Roll or roller – With antideflection means – Rotatable relative to supporting shaft
Patent
1993-03-12
1994-08-16
Cuda, Irene
Roll or roller
With antideflection means
Rotatable relative to supporting shaft
492 2, B30B 304
Patent
active
053382790
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a sag-compensation roll for treating a traveling web of paper, which roll includes a roll having a rotatable roll shell and a stationary yoke as well as at least one radially displaceable oblong pressure shoe for transmitting a pressing force from the roll shell to the yoke.
The pressure shoe has pressure pockets which are defined by surrounding ridge surfaces which fit the contour of the inner surface of the roll shell. By means of a flow of oil conducted into the pressure pockets a slot is produced between the shell and the ridge surfaces through which slot the oil discharges.
Rolls which, for instance, have a plurality of pressure shoes distributed over the width of the ridge (i.e. length of the roll) are already known, for instance, from Federal Republic of Germany 22 45 597 (U.S. Pat. No. 3,846,883). Other known rolls have only a few and, in the extreme case, only a single oblong pressure shoe which extends parallel to the axis of the roll, for instance as shown in U.S. Pat. No. 3,802,044 (FIGS. 6 and 7) or in Federal Republic of Germany 25 02 161 (GB 1506801). In the latter development, the pressure shoe which contains the pressure pockets is pressed by a piston, via an articulated strip, against the shell of the roll. The roll shell contains a long, relatively wide central pocket which is surrounded on both sides by narrow positioning pockets.
The positioning pockets are divided in the longitudinal direction into several sections by intermediate ridges. Into each of these sections there debouches a capillary which extends from the central pocket, and through which flows amounts of oil which determine the width of the slot between the ridges and the shell of the roll. The inner line force exerted on the roll shell is determined by the product of piston width times hydraulic pressure on the piston.
One disadvantage of such hydrostatic rolls as compared with the conventional S roll (in accordance with U.S. Pat. No. 3,196,520) or a roll with slide-bearing shoe (in accordance with U.S. Pat. No. 3,726,338) is that the pressure fluid (oil) continuously escapes through the capillaries and slots. In this way, more is required in order to convey the pressure oil which continuously flows out, since the power increases in proportion to the product of the hydraulic pump pressure times the delivery flow.
Another disadvantage, of the above described prior art constructions is the power that must be provided to overcome significant so-called shearing forces that build up, as rotational speed increases, in the oil that is within the region of the narrow slots between the roll shell and the ridges of the hydrostatic elements.
The prior art attempted to reduce power consumption (reactive power) by, for instance, selection of a less viscous oil and narrower slots. In this connection, the capillaries then become so small that they become clogged by sporadically occurring particles of dirt. Furthermore, the ridges are able to scrape against the roll shell.
For these reasons, it is has become customary, since introduction of the hydrostatic sag-compensation rolls about 20 years ago, to make the ridge widths large and the pressures high, with the use of an oil of high viscosity, for instance VG 150 or VG 220. In this way, it was possible to limit the amounts of oil in the case of sufficiently large capillaries and slot widths, but a relatively high internal friction had to be tolerated.
The main object of the present invention is to develop a hydrostatically operating sag-compensation roll that enables the reactive power (namely pump delivery power plus power loss by internal friction) to be a fraction of values that are customary today.
Further objects of the present invention are a simple, cost-saving design and a uniform temperature distribution over the width of the ridge. Furthermore, dependable operation of all parts is assured and, in particular, the hydrostatic elements function in all positions of installation relative to the direction of gravity.
It is also important that pressure
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Cuda Irene
J. M. Voith GmbH
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