This application claims priority under 35 U.S.C § 119, from Austrian Patent Application No. A1552/2002 filed Oct. 14, 2002.
The invention relates to a device for continuous drying of a pulp sheet, particularly a tissue web, with a drying drum and an air circulating system.
In conventional tissue plants, the drying process begins at an inlet dryness of some 40 to 45% in the tissue web. In order to achieve higher paper volume, mechanical pre-dewatering on presses is omitted and the inlet dryness to this equipment nowadays is approximately 20 to 25%. These plants operate with through drying. If there is no paper in the plant, e.g. if there is a sheet break, there is a problem because the drying drum is exposed to high temperatures in the vicinity of the paper web for short periods and the difference in temperature between drum and end cover can cause increased stress and thus, damage to the drum. The aim of the invention is to eliminate this disadvantage.
The invention is characterised by the drying drum having a perforated cylinder that is supported by external radial bearing rings. With this design the drum shell is centered, thus guaranteeing exact roundness at all times.
A favorable configuration of the invention is characterised by the perforations in the cylinder being in the form of holes.
In one aspect the invention is directed to the combination of a drum, axle means along the drum centerline for supporting the weight of the drum, journal means associated with the drum and the axle, a motor for imparting a rotational torque to the drum, and a hot air supply for delivering a flow of hot air to the drum for drying a paper pulp sheet or web carried on a circumferential portion of the drum as the drum rotates, wherein the improvement comprises that the drum has means for rigidly supporting a perforated drum cylinder relative to the journal means, and an outer shell including the perforated cylinder and a plurality of circumferential bearing rings fixed to the exterior of the cylinder. Preferably, at least three radial bearing rings are welded to the cylinder.
The radial bearing rings in essence provide a series of belts around the cylinder that tightly (via welding) support the cylinder wall at the outside as the cylinder tries to expand non-uniformly during transient conditions.
An advantageous further development of the invention is characterised by longitudinal ribs being provided in the axial direction, where the longitudinal ribs can be arranged at a distance of 40 to 80 mm from one another. The longitudinal ribs provide stability for the drying shell. If the longitudinal ribs are welded to the radial bearing rings as well as to the perforated cylinder, this results in a complete, load-bearing unit.
A particularly favorable further development of the invention is characterised by the longitudinal ribs at the edges of the cylinder being welded to the outermost radial bearing ring only, where the outermost radial bearing ring is not connected to the cylinder. As a result, the drum can adjust to the various temperatures between the hot blow-air applied over the working width and the lower temperatures at the peripheral areas in such a way that there is no increased thermal stress in the shell and thus, the risk of cracks is virtually eliminated.
An advantageous configuration of the invention is characterised by a circumferential ring being secured to each of the outermost radial bearing rings, which extends from the end cover internal flanges to the edge of the paper web, where the circumferential ring can have a pattern of perforations. As a result, a certain amount of cooling air, which is blown out of the high-efficiency hood onto the edge of the drum, can be discharged.
A favorable further development of the invention is characterised by end covers screwed to the drum shell, being provided on the end faces of the cylinder in order to stabilize the drum shell. This design guarantees improved stability of the drum shell and, in particular, prevents any sliding movement between end cover and drum shell in the event of radial expansion due to the temperature.
An advantageous configuration of the invention is characterised by the drying drum having a drum body that is welded only. This design virtually eliminates the risk of areas in which cracks could occur.
The invention will now be described using the examples in the drawings, wherein:
a is an extract from
a illustrates the structure of the drum shell 12 in an extract according to the circle marked V in
The same extract is shown in
The circumferential ring 25 attached to the outermost bearing ring 24 covers the end region of the drying drum 1 that has no contact with the paper web and has perforations, preferably with round holes, in an area b acting as an edge cooling zone, in order to discharge a certain amount of cooling air that is blown out of the high-efficiency hood onto the edge of the drum. Rings 25 prevents hot gases from exiting the shell at the ends. The hood has separate areas at the end side to blow cool air, i.e., cooler than the drying air, with temperatures up to 100° C. to the (end) rings 25 so that also here the terminal stresses to the end covers will be reduced.
In addition, this Figure shows where the face end covers 15, 16 are secured to the drum shell 12 (flange 26) by screws 18. This ensures that there is no sliding movement between the end covers 15, 16 and the drum shell 12 if there is radial expansion due to the effect of heat, and that a firm connection is always guaranteed.
Number | Date | Country | Kind |
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A 1552/2002 | Oct 2002 | AT | national |
Number | Name | Date | Kind |
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3781957 | Luthi | Jan 1974 | A |
4184268 | Christin et al. | Jan 1980 | A |
4781795 | Miller | Nov 1988 | A |
4990751 | Nous | Feb 1991 | A |
5575080 | Fleissner | Nov 1996 | A |
Number | Date | Country | |
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20040128855 A1 | Jul 2004 | US |