CH671186A5 - Processing extruded thermoplastic foam - high pressures at e.g. extruder screw tip are isolated from subsequent processing tools by suitable form of back flow valve - Google Patents

Processing extruded thermoplastic foam - high pressures at e.g. extruder screw tip are isolated from subsequent processing tools by suitable form of back flow valve Download PDF

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Publication number
CH671186A5
CH671186A5 CH5184/86A CH518486A CH671186A5 CH 671186 A5 CH671186 A5 CH 671186A5 CH 5184/86 A CH5184/86 A CH 5184/86A CH 518486 A CH518486 A CH 518486A CH 671186 A5 CH671186 A5 CH 671186A5
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CH
Switzerland
Prior art keywords
extruder
pressure
gears
tool
mass flow
Prior art date
Application number
CH5184/86A
Other languages
German (de)
Inventor
Harald Dr Severus
Original Assignee
Alusuisse
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Publication date
Application filed by Alusuisse filed Critical Alusuisse
Priority to CH5184/86A priority Critical patent/CH671186A5/en
Publication of CH671186A5 publication Critical patent/CH671186A5/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/3442—Mixing, kneading or conveying the foamable material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/36—Feeding the material to be shaped
    • B29C44/46—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length
    • B29C44/50—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length using pressure difference, e.g. by extrusion or by spraying
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/36—Feeding the material to be shaped
    • B29C44/46—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length
    • B29C44/50—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length using pressure difference, e.g. by extrusion or by spraying
    • B29C44/505—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length using pressure difference, e.g. by extrusion or by spraying extruding the compound through a flat die
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/36—Feeding the material to be shaped
    • B29C44/46—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length
    • B29C44/50—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length using pressure difference, e.g. by extrusion or by spraying
    • B29C44/507—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length using pressure difference, e.g. by extrusion or by spraying extruding the compound through an annular die
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/36—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die
    • B29C48/365—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die using pumps, e.g. piston pumps
    • B29C48/37—Gear pumps
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/36—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die
    • B29C48/375—Plasticisers, homogenisers or feeders comprising two or more stages
    • B29C48/387—Plasticisers, homogenisers or feeders comprising two or more stages using a screw extruder and a gear pump
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/36—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die
    • B29C48/395—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die using screws surrounded by a cooperating barrel, e.g. single screw extruders
    • B29C48/40—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die using screws surrounded by a cooperating barrel, e.g. single screw extruders using two or more parallel screws or at least two parallel non-intermeshing screws, e.g. twin screw extruders
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/92—Measuring, controlling or regulating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C2948/00—Indexing scheme relating to extrusion moulding
    • B29C2948/92—Measuring, controlling or regulating
    • B29C2948/92504—Controlled parameter
    • B29C2948/92514—Pressure
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C2948/00—Indexing scheme relating to extrusion moulding
    • B29C2948/92—Measuring, controlling or regulating
    • B29C2948/92504—Controlled parameter
    • B29C2948/9258—Velocity
    • B29C2948/9259—Angular velocity
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C2948/00—Indexing scheme relating to extrusion moulding
    • B29C2948/92—Measuring, controlling or regulating
    • B29C2948/92504—Controlled parameter
    • B29C2948/9258—Velocity
    • B29C2948/926—Flow or feed rate
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C2948/00—Indexing scheme relating to extrusion moulding
    • B29C2948/92—Measuring, controlling or regulating
    • B29C2948/92819—Location or phase of control
    • B29C2948/92857—Extrusion unit
    • B29C2948/92876—Feeding, melting, plasticising or pumping zones, e.g. the melt itself
    • B29C2948/92885—Screw or gear
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C2948/00—Indexing scheme relating to extrusion moulding
    • B29C2948/92—Measuring, controlling or regulating
    • B29C2948/92819—Location or phase of control
    • B29C2948/92857—Extrusion unit
    • B29C2948/92904—Die; Nozzle zone
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
    • B29C48/07—Flat, e.g. panels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
    • B29C48/09—Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Extrusion Moulding Of Plastics Or The Like (AREA)

Abstract

Thermoplastic foams are produced in the form of tubes, profiled sections and sheets by means of single or multiple-screw extruders and the necessary processing equipment. This equipment is operated with the material at a pressure of 50 to 1,000 bar which is kept separated from the lower pressure material by a valve; the high pressure is not allowed to act on the extruder even though the material is fed from the extruder to the processing tool. ADVANTAGES - The system prevents the difficulties which arise when the high material pressure at the extruder screw tip is allowed to reach the processing equipment, especially if the latter is extruding thermoplastic foam.

Description

       

  
 



   BESCHREIBUNG



   Die Herstellung von Kunstschaumstoffen nach dem Extrusionsverfahren ist für thermoplastische Kunststoffe als Homopolymerisate, Copolymerisate oder als Mischungen (Blends) verschiedener Thermoplaste oder als Compounds, bestehend aus thermoplastischem Harz mit verschiedenen Zusatzstoffen (Stabilisatoren, Gleitmitteln, Füllstoffen), unter Zusatz von Treibmitteln in gasförmigem, festem oder flüssigem Zustand bekannt.



   In den bisher bekannten Verfahren werden Extruder in Form von Ein- oder Doppelschneckenextruder mit zylindrischen oder konischen Schnecken verwendet, die innentemperiert sein können. Weiters werden Extruder verwendet, die auch mehr als zwei Schnecken aufweisen oder in Form von   2-stufigen    Maschinen als Kaskadenextrusionsanlagen oder Tandem-Extrusionsanlagen bekannt sind.



   Bei den genannten Anlagen zur Herstellung thermoplastischer Schaumstoffe in Form von Profilen, Rohren oder Platten wird so gearbeitet, dass ein mehr oder weniger stetiger Druckaufbau von der Eintrittsöffnung des thermoplastischen Granulates oder Pulvers oder Mahlgutes in den Extruder bis hin zur Austrittsöffnung des herzustellenden Produktes aus der Extrusionsmaschine erfolgt. Dieser Druckaufbau hat bei jenen Anlagen mit Entgasungsöffnung im Bereich dieser Entgasungszone eine Niederdruckstufe, in welcher die homogene, plastifizierte Kunststoffmasse entgast wird, ohne dass die in der thermoplastischen Masse enthaltenen Treibmittel abgebaut werden.

  Nach der Entgasungszone in der Extrusionsanlage oder - sofern keine Entgasung angewendet wird - nach der Einzugs- oder Meteringzone des Extruders erfolgt ein mehr oder weniger steiler Druckanstieg in der plastifizierten Kunststoffmasse im Extruder. Dieser Druck erreicht im letzten Teil des Extruders durch die Wirkung der Kompressionszonen der Schnecken und am Schneckenende beim Übergang in das Ausformwerkzeug den höchsten Wert - über den Extruderzylinder betrachtet    ¯und    wird im Bereich des Ausformwerkzeuges mit Hilfe von verschiedenen Massnahmen wie Staubalken, Torpedokörper im Strömungsverlauf, Temperier- bzw. Kühlmassnahmen im Bereich der Austrittsöffnungen weiter gesteigert.



  Mit ein Grund dafür ist, dass das beim Austritt aus dem Formwerkzeug die Schäumung bewirkende Mittel im Werkzeug noch nicht zu Blasenbildung im Kunststoff führt. Es muss unter Druck in Lösung in der Kunststoffschmelze gehalten werden.



   Die Fliessvorgänge in grossen bzw. breiten Werkzeugen mit den genannten Einbauten wie Staubalken, Torpedos sowie gekrümmten Fliesswege führen dazu, dass infolge von Scherung bzw. Reibung des Kunststoffplastifikates an den genannten Gegendruckkörpern unterschiedliche Temperaturen in der Kunststoffschmelze auftreten sowie stark unterschiedliche Strömungsprofile entstehen können. Insbesondere bei Kunststoffschmelzen der genannten Art, d.h. jener thermoplastischen Kunststoffe, die zur Schäumung am Austritt des Formwerkzeuges Treibmittel in gasförmiger, fester oder flüssiger Form enthalten und diese im Werkzeug in Lösung halten müssen, strebt man in diesem Bereich der Ausformung, d.h. nach dem Ubergang von der Extruderschnekkenspitze in das Ausformwerkzeug und in diesem Werkzeug, Drücke von 50 bis 1000 bar, insbesondere von 100 bis 700 bar, an.

  Das vom Extruder an der Schneckenspitze angelieferte Thermoplastifikat weist Drücke von 20 bis 300 bar auf. Es ist verständlich, dass ein derartiger Druckanstieg im Ausformwerkzeug, insbesondere bei Extrusion thermoplastischer Schaumstoffe, infolge von Unstetigkeiten im Druck-, Temperatur- und Viskositätsverlauf im Werkzeug und an dessen Austrittsöffnung zu Schwierigkeiten führen kann. Es ist nun Gegenstand der vorliegenden Erfindung, eine Rückschlag- oder Rückdrucksperre zwischen dem die Thermoplastschmelze anfördernden Extruder und dem Ausformwerkzeug zu installieren.



   Eine solche Rückdrucksperre kann ein geeignetes Ventil im herkömmlichen Sinne sein, das als selbsttätig wirkendes Absperrorgan, ab einem bestimmten einstellbaren Druck im Ausformbereich die Möglichkeit einer Auswirkung dieses Druckes auf den Extruder in seiner Förderfunktion verhindert, indem durch eine geeignete Steuerung bei in Förderrichtung geschlossenem Rückdruckventil die Zudosierung von Kunststoffpulver oder Granulat in den Extruder und/ oder die Schneckendrehzahl entsprechend reduziert wird.



  Das Rückschlagorgan verhindert auch die Ausbildung eines hohen Rückdruckes auf die Lager der Schnecken des Extruders und die Entstehung des Bedarfes eines hohen Antriebsmomentes des die Extruderschnecken antreibenden Motors.



   Abgesehen von anderen Ausführungsformen kann dieses erfindungsgemässe Rückdruckventil aus einem oder zwei oder mehreren Zahnrädern gebildet sein, das oder die in der Lage ist oder sind, den vom Extruder angelieferten Masse  strom durch Rotation in eine Richtung zu bewegen und die Bewegung des Massestromes in die Gegenrichtung zu verhindern und die Auswirkung eines hohen Druckes im Ausformwerkzeug gegen die Extruderschnecken hin verhindert.



   Der von den Schnecken des Extruders angelieferte Massestrom wird in den Zahnlücken eines oder zweier ineinander kämmender Zahnräder weiter transportiert in Richtung des Ausformwerkzeuges. Ein Strom in Gegenrichtung, d. h.



  ein Rückstrom oder die Ausbildung eines Rückdruckes in Richtung der Extruderschnecken, wird durch entsprechende Sperrung des Drehsinnes des oder der Zahnräder verhindert.



  Eine Art der Verhinderung der Ausbildung eines Rückstromes oder Rückdruckes ist der Antrieb des oder der Zahnräder oder eines von zweien oder mehreren Zahnrädern durch einen Elektromotor, vorzugsweise einen Gleichstrommotor mit stufenlos variierbarer Drehzahl. Ein solches Rückstromoder Rückdrucksperrorgan mit zwei oder mehreren Zahnräderen von denen mindestens eines angetrieben ist stellt eine Zahnradpumpe dar.



   Solche Zahnradpumpen. insbesondere mit konisch ausgebildeten Ein- und   Auslaufleilen    in denen die Schmelze einer gleichmässigen Strömung zu und von den Zahnrädern unterliegt. eignen sich gut für die erfindungsgemässe Mass   nahm,    bei der Herstellung thermoplastischer Schaumstoffe den notwendigen hohen Druck im Ausformwerkzeug von   50 - 1000    bar gegenüber dem die Schmelze anliefernden Extruderschneckenteil abzusperren und gleichwohl einen gleichmässigen Antransport von homogenisiertem und plastifiziertem Kunststoff mit vorwiegend nicht Neutron'schem Viskositäts- und Druckverhalten zu gewährleisten. Die der Anlieferung entsprechende Masse verlässt das Ausformwerkzeug als beim Austritt aus diesem Werkzeug entstehender weitgehend geschlossenzelliger Schaumstoff mit dichter Oberflächenschicht. 



  
 



   DESCRIPTION



   The production of plastic foams by the extrusion process is for thermoplastic plastics as homopolymers, copolymers or as mixtures (blends) of different thermoplastics or as compounds consisting of thermoplastic resin with various additives (stabilizers, lubricants, fillers), with the addition of blowing agents in gaseous, solid or liquid state known.



   In the processes known hitherto, extruders in the form of single- or twin-screw extruders with cylindrical or conical screws are used, which can be internally tempered. Furthermore, extruders are used which also have more than two screws or are known in the form of 2-stage machines as cascade extrusion systems or tandem extrusion systems.



   In the systems mentioned for the production of thermoplastic foams in the form of profiles, tubes or plates, work is carried out in such a way that a more or less constant build-up of pressure from the inlet opening of the thermoplastic granules or powder or ground material into the extruder up to the outlet opening of the product to be produced from the extrusion machine he follows. In those systems with a degassing opening, this pressure build-up has a low-pressure stage in the region of this degassing zone, in which the homogeneous, plasticized plastic compound is degassed without the blowing agents contained in the thermoplastic compound being broken down.

  After the degassing zone in the extrusion system or - if no degassing is used - after the feed or metering zone of the extruder, there is a more or less steep increase in pressure in the plasticized plastic mass in the extruder. This pressure reaches the highest value in the last part of the extruder due to the effect of the compression zones of the screws and at the screw end at the transition into the forming tool - viewed through the extruder cylinder ¯ and is achieved in the area of the forming tool with the help of various measures such as dust bars, torpedo bodies in the flow pattern, Temperature control and cooling measures in the area of the outlet openings further increased.



  One of the reasons for this is that the foaming agent in the mold when it emerges from the mold does not yet lead to the formation of bubbles in the plastic. It must be kept in solution in the plastic melt under pressure.



   The flow processes in large or wide tools with the built-in components such as dust bars, torpedoes and curved flow paths result in different temperatures occurring in the plastic melt as a result of shear or friction of the plastic plastic on the counter-pressure bodies mentioned, and that very different flow profiles can arise. Particularly in the case of plastic melts of the type mentioned, i.e. Those thermoplastic materials which contain foaming agents in gaseous, solid or liquid form for foaming at the outlet of the mold and which have to keep them in solution in the mold are aimed in this area of the molding, i.e. after the transition from the extruder screw tip into the shaping tool and in this tool, pressures from 50 to 1000 bar, in particular from 100 to 700 bar.

  The thermoplastic supplied by the extruder at the screw tip has pressures of 20 to 300 bar. It is understandable that such an increase in pressure in the molding tool, in particular in the case of extrusion of thermoplastic foams, can lead to difficulties as a result of discontinuities in the pressure, temperature and viscosity curve in the tool and at its outlet opening. It is now the object of the present invention to install a non-return or back pressure barrier between the extruder feeding the thermoplastic melt and the shaping tool.



   Such a back pressure lock can be a suitable valve in the conventional sense, which, as an automatically acting shut-off device, prevents the possibility of an effect of this pressure on the extruder in its conveying function from a certain adjustable pressure in the shaping area, by using a suitable control with the back pressure valve closed in the conveying direction Dosing of plastic powder or granules in the extruder and / or the screw speed is reduced accordingly.



  The check element also prevents the formation of a high back pressure on the bearings of the screws of the extruder and the development of the need for a high drive torque of the motor driving the extruder screws.



   Apart from other embodiments, this back pressure valve according to the invention can be formed from one or two or more gear wheels which is or are able to move the mass flow supplied by the extruder in one direction by rotation and to move the mass flow in the opposite direction prevent and the effect of high pressure in the forming tool against the extruder screws prevented.



   The mass flow delivered by the screws of the extruder is transported further in the tooth gaps of one or two intermeshing gear wheels in the direction of the shaping tool. A current in the opposite direction, i. H.



  a backflow or the formation of a back pressure in the direction of the extruder screws is prevented by a corresponding blocking of the direction of rotation of the gear or wheels.



  One way of preventing the formation of a back flow or back pressure is to drive the gear or gears or one of two or more gears by an electric motor, preferably a DC motor with a continuously variable speed. Such a backflow or backpressure shut-off device with two or more gearwheels, at least one of which is driven, represents a gearwheel pump.



   Such gear pumps. especially with conical inlet and outlet lines in which the melt is subject to a uniform flow to and from the gear wheels. are well suited for the measure according to the invention, in the production of thermoplastic foams to shut off the necessary high pressure in the molding tool of 50-1000 bar compared to the extruder screw part delivering the melt and nevertheless a uniform transport of homogenized and plasticized plastic with predominantly non-neutronic viscosity and to ensure printing behavior. The mass corresponding to the delivery leaves the molding tool as a largely closed-cell foam with a dense surface layer that emerges when it emerges from this tool.

Claims (6)

PATENTANSPRUCH 1. Verfahren zur Herstellung thermoplastischer Schaumstoffe in Form von Rohren, Profilen und Platten mittels Einund Mehrschneckenextrusionsanlagen und entsprechender Ausformwerkzeuge, dadurch gekennzeichnet, dass im Ausformwerkzeug ein Massedruck von 50 bis 1000 bar erreicht wird, der gegenüber dem niedrigeren Massedruck im Extruder bzw. an der Schneckenspitze des Extruders mit einem Absperrorgan getrennt wird, indem sich der hohe Druck im Ausformwerkzeug nicht als Rückdruck auf den Extruder auswirkt und gleichwohl ein Massestrom in Richtung des Werkzeuges vom Extruder fliesst.  PATENT CLAIM 1. A process for the production of thermoplastic foams in the form of pipes, profiles and plates by means of single and multi-screw extrusion systems and corresponding molding tools, characterized in that a melt pressure of 50 to 1000 bar is achieved in the molding tool, which is compared to the lower melt pressure in the extruder or at the screw tip of the extruder is separated with a shut-off device, in that the high pressure in the molding tool does not act as back pressure on the extruder and nevertheless a mass flow flows in the direction of the tool from the extruder. 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass dieses Rückdruckabsperrorgan aus mindestens einem, besser aber zwei ineinander greifenden Zahnrädern besteht, von denen mindestens eines angetrieben ist und in deren Zahnzwischenräumen, die schrägverzahnt sein können, entsprechende Masseströme gefördert werden und durch das ineinander kämmende Eingreifen der Räder in Förderrichtung, d.h. in Richtung des Ausformwerkzeuges, ausgetragen werden.  2. The method according to claim 1, characterized in that this back pressure shut-off device consists of at least one, but better two intermeshing gears, at least one of which is driven and in whose interdental spaces, which can be helically toothed, corresponding mass flows are conveyed and by the intermeshing Intervention of the wheels in the direction of conveyance, ie in the direction of the molding tool. 3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die Masseströme vor und nach den Zahnrä dem in konisch zu- bzw. auslaufenden Fliesskanälen geführt werden.  3. The method according to claim 1 or 2, characterized in that the mass flows before and after the Zahnrä are guided in the conically tapered or tapered flow channels. 4. Verfahren nach Anspruch 2 oder 3, dadurch gekennzeichnet, dass die Zahnräder Schrägverzahnung aufweisen und eine Breite haben, die einen der Dimension des Extruders entsprechenden Massestrom durchzusetzen gestattet.  4. The method according to claim 2 or 3, characterized in that the gears have helical teeth and have a width that allows a mass flow corresponding to the dimension of the extruder to be enforced. 5. Verfahren nach einem der Ansprüche 2 bis 4, dadurch gekennzeichnet, dass die Drehzahl der Zahnräder in einem weiten Bereich stufenlos regelbar ist und der Druck des ankommenden Massestroms vor den Zahnrädern gemessen und durch Regelung der Drehzahl der Schnecken des Extruders konstant gehalten wird.  5. The method according to any one of claims 2 to 4, characterized in that the speed of the gears is continuously adjustable over a wide range and the pressure of the incoming mass flow in front of the gears is measured and kept constant by controlling the speed of the screws of the extruder. 6. Verfahren nach einem der Ansprüche 2 bis 5, dadurch gekennzeichnet, dass der durch die Zahnräder quasi als Pumpe (Zahnradpumpe) geförderte Massestrom im Ausformwerkzeug solchen Druck erreicht oder zulässt, dass die Kunststoffschmelze, welche Treibmittel enthält, im Werkzeug nicht aufschäumt, sondern erst beim Austritt aus dem Formwerkzeug.  6. The method according to any one of claims 2 to 5, characterized in that the mass flow conveyed by the gears quasi as a pump (gear pump) in the shaping tool reaches or permits such pressure that the plastic melt, which contains blowing agent, does not foam in the tool, but only when leaving the mold.
CH5184/86A 1986-12-24 1986-12-24 Processing extruded thermoplastic foam - high pressures at e.g. extruder screw tip are isolated from subsequent processing tools by suitable form of back flow valve CH671186A5 (en)

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CH5184/86A CH671186A5 (en) 1986-12-24 1986-12-24 Processing extruded thermoplastic foam - high pressures at e.g. extruder screw tip are isolated from subsequent processing tools by suitable form of back flow valve

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CH5184/86A CH671186A5 (en) 1986-12-24 1986-12-24 Processing extruded thermoplastic foam - high pressures at e.g. extruder screw tip are isolated from subsequent processing tools by suitable form of back flow valve

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996041709A1 (en) * 1995-06-13 1996-12-27 Torsten Herrmann Process and device for producing a foamed polymer

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2144816A1 (en) * 1971-07-07 1973-02-16 Siemens Ag
DE2716669A1 (en) * 1975-09-03 1978-10-19 Union Carbide Corp Polymer gear pump - with gear chamber and sealed zone shaped for optimum efficiency

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2144816A1 (en) * 1971-07-07 1973-02-16 Siemens Ag
DE2716669A1 (en) * 1975-09-03 1978-10-19 Union Carbide Corp Polymer gear pump - with gear chamber and sealed zone shaped for optimum efficiency

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996041709A1 (en) * 1995-06-13 1996-12-27 Torsten Herrmann Process and device for producing a foamed polymer
US5889064A (en) * 1995-06-13 1999-03-30 Herrmann; Torsten Process and apparatus for producing a foamed polymer

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