Drying and gas or vapor contact with solids – Apparatus – Rotary drums or receptacles
Reexamination Certificate
2000-06-20
2002-12-03
Walberg, Teresa (Department: 3742)
Drying and gas or vapor contact with solids
Apparatus
Rotary drums or receptacles
C034S128000, C034S420000
Reexamination Certificate
active
06487789
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 29 520.4, filed on Jun. 28, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a heated cylinder for drying a fibrous material web, particularly a paper, cardboard, or tissue web in machines for producing or refining the same, including a cylinder jacket whose outer layer exhibits good heat conductivity.
2. Discussion of Background Information
Drying cylinders of this kind are generally known and are usually heated with steam from the inside. Additional external heating elements can be provided based upon induction heating technology. Here, an equalization of temperature is reached between the internal and external side of the cylinder jacket, which limits the maximum surface temperature of the drying cylinder.
In addition, metal drying cylinders of this kind, for reasons of production and strength, have a large jacket thickness. The low heat resistance associated therewith also limits the maximum temperature difference between individual heating zones along the drying cylinder. An additional factor is the relatively long periods required for the cylinder material to heat up and cool down.
SUMMARY OF THE INVENTION
The object of the invention is therefore to increase the maximum surface temperature of the cylinder jacket in a heated cylinder and to improve the heat flow proceeding from the heating unit to the fibrous material web via the cylinder jacket.
According to the invention, this goal is achieved in that at least one heating system positioned outside the cylinder is assigned to the outer jacket layer for the purpose of heating and in that a heat-insulating layer lies contiguous to the outer jacket layer but inside the cylinder jacket. This insulation prevents heat flow to the internal part of the cylinder, with the result both that greater surface temperatures are possible and that a large quantity of heat can be released from the heating system to the fibrous material web. The insulation also renders unnecessary an internal heating system for the cylinder jacket.
To reduce the heating up and cooling off periods, the external jacket layer should preferably include metal and be as thin as possible. This also increases the maximum temperature difference between the different heating zones.
Even for the case in which the external jacket layer is among the essential factors determining the stability of form and the strength of the cylinder, it is desirable for the thickness of the external jacket layer to be less than about 30 mm, preferably less than about 5 mm.
However, if the stability of form and strength of the cylinder are primarily determined by the insulating layer and/or by a support structure within the cylinder jacket and contiguous to the insulating layer, it is advantageous if the external jacket layer has a thickness of less than about 5 mm, ideally less than about 1 mm, and particularly less than about 0.2 mm.
The support structure may include metal, in which case the thermal effect of an induction heating system must be taken into account.
Lighter cylinders generally result, however, when the supporting insulting layer and/or the supporting structure include a fiber-reinforced, thermally insulating plastic. This means that the insulating layer and the support structure can optionally also form a single element of the cylinder jacket, one that is structured or multi-layered.
Under certain circumstances, advantages with respect to stability and strength, or advantages relating to production, will also result if the insulating layer and/or the supporting structure occupy at least a considerable portion of the inner compartment of the cylinder; ideally they will occupy the entirety of the inner compartment.
The diameter of the cylinder determines the jacket surface to be heated, which in turn limits the maximum diameter; at the same time, however, it has an effect on the period of contact with the fibrous material web, which results in a minimum.
Particularly good results were achieved with cylinders whose diameters lie in the range of about 500 to 3000 mm, preferably between about 1200 and 1800 mm.
To profile the moisture distribution crosswise to the fibrous material web, the heating system will preferably include an infrared and/or induction heating system and should have a plurality of heating zones along the cylinder which can be separately controlled and which should have a zone width of preferably less than about 200 mm. The optimal zone width will be determined by the expense of the heating system and by the heat flow between the heating zones. Good results can be achieved with zone widths in a range of about 30 to 100 mm, chiefly in a range between about 40 and 75 mm.
In this connection, the heat flow between the heating zones can be further reduced if the external jacket layer has a reduced thickness in the area between the heating zones. This can be achieved in a simple manner, with a narrow circumferential groove, preferably one that runs outward and does not compromise the quality of the fibrous material web.
To efficiently influence the moisture distribution or the drying of the fibrous material web overall, while avoiding heat damage to the web surface, the maximum surface temperature of the cylinder should lie between about 120 and 250° C., preferably between about 150 and 200° C. To this end, it is usually necessary for the entire available heating capacity to be at least about 60 kW/m for a cylinder diameter of up to about 1200 mm; for a cylinder diameter between about 1200 and 1800 mm it should be at least about 80 kW/m, and for a cylinder diameter of greater than about 1800 mm at least about 120 kW/m.
In addition, in order to guarantee a sufficient heat flow to the fibrous material web, the contact period of the cylinder with the fibrous material web should be at least about 50 ms, preferably a minimum of about 80 ms, and particularly a minimum of about 120 ms.
The present invention is directed to a heated cylinder for heating a fibrous material web in machines for one of producing and refining the fibrous material web. The heated cylinder includes a cylinder jacket having an outer jacket layer with good heat conductivity, a heat insulating layer positioned contiguous to and inside of the outer jacket layer, and at least one heating system positioned outside the cylinder jacket adapted to heat at least a surface of the cylinder.
In accordance with a feature of the present invention, the fibrous material can be one of a paper, a cardboard, and a tissue web.
According to another feature of the instant invention, the outer jacket layer can include metal. A stability of form and strength of the cylinder may be fundamentally determined by the outer jacket layer. The outer jacket layer can have a thickness of less than about 30 mm, and preferably less than about 5 mm. Further, greater than 80% of the shape stability and firmness of the cylinder can be determined by the outer jacket layer. Moreover, other materials, such as those utilized in standard dry cylinders, can be used for the outer jacket layer.
In accordance with another feature of the invention, the insulating layer fundamentally determines a stability of form and strength of the cylinder. The insulating layer may include a fiber-reinforced plastic (GFK or CFK). Further, the outer jacket layer has a thickness of less than about 5 mm, preferably less than about 1 mm, and, in particular, less than about 0.2 mm. Further, greater than 80% of the shape stability and firmness of the cylinder can be determined by the insulating layer.
According to still another feature of the instant invention, a supporting structure may be positioned contiguous to and inside the insulating layer. A stability of form and strength of the cylinder may be fundamentally determined by at least one of the insulating layer and the supporting structure. For example,
Oechsle Markus
Wegehaupt Frank
Wolf Robert
Dahbour Fadi H.
Walberg Teresa
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