Presses – Methods – Forcing through constricted passage
Reexamination Certificate
2000-06-02
2003-12-30
Ostrager, Allen (Department: 3725)
Presses
Methods
Forcing through constricted passage
C100S16300R, C100S169000, C492S048000, C492S054000
Reexamination Certificate
active
06668711
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 199 25 420.6, filed on Jun. 2, 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 roller, which is especially useful for smoothing paper webs. The roller has a hard roller core formed of metal and an outer side having an elastic coating layer formed of an elastic matrix material. The present invention also relates to a method for producing such a roller.
2. Discussion of Background Information
Elastic rollers are used in glazing paper webs. For this purpose, one elastic roller and one hard roller together form a pressing nip through which a paper web to be processed is guided. The hard roller has a very smooth surface made of, for example, steel or chilled iron and smooths the side of the paper web facing it. The elastic roller acting on the opposite side of the paper web increases uniformity and effects compression of the paper web in the pressing nip. The length of each roller is within the range of about 3 to about 12 meters and the diameter of each roll is within the range of about 450 to about 1500 mm. The rollers are able to withstand linear forces of up to about 600 N/mm and compressive strain of up to about 130 N/mm
2
.
The trend in paper manufacture is to perform the glazing in online operation, i.e., the paper web leaving the paper machine or the coating machine is directly guided through the paper smoothing device (calender). The rollers of the smoothing device require higher temperature resistance than the prior art rollers, e.g., due to increased roller temperatures resulting from a number of factors, such as high transport speeds of the paper web required for online operation, resulting high rotation speeds of the calender rollers, and increased nip frequency, i.e., the frequency with which the coating is compressed and released again. The high temperatures resulting from online operation may cause problems, such as the destruction of the plastic coating in prior art elastic rollers. On the one hand, prior art plastic coatings have acceptable maximum temperature differentials of approximately 20° C. over the width of the rollers. On the other hand, the plastic materials conventionally used for the coating have a substantially higher thermal expansion coefficient than the conventionally employed steel rollers or chilled iron rollers. This is undesirable because a temperature increase causes high axial stress between the steel roller or the chilled iron roller and the plastic coating connected therewith.
These high stresses together with especially localized heat points within the plastic coating may result in so-called hot spots, which may be located where a detachment or even a rupture of the plastic layer will occur.
In addition to mechanical stresses and relatively high temperatures causing hot spots, hot spots may also occur especially when crystallization points are present. Crystallization points may result from faulty adhesive connections or deposits, or from above average indentations of the elastic coating which may be caused by folds or foreign bodies on the paper web. As a consequence, the temperature at these crystallization points may increase from a conventional range of between about 80° C. and 90° C. to about 150° C., thereby resulting in the aforementioned destruction of the plastic layer.
DE-A-4126232 discloses a roller whose elastic coating layer is provided with an additional metal coating. The metallic cover layer increases the thermal conductivity at the outer side of the roller so that undesirable heat occurring within the pressing nip may be quickly dissipated, thereby keeping substantially constant the temperature during treatment of the material web.
The metallic cover layer, however, has a disadvantage, when disturbance locations occur within the pressing nip which disturbance locations may be caused by contaminations within the material web, or by foreign bodies entering the pressing nip or folds within the material web. The disturbance locations may also be caused by impressions or depressions created in the metallic cover layer, which impressions or depressions may possibly be irreversible. These depressions represent disturbance locations in the highly polished surface of the elastic roller and result in markings, which are irregularities in the surface of the smoothed material web.
SUMMARY OF THE INVENTION
The present invention provides an elastic roller which has good thermal conductivity at least at its surface and which prevents the risk of the occurrence of markings. The present invention also provides for a method for producing such a roller.
The present invention further relates to an elastic roller whose outer side of matrix material is coated with a memory metal. The present invention,relates to a method for applying at least one layer of a memory metal to the coating layer, i.e., onto the outer side of the matrix material.
Employing a memory metal as a cover layer of the elastic coating layer results in the depressions of the cover layer, which occur at disturbance locations during operation, being reversible, i.e., a self-healing of the surface of the elastic roller is realized. Memory metal, which is also referred to as shape memory alloy, has the property upon heating to a certain temperature to take on a predetermined shape memorized in the metal. The present invention makes it possible to produce the cover layer of memory metal such that the cover layer takes on its predefined, concentric shape with extremely smooth surface over its entire extension at the temperatures occurring during the smoothing operation. When a disturbance, such as a foreign body, a contamination of the paper web or a fold in the paper web, causes a depression in the cover layer, the cover layer, after removal of the disturbance, again takes on its original shape. Thus, the depression in the surface of the cover layer disappears automatically after the disturbance location has passed through and the surface of the elastic roller is again optimally smooth because of the memory effect.
The temperature at which the shape memory alloy again takes on its original shape may be selected to be higher than the operating temperature in the pressing nip. Thus, depressions occurring during operation within the cover layer are not automatically repaired during the on-going operation, but rather are repaired after shutdown of the on-going operation. After shut-down, the temperature of the cover layer may be increased to the required temperature, without removing the roller from the smoothing device, to affect the repair of the cover layer.
The metallic cover layer also provides very good thermal conductivity in the outer side of the elastic roller, thereby quickly dissipating to the exterior undesirable heat occurring within the pressing nip. This ensures that the temperature during the treatment of the material web in the pressing nip may be kept substantially constant.
According to another embodiment of the present invention, the memory metal layer may be composed of a nickel-titanium alloy. In principle, any other shape memory alloy is suitable for the manufacture of the cover layer as long as the alloy provides the desired smoothness of the surface of the elastic roller. Advantageously, the temperature at which the shape memory alloy takes on its original shape may be below the operating temperature in the pressing nip in order to allow the mentioned automatic self-healing.
In accordance with a preferred embodiment of the present invention, the memory metal layer may have a radial thickness of between approximately 2 &mgr;m and 30 &mgr;m, and preferably between approximately 5 &mgr;m and 10 &mgr;m. The indicated thickness values ensure that the roller has the required elasticity for the smoothing process despite the cover layer being formed of metal.
According to another preferred embodiment of
Greenblum & Bernstein P.L.C.
Ostrager Allen
Self Shelley
Voith Sulzer Papiertechnik Patent GmbH
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