Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
1998-08-19
2001-02-06
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S300000, C162S352000
Reexamination Certificate
active
06183602
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a twin wire former for a paper machine, and particularly to a twin wire former dewatering device for dewatering with dewatering blades.
2. Description of the Prior Art
Conventionally, a twin wire former is known as a paper layer forming apparatus for a paper machine. In the conventional twin wire former, two wires form a closed loop, respectively. As the paper stock (the pulp suspension) supplied between the wires travels along with wires, it is gradually dewatered by various dewatering devices including various dewatering elements. A paper layer or a fiber mat is thus grown which is further dewatered by a press part subsequent to the twin wire former to form a wet paper.
An example of the conventional twin wire former is schematically shown in
FIG. 5
, and will be referred to hereinafter.
In
FIG. 5
, a paper stock
7
filled in a headbox
6
is injected from the headbox
6
to a wedge-shaped gap
5
which is formed by a top wire
1
and a bottom wire
2
.
FIG. 5
shows the top wire
1
on the left and the bottom wire
2
on the right. The top wire
1
is operated by a drive roller (not shown) and guided by a forming roll
3
and guide rolls
31
A to
31
D, while the bottom wire
2
is typically operated by a drive motor (not shown) and guided by a breast roll
4
, a suction couch roll
12
, guide rolls
32
A to
32
e
and the like. In
FIG. 5
, the wires
1
and
2
are rotated in the directions indicated by the arrows. The above mentioned gap
5
is formed between the wires
1
and
2
. The paper stock
7
is injected to the gap
5
from a headbox
6
. The paper stock
7
is dewatered by various dewatering devices
14
,
23
,
15
and
11
to form paper web
13
while running along with the wires
1
and
2
in the gap
5
at the same rate as the wires.
A first dewatering device
14
on which a plurality of dewatering blades
9
are formed so as to be spaced apart from each other is provided at the bottom wire.
2
downstream from the forming roll
3
and the breast roll
4
. The plurality of dewatering blades
9
contact, at the top ends thereof, the inside back surface of the bottom wire
2
. The bottom wire
2
and the top wire
1
have a predetermined curvature (radius R) and are arranged so that the gap
5
, formed between the bottom wire
2
and the top wire
1
, gradually converges downstream.
Accordingly, while the paper stock
7
passing through the first dewatering device
14
travels within the gap
5
which gradually converges at the predetermined curvature (radius R), a dewatering process is performed at both sides (the sides of the bottom wire
2
and the top wire
1
) of the paper stock by dewatering pressure generated by the plurality of dewatering blades to gradually form a fiber mat.
Second dewatering devices
23
and
15
are mounted at the downstream side of the first dewatering device
14
. The second devices
23
and
15
are arranged so as to face each other over the top wire
1
, the paper stock
7
and the bottom wire
2
; the device
23
is provided at the top wire
1
, and the device
15
is provided at the bottom wire
2
.
FIG. 6
is an enlarged view showing an essential portion of the dewatering devices
23
and
15
. The device
23
includes a plurality of dewatering blades
20
mounted so as to be spaced apart from each other on the device body
23
A. The dewatering blades
20
are fixed by mounting portions
23
B of the device body
23
A. Each of the dewatering blades
20
is formed as a wedge-shaped type dewatering blade having a flat plane
20
A and a slanted portion
20
B.
The flat plane
20
A is formed inside the loop of the top wire
1
and is arranged so as to contact the back surface of the top wire
1
to support the top wire
1
. The slanted portion
20
B is formed at a wire entering side (at the upstream side of the wire running direction) relative to the flat plane
20
A so as to gradually slope away from the top wire
1
toward the upstream of the wire running direction.
A wedge-shaped clearance
20
c
is thus formed between the slant portion
20
B and the top wire
1
. The slant portion
20
B has an angle &thgr; referred to as a wedge angle.
The dewatering device
23
faces, over the wires, a dewatering device
15
provided with a plurality of dewatering blades
21
spaced apart from each other on the device body
15
A. The dewatering blades
21
depress the back surface of the bottom wire
2
, and the pressure applied by the dewatering blades
21
is externally adjustable by application of fluid pressure during operation of the paper machine.
Accordingly, each dewatering blade
21
is attached to a base
22
of the dewatering device
15
, and the base
22
can be moved in a direction such that the bottom wire
2
and the device body
15
A are brought close to or away from each other. The pressure applied to the bottom wire
2
by the dewatering blade
21
is adjustable by controlling fluid pressure, such as the air pressure and the hydraulic pressure, within a tube
24
formed between the base
22
and the device body
15
A.
Such a pressure adjustment by means of the dewatering blade
21
allows the dewatering pressure generated in the paper stock
7
, pinched between the top wire
1
and the bottom wire
2
, to be controlled.
Referring again to
FIG. 5
, a third dewatering device
11
, also called a suction box, is further provided inside the loop of the bottom wire
2
downstream from the second dewatering device
23
. The third dewatering device
11
and a suction couch roll
12
dewater the paper stock
7
by vacuum to form a paper web which is securely conveyed onto the bottom wire
2
and transferred by a suction pick-up roll (not shown) to a press part subsequent to the wire part.
Conventionally, the second dewatering devices
23
and
15
adjust the dewatering pressure generated between the wires
1
and
2
by varying the pressure applied by the dewatering blades
21
of the dewatering device
15
. However, there is a problem in that the dewatering pressure is adjusted in a narrow range in such a conventional pressure adjustment system, and it is difficult to make all the paper producing conditions adjustable for the appropriate dewatering pressure state.
Consequently, the dewatering pressure is normally set to achieve the most frequently used paper type with high quality. However, in this case, variation of the paper producing conditions would force the dewatering operation out of the optimum with the result that deteriorated paper quality must be more or less accepted, and it becomes difficult to prepare various types of low production volume paper.
Further, an intensive study has revealed that with a wedge-shaped dewatering blade, such as the above-mentioned blade
20
, the dewatering pressure is greatly regulated by the wedge angle &thgr;. Therefore, with the wedge-shaped dewatering blade, adjustment of the wedge angle would enable an appropriate dewatering pressure state to be obtained in a wide range of paper producing conditions.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned problems, and it is an object of the present invention to provide a twin wire former dewatering device for a paper machine capable of adjusting a suitable dewatering pressure in a wide range of paper producing conditions.
To achieve the above-mentioned object, according to one aspect of the present invention, there is provided a twin wire former dewatering device for a paper machine. In a twin wire former for a paper machine, including two wires forming closed loops, respectively, arranged so as to face each other and form a gap for paper formation, the two wires pinch paper stock supplied to the gap for paper formation therebetween and convey the paper stock while running, a twin wire former dewatering device for the paper machine comprises: a plurality of dewatering blades which are arranged inside one of the closed loops; and wires for defining the closed loops where the dewatering blades are arranged, the g
Hasuike Makio
Iwata Hiroshi
Matsumoto Masanobu
Naito Kazuhiro
Hastings Karen M.
Mitsubishi Heavy Industries Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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