DE102016109087A1 - Method for controlling and controlling pipe extrusion plants - Google Patents

Abstract

The present invention relates to a method for controlling and controlling pipe extrusion plants, including measurement data of a produced pipe (4), wherein a melt tube (4 ') emerging from an annular gap (11) of an extruder unit (1) is oversized into a subsequent calibration device (6 ) enters. The object of the present invention is to provide such a method which works with measured values which ensure an optimal mode of operation of the extrusion system even with a dimensional change. This object is achieved by exactly determining the diameter, the wall thickness, any shape deviations and the sagging of the melt tube (4 ') between the extrusion die (3) and the calibration device (6) at several points, and these measured values or data calculated therefrom Control and control of the extrusion system are used.

Description

The present invention relates to a method for controlling and controlling pipe extrusion plants according to the preamble of claim 1.

In a tube extrusion, a plastic granulate is melted by means of an extruder and pressed in an extrusion die through an annular gap which is formed by a nozzle and a mandrel arranged therein. The hot melt tube thus produced is pressed and cooled in a subsequent calibration device under negative pressure against an external calibration device, usually a calibration sleeve. The calibrated and cooled tube is drawn by means of a draw-off device from the extrusion die through the calibration device and optionally by further extrusion follower devices.

In this method, the annular gap of the extrusion tool is greater than the diameter of the vacuum device working with the caliper, so that the melt tube run in excess and seal the calibration device against the ambient pressure. In addition to the oversize, the inlet angle of the melt tube into the calibration device is important, which can be influenced by the distance between the extrusion tool and the calibration device. If the oversize is too small or the inlet angle is too low, it is no longer possible to seal the calibration device against the ambient pressure. If the oversize is too great or the lead-in angle too steep, the melt tube is stretched too quickly, which can lead to stresses in the finished tube or even to tearing of the molten tube before or in the calibration device.

For driving the extrusion system Auslegekriterien be used, which according to the prior art as a measurement technique, the ultrasonic measurement method is used, such. B. in the DE 10 2006 056 735 A1 described.

One of the design criteria is the oversize with which the melt tube enters the calibrator. It is described with the Dimension Draw Down (DDR) parameter: DDR = (D _nozzle - D _Kali ) / D _nozzle .

This value should be between 5% and 50% for the most important plastic pipe material HDPE (high-density polyethylene) according to the prior art.

D_Düse

Außendurchmesser Düse

D_Kali

Innendurchmesser Kalibrierhülse

d_Spalt

Ringspalt Extrusionswerkzeug

d_Rohr

Wandstärke Rohr

In this and the following formulas mean:

D _nozzle

Outer diameter nozzle

D _Kali

Inner diameter calibration sleeve

d _gap

Annular gap extrusion tool

d _tube

Wall thickness tube

The wall thickness of the extruded tube, since the outer diameter is fixed by the calibrator, results from the mass flow rate of the extruder and the speed with which the tube is pulled by the extraction device. Here, starting from the annular gap of the extrusion die, the melt tube is drawn on the one hand to the diameter of the calibration, but at the same time reduces the wall thickness of the melt tube depending on the speed of the trigger. This double stretching of the melt tube is only possible within limits and is described by the characteristic dimension ration balance (DRB):

This value should be between 0.97 and 1.095 for the most important plastic pipe material HDPE (high density polyethylene) according to the prior art.

In addition, it should be noted that the hot, soft melt hose in the extrusion plant must always be in train, so as not to accumulate in the plant. At the same time the train must not be too high, because otherwise the melt tube constricts and tears off. The train on the melt tube is described by the ratio of the exit surface of the melt from the tool to the inlet surface of the molten tube in the calibration

This value should be between 130% and 700% for the most important plastic pipe material HDPE (high-density polyethylene) according to the prior art.

In order to reduce the effort for set-up processes when changing from one pipe dimension (diameter and wall thickness) to another, it is of great benefit if the annular gap of the extrusion tool is optimized for as many product variants as possible. Especially if an adjustable calibration device is additionally used in the process, a large product window can be covered without plant stop and conversion work with such an optimized design of the extrusion tool. The above-mentioned design criteria are insufficient for this.

It is therefore an object of the present invention to provide a generic method which works with measured values which ensure an optimal mode of operation of the extrusion system even when changing the dimensions.

This object is achieved by a method having the features of claim 1.

According to the invention, the diameter, the wall thickness, any shape deviations and the sagging of the melt tube are determined at several points between the extrusion tool and the calibration device. Thus, four major effects in pipe extrusion can be included in the design of the extrusion tool, which were previously not considered.

One of these effects is the strand expansion of the melt after leaving the extrusion die. In the extrusion die, the molten plastic material is forced under high pressure through narrow channels and finally the annular gap at the outlet. In this case, the freely movable macromolecules of the plastic are oriented in the extrusion direction. After leaving the extrusion die, the macromolecules are no longer subject to such great external constraint that they contract again and lead to an expansion of the diameter and an increase in the wall thickness of the melt tube.

Another effect is the sagging of the soft melt tube between the extrusion die and the calibration device, which must be counteracted with large pipe diameters with a height offset between the extrusion die and the calibration device.

Finally, another effect is the so-called sagging, the flow of hot, flowable plastic material from the top of the molten tube to its bottom.

In addition, these measurement data can be used for optimum centering of the nozzle and mandrel of the extrusion tool as well as for setting an optimal inlet angle of the molten tube into the calibration device.

In an advantageous embodiment of the invention, the optical or fully electronic terahertz or gigahertz measuring technique is used to acquire the measured data. Since this type of measurement technique operates without contact and without coupling medium, a measurement can also be made on hot, touch-sensitive bodies, such as a melt tube, directly after the extrusion tool in the tube extrusion.

• – die Vermessung der Abstände zwischen den Sensoren und dem Schmelzeschlauch und damit die Berechnung des Durchmessers der Schmelzvorlage und des Durchhängens des Schmelzeschlauches
• – die Vermessung der Wandstärken des Schmelzeschlauchs an den Sensorpositionen und, über die die Unterschiede auf dem Umfang, die Exzentrizität der Wandstärke
• – durch Vergleich der Abstands-Messwerte nach dem Extrusionswerkzeug und vor der Kalibriervorrichtung, die Berechnung der Einlaufwinkel des Schmelzeschlauchs in die Kalibriervorrichtung über den Umfang (bedingt durch die Schwerkraft ist der Einlaufwinkel an der Unterseite des Schmelzeschlauches immer anders als an der Oberseite)
• – durch Vergleich der Wandstärkenmesswerte nach dem Extrusionswerkzeug und vor der Kalibriervorrichtung, die Berechnung des Sagging der Kunststoffschmelze nach Austritt aus dem Extrusionswerkzeug.

If one associates gigahertz or terahertz sensors at several positions of the circumference of the melt tube directly after exiting the extrusion die and also at several positions of the circumference immediately before entry into the calibration device, this allows:

• - The measurement of the distances between the sensors and the melt tube and thus the calculation of the diameter of the melt template and the sagging of the melt tube
• - Measuring the wall thicknesses of the melt tube at the sensor positions and, beyond the differences on the circumference, the eccentricity of the wall thickness
• - by comparing the distance measurements after the extrusion tool and before the calibration device, the calculation of the inlet angle of the molten tube into the calibrator over the circumference (due to gravity, the inlet angle at the bottom of the molten tube is always different than at the top)
• - By comparing the wall thickness readings after the extrusion die and before the calibration, the calculation of Sagging the plastic melt after exiting the extrusion die.

The invention will be explained in more detail below with reference to an embodiment. In the accompanying drawing shows:

1 an extrusion plant for the production of plastic pipes with their main components in a schematic representation, and

2 a very schematic representation of a forming between the exit of the extrusion die and the inlet of the Kalibrierhülse melt tube.

In the 1 shown extrusion line for plastic pipes comprises an extruder unit 1 with a hopper 2 , over the extruder unit 1 a thermoplastic resin is supplied in granular or powder form. In the extruder unit 1 the granules or the powder is heated, kneaded and plasticized. Subsequently, the plastic as a moldable material in an extrusion die 3 promoted and there by an annular gap 11 pressed. The resulting hot, yet deformable melt tube 4 ' runs with oversize in a calibration device 6 one who has a vacuum tank 7 with a perforated calibration sleeve arranged at its entrance 8th having. The calibration sleeve 8th is infinitely adjustable in diameter, allowing the extruded tube 4 can be fixed to the desired outer diameter. After leaving the calibration device 6 kick the tube 4 in a cooling section 9 in which it is cooled to about room temperature. At the end of the extrusion line is a saw 10 arranged in the extruded tube 4 is cut to a predetermined length. The produced pipe 4 is by means of a deduction unit 5 pulled through the upstream facilities of the extrusion plant.

How out 2 shows that runs out of the between a nozzle 12 and a thorn 13 of the extrusion tool 3 formed annular gap 11 exiting melt tube 4 ' with oversize in the calibration sleeve 8th the calibration device 6 one. Immediately after exiting the extrusion die 3 and immediately before entering the calibration sleeve 8th the calibration device 6 are on the perimeter of the melt tube 4 ' distributes several gigahertz or terahertz sensors 14 arranged. By means of these sensors 14 become the geometry data of the melt tube 4 ' determined. This is how the distances between the sensors become 14 and the melt tube 4 ' measure, from which the diameter of the melt tube 4 ' and calculate its sagging. Furthermore, the wall thickness of the melt tube 4 ' at the positions of the sensors 14 Measured, and distributed from the measured differences over the circumference, determines the eccentricity of the wall thickness. Further, by comparing the distance measurements of the sensors 14 after the extrusion tool 3 and in front of the calibration device 6 the inlet angle of the melt tube 4 ' into the calibration device 6 be calculated. In addition, by comparing the wall thickness readings to the extrusion tool 3 and in front of the calibration device 6 the sagging of the plastic melt after exiting the extrusion die 3 be calculated.

The measured data obtained or the values calculated therefrom can be used in a variety of ways to optimize the process.

Preferably, by the measurement data with suitable algorithms via the plant control either automatically make a correction of the control variables or suggest a detailed graphical user interface (GUI) the operator detailed settings. Here, the measured data and the correlating control variables are the following: reading eccentricity control variable Centering screws of the extrusion tool Temperature zones of the extrusion tool (for thermal tube head centering) reading sagging control variable Height offset between extrusion tool and calibration device reading entry angle control variable Distance between extrusion tool and calibration device

Furthermore, the measured data obtained can also be used to optimize the design of the extrusion tool 3 , are specially used to calculate the optimal annular gap geometry for a wide range of applications. Here, in particular, instead of the dimensions of the annular gap 11 of the extrusion tool 3 the actual measured diameter and wall thickness of the enlarged by the strand expansion melt tube 4 ' into the design.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006056735 A1 [0004]

Claims (6)

Method for controlling and controlling pipe extrusion plants including measurement data of a produced pipe ( 4 ), one of an annular gap ( 11 ) an extruder unit ( 1 ) exiting melt tube ( 4 ' ) with oversize into a subsequent calibration device ( 6 ), characterized in that between extrusion die ( 3 ) and calibration device ( 6 ) at several points exactly the diameter, the wall thickness, any shape deviations, the ovality and the sagging of the molten tube ( 4 ' ), and these measured values or data calculated therefrom are used to control and control the extrusion plant. A method according to claim 1, characterized in that the measurement data are detected without contact. A method according to claim 2, characterized in that the measurement data by means of optical or fully electronic metrology in the gigahertz or terahertz range are detected. Method according to one of the preceding claims, characterized in that the measured data and the data calculated therefrom for an automatic continuous control of the extrusion plant (distance extrusion tool ( 3 ) to the calibration device ( 6 ), Height offset extrusion tool ( 3 ) to the calibration device ( 6 ), Centering nozzle ( 12 ) to thorn ( 13 )) be used. Method according to one of the preceding claims, characterized in that the control of the extrusion plant on the basis of the measured data and the data calculated therefrom by a detailed user guidance via a suitable graphical user interface (GUI). Arrangement for carrying out the method according to one of the preceding claims, characterized in that for detecting the measurement data a plurality of sensors ( 14 ) immediately after the outlet of the melt tube ( 4 ' ) from the extrusion tool ( 3 ) and immediately before it enters the calibration device ( 6 ) each on the circumference of the molten tube ( 4 ' ) are arranged distributed.

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