Headbox for a papermaking machine

A headbox contains a nozzle channel which, in the direction of flow of the stock suspension or pulp. converges towards an outlet gap or slice. The nozzle channel contains two lips. At least one of these lips has a wall portion or section which is concave with respect to the stock suspension. This wall section is defined by imaginary curved reference lines. This wall section or portion is formed by steps or step portions extending essentially parallel to the outlet gap. Each of the step portions comprises a substantially planar partial surface extending comparable to the direction of flow of the stock suspension and an end surface disposed transversely with respect to its related planar or flat partial surface. At the region of this particularly simple to fabricate wall section there is thus produced microturbulence directly prior to the sheet formation. Such microturbulence ensures for a uniform formation of the stock fibers which are suspended at the region of the marginal flow or boundary region of the stock suspension.

CROSS REFERENCE TO RELATED CASE: 
This application is related to the commonly assigned, copending U.S. patent 
application Ser. No. 322,020 filed Nov. 16, 1981, entitled "HEADBOX FOR A 
PAPERMAKING MACHINE", and listing as the inventors Alfred Bubik, Hans Dahl 
and Rudiger Kurtz. 
BACKGROUND OF THE INVENTION 
The present invention relates to a new and improved construction of a 
headbox for a papermaking machine. 
Generally speaking, the headbox arranqement of the present development is 
of the type containinq an infeed channel for the stock suspension or pulp 
which is being processed. Merging with this infeed channel is a nozzle 
channel which converges in the direction of an outlet gap or slice. The 
nozzle channel is bounded by two lips or lip members. One of these lip 
members possesses at its inner surface at least one step portion extending 
transversely with respect to the primary flow direction of the stock 
suspension. This step portion is formed by an essentially flat or planar 
partial surface of the inner surface and an end surface disposed 
transversely with respect to the primary flow direction. This flat or 
planar partial surface extends in the lengthwise direction of the headbox 
in a manner corresponding essentially to the primary flow direction of the 
stock suspension. 
In European Patent Application No. 0 015 670, filed Feb. 14, 1980 and the 
cognate U.S. Pat. No. 4,345,970 there is disclosed a prior art headbox 
arrangement of the aforementioned type. Here, the step portions are formed 
at the underside of an upper lip which is curved in a convex fashion with 
respect to the stock suspension. This upper lip or lip member extends from 
the top towards the bottom of the headbox arrangement. This upper lip is 
prolonged by a rigid lip portion which protrudes past the outlet gap. At 
the lower lip or lip member there is attached at the outlet gap a 
flexible, foil-like lip portion which bears by means of its free end upon 
a movable web of a sheet forming device. The rigid lip portion of the 
state-of-the-art equipment serves for guiding the flow of the stock 
suspension effluxing out of the nozzle channel. 
SUMMARY OF THE INVENTION 
Therefore, with the foregoing in mind it is a primary object of the present 
invention to provide a new and improved construction of a headbox for a 
papermaking machine which improves the guiding of the flow of the stock 
suspension within the nozzle channel and enables fabricating in a most 
simple manner the headbox such that, by virtue of turbulence of the stock 
fibers located at the region of the marginal flow of the stock suspension, 
there is effectively precluded the formation of otherwise formed 
turbulence threads or jets which arise at the region of concave wall 
portions. 
Another important object of the present invention and in keeping with the 
immediately preceding object is to devise a new and improved construction 
of headbox which affords a uniform distribution of the stock suspension 
flowing towards the outlet gap or slice, and thus, provides for a 
substantially constant quality of the paper which is to be fabricated. 
Yet a further significant object of the present invention is directed to a 
new and improved construction of headbox for a papermaking machine, which 
is relatively simple in construction and design, extremely economical to 
manufacture, highly reliable in operation, not readily subject to 
breakdown or malfunction, and requires a minimum of maintenance and 
servicing. 
Now in order to implement these and still further objects of the invention, 
which will become more readily apparent as the description proceeds, the 
headbox of the present development is manifested by the features that the 
step portion is arranged at a section of the inner surface which is 
concave with respect to the stock suspension. This inner surface is 
defined by imaginary reference lines which extend in a curved fashion in 
the primary flow direction of the stock suspension, and at the region of 
such imaginary reference lines there is located a corner of the step 
portion. 
By virtue of the inventive arrangement of the step portion there is 
produced microturbulence at the marginal flow of the stock suspension. By 
the action of this microturbulence there is annihilated the secondary flow 
at the region of the concave inner surface which is caused by the 
centrifugal force effective at the stock suspension. The secondary flow is 
formed by virtue of displacement of the boundary layer. Due to 
annihilation of the secondary flow there is precluded the formation of the 
so-called turbulence threads or jets which become perceivable in the form 
of, for instance, disturbing streaks or strips in the paper web which is 
to be fabricated. 
According to a particularly advantageous construction of the invention the 
step portion can be arranqed between a guide device through which flows 
the stock suspension and a portion of the inner surface of the headbox 
which extends at least approximately parallel to a substantially 
band-shaped movable dewatering surface and also extends in the direction 
of the outlet qap. The guide device through which flows the stock 
suspension is located at an acute angle with respect to the band-shaped 
movable dewatering surface. This headbox construction is particularly 
suitable for secondary headboxes, by means of which the layer of the stock 
suspension which is to be formed is intended to be deposited upon one or 
more existing layers or plies. 
According to a further advantageous construction of the headbox the step 
portion can merge upstream and downstream with a respective flat or planar 
portion of the inner surface of the headbox. In this manner the entire 
concave portion of the related inner surface of the lip member or lip can 
be replaced by a step or step portion or also a series of successive step 
or step portions, so that the entire inner surface is composed of flat or 
planar surface portions. Also, it is possible to thus dispense with the 
otherwise relatively complicated and cumbersome machining of a curved 
inner surface, which appreciably simplifies the fabrication of the lip or 
lip member. 
To preclude any depositing of stock fibers at the corner of the step 
portion, namely the peripheral corner with respect to the curvature, the 
end surface of the step portion can be connected by a groove or 
fillet-like corner portion with the portion of the inner surface which 
merges at the periphery of the end surface. 
In order to be able to infuence the flow behaviour within the nozzle 
channel and to facilitate the fine setting or adjustment of the outlet gap 
or slice, it is advantageous if at least one of the lip members is movably 
arranged with respect to the other lip member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Describing now the drawings, it is to be understood that only enough of the 
construction of the various embodiments of headboxes disclosed herein and 
useful for papermaking machines have been illustrated therein in order to 
enable those skilled in the art to readily understand the underlying 
principles and concepts of the present development while simplifying the 
showing of the drawings. Turning attention now to FIG. 1, the headbox 
construction depicted by way of example therein, will be seen to comprise 
a distributor line or manifold 1 or equivalent structure which is 
connected in any suitable and well known manner in this technology with a 
here not further illustrated infeed line for the stock suspension or pulp 
or the like which is being processed. Laterally merging with the manifold 
or distributor line 1 is a guide device 2 which, in the embodiment under 
discussion, is provided with cylindrical openings or channels 3. An 
appropriate construction of manifold or distributor line which can be used 
with the headbox of the present development, and which does not however 
constitute subject matter of this invention, has been disclosed, for 
instance, in the German Patent Publication No. 2,607,823 and the cognate 
U.S. Pat. No. 4,087,321, granted May 2, 1978. 
The lengthwise axes of the openings or channels 3 of the guide device 2 are 
disposed at an acute angle .crclbar. with respect to a substantially 
band-shaped dewatering surface 17 of a here not further illustrated sheet 
forming device of a papermaking machine. This band-shaped dewatering 
surface 17 is movable in the direction of the arrow 16 shown in FIG. 1. 
Merging with the guide device 2 is a nozzle channel 5 which converges 
towards an outlet gap or slice 4. This nozzle channel 5 is bounded by two 
rigid lips or lip members 6 and 7 which are attached to the guide device 2 
in any appropriate fashion. The upper lip member or lip 6 shown in FIG. 1 
will be seen to comprise a flat or planar inner surface which extends 
essentially parallel to the lengthwise axes of the openings or channels 3 
of the guide device 2. This upper lip member 6 is provided at its tip or 
free end with a diaphragm 10 or equivalent closure element which can be 
selectively displaced in the direction of doubleheaded arrow 8 and fixed 
in the selected position in any appropriate fashion, so that there can be 
adjusted the width S of the outlet gap 4. The lower lip or lip member 7 
shown in FIG. 1 will be seen to contain at its inner surface a section or 
portion 11 which is concave with respect to the stock suspension which is 
being processed. This concave wall portion or section 11 of the headbox is 
defined by curved reference lines 13 extending in the primary flow 
direction of the stock suspension as indicated by the arrow 12. This 
concave wall portion or section 11 transforms into a flat partial surface 
7d of the inner surface of the lip member 7. This flat or planar partial 
surface 7d extends towards the outlet gap 4 and runs essentially parallel 
to the dewatering surface 17. 
The concave wall portion or section 11 of the inner surface of the headbox 
or lip member 7 possesses, in the embodiment under discussion, three step 
portions or steps 14 which are located in succession with respect to the 
direction of flow of the stock suspension. These step portions or steps 14 
are each formed by a respective flat or planar partial surface 7a, 7b and 
7c of the inner surface of the lip member 7 and a related end surface 15 
confrontinq the outlet gap 4 and extending essentially parallel to said 
outlet gap 4. The corners of the step portions 14, constituting peripheral 
portions with respect to the curvature and formed between the end surfaces 
or faces 15 and the partial surfaces 7b, 7c and 7d which merge with the 
related end surface 15 downstream thereof, are located at the region of 
the reference lines 13 (see for instance FIG. 2). 
The partial surfaces 7a, 7b and 7c are each inclined in a flow downstream 
decreasing angle towards the partial surface 7d and form with the 
oppositely situated portion of the inner surface of the lip member 6 a 
respective converging channel section. 
With this embodiment an imaginary concave reference surface, defined by the 
reference lines 13, is replaced by the three successively arranged step 
portions 14 and the tip or front of the lip member 7. 
During operation there is infed a stock suspension through the manifold or 
distributor line 1 to the headbox. This stock suspension is uniformly 
distributed by the openings or channels 3 of the guide device 2 throughout 
the width of the nozzle channel 5 measured perpendicular to the plane of 
the drawing of FIG. 1. At the region of the concave section or portion 11 
stock suspension is deflected in a direction parallel to the dewatering 
surface 17 and is applied, through the outlet gap or slice 4, onto such 
dewatering surface 17. 
During such time as the stock suspension flows through the nozzle channel 5 
this stock suspension is continuously accelerated at the regions of the 
partial surfaces 7a, 7b, 7c and 7d. By virtue of the rigid construction of 
the lip members 6 and 7 the cross-sectional area of the nozzle 5 and the 
outlet gap 4 is maintained constant and there is precluded any deviation 
or deflection of one of the lip members 6 and 7. At the marginal regions 
of the stock suspension, flowing along the step portions 14, there is 
produced in each case microturbulence at the region of the end surfaces 
15. This microturbulence, with appropriate sharp-edged configured free 
corners of the step portions 14, causes a detachment of the flow at least 
from the end surfaces or faces 15. 
Consequently, there are advantageously produced high shear stresses at the 
region of the outlet gap 4, i.e. practically directly prior to the sheet 
formation, at the marginal or boundary region of the stock flow. These 
high sheer stresses produce a particularly intensive turbulence of the 
stock fiber suspended in the stock suspension or pulp, and thus, ensure 
for a substantially uniform, streak-free formation of the stock fibers. 
As will be particularly evident by referring to FIG. 5, the end surfaces or 
faces 15 enclose with the flow upstream neighbouring partial surfaces 7a, 
7b and 7c a respective angle .alpha., and with the flow downstream 
neighbouring partial surfaces 7b, 7c and 7d a respective angle .beta.. In 
the solid line position of the end surface 15 the angles .alpha. and 
.beta. each amount to approximately somewhat what more than 90.degree.. In 
accordance with the modified phantom line shown positions of the end 
surfaces 15' and 15" the angles .alpha. and .beta. each can be 
approximately in a range of 40.degree. to 150.degree.. Particularly 
favorable for the flow are headbox constructions having a larger number of 
steps or step portions than shown in the exemplary embodiment of FIG. 1, 
the height H of which step portions amounts to at least 2 mm, and their 
length L, measured in the flow direction, each amounts to at least 
threefold, preferably five to tenfold of the height H. 
As will be seen from the embodiment shown in FIG. 2 the manifold or 
distributor line 1 is connected with a guide device 18 which is equipped 
with step-like widened throughflow openings or channels 20. The lower 
portion of the guide device 18 transforms into a rigid lower lip or lip 
member 21. At the upper portion of the guide device 18 there is pivotably 
connected in conventional fashion a rigid upper lip or lip member 22 which 
bounds the nozzle channel 5. This rigid upper lip member 22 is pivotable 
about a cylindrical part or portion 23 which extends essentially parallel 
to the outlet gap or slice 4. This lip member 22 possesses a convex 
underside and is adjustable in relation to the lip member 21 by means of 
an adjustment rod or linkage 24 or equivalent adjustment element which is 
operatively connected with a not here particularly shown but conventional 
adjustment device. With this embodiment the free edges of the step 
portions 14, which are the inner edges in relation to the curvature, are 
positioned at the region of the reference lines 13. By means of the 
adjustment rod or linkage 24 it is possible to regulate in known manner 
the width S of the outlet gap 4. 
With the modified embodiment of headbox shown in FIG. 3 the guide device 18 
is structured as an open connection channel which, for instance, is 
connected with a here not shown container or receptacle. The lower portion 
of the guide device 18 merges into a lip or lip member 27 which is 
provided at the domed or arched region of its inner surface, defined by 
the reference lines 13, with step portions or steps 28. Each of these 
steps or step portions 28 is formed by an end surface or face 30 directed 
opposite to the primary flow direction of the stock suspension indicated 
by the arrow 12 and a related partial surface 27b, 27c and 27d of the 
inner surface of the lip 27 and which corresponding partial surface merges 
with the related end surface 30 downstream with respect to the direction 
of flow. Also the partial surfaces 27b and 27c are each inclined at a 
smaller angle towards the partial surface 27d leading to the outlet gap 4 
than in relation to the neighbouring flow upstream partial surfaces 27a 
and 27b, respectively. At the region of the step portions 28 there is 
produced a particularly intensive turbulence of the stock fibers which are 
located at the marginal flow or boundary zone of the stock suspension, 
with otherwise practically undisturbed course of the marginal flow, if the 
end surfaces 30 each are disposed at an angle of about 40.degree. to 
90.degree. with respect to the related flow upstream partial surface 27a, 
27b and 27c, respectively. 
The previously described headbox constructions have been found to be 
particularly suitable for use as secondary headboxes, by means of which 
the layer or ply which is to be formed can be deposited in known manner 
upon a first layer which already is located upon the dewatering surface 
17. 
The headbox construction shown in FIG. 4 contains an infeed channel 33 for 
the stock suspension. This infeed channel 33 is subdivided by a partition 
or separation wall 34 into two essentially parallel partial channels and 
at which merges a nozzle channel 35 converging towards the outlet gap 4. 
This nozzle channel 35 is bounded by two mutually symmetrical lip members 
or lips 36. Each of these lip members 36 possesses a concave portion or 
section 11 which merges with the infeed channel 33 and a section or 
portion 37 which merges with the concave section 11 downstream thereof and 
which is convex with respect to the flow of the stock suspension. With 
this construction both the concave sections 11 are each formed by the flat 
partial surfaces 7a, 7b and 7c and the related end surface or face 15. 
Finally, as shown in FIGS. 6 and 7 the end surfaces or faces 15 and 30 of 
the step portions 14 and 28, respectively, also in each case can merge by 
means of a groove or fillet-like corner portion 40 w1th the partial 
surface of the inner surface which peripherally merges thereat with 
respect to the curvature. Instead of such type of rounded portions there 
also could be provided approximately fillet weld-like fills or beads at 
the corresponding corners. 
While there are shown and described present preferred embodiments of the 
invention, it is to be distinctly understood that the invention is not 
limited thereto, but may be otherwise variously embodied and practiced 
within the scope of the following claims. Accordingly,