Paper making and fiber liberation – Processes and products – Lead strip forming and/or guiding
Reexamination Certificate
2000-08-25
2002-03-19
Fortuna, José (Department: 1731)
Paper making and fiber liberation
Processes and products
Lead strip forming and/or guiding
C162S194000, C162S286000, C162S363000, C034S117000, C034S120000, C226S007000, C226S091000, C226S092000
Reexamination Certificate
active
06358366
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The object of the present invention is a system and method for threading a moist web in a pulp machine or the like, such as a paper or board machine, from one section to the following section.
The object of the present invention is then typically a system for threading the tail of a pulp web from the press section to the dryer of the pulp machine. In pulp, board or paper machines there may be other corresponding points where it is necessary to transfer the moist web tail from one section of the machine to the following one. In such a case, the present invention obviously also concerns systems and methods for transferring the moist web at these points.
In this description of the invention, “the web tail”refers to the narrow, typically 120 mm wide, “web strip”, which is cut off from the edge of the web by a cut parallel with the longitudinal direction of the track, the said strip being that part of the web which is passed first from one section of the machine, e.g. the press section, to the following section, e.g. the dryer, for example, after a web break or at the start-up of the machine. A so-called tail threading belt or the like is used for passing the web strip forward. Once the tail end of the web strip has run the desired distance through the second section of the machine, the narrow part of the web passing through the machine is allowed to broaden to normal web width.
In a typical pulp machine, the dry-matter content of the pulp web is increased in the press section to approximately 50%. After the press section, the pulp web is typically dried in an air dryer comprising several drying levels on top of each other, through which the pulp web is passed in a winding manner from the upper part of the dryer to its lower part. The length of the air dryer is typically about 20-50 m and the number of drying levels about 10-30. The length of the route-that the pulp web runs through the air dryer is thus typically approximately 500-1000 m.
At present, a pulp web is typically passed in a free transfer from the press section to the dryer. The above-mentioned narrow web strip cut off from the edge of the pulp web is used to facilitate the feeding of the moist pulp web from the press section to the dryer, the strip being typically passed through the entire dryer, before the web is allowed to broaden to its full width. In this case, the length of the web strip is also for the most part the same as that of the drying route, that is, for example approximately 500-1000 m.
A typical system for threading the moist tail of a pulp web, that is, the above-mentioned web strip, through the pulp dryer comprises a tail threading belt which forms a closed loop. The loop is typically arranged to pass through the dryer along the route of the pulp web to be dried from the point of entry of the web to the point of its exit, and once the tail of the web has been detached from the belt, to continue outside the actual dryer, from the point of exit of the web back to the point of its entry.
The tail threading belt is typically a belt folded over once, inside which fold the tail of the pulp web, that is, the web strip, is passed through the dryer. The moist tail of the pulp web is at present passed manually from the last support wire of the press section into contact with the tail threading belt. In this case, the fold of the moving tail threading belt is first opened to allow the tail of the pulp web to be placed inside the fold. When the tail of the pulp web has been placed inside the fold, the fold is closed in order to secure the tail of the pulp web inside the fold. After this the tail threading belt is passed to the dryer. The opening and closing of the belt fold usually takes place by means of opening wheels and closing pins known as such.
FIG. 1
shows a prior art system for passing a pulp web from the support wire
10
of the press section, by means of the tail threading belt
12
, to the air dryer, of which only the first roll is shown in FIG.
1
. The tail threading belt
12
is a belt folded over once, the fold of which is opened to bring the tail of the web inside the fold of the belt, and closed to hold the tail of the web secured to the belt while it conveys the tail of the web through the dryer. Prior to the stage shown in
FIG. 1
, the tail end of the moist web strip
18
has been manually brought into contact with the tail threading belt, after it has come out of the press section supported by the last support wire
10
and fallen down freely from the roll
14
.
FIG. 1
also shows by means of broken lines, the running of the pulp web
18
′ in the pulp machine during normal operation.
The functioning of a closing tail threading belt is previously known, for example, from the Finnish patent publication no. 55882. In the present description, “a tail threading belt or the like” refers to other tail threading arrangements known as such and comprised of endless rope, chain or cord-like means in addition to the tail threading belt disclosed in the above-mentioned Finnish patent publication, in which arrangements the web strip is pressed between two or more ropes, chains or cord-like means.
When, in the case shown in
FIG. 1
, the tail threading belt
16
has conveyed the tail end of the moist web strip
14
through the dryer, the forming of the strip is discontinued and the web is allowed to broaden to its normal full width. The use of the tail threading belt
16
can be discontinued after this. The pulp web will then typically run in a free transfer from the press section to the dryer, as shown by the broken lines.
Thus, at present the passing of the moist tail of the pulp web from the press to the dryer requires—in connection with each start-up e.g. after each interruption—a person who will take the moist tail of the pulp web manually from the press section towards the dryer and place this tail in the opened gap of the fold of the tail threading belt running at a considerable speed. This type of manual feed should be eliminated, if only because of the risk of accident.
The tail of the pulp web can usually be placed manually only in machines running at slow speeds of <150 m/min. At higher speeds, the risk of unsuccessful threading increases. Today, the speed of pulp machines is often as high as 160 m/min, and there is a need to run at even higher speeds exceeding 200 m/min, in future even at speeds of 300 m/min. At present, for the above-mentioned reasons relating to manual feed, the speed of the machine has to be slowed down to<150 m/min for the duration of the tail threading of the web, that is, the manual escorting stage, which then slows down the start-up of the machine.
Passing the web strip manually requires considerable skill. Transferring the pulp web strip freely, for example, from the press section to the dryer is not easy either, because the pulp web, which typically weighs about 500-1000 g/m2, may easily break when it is lifted freely to a relatively great height.
Nowadays, the tightening of the tail threading belt typically takes place in vertical tail threading belt tightening towers. In the tightening towers, the tail threading belt is guided to pass through a U-shaped loop, the lower part of the loop being fitted with a weight, which tightens the belt to the desired tightness. The tightening tower can usually not be fitted to the optimal point for the running of the tail threading belt at the wet end of the dryer, but instead it has to be fitted on the side of the machine, on the tending side of the machine, so that the tightening tower will not be in the way of the tender platform, which moves in front of the dryer, or the broke sail guiding the broke. At the dry end there is no need to make corresponding transfers of the tail threading belt, because the tail of the pulp web can be guided directly into the pulper chute.
In order to guide the tail threading belt into the tightening tower at the wet end of the dryer, the belt has to be moved sideways, that is, in the cross-web direction several times. The tail threading belt the
Hongisto Pertti
Sairanen Paavo
Tammekas Time
Virta Raimo
Fortuna Jose
Metso Paper Inc.
Nixon & Vanderhye PC
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