Source: http://www.google.com/patents/US4105386?dq=6,788,314
Timestamp: 2015-05-06 22:07:47
Document Index: 78182422

Matched Legal Cases: ['art.\n32', 'art.\n35', 'art 116', 'art 117', 'art 117', 'art 116']

Patent US4105386 - Apparatus for the manufacture of thin-walled shaped articles of ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsThin-walled articles of thermoplastic material are formed in a continuous apparatus starting with heating and extruding granular thermoplastic raw material in the form of a continuous web which is immediately stabilized by rapid cooling of its opposite surfaces and the stabilized web wherein the material...http://www.google.com/patents/US4105386?utm_source=gb-gplus-sharePatent US4105386 - Apparatus for the manufacture of thin-walled shaped articles of thermoplastic materialAdvanced Patent SearchPublication numberUS4105386 APublication typeGrantApplication numberUS 05/717,751Publication dateAug 8, 1978Filing dateAug 25, 1976Priority dateOct 19, 1973Publication number05717751, 717751, US 4105386 A, US 4105386A, US-A-4105386, US4105386 A, US4105386AInventorsAlfons W. Thiel, Hans HellOriginal AssigneeBellaplast GmbhExport CitationBiBTeX, EndNote, RefManPatent Citations (9), Referenced by (36), Classifications (37) External Links: USPTO, USPTO Assignment, EspacenetApparatus for the manufacture of thin-walled shaped articles of thermoplastic material
US 4105386 AAbstract
Thin-walled articles of thermoplastic material are formed in a continuous apparatus starting with heating and extruding granular thermoplastic raw material in the form of a continuous web which is immediately stabilized by rapid cooling of its opposite surfaces and the stabilized web wherein the material sandwiched between the precooled outer surface layers remains at or near extrusion temperature is fed into a thermal forming station wherein shaping tools form the articles in the web without the need for further heating of the web. Adjustments are provided for correlating the cooling action to different materials and web feed rates, for varying the web feed rates and increments, and for varying the shaping tool movements to adapt for different materials and sizes of articles. After the formed articles are separated from the web the web residue is fed back to be mixed with incoming raw material at the extrusion station.
1. Apparatus for manufacturing thin-walled articles comprising means including extrusion means for forming a continuous hot plastic web of thermoplastic material, means for continuously advancing said web, means defining a stabilization station through which said web passes and wherein opposite surfaces of said moving web are cooled to provide supportive outer layers therealong, means defining a thermal forming station positioned for receiving said stabilised web and wherein successive areas of said web are subjected to shaping tool operation for forming articles of desired shape in the web, means intermediate said stabilization and thermal forming stations for converting continuous motion of said web into intermittent motion for disposing successive web areas for a predetermined time at said thermal forming station, means providing a dwell station for equalizing the surface temperature conditions of said web within said successive web areas before said respective web areas are disposed at said thermal forming station and means for actuating said web moving means and the shaping tools at said thermal forming station in synchronism and in such correlation with the temperature of said web at extrusion and the speed of advance of the web that the stabilized web arrives at said thermal forming station while it retains sufficient heat for achievement of thermal forming when operated upon by said shaping tools.
2. The apparatus defined in claim 1, wherein said extrusion means comprises means for heating granular or other particulate raw thermoplastic material to extrusion temperature and discharging it through a web defining nozzle.
3. The apparatus defined in claim 2, wherein means is provided for separating the formed articles from said web, and means is provided for returning the residue of the web back to said extrusion means for admixture in predetermined proportion with said raw material.
4. Apparatus as defined in claim 1, wherein a motor driven mechanism unit is provided as a common source of power for web movement and tool operation, said mechanism having a continuously driven system connected to effect continuous advance of the web, an intermittently driven system for effecting intermittent movement of the web and a cam-controlled lever system for effecting tool operation.
5. Apparatus as defined in claim 1, comprising adjustable means for varying the continuous and intermittent feed movements of said web and adjustable means for varying the movements of said shaping tools, all of said adjustable means being correlated to the size and shape of the articles to be formed at said thermal forming station.
6. Apparatus as defined in claim 1, wherein said stabilization station includes at least two relatively rotatable cooling rollers in peripheral area contact with opposite sides of said web, said rollers being relatively adjustable for similarly varying their contact areas with said web.
7. The apparatus defined in claim 1, wherein said motion converting means includes relatively movable loop forming roller means over which said web passes, the web being continuously fed into said loop at one side and periodically withdrawn from said loop at the other side.
8. The apparatus defined in claim 1, wherein a temperature compensation station is provided intermediate said motion converting means and said thermal forming station for providing uniform temperature distribution over said successive web surface areas before they move into said thermal forming station.
9. Apparatus as defined in claim 1, wherein said thermal forming station comprises at least one tool support mounted for reciprocable movement, and said actuating means for the thermal forming means comprises a pivoted lift lever operably connected to said tool support, and motor driven cam mechanism connected to rock said lift lever to effect tool movement, and means for damping operational movements of said tool support.
10. Apparatus as defined in claim 9, comprising a second tool support mounted for reciprocable movement in cooperation with the first tool support, and two lift rods pivotally connected to said lift lever, each of said lift rods being pivotally connected to a respective tool support.
11. Apparatus as defined in claim 10, wherein said tool supports are arranged one above the other, and means is provided whereby the lift rod for the upper tool support may be selectively pivotally connected to said lift lever either eccentrically or concentrically of the pivot of said lift lever.
12. Apparatus for manufacturing thin-walled articles comprising means including extrusion means for forming a continuous hot plastic web of thermoplastic material, means for continuously advancing said web, means defining a stabilization station through which said web passes and wherein opposite surfaces of said moving web are cooled to provide supportive outer layers therealong, said stabilization station comprising a stabilizing and cooling device directly receiving the web coming from said extrusion means, and said device comprising cooling members adapted for gripping opposite sides of the web in heat-conducting contact and connected to means for varying the cooling temperature, means defining a thermal forming station positioned for receiving said stabilized web and wherein successive areas of said web are subjected to shaping tool operation for forming articles of desired shape in the web, means for feeding and guiding the web to be shaped in its longitudinal direction through the thermal forming station, means providing an arrangement of tools to act on the web in the thermal forming station wherein at least one of the tools is opposite the web and guided for movement substantially at right angles to the web surface, and means mounted at the thermal forming station for separating the shaped articles from the web, one part of the separation means being movably associated with the tool and a second cooperating part of the separation means being mounted at the side of said web guiding means opposite said first part, means intermediate said stabilization and thermal forming stations for converting continuous motion of said web into intermittent motion for disposing successive web areas for a predetermined time at said thermal forming station, and means for actuating said web moving means and the shaping tools at said thermal forming station in synchronism and in such correlation with the temperature of said web at extrusion and the speed of advance of the web that the stabilized web arrives at said thermal forming station while it retains sufficient heat for achievement of thermal forming when operated upon by said shaping tools.
13. Apparatus as defined in claim 12, characterized in that the thermal forming station is provided with a tool support pivotably mounted for movement about a axis and carrying two or more forming tools, means is provided for moving said support to different angular positions in each of which a tool is opposite the web to be shaped.
14. Apparatus as defined in claim 13, characterized in that the part of the separation means associated with the tool is a plate having a recess, the tool having a rim around a forming cavity inserted with play into this recess and the peripheral edge of this recess forming a separation edge cooperating with the second part of the separation means.
15. Apparatus as defined in claim 14, characterized in that said tool penetrating said recess is as long as the thickness of the separation device part, and in that the tool under the influence of the second part of the separation means abutting against it may be moved axially into the die support against the action of return means.
16. Apparatus as defined in claim 13, characterized in that the die support is moved to and fro with respect to a frame system carrying the vertical web supply and means is provided to control such motion.
17. Apparatus as defined in claim 16, characterized in that the part of the separation means associated with the tool is mounted to be displaceable against the action of return means through the die support toward the frame system, while the second part of the separation device is essentially rigidly mounted on the frame system.
18. Apparatus as defined in claim 17, characterized in that the part of the separation device associated with the tool also has a clamping frame part on the side adjacent the web guide and in that a second clamping frame part is provided in the form of a plate mounted on the opposite side of the web guide which latter is displaceable and guided along the frame system by the first clamping frame part acting against spring means.
19. Apparatus as defined in claim 13, characterized in that the die support is pivoted on the frame system on a fixed horizontal axis and the web guide and the parts of the separation device are horizontally movably mounted.
20. Apparatus as defined in claim 13, characterized in that at least one article forming element mounted in the tool is of the cavity type.
21. Apparatus as defined in claim 12, characterized in that a cooled stabilizing and conveying system is provided for the intermittent feeding of the web to the forming station, said system being adapted to engage substantially only those web parts not to be thermally shaped.
22. Apparatus as defined in claim 20, characterized in that the web is vertically downwardly fed and in that the stabilizing and conveying system contains a compensating roller and a cooled gripper system moving up and down, wherein the latter is so constructed with respect to the thermal forming system as to only touch those areas which later will remain in the residual web after separation of the formed articles.
23. Apparatus as defined in claim 22, characterized in that the gripper system and the compensating roller are controlled for synchronous up-and-down motions, the upward motion taking place, at least as regards the compensating roller, continuously as a function of the continuously incoming web and the downward motion being intermittent and synchronized with the thermal forming operation.
24. Apparatus as defined in claim 13, characterized in that the die support is provided with a drive system effecting its discrete rotation and synchronously controlled together with the stabilizing and conveying device, and also provided with an ejection device for removing the shaped articles which is also synchronously controlled with the stabilizing and conveying device, in order to eject the shaped articles from the particular tool at a position remote from the web.
25. Apparatus as defined in claim 24, characterized in that a removal device for the residual web is operably connected to the drive system of the die support.
26. Apparatus as defined in claim 12, characterized in that a central control is provided for the relative to-and-fro motion of the die support and the web guiding and separating means, for the to-and-fro motion of the forming tools, for the article ejector system and for the motion of the stabilizing and cooling system.
27. Apparatus as defined in claim 12, characterized in that the stabilizing and cooling system is provided with a plurality of tempering rollers mounted in close alternating sequence on opposite sides of the web and in the path of motion of the hot thermoplastic web coming from the extrusion means, at least one tempering roller being transverse to the path of the web and being adjustable with respect to that path.
28. Apparatus as defined in claim 12, characterized in that a material reduction device is mounted at the outlet of the thermal shaping station receiving the residual web after separation of the formed articles.
29. Apparatus as defined in claim 12, characterized in that the stabilizing and cooling device and the devices that act on the web thereafter are combined into a unit which is mounted for adjustment as an entirety with respect to the position of the extrusion means in the direction of advance of the web.
30. In the apparatus defined in claim 12, said one part of the separation means being spaced and thereby thermally insulated from said tool except when the tool is acting on said web.
31. Apparatus for manufacturing thin-walled articles comprising means for producing a continuous hot plastic web of thermoplastic material, means defining a thermal forming station adapted for receiving said hot web and wherein successive areas of said web are subjected to a shaping tool operation for forming articles of desired shape in the web, means for intermittently advancing said hot web in its longitudinal direction through said thermal forming station for disposing successive web areas for a predetermined time at said thermal forming station, forming tools in said thermal forming station disposed on opposite sides of the web for acting on the web to shape articles therein during web dwell periods, a tool support in said thermal forming station pivotally mounted for movement about a horizontal axis, means for moving said support to different angular positions in each of which a tool is opposite the web to be shaped, means whereby said tool support is moved to-and-fro with respect to a frame system carrying the web and means whereby to control such motion, and means mounted in the thermal forming station for separating the shaped articles from the web, one part of said separation means being associated with a tool at one side of the web and a second cooperating part of the separation means mounted at the side of the web opposite said first part.
32. Apparatus as defined in claim 31, characterized in that the part of the separation means associated with the tool is mounted to be displaceable against the action of return means through the tool support toward the frame system, while the second part of the separation means is essentially rigidly mounted on the frame system.
33. Apparatus as defined in claim 32 characterized in that the part of the separation means associated with the tool also has a clamping frame part adjacent to the web guide and in that a second clamping frame part is provided in the form of a member mounted on the opposite side of the web guide, which latter is displaceable and guided along the frame system by the first clamping frame part acting against spring means.
34. Apparatus for manufacturing thin-walled articles comprising means for producing a continuous hot plastic web of thermoplastic material, means defining a thermal forming station adapted for receiving said hot web and wherein successive areas of said web are subjected to a shaping tool operation for forming articles of desired shape in the web, means providing a dwell station for equalizing the surface temperature conditions of said web within said successive web areas before said respective web areas are disposed at said thermal station, means for intermittently advancing said web in its longitudinal direction through said thermal forming station for disposing successive web areas for a predetermined time at said thermal forming station, forming tools in said thermal forming station disposed on opposite sides of the web for acting on the web to shape articles therein during web dwell periods, and means mounted in the thermal forming station for separating the shaped articles from the web, one part of said separation means being movably associated with a tool at one side of the web and a second cooperating part of the separation means mounted at the side of the web opposite said first part.
35. Apparatus as defined in claim 34, characterized in that the part of the separation means associated with the tool is a member having a recess, the tool having a rim around a forming cavity adapted to be inserted with play into this recess and the peripheral edge of this recess forming a separation edge cooperating with the second part of the separation means.
36. Apparatus as defined in claim 35, characterized in that said tool rim for insertion into said recess is substantially as long as the thickness of the separation part, and in that the tool under the influence of the second part of the separation means abutting against it may be moved axially into a tool support against the action of a return means.
37. Apparatus for manufacturing thin-wall articles comprising means including extrusion means for forming a continuous hot plastic web of thermoplastic material, means for continuously advancing said web, means defining a stablization station through which said web passes for stabilizing said web at its opposite surfaces, means defining a thermal forming station positioned for receiving said stabilized web and wherein successive areas of said web are subjected to shaping tool operation for forming articles of desired shape in the web, said apparatus further comprising:(a) in said stabilization station a stabilizing and cooling device, directly receiving the web coming from said extrusion means, said device comprising cooling members, adapted for engaging opposite sides of the web in heat-conducting contact and connected to means for varying the cooling temperature; (b) means intermediate said stabilization and thermal forming stations for converting continuous motion of said web into intermittent motion for disposing successive web areas for a predetermined time at said thermal forming station and for feeding and guiding the web to be shaped in its longitudinal direction through the thermal forming station; (c) means providing a dwell station adapted to equalize the surface temperature of said web within each successive web area before said respective web area is disposed at said thermal forming station; (d) an arrangement of the tools in the thermal forming station wherein at least one tool to act on the web is opposite the web and guided for movement substantially perpendicularly with respect to the web surface; and (e) means mounted at the thermal forming station for separating the shaped articles from the web, one part of the separation means being associated with a tool, and a second cooperating part of the separation means being mounted at the side of said web guiding means opposite said first part. Description
This is a continuation-in-part of copending application Ser. No. 408,083 filed Oct. 19, 1973 for Method and Apparatus for Forming Thin-Walled Articles From Thermoplastic Material, now abandoned.
It is a major object of the invention to provide novel apparatus for manufacturing articles from thermoplastic material wherein an extruded hot plastic web is immediately stabilized by being cooled along its opposite surfaces to provide along those surfaces shell or supportive outer layers that are warm and soft enough to be deformable by subsequent shaping die action while the thermoplastic material internally of those layers remains sufficiently hot to retain plasticity and be capable of redistribution between the outer layers during die action.
Another object of the invention is to provide novel apparatus for the manufacture of articles from thermoplastic material, wherein the material is compressed and heated in an extruder to liquefaction and is cast into a hot plastic web (or several hot plastic web components may be cast and superposed to form a composite web) and the web immediately upon leaving the extruder nozzle or nozzles will be stabilized while still in the hot plastic state by being so cooled at both surfaces that the thermoplastic material at those surfaces will form supportive layers that are deformable even though stable, while the material interiorly of those layers essentially remains at the extrusion temperature and in the fluid or plastic state, and then subjecting the web so stabilized to a thermal forming operation.
Another object of the invention is to provide in the foregoing novel apparatus providing an additional sequence between surface cooling of the web and shaping the web, whereby the temperature at the web surfaces is made uniform over section of the web to be subjected to shaping in a subsequent operation. Pursuant to this object novel apparatus is contemplated wherein the surface temperature distribution over the web section may be accomplished by reflectors proportionately reflecting heat radiated from the hot plastic web, and/or heated air circulation systems effective at the web surfaces.
Another object of the invention is to form a composite web from thermoplastic materials, the material at the surface or surfaces being a polyolefin, for example polypropylene or polyethylene, while the material at the core will be a polystyrene or a polystyrene reacted with butadiene-rubber. An appreciably more marked surface sheen may be achieved in this manner, with improved relief shaping and considerably increased water vapor sealing in the formed articles.
A further object of the invention is to form a composite web from thermoplastic materials, the material being a polycarbonate at the surfaces and a standard polystyrene, or one modified with an impact-proof butadiene-rubber, at the core. Formed articles may be economically made in such manner that will remain rigid, temperature-resistant and glossy to a temperature range of 130�-135� C.
It is a further main object of the invention to provide apparatus for the manufacture of thin-walled thermoplastically shaped articles comprising in sequence an extrusion device suited to receive granular thermoplastic material and to continuously compress and heat same until liquefaction and a web-spraying mold as in the form of a fish-tail nozzle connected to the extrusion device and provided with temperature regulators, a stabilizing and cooling device directly receiving the web from the nozzle and having cooling elements contacting directly both sides of the web and conducting heat away and preferably connected to regulators adjusting the applied cooling temperature, a thermal forming device to shape articles from the web by deep-drawing or stamping and devices for cutting the articles from the web. By means of this equipment, molded articles may be line-produced, preferably from granular synthetics, this equipment being marked by reliable, rapid operation because the hot plastic web will be immediately stabilized in the cooling device to an extent sufficient for further processing without losing appreciable amounts of the heat stored in it, so that the stored heat of extrusion suffices entirely for the thermal forming process and no auxiliary or extra heating equipment may be needed.
(a) changing the length of the heat exchange contact between web surfaces and cooling elements of the stabilizing and cooling device, for instance by altering the looping angle of the web around one or more cooling rollers;
(b) changing temperature in the cooling medium in the stabilizing and cooling device; and
(c) changing the frequency of operation of the thormal forming device.
If one wishes avoiding altering tho weights of the manufactured articles on account of changes in the frequency of operation of the thermal shaping device, one must simultaneously undertake an alteration in the output of the extrusion device and the web-spraying mold. The foregoing controls should be automatically introduced in the sequence by means of the regulation device if each preceding measure no longer should suffice.
A further important object of the invention consists in creating apparatus of the above indicated kind, wherein the web at the shaping temperature will be precooled prior to thermal shaping outside the areas which are to be formed into the shaped articles in order to strengthen the residual material areas surrounding the shaped articles and eliminate the necessity for unduly long cooling periods. This is of special significance if the wall thickness of the shaped articles is appreciably less than the thickness of the web. For example, within the scope of the invention, it is feasible to thermally form in a web about 2.5mm thick shaped articles which are only 0.5 to 0.6mm in wall thickness.
The cooling time required for the solidification of the material being a quadratic function of the material's thickness, solidification of residual material that has remained at its initial thickness and temperature would require a cooling time about twenty times greater than the thinner shaped areas of the web. Even though it may not be absolutely indispensable that the residual material surrounding the areas of the shaped articles be completely cooled and solidified, a certain degree of cooling and solidification may be required in order to reliably convey the web with the shaped articles to the next treating station, for a stamping station. By precooling those web parts which are not to be formed, the time required for minimal cooling and solidification of the non-shaped parts of the web will be better related to the times required for cooling the shaped articles. Precooling also allows appreciably better control of the shrinking effects occuring in the residual material.
It is a further object of the invention to provide at least one cooperating pair of precooling device and counterprecooling device, which pair(s) comprise(s) cooperating related positive and negative shaping components in order to impart a framelike bracing structure into the web during precooling.
A further object of the invention lies in providing a novel In-Line process and a novel apparatus of the kind described above for the continuous manufacture of thin-walled shaped articles from thermoplastic materials, where
(a) the stabilized web at the shaping temperature is passed through the thermal forming station in essentially vertical motion and where the shaped articles are formed out of the web in an essentially horizontal direction; and
(b) where the shaped articles simultaneously or within the same stage as thermal forming are separated from the web and may be further cooled even after this separation.
Thereby is created a novel feasibility of forming and processing relatively thick plastic webs, for example exceeding 3mm in thickness, by means of the above In-Line process. The shaping and working of such thick webs in the In-Line process offers the feasibility of manufacturing articles with depth dimensions much in excess of the diameters of the apertures or of other opening dimensions. The very thick webs shaped in the In-Line process however are especially soft and delicate and therefore prior to the invention could not be worked in ordinary thermal forming processes and machines, especially if the web had to be advanced horizontally. Nor was it possible prior to the invention to adequately solidify the areas of residual material surrounding the shaped articles for such thick webs during the In-Line process, so that the web with its shaped articles therein could be reliably conveyed to a further treating station. Nor was this possible in the absence of precooling the web in those areas which were not to be shaped. The vertical conveying of the web through the thermal shaping station and the cutting-out of the shaped articles all in one stage with thermal shaping, as well as post-cooling of the shaped articles, has provided now possibilities for the forming and working of very thick webs in the In-Line process.
A further object of the invention lies in providing a thermal forming apparatus having a die support that may swing about a horizontal axis, such support holding two or more dies or multiple dies, rotational positions of the die support being provided for in each of which a die or a multiple die will be opposite the web to be shaped. This rotating die support allows leaving the shaped article after thermal forming proper in the die for a certain time and acts to cool it even further by contact with the die surfaces.
FIG. 3 is a diagrammatic view showing the method and apparatus in an embodiment incorporating three sources of thermoplastic material producing a composite laminat.d web;
The web is then advanced to and subjected to thermal shaping at the thermal shaping station 6 where a mechanically acting stretching element may be applied to one web surface to urge the other precooled web surface against a shaping tool surface where it is further cooled. Alternatively the web at least temporarily may be subjected at the shaping station to compressed air at one of the precooled surfaces and thereby have its other surface pressed against the shaping tool surface where it is further cooled.
The web is now fed into stamping station 7. Following stamping-out of the shaped articles at station 7, the residual web is brought to a receiving station 8 provided with a suitable device 81 for reducing the web material into granular form, so that this residual material may be fed back and recycled through a metering device 82 to mix with the fresh material at extrusion device 1 in a predetermined ratio.
A composite web II so manufactured may evidence properties at one or both precooled outer surfaces which are different from those at the hot plastic core. For example, where two different kinds of material are laminated, the first material may be a standard polystyrene, and tho other material may be an impact resistant plastic such as a butadiene-rubber modified polystyrene. The composite web may also include outer layers of the impact resistant plastic on both surfaces of a standard polystyrene web, the precooled surface layers being formed on the outer webs while the materials internally of those layers all remain substantially at extrusion temperatures.
(a) their forming temperature range in the crystalline melting point range is narrow;
(b) they must be shaped at high forming temperatures;
(c) both, but especially polypropylene, may not be heated without air support in conventional thermal shaping because the foils will strongly sag shortly above the crystalline melting point which will cause marked, interfering folds in the die;
(d) they require very even temperature distribution over the shaping surface (due to danger of crystalline residues and making folds).
The invention takes the foregoing into consideration and enables maintaining the temperature very evenly and sufficiently high for very small and controlled cooling, especially at the temperature compensation dwell station. There is no need to fear premature cooling of the web because the inner layer, whether of standard polystyrene or the impact-resistant polystyrene, will steadily and uniformly release heat to the outer polyolefin or other layer or layers. There is no tendency toward sagging of the composite web because the hot internal layer of the first material will not tend to sag even if the layer is subjected to the temperature required for shaping the outer polyolefin layer or layers (ca. 170� C = 340� F). Parts shaped from a composite web II with a polypropylene outer layer or layers are particularly shape retaining at higher temperatures.
One may further achieve a composite web II where the outer surface thermoplastic material is a polycarbonate and the core material a standard polystyrene or an impact-resistant, butadiene-rubber modified polystyrene. Shaped articles may be made in this manner which will maintain their shapes up to temperature ranges of 130� to 135� C (266�-275� F), and will be weather-resistant, of high gloss and nevertheless economical.
As the polycarbonate foils are per se highly hygroscopic, the longer such foils are kept sandwiched, the larger the danger of bubble formation during thermal forming and the danger of reduced mechanical strength. The bubble formation, which is also determined by thermal decay, increases with foil temperature. However, the invention allows the processing of composite polycarbonate foils of the foregoing type without being subjected to these drawbacks, because:
(a) there is no sandwiching of the web; and
(b) polycarbonates may be thermally shaped at relatively low temperatures, mainly because the internal or carrier layer may be thermally shaped because of the retained heat of extrusion.
An important feature of the invention is that the plastic web after having left the extrusion nozzle is not only precooled but it is rapidly and uniformly chilled at both its surfaces. Such chilling means that in the relatively thin outer surface regions along the web the temperature of the material is rapidly and suddenly decreased below the lower limit of the formability temperature range. When the thermoplastic material is so cooled it exhibits more or less steady transition regions between the outer thin solidified elastic layers and the still hot fluent liquid core. The various temperature identifiable conditions present in the web in the invention are illustrated in FIGS. 4A and 4B where:
Curve B1 of FIG. 4A shows the temperature gradient in a plasticized web which had been extruded in a conventional method and is thermoformed directly. In such extruding and direct thermoforming the extrusion temperature is controlled to be as low as possible in order that the extruded web can be manipulated to be transported to the thermoforming means. In such methods (known by German Auslegeschrift No. 1,165,241 and Shelby U.S. Pat. No. 2,891,980) the web temperatures are as low as possible during extrusion so that the web may be immediately fed to the former.
Curve B2 of FIG. 4A shows the temperature gradient in a plasticized web made by extrusion similar to that discussed above in connection with curve B1, but after the web has been precooled as it has already been proposed by Crenshaw U.S. patent No. 3,354,693. Such precooling causes the temperature at the inner regions of the web to decrease substantially due to heat transport during the precooling time. After the material attains a temperature gradient as shown by curve B2 shaping is only possible if the web is not deeply formed, but for deep-drawing or other deep thermoforming the material must be cooled so much that the article wall would be stretched at an intolerable rate.
Curve C of FIG. 4A shows the temperature gradient in a plasticized web which in accord with the present invention has been prepared for thermoforming. Such a web has been stabilized by chilling over its entire opposite surfaces directly after it has been extruded from the nozzle. Such chilling results in two outer stiffened supporting surface layers or shells and a very warm web core. As chilling involves a very rapid temperature decrease at the web surfaces there is no time for heat transport from the inner core region to the outer surface regions of the web during the chilling step. For this reason the surface layers or shells are relatively thin.
The surface temperatures during forming are relatively low and the temperature differences with respect to the cool die surfaces at the shaping station are advantageously low. This eliminates to a great extent the danger of setting up stresses in the final product. The two outer supportive surfaces undergo stretching in the shaping process and are connected to each other by the relatively fluid elastic core that remains heated extremely close to the melting point or extrusion temperature, so that each of these surfaces may be differently shaped so as to correspond with a desired end product. A very uniform material distribution is thus obtained, with no voids or weakened regions, the attainment of which has always presented a serious problem in previous processes using thermal forming.
FIG. 4B shows curve C in comparison with some temperature gradient curves which could be realized during the several steps of the method according to the present invention. Curve C2 shows the temperature gradient in the plastic web when leaving the extrusion nozzle. In the invention this extrusion temperature is much higher, for example 50� C higher, than the normal extrusion temperature for such material such as is used in the Crenshaw patent process for example. As may be seen from FIG. 4B the extrusion temperature is very close to the upper limit of the extrusion temperature range γ in which the extruded material is in a fluid condition, whereas in the upper temperature stage ∫ beyond the above mentioned limit the material would be so fluid and liquid that it merely would drop down when leaving the extrusion nozzle and would not be able to hold together and support itself as a web. Immediately after leaving the extrusion nozzle the web is stabilized by being chilled at both its surfaces by contact with cool heat transferring surfaces. By such chilling a desirable temperature gradient across the web may be realized as shown in curve C1.
During transportation of the web from the chilling station 3 to the thermoforming station 6, heat balancing distribution will occur in the web. This means that some heat is transferred by conduction from the hot core c to the cooled surface layers l. This heat transfer results in the web attaining the condition of curve C in FIG. 4B, wherein the outer surfaces layers have been reheated to a temperature in the range β and are in elastic plastic condition. The outer surface layers l built up by the material in the somewhat elastic plasticized condition and within the temperature range β may become progressively thicker as illustrated in FIG. 4C and such built up material will become reheated by heat derived from the core to a temperature preferably substantially at the lower limit of the temperature range β. Due to such reheating the surface layers may be readily thermoformed with development of molecular orientation as pointed out above. The foregoing reheating step takes place mainly at the dwell station 5 in FIGS. 1-3.
FIG. 8 shows a control apparatus at station 4 for the purpose of converting continuous web advance into step-wise advance. The compensating roller 41 shown here preferably is controlled by means of the illustrated belt or chain drive, sprocket wheels being mounted at the front side of compensating roller 41 and at the front sides of fixed axis guide rollers 42 and 43. The sprocket at 42 is continuously driven. The sprocket at 43 is intermittently driven at a frequency corresponding to the dwell time needed for the operations at the succeeding temperature compensation, thermal shaping and cutout stations. Compensating roller 41 is suitable guided for free movement vertically as indicated by the double arrow 44. The compensating roller 41 may be so controlled as by suitable biasing springs (not shown) that the web will be fed substantially free of tension. It must be arranged in this respect that output of the thermal forming device 6 and that of the extrusion device will be so correlated that the compensating roller 41 never reaches one or the other possible vertical terminal positions even during long time operation. It may happen that rapid and intermittent motion past the dwell station 5 into the thermal shaper at 6 will cause high accelerations. The weight of the web must be added to these effects, and the limit may be set by the inherent weight of the web, so that it may not be subjected to stretching when rapid step-wise motion occurs. To prevent this from happening, compensating roller 41 is employed, and expecially when dealing with thin webs, it will preferably operate from top to bottom, because the momentary acceleration during motion is near in value to the acceleration of free fall (g = 9.81 m/sec2), so that the weight of the web and the forces of acceleration will compensate, and for exact compensation, the web will be more or less in free if controlled fall. The compensating roller 41 and the guide rollers 42 and 43 in every case preferably are as nearly as possible thermally neutral, that is, they may neither heat nor cool the web. This is preferably achieved by using a very thin sheet metal roller at 41 with an insulator covering such as felt or another textile that will very rapidly reach a certain temperature and thereafter neither withdraw nor impart heat from and to the web.
In operation with a section of web disposed between reflector members 5' as illustrated in FIG. 9 it will be appreciated that the amount of heat per unit area radiated from the web at region 51 is greater than that radiated per unit area at region 52, for the reason that region 52 is more distant from the extrusion device and hence has had time to cool down more than region 51. By providing smaller heat reflective areas 5a opposite the warmer web portions and gradually compensatively increasing those areas in size toward the cooler web portions, the web surfaces between the reflector members are raised to uniform temperatures over their entire areas. The same effect may be produced by making reflection areas 5a of increasingly greater heat reflective value, instead of increased sized, from left to right in FIG. 9.
A further embodiment of dwell station 5 is shown in FIG. 12. Depending on the characteristics and properties of the thermoplastic web, certain materials may require an air circulation chamber keeping the plastic web at a constant temperature. This applies particularly to polymers for which thermal shaping must take place in an extremely critical temperature processing range. It is known for example that modified polystyrene allows a temperature range of �10� C (18� F) within which the product will not be affected. This temperature range is still more narrow for polyolefins and polycarbonates, so that the above disclosed reflector arrangements may not suffice. The station 5 circulation chamber is not meant to increase temperature overall but rather to maintain a desired temperature by compensatively distributing the warm air over the web surfaces between regions 51 and 52. The web surface temperature distribution will be the most uniform if the circulating air is made to move in a direction opposite to the advance of the web as shown by the arrows in FIG. 12. There may be one fan 54 and one heater 55 for each of the upper and lower parts of chamber 5d to set circulation at the required degree.
Various possibilities are diagrammatically shown in FIGS. 13 and 14 for thermal shaping at station 6. A negative die is shown in FIG. 13, working together with a stretching element 61 which is coated at the web engaging surface with a heat-insulating, porous layer, for example a felt layer 63. Element 61 is provided with an inlet bore 60 and branching bore holes 64 adapted to be connected to supply compressed air which will be finely distributed by the felt covering 63. The interior of the negative die 62 is provided at the other side of the web with evacuation bores 65 allowing timed application of vacuum. The design and the operation of such shaping devices are known per se. However, as shown in FIG. 13, in the invention the outer layers Ia of the web are like shells holding between them the hot fluid plastic core Ib. When compressed air is supplied through bore 60 and vacuum is connected to bores 65 the felt layer 63 and the cooled metal inner cavity surface of the die negative 62 contact the opposed shell like surfaces of the web to form the article shape. This action causes distribution of the external mechanical forces in the plastic core Ib, which in turn enhances internal distribution of the plastic between the shells when the web is pressed against the inner surface of die 62 under the combined influence of the vacuum from bore 65 and pressure from bore 64.
Lever 102 is pivoted on fixed axis at 120, and is pivotally connected at 113 to one end of a link rod 110. The other end of rod 110 is pivotally connected at 114 to one end of a lifter lever 109 pivoted intermediate its ends on a fixed axis shaft 121. The other end of lever 109 is pivotally connected at 122 to the lower end of a lift rod 111, and the upper end of rod 111 is pivotally connected at 123 to the lower die support 105. Lift rod 112 is operated from shaft 121 and pivotally connected to die support 106 at 125, in the manner shown in FIG. 18.
FIG. 15 shows the drive means used in connection with the present invention for a thermal shaping machine 157 following a plastic web extruder 156. A thermal shaping machine of this type is disclosed in Thiel patent No. 3,836,309 issued September 17, 1974. A cooling and stabilizing device 158 is connected to the plastic extruder, comprising an idle counterpressure roller 161 functioning together with the first cooling roller 159 to pass the extruded web. The second cooling roller 160, as shown by double arrow 162, may be adjusted with respect to roller 159, in order to vary the looping angle of the web around both cooling rollers 159 and 160 as in FIG. 6. Roller 159 is continuously driven from the continuously rotation sprocket wheel 104 of the cam and gear unit 101, as by the chain drive connection 163, 164.
A motion converter 165 similar to that of FIG. 8 is connected to follow the cooling and stabilizing device 158 and comprises an upward moving compensating roller 166. Compensating roller 166 is held in a continuous chain arrangement 167 on its input side facing the spray-casting device 156, that chain being driven from the continuously running chain linkage 163. On the output side facing the thermal shaping machine 157, compensating roller 166 moves in an intermittently operating chain arrangement 168 which is driven in turn through drive 169 connected to intermittently operating chain 151 of advance device 152. Because of the continuous drive of the chain arrangement 167, the compensating roller will be steadily lifted in accordance with the supply of the continuously moving web, as long as the intermittently operable advance device 152 is stationary. When the thermal shaping machine 157 operational sequence actuates the web advance device 152, the second chain arrangement 168 of the compensating roller will also start running and this causes the compensating roller to be lowered in proportion to the web section to be supplied to the thermal shaping machine 157. The total web advance is the same for both kinds of motion. This is ensured by design of the drive devices of the cam and gear unit connected to sprocket wheels 103 and 104.
The location of cam follower rollers 118 and 119 and the contours of cam disks 116 and 117 are so determined with respect to one another that the cam follower rollers will always be in contact with the peripheral surfaces of the respective cam disks during operation. When roller 118 enters a radially recessed part 116a of its cam 116, roller 119 will be in contact with a radially projecting part 117a of its cam 117. Roller 119 proceeds inversely on a radially recessed part 117b of its cam 117 when roller 118 runs on a radially projecting part 116b of its cam 116. In operation the movements of lever 102 under cam control are transmitted through eccentric pin 113 to link rod 110 which in turn acts through eccentric pivot 114 to rock lifter 109 and actuate the die supports. Cam 115 is continuously rotated by the electrical motor, while the vertical motion of die supports 105 and 106 is solely determined by the peripheral shape of cam disks 116 and 117. Operational synchronism of die supports 105 and 106 may be varied by a continuously adjustable speed reducer inserted between the motor and cam 115, or by changing the motor speed.
The lift range may be continuously adjusted between minimum and maximum. By selecting the eccentric magnitudes with respect to the minimum values for the lever arms X and Y, the range of the lift adjustment may be determined. In a current machine, a lift adjustment in the ratio of 1:1-1/2 minimum: maximum is used.
To achieve self-locking performance of the dies, shaft 121, pivots 122 and 123 of lift rod 111, and pivots 124 and 125 indicated in FIG. 17 should be in a single, preferably vertical, plane in the closed position of the dies as shown in FIG. 16. To achieve this, link rod 110 is adjustable in length, so that for any adjusted position of eccentric pivots 113 and 114, the desired self-locking position of the parts may be set when the die is closed. So as to have the capability of setting die support 105 for closed die position, lift rod 111 is also adjustable in length. Lift rods 112 also may be made adjustable in length as required.
FIG. 17 shows an embodiment of a thermal shaping machine, which is similar to that of FIG. 16. The same reference numberals are used as in FIG. 16 for similar parts. The following modifications exist with respect to FIG. 16:
(1) in FIG. 17, the lift adjustment is not made by eccentric pivots as in FIG. 16, but instead by adjustment of a block 113a mounted for slidable displacement along a guide slot 113c in lever 102.
Adjustment of block 113a which is pivotally connected to link rod 110 is achieved by a threaded spindle 113b. The disclosed arrangement of sliding block 113a on lever 102 provides the advantage of a longer adjustment path and also of a more rapid and continuous setting of the lift path. At the dwell state shown in FIG. 17, slot 113c extends along a circular arc about the axis of the stud bearing at 114a which is similar to stud 146, so that the rest state of lifter 109 will remain unaffected by adjustment of block 113a. In order to still further enlarge the range of lift adjustment, the stud bearing 114a shown in FIG. 17 may also be provided with a sliding adjustment (indicated but not shown), by means of which the spacing Y between stud bearing 114a and axis of shaft 121 may be varied.
(2) FIG. 17 shows the upper die support 106a with several, for example, three boreholes 125a vertically aligned one above the other. The pivot 125 of lift rod 112 may be placed in any of those holes 125a to locate upper tool 190 at various heights. (FIG. 17 shows a tentering frame as an example of an upper tool 190).
(3) The embodiment of a thermal shaping machine shown in FIG. 17 is provided with two pressure cylinders 180, preferably pneumatic, that are double-acting and located at the lower die support 105, and they eliminate conventional ejector springs. Such ejector springs on account of their bulk requirements in the tools, the difficulty in determination their moments of force, their usually constant and uncontrollable pressure and the fact that they require changing for different tools, may be disadvantageous. On the other hand, the double acting pressure-cylinders 180 act as ejectors and peel-off cylinders to provide the advantage of lesser bulk, being mounted outside the tool, and further allowing adjustment to the moment of force required in a particular arrangement. Also, the cylinders need not be replaced for different jobs. The piston rods 181 may be used as automatic ejectors. All operational parts previously located inside a tool employing springs will be on the side of the machine when the double acting cylinders are used, and tool simplification results.
In further relation to FIGS. 15-17, to prevent the generation of shocks during the vertical motions of die support 105 as well as affecting the relatively soft and sensible web material as acting upon the die parts or auxiliary equipment mounted thereon, and to prevent such shocks from being reflected into the unit 101 and from interfering with the smooth operation of the machine and its drive, a weight compensation or shock absorbing system has been provided which has at least one power-storage element that reaches below the lower die support 105. This weight compensating device comprises at least one compressed fluid cylinder, preferably four compressed air cylinders 126 reaching below the four corner areas of lower die support 105 which are connected in parallel to a compressed air source that may be set for controlled supply or removal and measurement of the pressure to the desired pressurization by means of apparatus. Compressed air cylinders 126 together with the pressurized air source provide a power storage, braking in a definite manner determined by the selected pressure in source, the downward motion of die support 105 while supporting its upward motion, the transmission of damaging shocks thus being prevented. As shown in FIG. 16, the weight compensation device may instead be provided with hydraulic cylinders 129 connected to a hydraulic pressure source container 130 operating in concert with an air cushion. Hydraulic pressure container 130 is also provided with an apparatus 128 for selectively setting the pressure of the shock absorbing cushion. Usually there are only two hydraulic cylinders 129 below the lower die support 105, in diagonal arrangement as indicated in FIG. 18. However, four such cylinders may be provided. It is also conceivable that only one hydraulic or pneumatic cylinder be used, which might be mounted centrally before the lower die support. As shown by FIGS. 15 and 17, the piston rods of the hydraulic or pneumatic cylinders (126, 129 respectively) will only engage the lower side of the lower die support 105. One may therefore readily also operate without any weight compensating device by removing the pressures in sources 127 or 130. Also, the pressure in the said sources may be selected so low that there will be some braking and damping action, but that the upward motion of die support 105 will be faster than that of the piston rods so that the upward motion of die support 105 for the purpose of die closing will not be affected by the shock absorbing or damping cylinders. A pressure valve allows operating the apparatus almost weightlessly, that is, for constant pressure applied to the pistons of the compensating cylinder, the same force for the same weight will always be obtained.
If the surface temperature of web I determined by measuring element 171 falls below the selected value, then the central control device first actuates drive 174 to displace roller 160 until either the desired temperature has been obtained or roller 160 reaches the right-end limit position in FIG. 15. If the latter is the case, drive device 174 emits a feedback signal via line 175 to the central control device 170. The latter then regulates the tempering device 177 in order to raise the temperature of the cooling medium for at least one of the rollers, say roller 160, or for all three 159, 160 and 161. If this regulation is insufficient, or if an upper temperature limit of the cooling medium is reached, tempering device 177 will emit a feedback signal via line 176 to the central control device 170. If in that case the surface temperature of web I determined by the measuring element 171 is still too low then the central control device 170 will cause the drive for cam and gear unit 101 and that of the supply mechanism of the extruder 156 to operate at a lower rate, so that the heating equipment of extruder 156 will be more effective with respect to the material output, or else the central control device 170 causes an increase in heat output at extruder 156 via line 179 (if the plastic used allows).
The bottom face of frame 222 together with the upper face of thermal forming die 201 forms the third cooling stage for the residual material in the web. This third cooling stage is substantially concurrent with the thermal forming stage. Frame 222 is a plate provided with apertures 225 for passage of the upper shaping forms 221 and the lower end of passages 225 are countersunk at 226 to cooperate with an annular, upward projecting die rib projection 203 adapted to form the rim 243 (FIG. 19) of the shaped article. The actual cup-like shaped article 244 is formed in the web by the descending formed 221 entering the correspondingly shaped female form recesses in the lower die support and drawing the web material to the desired shape.
Each length of the advance E of the web is equal to the length of the successive stages of thermal die 201 in the same direction as regards the precooling tools 231, 233 and the precooling-countertools 232 and 234.
When the lower die support 105 is lifted and the 2nd support is lowered in operation, the precooling tools 231 and 233 as well as the face of thermal die 201 will be applied from below against web I, while the precooling countertools 232 and 234 as well as frame 222 are lowered from above against web I. When further bringing together die support 105 and the second support 106, springs 235 and 223 will become stressed, so that the precooling tools 231 and 233 as well as the precooling countertools 232 and 234 will be urged under predetermined pressures against the surfaces of web I. In the process, the above described area wise precooling of web I occurs simultaneously in both the first and second precooling stages. Simultaneously, there also takes place, during the thermal shaping process in the non-precooled areas of web I due to the cooperation of thermal die 201 with frame 222 and forms 221, cooling in the third stage.
Thus, each time the upper and lower die supports are brought toward each other by rocking of lever 109, assuming that a length of heated web I equal to three times the distance E is disposed between the tools, at first stage S1 the section of the web pressed between tools 231 and 232 is precooled except at areas 241 of FIG. 19; at second stage S2 the section of the web pressed between tools 234 and 235 is further precooled except at areas 242 of FIG. 19, and at stage S3 the articles are thermally formed in the stabilized web by the action of projecting forms 221 entering recesses forms 202 and at the same time the web surfaces around the formed areas 243, 244 of FIG. 19 are further cooled by engagement of the opposite surfaces of the web with surfaces of die 201 and frame 222. Each time the dies are separated, there is an intermittent advance of the web I for the distance E before the next cooling and shaping stroke.
Somewhat modified tools or dies are illustrated as mounted on the lower tool support 105 and on the 2nd support 106 in the example of FIGS. 20-23. All parts similar to those of FIGS. 18 and 19 have the same reference numerals. The recesses 255 in the precooling tool 251 no longer are surrounded by cooling fields, but rather by cooling-and-shaping fins 256 cooperating with similar cooling-and-shaping fins 257 of the associated precooling countertool 252. Fins 256 and 257 are peripherally continuous and although shown as rectangular may be any outline. The fins have countersunk mating regions around their peripheries. In this manner, grid-like ribs 245 are formed in web I at the first precooling stage, while the intervening and rectangular or roughly square areas 246 of the example shown remain uncooled. Precooling tool 253 and precooling countertool 254 in the second stage are provided with recesses 258 at the second precooling stage, and these recesses are surrounded with oppositely contoured precooling-and-shaping fins 259. In this manner, there is formed within ribs 245 a second oppositely shaped rib arrangement 247 surrounding uncooled areas 248 in FIGS. 22 and 23.
This structure of the thermal die (FIGS. 22, 23) allows shaping a wavelike rib structure 250 surrounding each shaped article area 249 during the precooling stages and the thermal forming stage in the residual web material, so that the residual material is subjected to a more intense cooling and desirably becomes a stiffened, framelike structure which may be efficiently transported to and accurately centered in an adjoining stamping station.
Stabilizing and cooling device 322 may be provided with three cooling rollers 323a, 323b and 232c. As indicated in dashed lines, cooling rollers 323b and 323c may be adjusted transversely of the conveying movement of the web 314, in order to vary the looping angle and areas that web 314 passes in heat conducting contact over the cooling rollers. However, as in the earlier embodiments, the stabilizing and cooling device 322 cools only a thin guter range of web 314, and stiffens the web only slightly, while the material inside these surfaces of stabilized web 314 essentially remains at the extrusion temperature and in the plastic state.
As shown in FIGS. 24 and 25, thermal shaping station 330 comprises a die support 331 which may rotate about a horizontal axis, and it contains four spaced independent tools 332 that are 90� apart from each other. For the sake of simplicity, the drawing shows only single tools 332, but practically these will be multiple tools in order to produce a plurality of shaped articles during each single sequence of operation at the thermal shaping station.
As shown in FIG. 25, each of the four tools 332 is recessed to receive a forming element and is radially slidably supported in the die support 331 so as to be displaceable against the action of springs 333. The rotational axis of support 331 is indicated at 336. Devices (not shown) may be mounted at the center of the die support 331 which will retain die 332 in a retracted position, for a predetermined time, for example until the shaped article is ejected, at least until die support 331 has reached its initial horizontal position. This avoids pushing back the shaped articles toward the residual web after termination of the shaping and stamping process.
A holding and stripper assembly 343 composed of three plates and operating on web 314 is mounted on the centering rods 328. Assembly 343 comprises a rear stop plate 344, a center plate 345 and a front plate 346 facing the support 331. The rear stop plate 344 is mounted on guide member 329, whereas the center and front plates 345 and 346 are slidable along the centering rods 328. The three plates 344, 345 and 346 are biased spaced apart by compression springs 347 disposed between rear stop plate 344 and center plate 345 and by compression springs 348 also mounted on centering rods 328 and disposed between the center and front plates 345 and 346. However these plates will be pushed toward each other against the action of springs 347 and 348 when the die support 331 approaches and engages in operation, and thereby be strongly compressed while resiliently clamping web 314 under pressure, so that the die support in moving over centering rods 328 will abut the adjacent end face of tool 332 against the front plate 346. The center and front stretching frame plates 345 and 346 are provided with oppositely located tensioning rails 349 engaging web 314 in operation.
At the end of the article forming operation wherein the tool 332 is horizontally engaged with the assembly 343 and form 341 is advanced to draw the web material into the recess of tool 332, the die support 331 is moved away from assembly 343 and at the same time form 341 is retracted to the FIG. 25 position, leaving the formed article, or articles, in the recessed tool 332. The residual web is then moved downward.
A removal device 360 for the residual web 314a is mounted below the actual thermal shaping device 330, and in the example shown this consists of an intermittently driven removal roller 361 and counter roller 362. The residual web is led from this removal system 360 to the size-reducing device 370 shown schematically in FIG. 24 and mounted on the web processing unit 302. The residual web may thus be reconverted into granular material in unit 370 and then immediately fed back to the extruder hopper 312 in the system as indicated by line 371. As shown by arrow 372, the feedback material may be mixed with fresh material in the hopper. However, one may also store the granulated material and make use of it only later.
As shown in FIG. 24, devices 380 for catching and removing shaped articles ejected from tools 332 when they reach the position 180� from the forming position are mounted at the side of die support 331 opposite web 314. The ejection of the shaped articles is effected by vacuum and compressed air lines 381 opening into the cavities in dies 332, and these lines are connected via valves controlled from the central machine control to suitable vacuum and compressed air sources. The periodic rotation of die support 331 and of removal roller 361 is preferably effected by an electrical motor 382 periodically energized from the central machine control. The drive of crank drive is effected by an electrical motor 383, which may also operate periodically and be controlled from the central machine control. Preferably however, a continuously operating drive motor 383 will be used, and the central control for the continuously or periodically operating devices of the web processing unit 302 will be connected to shaft 384 of the crank drive at 339. By controlling the speed of drive motor 383, one may regulate over a sufficiently wide range the operational rate or output of the web processing unit 302 so as to adapt it to the output of extruder 311 and nozzle 313. Further, extruder 311 may be controlled in known manner with respect to its own output.
Web 314 issuing from nozzle 313 enters the stabilizing and cooling device 322. By proper setting of the cooling rollers 323b and 323c, the first processing step of the invention is executed, namely a stabilizing surface temperature is provided for the hot plastic web 314 coming from nozzle 313, which temperature is low enough to stabilize the surfaces of that web, so that the continuously incoming web may be intermittently moved through the thermal forming machine. Web 314 is fed continuously from the stabilizing and cooling device 322 to the compensating roller 325, which converts continuous web motion to intermittent downward vertical motion, the synchronism and the length of such intermittent motion being determined by the central control system. The compensating roller 325 is supported by the gripper system 326. When the thermal shaping device 331 is in the open position shown in FIG. 25 and therefore with the plates of frame 343 biased to open condition by springs 347 and 348, compensating roller 325 and the gripper system 326 will be driven downward in the sense of the solid arrow 326a, both parts of the gripper system 326 being pressed toward each other to resiliently clamp the web between them. The length of such discrete motion may be adjusted to the vertical length of the web section gripped by clamping ribs 349 on frame 343, plus a minor length of web which is touched by upper and lower transverse ribs on gripper system 326. The compensating roller 325 again moves from its lower position, showed in dash lines, towards its upper position in a loop forming function during the continuous feeding of web 314. The parts of the gripper system 326 will be separated from one another and from web 314 after reaching the lower position and then moved back upward according to dashed arrow 326b into the initial position.
Motor 383 is also is switched ON by the central control system during the downward web advance step. Thereby, the residual section of web in the thermal forming station is removed simultaneously with the feeding of a new section into the thermal forming station 330. Also, die support 331 is rotated by 90� in the sense of arrow 331a, so that the next tool 332 moved into position now faces a new section of web 314. The central control system may be so connected with shaft 384 of the crank drive 339 that shortly after termination of the web advance step, crank drive 339 will move the die support 331 into contact with the front plate 346. The rim 334 of die 332 will then extend into the aperture 351 of the front plate 346. The thickness of latter inside the clamping rib 349 is equal to the height of the aperture rim 334, so that the front face of the die 332 will lie in the plane of the rear area of the front plate 346 and within the clamping rib.
Springs 348 being considerably weaker than springs 347, the front plate 346 at first will be urged against the center plate 345 while clamping web 314. At this moment, the central control system energizes the pressure cylinder 342 of form element 341 for the initiation of the actual thermal forming process, so that the element 341 pushes the central region of the clamped area to be shaped of web 314 into the hollow space of die 332. Upon further rotation of crank drive 339, both plates 345 and 346 will be advanced along rods 328, compressing springs 347, until the center plate 345 abuts stop plate 344. During this motion, first the front face of the stamping knife 353 will contact web 314 which already has been subjected to shaping by form element 341. Subsequently the front face of the opening rim 334 presses the web in the area surrounding the shaped article against the front face of the stamping knife 353, so that the space surrounding the latter is sealed at the side toward web 314. If form element 341 is being moved toward the web at this time the pressure of compressed air generated in the sealed region together with the vacuum applied to supply lines 381 in the die support 331 will combine with the forming action of the tool to effect complete forming of the shaped articles in the web.
Once the tool support 331 has been moved away from the web at least so far that the bores 335 leave centering rods 328, and after the opening rim 334 of the die 332 has left the recess 331 of the front frame plate 346, the next advance step for web 314 may be initiated by the central control system. As explained above, the die carrier 331 will be rotated by 90� clockwise in FIG. 24, so that the previously upward pointing tool 332 now will face web 314. The supply line 381 still remains connected to the vacuum, so that the separated shaped article received by the tool 332 remains in the tool after completion of the thermal forming operation and will be cooled therein. After termination of the next thermal forming operation when the die support 331 has been rotated by 180� from the article forming position, the supply line 381 is disconnected from the vacuum source and is connected thereafter to a compressed air source so that the cooled shaped article may be ejected by air pressure from die 332 and transferred to the receiving and removing device 380. Any suitable arrangement for selectively connecting the different lines 381 to sources of vacuum and air pressure depending on the rotated position of support 331 may be provided. In any event vacuum is applied into the bottom of the cavity of the tool 332 facing the web, and air pressure for ejecting the article is supplied into the bottom of the cavity but is 180� away from the forming position.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS2541203 *Oct 11, 1947Feb 13, 1951Plax CorpApparatus for forming plastic sheetsUS3161915 *Aug 24, 1960Dec 22, 1964Thiel Alfons WilhelmApparatus for the production of thinwalled plastic articlesUS3333032 *Nov 12, 1963Jul 25, 1967Union Carbide CorpTreated polymer surfaces of shaped articlesUS3335927 *Aug 31, 1965Aug 15, 1967Norman ZwiebelStacking apparatusUS3454693 *Oct 23, 1963Jul 8, 1969Helene M CrenshawProcess for forming plastic objectsUS3667885 *Nov 5, 1970Jun 6, 1972Shelby Richard KMolding machinesUS3733160 *Mar 18, 1971May 15, 1973Standard Oil CoMaterial handling system for plastic film molding apparatusUS3830611 *Jul 25, 1972Aug 20, 1974Irwin JApparatus for matched-mold thermo-formingUS3904338 *Dec 28, 1973Sep 9, 1975Industrial Nucleonics CorpSystem and method for controlling a machine continuously feeding a sheet to intermittently activated station* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS4234536 *Sep 27, 1978Nov 18, 1980Thiel Alfons WMethod for the manufacture of thin-walled shaped articles of crystalline thermoplastic materialUS4255382 *Mar 20, 1980Mar 10, 1981Leesona CorporationThermoforming machine with automatically mechanically operated web stripping elementUS4409173 *Nov 9, 1981Oct 11, 1983O.M.V. SpaProcess and apparatus for the manufacture of objects of crystalline polystyreneUS4509909 *Apr 14, 1983Apr 9, 1985Leesona CorporationClamp mechanism for differential pressure thermoformerUS4994229 *Mar 17, 1988Feb 19, 1991Hitek LimitedForming thermoplastic web materialsUS4997358 *Sep 5, 1989Mar 5, 1991Hpm CorporationApparatus for reconfiguring finishing rolls in a plastic sheet fabrication sheetlineUS5135383 *Dec 20, 1990Aug 4, 1992Massimo MarchesiniEquipment for thermoforming polypropylene bandsUS5238632 *Apr 3, 1990Aug 24, 1993Hitek LimitedContinuous feed thermoforming method and apparatusUS5397526 *Jan 14, 1994Mar 14, 1995Hpm CorporationMethod for reconfiguring finishing rolls in a plastic sheet fabrication sheetlineUS5893994 *Apr 17, 1996Apr 13, 1999Irwin Research & Development, Inc.Adjustable length heat tunnel for varying shot lengthsUS6129538 *May 1, 1998Oct 10, 2000Emerging Technologies TrustPre-cut roll and thermoformer machineUS6314873 *Aug 21, 2000Nov 13, 2001Myron G. LeeThermal presses for forming articles from a web of thermoplastic material and methods of operating thermal pressesUS6393942 *Sep 27, 2001May 28, 2002Brown Machine, LlcMethod of driving ejector pins to eject formed partsUS6399184Sep 22, 1999Jun 4, 2002Emerging Technologies TrustPrecut blister roll for thermoformer machineUS6409496Sep 1, 2000Jun 25, 2002Emerging Technologies TrustThermoformer machineUS6443721May 5, 1999Sep 3, 2002Maytag CorporationApparatus for creating a substantially uniform temperature across a plastic sheet for delivery to an appliance liner thermoforming deviceUS6490844Jun 21, 2001Dec 10, 2002Emerging Technologies TrustFilm wrap packaging apparatus and methodUS7101500May 31, 2001Sep 5, 2006Maytag CorporationMethod for creating a substantially uniform temperature across a plastic sheet for delivery to an appliance liner thermoforming deviceUS7257364 *Dec 10, 2004Aug 14, 2007Pentax CorporationPaper feeding mechanism for continuous form printerUS7754299Feb 16, 2005Jul 13, 2010Pactiv CorporationMultilayer polymer articles and process for making the sameUS7946841 *Apr 7, 2005May 24, 2011Windmoeller & Hoelscher KgDevice for conveying a tubular filmUS8262966Nov 5, 2009Sep 11, 2012Battenfeld-Cincinnati Germany GmbhProcess for cooling flat plastic productsUS8602767 *Jan 5, 2011Dec 10, 2013Omv Machinery S.R.L.Cutting unit for a thermoforming machine or press and a thermoforming machine equipped with such cutting unitUS20110165281 *Jan 5, 2011Jul 7, 2011Giancarlo BissoliCutting unit for a thermoforming machine or press and a thermoforming machine equipped with such cutting unitDE3220954A1 *Jun 3, 1982Jul 14, 1983Yamakawa Ind Co LtdVerfahren zum fortlaufenden pressformen von duennen harzplatten oder -folienEP0038371A2 *Apr 21, 1980Oct 28, 1981Plastona (John Waddington) LimitedMethod of producing thermoformed beverage containers and containers produced by thisEP0067238A2 *Jun 13, 1981Dec 22, 1982Maryland Cup CorporationMethod and apparatus for the continuous formation of biaxially oriented thermoplastic materials and forming articles therefrom by intermittent forming means interfaced therewithEP0283284A2 *Mar 17, 1988Sep 21, 1988Tetra Laval Holdings &amp; Finance SAForming thermoplastic web materialsEP0302996A2 *Apr 14, 1988Feb 15, 1989Paper Converting Machine GmbHApparatus for longitudinally welding thermoplastic sheets togetherEP0947306A1 *Mar 11, 1999Oct 6, 1999Illig, Adolf Maschinenbau GmbH &amp; Co.Apparatus for punching out or combined forming and punching out of parts which are deep drawn from thermoplastic sheetsEP1149684A2 *Mar 23, 2001Oct 31, 2001Welex IncorporatedSheet processing systemEP1431224A1 *Dec 19, 2003Jun 23, 2004Asahi Glass Company Ltd.Method and apparatus for producing a plate-like body attached with a resin frameEP1600277A2 *Apr 25, 2005Nov 30, 2005Battenfeld Extrusionstechnik GmbHCooling DeviceEP2184156A2 *Oct 30, 2009May 12, 2010Battenfeld Extrusionstechnik GmbHProcess for cooling flat plastic productsWO1988006965A1 *Mar 17, 1988Sep 22, 1988Hitek LtdForming thermoplastic web materialsWO1990011881A1 *Apr 3, 1990Oct 8, 1990Hitek LtdContinuous feed thermoforming method and apparatus* Cited by examinerClassifications U.S. Classification425/217, 425/327, 425/324.1, 425/387.1, 425/378.1, 425/367, 425/326.1, 425/DIG.201International ClassificationB29C47/06, B29C51/42, B29C51/22, B29C47/00, B29C51/18, B29C51/44, B29C47/34, B29C51/46, B29C47/88Cooperative ClassificationB29C51/423, B29C51/22, Y10S425/201, B29C47/065, B29C47/043, B29K2995/0096, B29C51/18, B29C47/8845, B29C47/00, B29C47/0021, B29C51/46, B29C51/422, B29C51/445, B29C47/34European ClassificationB29C51/22, B29C51/18, B29C47/88C4B, B29C51/42B2B, B29C51/42B2, B29C51/44BRotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services