Patent Grant
7648613
This is a national stage of application No. PCT/FI2005/000257, filed on Jun. 3, 2005. Priority is claimed on Application No. 20040761, filed in Finland on Jun. 3, 2004.
The invention relates to a method and an arrangement in a paper machine or the like close to a moving web to be dried and usually supported against a wire, to a sealing device, and to a paper machine, according to what is presented in the pre-ambles of the independent claims presented below. The invention relates particularly to a new manner to arrange sealings in the drying section of a paper machine.
In this text a paper machine or the like means particularly a paper machine or a board machine. A web means a paper web, which moves in the paper machine or a web of some other material, which is to be dried. A wire means an air permeable supporting surface, which in a paper machine or the like is used to support the web, the wire being for instance a net, a textile, a felt or a corresponding fabric.
In a paper machine, it is known to arrange regions of different pressures close to the moving web and wire in order to optimise their run. In order to maintain these pressure differences, different mechanical seals, among other things, have been used at the border between these regions of different pressures. The negative pressure regions and the seals are typically located on one side of the wire, and the web is located on the opposite side.
Mechanical seals will wear when they contact the moving wire. At the same time they can cause damage to the moving wire. Among other things, this makes it necessary to control the distance between a mechanical seal and the wire. It would be beneficiary to be able to change the distance between the seal and the wire during a run, for instance by remote control. It would be useful to have an accurate control of the distance, as the required changes of the pressure differences and air streams during the run are often very small and fast.
The seal is usually positioned against the wire, which in a normal running situation slightly moves toward the seal and away from it. Then a stationary or slowly moving seal can easily get in contact with the wire, which damages the wire and/or the seal. If the wire comes very close to the seal, then the wire and the web can be sucked fairly tightly against a suction box or the like having a negative pressure.
Different solutions have been proposed in order to provide a moving seal. However, there have been some difficulties in accurately controlling the distance between a mechanical seal and the wire. It is often difficult to obtain a seal, which can be accurately moved, but at the same time moved rapidly, when required. In addition, the seal should have a stable location so that it will not slide out of its position during use, against the will of the apparatus operator.
The published PCT application WO 2004/046460 presents a seal, where the distance between the seal and the wire is guided by controlling the pressure of the bellows-like space arranged behind the seal moving in relation to the wire. In some operation situations it is difficult to measure and control the pressures with the required accuracy, and this operation is also quite slow. Thus the adjustment of the seal's position will easily be inaccurate, unstable and slow.
The published PCT application WO 2003/040468 presents a blow box where the Coanda surfaces of the box are hinged in order to allow their movement.
In the prior art solutions the seal can be moved into a different position with the aid of external energy and based on external information, due to particular actions of the operative staff.
The object of the present invention is to reduce or even to eliminate the above mentioned problems occurring in prior art.
An object of the present invention is particularly to provide a new method in the drying section of a paper machine or the like for controlling the distance between the wire and the seals used close to the moving web and wire.
In order to realise, among other things, the above mentioned objects in a paper machine or the like, the method and arrangement according to the invention close to the moving web to be dried and usually supported against a wire, the sealing device, and the paper machine are characterised in what is presented in the characterising parts of the enclosed independent claims.
The embodiment examples and advantages mentioned in this text relate, when applicable, both to the method, the arrangement, the sealing device and the paper machine according to the invention, even if this is not always particularly mentioned.
According to a typical method and arrangement according to the invention in a paper machine or the like, at least two spaces at least mainly separated from each other are created close to the web to be dried and/or the wire typically supporting it, in which spaces different air pressures are typically maintained. Advantageously conduits known as well as possible are located between the spaces for transporting air in a controlled manner between the spaces. According to the invention, it is advantageous that the air streams supplied to these spaces and discharged from them are known and that they can be controlled as accurately as possible. Advantageously said spaces are thus relatively tight. The first and the second spaces are typically arranged close to the moving web or wire. At least one of these spaces at least partly borders on the moving web or wire. A seal is typically arranged between the first and second spaces, whereby the seal can move in relation to the web or the wire supporting it. Typically the distance of said seal from the web or the wire can be controlled. The second side of the seal is typically one of the walls of a possible third space. The pressures in said spaces and the air streams between these spaces are thus related to the distance of the seal from the web. According to the invention the seal's movement towards the web or away from the web is connected to the pressures in said spaces so that the pressure variations of said spaces directly move the seal. Thus in a normal operating situation no external control actions are required to move the seal according to the invention, but the pressures and air streams will automatically control the seal.
The invention can also be described as follows: A movable sealing element located between the first and the second spaces maintains the pressure difference prevailing over it as constant as possible, at the set point. The pressure difference created by the seal has an effect on means in the apparatus, for instance on the surfaces of the spaces, so that a feedback is created. This means that if the pressure difference deviates from the set point, then for instance the said means act on the seal with a correcting force depending on the magnitude of the deviation. The information about the set point can be input to the system for instance as the magnitude of a pressure or of an air stream. Said means and the manner in which the set point is determined are further explained below.
In the conditions referred to in the invention the measurement and control of the pressures has been traditionally difficult, inaccurate and time consuming. Now we have surprisingly found that the pressures present in the spaces can be controlled indirectly by measuring and controlling for instance the control air streams supplied to said spaces and discharged from them, and by arranging the sealing solution to be self-adjusting. When said control air streams in a solution according to the invention have been adjusted to be constant, then the pressures in the spaces and the distance of the seal from the web will find a state of equilibrium. By controlling the control air streams this state of equilibrium can thus be set as desired. The measurement and control of the volume air streams is accurate and rapid with the aid of conventional control and measurement devices for air streams. Also with current devices it is easy to have an almost continuous control of the air streams. According to the invention, when the control air streams have once been adjusted to the desired values, then in the normal operating situation the seal moves in relation to the web due to the pressures prevailing in said spaces and gaps and due to the effect of the air streams, without any particular control actions. A normal operating situation includes slight changes in the conditions, such as web flutter, wire swing or small variations in the control air streams, which will be automatically corrected as the seal can rapidly move due to the effect of the pressures and air streams. The invention provides a position control of the seal, which is more accurate and rapid than previously.
The invention is suitably used in a paper machine at least during threading, web spreading and during production with a normal full-width paper web.
A method according to the invention in a paper machine or the like close to a moving web to be dried and typically a wire arranged to support it comprises the following steps:
The invention makes it possible to retain a substantially constant pressure difference between the first and second spaces, even if any disturbances would occur in the process.
The arrangement according to the invention presented above operates in the following way: Assume that the first and second control air streams have been adjusted to be constant, so that a state of equilibrium has been achieved, whereby the second space has reached a suitable negative pressure compared to the first space and the seal is at a suitable distance from the web. The pressure of the first space can be assumed to be for instance the normal air pressure prevailing in the machine room of the paper mill. If now the web or the wire supporting it begins to move toward the seal, then the first gap is reduced and the air volume streaming through the first gap is reduced. Then the pressure in the second space is reduced, because a first control air stream with a substantially constant volume is continuously sucked out from the second space. This causes an increasing pressure difference between the second and third spaces, whereby more air begins to stream from the third space through the second gap into the second space. Then the pressure in the third space is reduced, because a second control air stream with a substantially constant volume is continuously supplied to the third space. As the pressure difference between the normal air pressure in the first space and the third space changes, the seal then moves toward the third space, i.e. away from the web and/or the wire. Then the first gap grows and more air begins to stream from the first space into the second space. Then the pressure in the second space increases and the state of equilibrium is re-established.
If the web initially moves away from the seal, then the arrangement according to the invention operates in a corresponding manner and re-establishes the state of equilibrium by reverse actions compared to those described above.
A resistive member can be connected to the seal, such as a spring, which can adjust the resistance of the seal's motion in different positions of its path. The seal can also be shaped so, or mounted in a certain position, for instance hinged, so that forces of different magnitudes are required to move the seal at different positions of its path.
Thus, the first and second control air streams will regulate the desired pressure difference between the first and second spaces as well as the desired distance between the seal and the wire or web. In one embodiment of the invention, the first control air stream and/or the second control air stream are kept mainly constant in a normal operating situation. When necessary, the control air streams can of course be adjusted also during a normal operating situation, for instance when it is desired to increase the negative pressure of the second space, or to move the seal closer to the wire or web. In practice it is so that changing the first control air stream has an influence mainly on the seal's distance from the wire or web in the state of equilibrium. Changing the second control air stream mainly affects the negative pressure in the second space compared to the first space in the state of equilibrium.
The arrangement according to the invention described above is very rapid. The automatic control actions are typically performed in fractions of a second. Even a rapid movement of the seal will not cause any substantial vibrations in the apparatus to which it is fastened, as the moving seal can be arranged to be very light and easily movable in the arrangement according to the invention.
In a normal operating situation there will be less contact between the moving wire and web and the seal due to the invention. A seal according to the invention tends the whole time to be at a constant distance from the wire and web. Thus, there is less wear of the seal, and damage of the wire or web will be reduced.
With the aid of the invention, the seal can be kept close to the wire and web, whereby the solution is economical. As the first gap is small, there flows very little discharged air to the second space. The volume of supplied air, i.e. the second control air stream, is also quite small. Thus, small air volumes are sufficient in an arrangement according to the invention. Then for instance the blowers used to discharge the air require only a low effect.
In a normal operating situation the invention operates automatically and fully mechanically, even without any electric control devices. The feedback control takes place locally via air streams, pressures and the seal's motion. No information needs to be used outside the arrangement according to the invention. In a sense, the control air streams according to the invention can transport all the data required for the control from the user to the seal and in the opposite direction. There is no need to transform the data required by the control from one energy form to another at the seal or in its vicinity.
With the aid of the invention, the second space can reach greater negative pressures than previously, as the risk of the wire or web to be sucked against the seal or the suction box where the second space with the negative pressure has been arranged is lower than in prior art solutions.
For an accurate operation of the invention, it is usually advantageous that the supplied second control air stream is kept as constant as possible. In one embodiment of the invention, the second control air stream is thus taken from a compressed air network, advantageously through a strongly acting throttle, whereby a reasonably constant air stream can be obtained.
If the invention comprises several shorter arrangements according to the invention located side by side in the machine's cross direction, it is easy to accurately adjust the negative pressure level and sealing also in the machine's cross direction. This is advantageous particularly in wide paper machines, because the wire tends to bend in the machine's cross direction. One such arrangement could then have a length of for instance about one metre in the machine's cross direction.
For the first control air stream it is possible to realise a sufficiently even volume flow for instance in the following manner. A stronger negative pressure is kept in the suction system than in the second space according to the invention, and the air stream from the second space is guided through a throttle to the suction system. Then the throttle's share of the total pressure difference determines the magnitude of the variation in the air stream during a regulating situation. The variation of the volume flow in the first control air stream mainly acts only on the distance between the seal and the wire, but not on the magnitude of the negative pressure formed in the second space. A small variation of the distance between the seal and the wire will not usually have any practical influence on the operation of the apparatus.
When both the first and second control air streams are measured and controlled, it is possible to accurately and rapidly adjust both the distance of the seal from the moving wire or web and the pressure difference between the first and second spaces.
In an embodiment of the invention, the seal comprises a movable edge, which moves at a distance from one wall of the third space as the seal moves in relation to the third space, so that a second gap is formed between said edge and the wall of the third space. Then air can pass through this gap from the third space to the second space. When the second gap is formed between the moving seal and the stationary wall of the third space, there is no need to make any separate opening in the wall of the third space for the gap.
In an embodiment of the invention, the seal is hinged at its upper edge, whereby its lower edge moves at a distance from the wall of the third space when the seal moves, so that a second gap is formed between the lower edge of the seal and the wall of said third space. As the seal is hinged at its upper edge, it can be easily arranged so that its movement is easily controlled. It can be easily arranged to have a stable position, so that in the case of a possible operating disturbance, for instance if all control air pressures are stopped, then the seal turns around its hinge, away from the web or wire.
In an embodiment of the invention, the seal is arranged so that in a normal operating situation the distance of the seal's lower edge from the wall of the third space remains substantially constant. In other words, the size of the second gap remains substantially the same. Then it is easy to control the apparatus, as the air volume flowing from the second gap is very predictable.
In an embodiment of the invention, the seal is hinged in relation to the third space, so that the seal can turn and so that its distance from the wire, or the size of the first gap, will change as a function of the turning angle when the seal turns around its hinge. This simplifies and facilitates the controllability of the seal.
With the aid of an embodiment of this invention, the negative pressure in the negative pressure regions arranged close to the paper machine's moving web and wire can be created without using the prior art ejector principle. Then an arrangement according to the invention does not require air blows to be discharged through the gap between the web or wire and the seal, from the space where the negative pressure has to be created. When the machine is running the arrangement according to the invention acts as a rapid constant pressure regulator for the negative pressure regions. In a normal operating situation, the seal does not necessarily have any stationary position, but the seal can be arranged to be constantly moving. The arrangement according to the invention can be considered as a regulator, which controls the negative pressure to be maintained and the position of the seal in relation to the wire or web. The regulator is supplied with the set point value for the negative pressure to be maintained and the set point value for the seal's position in the form of separate control air streams. The magnitude of the control air stream can be considered to be the set point. The task of the control air streams is to regulate the seal's position in real time, so that the pressure remains at its set point. The control air stream also supplies the operating energy for the control function.
The invention provides a continuous, automatic and rapid control function including feedback.
The invention is described below in more detail with reference to the enclosed schematic drawing, in which
The upper part 13 of the seal's 5 frame part is hinged by a swinging hinge 14 to the upper wall 15 of the third space. When the seal turns around the hinge 14 the size of the gap 16 between the wire 1 and the sealing part 7 varies as a function of the seal's turning angle. The size of this first gap 16 determines the air volume passing between the first space 3 and the second space 4, and thus the pressure difference prevailing between them. The lower wall 17 of the third space mainly separates the third space 8 and the second space 4 from each other. An edge 18 is formed in that part of the lower edge of the seal 5, which is toward the third space. The seal 5 and the wall 17 are shaped so that in a normal operating situation the gap between the edge 18 and the wall 17 retains a constant size, regardless of the distance between the seal 5 and the wire 1. The arrow 19 represents the distance of the edge 18 from the hinge 14, and the arrow 20 represents the distance of the wall 17 from the hinge 14. The size of the second gap 21 formed between the edge 18 and the wall 17 equals the difference between the lengths of the arrows 20 and 19. Air can flow through the second gap 21 from the third space 8 to the second space 4. Mechanical limiters (not shown) can limit the motion of the seal 5. The maximum motion path of the seal can be for instance 10, 20, 30, 40 or 50 mm.
Assume that the pressure loss S1 caused by the first gap 16 and the pressure loss S2 caused by the second gap 21 are constant. Assume further that the volume flows V1 and V2 are constant. Then it is easy to show by simple deduction that the seal 5 will find a stable state of equilibrium at a certain distance from the web, whereby this distance is greater than zero, and whereby this distance depends on the volume flows V1 and V2 and on the resistance terms S1 and S2. The pressures prevailing in the different spaces in connection with the state of equilibrium can be calculated when the resistance terms S1 and S2 are known. Thus, a structure like that described above can control, in a relatively continuous and accurate manner, both the size of the first gap 16 and the pressure in the space 4 with the negative pressure, only by regulating the control air streams V1 and V2.
The calculations above are relatively easy to make for each solution. The resistance terms S1 and S2 can be estimated relatively accurately, and the estimations can be easily improved on the basis of measurement results. The results are easily programmed into required control logics.
The adjustment of the control air streams presented above is usually performed only occasionally, for instance when the paper quality is changed, or when some other running parameters of the paper machine are changed. When the set points of the negative pressure and the seal's position are once adjusted to the required value, then there is no need to adjust them in a normal operating situation. The arrangement according to the invention is self-adjusting.
The figures show only advantageous embodiment examples according to the invention. The figures do not specifically show facts that are secondary regarding the main idea of the invention, facts known as such, or facts, which as such are obvious to a person skilled in the art, such as power sources or any supporting structures possibly required by the invention, or other parts of a paper machine. To a person skilled in the art it is obvious that the invention is not limited to the examples presented above, but that the invention may vary within the scope of the claims presented below. For instance, the means for moving a seal can be realised in many different ways. The manner, in which the set points are set with the aid of control air streams supplied to and discharged from the arrangement, is only one example of how the self-adjusting sealing arrangement according to the invention can be realised. The dependent claims present some possible embodiments of the invention, and as such they should not be considered to limit the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20040761 | Jun 2004 | FI | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FI2005/000257 | 6/3/2005 | WO | 00 | 10/16/2006 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2005/118951 | 12/15/2005 | WO | A |
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|---|---|---|---|
| 5230168 | Heinzmann et al. | Jul 1993 | A |
| 5341579 | Schiel et al. | Aug 1994 | A |
| 6192597 | Kahl et al. | Feb 2001 | B1 |
| 6247247 | Yömaa et al. | Jun 2001 | B1 |
| 6848195 | Leimu | Feb 2005 | B2 |
| 20030034139 | Kahl et al. | Feb 2003 | A1 |
| 20060070258 | Leimu et al. | Apr 2006 | A1 |
| Number | Date | Country |
|---|---|---|
| 925656 | Dec 1992 | FI |
| 102774 | Oct 1998 | FI |
| 111280 | May 2003 | FI |
| WO 03040468 | May 2003 | WO |
| WO 2004046460 | Jun 2004 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20080060776 A1 | Mar 2008 | US |
