Roll or roller – Concentric layered annulus – Fiber or wire reinforced
Reexamination Certificate
2000-04-28
2002-08-06
Cuda-Rosenbaum, I (Department: 3726)
Roll or roller
Concentric layered annulus
Fiber or wire reinforced
C492S053000, C492S056000, C492S049000
Reexamination Certificate
active
06428455
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 199 19 569 2, filed on Apr. 29, 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 a resilient covering layer. The covering layer may be a resilient matrix material with fibers embedded in the matrix material. Furthermore, the invention is directed to a process for producing such a roll.
2. Discussion of Background Information
Resilient rolls of this type are typically used, for example, in the calendering of paper webs. Such calenders often use an elastic roll together with a hard roll in forming a press nip. The paper web is calendered by feeding it through one or more of these nips. The hard rolls generally have a very smooth surface and are made of, for example, steel or hard cast iron. They function in smoothing that side of the paper web which faces it. Resilient rolls which act on the opposite side of the paper web have the effect of evening and compacting the paper web in the press nip. The resilience of this second or opposite roll in the nip acts to limit intensive compaction of the paper web, which would lead to a specky appearance of the paper web. Such rolls are generally large and typically have lengths of from 3 to 12 meters and diameters from 450 to 1500 mm. Moreover, they are designed to withstand line forces up to 600 N/mm and compressive stresses up to 130 N/mm
2
.
The tendency in paper manufacture is for calendering to be carried out on-line, that is to say the paper web leaving the papermaking machine or coating machine is led immediately through the paper smoothing device (calender). This design places high requirements or demands on the rolls of the calender or smoothing device. In particular, this design subjects the rolls to higher temperatures so that they are require to have temperature resistance. The high transport speeds of the paper web, necessitated by on-line operation, and the associated high rotational speeds of the calender rolls increase the alternating flexure frequency of the rolls. It is these factors which in turn leads to increased roll temperatures.
These high temperatures which are produced in on-line operation lead to problems which, in the case of conventional resilient rolls, can lead to the destruction of the synthetic covering. Such conventional synthetic coverings can function only with a maximum temperature differences of about 20° C. over the width of the roll. Moreover, the polymers normally used for the roll coating have a significantly higher coefficient of thermal expansion than the steel rolls or hard cast rolls normally used. Thus, when there is an increase in the temperature of the rolls, high axial stresses occur between the steel roll or hard cast roll and the synthetic coating which is connected to it.
Moreover, such rolls also experience high stresses in localized regions of the roll due to these regions being heated more so than surrounding areas. Such hot spots in the synthetic coating can cause the synthetic layer to separate or burst from the metal roll.
These hot spots can occur when, in addition to the mechanical stresses and the relatively high temperatures experienced by the rolls, there are crystallization points in the form, for example, of faulty adhesive bonds between the layer and the metal. Additionally, deposits or above-avenge bulges in the resilient covering which result from creases or foreign bodies on the paper web can produce these hot spots or crystallization points. In these cases, the temperature of these crystallization points often rises from normally 80° C. to 90° C. to more than 150° C., which results in the aforementioned destruction of the synthetic layer.
In order to control the characteristics of the resilient covering layer, powered fillers and/or fibers may be introduced into the matrix material. Depending on the quantity as well as the physical characteristics of these fillers and/or the fibers, the physical characteristics of the resilient covering layer may be positively influenced by the fillers or the fibers.
The invention recognizes an effect which is normally undesired in calendering, referred to as black calendering, which is used for the production of transparent paper. In this production process, rolls with covering layers of higher stiffness are typically used, so that the fibers of the paper web introduced into the press nip collapse due to the increased pressure. This increased pressure accordingly produces the desired transparency.
Moreover, it is true that a general increase in the stiffness of the covering layer increases the probability of the uniform application of pressure in the press nip and that this can produce the desired transparency. However, the same general increase in the stiffness of the covering layer can also result in a reduction in the quality of the transparent paper.
SUMMARY OF THE INVENTION
The present invention therefore provides a process for producing a resilient roll of the aformentioned type. Moreover, the invention is also directed to a corresponding roll. Additionally, the roll of the invention is designed to withstand the formation or occurrence of hot spots. Further, the roll should be suitable for the production of high-quality transparent paper.
According to the invention, the roll utilizes at least some fillers which are formed as elongated, and in particular rod-like particles. Moreover, it is preferred that the length of the particles are less than the radial thickness of the resilient covering layer. A corresponding process according to the invention utilizes at least one filler in the form of elongated, and in particular rod-like particles, which are introduced into the resilient matrix material. Again, it is preferred that their length is less than the radial thickness of the resilient covering layer.
Both the thermal conductivity and the stiffness of the resilient covering layer can be improved by utilizing the elongated particles which are introduced into the matrix material. Because of the increased thermal conductivity, the excessive heat which typically occurs at critical points, can be dissipated more rapidly. As a result, even when parts of the covering experience critical temperatures, the occurrence of hot spots can be prevented. In this regard, in particular, the elongated formation of the particles is advantageous for rapid dissipation of heat from the critical points. Moreover, these may be, for example, in the direction of the roll core.
The elongated form of the particles also provides an advantage when those particles are aligned essentially in the radial direction, since this acts to increase the stiffness of the resilient covering layer at certain points. As a result of utilizing the elongated particles, the resilient covering layer will have a large number of points of increased stiffness.
By tailoring the covering design to the specific requirement of the paper, the transparent paper can be produced more efficiently with an appropriately equipped roll.
Moreover, by utilizing a length of the particles which is less than the radial thickness of the resilient covering layer, the elongated particles will not extend from the surface of the covering layer. Additionally, the resilient covering will take advantage of the regions between individual particles which are free of the particles, so that a certain resilience of the covering layer is maintained. As a result, the quality of the transparent paper produced can be increased when compared to completely rigid coating.
Likewise, in the axial direction of the roll, between point-like rigid points, there may be resilient regions which are essentially free of the fillers, so that given a uniform distribution of the elongated particles both in the radial and in the axial directi
Cuda-Rosenbaum I
Greenblum & Bernstein P.L.C.
Voith Sulzer Papiertechnik Patent GmbH
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