Thermal translator device

Details Thermal translator device Thermal translator device

2000-05-16

2001-07-24

Simmons, David A. (Department: 1724)

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

C425S466000

Reissue Patent

active

RE037293

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to improved control of an extrusion apparatus lip gap.
As exemplified by U.S. Pat. Nos. 5,208,047 and 5,423,668, having Peter F. Cloeren as a common inventor, an extrusion apparatus having an adjustment assembly for thermal and mechanical, localized adjustment of lip gap, is known. In the '047 patent, a cartridge heater is removably disposed within a bore in a push rod which extends to operatively contact the flex lip thereof, and which is constructed of a thermally responsive material for expansion and contraction and thereby for thermal adjustment of the lip gap. Also described in the '047 patent is a temperature-responsive push rod with a resistance heater wire coiled around in direct heat transfer contact. In either case, the thermal output is adjusted in response to thickness measurement of the film or sheet passing through the lip gap.
As described in the '047 and '668 patents, a lip adjustment screw having an end bearing upon a push rod for mechanical adjustment of the lip gap, is likewise known. The lip adjustment screw may be in threaded engagement with a nut disposed in a shoulder recess. Variations using a differential thread, adjustment screw are also known, for instance, a differential thread, adjustment screw in axial alignment with a push rod, rather than offset from the push rod axis, with coarser pitch threads in engagement with a nut disposed in a shoulder recess and with finer pitch threads in engagement with the push rod. Alternatively, the finer pitch threads may be in engagement with a second nut.
Again with regard to thermal adjustment of the lip gap, the state of the art as further illustrated by U.S. Pat. Nos. 3,940,221 to Nissel, 4,454,084 to Smith et al, and 4,753,587 to Djordjevic et al, is a push rod of significantly greater length than the removably mounted, cartridge heater. As a result, the heating response of the push rod is dependent upon a substantially shorter heat source. The push rod functions as a translator to convert heat energy to mechanical force exerted upon the lip, by expansion and contraction.
In the Nissel device, the push rod passes through a thermal transfer block in which the cartridge heater is disposed. In the Smith structure and with particular reference to
FIG. 3
, a threaded push rod has an internally disposed cartridge heater, which by scale is about 70% of the push rod length. The Djordjevic device shown in
FIG. 1
is similar, and by scale, the internally disposed cartridge heater is about 50% of the push rod length.
Also commercially known is an extrusion apparatus having a cartridge heater/push rod combination in which the internally disposed, cartridge heater is about 60% of the push rod length. In this apparatus, the push rod does not operatively contact the die lip; instead, this push rod bears upon another push rod which does operatively contact the die lip.
With reference particularly to
FIG. 4
of Cloeren '047, the push rod structure corresponding thereto in commercial use, has a length of 6 inches and the cartridge heater has a length of 4 inches. In this device, the cartridge heater is about 66% of the push rod length.
The relatively greater length increases the structural mass of the push rod. In addition, whereas an exteriorly disposed, resistance heater wire as in
FIG. 3
of Cloeren '047, provides for direct heat transfer contact with a temperature-responsive push rod, a drawback with an interiorly disposed, removable cartridge heater is lack of efficient thermal energy transfer to the temperature-responsive push rod.
Therefore, there is a long felt need to improve the performance of a thermal energy translator having an interiorly disposed, thermal energy source. More particularly, there exists a need for a thermal energy source/translator combination having faster expansion response, improved heat transfer from the thermal energy source to the thermal energy translator, and a more beneficial balance between the length of the heat source and the length of the thermal energy translator. In addition, there is an over-arching need to improve energy efficiency in connection with thermal control of the lip gap.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide improved performance to an extrusion apparatus including thermal energy translators each having an interiorly located, heat source.
It is, in particular, a further object to provide faster expansion response.
It is a still further object to improve thermal energy efficiency in connection with thermal control of the lip gap.
Additional objects, advantages and novel features of the present invention are set forth in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following description or may be learned by practice of the invention.
In a typical prior art, cartridge heater, the outer sleeve or sheath is fabricated as thin as possible, nominally about 0.06 inches, so as to allow thermal transfer therethrough as quickly and efficiently as possible. As a result, a cartridge heater does not have the structural strength to be useful in an extrusion apparatus as a translator to convert heat energy to mechanical force. Moreover, the air gap between the interiorly disposed, removable cartridge heater and surrounding push rod structure, reduces thermal efficiency.
To achieve the foregoing objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is beneficially provided a thermal translator device which includes a thermal energy source disposed within a thermally responsive structure. As will become understood, the thermal energy source is inseparable from the integral to a thermally responsive structure effective for converting heat energy to mechanical force by expansion and contraction.
In an advantageous embodiment, the thermal translator device includes a thermal energy source swaged in a structural member or sleeve of appropriate mechanical integrity to provide the column strength necessary to serve as a thermal energy translator. In a preferred embodiment, the structural member consists of an inner tube and an outer member, and the outer member is swaged onto the inner tube so that the inner tube and outer member are inseparable from one another. Swaging beneficially produces an integral thermal translator assembly and eliminates air gaps interfering with heat conduction.
Typically, the thermal energy source is a resistance heater wire wrapped around an insulating core. It is highly preferred that this structure or like structures, and the translator are of substantially the same length. By “substantially the same length” is meant that the length is about 85% or more of the length of the thermal energy translator.
Also in accordance with the present invention and with reference to an individual assembly for localized gap adjustment, there is provided an extrusion apparatus including a lip forming an exit opening or slot which extends along the width of the apparatus, and including a flow passageway that terminates in the exit opening. Beneficially, the apparatus includes an assembly for thermally actuated, localized adjustment of the gap of the exit orifice, by localized action upon the lip. This assembly includes a plurality of spaced-apart, thermal energy sources operatively arranged and preferably independently controllable to provide localized adjustment. Beneficially, thermal translator devices in accordance with the present invention, are used for the localized action upon the lip.
In accordance with a preferred embodiment of the invention, localized action upon the lip, is provided by a lip adjustment member which operatively contacts the lip, a thermal translator device in accordance with the invention which bears upon the lip adjustment member, and a mechanical lip adjustment screw which bears upon the thermal translator.
In the drawing and detailed description of the invention that follow, there are show

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