Method for changing the material in an extrusion device

Abstract

The present invention relates to a method for changing material in an extrusion device comprising at least two supply devices for supplying feedstock for an extruder, comprising the following steps: identifying a change request for changing material in an extrusion device, predetermining a production stability for a time after the material of at least one supply device has been changed, comparing the predetermined production stability to a threshold value of stability, changing the material in at least one supply device depending on the result of comparison.

Claims

1. A method for changing feedstock material in an extrusion device for producing plastic films comprising at least two supply devices for supplying feedstock for an extruder, comprising the following steps: identifying a change request for changing feedstock material in the extrusion device, calculating a predicted stability of a plastic film for a time after the feedstock material of at least one supply device has been changed, comparing the predicted stability to a threshold value of stability, and changing the feedstock material in the at least one supply device depending on the result of the comparison of the predicted stability to the threshold value of stability and as long as the predicted stability is above the threshold value of stability for at least one layer of the plastic film, wherein the step of calculating the predicted stability of the plastic film for the time after the feedstock material has been changed further comprises verifying how the subsequent change of the feedstock material of the at least one supply device will impact the predicted stability and further considering the correlation of the at least one supply device with the at least one layer of the plastic film that is to be produced.

2. The method according to claim 1, wherein the step of calculating the predicted stability of the plastic film further comprises retrieving material data concerning a presently-used feedstock material and a new feedstock material from a database and calculating the predicted stability of the plastic film based on the material data.

3. The method according to claim 1, wherein the plastic film is a multi-layer film, and wherein the step of calculating the predicted stability of the plastic film further comprises calculating a predicted stability of a first layer of the multi-layer film when the feedstock material for the first layer is supplied by a first supply device of the at least two supply devices and calculating a predicted stability of a second layer of the multi-layer film when the feedstock material for the second layer is supplied by a second supply device of the at least two supply devices.

4. The method according to claim 1, wherein the plastic film is a multi-layer film, and wherein the predicted stability for each layer of the multi-layer film is calculated and simulated for each of the at least two supply devices.

5. The method according to claim 1, wherein the steps of calculating the predicted stability of the plastic film and comparing the predicted stability to the threshold value of stability are carried out for each of the at least two supply devices, and an order of the at least two supply devices for changing the feedstock material is subsequently provided.

6. The method according to claim 1, wherein a measured stability of the plastic film is monitored and recorded at least while or after changing the feedstock material in at least one supply device.

7. The method according to claim 1, wherein the steps of calculating the predicted stability of the plastic film and comparing the predicted stability to the threshold value of stability are carried out based on user defined input parameters during an extrusion process.

8. The method according to claim 1, wherein at least one production parameter is adapted while changing the feedstock material for at least one supply device depending on the result of the comparison of the predicted stability to the threshold value of stability.

9. The method according to claim 1, wherein a rinsing time is determined for each feedstock material which is to be changed, and wherein the rinsing time is considered for a selection of an order of the supply devices.

10. The method according to claim 1, wherein the step of calculating the predicted stability of the plastic film further comprises calculating the predicted stability of the plastic film based on a speed with which the feedstock material is provided to the at least two supply devices, and wherein the step of changing the feedstock material in at least one supply device further comprises changing the speed with which the feedstock material is provided based on the comparison of the predicted stability to the threshold value of stability.

11. The method according to claim 1, wherein the steps of calculating the predicted stability of the plastic film and comparing the predicted stability to the threshold value of stability are repeated while changing the feedstock material.

12. The method according to claim 4, wherein at least two different orders of the at least two supply devices are simulated when changing the feedstock material in terms of the predicted stability of the plastic film.

13. The method according to claim 4, wherein all different orders of the at least two supply devices are simulated when changing the feedstock material in terms of the predicted stability of the plastic film.

14. The method according to claim 8, wherein at least one of the following production parameters is adapted while changing the feedstock material for at least one supply device of the at least two supply devices depending on the result of comparison of the predicted stability to the threshold value of stability: temperature of the extruder, film thickness, speed of the production, extruder output, and blow-up ratio.

15. The method according to claim 1, wherein the steps of calculating the predicted stability of the plastic film and comparing the predicted stability to the threshold value of stability are carried out continuously while changing the feedstock material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a first embodiment of an extrusion device according to the invention in the operating state,

(2) FIG. 2 shows the embodiment of FIG. 1 during a lowering of the filling levels,

(3) FIG. 3 shows the embodiment of FIGS. 1 and 2 with a filling level at changing filling level,

(4) FIG. 4 shows the embodiments of FIGS. 1 to 3 with a fluctuating filling level, which is kept at changing filling level,

(5) FIG. 5 shows the embodiment of FIGS. 1 to 4 during a cleaning situation,

(6) FIG. 6 shows the embodiment of FIGS. 1 to 5 during the refilling with a subsequent material,

(7) FIG. 7 shows an option of a course of the production stability,

(8) FIG. 8 shows a further option of a course of a production stability,

(9) FIG. 9 shows a further option of a course of a production stability and

(10) FIG. 10 shows an alternative embodiment of an extrusion device.

DETAILED DESCRIPTION

(11) FIGS. 1 to 6 illustrate an extrusion device 10 schematically, which is equipped with two supply devices 20. Each of these supply devices 20 is equipped with a feed container 26, a down pipe 24 and a weighing funnel 22. FIG. 1 shows the operating situation, wherein each supply device 20 is filled with a feedstock E up to a full operating filling level BF. In this state, the respective feedstock E is supplied to an extruder 30 via dosing screws 28 and is used for the production of the plastic film there. A method according to the invention is thereby carried out in a corresponding control device 40.

(12) As preparation for changing the material, FIG. 2 shows how a lowering of the filling levels F of the feedstock E takes place. By further production without refilling into the supply devices 20, the filling level F now drops, until it reaches a changing filling level WF according to FIG. 3. So as not to fall below this changing filling level WF, provision is made for corresponding filling level sensors 42, so that a short refilling in the form of a refilling push takes place at the point in time according to FIG. 3, so that substantially a fluctuating holding of the filling level F at the level according to FIGS. 3 and 4 takes place.

(13) FIG. 5 shows, how the feedstock E can be completely discharged downwards from the supply devices 20 at the time of actually changing the material. The catching can occur in a discharge container 60 as well as with the help of a returning device 70. For the discharging, here discharge openings 50 are provided, which are closed by means of a discharge closure 52. The corresponding arrangement of the discharge containers 60 is possible via a container interface 54. Last but not least, provision is made for an opening sensor 58, which can in particular be used in response to a cleaning step, which is to be carried out, with a cleaning device 80 comprising a plurality of cleaning means 82.

(14) It is illustrated in FIG. 6, how a subsequent material EF can already be filled back into the feed containers 26 of the supply devices 20 at this point in time, so that the switchover between the feedstock F and the subsequent material EF can subsequently take place particularly quickly and with small mixing.

(15) FIGS. 7 to 9 show options of a course of the production stability PS over time. FIG. 7 shows, how a transition is to be made to an average production stability PS on the very right by means of the dashed line. On the left, the situation in the case of application formula is shown, and the situation in the case of subsequent formula is shown on the right. In the case of this course, it can be seen that the production stability PS is always above the threshold for stability SG. It is illustrated by means of the two curved illustrations that unwanted gradient courses exist here, even though the threshold for stability SG is always exceeded. The dashed line, by means of which a linear transition between the individual production stabilities PS is provided with substantially consistent and constant gradients, is preferred.

(16) FIG. 8 shows a situation, which is unwanted and which is avoided by predetermining the production stability PS. In the course at the transition between the two formulas, a decrease of the production stability PS below the threshold for stability SG is thus at hand here, so that this path is avoided for a change strategy.

(17) FIG. 9 shows a substantially optimized change strategy, so that the production stability PS lies at a higher level for the majority of time of the change between the two formulas, than in the case of the application formula. The production stability PS decreases strongly only shortly prior to the end of changing the material and then remains on the level of the subsequent formula. The threshold for stability SG is also never fallen below here.

(18) FIG. 10 shows an alternative embodiment of an extrusion device 10. With regard to the advantages described according to the invention, said extrusion device is based on the embodiment of FIG. 1, but differs in the refilling function. A so-called batch process is thus provided here for the refilling. The feed container 26 is equipped with separate volumes, so that each volume of the feed container 26 can be understood to be a supply device 20. Components in the form of the down pipe 24 and of the weighing funnel 22 arranged therebelow are thus common components of the different supply devices 20. Below the weighing funnel 22, a mixing funnel, in particular comprising a mixer drive, is provided which allows for a homogenization prior to entering the extruder.

(19) The above discussion of the embodiments describes the present invention only in the context of examples. It goes without saying that individual features of the embodiments, if technically expedient, can be combined freely with one another, without leaving the scope of the present invention.

LIST OF REFERENCE NUMERALS

(20) 10 extrusion device

(21) 20 supply device

(22) 22 weighing funnel

(23) 23 funnel opening

(24) 24 down pipe

(25) 26 feed container

(26) 28 dosing screw

(27) 30 extruder

(28) 32 emergency sensor

(29) 40 control device

(30) 42 filling level sensor

(31) 50 discharge opening

(32) 52 discharge closure

(33) 54 container interface

(34) 56 sensor device

(35) 58 opening sensor

(36) 60 discharge container

(37) 62 discharge volume

(38) 70 return device

(39) 80 cleaning device

(40) 82 cleaning means

(41) 84 dust sensor

(42) E feedstock

(43) EF subsequent material

(44) BF operating filling level

(45) WF changing filling level

(46) F filling level

(47) PS production stability

(48) SG threshold value of stability