Arrangement in tissue machine

Details Arrangement in tissue machine Arrangement in tissue machine

1999-04-20

2001-03-13

Silverman, Stanley S. (Department: 1731)

Paper making and fiber liberation

Processes and products

Running or indefinite length work forming and/or treating...

C162S206000, C162S289000, C162S290000

Reexamination Certificate

active

06200425

ABSTRACT:

The invention relates to an arrangement in a tissue machine, which arrangement comprises a Yankee cylinder, a roll and a steam box having a steaming area, whereby a paper web is formed in the tissue machine and the roll is arranged to press the web against the Yankee cylinder.
When tissue paper is manufactured by a tissue machine, paper stock is first fed from a headbox onto a wire to form a web. The web proceeds with the wire through a nip formed by the roll, for instance a suction press roll, and a Yankee cylinder for drying into a drying section formed by the Yankee cylinder and a hood, where the web is typically dried to a dry solids content of about 90 to 95%.
In connection with the suction press roll there is often arranged a steam box, which feeds steam on the web and wire on the suction press roll. When condensing, the steam raises the temperature of the web and the wire, which in turn reduces the viscosity of the water on the web, i.e. increases the fluidity of water. Thus the water drains more readily off the web and further from the wire, and the dry solids content of the web increases at the nip, which improves the drying result to be achieved. By means of the steam box the capacity of the machine's drying section can thus be increased.
FIG. 1
illustrates a press section and a drying section of a prior art tissue machine. In accordance with the prior art, a steam box
8
is arranged on a suction press roll
4
substantially in the horizontal center line A of the suction press roll or below the center line A such that a paper web
2
and a wire
3
between the paper web and the suction press roll
4
run between said steam box
8
and the roll
4
. When the web turns round the suction press roll
4
, by the effect of centrifugal force the web
2
releases pulp splashes which hit and stick to the steam box
8
arranged at a distance from the web and to the steaming area
8
a
thereof. Pulp splashes foul the steaming area and block the nozzles located in that area. It becomes more difficult for the steam to pass from the steam box to the web, and in the worst case it may be prevented completely. Then the steam treatment of the web will change and the temperature or the dry solids content of the web will no longer correspond to design, which will have an adverse effect on the operation of the entire drying section. Gradually the amount of dirt accumulated in the steam box increases to the extent that dirt drips or drifts along with the steam to be blown onto the web. As a result, a web break occurs, which causes considerable costs.
The object of the present invention is to provide an arrangement which can eliminate at least some of the above drawbacks.
The arrangement in accordance with the invention is characterized in that the steam box is arranged on the roll such that the steaming area of the steam box is arranged against the web substantially above the horizontal center line of the roll.
The basic idea of the invention is that the steam box is arranged in connection with the roll arranged in the Yankee cylinder of the tissue machine, the steaming area of the steam box being arranged above the horizontal center line of the roll, whereby outward-flying pulp splashes do not substantially enter the steaming area of the steam box. The idea of one preferred embodiment is that a splash surface is arranged to extend from the lower edge of the steam box steaming area. The idea of one preferred embodiment is that the splash surface is arranged outside the web's outermost point in connection with the roll. The idea of a third preferred embodiment is that the splash surface is formed concave.
The invention has an advantage that pulp splashes, which would foul the steaming area and impede the operation of the steam box and of the entire drying section, will not fly off the web to the steaming area of the steam box. A further advantage can be achieved that the pulp splashes flying off the web will not fall or otherwise drift from the steam box back onto the web surface giving rise to a web break.


REFERENCES:
patent: 3560333 (1971-02-01), Douglas et al.
patent: 197 48 708 A1 (1998-05-01), None

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