Elastic roll and method of making the roll

Details Elastic roll and method of making the roll Elastic roll and method of making the roll

2001-09-17

2004-01-27

Vidovich, Gregory (Department: 3726)

Roll or roller

Concentric layered annulus

Fiber or wire reinforced

C492S059000, C029S895211, C029S895320

Reexamination Certificate

active

06682467

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 100 46 0550.0 filed on Sep. 18, 2000, the diclosure 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, in particular a roll for the smoothing of paper webs. The roll has a hard roll core made of, in particular, metal and is provided on its outside with an elastic covering layer which includes an elastic matrix material and fibers embedded into the matrix material. The invention is further directed to a method for the manufacture of such a roll.
2. Discussion of Background Information
Elastic rolls of this kind are used, for example, in the satining of paper webs. Here, 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 has a very smooth surface consisting, 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 order of magnitude of the rolls ranges from lengths of 3 m to 12 m and diameters from 450 to 1500 mm. They can withstand line forces of up to 600 N/mm and compressive stresses of up to 130 N/mm
2
.
To achieve a smoothing on both sides of the paper web, normally a plurality of roll pairs of this kind are successively disposed in a calender, with each of the two sides of the paper web alternately coming into contact now with the hard metal roll and now with the elastic roll in successive gaps. Since the surface of the elastic roll has a relatively high roughness with respect to the extremely smooth surface of the hard roll, the previously achieved smoothing result is at least partly again ruined in each case at the side of the paper web which is being guided over the elastic roll in the current smoothing gap.
A further problem lies in the fact that the required multi-roll calenders are expensive and the transport speed of the paper web is limited when multi-roll calenders are used. This is particularly disadvantageous since the trend in paper manufacturing is towards carrying out satining in an online operation. The paper web exiting the paper making machine or coating machine is here guided directly through the paper smoothing apparatus (e.g., a calender), whereby higher demands than previously are made on the rolls of the smoothing apparatus, particularly with respect to temperature resistance. 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, their nip frequency, that is the frequency with which the covering is compressed and relieved of its load again, is increased, which in turn leads to increased roll temperatures. These high temperatures arising in online operation result in problems which can even result in the destruction of the plastic coatings in known elastic rolls. On the one hand, with known plastic coatings, maximum temperature differences of around 20° C. are permissible over the width of the roll and, on the other hand, the plastics conventionally used for the coating have a substantially higher coefficient of thermal expansion than the conventionally used steel rolls or chilled cast-iron rolls so that high axial stresses occur between the steel roll or the chilled cast-iron roll and the plastic coating connected to it due to an increase in temperature.
So-called hot spots, at which a peeling or even a breaking open of the plastic layer occurs, can 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 are present in the form of, for example, defective adhesive bonds, deposits or above-average recesses in the elastic coating, for example due to creases or foreign bodies in the paper web. In these cases, the temperature at the crystallization spots can increase from the normal 80° C. to 90° C. to more than 150° C., whereby the above-mentioned destruction of the plastic layer occurs.
To control the properties of the elastic covering layer, fillers are normally introduced into the matrix material in the form of fibers or powder. Depending on the quantity and physical property of these fillers, the physical properties of the elastic covering layer are dominated or influenced by the fillers. For example, the thermal conductivity of the elastic covering layer can be improved by using fillers having a high thermal conductivity.
The smoothness of the surface of the covering layer is normally achieved by an appropriate grinding and polishing of the covering layer. Due to the size of the normally used fillers, however, only a listed smoothness of the surface of the covering layer can be achieved. For example, fibers previously used as a filler typically have diameters between 8 &mgr;m up to 20 &mgr;m. Since these fillers come to lie at the surface in the grinding of the surface, and exit this in part, the smoothness of the surface of known elastic rolls is substantially lower than the smoothness of the known hard rolls.
SUMMARY OF THE INVENTION
The present invention provides for an elastic roll of the kind initially mentioned, and a method for the manufacture of such a roll, with which the result in the smoothing procedure is further improved with respect to conventional elastic rolls and the risk of the occurrence of hot spots is reduced.
Starting from a roll of the kind initially mentioned, the invention provides that the diameter of the fibers is less than 800 nm so that the surface of the elastic covering layer has an extremely high smoothness, in particular an Ra value of less than around 0.6 &mgr;m, in that the thickness of the elastic covering layer amounts to between 3 and 20 mm and in that, in addition to the fibers, powdery fillers are embedded in the matrix material whose outer dimensions are in each case less than 1 &mgr;m at least in one direction.
A corresponding method is characterized in that, to produce an extremely high smoothness of the elastic covering layer, in particular an Ra value of less than around 0.6 &mgr;m, substantially only fibers are introduced into the elastic matrix material whose diameters are less than 800 nm, in that, in addition to the fibers, powdery fillers are introduced into the matrix material whose outer dimensions are in each case less than 1 &mgr;m at least in one direction and in that the elastic covering layer is formed with a thickness of between 3 and 20 mm.
In a roll of the invention, exclusively fibers and powdery fillers (both generally termed fillers in the following) having dimensions which are many times smaller than the dimensions of conventional fillers are thus used. A plurality of advantages are achieved thereby. On the one hand, the surface of the elastic covering layer including these extremely small fillers is substantially smoother than the surface of conventional elastic rolls after the grinding and polishing since the filler sections projecting out of the surface have correspondingly small dimensions.
On the other hand, due to the small dimensions of the fillers, a substantially finer distribution of the fillers within the covering layer is possible, whereby both a better thermal conductivity and a higher strength of the covering layer is achieved. The improved thermal conductivity results in the high temperatures occurring in operation, in particular at defective locations, being dissipated very quickly so that the occurrence of hot spots is largely prevented. The higher strength which is achieved by the better homogeneity of the covering layer material also here results in a reduction in the probability of hot spots occurring.
The improved thermal conductivity is reached

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