JPH0160113B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is characterized in that hydro-oil made of sintered ceramic oxide is applied over the entire width of the paper machine to the underside of the screen which is curved and guided in an arc in the wet area. It relates to a type of paper machine arranged in the form of individual segments extending abutting one another.

Modern paper machines are extremely sophisticated machines,
The speed of plow nets ranges from 800 to 1000 m/min or more. In order to significantly reduce the severe screen wear and lining wear that occurs at such speeds, known paper machines generally use a large number of ceramic elements (hydrofoil) for the dewatering of the stock and the support of the fourdrinier. Equipped with The screen slides over the top surface of the ceramic element at a high altitude. In this case the water passes through the plow net. The stock stock solution in the form of a fiber suspension that flows out of the flow box of the paper machine and onto the screen is dehydrated very quickly, so that after a relatively short period of time the paper stock stock solution is already in continuous form. It becomes dehydrated to the extent that it can be removed from the plow net as a wet paper fish. The plow net itself is under tension, which creates a certain friction between the plow screen and the hydrophilic oil. This friction is significantly reduced by the passing water, but on the other hand (double sieve system in which an endless second sieve is guided above the stock solution, circulating at a constant speed to aid dewatering). In the case of a paper machine), it is strengthened by the strong pressing force generated by the second screen. In this type of paper machine, dewatering takes place on both sides, i.e. upwardly through the upper screen and also downwardly through the lower screen.

When the paper machine operates at a high speed, it is necessary to tension the screen tightly, and the high tension of the screen causes various problems when starting and stopping the paper machine. When the paper machine is started, there is still not enough water that can pass through the screen or that is squeezed through the screen, and when the paper machine is stopped, there is no longer enough water, so that a correspondingly identical situation occurs.
In other words, the friction between the plow net and the hydro-oil lining increases both when starting and when stopping.
In short, a type of dry operation occurs in which the temperature is raised to over 100°C. The strip-shaped hydro-oil that allows the lower plow net to run horizontally in contact with the upper surface is relatively narrow, with a width of 20 to 80 mm when viewed in the direction of machine operation.
If it has a width of mm and only a few mm of this width are in direct contact with the paper machine screen, friction will not have such a negative effect. That is,
Since the frictional force is small, the Hydrofoil acts as a suction device and sucks any moisture that is still present downward, which means that it can be used between the paper machine screen and the Hydrofoil for a short period of time to varying degrees. This is because lubrication is achieved without any lubrication. The same applies to wet suction devices and suction boxes. However, supporting elements which serve only for guiding and supporting the plow net and which have a closed, fairly large surface seen in the direction of travel of the plow net, and which therefore do not carry out water removal through the gaps, do not require such water lubrication. Not affected. This applies in particular to forming shoes for double screen paper machines. However, in this case, the exact opposite phenomenon occurs. This is because the screen is curved and, due to this radius of curvature, any water that is still present is thrown away upwards under centrifugal action. Since the forming shoe can have a length of more than 1.5 m in the direction of travel of the plow net, in other words many times as long as, for example, the hydrofoil, extremely high temperatures occur in this case. Although ceramic itself can withstand much higher temperatures than those encountered here, there are two additional factors that present significant problems. Firstly, ceramic has a completely different coefficient of expansion than the support material disposed below it, that is, steel. Second, ceramics are sensitive to heat shock. This sensitivity becomes even greater as the size of the ceramic component increases. When starting up the paper machine, the screen must first start running before the stock stock solution is supplied, so dry friction inevitably occurs first, heating the ceramic support element and the dewatering element, and then , an impulsive cooling of the element is effected by enveloping it with water. This allows especially in the forming show range.
Microcracks, even cracks visible to the naked eye, form in the ceramic lining. This is because the forming show is the biggest supporting element.

In short, the object of the invention is to provide the possibility of reducing friction and satisfactorily eliminating thermal shocks, especially when using plastic screen screens.

The invention solves this problem by disposing the hydro-oil made of sintered ceramic oxide on the underside of the screen in the form of individual segments that extend abutting one another over the entire width of the paper machine. In paper machines of this type, in particular those with an arc-shaped guide guide in the wet part, several segments are arranged one after the other in the running direction of the screen. At the butt point between segments arranged one after the other and having a maximum vertical dimension of up to 700 mm per segment,
A gap for supplying cooling water to the screen extends over the entire width of the paper machine, and below the gap a spray tube of a length approximately equal to the width of the paper machine is arranged. be. By dividing the forming shoe into at least two segments and by limiting the longitudinal dimension of the segments in the direction of mesh running to a maximum of 700 mm, the sensitivity of the ceramic to thermal stresses itself is reduced. Ru. Furthermore, cooling of the segments is made possible by the provision of gaps between the individual segments, seen in the direction of travel of the net. This cooling effect is obtained by the cooling water sprayed through the gap, and besides this cooling, the lubrication of the screen is also achieved at the same time, as if after start-up the water from the stock stock passes through the screen. Conditions that occur automatically during the start-up phase also occur during the start-up phase.

In a preferred embodiment of the invention, the segment is connected to the support beam in the region of the gap and is sealed to the support beam. This seal creates a hollow space between the support beam and the segment in the area of the gap, which is directly supplied with pressurized water so that the water can flow upward through the gap over the entire width of the paper machine. It can inevitably erupt towards.

In a preferred embodiment of the invention, the spray tube has a plurality of holes or, more preferably, a plurality of nozzles, the nozzles being flat jet nozzles (slit-orifice nozzles). Advantageously, it is configured as The arrangement of the spray tubes allows for more precise metering of the feed water. At the same time, it is also possible to select relatively large gap widths, which do not have a negative effect on the formation. in this case,
The flat jet flow nozzle installed on the spray pipe is
The jet water stream is installed so that it can be distributed over the entire width of the plow net without any corners.

The water pressure of the water sprayed against the plow net is 1 to 10
Advantageously, it is a crowbar. Water volume is gap length
It is 5 to 25/min per 1m.

In a preferred embodiment of the invention, the cooling water is controlled via a cooling regulator, which comprises at least a detector, an actual value/setpoint converter, a transmitter, a valve, a pump and a supply line. There is. This ensures automatic control of the entire paper machine. In other words, the detector configured as a temperature sensor or as a moisture detector detects the aforementioned effects if the water film on the screen guide mechanism has decreased significantly or if the temperature of the screen guide mechanism has already increased. Transmits the signal to the actual value-setpoint converter. Via the transducer and transmitter, a valve is then opened so that the pump can pump water through the supply conduit to the danger area and inject it through the gap into the screen.

Next, embodiments of the present invention will be explained in detail with reference to the drawings. The lower screen 1 passes via a breast roll 7 through a screen table 8 and a subsequent hydro-oil (supporting and dewatering strip) 9. In this screen region, the lower screen 1 extends essentially directly and has a gentle upward slope. The lower screen then reaches an arcuate screen area 29 which is supported by a forming shoe 10, which is followed by an area of suction boxes 11. From this suction box range, the lower plow net 1 has a plurality of overhanging/guide rolls 30, 31.
is guided through the breast roll 7 or back to the flow box 39. The upper plow net 12 is overhanging and
It is held only by the guide and deflection roll 32 and rests in its convexly curved area on the corresponding arc-shaped screen area 29 of the lower screen 1, ie the upper screen 12 is supported by the forming screen. It joins the lower plow net 1 a little before the U 10, rests on the lower plow net, and runs at the same speed as the lower plow net until it reaches the rear of the suction box 11. The forming shoe 10 consists of a large number of segments 3 arranged parallel to each other and one after the other, these segments having a width of 650 mm for a width of 300 mm.
It has a length of mm. The segments 3 are made of sintered aluminum oxide and have a flat bottom surface 13, which has dovetail-shaped recesses 1 on both narrow sides extending transversely at right angles to the net running direction.
It is moving to 4. The top surface 15 of the segment 3 is curved into an arc, and this arc is 500~
It has a radius of curvature of 5000mm. The degree of curvature then depends on the particular purpose of use of the paper machine and, to a large extent, also determines the dewatering efficiency. The dehydration effect is indicated by arrow 35 in FIG.

The segment 3 includes a plurality of support beams 5, 5',
5", which support beam rests over the entire width of the paper machine on a strut 16, which is connected to the machine frame via a collecting casing 33. Segment 3 The fixation is carried out on one side by means of a clamping jaw 17 which is screwed onto the support beam 5 and which engages an inclined surface of the recess 14 of the segment 3 and which is provided on the opposite side of the same segment. The segment is pressed into the recess 18 of the supporting beam 5' which is located in the center of the support beam 5'. Between the narrow sides 19 of adjacent segments 3 there is a gap 4 which communicates with the hollow chamber 20. Chamber 20 is slope 2 of segment 3
1, a support beam 5, 5', 5'' and optionally a metal base plate 22, which may extend over the entire upper surface of the strut 16. As shown in FIG. 3, it is sealed by a cover piece 23 via a rubber intermediate layer 24. Between the segment 3 and the supporting beam 5, 5', 5'' or the clamping jaw 17 there is in each case a sealing strip. Since the supply conduit 25 is interposed, the supply conduit 26
The pressurized water as cooling medium supplied into the spray pipe 6 via the nozzles 7, 7' can only exit through the gap 4.

Another embodiment of the invention is shown in FIG.
In this case, the gap 4' is kept wider than the gap 4 shown in FIGS. 'have. Seen from the side of the paper machine, the nozzle 27' tapers upwards and widens significantly in the transverse direction perpendicular to the working direction of the paper machine, ie in the direction of the extension of the gap 4, so that the gap 4' Pressure water is supplied to the entire area by multiple nozzle orifices. The part shown in FIG. 4 is precisely the central area of the forming show 10. The support beam 5'' located in the central area is constructed as a dovetail beam, on which segments 3 are crimped from both sides. Above the segment 3, a lower screen 1 is shown. On the upper surface of the lower screen, a paper layer 28 covered by the upper screen 12 and already partially dewatered is located and guided in the direction of the arrow 34.

In particular, as shown in FIG. 1, devices are provided for regulating lubrication or cooling and thus preventing dry operation. The device comprises one or more detectors 4
0, the detector is responsive to moisture and/or temperature and is located at the outlet of the dehydrator.

Line 41 transmits the actual state to an actual value/setpoint value converter and transmitter 42 , which transmits the adjustment variable to the valve or valves 43 . Pressurized water is then supplied to the spray pipe 6 from the tank 45 via the pump 44 and the supply conduit 26 .

[Brief explanation of drawings]

Figure 1 is a principle diagram of a double screen high-speed paper machine with a screen running path curved in an arc shape;
The figure shows the curved plow net running surface and the first part of the cooling device.
FIG. 3 is a detailed perspective view of the embodiment shown in FIG. 2, and FIG. 4 is a perspective view of the second embodiment of the cooling device. be. 1... Lower plow net, 3... Segment, 4,
4'...Gap, 5,5',5''...Support beam,
6...Spray tube, 7...Breast roll, 8...
...Plow net table, 9...Hydrof oil, 1
0...Forming show, 11...Suction box, 12...Top net, 13...Bottom surface,
14... Recessed portion, 15... Top surface, 16... Strut material,
17... Clamp jaw, 18... Recessed part, 19
...Narrow side, 20...Hollow chamber, 21...Slope, 2
2...Metal bottom plate, 23...Cover piece, 24...Rubber intermediate layer, 25...Seal strip, 26...
Supply conduit, 27, 27'... Nozzle, 28... Paper layer, 29... Arc-shaped screen range, 30, 31...
Overhang/guide roll, 32... Overhang/guide/direction change roll, 33... Collection casing, 34
... Running direction of the paper layer, 35 ... Arrow indicating dehydration action, 39 ... Flow box, 40 ... Detector,
41... conductor, 42... actual value-set value converter and transmitter, 43... valve, 44... pump, 45...
…tank.

Claims (1)

[Claims] 1. On the underside of the screen 1, a hydro-oil made of sintered oxidized ceramic is arranged in the form of individual segments 3 which extend adjacent to each other over the entire paper machine. In a paper machine of this type, a number of segments 3 are arranged one after the other when viewed in the running direction of the screen, have a maximum vertical dimension of 700 mm per segment, and are arranged one after the other. At the abutment point between the segments 3, which have been cut, a gap 4 for supplying cooling water to the screen extends over the entire width of the paper machine, and below this gap a gap 4 having a length approximately equal to the width of the paper machine A paper machine characterized in that a spray pipe 6 is arranged. 2. Paper machine according to claim 1, wherein the segment 3 is connected to the support beam 5 in the region of the gap 4 and is sealed to the support beam 5. 3. A cooling control device according to claim 1 or 2, comprising at least a detector 40, an actual value-setpoint value converter and a transmitter 42, a valve 43, a pump 44 and a supply conduit 26. paper machine.