Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Patent
1986-06-25
1987-12-22
Bashore, S. Leon
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
162301, 162351, D21F 902, D21F 100
Patent
active
047145218
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a twin wire former that is used as a former (i.e. having a formation forming section) in a paper making machine.
DESCRIPTION OF THE RELATED ART
What determines the nature of a paper sheet is mostly the performance of a paper making machine from an initial portion thereof to a former. With respect to the performance required for this former, it is required that retention of raw material is good, that a paper sheet having a large strength can be formed, that only small differences in quality exists such as printability or the like between the front and back surfaces of the paper sheet, that a paper sheet having a large surface strength can be formed, that high speed operation is possible, and that the former can be operated consistently, etc. While various types of formers have been invented in order to fulfill these requirements, any one of them has not fulfilled all the requirements. In the case of the Bel-Baie former in the prior art as shown in FIG. 3, although these requirements were almost fulfilled, there were difficulties in the retention of fine raw material and in the coupling strength in a thicknesswise direction of paper sheets formed thereby.
According to research and investigation, it has been known that after a raw material liquid has been sandwiched between two wires, if dewatering is carried out while scrubbing the wire with a fixed body, then a lot of fine raw material would flow therefrom, that is, retention is lowered. If one employs the construction such that the number of fixed bodies for scrubbing the wire such as shoe blades a, suction boxes b and the like in FIG. 3 are reduced and the number of dewatering means comprising a rotary body such as a suction couch roll c and the like are increased in order to improve the retention, then while the retention is improved, the formation is deteriorated.
With regard to the strength in the thicknesswise direction of a paper sheet, if a paper raw material liquid is sandwiched between two wires d and e and dewatering is effected from the both surfaces to form a fiber mat, then a paper sheet having a structure in which the coupling strength in the thicknesswise direction is low as compared to the case where dewatering is effected from only one surface to form a fiber mat, is formed. In order to reduce differences between the top and bottom surfaces of a paper sheet, it is necessary to dewater at both surfaces to form a mat, and for that purpose, considerably asymmetric both-surface dewatering would suffice. In the case of the asymmetric both-surface dewatering, lowering of the coupling strength in the thicknesswise direction can be also suppressed to a little extent.
In the above-mentioned type of formers, many formers in which a top wire unit is provided at a rear portion of a long wire, are known. One example of the formers is illustrated in FIG. 4. However, in such type of former as shown in FIG. 4, that is, in the former of the type that a long wire f and a twin wire former g in the prior art are joined together (hybrid former), when carrying out high speed operation, a raw material liquid is subjected to an excessive influence by pulse pressure produced by dewatering elements such as foils or the like provided in the portion of the long wire f, resulting in the destruction of the texture of the paper. Therefore, the former was not always suitable for high speed operation. It is to be noted that h in FIGS. 3 and 4 represents a headbox, i in FIG. 3 represents a water deflector, and j represents a vacuum deflector.
SUMMARY OF THE INVENTION
It is therefore one object of the present invention to resolve the difficulties in the prior art twin wire formers with respect to the retention to fine raw material and the coupling strength in the thicknesswise direction of a paper sheet, without an accompanying problem of the texture is being deteriorated or that the former is not suitable for high speed operation being presented.
To that end, according to the present invention, in a twin wire f
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patent: 3797384 (1974-03-01), Hoff
patent: 3810818 (1974-05-01), Arledter
patent: 3840430 (1974-10-01), Ely
patent: 4417950 (1983-11-01), Bubik et al.
patent: 4491521 (1985-01-01), Wenske et al.
Bashore S. Leon
Hastings K. M.
Mitsubishi Jukogyo Kabushiki Kaisha
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