Drying and gas or vapor contact with solids – Apparatus – Rotary drums or receptacles
Reexamination Certificate
2002-01-17
2003-06-10
Lazarus, Ira S. (Department: 3749)
Drying and gas or vapor contact with solids
Apparatus
Rotary drums or receptacles
C034S115000, C034S116000, C034S123000
Reexamination Certificate
active
06574884
ABSTRACT:
The present invention relates to a blowing device according to the preamble of the claim 1 presented below, in a paper machine or the like, such as in a paperboard or a finishing machine or in another web treatment machine.
The invention is particularly intended to be applied in the drying sections of paper, paperboard or finishing machines or the like. The intention is then to be able to apply the invention in drying sections provided with a single wire or a twin wire run, where a wire pocket is formed between two drying cylinders and a roll below them which redirects the wire travel. An intention is also to be able to apply the invention in drying sections provided with a so called inverted run, i.e. in such drying sections where the roll turning the wire travel is arranged above the drying cylinders, or in solutions where drying cylinders are arranged above each other on two or more levels. Further the intention is to be able to apply the invention in drying sections provided with combinations of the above mentioned drying sections. The intention is further to be able to apply the invention in suitable respects in other parts of the above mentioned machines.
Previously it has been noted that the need for a negative pressure in the wire pocket is high particularly at the opening gap between the drying cylinder and the wire, so that it is possible to ensure that the wire comes off from the surface of the drying cylinder. However, an increase of the negative pressure in the whole pocket to the required negative pressure level causes certain disadvantages. Large amounts of energy must be used when the whole pocket space must be brought to the same high negative pressure level. Large air leaks may make it impossible to reach a sufficiently high negative pressure and to maintain it. So far it has generally been possible to have a sufficient increase in the negative pressure with the aid of blow boxes.
The object of the invention is typically a blowing device in a drying section which is provided with a single wire run where the web is transported between the wire and the drying cylinder over the drying cylinder. The blowing device comprises a blow box or a blow box combination extending over the whole width of the web, and the device is intended to ensure that the wire comes off from the drying cylinder in the opening nip of the wire in order to keep the web in a controlled way attached to the wire over a desired distance, even after the opening nip.
The blowing device is typically combined with means generating blowing air and arranged on that side of the wire which is away from the cylinder, mainly at the opening nip between the wire and the cylinder so that it extends, from the actual point where the wire and cylinder are disengaged, a short distance forward in the travel direction of the web. The blowing device is typically provided with two nozzles, such as gap nozzles, ejecting nozzles or the like, arranged cross-wise regarding the travel direction of the web and close to wire. The first nozzle is arranged mainly at the opening nip between the wire and the cylinder, however preferably before the actual point where the wire is disengaged from the cylinder. The second nozzle is arranged, in the travel direction of the web, at a distance from the first nozzle and the opening nip.
The nozzles are arranged in the blowing device to blow air jets away from the gap between the blowing device and the wire, so that the air jets discharged from the nozzles prevent air from entering the gap and/or suck with their ejection effect air away from the gap between the blowing device and the wire, and thus negative pressure required to support the web is maintained in the gap.
The travel of the web in the opening nip between the drying cylinder and the wire will be the more difficult to control the more the speeds of the paper machine will increase, because when the speeds increase the web will all the more tend to follow the drying cylinder. A speed increase of a few hundred meters may require a doubled negative pressure level, e.g. from a negative pressure of 500 Pa to a negative pressure of 1000 Pa.
The dry solids content of the web has also an effect on how the web comes off from the cylinder. The higher moisture the web has the more difficult it is to disengage it from the drying cylinder and the more difficult it is to achieve a good runability. A dry web will so to speak burn to the surface of the hot drying cylinder, the more easily the higher the temperature of the cylinder is. Therefore the detachment of the web from the cylinder and supporting it on the wire requires higher and higher negative pressures when the production is made more effective and the speeds are increased.
For the time being it has generally been possible to obtain a sufficiently increased negative pressure with the blow boxes. However, when the speeds increase further we get into a situation where it is cumbersome and expensive to further increase the negative pressure.
The need for the negative pressure is different in different parts of the wire pocket formed between the drying cylinders. The highest negative pressure is required at the opening nip between the cylinder and the wire for disengagement the web from the cylinder and for attaching it to the wire. In other parts of the pocket a lower negative pressure would generally be sufficient. However, with present blow box techniques we have to maintain the same negative pressure in the pockets between the drying cylinders, in the whole region over which the effect of the blow boxes extends. Large air leaks to the pocket with the negative pressure cause, particularly in fast machines, difficulties in reaching and maintaining such a particularly high negative pressure which is required at the opening nip mentioned above. Large amounts of energy must be used when the whole large pocket space must be brought to the same high negative pressure level.
Further, increasing the whole negative pressure of the pocket to a high negative pressure level may cause disadvantages. A high negative pressure may on long wire runs bend the wire, which then can come to touch surfaces of the blow box or other inflexible surfaces, and thus cause wire damages and impair the runability. A too high negative pressure in the whole pocket region can also have an effect on the web itself, and it may e.g. prevent the shrinking of the web in the cross direction too much, whereby the web may even split.
An aim is to make the travel of the web in the opening gap between the drying cylinder and the wire more secure by increasing the tension of the paper web. Tension means that a a speed difference is used to create tension in the web. However, an increased tension is not always possible, because a too high tension would decrease the tensile strength of the pare, impair the paper quality, often impair the runability and create more web breaks.
The respective negative pressure required at the paper machine in the opening nip between the drying cylinder and the web, and also in other parts of the pocket space, depends on many factors, both on production parameters and on the paper quality being produced. The requirements on the negative pressure are affected i.a. by the machine speed, the dry solid contents of the paper, the paper profile after the press, the paper quality, the paper grammage, tension differences between the press and the drying section, generally the chemistry of the wet end, the operation of the press, and the geometry and structure of the wet end. It should be possible to control the negative pressure when any of these parameters changes. It should be possible to control the negative pressure separately in the opening nip and in other regions with negative pressure.
Previously it has also been proposed to arrange a special suction box at the opening gap between the cylinder and the wire to create a higher negative pressure. The American patent publication U.S. Pat. No. 5,341,579 proposes to arrange a particular small suction box at the opening gap, with which a certain negativ
Lathrop & Clark LLP
Lazarus Ira S.
Metso Paper Inc.
O'Malley Kathryn S.
LandOfFree
Blowing apparatus in a paper machine or the like does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Blowing apparatus in a paper machine or the like, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Blowing apparatus in a paper machine or the like will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3088498