Heat exchange – Movable heating or cooling surface – Rotary drum
Reexamination Certificate
2000-12-01
2002-10-08
Bennett, Henry (Department: 3743)
Heat exchange
Movable heating or cooling surface
Rotary drum
C165S135000, C165S096000
Reexamination Certificate
active
06460611
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a roll for thermal and mechanical treatment of a web-shaped product, the roll comprising an elongatable thermal rim insulation.
It is regularly striven to construct heated or cooled rolls for thermal and mechanical treatment of web-shaped products so that the surface temperature is uniform over the full contact area. The shape of the roll is also required to remain as created at ambient temperature despite thermal expansion, this being the only way to also ensure that the pressure in the nip is uniform.
One particular problem in this respect is always the rim portion of the roll or, more precisely, the portion in which the web-shaped medium ends. It is here, for example, in heated rolls that the elevated reduction in heat by the web ends, and heat is given off to the environment only by convection and—usually negligible—radiation. Since this heat flow is significantly less than that in the web, the temperature increases in the surface portion of the roll having no web contact. Due to heat conduction beneath the surface of the roll, this increase in temperature usually extends also into the edge portion of the web, where it has a negative effect on the results of treatment.
This increase in temperature also involves thermal expansion of the roll diameter, resulting in a reduction in the nip in the edge portion of the paper web, where the specific pressure on the web increases and leads to a further negative effect on the results of treatment. If, in a paper calender, the web is overpressed at the ends in this way, the paper becomes thinner and loses its stiffness.
When the hot rim portion of a roll comes into contact with the companion roll, this may also result in damage if, for instance, the companion roll is coated with a temperature-sensitive flexible coating.
2. Description of Related Art
The measures proposed and also taken in attempting to solve the problems associated with rim heating are numerous. Correspondingly extensive is the prior art literature in this respect. For example, cited here is DE 31 40 425 regarding a roll having a shrink-fit positive displacer. It is intended that the heat flow be reduced from the heat transfer medium to the surface of the roll by an internal insulation. This reduces both the surface temperature and the expansion or so-called oxbow effect associated therewith in the rim portion.
In the case of rolls heated via a heat transfer medium flowing in axial-parallel conduits near to the surface of the rolls, rim insulation with higher heating performance has become prior art. In this case, the insulation is achieved by tubes or shells of an insulating material, such as, for example, Teflon, inserted in the edge portion of the conduits.
Since the expansion of the roll trunnion also affects the shape of the roll body in the rim portion, the insulation was also extended to the trunnion area of thermal treatment rolls, DE 35 18 808 C2 being an example of this. This requires, in general, that ovalization of the usually tubular roll body under linear pressure, the stiffening effect of the trunnion and the differing expansion coefficients of the materials, be carefully adapted to the measures taken in insulation.
Common to all of these means of optimization is that they can only be defined for a specific operating condition, i.e. as soon as the operating conditions such as, for example, the web width or the temperatures change, then the disadvantages cited at the outset reoccur more or less severely. Apart from this, taking into account all of the influencing factors involved is very difficult. Even after optimization there is often the need to adapt the dimensioning of the insulating measures as selected in design to the operating results as actually observed.
This is why there has been no lack of proposals to configure heating in the rim portion variable in order to also keep as much as possible to the optimum distribution of temperature and pressure given changes in the operating behavior.
Representative of this, a few proposals are cited from prior art in this respect.
Thus, it is proposed, for example, in DE 30 14 891 A1 to provide separate thermal treatment of the rim portions of heated rolls by means of separate heat transfer medium circuits. This idea presupposes the availability of rotary ducts having more than two connections when only one trunnion is available for the input and output of the heat transfer medium. As far as is known, no rotary ducts exist with the necessary cross-sections and the idea has never been put into actual practice.
In DE 43 43 172 C1, it is proposed for peripherally drilled thermal treatment rolls to provide several inputs for the heat transfer medium in the roll body, which intercept the peripheral drillings at various distances away from the rim. Using externally operable gate valves, the heat transfer medium can then be input and output at various distances away from the rim. However, such a variable rim heating was likewise never achieved, because weakening the highly loaded roll body in the rim portion by a plurality of communicating drillings is not without its problems.
In DE 31 40 425 A1, it is proposed, for a positive displacer roll, to employ an axially shiftable thermal insulating sleeve over a positioner guided outwards by means of a screw thread for thermally influencing the rim portion.
The same idea is to be found in DE 42 44 812 C2, however, for a peripherally drilled roll shell and, thus, applied to the insulating tubes used therein. As in DE 31 40 425, the intention is to provide external axial shifting of a sleeve of insulating material by rotating a positioner, guided externally, on which a screw thread is fitted.
However, to date, axially shiftable insulating sleeves—either in positive displacement rolls or in peripherally drilled rolls—have not entered practice.
The reason for this would seem to be the decisive sealing problem involved. Thus great care is taken to seal off the oil-guided portions from loss of the thermal oil in the case of modern thermal oil-heated rolls, in which the thermal oil is directed via distribution conduits in the trunnion flanges to the peripheral drillings. Such rolls are designed, more particularly, with double-acting sealing systems in which the oil needs to overcome two seals in sequence, before any leakage can occur. DE 42 44 812 C2 requires, for each side of each peripheral drilling, an additional sealed rotary duct to the exterior for the positioners.
Positioning the insulating sleeves in common at one side of the roll is not possible. Each sleeve needs to be moved individually. This is also the case in positioning the insulating ring on the positive displacer roll according to DE 31 40 425 A1, since a single adjusting screw would distort the ring.
Finally, there is no outward indication of the momentary positions of the individual axially shiftable insulating sleeves. It is thus easy to imagine that even minor negligence of the operating personnel and incomplete documentation of the positioning procedures may result in total disorientation as to the position of the sleeves, which can then only be established after having dismantled the roll trunnion.
Simply shifting the insulating sleeves is disadvantageous since a shift towards the middle of the roll exposes a non-insulated portion at the roll rim, resulting in the roll body being heated at a location where no heat is taken away.
Adjusting the thermal effect of the trunnion portion at the drive end of thermal treatment rolls is the subject matter of DE 195 13 500.8-12, Part of the heat transfer medium flow is directed through the central portion of the trunnion to enhance adapting the trunnion diameter to the changing operating temperatures via the heating in this portion, i.e. the shape of the roll in the rim portion is changed via the shape of the trunnion and not by the temperature of the roll body itself.
SUMMARY OF THE INVENTION
An object of the invention for a roll for thermal and mechanical treatment of a web-shaped product, c
Bennett Henry
McKinnon Terrell
RatnerPrestia
Schwäbische Hüttenwerke GmbH
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