Note: Descriptions are shown in the official language in which they were submitted.
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P/563-89
METHOD AND HEADBOX FOR A PAPER MACHINE
BACKGROUND OF THE INVENTION
The present invention relates to a method and a
headbox for a paper machine. In particular, the
invention concerns a headbox with inserts for producing
or controlling turbulence in the flow of pulp suspension
through the headbox.
Relevant prior art documents are:
(1) US 3,769,155
(2) US 3,514,372
(3) DE 43 21 697
(4) DE 32 27 218 Al
(S) US 3,843,470
(6) DE 44 02 625 Al
These documents disclose elements within the
flow chamber of the headbox that influence the fluid
hydraulics. Such elements can, for instance, comprise
separate blades in the case of multi-layer headboxes.
Their influence on the fluid hydraulics is due primarily
to the fluid friction. Particularly, the degree of
turbulence in the flow is affected by the elements. This
is of great importance for forming the sheet or web of
paper.
~ Document (5) describes a headbox in which the
upstream ends of the flow elements do not extend up into
the region of the outlet slot. Document (6) describes a
headbox in which the surfaces of the flow elements are
variable in their positions in the headbox.
Known headboxes which have elements in the flow
chamber for controlling turbulence have a serious
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disadvantage. Control of the conditions of flow, and
particularly the turbulence, is not possible during
operation. Each headbox has very specific
characteristics which cannot be changed. This is
disadvantageous since numerous operating parameters are
subject to continuous change during operation, for
instance, the composition of the pulp, the temperature,
and the velocity of flow.
SUMMARY OF THE INVENTION
The object of the present invention is to
provide a method for use of a headbox and a headbox
wherein the hydraulics of the pulp slurry, and
particularly the degree of turbulence, can be controlled
in a variable manner during operation.
According to the invention, the surfaces of the
flow elements in the flow chamber which are contacted by
the pulp suspension or slurry are variable during
operation of the headbox. On the other hand, the
downstream ends of those flow elements have no effect on
the height above the wire or the width across the wire of
the outlet slot of the headbox. A headbox for a paper
machine has a flow chamber through which the pulp
suspension flows and an outlet slot through which the
suspension exits. For controlling turbulence and flow in
the flow chamber, a plurality of flow elements are
disposed in the flow chamber along the suspension path.
The flow elements are adjustable in their respective
sizes in the chamber, e.g., by moving into and out of
respective pockets, during operation. The flow elements
may comprise plates extending across the width of the
slot or rods arranged in one or more rows across the
width of the slot and each flow element is individually
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.
controllable. The flow elements either do not extend
through or extend through the outlet slot. Regardless of
that dimension, during operation of the flow elements,
they do not affect the width or height of the outlet
slot.
The inventors have discovered that changing the
size of the flow contacted surfaces by itself has a very
considerable effect on the flow hydraulics. Thus, one
may change not only the shape of inserts present in the
flow chamber to have such effect, but also their
respectlve sizes.
Document (4) discloses a multi-layer headbox
having a nozzle-like outlet channel which is divided into
three individual channels. The individual channels are
separated from each other by tongues which are
, .
displaceable in the direction of flow. Displacement of
these tongues, however, does not increase the flow
contacted surfaces of the tongues, but instead adjusts
the width of the outlet slot of the individual channels.
Other features and advantages of the present
invention will become apparent from the following
description of the invention which refers to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic side view of a headbox
for a paper machine;
Fig. 2 schematically shows the outlet nozzle of
the headbox, also in side view, with flow elements in
accordance with the invention;
Fig. 3 is a top view of the outlet nozzle of
Fig. 2;
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.
-- 4
Fig. 4 schematically shows another embodiment
of the invention, in a view similar to that of Fig. 2;
Fig. 5 schematically shows a multi-layer
headbox in side view; and
Fig. 6 schematically shows a three-layer
headbox in side view.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTICN
The headbox shown in Fig. 1 comprises a flow
chamber 1. The chamber has an inlet 2 at one side of the
headbox. An outlet nozzle 3 is arranged at another side
of the headbox following the flow chamber 1 in the path
of flow through the headbox. The outlet nozzle dispenses
liquid pulp suspension or slurry onto a conventional
forming section wire screen (not shown) that moves
beneath the nozzle and receives suspension from the
nozzle outlet.
The flow chamber 1 contains a bundle comprised
of a plurality of tubes 1.1 which are arrayed vertically
in rows, as shown in Fig. 2, which rows are also arrayed
across the headbox mapping a multi-tube matrix across the
headbox. The tubes extend in the direction of flow.
They serve, in known manner, to produce microturbulence
in the pulp slurry.
Figs. 2 and 3 detail the outlet nozzle 3 having
the flow elements in accordance with the invention. Fig.
2 shows the outlet nozzle 3 having two external bottom
and top limiting walls 3.1 and 3.2 which taper toward
each other to form an outlet slot 3.3 with each other at
their downstream ends. Figs. 2 and 3 show pockets
located in the flow chamber in which flow elements in
accordance with the invention are mounted. Fig. 2 shows
three rows of pockets with their corresponding flow
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elements and arranged one row above the other. These
include a top row of separated pockets 3.4, each with a
corresponding flow element 3.41, a middle row of pockets
3.5, each with a corresponding flow element 3.51, and a
bottom row of pockets 3.6, each with a corresponding flow
element 3.61. The flow elements are illustrated as round
rods. Any other cross-sectional shape may be employed,
e.g., oval, rectangular. They are movable in and out of
their respective pockets in the direction of suspension
flow, as indicated by the double-ended arrow in Fig. 3.
Inward and outward movement of any flow element
3.41, 3.51, and 3.61 changes the respective size of its
flow contacted surfaces. This influences the flow
hydraulics. Figs 2 and 3 show a total of twelve round
rods and their corresponding pockets. All or some of the
round rods in each single row of round rods can be moved
in or out to a respective different extent. However, all
round rods of all lines can also be moved out to
different extents. The flow is influenced in accordance
with the extent to which the individual round rods are
moved out.
Although each of the rods is illustrated as a
solid rod, at least some if not all of the rods may be
hollow, and their hollows may be connected by appropriate
conduits to a source of vacuum or pressure. Such rods
are open, e.g., at their free ends, into the flow
chamber, and the suction at their openings also affects
turbulence of the suspension.
The embodiment in Fig. 4 shows an outlet nozzle
3 of an entirely different shape. The pulp slurry is
conducted by a plurality of channels 5.1, 5.2, 5.3 to the
outlet slot 3.3. The channels are drilled through
respective solid blocks 6.1, 6.2, 6.3. The limiting
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walls 3.1, 3.2 are in the downstream end region of the
outlet nozzle 3 and are fixed.
Flow elements 3.71 and 3.81 in accordance with
the invention are provided. These flow elements are of
plate shape, rather than rod shape. Each plate element
extends over the entire working width of the headbox.
The elements are again mounted in respective pockets 3.7
and 3.8 defined in the interfaces between neighboring
blocks 6.1, 6.2, 6.3. In the same manner as the round
rods of Figs. 2 and 3, the flow elements can also be
moved along the direction of flow, so that the sizes of
the flow contacted surfaces of these flow elements 3.71,
3.81 can be changed.
As can be seen, the plate shaped flow elements
3.71 and 3.81 can in the present case be moved out to
extend beyond the outlet slot 3.3.
In a particularly interesting embodiment, the
flow elements, i.e., rods or plates, have surface regions
of different roughness along the direction of their
displacement. For instance, a downstream part can be
have a particularly small degree of roughness while the
roughness increases in the upstream direction. The
effect of moving out individual flow elements is thereby
progressively increased. This enhances the effect upon
turbulence of the suspension.
In the embodiment shown in Fig. 5, the
turbulence producing element 3.41 extends beyond the
outlet slots 3.31 and 3.32 defined by the walls 3.1 and
3.2. The flow element 3.41 produces additional
turbulence due to its boundary-layer friction with the
fiber slurry or pulp suspension (not shown) which has
already emerged from the nozzle 3. As long as the tip of
the flow element 3.41 is not withdrawn behind the slots
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3.31 and 3.32, the widths of the outlet slots 3.31 and
3.41 remain constant. This same is also true when the
flow elements move only inside the nozzle. In this way,
the degree of turbulence in the slurry or suspension can
be adjusted without thereby changing the amount of slurry
which flows out.
Fig. 6 shows a variant of Fig. 5. Instead of
there being only one flow element, two flow elements are
present. (However, still further flow elements are
possible). Within the nozzle 3 the courses of the flow
elements 3.41 and 3.51 are arranged to be converging in
the direction of flow for reasons of fluid mechanics.
In order that the heights (above the wire) of
the three outlet slots 3.31, 3.32 and 3.33 not change
upon displacement of the flow elements 3.41 and 3.51, it
is necessary for the flow elements 3.41 and 3.51 to be of
resilient material and to extend parallel to each other
where they pass through the outlet openings. This
parallel alignment is produced by specific control of the
pressures of the individual streams in the nozzle 3 and
by dimensioning of the bending stress in the flow
elements 3.41 and 3.51.
It is obvious that the flow elements in Figs. 5
and 6 can be either flat as in Fig. 4 or of rod shape as
in Fig. 2.
Although the present invention has been
described in relation to particular embodiments thereof,
many other variations and modifications and other uses
will become apparent to those skilled in the art. It is
preferred, therefore, that the present invention be
- limited not by the specific disclosure herein, but only
by the appended claims.
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