CA1243527A

CA1243527A - Headbox in a paper machine

Info

Publication number: CA1243527A
Application number: CA000456882A
Authority: CA
Inventors: Haruyoshi Fujiwara; Tetsuo Makino; Tosimi Tajima; Akira Eguchi; Norio Fujita; Akihito Nagano; Takashi Bando
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 1983-06-20
Filing date: 1984-06-19
Publication date: 1988-10-25
Also published as: FI842401A0; DE3422846C2; FI80486B; FI80486C; FI842401A; JPS602792A; DE3422846A1; JPH0260792B2

Abstract

ABSTRACT OF THE DISCLOSURE
A headbox in a paper machine is improved in that there are provided a first flow path having a uniform cross-section in the widthwise direction for causing separation in a flow therethrough to give turbulence to the flow and thereby stir a raw paper liquid, and a second flow path having a uniform cross-section in the widthwise direction and disposed contiguously to and downstream of the first flow path, whose longitudinal cross-sectional area is smoothly decreased and increased to repeatedly subject the raw paper liquid to acceleration and deceleration without giving turbulence to the flow.

Description

~2A35Z7 BACKGROUND OF THE INVENTION
1 The present invention relates to an improved headbox in a paper machine, and more particularly to a headbox in a paper machine which is adapted to make paper of improved quality.
Fibers in a raw paper liquid become entangled due to turbulence in the flow thereof generated at projections and recesses on the inner surface or bending portions of the piping in the midway of the flow path for feeding the raw paper liquid to a headbox, resulting in agglemeration into flocks of fibers. If such raw paper liquid is ejected as it is from the headbox to make paper, then the finished paper sheet will have a clear pattern consisting of light portions and dark portions as viewed with penetrating light.
Since such a paper sheet having unsatisfactory formation due to poor distribution of fibers is generally inferior in quality, such as mechanical strength, to a paper sheet having satisfactory formation due to good distribution of fibers, a headbox is required to eject a raw paper liquid after the flocks in the raw paper liquid have been dispersed a much as possible. In addition, if the surface of the ejected eject becomes irregular, then I, iL.'f2~SZ7 1 dewatering of the raw paper liquid on a wire becomes irregular, resulting in unsatisfactory formation due to poor distribution of fibers, and hence it is necessary to eject a jet having a smooth surface.
In the headbox of a paper machine in the prior art, dispersion of the flocks generally has been achieved by imparting turbulence to a flow. According Jo this prior art method, as a practical procedure for imparting turbulence to a flow, separation of the flow is induced by providing protrusions of various configurations on a wall surface or by changing the direction of the flow. Thus the flocks are disintegrated and mixed together by stirring oE the raw paper liquid generated at this time, and thereby fibers are distributed macroscopically uniformly.
However, fiber dispersion caused by stirring has the following shortcomings:
(1) Since turbulence is present in the flow, if the flow is ejected as it is, then the jet becomes irregular, Chile if it is attempted to obtain a smooth jet, then a section for attenuating the turbulence is necessary.

(2) When the flow is being stirred, even if the flocks have been disintegrated into small flocks by the turbulence of small size, in the event that a section B

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1 for attenuating the turbulence is provided in order to obtain a smooth jet in the downstream flow path, turbulence of small size Jill be attenuated more quickly. Hence, turbulence o large size will become more predominant, and the so-called reflocking in which flocks of large size are newly produced will occur.
(3) If separation of the flow is induced for the purpose of imparting turbulence to the flow, vortexes will be generated, and a difference in concentration will be produced due to the fact that the fibers are moved outwardly by centrifugal forces, and thereby new flocks are produced.

(4) In addition, if vortexes are generated, twisting of fibers is liable to occur due to rotation of the fibers, and this causes production of flocks which are difficult to disintegrate.

(5) Furthermore, there is a tendency that a paper sheet having a large variation of the degree of brightness between a portion containing flocks and a portion not containing flocks as viewed with penetrating light is apt to be produced.
On the other hand, in Laid-Open Japanese Patent Specification No 57-35092 there is disclosed a method in which dispersion is achieved by repeatedly ; 25 subjecting a raw paper liquid to acceleration and 4 5~

1 deceleration without giving turbulence to the flow of the raw paper liquid, According to this method, the raw paper liquid is subjected to acceleration and deceleration by gradually decreasing and increasing along the direction of the flow the cross-sectional area of the flow path which is uniform in the widthwise direction so that turbulence may not be generated due to separation of the flow. Thus, flocks are divided finely by exerting a force adapted to pull and tear off the flocks when they are in the accelerating region, while exerting a force adapted to push and extend the flocks when they are in the decelerating region, and thereby dispersion of the fibers can be achieved.
Moreover, upon dispersion caused by acceleration and deceleration, as will be described in more detail later, since the concentration of the fibers is different between a central portion of a flock and a peripheral portion thereof, the forces exerted upon the respective portions by water are different, and hence the fibers will diffuse. In such a dispersion process, a dispersing force will act upon every flock in the raw paper liquid. Hence, fibers in the peripheral portion of the flock itself will diffuse into the surrounding raw paper liquid, and thus the flock will be dispersed. Therefore, there is provided .~

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1 a paper sheet having excellent formation and fiber distribution such that variation in brightness between a portion containing flocks and a portion not containing flocks as viewed with penetrating light is small compared to a paper sheet obtained by disintegrating flocks merely by stirring the raw paper liquid.
SUMMARY OF THE INVENTION
The object of the present invention is as an object, to achieve improvements in quality such as formation or fiber distribution, mechanical strength, etc. of a paper sheet which has been produced by dispersing flocks in a raw paper liquid within a headbox, in distinction from the prior art as described above, thereafter ejecting this raw paper liquid and dewatering.
In view of the Eact that, while stirring has the efEect of disintegrating flocks in a raw paper liquid and mixing the raw paper liquid to make fibers distribute macroscopically uniformly, it also has the effect of producing new flocks, in the headbox in a paper machine according to the present invention,-although there is provided a flow path in which at first separation is caused in a flow to generate turbulence in the flow and thereby a raw paper liquid

6 ~Z~ z7 1 is stirred for the purpose of effectively utilizing the former effect, in order that the turbulence of the flow generated by stirring will not become large, an accelerating and decelerating flow path is provided continuously to the first-mentioned flow path to repeatedly subject the raw paper liquid to acceleration and deceleration without giving turbulence to the flow at all. Thereby, the turbulence of the flow generated in the stirring flow path section is made to disappear r and it is intended to achieve dispersion of fibers due to acceleration and deceleration.
In other words, the present invention is characterized by the fact that there are provided a first flow path having a uniform cross-section in the widthwise dlrection to cause separation in a flow therethrough to impart turbulence to the flow and thereby stir a raw paper liquid, and a second flow path having a uniform cross-section in the widthwise direction and disposed contiguously to and downstream of the first flow path for repeatedly subjecting the raw paper liquid to acceleration and deceleration without giving turbulence to the flow at all.
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The above-mentioned and other objects, features and advantages of the present invention will

7 ~'h4~5Z7 1 become more apparent by reference to the following description of preferred embodiments of the invention taken in conjunction with the accompanying drawings, wherein Fig. 1 is a longitudinal cross-section side view of a headbox in a paper machine according to one preferred embodiment of the present invention, Fig. 2 is a longitudinal cross-section side view of a headbox in a paper machine according to another preferred embodiment of the present invention, and Fig. 3 is a longitudinal cross-section side view of a headbox in a paper machine according to still another preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
_ In the following, the present invention will be described in greater detail in connection with the preferred embodiments illustrated in the accompanying drawings. At fist referring to Fig. 1, a raw paper liquid flows through a rectangular header 1 which is narrowed towards its tip end in the widthwise direction, then it is diverted by 90 and passes through holes in a perforated plate 2, and the raw paper liquid enters into a flow path having a uniform cross-section in the widthwise direction which is

8 ~2~5Z7 1 defined by an upper plate 3 and a lower plate 4. A
depth of the flow path at the inlet of this portion is smaller that the holes in the diameter of the perforated plate.
The depth of the flow path just before entering into a stirring chamber 5 is made small, and the depth of the flow path is abruptly enlarged in the stirring chamber 5. The dimensions of the stirring chamber 5 are appropriately determined depending upon the properties of the raw paper liquid. Immediately after the raw paper liquid has been stirred in the stirring chamber 5, the cross-sectional area of the flow path is reduced to accelerate the flow, and the stirring chamber 5 is thus connected to an accelerating and decelerating flow path 6 in which the cross-sectional area of the flow path is smoothly decreased and increased without giving turbulence to the flow at all.
A nozzle lip 7 is flexible, such that the opening of an ejecting port partially defined thereby can be adjusted by displacing the tip end of the nozzle lip.with the aid of an adjusting rod, not shown.
With reference to Fig. 1, the depth of the flow path just before entering into the stirring chamber 5, which flow path has a uniform cross-section

9 1'~4~5Z7 1 in the widthwise direction, is made small. In this portion of the flow path, the raw paper liquid is accelerated into a uniform velocity along the widthwise direction, and is made to have a flow velocity that is necessary for stirring.
In addition, since the depth of the flow path is abruptly enlarged at the inlet of the stirring chamber, the flow will separate simultaneously along the widthwise direction, the main flow and the separated flow will mix together, and thus fibers in the raw paper liquid will distribute macroscopically uniformly. Also, while the raw paper liquid is being stirred, flocks will be disintegrated.
Moreover, the dimensions of the stirring chamber are appropriately determined depending upon the properties of the raw paper liquid. With the flow path having a uniform cross-section in the widthwise direction the flow will separate simultaneously, and uniform stirring is effected in the widthwise direction as well as in the direction o the depth of the flow path. In addition immediately after stirring, the flow is subjected to acceleration, and turbulence contained in the flow will be attenuated rapidly, so that regeneration of flocks will be suppressed.

l Also, there is provided an accelerating and decelerating flow path 6 in which acceleration and deceleration are repeated without giving turbulence to the flow, contiguously to and downstream of the stirring chamber 5. Since there exists the property that if a flow is accelerated, then turbulence contained in the flow would be attenuated rapidly, in the accelerating section the turbulence in the flow would be attenuated rapidly, while in the decelerating section since the flow is decelerated so as not to generate turbulence in the flow, the turbulence contained in the flow will be attenuated as the raw paper liquid flows. As such acceleration and deceleration are repeated, the turbulence generated in the stirring chamber will disappear quickly.
Accordingly, it will never occur that the size of the turbulence grows and flocks again are produced, or that the surface of the jet becomes irregular due to turbulence in the flow.
With regard to dispersion of fibers in the accelerating and decelerating flow path, by varying the cross-section area of the flow path acceleration and deceleration are caused in the flow of the raw paper liquid flowing through the flow path. When a flock in the raw paper liquid is in an accelerating region, .~

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1 since the flow velocity on the upstream side is low and the flow velocity on the downstream side is high, the flock will be pulled and torn off, and thereby fibers will be dispersed. Whereas in a decelerating region, since the relation of the high and low flow velocities is reversed, a flock will be pushed and extended in the directions at right angles to the average traveling direction, that is, in the widthwise and thicknesswise directions. By repeating such processes, the flocks will be divided finely, and the fibers will be dispersed uniformly in the raw paper liquid.
In addition, when acceleration and deceleration are caused in a flow of a raw paper liquid flowing through a flow path by varying the cross-sectional area of the flow path, flocks in the raw paper liquid will be accelerated and decelerated as exerted forces from the flow of water. However, since the concentration of the fibers is high at a central portion of the flock and low at a peripheral portion of the flock, the forces exerted upon the fibers from the flow of water will be different depending upon the portions of the flock. At the central portion the force exerted upon fibers from the water upon acceleration and deceleration is weak because the fibers become overlapped with one another, whereas at the peripheral portion the same force is strong.

12 ~;~4~527 1 Therefore, when a flock is in an accelerating region the peripheral portion of the flock will expand in the traveling direction of the flow, whereas when a flock is in a deceleration region, the peripheral portion of the flock will expand in the upstream direction of the flow. As such acceleration and deceleration are repeated, a flock will diffuse from its peripheral portion, and fibers will be dispersed uniformly in the raw paper liquid. Even at the central portion of the flock, if there is a difference in concentration of the flock or where a network of fibers is weak, then dividing of the flock will start also from that portion for the above-mentioned reasons.
While the fibers are directed in the average traveling direction in the accelerating region, in the decelerating region the directions of the fibers will become random because the fibers are pushed from the rear. Accordingly, the dispersed fibers will become non-directionalS and even undispersed flocks will be directed randomly unless the flocks have a spherical configuration with respect to flow resistance.
Accordingly, undispersed flocks will be subjected to dispersing forces directed in various directions.
In a modified embodiment of the present invention illustrated in Fig. 2, in a flow path having 13 ~LZ4~Z7 1 a uniform cross-section in the widthwise direction that is defined by an upper plate 8 and a lower plate 9, the configuration of the longitudinal cross-section of the stirring flow path is different from that of the first embodiment shown in Fig. l. Also, the number of stirring processes is larger in this modified embodiment. More particularly, in the stirring flow path there are provided asymmetric proiections and recesses on the upper and lower walls so that separation Jay be caused in a flow therethrough to give turbulence to the flow and thereby the raw paper liquid is stirred. However, with regard to practical means for causing such stirring, various methods for stirring in the prior art such that various shapes of projections are provided on the wall surfaces or the direction of the flow is changed, can be employed in the portion of the stirring flow path shown in Fig. 2, in place of the illustrated flow path structure.
In a further modified embodiment of the present invention illustrated in Fig. 3, one end of a flow restraining element 12 is held in a groove of a holder ll that is fixedly secured to a perforated plate

10. Thus, two upper and lower flow paths having - uniform cross-sections in the widthwise direction are formed by the holder ll, flow restraining element 12, ,~

1 upper plate 13 and lower plate 14, and each of the flow paths is formed of a flow path portion for effecting stirring and a flow path portion for carrying out acceleration and deceleration. Although the structural configurations are different, neither of the modified embodiments shown in Figs. 2 and 3 is different in operation and advantages from the embodiment shown in Fig. 1.
The headbox in a paper machine according to the present invention is constructed in the above-described manner, and in this improved headbox, flocks are disintegrated and mixed together by stirring, and after the fibers have been distributed macroscopically uniformly, the flocks are further divided finely by acceleration and deceleration. Moreover, fibers in the peripheral portions of the flocks will diffuse into the raw paper liquid around the flocks due to the acceleration and deceleration! so that the flocks are dispersed. Therefore, both macroscopically and microscopically, a raw paper liquid in which fibers are dispersed far more throughly than in the prior art can be produced in a headbox having a short flow path.
In addition, turbulence generated in the stirring flow path will disappear quickly in the accelerating and decelerating flow path, so that the 1 S ~;~,L~5Z~

1 resultant fiber dispersion in the raw paper liquid will not be deteriorated, and a smooth jet can be obtained. Accordingly, a paper sheet obtained by ejecting this raw paper liquid on a wire is of high quality in that formation or distribution of the fibers is good and the mechanical strength thereof is high.
Since many changes and modifications can be made to the above-described construction without departing from the spirit of the present invention, it is intended that all matter contained in the above description and illustrated in the accompanying drawings shall be interpreted to be illustrative and not limiting.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A headbox for a paper making machine for dispensing throughout a raw paper liquid fibers contained therein, said headbox comprising:
a header for the supply therethrough of raw paper liquid;
a perforated plate defining one side of said header, said plate having therethrough openings for passage of said liquid form said header;
upper and lower plate members defining a flow path for passage of said liquid in a downstream direction from said openings in said plate, said flow path comprising in sequential order an intermediate flow section, a stirring chamber and an accelerating and decelerating flow path section;
said intermediate flow section being defined by parallel walls of said upper and lower plate members, with edges of said upper and lower plate members partially covering said openings in said plate, such that the cross-sectional size of said intermediate section is smaller than that of said openings in said plate, and said intermediate flow section having at the outlet thereof a throttled portion leading to said stirring chamber;

Claim 1 continued...

said stirring chamber has an inlet end of abruptly enlarged size at least as great as the size of said openings in said plate, thereby defining means for causing separation of the flow of said liquid, and said stirring chamber having an outlet end throttled to the same size as said throttle portion of said intermediate flow section; and said accelerating and decelerating flow path section having a cross-sectional area in the logintudinal direction repeatedly increasing and decreasing smoothly and gradually from said outlet end of said stirring chamber to the outlet of said headbox, thereby defining means to repeatedly decelerate and accelerate said liquid while preventing turbulence thereof due to separation of the flow thereof.
2. A headbox as claimed in claim 1, wherein plural said flow paths are defined by said upper and lower plate members and at least one flow restraining element positioned therebetween and retained in a groove in a holder member fixed to said perforated plate.