Roll or roller – Concentric layered annulus – Fiber or wire reinforced
Reexamination Certificate
2001-01-16
2004-11-02
Jimenez, Marc (Department: 3726)
Roll or roller
Concentric layered annulus
Fiber or wire reinforced
C492S056000, C492S059000, C029S895100, C029S895320, C029S402090, C029S402210
Reexamination Certificate
active
06811524
ABSTRACT:
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 comprising an elastic matrix material. Furthermore, the invention is directed to a process for producing such a roll.
2. Discussion of Background Information
The present invention relates to rolls which may be used for the smoothing of paper webs. Such rolls typically have a hard roll core consisting of metal and being provided on the outside with an elastic covering layer comprising an elastic matrix material.
Elastic rolls of this kind are used, for example, in the satining of paper webs. In such cases, one elastic roll is arranged together with a hard roll in order to form a press gap or press nip through which the paper web to be treated is guided. The hard roll typically has a very smooth surface by virtue of it consisting, for example, of steel or chilled cast iron and this metal roll is responsible for the smoothing of the side of the paper web facing it. However, 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 order of magnitude of such rolls range from approximate lengths of 3 to 12 m and approximate diameters from 450 to 1500 mm. They can typically withstand line forces of up to approximately 600 N/mm and compressive stresses of up to approximately 130 N/mm
2
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A known problem with conventional elastic rolls relates to their susceptibility of so-called markings; these markings are impressions which occur or are formed on the outside of the covering layer. Such markings can arise, for example, when foreign bodies or folds in the paper web create indentations in the elastic roll cover, e.g., these are typically created when the web passes through the press nip with such folds or foreign bodies. Often, these markings are permanently formed in the surface of the covering layer so that they are transferred to the surface of the paper web which is guided through the nip. As a result, a paper web which runs through such a marked up nip may have a lower quality. Thus, it may be necessary to remove the markings in the roll covers, in order to improve the quality of the paper web.
In addition to these quality related problems, markings can also result in the destruction of the roll covering the layer itself. As the trend in paper manufacturing is towards performing the satining in an online operation, i.e. towards guiding the paper web exiting a paper machine or coating machine directly through the paper smoothing apparatus (e.g., a calender), correspondingly high transportation speeds of the paper web and high rotation speeds of the calender rolls associated therewith are typically required. As a result of these high web transportation speeds, the nip frequency, that is the frequency with which the covering is compressed and relieved of its load again, is increased. This, in turn, can lead to increased roll temperatures. Such increased temperatures can give rise to so-called hot spots which lead to peeling or even chipping of the covering layer. Moreover, the existence of very distinct markings in conjunction with the increased roll temperatures can aggravate and/or accelerate the problem of peeling or chipping.
Thermosetting plastics are nowadays usually used as the base material for the covering layer of elastic rolls. Thermosetting plastics have the advantage that they have a high elasticity up to their respective glass transition temperature Tg and are therefore well suited for the formation of the elastic covering layer. However, thermosetting plastics have the property that they can only be exposed to temperatures below the Tg value after a one-time heating into the range of the Tg temperature value and a subsequent hardening, since they are destroyed at temperatures above the Tg value after hardening.
Elastic rolls having a covering layer based on pure thermosetting plastics thus have the disadvantage that the covering layer is destroyed if its temperature is raised above the Tg value. Markings in the surface of the covering layer can only be removed from such rolls by, e.g., abrading the whole covering layer surface. The abrading of elastic rolls is, however, a very time-consuming mechanical process which requires special machines. Such processes therefore result in relatively long down times of a corresponding paper smoothing apparatus.
SUMMARY OF THE INVENTION
The present invention therefore provides an elastic roll in which markings in the surface of the covering layer can be repaired relatively easily. Accordingly, the roll may be repaired in a simple manner by heating the roll cover. Moreover, temperature increases into the range of the glass transition temperature of the matrix material should not result in the destruction of the cover layer. The invention also provides for a method for the manufacture and repair of such a roll.
The invention therefore provides for an elastic roll which is made of an elastic matrix material comprising a mixture of at least one thermosetting plastic and at least one thermoplastic. A method of making the roll is also provided in which the at least one thermosetting plastic and at least one thermoplastic are mixed with one another to form the elastic covering layer and the resulting mixture is applied to a roll core. Finally, the invention provides a method of repairing the roll, which is made of a mixture of at least one thermosetting plastic and at least one thermoplastic, by heating the roll until the surface is free of any surface markings. The roll may also be rotated in addition to being heated and thereafter smoothed.
In accordance with the invention, the advantages of the known thermosetting plastics, in particular their high elasticity, are thus combined with the advantage of thermoplastics, namely a repeatable melting capability. Thus, markings in a covering layer which are typically formed in the calendering process can be removed without resort to mechanical abrading. Accordingly, the markings can be removed by using a simple heating process, i.e., heating the matrix material above the melting temperature of the thermoplastic. An adequate surface quality of the repaired covering layer can also be achieved without additional rework, e.g., in particular when the roll is set into rotation during the heating process. In order to repair deeper markings, the surface of the cover may be subjected to a smoothing treatment which can be carried out, e.g., simultaneously during or after the heating.
According to one advantageous embodiment of the invention, the proportion of thermosetting plastic is made higher than the proportion of thermoplastic and is advantageously between approximately 50% and 80%, and may be in particular between approximately 60% and 75%, and preferably amounts to approximately 70%. In order to ensure that the elasticity of the covering layer is sufficiently high, the mixing ratio may be influenced, e.g., taking advantage of the fact that the thermosetting plastics usually have a higher elasticity than thermoplastics.
According to another embodiment of the invention, the mixture contains different thermosetting plastics and/or different thermoplastics. In this way, the desired physical properties of the covering layer can be set and/or influenced, e.g., by using different basic materials. For example, the overall heat transmission temperature of the thermosetting plastics can be set and/or controlled by mixing different thermosetting plastics, while the overall melting temperature of the thermoplastics can be set and/or controlled by mixing different thermoplastics.
The mixing ratio of thermosetting plastics and thermoplastics may advantageously be essentially constant over the axial length of the covering layer. Such a design can ensure that the physical properties of the covering layer, such as elasticity, temperature resistance and melting point, are uniform in an axial directi
Jimenez Marc
Voith Paper Patent GmbH
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