Roll or roller – With internal anchor for annular member
Reexamination Certificate
2000-06-22
2003-02-18
Vidovich, Gregory M. (Department: 3726)
Roll or roller
With internal anchor for annular member
C492S050000
Reexamination Certificate
active
06520896
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 28 753.8, filed on Jun. 23, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a roll of the type used for smoothing paper webs. The roll has a hard roll core which can be a metal and an outside surface utilizing an elastic covering layer. The covering layer may be an elastic matrix material. Furthermore, the invention is directed to a process for producing such a roll.
2. Discussion of Background Information
Elastic rolls of this kind are used, for example, in the satining of paper webs. In such cases, one elastic roll forms, in each case together with a hard roll, a press gap through which the paper web to be treated is guided. The hard roll typically has a very smooth surface made, for example, of steel or chilled cast iron and is responsible for the smoothing of that side of the paper web facing it. The elastic roll acting on the opposite side of the paper web effects a homogenizing and compacting of the paper web in the nip. The size of the rolls can typically range from lengths of approximately 3 to approximately 12 m and the diameters can vary from approximately 450 to approximately 1500 mm. Moreover, they can withstand line forces of up to approximately 600 N/mm and compressive stresses of up to approximately 130 N/mm
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As the trend in paper manufacturing is on performing satining in an online operation, i.e. towards guiding the paper web exiting a paper machine or coating machine directly through a paper smoothing apparatus (e.g., a calender), higher demands than were previously made are put on the rolls of the smoothing apparatus. This is particularly true with regard to temperature resistance. Further, as a result of the high transportation speeds of the paper web required in online operation and the high rotation speeds of the calender rolls associated with this design, its nip frequency, that is the frequency with which the covering is compressed and relieved of its load again, is increased. This in turn leads to increased roll temperatures. However, these higher temperatures which arise in online operations, lead to problems which can lead to the destruction of the plastic coatings in conventional elastic rolls.
On the one hand, conventional plastic coatings may withstand maximum temperature differences of around approximately 20° C. over the width of the roll. On the other hand, the plastics which are conventionally used for the coating have a substantially higher coefficient of thermal expansion than the conventionally used steel rolls or chilled cast-iron rolls. Accordingly, due to an increase in temperature, high axial stresses occur between the steel roll or the chilled cast-iron roll and the plastic coating associated with it. Additionally, so-called hot spots, at which a peeling or even a breaking open of the plastic layer occurs, often arise due to these high stresses in conjunction with hot regions occurring particularly in spot-form.
These hot spots occur, in particular, when in addition to the mechanical stresses and the relatively high temperature, crystallization spots exist in the form of, for example, defective adhesive bonds, deposits or above-average recesses in the elastic coating. These may be, for example, due to creases or foreign bodies on the paper web. In such cases, the temperature at the crystallization spots can increase from a normal temperature in the range of approximately 80° C. to approximately 90° C. to more than approximately 150° C. Accordingly, this can cause the above-mentioned destruction of the plastic layer to occur.
SUMMARY OF THE INVENTION
The present invention provides a process for producing a roll of the above mentioned type. Moreover, the invention is also directed to a corresponding roll. The roll of the invention is designed to withstand the formation or occurrence hot spots.
The invention is therefore directed to a roll which utilizes an elastic covering layer which is rotationally fixedly, but longitudinally displaceably arranged on the roll core. Moreover, the invention concerns a process of making a roll in which the elastic covering layer is applied to be longitudinally displaceable, but rotationally fixed to the roll core.
As a result of the elastic covering layer being arranged in accordance with the invention, i.e., longitudinally displaceably on the roll core, a situation is achieved in which none or very little longitudinal stresses occur between the roll core and the elastic covering layer. This will be the case even when the elastic roll-heats up, for example, such as when in operation.
This design allows the roll to heat up such that the elastic covering layer expands in an axial direction more than the roll core due to the higher coefficient of thermal expansion. However, the longitudinal displaceability of the covering layer, only leads to a relative movement occurring between the elastic covering layer and the roll core in an axial direction. In this design, either the two ends of the elastic covering layer can be axially displaced in opposite directions relative to the roll core or an asymmetrical longitudinal displacement of the elastic covering layer on the roll core can be allowed to occur. Depending on the different coefficients of thermal expansion and the temperatures which result, the relative displacement between the covering layer and the roll core can, for example, amount to around approximately 5 to approximately 50 mm, and commonly approximately 10 to approximately 20 mm.
In a roll designed in accordance with the invention, there is a stress-free connection between the elastic covering layer and the roll core. Accordingly, this design leads to a reduction in hot spots. Further, the risk of occurrence of a peeling of the covering layer from the roll core is significantly reduced and/or eliminated entirely.
By utilizing a rotationally fixed arrangement of the elastic covering layer on the roll core, it is ensured that, in operation, the covering layer is rotated securely together with the roll core as one unit. This ensures a uniform quality of the web of material which is to be smoothed.
According to one aspect of the invention, the elastic covering layer is disposed free from play on the roll core, in particular in force fit. A separation layer is preferably provided between the elastic covering layer and the roll core. This can, in particular, reduce the friction between the elastic covering layer and the roll core. This separation layer can advantageously include silicone and/or an essentially monomolecular layer and/or a corrosion- inhibiting or corrosion-preventing material.
As a result of the elastic covering layer being disposed free from play, e.g., in a force fit relationship, it is ensured that this layer lies positively over its whole circumference against the surface of the roll core. This is particularly important in a smoothing operation and when a relatively high mechanical load is placed on the covering layer. Any compression and/or crease formation in the covering layer, which can lead to a reduction in the quality of the treated material web, is thus prevented. Moreover, by utilizing a separation layer, for instance, the friction between the elastic covering layer and the roll core is reduced. Therefore, when the roll heats up, the desired longitudinal displacement can occur between the covering layer and the roll core.
However, it should be noted that the thinner the separation layer is designed here, the tighter the seating of the covering layer on the roll core. Moreover, due to the longitudinally displaceable support of the elastic covering layer on the roll core, it is generally possible for moisture to penetrate between the elastic covering layer and the roll core. This can allow for corrosion to arise on the metallic roll core. Accordingly, in an effort to prevent this, the separation layer can adva
Greenblum & Bernstein P.L.C.
Jimenez Marc
Voith Sulzer Papiertechnik Patent GmbH
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