Drying and gas or vapor contact with solids – Apparatus – Rotary drums or receptacles
Reexamination Certificate
2001-05-10
2003-12-09
Lazarus, Ira S. (Department: 3749)
Drying and gas or vapor contact with solids
Apparatus
Rotary drums or receptacles
C034S123000, C034S611000
Reexamination Certificate
active
06658758
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 100 25 560.4 filed May 24, 2000 and of German Patent Application No. 200 17 924.1 filed Oct. 19, 2000, the disclosures of which are expressly incorporated by reference herein in their entireties.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a drying section of a machine for producing a material web, e.g., a paper or cardboard web.
2. Discussion of Background Information
In the multi-cylinder drying sections that have been common 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 for the purpose of drying it. Especially at the beginning of the drying process, when the moist paper does not yet have sufficient strength, problems often occur with regard to the web guidance, which can be attributed, in particular, to the fact that the still-moist web sticks to the smooth surfaces, which are absolutely necessary for sufficient heat conduction. In order to be able to remove the web from the cylinders, a sufficient web tension is necessary, which can only be produced by pulling, i.e., a differential speed, before or directly after the first smooth contact surface. This often causes tears and an overstretching of the edges and the speed of the paper machine is limited correspondingly because the above-mentioned problems occur more intensely at higher speeds and the tension must be increased.
One possible solution is to provide a large cylinder or a large suction roll with an associated impingement hood between the pressing section and the multi-cylinder drying section (see, e.g., DE 19 841 768 and DE 19 935 138). However, this usually produces one or more longer transfer paths that are straight or only slightly curved between the last pressing nip and the large roll or cylinder for the purpose of creating a certain distance between the last press and the large roll or cylinder; in these transfer paths, the web must be held, e.g., on a wire or felt by transfer foils. Because of the relatively straight web guidance that results, web travel problems occur, such as, in particular, lifting or turning down of the edges or transfer difficulties.
SUMMARY OF THE INVENTION
The present invention provides a drying section of the type mentioned at the outset which, at the same time, essentially guarantees at high speeds as optimal a drying rate as possible at the beginning of drying as well as a secure web guidance. Further, a reliable transfer should especially be ensured.
According to the invention, a pick-up suction roll, in particular a larger one, is provided between the last pressing nip of a pressing section and a subsequent impingement or jet impingement drying unit. The roll removes the material web from a press felt guided through the last pressing nip or from a transfer belt and transfers it to the impingement drying unit.
Because of this construction, the above-mentioned web travel paths, which are rather long and straight or only slightly curved, are prevented. In this manner, a reliable transfer and a secure web travel is achieved on the edges as well. Due to the web guidance now being curved, the danger of lifting or turning down of the edges is removed and the transfer of the web is facilitated.
The outer diameter of the pick-up suction roll preferably lies in the range of approximately 1.2 to approximately 2.5 m.
In an exemplary embodiment of the drying section according to the invention, the pick-up suction roll is wrapped by a wire. The wire in question is correspondingly tensed. Here, in particular, a wire travel regulator can be provided as well. The wire tension can also be regulated correspondingly.
Instead of a wire, it is also conceivable for the pick-up roll to be provided with an appropriate surface. Thus, this pick-up suction roll can, e.g., be coated with a screen stocking.
The pick-up suction roll can be provided with a suction box located in its interior or can be provided with suction by way of its jacket from an outside suction box. For this purpose, the jacket can be provided, e.g., with indentations such as grooves or the like.
It is advantageous to provide the pick-up suction roll with a multi-zone suction box in order to set various levels of vacuum in the crosswise direction and/or in the machine direction and/or to be able to utilize various suction box angles.
The impingement drying unit advantageously includes a support roll, e.g., a larger support roll, or the like with an impingement dryer assigned thereto, with the material web being transferred onto the support roll by the pick-up suction roll.
It is also possible to provide one or even several, preferably two or three, such impingement drying units, preferably including a support roll, e.g., a larger support roll, and an impingement dryer assigned thereto.
It is useful for the outer diameter of a given support roll to lie in the range of approximately 2.5 to approximately 8 m and preferably in the range of approximately 3 to approximately 5 m.
The outer diameter of the enlarged pick-up suction roll is preferably smaller than the one given support roll.
In a preferred embodiment of the drying section according to the invention, the support roll is wrapped by a wire. Correspondingly, the material web is transferred from the pick-up suction roll to this wire wrapping the support roll of the impingement drying unit.
The support roll of a given impingement drying unit can be formed, e.g., by a suction roll or a cylinder. However, instead of the support roll, a support belt guided over several support rolls can be provided. In this case, it is useful for the support rolls to be at least partially arranged on the arc of a circle.
Preferably, at least one impingement drying unit with an impingement hood is provided.
Preferably, the web is blown on directly from such an impingement hood. Several impingement units directly following one another, preferably two or three such units, can be provided before the first cylinder group in the web travel direction. The material web can be dried, e.g., up to a dry content in the range of approximately 55 to approximately 65% before it is guided to the first cylinder group. Thus, the dry content achieved before the first cylinder group must be higher the lower the basis weight, the higher the ash content, and the higher the machine speed.
In an advantageous embodiment of the drying section according to the invention, the impingement hood is positioned in the impingement drying unit provided subsequently to the last pressing nip or the wrapping angle covered by the impingement hood is selected in such a way that a minimal distance between the associated larger support roll and the last pressing nip is made possible. The impingement drying unit provided subsequently to the last pressing nip preferably includes a one-piece impingement hood while any other drying unit that may be provided after it is usefully provided with a two-part hood.
If at least two impingement drying units following one another are provided, the material web is preferably transferred from the wire of the one, preceding unit immediately to the large support roll of the subsequent other unit. Thus, the straight section of the web travel between the two units in question is kept as short as possible.
Impingement drying units following one another can be arranged in an alternating fashion in such a way that different sides of the web can be impinged by the impingement drying units in question. It is advantageous for the impingement drying unit provided subsequently to the last pressing nip to impinge the upper side and for the subsequent impingement drying unit to impinge the lower side of the material web. In principle, however, it is also possible to impinge first the lower side and then the upper side of the material web.
Thus, the pick-up suction roll, in particular the larger pick-up suction roll, according to the invention can thus be use
Kahl Peter
Kugler Georg
Mayer Roland
Mayer Wolfgang
Oechsle Markus
Lazarus Ira S.
Ragonese Andrea M.
Voith Paper Patent GmbH
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