METHOD AND DEVICE FOR DETERMINING A LAYER PROPERTY OF A LAYER IN AN EXTRUSION PROCESS

Abstract

The invention relates to a method for determining at least one layer property of a layer to be determined, in particular a foam layer (16), in an extrusion process, where a supply material (7) is at least partially foamed and an extrusion product (2) with the foam layer (16) is put out, comprising at least the following steps: a) irradiating said extrusion product (2) using electro-magnetic radiation (S), b) electro-magnetically measuring at least one radiation (R) having travelled through said foam layer (16), c) measuring at least one feed-in rate or feed-in volume of the supply material (7), and d) determining the at least one material property of said layer (16) to be determined from the measured feed-in volume (z) and the electro-magnetic measurement.

Claims

1. Method for determining at least one layer property (n16, wd16) of a layer (16) to be determined regarding at least one property thereof in an extrusion process, whereby a supply material (7) is mixed or superimposed at least in part and an extrusion product (2) with the layer (16) to be determined is put out, comprising at least the following steps: a) irradiation of said extrusion product (2) using electro-magnetic radiation (S), b) electro-magnetic measuring of at least one radiation (R) having travelled through said layer (16) to be determined, c) measuring at least one feed-in rate (z) or feed-in volume of said supply material (7), and d) determining at least one layer property (n16, wd16) of said layer (16) to be determined from the measured feed-in volume (z) and the electro-magnetic measurement.

2. Method according to claim 1, characterized in that in the extrusion process said extrusion product (2) is made of a plastics material and said at least one layer (16) to be determined is made of mixed plastics comprising at least two substances.

3. Method according to claim 2, characterized in that, as said layer (16) to be determined, a foam layer (16) is investigated which is made from a plastics material with a gas during the extrusion.

4. Method according to one of the preceding claims, characterized in that, as electro-magnetic radiation, Terahertz radiation (S), in particular in a frequency range between 0.1 and 50 THz is irradiated.

5. Method according to claim 4, characterized in that a reflection measurement of at least one boundary layer (15a, 15b, 17a, 17b) of said extrusion product (2), in particular a boundary layer (15b, 17a) of said layer (16) to be determined, is carried out, and a runtime measurement determining at least one runtime (t15, t16, t17) of the Terahertz radiation (S) in at least one layer (15, 16, 17) of said extrusion product (2) is carried out.

6. Method according to one of the preceding claims, characterized in that said extrusion product (2) is measured electro-magnetically during the conveyance involving relative adjustment of said extrusion product (2) in its direction of conveyance, preferably without rotation of said extrusion product (2).

7. Method according to one of the preceding claims, characterized in that the feed-in rate (z) is measured gravimetrically and/or involving measurement of a supply mass per time, e.g. by means of a scales device (9), and/or involving measurement of a supply volume per time.

8. Method according to one of the preceding claims, characterized in that, further, a retraction velocity (v) of said extrusion product (2) is determined and used for determining said at least one layer property (n16, wd16).

9. Method according to claim 8, characterized in that from said retraction velocity (v) and said feed-in rate (z) a cross-section surface (A) of said layer (16) to be determined and/or a fictitious partial material layer (116) of said layer (16) to be determined, in particular a layer (16) mixed from two substances layer, is determined.

10. Method according to claim 9, characterized in that said mixed layer (16) with its layer thickness (wd16) is determined as the sum or superimposition of a fictitious continuous material layer (116) of a first plastics component with a first partial wall thickness (wd116) and a fictitious second layer, e.g. gas layer (216), with a second partial wall thickness (wd216), whereby the two partial wall thicknesses (wd116, wd216) together form the wall thickness (wd16) of the mixed layer (16).

11. Method according to one of the preceding claims, characterized in that, as layer property of said mixed layer (16), a refraction index (n16) and/or a wall thickness (wd16) is determined.

12. Method according to one of the preceding claims, characterized in that, upon determining the layer property (n16, wd16), further, at least one dimension, e.g. a diameter (D), of said extrusion product (2) or of a layer of said extrusion product (2) is included.

13. Method for manufacturing an extrusion product (2) from a plastics material, where at least one supply material (7) is continuously fed to an extruder (3) and foamed at least in part, and an extrusion product (2) is continuously extruded and extracted, whereby said extrusion product (2) contains at least one layer (16) to be determined, at least one layer property (n16, wd16) of said the layer (16) to be determined is determined using a method according to one of the preceding claims, and as a function of said at least one determined layer property (n16, wd16) the feed-in rate (Z) or feed-in volume of said supply material (7) is adjusted for regulating said at least one layer property (n16, wd16).

14. Method according to claim 13, characterized in that said supply material (7) is fed in as bulk material, e.g. granules or powder, and said extrusion product (2) is a pipe having at least one mixed layer, e.g. a foam layer (16) or fiber reinforced layer, e.g. having a continuous outer pipe (15) and a continuous inner pipe (17) and a mixed layer (16) disposed in-between.

15. Device (1) for manufacturing an extrusion product (2), said device (50) comprising at least: a conveyor device (6) for conveying a supply material (7), an extruder (3) for receiving said supply material (7), comprising an extrusion nozzle (3c) for continuous output of said extrusion product (2), an extractor and sawing device (5) for extracting or conveying said extrusion product (2) output by said extruder (3), an electro-magnetic measuring device (10) for electro-magnetic measuring of said extrusion product (2) during the conveyance from said extruder (3) while measuring at least one layer property (n16, wd16) and generating a second measuring signal (S2), a feed-in volume measuring device (9) for measuring a feed-in rate (Z) of said fed-in supply material (7) and putting out a first measuring signal (S1), a controller (12) for receiving a first measuring signal (S1) of said feed-in volume measuring device (9) and said measuring signal (S2) of said electro-magnetic measuring device (10) and putting out a volume adjustment signal (S3) to said conveyor device (6), for regulating said at least one layer property (n16, wd16) while measuring the two measuring signals (S1, S2) and adjusting said the feed-in volume (Z).

Description

[0029] Subsequently, the invention will be further illustrated by means of the attached drawings in a few embodiment examples. Hereby, by way of example only, in particular, foam is described as a mixed material while e.g. other mixtures may also be examined similarly. It is shown in:

[0030] FIG. 1 an extrusion device for manufacturing a foam pipe with a measuring device according to an embodiment of the invention;

[0031] FIG. 2 the section through a multi-layer wall of an extrusion product with a middle foam layer;

[0032] FIG. 3 a section through a foam pipe with a middle foam layer;

[0033] FIG. 4 a diagram with a measuring signal;

[0034] FIG. 5 a flow chart of a procedure according to the invention.

[0035] According to FIG. 1, an extrusion device 1 for manufacturing extrusion products 2, in particular, in the case at hand, foam pipes 2, comprises an extruder 3, a cooling device 4 and an extractor and sawing device 5. Furthermore, the extrusion device comprises a conveyor device 6 extracting the supply material 7, e.g. synthetic granules, plastics powder or plastics pellets, from a reservoir 8 and conveying it via a scales device 9 to an input opening 3a, e.g. a funnel, of the extruder 3. The conveyor device 6 may be designed e.g. as adjustable input opening regulating a falling stream of the supply material 7 by means of a corresponding cross-section adjustment.

[0036] In a manner known as such the extruder 3 further comprises a feed zone, a smelting device 3b, as well as a nozzle 3c which puts out, in a manner known as such, the extrusion product, in this case as a foam pipe 2, from the molten supply material 7. In order to create e.g. a foam pipe 2 according to FIG. 3 having several concentric tubes the extruder 3 may be designed correspondingly more complex and/or having several nozzles 3c.

[0037] It is also possible to use a mixture of different supply materials, e.g. several granulates, as supply material 7. Foaming agents may be added to induce chemical foaming.

[0038] The scales device 9 determines the fee-in rate z or, respectively, the temporal feed-in amount as mass per time, i.e. in kg/s, and puts out a first measuring signal S1 to a controller 12. Thereafter, the supply material 7 is received by the extruder 1, molten and pressed out via its nozzle 3c as foam pipe 2, subsequently cooled in the cooler device 2, and correspondingly extracted or removed and cut into pieces by the extractor and sawing device 3.

[0039] Furthermore, the extruder device 1 comprises a Terahertz measuring device 10, which may basically be provided at any location downstream from the extruder 3, to measure the generated extrusion product 2. The Terahertz measuring device 10 emits Terahertz radiation S, receives reflected radiation R and, if appropriate, following a partial evaluation, puts out second measuring signals S2 to the controller 12. Hereby, the conveyed foam pipe 2 may be measured in its full circumference without rotating or shifting while still inside the extrusion device 1. The Terahertz measuring device 10 comprises a transmitter 10a and a receiver 10b which e.g. rotate around the extrusion product 2 in order to measure the full circumference thereof.

[0040] The extraction device 5 supplies a third a measuring signal S3 relating to an extraction velocity v of the extrusion product 2 to the controller 12. Moreover, the controller 12 puts out a volume adjustment signal S4 to the conveyer unit 6, in order to adjust the feed-in rate z e.g. by adjusting a feed cross-section or a spiral conveyor. Furthermore, the controller 12 may also receive measuring signals of the extruder 3, e.g. relating to temperature, or even a further velocity signal, e.g. of a melting pump, as a further measuring signal.

[0041] FIG. 2 shows a wall 14 of the extrusion product 2, e.g. a wall 14 of a foam pipe, shown in FIG. 3 as extrusion product. The wall 14 comprises an outer wall layer 15, a middle foam layer 16 and an inner wall layer 17. For clarity, in FIG. 2 the layers 15, 16, 17 are shown flat; FIG. 3 shows the embodiment of a foam pipe 2 in which these layers have correspondingly ring-shaped shapes.

[0042] According to FIG. 2, Terahertz radiation S emitted from the Terahertz measuring device 10 hits the layers 15, 16, 17, having refraction indexes n15, n16, n17, at a right angle from the outside. According to FIG. 3, in the case of a round foam pipe 2 the radiation S impacts radially distributed over the circumference. The radiation S is partially reflected at the boundary layers, where the refraction index n changes, always according to Snell's law. Thus, the radiation S is reflected towards the outside 15a and the inside 15b of the first layer 15, reflected at the inner boundary surface 15b corresponding to its change of refraction index from n15 to n16. In the middle foam layer 16 there is a refraction index n16 resulting from an averaging between the refraction index n0 of the air at n0=1 and n15=n171,5. Thus, n16 lies between n0=1 and n15=n161,5, depending on the material portion in the middle foam layer 16.

[0043] In FIG. 2 the middle foam layer 16 is shown schematically; in actual fact, there is a multiplicity of bubbles 16a or pore respectively with bridges 16b there between. Thus, the radiation S transits the foam layer 16 and is reflected again at the boundary layers 17a and 17b of the inner wall layer 17.

[0044] In case of a pure foam pipe comprising merely one foam layer 16, corresponding transitions of the foam layer 16 to the air are being measured.

[0045] FIG. 4 shows in a simplified form a measuring diagram as reflection signal of the reflected radiation R. The Terahertz radiation S is emitted by the transmitter in a pulsed form so that in the reflected radiation R a runtime measurement of the reflection peaks at the boundary surfaces is possible. Thus, according to FIG. 5, it is possible, when conducting the runtime measurement of a measuring pulse, to obtain e.g. a measuring signal with the four peaks p15a, p15b, p17a, p17b, corresponding to the boundary surfaces 15a, 15b, 17a, 17b.

[0046] For the subsequent calculation it must be taken into consideration that e.g. for the reflection at the boundary surface 15b the radiation S transits the layer thickness d15 of the outer layer 15 twice, i.e. from the first boundary surface 15a to 15b, and, after be reflected, back to 15a.

[0047] The wall thickness wd of a pipe, e.g. the wall thickness wd15 of the outer pipe 15, may be determined from the determined time difference t according to the following formula:

[00001]$\begin{array}{cc}w.Math..Math.d=\frac{t*c}{2*n}& \left(\mathrm{GL1}\right)\end{array}$

[0048] where c=speed of light in a vacuum, n0=refraction index.

[0049] Thus, the wall thicknesses wd15 and wd17 of the through pipes 15 and 17 may be determined, with n=1,5.

[0050] For the middle foam layer 16, too, the following applies

[00002]$\begin{array}{cc}w.Math..Math.d_{16}=\frac{t_{16}*c}{2*n_{16}},& \left(\mathrm{GL2}\right)\end{array}$

[0051] with unknown n16.

[0052] Hereby, the refraction index n16 is a characteristic value for identifying the foam layer 16 which is to be determined.

[0053] In order to determine the refraction index n16 of the foam layer 16 it is calculated as follows:

[0054] The foam layer 16 is first assumed as averaged value or sum of afictitiousplastics layer 116 with layer thickness wd116 and afictitiousair layer 216 with layer thickness wd216, as indicated in FIG. 2 on the right side. The following applies

t.sub.16=t.sub.116+t.sub.216

t.sub.216=t.sub.16t.sub.116t.sub.116=2*wd.sub.116*n.sub.116/c (GL3)

[0055] where n116=n15=n17=1,5 and

[0056] t16, t116, t216 runtimes in the layers 16, 116, 216.

[0057] Hereby, the layer thickness wd116 is determined via the feed-in rate z of the dimension mass per time or kg/s, determined as first measuring signal S1, and further the third measuring signal S3 of the extraction velocity v. Subsequently, firstly, a length mass Lg of the dimension mass per unit length, i.e. kg/m, may be determined, i.e. the length mass Lg is determined as quotient of the fee-in rate z and the extraction velocity v or, respectively, the foam pipe (extrusion product) 2,

i.e. Lg=z/v. (GL4)

[0058] The fictitious material layer 116 may be calculated e.g. from theknownouter diameter R16 of the foam layer 16, i.e. the inner diameter of the outer tube 15. The entire pipe diameter D=2R15, with R15 outer radius of the outer layer (outer tube) 15, is known; R15 may be determined e.g. optically by means of image capture of the extrusion product 2 or by knowledge of the exit opening of the nozzle 3c. Thus, from R15 and the layer thickness wd15 of the outer layer 15 determined from the runtime measurement results the outer radius R16 of the foam layer 16 as R16=R15wd15.

[0059] Subsequently, the cross-sectional surface A, indicated in FIG. 3, may be determined from the length mass Lg and the density 116 of the continuous plastic material of the entire ring-shaped layer 116 by formation of quotients as:

A=Lg/(GL5)

[0060] Thus, the cross-sectional surface A and also the outer radius R16 of the ring-shaped foam layer 16 is known. The following applies

A*R16*wd116 (GL6)

[0061] Thus, from this wd116 is determined.

[0062] Therefore, from

wd16=wd116+wd216 (GL7)

[0063] and Gl 2 follows:

[00003]$\begin{array}{cc}{n}_{16}=\frac{t_{16}*c}{2*w.Math..Math.d_{16}}=\frac{t_{16}*c}{2*w.Math..Math.d_{116}\left(1-n_{116}\right)+t_{16}*c}& \left(\mathrm{GL8}\right)\end{array}$

[0064] Using equation GL2 the wall thickness wd16 of the foam layer 16 may be calculated or determined respectively from the refraction index n16.

[0065] Thus, the refraction index n16 of the foam layer 16 may be viewed as a material specific property of the foam layer 16 and may serve directly for regulating the feed-in rate z. Thus, the refraction index n16 can be compared to a refraction index nsoll. Hereby, it becomes apparent that already the refraction index n16 represents a good comparison value for adjustments of the feed-in rate z.

[0066] Thus, a regulation and therewith a method for manufacturing an extrusion product 2 can be created, where a regulation of the material feed and therewith a generation of extrusion products like the foam pipe 2 with high quality is possible by means of determining the refraction index n16 of the foam layer 16 and thereafter by the controller 12 by putting out amount related adjustment signals S3 to the conveyor device 6.

[0067] Instead of the refraction index n16 of the foam layer 16 it is also possible to determine another material specific variable, e.g. a foaming degree sg, which is determined as volume related portion of the plastics material in the foam layer 16. Thus, this relative value also corresponds to the relative surface value of the fictitious material layer 216 in the layer 16.

[0068] Even pure foam pipe, i.e. a foam layer 16 alone without the further layers 15 and 17, can be manufacture accordingly. In such a case the outer diameter D16=2R16 may be determined directly electro-magnetically or optically or even from knowledge of the outer diameter of the nozzle 3c.

[0069] When manufacturing plane, i.e. non-round, products a Terahertz measuring device may be chosen accordingly radiating directly at a right angle onto the extrusion product 2.

[0070] Thus, according to FIG. 6, the method according to the invention comprises the following steps: after the start in step St0, subsequently, in step St1, the signals are received, i.e. the first measuring signal S1 of the feed-in volume z (feed-in value measuring signal), the second measuring signal S2 of the electro-magnetic measurement, i.e. the runtimes t16, t15, t17, the third measuring signal S3 of the extraction velocity v. If applicable, the controller 12 can receive further measuring signal here, e.g. of the extruder 3. Furthermore, the controller 12 resorts to known material specific data and equations of an internal or external memory 13.

[0071] Subsequently, thus, the controller 12 determines the refraction index n16 of the foam layer 16 according to the afore-mentioned equations in step St2 and compares e.g. to a target value nsoll; if appropriate, also a degree of foaming or the wall thickness wd16 of the foam layer 16 is determined.

[0072] Then, in the subsequent regulation step St3 volume adjustment signals S3 are determined and put out to the conveyor device 6, whereupon the method is reset again to a position prior to step St1.

[0073] Instead of gas or air respectively as the second substance of the mixed layer it is also possible to use e.g. a fiber material with known refraction index (instead n0=1) or another mixture of two substances.