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
  • 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
  • B29C48/92—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
  • B29C2948/92009—Measured parameter
  • B29C2948/92085—Velocity
  • B29C2948/92095—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
  • B29C2948/92542—Energy, power, electric current or voltage
• • 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
  • B29C2948/92704—Temperature
• • 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
• • 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

Definitions

• the present invention relates to temperature control of machines intended to be used in the manufacture of plastic articles, in particular to a control rendering a desired melt temperature throughout the entire melt.
• the control in question is a control during production and not specifically the control only directed to heating and melting a raw material prior to starting the production.
• the raw material used for the manufacture of plastic articles is supplied to the machine in granular, pulverized or otherwise disintegrated form, possibly together with additives such as dies, antioxidants, UV-stabilisators or the like.
• the raw material is mechanically kneaded, normally by means of a screw or the like rotating within a cylinder, said screw also providing the molten raw material to be homogenized, pressurized and discharged into a nozzle, casting machine, mould or similar tool endowing to the product its final shape prior to any additional working such as longitudinal and transverse stretching.
• Normally working is performed with the aid of a screw rotating within a cylinder.
• the working is performed in a so-called working section from which the viscous plastic mass is fed through a screen pack assembly and an intermediate tube, so-called adapter, to the tool and wire via ducts or grooves therein out through the casting machine or out into the mould.
• the machine is provided with devices for heating and cooling.
• the heating device is so designed that parts or zones of the machine may be individually heated and controlled to the desired temperature independently of each other.
• the cooling is normally performed with the aid of fans each performing the cooling of a section or zone of the machine.
• the various zones are provided with heat detectors,' detection or measuring being performed within the metal mantle of the cylinder.
• the control of the temperature in the various zones of the cylinder will basically be a control of the temperature in the cylinder itself, i.e. a control of the metal temperature.
• the screw within the cylinder of the working section may be provided with devices for changing the temperature, e.g. in the form of cooling ducts and/or immersion heaters.
• the primary reason for the temperatuare control of the working section is to arrive at a desired melt temperature.
• the reason for the heat control of the screen, adapter and tool and any additional equipment is to prevent the temperature of the molten plastic to change during the transfer to the die or corresponding section of the machine.
• a control of the nozzle temperature is performed for the purpose of giving the product produced a desired surface structure and desirable optical properties.
• the invention refers to all these different purposes and is intended to solve the various partial problems in the simpliest and most rational way.
• the working section comprises a hopper for supplying the raw material, a screw rotating within a cylinder and a screen pack assembly containing a filter screen for filtering out contaminants from the melt.
• a hopper for supplying the raw material
• a screw rotating within a cylinder and a screen pack assembly containing a filter screen for filtering out contaminants from the melt.
• a screen pack assembly containing a filter screen for filtering out contaminants from the melt.
• Friction and thereby frictional heat will be produced during the rotation of the screw between the granulate and the screw, between the granulate and the cylinder, between the various granules of the raw material and within the melt.
• a change of the coefficient of friction and the viscosity thus results in a change of the friction of heat supplied and thereby the melt temperature.
• Another influencing factor is the return flow around the screw. The reason therefore is that the screw does not operate with an absolute seal against the cylinder wall, a portion of the mass flowing back in the gap between the flights of the screw and the cylinder wall.
• the pressure ahead of the screen pack assembly and the viscosity of the mass are factors directly influencing the return flow.
• the pressure must be increased, such increase directly changing the temperature of the melt and thereby the viscosity.
• Various raw materials have various coefficient of friction and in addition different viscosities at the same temperature.
• a higher viscosity requires an increased pressure in order to obtain constant production capacity. As defined, it contributes in addition to an increased frictional heat due to increased internal friction.
• a higher coefficient of friction melt/metal, granulate/metal and/or granulate/granulate also contributes towards increased frictional heat.
• a high surface temperature of the screw and/or cylinder melts the material which is in contact with the metal.
• This molten material acts as a lubricant and thus reduces the friction against the cylinder wall and/or the screw and thereby the frictional heat.
• the raw material normally is a polymer and has a varying molecular weight distribution between various qualities and also between various supplies of raw materials of the same specifications.
• the low molecular weights are melting at lower temperatures than the high molecular weights and in this case also act as a lubricant reducing the coefficient of friction.
• a second temperature detector is positioned close to the outs ide surface of the cylinder and this temperature is controlled to follow the melt or raw material temperature with a des ired temperature deviation in order to supply des ired frictional heat to the zone in question.
• the same principle may be applied for this control.
• Certain geometrical shapes of the s crew may supply too much or too little frictional heat and this may be compensated according to the above-explained principle . It is obvious that the frictional heat provides practically all the energy supplied to the melt and thereby determines the melt temperature obtained. The supply of energy from heating elements only complicates the problem to obtain the desired melt temperature. If instead the process is controlled exclusively by controlling the mechanically supplied energy for a given production, it will be possible to arrive at a desired melt temperature independent of variations of the raw material and the capacity in a simplier and quicker way.
• a change of the pressure immediately behind the screw directly affects the frictional heat and thereby the melt temperature. It also appears that the normal variation of the raw material, the production capacity and the like directly changes the amount of frictional heat.
• the pressure behind the screw may be changed by a change of the screw rpm, the through-flow area of the screen or the discharge section with or without a change of the screw rpm, or by separate control of the plastizing section and discharge section with the possibility to change the screw rpm independent of the production capacity.
• a change of the pressure yields an immediate change of the amount of mechanically supplied energy to a certain amount of raw material and thereby a change of the melt temperature thereof.
• the metal of the adapter and tool as well as any additional equipment is a good heat conductor whereas the melt itself is a bad heat conductor. If the metal temperature is higher than the temperature of the melt a molten layer will be formed adjacent to the metal surfaces, the molten layer being the thinner the smaller the temperature difference is. This thin molten layer reduces the friction against the metal surfaces and thereby reduces the viscosity of the melt and thereby also the flow resistance due to the reduced coefficient of friction and internal friction. If the metal temperature is lower than the melt temperature, heat energy is removed from the melt and due to the good heat conducting capacity of the metal is conducted through the metal and out into the air.
• the metal temperature is controlled in such a way that it automatically traces the measured melt temperature with a desired deviation therefrom, for example so, that it exceeds the melt temperature by +5°, both lower flow resistance and parallel flow are obtained whereby the risk for thickness variations in the cross direction is considerably reduced.
• a temperature control as explained above it is of course even possible to adjust the metal temperature to a constant desired value.
• a certain temperature deviation from the melt temperature in the metal part of the die gap is required, and also this may be controlled in a corresponding way.

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

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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• 1988
  • 1988-10-28 WO PCT/SE1988/000583 patent/WO1989003754A1/en not_active Application Discontinuation
  • 1988-10-28 EP EP88909641A patent/EP0386068A1/de not_active Withdrawn

Non-Patent Citations (1)

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