Roll

Details Roll Roll

1997-06-19

2002-06-18

Bennett, Henry (Department: 3743)

Heat exchange

Movable heating or cooling surface

Rotary drum

C165S089000, C492S046000, C034S124000

Reexamination Certificate

active

06405790

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
The present application claims the priority under 35 U.S.C. §119 of German Patent Application No. 196 24 737.3, filed on Jun. 21, 1996, the disclosure of which is incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a roll that includes a roll tube provided with an outer elastic coating. The sealed interior space may include a vaporizable liquid and a heat exchanger for cooling heat generated in the roll during use. The sealed interior space may form a closed system in which the heat in the roll tube may vaporize the vaporizable liquid and the heat exchanger may be set to condense the vaporized liquid.
2. Discussion of Background Information
Rolls of the type generally described above may be utilized, e.g., in supercalenders or soft calenders. Due to the elasticity of their surfaces, these rolls are often also referred to in the art as “soft” rolls. In use, the soft rolls and so-called hard rolls are positioned together form a nip though which, e.g., a material web is conducted to smooth the surface of the web by applying pressure and, if necessary, at an elevated temperature.
During operation, the surface of the soft roll heats up due to, e.g., the flexing work performed by the elastic coating. The resulting high temperature endangers the elastic coating which drastically reduces the roll's protection against destruction.
When a roll tube is utilized as a roll jacket, e.g., in a deflection adjustment roll or deflection compensating roll, the roll jacket is supported by a hydrostatic or hydrodynamic supporting elements. In this manner, heat can be dissipated by providing hydraulic oil in an interior space of the roll. This method for stabilizing the roll temperature, which occurs like a secondary phenomenon with deflection adjustment rolls, however, is relatively costly.
Further, it is known to provide peripheral bores in the roll jacket of “hard” rolls so as to enable a through flow of a heat carrier or coolant, e.g., through peripheral channels extending through the peripheral bores. The heat absorption or emission of this medium, however, must be maintained within relatively close limits so as to prevent an irregular temperature distribution across the width of the roll. In a cooling process, as coolant flows through the peripheral channels, the temperature of the coolant may generally only be allowed a maximum rise of 1° C., and never more than 2° C. Thus, this cooling process requires an adequate volume of coolant.
There is also a possibility of cooling the rolls from the outside, e.g., by blowing with cool air or spraying with cooling liquid. However, these possibilities for cooling the rolls are somewhat limited. In particular, when spraying with a cooling liquid, there is a risk that the cooling liquid may also contact the web being processed, which may adversely affect the intended finishing of the web.
SUMMARY OF THE INVENTION
Accordingly, a particular feature of the present invention may be directed to cooling a soft roll in a simpler manner than that disclosed in the prior art.
To achieve this above-noted feature, a roll may include a roll tube that has an elastic coating provided on an outside of the roll tube. The roll tube may include a sealed interior space within which a vaporizable liquid and a heat exchanger may be positioned.
In operation, the roll and roll tube may rotate. As a result of centrifugal force generated by the rotation of the roll, the liquid provided within the interior space may be pressed against an inside wall of the roll tube to form a liquid film. For practical purposes, an adequate volume of liquid should be provided in the interior space so that a closed film may form that has a thickness of, e.g., several millimeters. Further, heat may be transmitted to the liquid, e.g., from the outside of the roll, i.e., through the roll tube. The transmitted heat may vaporize the liquid to produce steam. The vaporized liquid or steam may contact a heat exchanger so as to withdraw or emit the heat from within the interior space. The steam may then condense or precipitate on the heat exchanger. The condensation, through the centrifugal force, may be forced toward the wall of the interior space, i.e., the inside surface of the roll tube. Thus, the cooling cycle may start over again.
The present invention produces an intensive cooling of the roll tube through relatively simple measures. For example, as the liquid film located on the inside of the roll tube develops evenly, i.e., as a result of the centrifugal force, a similar even heat dissipation may also be produced. Thus, an even temperature can be maintained with good feed across the axial length and circumference of the roll tube.
In a preferred embodiment, the temperature of the heat exchanger may be reduced to a temperature below the condensation temperature of the liquid. As a result, the steam may not only be condensed or precipitated on the heat exchanger, but the condensation may also be additionally cooled. Thus, this embodiment may produce an even greater temperature difference between the roll tube and the heat exchanger. Thus, because the heat exchanger may dissipate a large volume of heat, improved heat dissipation may be achieved through the present invention.
In another preferred embodiment, the interior space may be gas-tight so that no coolant may be lost. Further, the present invention may utilize water as the coolant. Alternatively, other liquids, e.g., those exhibiting a low boiling point, may be utilized as the coolant for the present invention. Accordingly, the ordinarily skilled artisan may set certain temperature limits within which the roll tube may be heated by selecting an appropriate coolant liquid, i.e., according to its boiling point.
In another embodiment of the present invention, the roll may be provided with journal bearings. Further, the interior space of the roll tube may be closed off or defined at the axial extremes of the roll tube by respective journals and associated components or walls. This arrangement may produce a gas-tight interior space. While typical journal bearing rolls of the prior art are generally characterized by a very low dead weight that results in a desired steep characteristic curve in the calender, by utilizing an additional heat exchanger in accordance with the present invention, the roll may be cooled by simple coolants. Thus, flexing work performed in the elastic coating may have no negative effects with respect to the roll temperature and, therefore, reduce the danger of damaging the coating.
In accordance with the present invention, the heat exchanger may jointly rotate with the roll tube. This embodiment may facilitate the sealing of the heat exchanger against the roll tube. That is, if the heat exchanger is jointly mounted with the roll tube, the interior space may be maintained stationary so that none of the gaps between the components have to be sealed. Further, the rotating heat exchanger may produce a better distribution of the liquid that is precipitated on the heat exchanger. Drops of liquid formed from the steam, i.e., which have precipitated at the heat exchanger, may be centrifuged against the wall of the roll tube where they can be revaporized. Thus, this feature of the present invention may act as a kind of pump within the coolant cycle.
In another preferred embodiment of the present invention, a flow of coolant may be fed to the heat exchanger. The application of coolant may be a relatively simple method for dissipating heat from the interior space of the roll tube. It may also be possible to use electrical components having negative temperature coefficients. However, the expenditure for dissipating volumes of heat may be relatively high. The coolant may be heated relatively fast in the heat exchanger. However, in contrast to the prior art, the present invention is not limited to allowing heating by only 1° C. or 2° C. Further, the cooling liquid may increase by 10° C., 20° C. or to an even higher tem

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