US3432384A

US3432384A - Fine-spreading and retarding device for the pulp suspension stream in a papermaking machine

Info

Publication number: US3432384A
Application number: US461788A
Authority: US
Inventors: Hans Dahl
Original assignee: Escher Wyss GmbH
Current assignee: Sulzer Escher Wyss GmbH
Priority date: 1964-06-13
Filing date: 1965-06-07
Publication date: 1969-03-11
Anticipated expiration: 1986-03-11
Also published as: GB1115030A; AT267307B; CH430422A

Description

March 11, 1969 H. DAHL 3,432,384

FINB-SPREADING AND RETARDING DEVICE FOR THE PULP SUSPENSION STREAM IN A PAPERMAKING MACHINE Filed June 7, 1965 Sheet of 5 FIG! PRIOR ART FIG.2

INVENTOR HANS DAH L ATTORNEYS March 11,1969 H. DAHL. 3,432,384

- F1NE*$PREADING AND RETARUING DEVICE FOR THE PULP SUSPENSION STREMI IN 'A' PAPERMAKING MACHINE Filed June 7, 1965 Sheet 2 of 5 FIG.5

FIG,6

INVENTOR HANS DAHL ATTORNEYS March 11, 1969 H. DAHL 3,432,384

FINE-SPREADING AND RETARDING DEVICE FOR THE PULP SUSPENSION STREAM IN A PAPERMAKING MACHINE Filed June 7, 1965 Sheet 3 of S INVENIOR HANS DAH L ATTORNEYS United States Patent 5 Claims Int. Cl. D21f 1/06 ABSTRACT OF THE DISCLOSURE A cylindrical spreading chamber for a papermaking machine including a guide wall-arranged to direct a sus pension of pulp in such a manner that the co-operative relationship between the cylindrical wall and the guide wall will enclose a whirling body of pulp.

This invention relates to a fine-spreading and retarding device for the pulp suspension stream in a papermaking machine. Such devices are usually inserted between the pulp pre-spreader and the breast box outlet gap of the machine, and their purpose is to stabilize the paper pulp suspension coming from the spreader, and to main tain constant velocity of flow over the entire width of the machine and in the direction of flow.

As is known, the requirement that feeding of the pulp to the wire should be as uniform as possible, a requirement which has to be made if a homogeneous paper web is to be produced, is all the more difficult to meet, the higher is the working speed of the machine, and the wider is the range in which the working speed has to be varied. In the last-mentioned case in particular the known spreading and retarding devices are unsatisfactory, because they operate in a stable manner only over comparatively narrow flow ranges. A known spreading device consists of a tubular spreading chamber having a circular cross section, into which two feed pipes for the pulp suspension open radially. The suspension flows away from this spreading chamber through a narrow slit, which extends over the entire width of the chamber. To improve the spreading, a second tubular chamber of circular cross section follows, into which the above-mentioned outlet slit opens through a narrow channel. In this device, the pulp stream enters the second chamber in such a manner that it forms a secant through the cross section of the second chamber. The result of this arrangement is that the flow impinges directly on the wall opposite the inlet gap and is led by said wall to the outlet gap. Between the pulp inlet and outlet gaps there is a bulged wall, in which is formed an eddy-like movement of the pulp suspension filling the chamber.

In this device, it is disadvantageous that, particularly at high velocities of flow, regions of flow separation are formed in the vicinity of the pulp inlet and outlet gaps, and that air separation at the centre of the eddy cannot be avoided.

Another known construction of a fine-spreading and retarding device consists of 'a chamber of substantially pearshaped cross section extending over the entire width of the machine. Streams of high velocity, coming from a coarse spreader, enter this chamber, pass through it radially and finally impinge on a guide wall situated opposite the pulp inlet. The direction of flow is deflected at the said wall, and the pulp suspension is fed to the breast box through one or more perforated rollers.

Due to the flow passing radially through the chamber, at least two eddies are formed, which however are unstable and are therefore prone to pulsate. It has been found that the pulsation of the eddies is propagated as far as the pulp outlet gap, and cannot be entirely suppressed, even by means of a rotating perforated roller arranged in front of the gap. The result is inhomogeneity of the paper Web, and in particularly serious cases, the still wet web may te'ar at places of low area weight.

According to the invention, a fine-spreading and retarding device is now proposed, which is hydro-dynamically stable even in the case of differently adjusted flow velocities. The new fine-spreading and retarding device comprises a spreading chamber of approximately pearshaped cross section extending over the entire machine width, and it has a guide wall for the pulp suspension, as Well as a wall situated opposite said guide wall. Seen in the direction of flow, the pulp inlet is situated in front of the guide wall, and the pulp outlet behind said wall. The device according to the invention is characterised in that the supply connections for the pulp suspension are so arranged that the suspension enters the spreading chamber substantially in the tangential direction of theguide wall. The angle 5, at which the supplied suspension meets the suspension already in the spreading chamber is less than 30", preferably less than 20. Particularly in cases where the pulp stream coming from the coarse spreader is subdivided into a number of partial streams, it is advantageous to provide in front of the spreading chamber according to the invention a pre-chamber, the width of which is substantially equal to the width of the spreading chamber, and the internal width of which, at the inlet point, is substantially equal to the internal width of the pulp suspension flow conduits opening into 'it. The length of the pre-chamber, viewed in the direction of flow, may be comparatively short. Advantageously, it is of such dimensions that complete unification of the partial streams and a certain equalization of the flow profile already occur in the pre-chamber.

The two large boundary walls of the pre-chamber may be parallel to each other, or may converge in the direction of flow of the pulp suspension.

A further safeguard against the formation of flowseparation regions and dead-water zones may be provided if the axis of the flow conduits for the pulp suspension fiow makes an angle 0: of 5 to 20, preferably about 10, with the pre-chamber wall adjacent the spreading chamber.

For further smoothing of the pulp flow and for equalizing the flow profile, it is advantageous if the cross section of the pulp discharge gap of the spreading chamber diminishes steadily in the direction of flow of the pulp. Instead of this diminution, a preferably rotating perforated roller may be arranged in known manner in the pulp discharge gap.

As already mentioned, the function of the fine-spreading and retarding chamber according to the invention is to render uniform the flow profile of the pulp suspension over the machine width and with regard to time, and to reduce the velocity of flow. To provide a picture of the necessary retardation of the flow velocity, which is essential to obtain in the breast box following the finespreading and retarding device, a flow controlled over the entire height and particulaly on the free surface, the following numerical values are given:

For a velocity of flow of 2-6 m./sec., entering the spreading chamber, the outlet velocity of the pulp suspension should amount to only 0.3-0.9 m./sec. In special cases, the inlet velocity may be l-8 m./sec. and the outlet velocity 0.2l.6 m./sec. In other words, the ratio between the flow velocities at inlet and outlet from the spreading chamber is about 5:1, with a maximum of about 10:1.

In explaining the new device more fully, reference will be made to the accompanying drawings, showing the device diagrammatically.

In these drawings:

FIG. 1 shows a conventional spreading chamber in cross section,

FIG. 2 shows a simple embodiment of the chamber according to the invention in cross section,

FIG. 3 shows another embodiment of the chamber according to the invention in cross section,

FIG. 4 shows another embodiment of the chamber according to the invention in cross section,

FIG. 5 shows another embodiment of the chamber according to the invention in cross section.

FIG. 6 shows another embodiment of the chamber according to the invention in cross section,

FIG. 7 shows a perspective view of the chamber according to the invention.

In the first place, FIG. 1 shows the form of a known spreading chamber in cross section. It consists of a chamber 1, to which one or more pulp feeding pipes 2 are attached so that the jet of pulp, i.e. the pulp suspension stream 3 passes radially through the chamber. It strikes against the guide wall 4, extending approximately in the direction of the pulp outlet. The stream 3 is deflected into the pulp outlet direction 20 and into the opposite direction 21, forming two whirling bodies 22 and 23, on the one hand, and a uniflow pulp stream 24 on the other.

Since the suspension stream 3 passes freely through the inner space of the chamber 1, any deviation in direction and intensity of this stream will atfect the position and turbulence of the two whirling bodies 22 and 23. This means that the whirling bodies are unstable and transmit their vibrations to the pulp stream 24. Experience has shown also that these vibrations cannot be suppressed completely by a perforated roller 17 arranged in the outlet gap 16.

FIG. 2 shows an embodiment of the fine-spreading chamber according to the invention in cross section in which, for producing only one whirling body, the pulp suspension is introduced tangentially. The spreading chamber 1 has a pear-shaped cross section, and after entering the chamber, the suspension stream flows along the guide wall 4. Opposite the guide wall is a bulged wall 25, in which only one whirling body 26 is formed. According to the invention, the device is so constructed that the angle which the pulp suspension stream 3 makes with the suspension already whirling in the spreading chamber is as small as possible. In practice, it has been found that with angles larger than 30 at the point at which the two streams meet, unstable eddies are formed. With angles of less than 30, or still better, less than 20, such eddies are, however, suppressed with certainty.

In the further development of the invention, adjoining the gap-like pulp inlet 5 is a pre-chamber 6, which the pulp suspension first enters. As the spreading chamber 1, the pre-chamber 6 extends over the entire machine width, but has only an internal width, see FIG. 7, which at the inlet position 9, is substantially equal to the internal width 10 of the flow conduits, i.e. the pipes 2 opening into it. Unification of the individual partial streams and extensive equalizations of the flow profile occur already in the pre-chamber 6. The pulp suspension, thus prestabilized, now enters the spreading chamber 1, in which its velocity of flow is reduced and its profile still further equalized.

In FIG. 2, the two boundary walls 11 and 12 of the pre-chamber are arranged parallel to each other. In the embodiments of FIGS. 3 to 5, they converge in the direction of flow. To reduce still further, and even at high velocities to suppress altogether, the tendency of the flowing pulp suspension to form eddies the moment it meets the suspension already present in the chamber, it is proposed to arrange the flow conduits, i.e. the pipes 2 so that their axis 13 (see FIG. 5) makes an angle a of from 5 to with the pre-chamber wall 11.

FIG. 3 shows an embodiment of the device according to the invention, in which the cross section of the spreading chamber 1 steadily tapers in the direction of flow of the pulp. There is thus formed a pulp outlet gap 16 of reduced cross section. This step also ensures equalization of the flow profile, and prevents the formation of flakes.

A preferably rotating perforated roller 17, as shown in FIGS. 2, 4, 5, 6, 7, or other known throttling elements, for example a perforated plate, a bar roller or the like, may also be arranged in the pulp outlet gap 16.

It is not necessary for the actual flow conduits of the pulp suspension flow to enter the spreading chamber at a specific angle. On the contrary, the flow conduits may be introduced into the spreading chamber in any direction and at any point, one or more guide plates 15 being provided to ensure that the entering pulp suspension stream is deflected into the desired direction (see FIG. 6).

In the example shown in FIG. 7, the pre-chamber 6 is connected by numerous feed pipes 2 to a coarse spreading device, consisting of a conically tapering pipe 27, from which the pipes 2 branch out at right-anges to the pipe axis. This spreader belongs to the prior art; it is mentioned here merely as example. The figure shows how the finespreading and retarding device is inserted between the coarse spreader and the breast box.

What is claimed is:

1. A fine-spreading and retarding device for the pulp suspension stream in a papermaking machine comprising means defining a cylindrical spreading chamber of pearshaped cross section, having cylindrical walls extending across the entire machine width and having a supply connection for the pulp suspension disposed in the region of the bulged end of said pear-shaped cross section and a discharge gap at the tapering end of said pear-shaped cross section; one of said cylindrical walls extending, along the circumference of said pear-shaped cross section, from said supply connection to said discharge gap and serving as a guide wall for the throughflowing pulp suspension, said guide wall having a trailing end arranged to direct the throughflowing suspension into said discharge gap; said supply connection being arranged to introduce the pulp suspension into said spreading chamber substantially in the tangential direction of said guide wall; and the cylindrical wall opposite said guide wall being bowed outward away from said trailing end so as to enclose, with the pulp suspension flowing along said guide wall, a substantially stationary whirling body of pulp suspension.

2. The device defined in claim 1 in which said supply connection for the pulp suspension comprises a prechamber preceding said spreading chamber in the direc tion of flow; flow conduits for feeding the pulp suspension into said pre-chamber, said pro-chamber having two walls which converge in the direction of flow and extend across the entire machine width, said walls forming a gap opening into said spreading chamber and in which at least one of said two pre-chamber walls makes with the flow axis of said flow conduits an angle of from 5 to 20, the internal width of said pre-chamber, in the region where said flow conduits enter it, being substantially equal to the internal width of said flow conduits.

3. The device defined in claim 1 in which said opposite wall is formed in such a manner that the entering pulp suspension meets said whirling body of pulp suspension at an angle of less than 30.

4. The device defined in claim 2 in which one of said walls of the pre-chamber joins tangentially with said guide wall of the spreading chamber, and the other of said walls of the pre-chamber makes with said opposite wall of the spreading chamber an angle of less than 30.

5. The device defined in claim 1 in which said supply connections comprise at least one plate arranged to guide the pulp suspension entering said spreading chamber into the tangential direction of said guide wall.

(References on following page) 5 6 References Cited DONALL H. SYLVESTER, Primary Examiner. UNITED STATES PATENTS I 3,255,074 6/1966 Solomon et a1 162-342 X HODGSON Amstmt Examme" OTHER REFERENCES 5 Libby: Pulp and Paper Science and Technology, v. II, 162340, 216 McGraW-Hill. New York, 1962, p. 178.