steam may be adjusted based on the
stock concentration obtained beforehand.
[0015] The papermaking machine of the present invention as set
forth in claim 2 is characterized in that, in the construction as
set forth in claim 1, the moisture removing part is a former (also
called a forming part or paper layer forming part) which forms a
layer of paper by holding the paper stock suspension jetted from
the head box into the shape of a layer, and removing moisture while
traveling the paper stock layer, or a press part which further
removes moisture by applying pressure to the paper stock layer
formed into the paper layer by the former.
[0016] The papermaking machine of the present invention as set
forth in claim 3 is characterized in that, in the construction as
set forth in claim 2, the forming part is constructed as twin wire
formers equipped with wires on both sides of the paper stock layer.
Note that the present invention is not always limited to twin
wires, but may be applied to a long wire former or on-top former
which holds only one side of a paper stock layer.
[0017] The papermaking machine of the present invention as set
forth in claim 4 is characterized in that, in the construction as
set forth in claim 3, the steam type heating means is provided with
a steam box for guiding the supply of steam to the paper stock
layer. In this case, the steam box is arranged so that the fringe
of its tip opening abuts the wire or is very near the wire.
[0018] The papermaking machine of the present invention as set
forth in claim 5 is characterized in that, in the construction as
set forth in claim 4, the fringe of the tip opening of the steam
box is provided with seal means for sealing the steam box.
[0019] The papermaking machine of the present invention as set
forth in claim 6 is characterized in that, in the construction as
set forth in claim 5, the seal means is a seal member which is
attached to the fringe of the tip opening of the steam box and
abuts the wire.
[0020] The papermaking machine of the present invention as set
forth in claim 7 is characterized in that, in the construction as
set forth in claim 5, the seal means is a gas jet device which is
provided upstream in the traveling direction of the paper stock
layer relative to the fringe of the tip opening of the steambox,
and suppresses incursion of wake of the paper stock layer into the
steam box by jetting gas. In this case, the gas jet device
preferably jets gas toward the upstream side at a jet angle which
is about 15 to 40.degree. to wet paper web.
[0021] The papermaking machine of the present invention as set
forth in claim 8 is characterized in that, in the construction as
set forth in any one of claims 4 to 7, it further includes a
suction box for suctioning steam jetted from the steam box toward a
side opposite to the steam box across the paper stock layer.
[0022] The papermaking machine of the present invention as set
forth in claim 9 is characterized in that, in the construction as
set forth in claim 8, a downstream end of the suction box in the
traveling direction of the paper stock layer is arranged downstream
relative to a downstream end of the steam box in the traveling
direction of the paper stock layer.
[0023] The papermaking machine of the present invention as set
forth in claim 10 is characterized in that, in the construction as
set forth in claim 8 or 9, it further includes another suction box
arranged on the side opposite to the steam box across the paper
stock layer and downstream in the traveling direction of the paper
stock layer.
[0024] The papermaking machine of the present invention as set
forth in claim 11 is characterized in that, in the construction as
set forth in claim 10, the suction force of the downstream suction
box in the traveling direction of the paper stock layer is set
larger than that of the upstream suction box.
[0025] The papermaking machine of the present invention as set
forth in claim 12 is characterized in that, in the construction as
set forth in any one of claims 8 to 11, the steam box is divided
into a plurality of parts in the width direction of the paper stock
layer and the suction box is divided into a plurality of parts so
as to correspond to the divided parts of the steam box. In this
case, a jet of steam and suction of steam are adjustable for each
of the divided parts.
[0026] The papermaking machine of the present invention as set
forth in claim 13 is characterized in that, in the construction as
set forth in any one of claims 1 to 12, the steam supplied by the
steam type heating means heats the paper stock layer by acting on
the paper stock layer as a collision jet.
[0027] The papermaking machine of the present invention as set
forth in claim 14 is characterized in that, in the construction as
set forth in any one of claims 1 to 13, it further includes control
means for automatically adjusting the adjustment means.
[0028] The papermaking machine of the present invention as set
forth in claim 15 is characterized in that, in the construction as
set forth in claim 14, it further includes stock concentration
detecting means, provided in the vicinity of the steam type heating
means, for detecting a stock concentration of the paper stock layer
when passing through the steam type heating means. In this case,
the control means controls the supply of steam performed by the
steam type heating means, on the basis of information detected by
the stock concentration detecting means, so that the paper stock
layer is raised to the target temperature.
[0029] In addition, the above-mentioned stock concentration
detecting means is, for example, moisture percentage sensor, and
the stock concentration can be estimated by moisture percentage of
paper stock layer detected by the moisture percentage sensor.
[0030] The papermaking machine of the present invention as set
forth in claim 16 is characterized in that, in the construction as
set forth in any one of claims 1 to 15, it further includes air jet
type heating means for blowing high-temperature air against the
paper stock layer and heating the paper stock layer by a collision
jet of the high-temperature air, provided as heating means for
heating the paper stock layer, downstream in the traveling
direction of the paper stock layer relative to a position at which
the steam type heating means is installed.
[0031] The papermaking machine of the present invention as set
forth in claim 17 is characterized in that, in the construction as
set forth in any one of claims 1 to 16, the heating means comprises
first heating means for performing heating on one side of the paper
stock layer, and second heating means for performing heating on the
other side of the paper stock layer.
[0032] The papermaking method of the present invention as set forth
in claim 18 is a papermaking method of making paper web by holding
a paper stock suspension jetted from a head box into the shape of a
layer, and removing moisture while traveling the paper stock layer.
The papermaking method comprises a step of supplying steam to the
paper stock layer at a heated position and heating the paper stock
layer by condensation of the steam, in such a way that the paper
stock layer reaches a preset target temperature, and a step of
suctioning and removing moisture from the paper stock layer. As
described above, the steam used in this method is not limited to
saturated steam, but may be heated steam, wet air, etc.
ADVANTAGES OF THE INVENTION
[0033] According to the papermaking machine of the present
invention as set forth in claims 1 to 3, in the moisture removing
part, the adjustment means adjusts the supply of the steam
performed by the steam type heating means, on the basis of a stock
concentration of the paper stock layer detected when passing
through the steam type heating means, so that the paper stock layer
reaches a preset target temperature. Therefore, the paper stock
layer can be raised in temperature and dehydrated with better
efficiency. As a result of this, the dehydration rate can be
raised.
[0034] According to the papermaking machine of the present
invention as set forth in claim 4, the steam type heating means is
provided with a steam box for guiding the supply of steam to the
paper stock layer. The steam box is arranged so that the fringe of
its tip opening abuts the wire or is very near the wire. Therefore,
steam can be supplied to the paper stock layer with good
efficiency.
[0035] According to the papermaking machine of the present
invention as set forth in claim 5, the fringe of the tip opening of
the steam box is provided with seal means for sealing the steam
box. Therefore, steam can be supplied to the paper stock layer with
better efficiency.
[0036] According to the papermaking machine of the present
invention as set forth in claim 6, the seal means is a seal member
which is attached to the fringe of the tip opening of the steam box
and abuts the wire. Therefore, sealing of the steam box can be
enhanced, whereby steam can be supplied to the paper stock layer
with good efficiency.
[0037] According to the papermaking machine of the present
invention as set forth in claim 7, the seal means is a gas jet
device which is provided upstream in the traveling direction of the
paper stock layer relative to the fringe of the tip opening of the
steam box, and suppresses incursion of wake of the paper stock
layer into the steam box by jetting gas. Therefore, incursion of
wake into the steam box can be reliably suppressed, whereby steam
can be supplied to the paper stock layer with good efficiency.
[0038] According to the papermaking machine of the present
invention as set forth in claim 8, the suction box suctions steam
jetted from the steam box toward a side opposite to the steam box
across the paper stock layer. Therefore, high-temperature water
condensed on the surface of the paper stock layer is able to
permeate through the paper stock layer. This makes it possible to
reliably raise the temperature of the entire paper stock layer and
dehydrate the entire paper stock layer.
[0039] According to the papermaking machine of the present
invention as set forth in claim 9, a downstream end of the suction
box in the traveling direction of the paper stock layer is arranged
downstream relative to a downstream end of the steam box in the
traveling direction of the paper stock layer. Therefore, moisture
in the paper stock layer raised in temperature can be further
removed, resulting in a further rise in the dehydration rate.
[0040] According to the papermaking machine of the present
invention as set forth in claim 10, in addition to the
above-mentioned suction box, the papermaking machine further
includes another suction box arranged on the side opposite to the
steam box across the paper stock layer and downstream in the
traveling direction of the paper stock layer. Therefore, the
dehydration rate can be further raised.
[0041] According to the papermaking machine of the present
invention as set forth in claim 11, the suction force of the
downstream suction box is set larger than that of the upstream
suction box. Therefore, water in the paper stock layer raised in
temperature by the upstream steam box can be further removed,
resulting in a further rise in the dehydration rate.
[0042] According to the papermaking machine of the present
invention as set forth in claim 12, the steam box is divided into a
plurality of parts in the width direction of the paper stock layer
and the suction box is divided into a plurality of parts so as to
correspond to the divided parts of the steam box, and a jet of
steam and a suction of steam are adjustable for each of the divided
parts. Therefore, the dehydration rate can be adjusted for each of
the divided parts.
[0043] According to the papermaking machine of the present
invention as set forth in claim 13, the steam supplied by the steam
type heating means heats the paper stock layer by acting on the
paper stock layer as a collision jet. Therefore, the paper stock
layer can be raised in temperature and dehydrated with better
efficiency.
[0044] According to the papermaking machine of the present
invention as set forth in claim 14, the papermaking machine further
includes control means for automatically adjusting the adjustment
means. Therefore, the supply of steam can be automatically
adjusted.
[0045] According to the papermaking machine of the present
invention as set forth in claim 15, the control means controls the
supply of steam performed by the steam type heating means, on the
basis of information detected by the stock concentration detecting
means, so that the paper stock layer is raised to the target
temperature. Therefore, the supply of steam can be adjusted so that
an optimum dehydration rate is obtained.
[0046] According to the papermaking machine of the present
invention as set forth in claim 16, the papermaking machine further
includes air jet type heating means for blowing high-temperature
air against the paper stock layer and heating the paper stock layer
by a collision jet of the high-temperature air. The air jet type
heating means is provided as heating means for heating the paper
stock layer, downstream in the traveling direction of the paper
stock layer from a position at which the steam type heating means
is installed. Therefore, the paper stock layer raised in
temperature by the steam type heating means can be further raised
in temperature and dehydrated, resulting in a further rise in the
dehydration rate.
[0047] According to the papermaking machine of the present
invention as set forth in claim 17, the heating means comprises
first heating means for performing heating on one side of the paper
stock layer, and second heating means for performing heating on the
other side of the paper stock layer. Therefore, it is possible to
evenly dehydrate both sides of the paper stock layer.
[0048] According to the papermaking method of the present invention
as set forth in claim 18, in such a way that the paper stock layer
reaches a preset target temperature, steam is supplied to the paper
stock layer at a heated position and the paper stock layer is
heated by condensation of the steam. Thereafter, moisture is
suctioned and removed from the paper stock layer. Therefore, the
paper stock layer can be raised in temperature and dehydrated with
better efficiency. This can raise the dehydration rate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] FIG. 1 is a schematic diagram showing a papermaking machine
according to a first embodiment of the present invention;
[0050] FIGS. 2(a) and 2(b) schematically show a steam box and a
suction box according to the first embodiment of the present
invention, FIG. 2(a) being a sectional view taken along the
direction in which wet paper web travels and FIG. 2(b) being a
sectional view taken along line A-A of FIG. 2(a);
[0051] FIG. 3 is a graph showing how the dehydration rate (effect
of accelerating dehydration) in the first embodiment of the present
invention varies with respect to the stock concentration of wet
paper web;
[0052] FIG. 4 is a schematic diagram showing a papermaking machine
according to a second embodiment of the present invention;
[0053] FIG. 5 is a schematic diagram showing a papermaking machine
according to a third embodiment of the present invention;
[0054] FIG. 6 is a schematic diagram showing a papermaking machine
according to a fourth embodiment of the present invention;
[0055] FIG. 7 is a schematic diagram showing a papermaking machine
according to a fifth embodiment of the present invention; and
[0056] FIGS. 8(a) and 8(b) schematically show a steam box and a
suction box according to a conventional papermaking machine, FIG.
8(a) being a sectional view taken along the direction in which wet
paper web travels and FIG. 8(b) being a sectional view taken along
line A-A of FIG. 8(a).
DESCRIPTION OF REFERENCE NUMERALS
[0057] 1 Wet paper web(paper stock layer)
[0058] 1a Pulp suspension (paper stock suspension)
[0059] 2 Head box
[0060] 3a, 3b Wire
[0061] 4 Forming roll
[0062] 5 Blade shoe
[0063] 6, 6', 60 Steam box (steam type heating means)
[0064] 6a Steam box main body
[0065] 6b Heat retaining body
[0066] 6c Seal member (seal means)
[0067] 6d Partition wall
[0068] 6e Steam supply chamber
[0069] 6f Steam introducing port
[0070] 6g Tip opening
[0071] 7, 7A, 7', 70 Suction box
[0072] 7d Partition wall
[0073] 7e Suction chamber
[0074] 7f Suction port
[0075] 7g Tip opening
[0076] 8 Suction roll
[0077] 9 Suction box
[0078] 10 Steam generator
[0079] 11 Valve (adjustment means)
[0080] 12 Controller (control means)
[0081] 13 Moisture percentage sensor (stock concentration detecting
means)
[0082] 14 Gas jet device (Seal means)
BEST MODE FOR CARRYING OUT THE INVENTION
[0083] Embodiments of the present invention will hereinafter be
described with reference to the drawings.
FIRST EMBODIMENT
[0084] FIGS. 1 to 3 are used for explaining a papermaking machine
constructed in accordance with a first embodiment of the present
invention. FIG. 1 is a schematic diagram showing the papermaking
machine. FIGS. 2(a) and 2(b) are diagrams schematically showing a
steam box and a suction box. FIG. 2(a) is a sectional view taken
along the direction in which wet paper web travels, and FIG. 2(b)
is a sectional view taken along line A-A of FIG. 2(a). FIG. 3 is a
graph showing how the dehydration rate (effect of accelerating
dehydration) varies with respect to the stock concentration of wet
paper web.
[0085] The papermaking machine of the first embodiment adopts twin
wire formers, as shown in FIG. 1. When a pulp suspension (paper
stock suspension) 1a is jetted and supplied from a head box 2 to a
slit between twin wires 3a and 3b, the pulp suspension 1a becomes a
wet paper web (a paper stock layer) 1 by being held into the shape
of layer between the twin wires 3a and 3b. This wet paper web 1 is
dehydrated by a forming roll 4 which performs dehydration by
tension of the wires 3a and 3b; a blade shoe 5 which performs
dehydration by curving a path of travel; and so forth.
[0086] Downstream of the blade shoe 5, the wet paper web 1 is
raised in temperature by a steam box 6 and is suctioned and
dehydrated by a suction box 7 installed across the wet paper web 1
from the steam box 6. Now, the steam box 6 and suction box 7 in the
first embodiment will be described in further detail.
[0087] As shown in FIGS. 2(a) and 2(b), the steam box (steam type
heating means) 6 as heating means is equipped with a steam box main
body 6a, a heat retaining body 6b, and a seal member (seal means)
6c.
[0088] The steam box main body 6a has, for example, a machine
length of about 100 to 1000 mm in the traveling direction of the
wet paper web 1, and the internal space is divided into a plurality
of steam supply chambers 6e in the width direction of the wet paper
web 1 by partition walls 6d. Each of the steam supply chambers 6e
divided by the partition walls 6d has a steam introducing port 6f
for taking in steam from a steam generator 10, and a tip opening 6g
facing the wire 3a. In the first embodiment, the tip opening 6g of
the steam box main body 6a has a seal member 6c attached thereto,
which abuts the wire 3a.
[0089] By supplying steam from the steam generator 10 to each of
the steam supply chambers 6e, the wires 3a, 3b and wet paper web 1
can be heated to about 40 to 100.degree. C. Note that it is also
possible to cause the supplied steam to act on the wet paper web 1
as a collision jet. This can heat the wet paper web 1
efficiently.
[0090] The heat retaining body 6b is, for example, a heat retaining
structure with a heat insulating material or heat insulating layer,
or a heating device such as an electric heater, a heating steam
jacket, a high-temperature air jacket, etc., and is attached to the
outside wall of the steam box main body 6a so that it can retain
the heat of the steam box main body 6a. This can prevent steam
condensation and dew condensation from occurring on the inside wall
surface of the steam box main body 6a (i.e., the inside wall
surface of the steam supply chamber 6e).
[0091] The seal member 6c is attached to the fringe of the tip
opening 6g of the each of steam supply chambers 6e so as to abut
the wire 3a, and functions to seal the steam box main body 6a and
each of the steam supply chambers 6e. This ensures sealing of the
interior of the steam box main body 6a and interior of each of the
steam supply chambers 6e. As to the seal member 6c, an elastic
material such as rubber is suitable from the viewpoint of sealing
performance, but since heat-resisting property is required, a
heating-resisting material such as bakelite is also suitable. Of
course, a material, such as heat-resisting rubber, which has both
elasticity and heat-resisting property is more suitable.
[0092] In the case where there is no seal member 6c, wake intrudes
through the gap between the upstream side of the tip opening 6g and
the wire 3a and may disturb the touch of steam with the wet paper
web 1, but the installation of the seal member 6c enables steam to
touch the whole of the wet paper web 1 located within each of the
steam supply chambers 6e. Therefore, a reduction in the efficiency
at which steam condenses and adheres to the wet paper web 1
(condensation and adhesion efficiency) can be prevented.
[0093] Supply pipes connected to each of the steam supply chambers
6e are provided with valves (adjustment means) 11, through which
steam is supplied from the steam generator 10 to the steambox 6. By
controlling the opening and closing operation of each valve 11 with
a controller 12, the supply of steam into the steam supply chambers
6e can be separately adjusted. Note that the steam used in the
first embodiment may be any of saturated steam, heated steam, and
wet air.
[0094] The suction box 7 has, for example, the same machine length
as the steambox 6 or a machine length shorter than the steam box 6,
and the interior space is divided into a plurality of suction
chambers 7e at intervals of the same width as the steam box main
body 6a in the width direction of the wet paper web 1 by partition
walls 7d. Each of the suction chambers 7e divided by the partition
walls 7d has a suction port 7f connected to a suction device (not
shown), and an tip opening 7g facing the wire 3b. The suction box 7
is installed so that the tip opening 7g abuts the surface of the
wire 3b.
[0095] Generally, the width of the steam box 6 and the width of the
wires 3a, 3b are set equal to each other. However, for example, in
the case where the width of the steam box 6 is larger than that of
the wires 3a and 3b, in order to prevent steam from leaking from
the exposed portion of the tip opening 6g, it is preferable to
include a member which abuts (or is very near) the exposed portion
to prevent the leakage of the steam. In the first embodiment, the
width of the suction box 7 is approximately the same as the width
of the steam box 6, so this suction box 7 fulfills the function of
the aforementioned member.
[0096] By the steam box 6 and suction box 7, the wet paper web 1 is
heated and dehydrated. Specifically, the steam supplied into the
steam box 6 is condensed into high-temperature water in the
vicinity of the surface of the wire 3a and surface of the wet paper
web 1. Then, the high-temperature water gets into the wet paper web
1 by the suction operation of the suction box 7, the entire wet
paper web 1 is raised in temperature by the heat transfer of the
high-temperature water, and by suctioning the moisture in the wet
paper web 1 by the suction box 7, the wet paper web 1 is
dehydrated.
[0097] Within the steam box 6 the temperature raising process is
being performed and the wet paper web 1 entering the steam box 6 is
progressively raised in temperature within the steam box 6, but a
time lag occurs until the whole of the wet paper web 1 is raised in
temperature. Hence, in the papermaking machine of the first
embodiment, as shown in FIG. 1, the wet paper web 1 in which the
effect of dehydration has become higher by being raised in
temperature within the steam box 6 is further dehydrated by a
suction roll 8 and a suction box 9 installed downstream of the
steam box 6. This makes it possible to perform dehydration with
better efficiency, resulting in a rise in the dehydration rate.
[0098] As previously mentioned, the inventors have found that there
are cases where, even if the supply of steam is increased to
further raise the dehydration rate, conversely the dehydration rate
will be reduced. A possible reason is that an increase in the
supply of steam increases the quantity of heat supplied, but the
quantity that steam condenses into water is increased and causes an
increase in the moisture percentage. Therefore, in order to raise
the dehydration rate, how to set the supply of steam becomes
important.
[0099] Hence, the inventors have investigated how the dehydration
rate varies with respect to the paper stock concentration of the
wet paper web 1 under a certain suction condition. The results are
shown in FIG. 3.
[0100] FIG. 3 shows dehydration raising characteristics due to the
temperature raising effect in the case of a large supply of steam
and the case of a low supply of steam, and a dehydration reducing
characteristic due to dehydration resistance in the case where
suction pressure is fixed.
[0101] For example, the characteristics of the dehydration
accelerating effect by steam supply are shown by lines M1 and M2 in
FIG. 3. That is, in both the case of a large supply of steam and
the case of a low supply of steam, the higher the stock
concentration, the less the moisture and the lower the mass of the
wet paper web 1, therefore the heat capacity becomes low, so that
the temperature of the wet paper web 1 is considerably raised,
resulting in a rise in the dehydration rate (i.e., the dehydration
rate is raised by the temperature raising effect of the wet paper
web 1). From the comparison of lines M1 and M2 it follows that the
case of a large supply of steam (M1) has a higher dehydration rate
than the case of a low supply of steam (M2).
[0102] On the other hand, in the case where the suction pressure is
fixed, the characteristic of the dehydration accelerating effect by
suction is shown by line S in FIG. 3. That is, the higher the stock
concentration the larger the dehydration resistance, so that the
dehydration rate is reduced.
[0103] Therefore, in the case of a large supply of steam, a
practical dehydration accelerating effect is obtained by adding the
dehydration accelerating effect by steam supply shown by the line
M1 and the dehydration accelerating effect by suction shown by the
line S together. As shown by line L1 in FIG. 3, this dehydration
accelerating effect has a mountainous characteristic that rises up
to a certain stock concentration and then drops gradually.
[0104] Similarly, in the case of a low supply of steam, a practical
dehydration accelerating effect is obtained by adding the
dehydration accelerating effect by steam supply shown by the line
M2 and the dehydration accelerating effect by suction shown by the
line S. That is to say, the practical dehydration accelerating
effect is represented by line L2.
[0105] Generally, the dehydrating speed v equivalent to the
dehydration raising rate is expressed according to Darcy's rule by
the following equation (1):
[0106] [Formula 1] v=.DELTA.P/(R.sub.mat+2R.sub.w).mu. (1) in which
[0107] v=dehydrating speed, [0108] .DELTA.P=vertical differential
pressure, [0109] R.sub.mat=dehydration resistance coefficient of
the wet Paper web, [0110] R.sub.w=dehydration resistance
coefficient of the wire, [0111] .mu.=water viscosity.
[0112] In the aforementioned equation (1), assuming that the
vertical differential pressure .DELTA.P, the dehydration resistance
coefficient R.sub.mat of the wet paper web, and the dehydration
resistance coefficient R.sub.w of the wire are constant, and
directing attention to the relation of the dehydrating speed v and
water viscosity .mu., the dehydrating speed v has an inversely
proportional relation to the water viscosity .mu.. In addition,
between the water viscosity .mu. and the temperature of the wet
paper web, there is a relation in which the water viscosity .mu.
becomes smaller as the temperature of the wet paper web becomes
higher. That is, there is a relation in which the dehydrating speed
v becomes faster as the temperature of the wet paper web becomes
higher.
[0113] Normally, according to Darcy' rule, the wet paper web 1 is
raised in temperature by heated steam and therefore the dehydrating
speed becomes faster and the dehydration rate becomes higher, but
at the same time, an increase in the stock concentration increases
resistance to dehydration. As a result, the dehydration
accelerating effect has a mountainous characteristic shown in FIG.
3, and the most efficient stock concentration exists according to
the state of steam supply.
[0114] Therefore, to raise the dehydration rate, it is preferable
to set an optimum steam supply according to the stock concentration
of the wet paper web 1, taking such a characteristic into account.
Because of this, the papermaking machine of the first embodiment,
as shown in FIG. 1, is provided with moisture percentage sensors
(stock concentration detecting means) 13 for detecting the moisture
percentage (which corresponds to the stock concentration (%)=100-
moisture percentage (%)) of the wet paper web 1 (in FIG. 1 there is
shown only one), which are disposed near the upstream end of the
steam box 6 and at the positions corresponding to the position of
each of the steam supply chambers 6e in the width direction of the
wet paper web 1 (i.e., at spots where the wet paper web 1 is
heated).
[0115] The controller 12 adjusts the opening and closing operation
of each valve 11 and controls the state of steam supplied to each
steam supply chamber 6e in real time, based on information detected
by each moisture percentage sensor 13, so that the temperature of
the wet paper web 1 passing through each steam supply chamber 6e
becomes a target wet paper temperature (which is a target
temperature set beforehand according to the stock concentration of
the wet paper web 1). For example, the steam supply chamber 6e is
disposed at a certain spot, and the reference stock concentration
of the wet paper web 1 coming to this spot is assumed to be 12%. If
the stock concentration of the wet paper web 1 detected by the
moisture percentage sensor 13 is 10%, the controller 12 controls
the valve 11 so that the supply of steam is increased. If the stock
concentration of the wet paper web 1 detected by the moisture
percentage sensor 13 is 14%, the controller 12 controls the valve
11 so that the supply of steam is reduced.
[0116] In addition, since the steam jetted state and steam
suctioned state can be adjusted for each of the divided regions in
the steam box 6 and suction box 7, the adjustment of dehydration in
the width direction of the wet paper web 1 can be easily
performed.
[0117] Besides, because steam is supplied to the wet paper web 1
through the wire 3a, there is no possibility that the fringe of the
tip opening 6g of the steam box 6 will touch the wet paper web 1
and destroy it. In addition, property and color changes of pulp
that occur when high-temperature steam directly touches the wet
paper web 1 can be prevented. That is, like prior art, in the case
where steam is blown directly against the wet paper web 1, it is
necessary to provide a gap between the steam box 6 and the wet
paper web 1 to prevent damage to the wet paper web 1, and
consequently, a large quantity of steam is discharged. However, in
the papermaking machine of the first embodiment, both sides of the
wet paper web 1 are supported by twin wires 3a and 3b and the steam
box 6 touches the wire 3a, whereby the aforementioned gap can be
eliminated without damaging the wet paper web 1 and, compared with
the prior art, the quantity of steam discharged can be suppressed.
That is, since steam loss can be prevented, steam can be
efficiently utilized.
[0118] Because sealing of the steam box 6 is ensured by the seal
member 6c of the steam box 6, the discharge of steam from inside
the steam box 6 to outside the steam box 6 can be further
suppressed.
[0119] In the conventional papermaking machine, the focus of
attention is that steam permeating into the wet paper web 1 raises
the temperature of the wet paper web 1 and dehydrates the wet paper
web 1. Because of this, it is necessary to install the steam box 60
and suction box 70 (see FIGS. 8(a) and 8(b)) at positions where
steam is in a permeable state, that is, a state before completion
of dehydration of the wet paper web 1 of the former final part, and
where the wet paper web 1 is caused to be in a porous state or a
state in which interstices are formed. On the other hand, in the
papermaking machine of the first embodiment, attention is further
directed to the following points. That is, by the suction operation
of the suction box 7, the moisture in the wet paper web 1 is
replaced with the high-temperature water condensed near the surface
of the wet paper web 1, whereby the wet paper web 1 is raised in
temperature and dehydrated. Therefore, steam does not always need
to permeate into the wet paper web 1, as is done in prior art.
[0120] That is, in prior art, the steam box has to be installed at
a position before completion of dehydration (i.e., near the former
outlet), but according to the present invention, it is possible to
install it more upstream. This makes it possible to accelerate the
dehydration of the wet paper web 1 in the former from the upstream
side. Moreover, as described above, because the papermaking machine
of the first embodiment performs optimum steam supply according to
the stock concentration of the wet paper web 1, the heating and
dehydration efficiency can be raised. Therefore, it becomes
possible to perform the dehydration in the former with great
efficiency, and consequently, the former can be made compact,
whereby space to install the former can be saved.
[0121] The heat transfer efficiency of the papermaking machine of
the first embodiment by steam condensation is about 25 times as
high as that of the conventional papermaking machine by steam
permeation and is extremely high compared with the prior art.
Therefore, a rise in the temperature of the wet paper web 1 by the
conventional papermaking machine is so insufficient that even if
the suction box 9 is provided downstream of the suction box 70, a
high effect of dehydration cannot be obtained. On the other hand,
in the papermaking machine of the first embodiment, a rise in the
temperature of the wet paper web 1 is so sufficient that a high
effect of dehydration is obtained by the suction roll 8 and suction
box 14 arranged downstream of the suction box 7. Thus, it is
possible to accelerate dehydration of the wet paper web 1.
[0122] In the first embodiment, the internal spaces of the steam
box 6 and suction box 7 are divided into several parts so that the
jetted state of steam and the suctioned state of steam can be
adjusted for each of the divided regions. However, in the case
where a stock concentration difference in the width direction of
the wet paper web 1 is practically negligible, it is not necessary
to divide these spaces (i.e., the partition walls 6d and 7d are not
needed). In this case, a representative stock concentration (e.g.,
at the laterally central portion of the wet paper web 1) may be
obtained from each moisture percentage sensor 13, and based on this
representative stock concentration, the supply of steam required
for the wet paper web 1 to rise to the target wet paper web
temperature may be set. Alternatively, a single moisture percentage
sensor 13 may be installed at a single spot in the width direction
of the wet paper web 1 (e.g., at the laterally central portion of
the wet paper web 1), and based on a stock concentration obtained
by this moisture percentage sensor 13, the supply of steam required
for the wet paper web 1 to rise to the target wet paper web
temperature may be set.
[0123] While the first embodiment is constructed such that the
opening and closing operations of the valves 11 are automatically
adjusted based on information detected from the moisture percentage
sensors 13 by the controller 12, the valve opening and closing
operations may be manually performed by the operator, based on
information detected from the moisture percentage sensors 13.
[0124] While the first embodiment is constructed such that the
steam box 6 and suction box 7 are provided in the former that forms
a layer of paper, they may be provided in a press part (which
applies pressure to the paper stock layer formed by the former to
further remove moisture) arranged downstream of the former.
SECOND EMBODIMENT
[0125] Next, a papermaking machine according to a second embodiment
of the present invention will be described.
[0126] As shown in FIG. 4, the papermaking machine of the second
embodiment, in addition to the construction of the first
embodiment, is equipped with another suction box 7A, which is
arranged in close proximity to the downstream side of the suction
box 7.
[0127] As described in the first embodiment, within the steam box 6
the temperature raising process is being performed and the wet
paper web 1 traveling through the steam box 6 is gradually raised
in temperature within the steam box 6, but a time lag occurs until
the whole of the wet paper web 1 is raised in temperature. Hence,
in the papermaking machine of the second embodiment, the wet paper
web 1 in which the effect of dehydration has become higher by being
raised in temperature within the steam box 6 is further dehydrated
by the suction box 7A. Since the suction box 7A suctions the wet
paper web 1 in which the effect of dehydration has become higher,
further dehydration can be performed, even if its suction force is
equal to that of the suction box 7. However, it is preferable to
set the suction force of the suction box 7A larger than that of the
suction box 7. This makes it possible to perform dehydration more
efficiently, whereby the dehydration rate can be raised.
THIRD EMBODIMENT
[0128] Next, a papermaking machine according to a third embodiment
of the present invention will be described.
[0129] As shown in FIG. 5, the papermaking machine of the third
embodiment is constructed such that in the construction of the
first embodiment, the downstream end of the suction box 7 is
arranged downstream relative to the downstream end of the steam box
6.
[0130] As described above, a time lag occurs until the whole of the
wet paper web 1 is raised in temperature within the suction box 6.
Therefore, by arranging the suction box 7 so as to be shifted
downstream, the wet paper web 1 can be dehydrated with better
efficiency, resulting in a further rise in the dehydration
rate.
[0131] In the third embodiment, the suction box 7 according to the
first embodiment is arranged so that it is shifted downstream by a
predetermined distance. However, with the upstream end of the
suction box 7 of the first embodiment fixed at its original
position, only the downstream end of the suction box 7 may be
positioned downstream relative to the downstream end of the steam
box 6.
FOURTH EMBODIMENT
[0132] Next, a papermaking machine according to a fourth embodiment
of the present invention will be described.
[0133] As shown in FIG. 6, the papermaking machine of the fourth
embodiment is constructed such that in the construction of the
first embodiment, it is further equipped with an air jet device
(seal means) 14 that jets air toward the upstream side, in the
vicinity of the upstream end of the steam box 6. It is preferable
that the air jet device 14 jet air toward the upstream side at an
angle .theta. of about 15 to 40 degrees relative to the wet paper
web 1.
[0134] This can suppress incursion of wake into the steam box 6
more reliably. In the case where wake can be sufficiently
suppressed by the air jet device 14, the upstream seal member 6c of
the steam box 6 may be omitted.
FIFTH EMBODIMENT
[0135] Next, a papermaking machine according to a fifth embodiment
of the present invention will be described.
[0136] As shown in FIG. 7, the papermaking machine of the fifth
embodiment is equipped with two sets of units comprising a steam
box 6 and a suction box 7 of the first embodiment. Specifically,
the fifth embodiment is provided with a first unit comprising a
steam box (first heating means) 6 and a suction box 7, and a second
unit comprising a steam box (second heating means) 6' and a suction
box 7'. The steam box 6 supplies steam to one side of the wet paper
web 1, while the steam box 6' supplies steam to the other side of
the wet paper web 1. This makes it possible to dehydrate both sides
of the wet paper web 1 evenly, whereby it becomes possible to
manufacture products in which both sides are so even that a
difference between them is slight.
OTHER EMBODIMENTS
[0137] While the present invention has been described with
reference to the preferred embodiments thereof, the invention is
not to be limited to the details given herein, but may be modified
within the scope of the invention hereinafter claimed.
[0138] The installation position of the steam box 6 can be
determined beforehand in making a design, and the stock
concentration (the reference stock concentration) of the wet paper
web 1 at the installation position can also be predicted in the
stage of the design. Therefore, in papermaking machines, steam
supply may be performed so that the temperature of the wet paper
web 1 becomes a target wet paper temperature which corresponds to
the reference stock concentration. In the above-described
embodiments, the actual stock concentration of the wet paper web 1
is detected by the moisture percentage sensor 13, and when there is
a difference between the stock concentration of the wet paper web 1
passing through the steam box 6 and the aforementioned reference
stock concentration, the supply of steam to the steam box 6 is
adjusted by feedback control in order to correct for this
difference. However, in the case where such a concentration
difference is almost negligible, a constant supply of steam may be
continuously performed in an open loop without providing the
moisture percentage sensor 13.
[0139] By providing means for detecting the temperature of the wet
paper web 1 and performing feedback control based on the detected
information, steam supply may be adjusted so that the wet paper web
1 reaches the target wet paper web temperature. Even in this case,
the wet paper web 1 can be raised in temperature and dehydrated
with good efficiency, resulting in arise in the dehydration
rate.
[0140] Downstream of the steam box 6, there may be provided air jet
type heating means for blowing high-temperature air against the wet
paper web 1 and heating the wet paper web 1 by a collision jet of
high-temperature air. With this configuration, the wet paper web 1
raised in temperature within the steam box 6 can be further raised
in temperature, whereby it becomes possible to further raise the
dehydration rate by the suction roll 8, suction box 9, etc.
[0141] Since the steam box 6 has a higher effect if it is employed
when the moisture percentage of the wet paper 1 is high, it is
preferable to install the steam box 6 in the former in which the
moisture percentage of the wet paper 1 is high, but it may be
installed in the upstream portion (near the inlet) of the press
part. Because the air jet type heating means has a higher effect if
it is employed in a state lower than the moisture percentage of the
wet paper web 1 in the former, it is preferable to install the air
jet type heating means in the press part which is lower in the
moisture percentage of the wet paper web 1 than the former, but it
maybe installed in the downstream portion (near the outlet) of the
former.
[0142] The above-described embodiments are constructed such that
the seal member 6c abuts the wire 3a in order to ensure sealing of
the steam box 6. However, if sealing of the steam box 6 can be
ensured, the seal member 6c may be provided in close proximity to
the wire 3a. If sealing of the steam box 6 is ensured by causing
the tip opening 6g of the steam box 6 to abut the wire 3a or
arranging the tip opening 6g in close proximity to the wire 3a,
there is no need to provide the seal member 6c.
[0143] The present invention is not limited to twin wires, but may
be applied to a long wire type former or on-top former which holds
only one side of the paper stock layer.
INDUSTRIAL APPLICABILITY
[0144] The present invention is applicable to a papermaking machine
and papermaking method for making paper web by holding a paper
stock suspension into the shape of a layer, and removing moisture
while making this paper stock layer travel.
* * * * *