Deflocculation of pulp stock suspension with pressure pulses

APPLICATION

Copending application Ser. No. 511,425, filed Dec. 3, 1965, and now abandoned, describes a method and apparatus for deflocculating a stock suspension web based upon a related principle.

BACKGROUND OF THE INVENTION (1) Field of the invention

The invention is in the field of treatment of the pulp suspension web while on the forming wire of a paper making machine to prevent flocculation of the fibers therein.

(2) Description of the prior art

As was pointed out in the aforementioned copending application, it is usually difficult to obtain a uniform distribution of fibers in the sheet being formed on the wire because there is a strong tendency for papermaking fibers to form flocs, that is, clumps of fibers that adhere to each other and separate only with difficulty. As a consequence, the resulting sheet of paper will vary in weight per unit area and is blotchy or mottled in appearance to transmitted light.

The usual manner of improving poor information is to dilute the suspension further but this presents serious problems because of the large quantities of water to be handled.

Another manner of combating flocculation is described in U.S. Pat. 3,149,026, issued Sept. 15, 1964, wherein jets of air are directed through the wire onto the suspension thereon.

SUMMARY OF THE INVENTION

In accordance with the present invention, flocculation of fibers in the suspension web on the forming wire is substantially reduced by applying a succession of pressure pulses to the web in reversely alternate directions.

These pulses are produced in a very simple manner by inducing drainage of liquid from the suspension in a series of spaced areas extending transversely of the wire and causing the drained liquid from each area to flow back against the wire in the space between the drainage areas.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a partial sectional side elevation of a device in accordance with the invention in operative relation to a forming wire,

FIG. 2 is an enlarged view of a portion of the sectional elevation of FIG. 1,

FIG. 3 is a partial perspective view, and

FIG. 4 is a partial sectional side elevation of a modified form of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1, 2 and 3, 10 is the conventional forming wire of a papermaking machine and 11 the web of stock suspension on one surface of the wire.

In accordance with the invention, a plurality of drainage foils 12 are applied to the opposite or drainside surface of the wire. Foils 12 each comprise an elongated surface extending transversely of the web and wire and from side to said thereof. Foils 12 may be integrally formed on a body member 13 suitably supported in wireengaging relation.

Foils 12 will, of course, induce drainage from the web in conventional manner. However, instead of withdrawing the drained liquid it is entirely or at least partially retained in the spaces between the foils and then forced back into the wire by means of channels 14. In the modification of FIGS. 1, 2 and 3, each channel has a closed bottom wall 15 and closed walls 16 converging from the foil surfaces towards the wall 15. The reverse flow of drained liquid occurs as a result of the converging channel walls and by the pressure created by the induced drainage of the foil (FIG. 2). The result is a succession of pressure pulses applied in alternating direction to the pulp suspension. The energy is dissipated by turbulence in the suspension which provides a deflocculation effect.

FIG. 4 shows an alternative arrangement wherein a plurality of foils 17 are provided with intervening channels 18 provided by downwardly converging walls 19. In this instance, however, bottom wall openings 20 in the channels provide outlets for part of the drained liquid into compartments 21 formed by side walls 22 and bottom walls 23. Means may be provided for controlling drainage from different sections as may be desirable. Such means, as shown, comprises a manifold 24 for each of a number of series of compartments 21, each manifold receiving liquid from passages 25 leading from the compartments in its series. Liquid may be drained from each manifold by means of an outlet 26 having a valve 27 therein.

The latter feature is of importance in some instances since flocculating action decreases as the concentration of fibers increases. It is consequently necessary to retain adequate water during deflocculation.

In some instances, it may be desirable to add water to enhance the action. If, for instance, the stock is very slow draining, the deflocculator will be less capable of developing a pumping action and sufficient additional water may be added to create a layer that can move in and out of the wire.

The geometry of the foils and the intervening channels may vary widely and will be determined in accordance with existing conditions. In general, the shortest spacing between foils and between opposite slopes in the intervening space, is desirable to provide rapid pulsation and to decrease space requirements. On the other hand, the wearing surface of the foil as contacted by the wire must be large enough to provide a useful life in service.

While the device is shown as applied to only one side of a suspension web, it will be apparent that, for instance, in a two-wire former, the device may be applied to both sides of the suspension web.