Drying and gas or vapor contact with solids – Process – Diverse types of drying operations
Reexamination Certificate
1999-10-20
2001-06-19
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Process
Diverse types of drying operations
C034S456000, C034S117000, C034S120000, C034S122000
Reexamination Certificate
active
06247247
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a blow box used in the drying section of a papermaking machine in accordance with the enclosed independent claims and to a method for sealing a pocket with a blow box in the drying section of a papermaking machine. The present invention also relates to an arrangement including a frame construction and a nozzle means for improving runnability in a papermaking machine.
In the drying section of a papermaking machine, the web is transported in a known way by using a single-wire or twin-wire draw. A single-wire draw refers to a draw in which the web runs from one drying cylinder to another supported by one single drying wire over the drying cylinders, the web runs between the cylinder and the drying wire.
A twin-wire draw refers to a draw in which separate upper and lower wires are used for supporting the web as it runs alternately over the upper and lower cylinders. Also in this case, the web runs over the drying cylinders between the cylinder and the drying wire. From the upper cylinder to the lower, or vice versa, the web runs partly unsupported. However, the turning rolls of the drying wires may be fitted so that the wire and the web simultaneously depart from the drying cylinder and so that the wire supports the web a short distance while it passes from one row of cylinders to another.
The drawback of previously known multicylinder single-wire dryers has been that the web is inclined to come loose from the drying wire surface as the wire and the web are transferred via a turning cylinder or roll from one drying cylinder to the next. In this connection problems particularly arise at
the point at which the web and the wire depart from the drying cylinder, along which the web has passed between the wire and the cylinder, and at which point the web tends to depart from the wire and follow the cylinder; and
the entry nips of the wire both on the drying cylinder and on the turning cylinders or rolls below, the web being inclined to depart from the wire at the nips, due to the overpressure induced in the nips.
The diverging of the web from the wire easily leads to the breaking of the web or at least to the web becoming baggy or formation of folds in the web. Thus, the diverging of the web from the wire leads to runnability problems which become emphasized as the speeds of the papermaking machines increase.
It has previously been known to use various blow boxes for improving the operation of papermaking machines. One such component improving the operation is disclosed in the American patent publication U.S. Pat. No. 4,905,380 relating to a blow suction box used in a multicylinder dryer of a papermaking machine. The ejection blow generated by the blow box is used for inducing an underpressure zone in a slot between the drying wire and the blow suction box wall, holding the web on the drying wire as the web passes from the drying cylinder to a turning roll underneath. An underpressure zone is generated downstream of the drying cylinder in the slot limited by the blow box wall and the wire leaving the drying cylinder, by ejecting air from the slot by air blows directed in the opposite direction to the running direction of the wire.
However, a problem with the arrangement described above is to safely seal the underpressure zone induced by blowing from the area remaining outside. In connection with malfunction, the papermaking machines create paper waste which often forms paper clods or causes the web to wrinkle, again causing problems in narrow places in the machine, for example, in the narrow spaces between the blow boxes and wires, cylinders or rolls. Due to paper clods travelling with the web, or other similar bulges in the web, it is not possible to install the blow box at a desired enough short distance from the wire run. Very long safety distances are often required between the wires and blow boxes so that the said bulges could run along with the wire past the blow box without touching it and without damaging its structures or the wire. Safety distances typically are 20 to 50 mm in single wire and 50 to 100 mm in two wire drying sections. When the blow nozzles for the blow boxes have to be placed within the said safety distance, for example, from the wire, the effects of the ejection blow often are inadequate. Neither is the underpressure zone sufficiently sealed.
It is known, for example, from the American patent publication U.S. Pat. No. 4,996,782 to use turning flaps to direct air blows to a given point from which air is to flow through the wire for ventilating the pocket formed by the wire loop. The purpose of the flap is not to seal the slot between the blow box and the wire.
The object of the present invention is to provide an improved blow box and an improved method for sealing a pocket provided with a blow box in the drying section of a papermaking machine.
The object of the invention is especially to develop further a blow box arrangement previously known so that the underpressure effect is further intensified during operation thereof.
It also is a further object of the invention to provide a blow box and method with which it is possible to control the air space between the wire and blow box also during tail threading.
An important object of the invention is further to produce a blow box with which underpressure is generated as close as possible to the element of the papermaking machine moving past the blow box, e.g. a wire, and which may be used both during normal operation and during tail threading.
It is further an object of the invention to produce such an arrangement which makes possible sufficient safety distances for a paper clod or another similar obstruction to pass the blow box along with the wire.
It also is an object of the invention to produce a nozzle for the blow box that is safe to take very close to the wire for generating ejection blowing or pocket ventilation. In this case, the object is especially to produce a nozzle the blow from which may be directed accurately and which may generate the necessary pressure differentials maintaining, however, the operational safety of the structures.
For achieving the above objects, the new blow box and method of the invention in the drying section of a papermaking machine are characterized in what is described in the characterizing part of the enclosed independent claims.
A typical blow box of the present invention used in the drying section of a papermaking machine is, in the said drying section, fitted into the pocket space limited by a wire running from the first drying cylinder to the second drying cylinder, and a turning element, such as a turning cylinder, a turning roll, a suction roll, etc. on this wire run, for ejecting air from the pocket space and for generating an underpressure zone in at least part of the pocket space. At the interface between the desired underpressure zone and the area remaining outside, the blow box is provided with one or several sealing means comprising a sealing element projecting towards the wire at a certain distance “d” from the wire, for forming a seal between the underpressure zone and the area remaining outside the underpressure zone. The said sealing element is preferably joined to the blow box so that the element may, either by pressing or by an actuator, be moved away from the wire to a distance “d′”, which is larger than the distance “d”.
In this specification and the enclosed claims, a blow box typically refers to box-shaped constructions extending across the web, or to other constructions extending across the web, such as beamshaped or tubular constructions, which may be used for leading ejection air to the pocket or a part of it. A blow box of the invention may also be used for sealing the slot between the end areas of the blow box and the edge areas of the wire for maintaining the underpressure zone at a desired value in the pockets also in the edge areas of the web. The arrangement of the invention may thus additionally, or solely, be used for sealing the edge zone of the pocket, and the res
Jokinen Reijo
Kokkala Hannu
Kurki Matti
Virta Raimo
Yömaa Seppo
Metso Paper Inc.
Nixon & Vanderhye P.C.
Wilson Pamela
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