Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2000-03-17
2001-06-12
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S404000, C425S066000, C425S140000
Reexamination Certificate
active
06246028
ABSTRACT:
The invention relates to a device for heating a blown film web, inflated into a blown film bubble between a pair of forward draw rolls and a pair of take off rolls. The device comprises a frame mounted, driven pair of forward draw rolls for a flat lying blown film web, comprises an opposite, stationarily mounted, driven pair of take off rolls, which are intended for the collapsed blown film web hauled off the inflated bubble, and upstream of which are collapsing mechanisms, preferably wedge shaped collapsing boards; comprises mechanisms for inflating the blown film web between the pairs of forward draw and take off rolls into a bubble and for refilling blowing air; and comprises a device for heating the inflated blown film web.
It is known to inflate a plastic blown film web, produced in the blown film process and wound into a roll, into a bubble by blowing up again and then to stretch by heating in order to achieve other properties or to improve strength values. In so doing, the heating is conducted at temperatures that are necessary to achieve the desired modified film properties. Preferably the inflated blown film web is heated in the area of its inflow into the bubble up to approximately its heat deformation temperature (glass transition temperature). The blown film web, pulled in by the pair of forward draw rolls, is blown up using injection needles. In this process the injection needles can be arranged so as to travel along or rotate in order to maintain the air pressure in the blown film bubble. The blown film web can also be inflated by evaporating the liquids.
A device of the aforementioned type is disclosed, for example, in the DE 198 44 434.6. In this prior art device the web of plastic film that is inflated into a tube is heated by frame mounted heating rings with infrared radiators, which enclose concentricly the tube of film.
However, one special problem associated with the devices ofthe aforementioned type lies in the fact that webs of plastic film that are inflated into tubes of film and that exhibit varying diameters are to be stretched again by inflating into a bubble. However, the requisite amount of energy to be delivered to the inflated tube can be supplied only with difficulty if the diameters ofthe heating rings are not adapted to the diameters of the film tube that is to be stretched again.
Therefore, the object of the invention is to provide a device of the aforementioned type, wherein the necessary amount of heat for inflating the blown film web into a bubble can be fed as desired with the heating device even if the diameter of the tube to be inflated varies.
The invention solves this problem in that the heating device comprises heating elements, which are arranged concentricly around the axis of the inflated blown film web and which can be moved toward and away from the blown film web by means of regulating drives in the radial direction.
In the device according to the invention the correct amount of heat for inflating into a bubble can be fed in a purposeful manner to the blown film web to be inflated into a tube in that the individual heating elements always exhibit the correct or desired radial distance from the blown film web.
Preferably the regulating drives move all of the heating elements simultaneously in the radial direction. To move the individual heating elements, servomotors can be provided that are controlled by a controller.
A preferred embodiment provides that the regulating drives comprise parallel cores, which are mounted stationarily on the frame and whose inner coupling members bear the heating elements, and that the coupling members are provided with slide bolts for the purpose of moving said coupling members radially. Said slide bolts are guided in oblong slots of an adjusting element, which lies parallel to the coupling member. To move the adjusting elements radially, there are spindle drives. The spindle drives can be driven over bevel gears by means a driven revolving chain.
Preferably the heating elements, which are mounted stationarily on the frame, are arranged between heating elements, moved to the largest diameter. This design accounts for the circumstance that the distance between the heating elements decreases in the circumferential direction when they are moved radially inwardly.
It is expedient that the heating elements be infrared radiators.
A preferred embodiment of the invention provides that the oblong heating elements are slanted relative to the axis of the blown film web. This design ensures that all of the film sectors sweep over the heating elements, whereby, seen in the axial direction, the end regions of the inclined heating elements can overlap advantageously.
Another embodiment of the invention provides a distance meter, which scans the diameter of the blown film web and whose signals are fed to a controller, which controls the regulating motor or motors for moving the heating elements to the desired distance. This design guarantees that in the device according to the invention two for stretching the blown film web of varying diameter adjust the heating elements always automaticly to the correct radial distance relative to the inflated tube.
Another preferred embodiment provides a device, measuring the density distribution of the wall thickness over the circumference of the blown film web or the collapsed film tube hauled off the bubble, and a regulator, which controls the amount of heating energy, fed to the respective heating elements in proportion to the deviation of the measured film thickness from the average film thickness (desired value). According to this design, the heating device feeds in the circumferential direction varying amounts of heat to the individual film sectors. Differential heating of a film tube over its circumference to compensate for the fluctuations in thickness is known and hence does not need to be described here in detail.
Another embodiment provides a device, measuring the thickness distribution of the wall thickness over the circumference of the blown film bubble or the collapsed film tube hauled off the bubble, and a regulator, which controls in such a maimer the regulating motors, assigned to the individual heating elements, that a proportionally greater or smaller amount of heat is fed to the respective film sectors. According to this design, the varying amounts of heat are not fed by radiating larger or smaller amounts of heat from the heating elements, but by suitably increasing or decreasing the radial distance between the heating elements and the wall of the film tube.
REFERENCES:
patent: 3904342 (1975-09-01), Sato et al.
patent: 4201741 (1980-05-01), Pannenbecker
patent: 4212908 (1980-07-01), Hendy et al.
patent: 4443399 (1984-04-01), Takashige et al.
patent: 5891480 (1999-04-01), Schmidt et al.
patent: 38 02 146 (1989-02-01), None
patent: 19816119 (1999-10-01), None
patent: 198 44 434 (2000-06-01), None
patent: 2 736 861 (1997-01-01), None
patent: 3-90332 (1991-04-01), None
patent: 6-106620 (1994-04-01), None
Jacobson Price Holman & Stern PLLC
Pelham Joseph
Windm{overscore (o)}ller & Hölscher
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