Headbox apparatus with stock dilution conduits for basis weight control

A headbox apparatus is disclosed for ejecting stock onto a forming wire for forming a web. The apparatus includes a housing which is connected to a pressurized source of the stock. The housing defines a tapered inlet for the flow therethrough of the stock. The tube bank has an upstream and a downstream end with the upstream end being connected to the tapered inlet such that the stock flows at a substantially constant flow rate through the inlet and through the upstream end of the tube bank to the downstream end of the tube bank. The tube bank includes a plurality of tubes for the flow therethrough of the stock. A member defines a slice chamber which has an upstream and a downstream extremity. The upstream extremity is connected to the downstream end of the tube bank, and the downstream extremity is disposed adjacent to the forming wire. The arrangement is such that the stock flows through the downstream end of the tube bank and through the upstream extremity of the slice chamber so that the stock is ejected from the downstream extremity of the slice chamber onto the forming wire. A plurality of supply conduits are connected to the upstream end of the tube back with each supply conduit being connected to a stock diluting source for permitting diluton of the stock flowing into the tube bank. A control device cooperates with the supply conduits for controlling the dilution of the stock flowing through at least some of the tubes of the tube bank for controlling the cross-machine directional basis weight of the resultant web.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION 
The present invention relates to a headbox apparatus for ejecting stock 
onto a forming wire for forming a web. More particularly, the present 
invention relates to a headbox having means for diluting the stock for 
controlling the cross-machine directional basis weight of the resultant 
web. 
INFORMATION DISCLOSURE STATEMENT 
In the papermaking art, stock is ejected from a headbox onto a fourdrinier 
forming wire which moves at approximately the same speed as the ribbon of 
stock being ejected from the headbox. Water drains from the stock through 
the forming wire so that a web is formed on the forming wire. 
More specifically, the stock is supplied at extremely high pressure to the 
headbox by means of pumping equipment so that the stock is ejected from 
the headbox through a slice lip. 
An attentuator is disposed upstream relative to the headbox for damping 
pressure pulses caused by the stock pumping equipment. The arrangement is 
such that the rate of flow of stock entering the headbox is relatively 
constant. 
Typically, the headbox inlet, or inlet header, is of tapered configuration. 
Such tapered inlet is required for the reason stated hereinafter. The 
stock flows from the tapered inlet through a plurality of distributor 
tubes disposed within a tube bank. Accordingly, it is essential that the 
rate of flow of stock through a distributor tube disposed at one side of 
the headbox be the same as the rate of flow of stock moving through a 
distributor tube disposed at the opposite side of the headbox. 
More particularly, the rate of flow of stock is, for example, the number of 
cubic feet of the stock passing a particular point every minute. Moreover, 
it is necessary in a headbox that such rate of flow remain constant or as 
constant as possible throughout the headbox. The basic reason why the rate 
of flow should remain constant is that if the stock during preparation has 
been thoroughly mixed, and if the slice lip opening is the same along the 
entire cross-machine directional width of the headbox, the weight of the 
fibers within the stock per inch of width across the ribbon of stock 
ejected through the slice lip will be constant. Accordingly, the resultant 
web will have a uniform basis weight in a cross-machine direction. 
In order to achieve such constant flow rate, the inlet header is tapered in 
a cross-machine direction so that the cross-sectional area of the inlet 
header is reduced by an area substantially equal to three times the total 
cross-sectional area of the tubes of the tube bank immediately upstream of 
the cross-sectional area of the header. That is, part of the main flow of 
stock flowing through the inlet header flows through a vertical tier of 
tubes. Therefore, the inlet is reduced in area by an amount substantially 
equivalent to three times the cross-sectional area of the tier of tubes in 
order to compensate for the loss of the diverted flow, thereby maintaining 
the same pressure in the header in the cross-machine direction to maintain 
the same flow through the tubes in the cross-machine direction. 
Consequently, the rate of flow of stock through all the tubes in a 
cross-machine direction is maintained substantially constant. 
However, in practice, it is very difficult to maintain a constant stock 
supply pressure due to pressure pulses of the pumping equipment and the 
inability of the pressure attenuators to completely dampen out such 
pressure pulses. 
Accordingly, various proposals have been disclosed for recirculating stock 
from the side of the inlet header opposite to the supply port of the 
inlet. 
Nevertheless, variations in the rate of flow of stock through the 
distributor tubes is almost impossible to eliminate. 
Furthermore, the maintenance of a completely even distribution of fibers 
within the stock present problems when endeavoring to maintain a uniform 
basis weight across the width of a formed web. 
Consequently, typical prior art headboxes include relatively complex 
mechanisms for adjusting or warping the upper slice lip of a headbox in 
order to vary in a cross-machine direction the volume of stock per minute 
ejected from the headbox. 
By varying the opening of the headbox slice at a particular point along the 
length thereof in a cross-machine direction, the weight of stock ejected 
per minute can be adjusted in a cross-machine direction so as to 
compensate for the aforementioned non-uniform rates of flow of stock and 
for such uneven distribution of fibers within the stock. 
Nevertheless, not only are the aforementioned proposals mechanically 
complex but also, when the rate of flow is altered at any one point across 
the width of a slice lip, such change in the rate of flow inherently 
affects the rate of flow on either side of such point so that the 
orientation of fibers within the stock is adversely affected. 
The present invention overcomes the aforementioned problems associated with 
altering a slice lip of a headbox by selectively diluting the stock 
flowing through certain of the tubes of the tube bank in order to 
compensate for variations in the basis weight of stock ejected from the 
headbox. 
In practice, measuring equipment disposed downstream from the headbox 
continuously measures the basis weight of the web along various points 
across the cross-machine direction of the web, and if there exists a 
variation at one particular point, a signal is sent to actuate one or more 
valves for supplying water, such as, for example, clarified white water, 
to the required location in order to compensate for the measured 
non-uniformity in basis weight. 
By the introduction of such water, which may be recirculated from the water 
removed from the fourdrinier wire, the rate of flow within such tube 
remains equivalent to the rate of flow through adjacent tubes. Such is the 
case because the diluting water does not introduce an increased pressure 
in the inlet. 
Although U.S. Pat. No. 3,407,114 to Springuel, which issued Oct. 22, 1988, 
taught controlling the cross-issued machine directional basis weight by 
the addition of white water to the headbox, such disclosure merely taught 
adding the white water to the pond of a headbox above the level of the 
stock as shown in FIG. 2 thereof. No disclosure is made therein of 
accurately metering a diluting solution to specific tubes of a headbox for 
accurately controlling the basis weight along the cross-machine 
directional width of a web. 
Therefore, it is a primary objective of the present invention to provide a 
headbox apparatus which overcomes the aforementioned inadequacies of the 
prior art proposals and which makes a considerable contribution to the art 
of evenly distributing stock onto a forming wire. 
Another object of the present invention is the provision of a headbox 
apparatus which includes a plurality of supply conduits connected to an 
upstream end of a tube bank so that each supply conduit is connected to a 
stock diluting source for permitting dilution of the stock flowing into 
the tube bank for controlling the cross-machine directional basis weight 
of the resultant web. 
Other objects and advantages of the present invention will be readily 
apparent to those skilled in the art by a consideration of the detailed 
description, taken in conjunction with the annexed drawings. 
SUMMARY OF THE INVENTION 
The present invention relates to a headbox apparatus and method for 
ejecting stock onto a forming wire for forming a web. The apparatus 
includes a housing which is connected to a pressurized source of the 
stock. The housing defines a tapered inlet for the flow therethrough of 
the stock. 
A tube bank has an upstream and a downstream end with the upstream end of 
the tube bank being connected to the tapered inlet such that the stock 
flows at a substantially constant flow rate through the inlet and through 
the upstream end of the tube bank to the downstream end of the tube bank. 
The tube bank includes a plurality of tubes for the flow therethrough of 
the stock. 
A member defines a slice chamber with the slice chamber having an upstream 
extremity and a downstream extremity. The upstream extremity is connected 
to the downstream end of the tube bank. The downstream extremity is 
disposed adjacent to the forming wire such that the stock flows through 
the downstream end of the tube bank and through the upstream extremity of 
the slice chamber so that the stock is ejected from the downstream 
extremity of the slice chamber onto the forming wire. 
A plurality of supply conduits are connected to the upstream end of the 
tube bank. Each supply conduit is connected to a stock diluting source for 
permitting dilution of the stock flowing into the tube bank. 
Control means cooperate with the supply conduits for controlling the 
dilution of stock flowing through at least some of the tubes of the tube 
bank for controlling the cross-machine directional basis weight of the 
resultant web. 
In a more specific embodiment of the present invention, the tapered inlet 
is tapered in a cross-machine direction such that the cross-sectional area 
for the flow therethrough of the stock progressively varies in a 
cross-machine direction. 
The housing includes an upstream and a downstream port in fluid 
communication with the tapered inlet. The upstream port is connected to 
the pressurized source of stock. The cross-sectional area of the tapered 
inlet is inversely proportional to the distance from the upstream port. 
The tube bank also includes a frame for mechanically supporting the 
plurality of tubes such that the stock flowing through the inlet and 
through the upstream end of the tube bank flows through the plurality of 
tubes. 
The plurality of tubes are rigidly supported by the frame, and the tubes 
are arranged in vertically spaced rows. Each tube within each row is 
vertically aligned relative to a tube of an adjacent row. 
Each tube of the plurality of tubes includes an upstream and a downstream 
portion. The upstream portion defines a substantially circular section 
taken in a direction normal to the direction of flow of the stock. The 
downstream portion includes an initial end of circular cross-sectional 
configuration and an outlet end defining a substantially rectangular 
cross-sectional configuration for maintaining a substantially constant 
volumetric flow of stock through the tube while increasing the velocity of 
the stock flow through the outlet end. 
The slice chamber also includes a plurality of trailing elements. Each 
trailing element has an end which is pivotally secured to the downstream 
end of the tube bank. Each trailing element is pivotally secured to the 
tube bank between adjacent rows of the plurality of rows. 
More particularly, the tube bank defines a plurality of dove-tail shaped 
grooves with each groove being disposed between adjacent rows of the 
plurality of rows. 
Each trailing element defines in the vicinity of the pivotally secured end 
thereof an enlargement which cooperates with one of the grooves for 
pivotally anchoring the element within the groove such that the stock 
flowing through the upstream extremity of the slice chamber is separated 
into a plurality of streams partitioned from each other by the plurality 
of trailing elements. 
The slice chamber converges in a direction from the upstream extremity to 
the downstream extremity such that the plurality of streams within the 
slice chamber converge relative to each other. 
The plurality of supply conduits extend through the tube bank between 
adjacent tubes of the plurality of tubes. 
More particularly, each supply conduit extends through the tube bank 
between adjacent tubes with each conduit having a termination disposed 
closely adjacent to and upstream relative to an adjacent tube of the 
plurality of tubes. The termination is disposed adjacent to the upstream 
end of the tube bank. 
The stock diluting source is fresh water or clarified white water removed 
from the stock through the forming wire. The water flows through the 
termination such that the water mingles with and dilutes the stock flowing 
through the adjacent tube without changing the flow rate through the 
adjacent tube. 
The flow of water through the termination is substantially normal to the 
flow of stock past the termination towards the adjacent tube. 
The control means includes a plurality of flow control valves. Each valve 
cooperates with a conduit such that each of the supply conduits is 
selectively connected to the stock diluting source for varying the basis 
weight of the resultant web in a cross-machine direction without changing 
the flow rate through the tube bank. 
Many modifications and variations of the present invention will be readily 
apparent to those skilled in the art by a consideration of the detailed 
description contained hereinafter, taken in conjunction with the annexed 
drawings. 
However, such modifications and variations fall within the spirit and scope 
of the present invention as defined by the appended claims.

Similar reference characters refer to similar parts throughout the various 
views of the drawings. 
DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a sectional view of a headbox apparatus, generally designated 10 
according to the present invention, for ejecting stock S onto a forming 
wire 12 for forming a web W. The apparatus 10 includes a housing, 
generally designated 14, which is connected to a pressurized source P of 
the stock S. The housing 14 defines a tapered inlet 16 for the flow 
therethrough of the stock S. 
A tube bank, generally designated 18, has an upstream and a downstream end 
20 and 22, respectively. The upstream end 20 of the tube bank 18 is 
connected to the tapered inlet 16 such that the stock S flows at a 
substantially constant flow rate through the inlet 16 and through the 
upstream end 20 of the tube bank 18 to the downstream end 22 of the tube 
bank 18. 
The tube bank 18 includes a plurality of tubes 24,25,26 and 27 for the flow 
therethrough of the stock S. 
A member, generally designated 28, defines a slice chamber 30. The slice 
chamber has an upstream extremity 32 and a downstream extremity 34. The 
upstream extremity 32 is connected to the downstream end 22 of the tube 
bank 18. The downstream extremity 34 is disposed adjacent to the forming 
wire 12 such that the stock S flows through the downstream end 22 of the 
tube bank 18 and through the upstream extremity 32 of the slice chamber 30 
so that the stock S is ejected from the downstream extremity 34 of the 
slice chamber 30 onto the forming wire 12. 
FIG. 2 is a perspective view of the inlet 16, tube bank 18 and slice 
chamber 30. 
As shown in FIG. 2, a plurality of supply conduits 36 and 37 are connected 
to the upstream end 20 of the tube bank 18. Each supply conduit 36 and 37 
of the plurality of supply conduits are connected to a stock diluting 
source 38 for permitting dilution of the stock S flowing into the tube 
bank 18. 
Control means, generally designated 40, cooperate with the supply conduits 
36 and 37 for controlling the dilution of the stock S flowing through at 
least some of the tubes 36 and 37 of the tube bank 18 for controlling the 
cross-machine directional basis weight of the resultant web. 
The tapered inlet 16 is tapered in a cross-machine direction, as indicated 
by the arrow CD, such that the cross-sectional area for the flow 
therethrough of the stock progressively varies in a cross-machine 
direction. 
More specifically, the housing 14 includes an upstream and a downstream 
port 42 and 44, respectively, in fluid communication with the tapered 
inlet 16. The upstream port 42 is connected to a pressurized source P of 
the stock S, as shown in FIG. 1. The cross-sectional area of the tapered 
inlet 16 is inversely proportional to the distance from the upstream port 
42. 
The tube bank 18 also includes a frame 48 for mechanically supporting the 
plurality of tubes 24 to 27 such that the stock flowing through the inlet 
16 and through the upstream end 20 of the tube bank 18 flows through the 
plurality of tubes 24 to 27. 
FIG. 3 is a sectional view taken on the line 3--3 of FIG. 1. 
FIG. 3 shows the plurality of tubes 24 to 27 rigidly supported by the frame 
48. Furthermore, the tubes 24 to 27 are arranged in vertically spaced rows 
50,51,52 and 53. The tube 26, for example, is disposed within the row 52, 
and the tube 26 is vertically aligned relative to the tube 27 of row 53. 
FIG. 4 is a perspective view of one of the tubes 26. As shown in FIG. 4, 
the tube 26 includes an upstream and a downstream portion 54 and 56. The 
upstream portion 54 defines a substantially circular section taken in a 
direction normal to the direction of flow, as indicated by the arrow 58, 
of the stock. The downstream portion 56 has an initial end 60 of circular 
cross-sectional configuration and an outlet end 62 defining a 
substantially rectangular cross-sectional configuration for maintaining a 
substantially constant volumetric flow of stock through the tube 26 while 
increasing the velocity of the stock flow through the outlet end 62. 
The slice chamber 30 also includes a plurality of trailing elements 
64,65,66 and 67, as shown in FIG. 2. Each trailing element 64 to 67 has an 
end 68 which is pivotally secured to the downstream end 22 of the tube 
bank 18. Each trailing element 64 to 67 is pivotally secured to the tube 
bank 18 between adjacent rows of the plurality of rows 50 to 53, shown in 
FIG. 3. 
FIG. 5 is an enlarged sectional view of the tube bank 18 showing the tubes 
24 to 27. The tube bank 18 defines a plurality of dove-tail shaped grooves 
70,71,72 and 73, as shown in FIG. 5. Each groove 70 to 72 is disposed 
between adjacent rows 50,51; 51,52; 52,53 of the plurality of rows 50 to 
53. 
Each trailing element, for example element 67, defines in the vicinity of 
the pivotally secured end 68 an enlargement 74 which cooperates with one 
of the grooves 74 for pivotally anchoring the element 67 within the groove 
74 such that the stock S flowing through the upstream extremity 32 of the 
slice chamber 30 is separated into a plurality of streams 76,77,78 and 79 
partitioned from each other by the plurality of elements 64 to 66. 
The slice chamber 30 converges in a direction from the upstream extremity 
32 to the downstream extremity 34 such that the plurality of stream 76 to 
79 within the slice chamber 30 converge relative to each other. 
As shown in FIGS. 2 and 3, the plurality of supply conduits 36,37 extend 
through the tube bank 18. The arrangement is such that the conduit 36 is 
disposed immediately upstream relative to the tube 24. 
Each supply conduit, for example conduit 36, extends through the tube bank 
18 between adjacent tubes 24 and an upstream tube 80 of row 50. The 
conduit 36 has a termination 82 which is disposed closely adjacent to and 
upstream relative to the adjacent tube 24 of the plurality of tubes 24 to 
27. The termination 82 is disposed adjacent to the upstream end 20 of the 
tube bank 18. 
The stock diluting source 38 is fresh water or white water removed from the 
stock through the forming wire 12 and clarified. The water flows through 
the termination 82 such that the water mingles with and dilutes the stock 
S flowing through the adjacent tube 24 without changing the flow rate 
through the adjacent tube 24. 
More specifically, the flow of water through the termination 82, as 
indicated by the arrow 84, is substantially normal to the direction of 
flow, as indicated by the arrow 86 shown in FIG. 3, of stock S past the 
termination 82 towards the adjacent tube 24. 
The control means 40 includes a plurality of flow control valves 88 and 89 
shown in FIG. 3. Each valve, for example valve 88, cooperates with a 
conduit 36 of the plurality of supply conduits 36 to 37 such that each of 
the supply conduits 36 to 37 is selectively connected to the stock 
diluting source 38 for varying the basis weight of the resultant web in a 
cross-machine direction without changing the flow rate through the tube 
bank 18. 
FIG. 6 is a diagrammatic representation of the headbox apparatus 10 
according to the present invention showing the operation of the apparatus 
for controlling dilution of the stock flowing through at least some of the 
tubes of the tube bank 18. 
The stock flows through the tapered inlet 16 of the housing 14. The flow of 
stock is indicated by the arrow 86. A portion, as indicated by the arrow 
90, flows through the upstream portion 54 of the tube 24. A supply conduit 
36 is connected to the upstream end 20 of the tube bank 18 so that the 
conduit 36 has a termination 82. The arrangement is such that water flows, 
as indicated by the arrow 91, substantially normal to the flow of stock 
86. The flow 91 and 86 mingle together so that substantially all of the 
water entering through termination 82 flows with the portion of stock 90 
through the upstream portion 54 of the tube 24. Consequently, the stock 
flowing through tube 24 is diluted. Therefore, the basis weight of the 
resultant web formed downstream on the forming wire is controlled in a 
cross-machine direction. More specifically, by such dilution, a sheet 
having a more uniform basis weight is achieved. 
The present invention provides an accurate means for controlling and 
maintaining a substantially constant basis weight of a web in a 
cross-machine direction by dilution of stock flowing through a tube bank.