Method and apparatus for the lateral sealing of a drainage wedge in a twin-wire paper machine

Apparatus and method for laterally sealing a drainage gap of a twin-wire paper machine. This lateral sealing has contact only with the lower wire. Between the upper wire and the lateral sealing, sealing is preferably effected by sealing water. Since this lateral sealing is elastic, it can adapt itself to the movements of the lower wire.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for the lateral 
sealing of a drainage wedge in the wire end of a twin-wire paper or board 
machine. 
Twin-wire paper or board machines have become known in large number and 
great variety. The two main types are the so-called gap former and the 
hybrid former. 
In the gap former, a wedge-shaped inlet gap for the injecting of a 
full-width jet of pulp slurry coming from the headbox is formed between 
two wires. The wires are contacted practically simultaneously by the 
slurry. The start of the inlet gap is located at the breast rolls which 
deflect the wires. The center lines of these rolls lie--seen in the 
direction of travel of the wire--more or less opposite each other. 
In the hybrid former, the jet of pulp is applied first to the lower one of 
the two wires and carried along by it a certain distance within which the 
pulp slurry is subjected to a preliminary dewatering and only then is the 
other wire brought against the partially dewatered pulp slurry so that the 
paper web which is now produced is surrounded in sandwich-like manner. The 
preliminary dewatering path can in this case be relatively short so that 
the transition between the gap former and the hybrid former is a fluid 
one. 
A problem area of such formers is the initial region of the dewatering 
path. In this connection, namely, the pulp slurry can emerge between the 
edges of the two wires unless other measures are taken. This emergence of 
the slurry leads to the loss of fiber material upon the formation of the 
sheet or between the wires and impairs, among other things, the thickness 
of the sheets and the orientation of the fibers in the region of the edge 
of the sheet, so that then relatively wide marginal strips of the paper 
are of poorer quality than the rest of the paper. Lateral seals consisting 
of stationary limiting surfaces have the disadvantage that substantial 
wear will take place between them and the two wires. 
SUMMARY OF THE INVENTION 
An object of the present invention is to develop a lateral sealing of the 
wedge gap between two wires of a twin-wire paper machine, particularly for 
use in the manufacture of heavier grades of paper--and therefore with 
relatively thick layers of pulp slurry--in such a manner that the 
emergence of pulp between the two wires is minimized while the amount of 
wear is still tolerable. 
The above and other objects are achieved by a method for laterally sealing 
a substantially wedge-shaped gap in a common drainage path between two 
wires of a twin-wire paper machine, the two wires for conveying a pulp 
slurry therebetween, the method comprising providing a sealing spacer 
between the two wires at lateral edges of the wires and fixed in the 
direction of travel of the pulp slurry when the paper machine is in 
operation producing paper; providing a gap between the sealing spacer and 
an upper one of the two wires; and sealing the gap with a sealing liquid. 
The objects of the invention are furthermore achieved by an apparatus for 
laterally sealing a substantially wedge-shaped gap in a common drainage 
path between two wires of a twin-wire paper machine, the two wires for 
conveying a pulp slurry therebetween, the apparatus comprising a sealing 
spacer disposed between the two wires at lateral edges of the two wires, 
the sealing spacer being fixed in the direction of travel of the pulp 
slurry when the paper machine is in operation producing paper, a gap being 
provided between the sealing spacer and an upper one of the two wires and 
a fluid connection for providing sealing fluid into the gap between the 
upper wire and the spacer. 
In the preferred embodiment of the invention, the sealing spacer lies on 
the lower wire. The upper wire rests under tension against upper 
stationary dewatering ledges. The sealing spacer is at a defined distance 
from these upper dewatering ledges and from spacers adjacent the upper 
dewatering ledges. This defined distance is greater than the thickness of 
the upper wire. The gap formed between the upper wire and the sealing 
spacer is acted on, in operation, preferably by sealing water so that the 
fiber slurry cannot flow into this gap. The contact surface between 
sealing spacer and lower wire is lubricated hydrodynamically with water 
present in the meshes of the wire. 
Since at least one lower dewatering ledge can be pressed resiliently by 
pressure hose against the lower wire, thus carrying out a vertical stroke, 
and the wire being also moved along, it is necessary for the sealing 
spacer to be flexible and to rest closely against the lower wire. 
In typical paper machines, since the wires may move out laterally during 
operation of the paper machine, the wires might, in case of a rigid 
lateral outer wall, experience a hard surface contacting against it and 
thus be subjected to wear. Conversely, upon the moving away of the wire, 
the sealing action would be lost. This is not possible in the case of the 
invention. Due to the formation of a sealing gap between the top of the 
sealing spacer and the surface of the upper wire facing it, there can be 
no striking against this edge of the web. Since the sealing spacer rests 
on the lower web, there can be no striking against the web there either. 
The sealing spacer is hydrodynamically lubricated by lying on the lower 
wire. 
The elasticity of the sealing spacer vertical to its longitudinal length 
can be achieved in two different manners. on the one hand, the use of a 
soft material assures the flexibility of the sealing spacer. On the other 
hand, the development of the sealing spacer from individual plates of even 
a rigid material permits this flexibility. The sealing spacer--either 
developed in one piece or of individual plates--then need merely be fixed 
at its thicker end during operation of the paper machine in order to avoid 
its being carried along in the direction of travel of the wire. 
Depending on the production circumstances, the two wires can be brought 
into a defined distance from each other. This means, in other words, that 
the dewatering gap varies. In order that the sealing spacer can be used 
for the different gap adjustments, it must be displaceable in and opposite 
the direction of travel of the web. 
Other features and advantages of the present invention will become apparent 
from the following description of the invention which refers to the 
accompanying drawings.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
With reference now to the drawings, FIG. 1 shows a transverse cross-section 
of a portion of a paper machine in the region of the edge of a twin-wire 
former according to the invention. The sealing spacer 1 shown consists of 
stacked plates 2 extending in the direction of travel of the wire, either 
into or out of the paper. In this case, the lowest plate is the longest. 
The ones arranged above it are increasingly shorter. The plates 2 are held 
together at one end in the vicinity of the headbox 12 (see FIG. 2) by an 
attachment, not shown. The spacer 1 is longitudinally movable, as shown by 
arrow 15, (FIG. 2) to take into account manufacturing circumstances. 
Due to the dewatering pressure between the wires S1, S2, the sealing spacer 
1 lies against the side supporting wall 5. The lower wire S1 lies on the 
lower dewatering ledges 3. The lower dewatering ledges 3 are pressed by a 
pressure hose 4 against the wire S1. The upper wire S2 lies against the 
upper stationary dewatering ledges 6. The space adjacent the upper 
dewatering ledges 6 is filled with spacers 8 in the region of the edge. 
These spacers 8 can be so-called deckle adjusting devices. The edge of the 
sealing spacer 1 facing the pulp slurry 17 is substantially flush with the 
inner edge of the spacer 8. Via the sealing-water connection 10 and a 
prechamber 9, sealing water flows through the gap 11 between the upper 
wire S2 and the sealing spacer 1 in the direction of the pulp slurry 17. 
The amount of sealing water is so determined that there is no penetration 
of particles of fiber into the gap 11. 
In FIG. 2, the upper wire S2 is conducted over the upper breast roll 14 to 
the pulp slurry 17. The drainage elements 3, 6 are so arranged that a long 
drainage gap is produced between the wires S1, S2. The former shown is a 
so-called hybrid former since the pulp slurry 17 coming from the headbox 
12 is deposited onto the lower wire S1 without the upper wire S2 also 
initially having contact with the pulp slurry 17. 
If the dimension A shown between the breast rolls 13, 14 were practically 
zero, then the pulp slurry 17 would come into contact with the wires S1, 
S2 simultaneously and the former would be a gap former. From the 
preceding, it is clear that the sealing spacer of the invention can be 
used for both types of former. If the distance between the wires S1, S2 
changes as a result of the production--for instance, upon change of the 
type of paper--there could either result a jamming of the sealing spacer 
or too large a gap between upper wire S1 and sealing spacer 1. For this 
reason, the sealing spacer 1 has a displacement path 15. Because the 
spacer 1 is wedge-shaped, moving it longitudinally will vary the size of 
the sealing gap 11. 
FIG. 3 shows further variants of the sealing of a drainage gap in a 
twin-wire former. In this case, the lower wire S1 is made water-impervious 
in the region of the edge R by a plastic, by the pasting-on of a foil, or 
by similar measures. The lower wire S1 is so guided by a wire guide that 
the water-pervious part W of the wire travels substantially symmetrically 
between the inner edges of the spacer 8 which face the slurry 17. The 
width of the water-pervious region W of the lower wire S1 corresponds in 
this connection substantially to the dimension F, which corresponds to the 
distance apart of the inner edges of the spacer 8 from the operator and 
drive sides. The dimension may, e.g., be up to 25 mm, 5 to 25 mm, smaller 
than the dimension F. 
A further development is the additional lubrication of the lower wire S1. 
With regard to this, two variants are shown in FIG. 3. In the one variant, 
the wire S1 is lubricated on its surface of contact with the sealing 
spacer 3. Via openings L in the sealing spacer 1, sealing liquid 9 comes 
against this contact surface. In the second variant, the contact surface 
of the wire S1 with the lower ledges 3 is lubricated via at least one, for 
instance, flat-jet nozzle D. Of course, these two possibilities of 
lubrication can also be applied simultaneously. 
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. 
Therefore, the present invention should be limited not by the specific 
disclosure herein, but only by the appended claims.