Patent Application
20080098613
This is a continuation of PCT application No. PCT/EP2006/061052, entitled “DRYING CYLINDER”, filed Mar. 27, 2006, which is incorporated herein by reference.
1. Field of the Invention
The invention relates to a drying cylinder for drying a paper, board, tissue or another fibrous web in a machine for producing and/or finishing the same, which is heated from the inside with a gaseous, condensable heat transfer medium, the inside of the roll shell having elevations which protrude out of the condensate of the heat transfer medium collecting on the inside.
2. Description of the Related Art
Drying cylinders of this type have been known for a long time, steam predominantly being used as the heating medium.
As a result of the extraction of heat during the drying of the fibrous web, a phase transition occurs and therefore the formation of condensate. At the usual machine speeds, as a result of centrifugal force, this condensate is deposited on the inside of the roll shell as a closed condensate ring.
This condensate ring is thermally highly insulating and thus worsens the heat transfer from the steam to the fibrous web.
Therefore, drying cylinders having grooves extending radially have been developed, their ribs protruding slightly out of the condensate.
However, this increasingly no longer meets the requirements for improved heat transfer, in particular in the event of a fluctuating thickness of the condensate ring. In addition, carrying the condensate away out of the radial grooves is problematic.
What is needed in the art is to improve the heat transfer with simple measures.
The present invention provides that the elevations have at least 1.2 times the height of the average condensate height and/or the cross section of the elevations decreases toward the inside (that is, in an inward radial direction of the roll shell).
In this case, the elevations protrude considerably out of the condensate film and, because of their direct contact with the gaseous heat transfer medium, improve the heat transfer substantially.
The widening of the cross-sectional area of the elevations toward the roll shell increases the thermal conductivity. In addition, this results in an increase in the quantity of condensate arising, leading to an enlargement of the condensate thickness only to a reduced extent, because of the free area between the elevations, which increases with increasing height.
In order to offer an adequate contact surface between the elevations and the gaseous heat transfer medium, the elevations should have at least 1.2 times, preferably 1.5 times and in particular 1.8 times the height of the average condensate height.
In this case, however, it is sufficient if the elevations have at most 10 times, preferably at most 5 times, the height of the average condensate height.
In many cases, in order to ensure adequate heat transport, it may already be sufficient if the elevations have at most 2 times, preferably at most 1.8 times, the height of the average condensate height.
For optimal heat transport, it is advantageous if the cross-sectional reduction in the size of the elevations is carried out in such a way that an approximately constant heat flow density prevails in the elevations.
Furthermore, the cross-sectional area of all the elevations on the inside should correspond approximately to half the inner shell area of the roll shell.
In this case, the size and spacing of the elevations should be chosen in such a way that, on the outside of the roll shell, which is contacted by the fibrous web, only the smallest possible temperature differences prevail between the regions opposite the elevations and the regions opposite the condensate surface.
In order to minimize the expenditure, the use of steam as heat transfer medium is recommended.
In this case, it is possible for the elevations and the roll shell to consist of the same, highly thermally conductive material.
This makes it possible to design the elevations and the roll shell in one piece.
For example, the elevations could be machined out of the roll shell by milling.
However, it may also be advantageous if the elevations consist of a different material with a good thermal conductivity, preferably better than the roll shell.
Here, it is a matter of a highly thermally conductive connection between elevations and the roll shell. Therefore, the fixing of the elevations to the roll shell can preferably be carried out by way of soldering, welding or adhesive bonding.
A relatively fine-mesh distribution of the elevations is possible if these have, at least to some extent, the form of pins or studs.
Another design results if the elevations have, at least to some extent, the form of ribs.
These ribs can extend axially, radially or spirally.
However, it is advantageous if the ribs extend axially. In order in this case to be able to lead the accumulating condensate away easily, the ribs at at least one shell end should lead to a connecting channel extending radially on the inner shell surface. From this connecting channel, the condensate can then easily be led out of the drying cylinder, for example with a stationary siphon.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
The drying of fibrous webs in production machines is carried out to a substantial extent by way of contact with the heated circumferential surface of rotating drying cylinders as they wrap around them.
For the purpose of simplification, the drying cylinders are in this case normally heated with hot steam. To this end, the latter is led into the interior of the drying cylinder.
Referring now to the drawings, and more particularly to
Since this condensate 2 is deposited on the inside as a closed and thermally insulating condensate layer, because of centrifugal force, measures have to be taken in order to improve the heat transfer from the steam to the fibrous web via the roll shell.
To this end, the roll shell 1 has on its inside a large number of ribs 3 arranged distributed uniformly over the circumference and extending axially.
In the interests of a good thermal connection, these ribs 3 are soldered onto the inside or otherwise connected in a highly thermally conductive manner. Like the roll shell 1, they also consist of a highly thermally conductive material and protrude out of the condensate layer.
As a result of the direct contact between the steam and the part of the ribs 3 protruding out of the condensate 2, the heat transfer to the roll shell 1 is improved considerably.
As illustrated in
As can be seen in
The average condensate height is generally between 2 and 10 mm, in particular between 3 and 5 mm, the ribs 3 having 1.3 to 1.6 times the height thereof.
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 022 233.1 | May 2005 | DE | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2006/061052 | Mar 2006 | US |
| Child | 11930965 | Oct 2007 | US |
