Unwinding apparatus for webs of material, in particular plastic

Winding – tensioning – or guiding – Coil holder or support – Spool or core

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226 97, 226197, 242 76, B65H 1720, B65H 2318, B65H 2332, B65H 5900

Patent

active

044614322

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION



Technical Field of the Invention

The invention relates to an unwinding apparatus for webs of material, in particular plastics films, having an unwinding shaft which is driven by a motor-generator, a direction-changing guide means, the interior of which is under an increased pressure and feeds an air cushion, and a driven direction-changing roller.


State of the Art

Plastics films are wound up in a more or less hot condition in a manufacturing plant, following a stretching section or the like. However, after the winding operation, ageing phenomena, shrinkage phenomena, crystallisation phenomena and the like still occur, and result in the length of the film being reduced. So that the wound coil of plastics film does not suffer due to those phenomena, which in general have the effect of causing shrinkage of the film, the film must be wound in a very loose winding so as to permit shrinkage of the plastics film. When loose rolls of this kind are stored, they suffer from the formation of out-of-roundness and other deformation phenomena. The winding becomes non-round and hangs down in what may be referred to as a belly below the coil.
When a coil which has been deformed in this manner is unwound in a processing installation, so-called pulsation phenomena occur, which result in abrupt changes in the tension of the web or the winding run. Such pulsation phenomena make the subsequent processing operation more difficult, in particular the operation of longitudinally cutting the web and the following operation of winding it up. In particular, the speed of operating on the web is detrimentally affected by the pulsation effects.
Attempts to overcome such pulsation phenomena by adapting the speed of rotation of the unwinding operation thereto have been found to be useless because, with the high mass of the coil to be unwound, it is technically not possible for the speed of unwinding rotation to be adaptively adjusted on a short-period basis. In this respect, account should be taken of the fact that the width of a coil may be several meters.
U.S. Pat. No. 2,945,637 discloses a direction-changing guide means wherein the web of material floats on an air cushion. This arrangement seeks to provide virtually inertia-less compensation of pulsation phenomena in a strip tension regulating means of a paper processing machine, wherein the motor generator which is connected to the unwinding roll is regulated by the increased pressure in the interior of the direction-changing guide means, which pressure produces the air cushion. The web of material is turned through about 90.degree. and guided around a non-driven guide roller.
Tests have shown that, when unwinding plastics films, it is not sufficient for the films to be passed around the guide means over an angle of only 90.degree. in order totally to compensate for possible out-of-roundness in the coil being unwound. It has also been found that a guide roller which is undriven and around which the film only passes over an angle of 90.degree. is not sufficient for isolating the residual pulsation effect from the subsequent processing section of the plant.
Controlling the unwinding operation using the increased pressure for feeding the air cushion, as described in U.S. Pat. No. 2,945,637 has also not proved to be a success in regard to plastics films. The reason for this is that, in order to produce a uniform air cushion pressure, there must be a high pressure loss at the air outlet openings between the direction-changing guide means and the air cushion, so that the feed pressure is not representative in respect of the pressure in the air cushion.


SUMMARY OF THE INVENTION

The object of the present invention is to design an unwinding apparatus such that pulsation phenomena are completely eliminated even when unwinding sensitive or delicate plastics films from a loose roll.
This object is achieved by the combination of the following features:
(a) the angle over which the web of material is passed around the direction-changing guide means is greater than 140.degree.;

REFERENCES:
patent: 2754883 (1956-07-01), Secrest
patent: 2945637 (1960-07-01), Derrick et al.
patent: 3057574 (1962-10-01), Justus
patent: 3156399 (1964-11-01), Wadey
patent: 3312415 (1967-04-01), Jeans
patent: 3455192 (1969-07-01), Moore et al.
patent: 3567093 (1971-03-01), Johnson
patent: 4182472 (1980-01-01), Peekna
patent: 4342413 (1982-08-01), Reba

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