Fluid jet supported headbox

A structure and method for the improved formation and dewatering of a papermaking web onto a porous forming surface wherein a layer of water is first formed by depositing water onto a traveling wire and a stock slurry is deposited from a headbox slice onto the layer of water so that the layer of stock first interfaces with the water and improved fiber formation occurs onto the forming surface.

DESCRIPTION 
The present invention relates to improvements in papermaking machines, and 
more particularly to an improved method and apparatus for dewatering paper 
stock on a forming surface. More particularly, the invention relates to an 
improved method and apparatus for first depositing the slurry onto the 
traveling forming surface in a manner wherein fiber orientation and 
drainage of fibers and fines is controlled in the critical period during 
and immediately after the stock is deposited onto the forming wire. 
A very critical step in the formation of paper web in a current high speed 
papermaking machine occurs when the jetstream of stock is first deposited 
onto the traveling forming wire. At that point in time, nonuniform deposit 
of the stream of stock from the headbox slice and undesirable differences 
in speed of the traveling forming surface and the layer of stock can 
substantially adversely affect the nature of the web which is formed. 
As the initial lower surface of a stock stream first engages the wire, 
improper orientation of the fibers can occur and loss of fibers and fines 
will occur at that initial point in time. There is an initial contact 
between the fibers of the stock closest to the wire which can result in 
drainages of fibers through the wire. The location where the jet of stock 
is first deposited onto the wire is significant in that excessive pumping 
can occur closely following the breast roll resulting in a loss of fibers 
and also resulting in disorientation of the fibers. 
It is highly desirable to obtain optimum circumstances at this location and 
efforts to avoid difficulties and improve formation at this point have 
been made. Such efforts include eliminating the free trajectory of the jet 
from the headbox slice and accurate control of the relative speeds of the 
wire and stock emitting from the headbox slice. If an improper 
relationship exists, the CD/MD quality of the paper can be adversely 
affected. Also, the web can be substantially nonuniform in an undesirable 
amount in comparing the wire side of the web with the upper side. 
Another problem exists when multiple layered web is to be made and the 
headbox is structured so that the stock is delivered in layers with each 
layer having a different characteristic. It is essential that the layers 
retain their characteristics and that undesirable mixing of the layers 
does not occur and that the lower layer be properly formed on the 
traveling forming surface. 
It is an object of the present invention to provide an improved structure 
and method for the smoother stock delivery from a headbox onto a traveling 
forming surface. 
A further object of the invention is to provide an improved headbox 
arrangement capable of use with multiple layered stock wherein a better CD 
basis weight control is obtained and there is less tendency to have the 
layers mix when stratified. 
A further object of the invention is to provide an improved headbox 
structure and stock delivery method wherein more uniform fiber orientation 
across the sheet occurs and better control of the CD/MD tensile ratio can 
be obtained. 
A still further object of the invention is to provide an improved headbox 
stock delivery arrangement wherein higher retention of fibers and fines 
occurs particularly at the point of initial deposit of the layer of stock 
onto the traveling forming surface. 
In accordance with the principles of the invention, the initial shock which 
occurs when stock emits from the headbox slice and engages the traveling 
forming wire is avoided with similar avoidance of the adverse effects. A 
layer of water is formed on the traveling forming surface, such as a 
fourdrinier wire, and the stock is deposited from the headbox slice to 
interface with the layer of water. Dewatering begins substantially 
immediately as the layer of water disappears through the forming surface 
but the initial shock and disorientation effects which occur with the 
stock directly engaging the traveling wire are avoided. The adverse 
effects of a relatively long free length of trajectory of the stock 
emitting from the headbox slice are also avoided by the stock being 
deposited directly onto the water layer. The water layer is deposited onto 
the wire upstream of the location where the stock engages the wire so that 
the first interface of the stock is with the layer of water rather than 
directly with the uneven surface of the traveling forming surface such as 
a fourdrinier wire.

As illustrated in the drawing, a headbox 10 is connected to receive a 
slurry of stock and the headbox is supported on a frame 12. The stock is 
deposited on a traveling forming surface, preferably in the form of a 
traveling fourdrinier wire 11. 
The looped forming wire passes over a breast roll 13 supported on swing 
arms 14 at the ends pivoted at 15. A position control rod 16 locates the 
breast roll to position the wire at the beginning of the forming run. At 
the offrunning side of the breast roll where the wire leaves the roll at 
the upper end is a doctor blade 17. 
The headbox is pivotally supported at 20 and a screw jack 18 raises or 
lowers the headbox to determine its location relative to the traveling 
forming wire 11. 
Stock is delivered to internal header chambers such as 19 within the 
headbox and the stock under pressure travels down to a slice chamber 
having an upper movable chamber wall 21. Within the slice chamber are 
trailing floating elements 24 which continue to divide the multistrata of 
forming stock. The stock flows forward in multiple layers to be emitted at 
a slice opening 22. The chamber wall 21 is pivoted at 23 and the slice 
opening, defined by slice lip 9 on the upper side, and by the downstream 
end of support surface 31 on the lower side, is controlled by a screw jack 
25 carried on the headbox. 
As the stock is delivered onto the traveling forming wire, it is dewatered 
in a downward direction when the wire reaches a suction box 33 and usual 
dewatering elements follow the suction box in a downstream direction. 
In accordance with the features of the invention, it is important that as 
the stock first engages the traveling dewatering wire 11, an excessive 
amount of fibers and fines are not immediately drained through the forming 
wire. It is also important that the random orientation of the fibers not 
be disturbed so that a CD/MD paper strength is not adversely affected. 
That is, the fibers should not become aligned either in a cross-machine or 
a machine direction to thereby weaken the paper in one direction. 
In accordance with the invention, a layer of water is generated onto the 
wire so that the stock is delivered onto the wire first interfacing with 
the layer of water. This eliminates the highly disruptive effect which can 
occur by the stock first engaging the porous traveling wire 11. 
To create this layer of water, a water slice 27 is provided extending 
across the machine supplied through a water supply conduit 26 in a manner 
so that a uniform thin layer of water is deposited onto the wire at 28 at 
substantially the same speed as the traveling forming wire 11. A lower 
ceramic wire guide 29 is positioned below the wire and an upper ceramic 
wire guide 30 is positioned above the lower guide to stabilize the wire. 
It is at the upstream location from these ceramic wire guides 29 and 30 
that the slice stream of water at 28 is applied to the wire. A supporting 
surface 31 extends beyond the lower wire guide 29 to retain the sheet of 
water on the wire so that the sheet of water is intact at the location 32. 
Thus, when the layers of stock are deposited onto the forming surface, 
they first interface with the layer of water to stabilize and to avoid the 
shock of the first engagement which normally occurs between the stock and 
the wire. As soon as the layer of stock on the layer of water reaches the 
suction box 33, the water disappears through the wire so that standard 
formation and dewatering can immediately result. This, however, provides 
for an initial relatively gentle laying of the fibers onto the wire so 
that the amount of fibers and fines, which can frequently be lost in the 
normal procedure for depositing the stock slurry from the slice onto the 
fourdrinier wire are not lost but are retained. Preferably, the layer of 
water is less thick than the thickness of the slurry. 
With this arrangement, by the stock first interfacing with the water layer, 
there is no shock which causes disruption of the fiber orientation. Also, 
the fiber orientation and retention of the multiple strata of stock is 
also retained. As the stock web continues to travel along on top of the 
forming wire, normal dewatering occurs with the formation of a web of 
paper having improved fiber orientation, and less loss of fibers on the 
lower surface. This, of course, insures a better CD basis weight control 
and less tendency of the layers to mix. If a stock is used with a single 
layer, the improved features are also utilized in that more uniform fiber 
orientation across the sheet length is attained. This makes it possible 
for easier control of the CD/MD tensile ratio. 
Thus, it will be seen that there has been provided an improved apparatus 
and method of deposit of a slurry of stock onto a forming surface which 
meet the objectives and advantages above set forth. The advantages are 
attained without reconstruction or replacement of existing equipment and 
the arrangement to generate a sheet or a layer or water again be added to 
existing equipment without substantially adversely affecting the rate of 
formation and the rate of dewatering.