Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Control means responsive to product weight or dimension
Reexamination Certificate
1999-03-19
2001-08-14
Nguyen, Nam (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Control means responsive to product weight or dimension
C425S379100, C425S465000, C425S466000
Reexamination Certificate
active
06273701
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERAL SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to automatic extrusion die constructions, especially for forming generally flat sheet or cast film polymer webs. More specifically, the present invention relates to automatic extrusion die constructions in which a plurality of individual, selectively controllable pressure developing thrust elements is supported from one lip of the die at points spaced longitudinally therealong and with each thrust element operative to apply a variable amount of thrust to the corresponding lip area in order to flex that lip area toward and away from the other lip and thereby selectively narrow or widen the die lip opening for a more uniform extruded resin thickness.
2. Description of Related Art
Current technology for automatic extrusion dies involves the use of either threaded bolts turned by servomotors, or by the use of electric heaters in a heat actuated expandable cartridge assembly in order to mechanically manipulate the flexible lip of a sheet die to accomplish gauge control of polymers. The automatic die works in conjunction with a downstream gauge scanning mechanism which gives a feedback signal via a microprocessor to individually actuate bolts or heat expandable cartridges of the autodie. In order to reduce areas of high gauge, the corresponding servomotors turn down the threaded bolts or apply power to the heat expandable cartridges in order to mechanically close the lip of the die in the corresponding areas in question. In the areas of low gauge the servomotors retract the threaded bolt, or cut off electrical power to the heat expandable lip cartridge to relax mechanical pressure on the die lip and thus allow natural relaxation of the die lip in response to internal pressure of the polymer and the die.
The state of the current technology is indicated by the disclosures of the following patents. U.S. Pat. No. 3,901,636, to Stanley C. Zink et al. discloses a plastic film extrusion apparatus including two melt chambers heated to different temperatures. The two heated chambers are each used to heat the resin of the thermoplastic material extruded through that chamber and the specific temperatures to which the chambers are heated are maintained above and below the temperature of oxidation of the resin of the thermoplastic material extruded through the die. The use of two melt chambers at temperatures below and above the oxidation temperature of the resin allows two webs or films to be extruded from the die with the high temperature film sandwiched between the low temperature film and a substrate, trapping the odor of the high temperature film.
U.S. Pat. No. 4,781,562, to Takayosyhi Sano et al. discloses heat actuated thrust units operatively associated with a die lip. Each thrust unit functions to increase the width of the die slot when the heat actuated thrust unit is activated and to decrease the width of the die slot when the heat actuated thrust unit is deactivated.
U.S. Pat. No. 5,229,140, to Guenther Crass et al. discloses a lip die having mechanical thrust developing structures associated with a flexible lip and also an elongated bar extending longitudinally of the flexible lip including selectively operable heaters spaced along the bar, the bar being adjustably reciprocated along the flexible die lip to achieve uniform heating of the die lip.
U.S. Pat. No. 5,401,454, to Kilian K. Mendel discloses an extrusion die and flow control method incorporating a flow control in the form of a flow diverter which extends transversely across the flow path.
U.S. Pat. No. 5,423,668, to Peter F. Cloeren discloses a thermally controlled lip gap mechanism or adjustment incorporating continuous heating and heat sink sources in an attempt to more quickly adjust a die lip gap or slit as deviation in produced web thickness occurs downstream from the die.
Finally, U.S. Pat. No. 5,487,655, to Detlef Frey et al. discloses an apparatus for producing a spun fiber fleece which insures a highly uniform or homogenous distribution of the mechanical properties described in the web and which allows, in particular, the elimination of detrimental local inhomogeneities.
It is also known in blown film applications having circular dies to use heaters in the air ring which sits atop the blown film die. The air from the air ring is normally employed to cool the bubble of blown film as it is extruded and stretched. The heaters selectively apply heat to the air directed at areas of thicker film thickness as controlled by a down stream gauge scanner. The added heat allows the film to continue to stretch and become thinner than it would without the heated air applied in the thicker film areas.
SUMMARY OF THE INVENTION
The instant invention involves the use of a series of small electrical cartridge heaters preferably embedded in one lip of an extrusion lip die for the purpose of making fine tuned gauge adjustments to the thickness of molten polymers extruded from the die.
More particularly, the instant invention involves the use of the existing autodie technology along with the application of the series of small lower wattage cartridge (rod) heaters in a modified lip design of a flat sheet or cast film die. The current technology stops with the use of the two styles of mechanical lip manipulation described above in connection with the prior art. In accordance with the instant invention involving the provision of lip heaters, the heat is preferably applied directly to the die lip. In areas of low gauge, heat is applied to the lip via a feedback signal from the gauge scanner mechanism. The extra heat, a matter of a few degrees increase, allows some lateral flow of polymer into the hotter areas, as polymers follow the path of least resistance with the additional heat providing the reduction in resistance. The increased polymer flow also increases the die opening in the heated area and additionally increases the web thickness in the desired location.
This new design in accordance with the present invention preferably involves the use of two different wattage heaters, with higher wattage heaters preferably in line with the existing technology mechanical lip manipulation assemblies described earlier. These are commonly set up at one inch intervals. The second and lower wattage heaters are placed also at one inch intervals, but preferably situated on centers at the points halfway between each pair of adjacent higher wattage heaters. Each separate lip heater constitutes a separate control zone, just as each individual mechanical lip manipulation assembly does in existing autodies.
The benefits associated with using these additional lip mounted larger and smaller wattage heaters are multiple. While the prior art servomotor/bolt system has quicker response time than the prior art heater/expandable cartridge system, there are space limitations in some industrial applications where these systems are commonly used. For the heat-expandable cartridge system, the response time is relatively slower and more so on the adjustment where the lip opening/relaxation is required. While both of these existing systems yield good control results, they cannot achieve results which are attainable with the additional use of the lip mounted heaters of the instant invention.
The new heaters in the lip system of the present invention reduce response time as well as allow for a higher degree of point-to-point gauge variation control of the polymer sheet in extrusion. In areas of low gauge, the application of electrical power to the lip heater in line with the mechanical die lip manipulator assembly speeds the flow of polymer into the lip area in question to more quickly force the die lip open and at the same time build-up the low gauge area due to the lateral flow of polymer into the lower gauge area. The smaller wattage lip heaters located halfway between the larger wattage lip heaters allow for greater point-to-point gauge control by enha
Jacobson & Holman PLLC
Leyson Joseph
Nguyen Nam
LandOfFree
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