Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
2001-08-10
2003-09-09
Bennett, Henry (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S452000, C034S500000
Reexamination Certificate
active
06615511
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 100 42 243.8, filed on Aug. 28, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for monitoring web breaks in a machine for producing a material web, in particular a paper or cardboard web. It further relates to a machine for producing a material web, in particular a paper or cardboard web, in which such a monitoring of web breaks is embodied.
2. Discussion of Background Information
In multi-cylinder drying sections commonly used up to now, the paper web is guided over several steam-heated cylinders or over an arrangement of several steam-heated cylinders and wire suction rolls in order to be dried; however, the use of at least one impingement dryer has been suggested for impinging the material web with a hot air and/or hot steam impingement (see, for example, DE 198 41 768.3).
Usually, in paper machines the detection of a web break occurs at several points in the machine running direction on the guidance side or drive side within the cylinder drying section. Such a web break detection is used to avoid an uncontrolled accumulation of paper in the drying section and a so-called wrapping of the cylinders. Each detection of a web break causes a striking off of the paper web and/or a raising of the pick-up roll.
One problem occurs when impingement dryers are used in that the drying wires may be damaged in the event of a web break.
SUMMARY OF THE INVENTION
The present invention provides a process and machine of the type mentioned at the outset which virtually eliminates the danger of such damage to the drying wire although several impingement dryers are used.
According to the invention, the process for monitoring for web breaks in a machine for producing a material web, in particular a paper or cardboard web, includes guiding the material web through at least one impingement dryer, monitoring the material web, viewed in a web travel direction, for web breaks in the region before the intake into the impingement dryer and/or in the region after the exit from the impingement dryer and/or within the impingement dryer, and at least partially deactivating the impingement dryer when a web break is detected.
In the exemplary embodiment, the material web is monitored for web breaks, viewed in the web travel direction, preferably directly before the intake into the impingement dryer and/or directly after the exit from the impingement dryer and/or between several impingement dryers.
In a preferred practical embodiment according to the invention, the material web is monitored for a web break at least essentially over the entire width. Such a width-wide monitoring can also detect when parts of the web are missing only so that even a sporadic overheating of the drying wires is avoided as well.
In certain cases, however, it may be sufficient to monitor the material web for web breaks only on one or both lateral web edges. Thus, a monitor of the web edges on the guidance side and the driving side is fundamentally conceivable as well.
Generally, each impingement dryer is provided with at least one impingement hood. When a web break is detected, preferably at least one of the impingement hoods is deactivated corresponding to the respective impingement dryer.
In order to deactivate a respective impingement dryer, this dryer is reversed from a normal operational state in which the material web is preferably impinged by a hot air impingement and/or a hot steam impingement to a web break operational state in which only the internal hot air and/or hot steam circulation occurs.
Alternatively or additionally, for the purpose of deactivating the impingement hood, the burner assigned to it can be reversed to minimum capacity.
Alternatively or additionally, it is possible for deactivating a respective impingement hood to transfer this hood away from the normal production line into a transfer line.
After a web break, the deactivation of the impingement dryer should occur within about 20 seconds, preferably within about 10 seconds so that, even at an air temperature of about 300-500° C., no overheating of the drying wires is caused.
According to a useful practical embodiment of the process according to the invention, when a web break is detected, in addition to the at least partial deactivation of the impingement dryer, at least one pick-up point is simultaneously opened as well, which is provided in the web travel direction before the impingement dryer and/or before and/or in the press section. This should occur within about 5 seconds, preferably less than about 2 seconds, after a web bread occurred.
Additionally, it is useful in certain cases for at least a partial deactivation of the impingement dryer to simultaneously cause the material web and/or paper web to be stricken off as well when a web break is detected.
According to a preferred practical embodiment, the material web is monitored for web breaks at least at one point by at least one sensor. Here, the use of most different types of sensors is conceivable. Advantageously, at least one optical sensor is used. In particular, a respective web break can be determined by color recognition or by image evaluation when a camera is used.
In certain cases, it is advantageous for at least one sensor to be directed to the material web, preferably directly after the respective impingement hood.
In the exemplary embodiment, the sensor can be directed towards the material web in a region in which the web is still positioned on a drying wire guided through the respective impingement dryer.
For example, it is also possible to direct the sensor to the material web in a region in which this web is positioned on the drying wire of a suctioned roll provided subsequent to the impingement dryer. This suctioned roll can be a suction roll or a so-called “DuoStabi-roll,” for example.
The drying wires are preferably made from plastic with the maximum allowable temperature being between about 100 and 300° C. However, no damages should occur at temperatures between about 300 and 500° C. on the drying wires during the deactivation of the impingement dryer.
However, it is also conceivable, to direct the sensor to the material web in the region of the first drying cylinder subsequent to the impingement dryer, with the material web being exposed after passing a previous wire and prior to the intake into another wire, with the sensor being directed towards the web section exposed. Therefore, the sensor can be directed towards the first cylinder after the impingement dryer when a group change occurs at this cylinder, thus resulting in a position at which the paper web is exposed.
In certain cases it can also be advantageous for the material web to be monitored in the region of a suctioned roll following the impingement dryer or one of the large suctioned rolls of the impingement dryer by monitoring the vacuum of this suctioned roll. As soon as the roll is no longer covered by the material web, particularly a paper web, the vacuum reduces considerably. For example, the suctioned roll can be a suction roll or a so-called “DuoStabi-roll” as well. Here, the suctioned roll is preferably provided inside of the first cylinder group subsequent to the impingement dryer. In particular, it can be provided before a detachment doctor, viewed in the web travel direction. In particular, it can be a the first suctioned roll subsequent to the impingement dryer.
The suctioned rolls to be monitored can also be the large suction rolls on which the impingement hoods are mounted.
According to a preferred useful embodiment of the process according to the invention, the material web is monitored for web breaks in the area of the impingement dryer positioned between a press section and a cylinder drying section of a machine for producing a material web.
In certain cases, it can be also advantageous to monitor the material web for web breaks in the
Augscheller Thomas
Mayer Roland
Bennett Henry
Greenblum & Bernstein P.L.C.
Ragonese Andrea M.
Voith Paper Patent GmbH
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