METHOD FOR OPERATING AN EXTRUDER, AND EXTRUDER

Abstract

A method for operating an extruder that has a screw, including the steps: (a) detection of a formulation identifier which is associated with material to be extruded and which encodes at least one operating variable, from which an ideal screw rotational frequency of the screw, which is to be set for the extrusion process, can be determined, (b) time-dependent detection of a throughput parameter, from which a throughput of the extruder can be deduced, (c) detection of a non-conformance point in time, at which the material can no longer be produced with a predefined quality, owing to excessive wear of the extruder, and (d) calculation of a limit throughput parameter from the throughput parameter, linking of the limit throughput parameter to the formulation identifier, and storing of the limit throughput parameter.

Claims

1. A method for operating an extruder (10), which has a screw (14), with the steps: (a) detecting a recipe identifier (R.sub.i), which is assigned to material (20) to be extruded and encodes at least one parameter, from which a target screw rotational frequency (f.sub.i,soll) of the screw (14) is able to be determined, which is to be preset at the extrusion, (b) time-dependent detecting of a throughput parameter (M), from which a conclusion can be drawn regarding a throughput (m) of the extruder (12), (c) detecting an error time (t.sub.P) at which the material (20), owing to too great a wear of the extruder (12), is no longer able to be produced with a predetermined quality and (d) calculating a threshold throughput parameter (M.sub.i(t.sub.P)) from the throughput parameter (M), linking with the recipe identifier (R.sub.i) and storing of the threshold throughput parameter (M.sub.i(t.sub.P)).

2. The method according to claim 1, further comprising the step: for recipe identifiers (R.sub.j) of material (20), which is processed within an equal wear interval (I.sub.e), about the error time (t.sub.P): storing of the throughput parameter (M.sub.i(t)) linked with the recipe identifier (R.sub.j) and a time stamp (t.sub.P), by means of which a conclusion can be drawn regarding the error time (t.sub.P), as equivalent throughput parameter (M.sub.i,eq(t.sub.P)).

3. The method according to claim 1, further comprising the steps: (a) at a change time (t.sub.W) changing the material (20) to be extruded from a current material (20) with a current recipe identifier (R.sub.i) to a future material (20) with a future recipe identifier (R.sub.j), (b) detecting the throughput parameter (M.sub.i(t.sub.W)) for the material (20) with the current recipe identifier (R.sub.i) at the change time (t.sub.W) or at an equivalent change time (t.sub.W,e) thereto which lies within the equal wear interval (I.sub.e) about the change time (t.sub.W), (c) detecting the throughput parameter (M.sub.j(t.sub.W)) for the material (20) with the future recipe identifier (R.sub.j) at the change time (t.sub.W) or at an equivalent change time (t.sub.W,e) thereto, which lies within the equal wear interval (I.sub.e) about the change time (t.sub.W), and (d) storing of an equivalent throughput characteristic diagram, which links the throughput parameter (M.sub.i(t.sub.W)) for the material (20) with the current recipe identifier (R.sub.i) at the change time (t.sub.W) or equivalent change time (t.sub.W,e) with the throughput parameter (M.sub.j(t.sub.W)) for the material (20) with the second recipe identifier (R.sub.j) at the change time (t.sub.W) or equivalent change time (t.sub.W,e).

4. The method according to claim 3, further comprising the steps: (i) before a change of material (20) with a current recipe identifier (R.sub.a) to material (20) with a future recipe identifier (R.sub.z) detecting the current throughput parameter (M.sub.a(t.sub.Wa)) for the material (20) with the current recipe identifier (R.sub.a) at the current change time (t.sub.Wa) and (ii) interpolating the equivalent throughput characteristic diagram, so that from the throughput parameter (M.sub.a(t.sub.Wa)) for the material (20) with the current recipe identifier (R.sub.a) at the current change time (t.sub.Wa) the throughput parameter (M.sub.z(t.sub.Wa)) for the material with the future recipe identifier (R.sub.z) at the current change time (t.sub.Wa) is obtained.

5. The method according to claim 1, further comprising the steps: before a change from a current material (20) with a current recipe identifier (R.sub.i) to a future material (20) with a future recipe identifier (R.sub.j): (a) determining the closest time (t.sub.Wn) at which for the throughput parameter (M.sub.i(t.sub.Wn)) with a current recipe identifier (R.sub.i) an equivalent throughput parameter (M.sub.j(t.sub.Wn)) exists for the future recipe identifier (R.sub.j), (b) determining a difference (M=M.sub.i(t.sub.Wn)) between the throughput parameters (M.sub.j(t.sub.Wn)), (c) adding a wear progress summand, which is calculated from the difference (M=M.sub.i(t.sub.Wn))M.sub.j(t.sub.Wn))), to the throughput parameter (M.sub.i(t.sub.Wn)) of the current recipe identifier, so that an estimated throughput parameter (M.sub.i(t.sub.Wn)) is obtained, and (d) when the estimated throughput parameter lies below the threshold throughput parameter (M.sub.j(t.sub.p)) of the future material (20) with the future recipe identifier (R.sub.j), emitting an alarm.

6. The method according to claim 1, further comprising the steps: before a change from a current material (20) with a current recipe identifier (R.sub.i) to a future material (20) with a future recipe identifier (R.sub.j): (a) determining the closest time (t.sub.Wn) at which for the throughput parameter (M.sub.i(t.sub.Wn)) with a current recipe identifier (R.sub.i) an equivalent throughput parameter (M.sub.j(t.sub.Wn)) for the future recipe identifier (R.sub.j) exists, (b) determining a quotient (Q=M.sub.i(t.sub.Wn))/M.sub.j(t.sub.Wn)) of the throughput parameters (M.sub.i(t.sub.Wn), (M.sub.j(t.sub.Wn)), (c) multiplying a wear progress factor, which is calculated from the quotient (Q), with the throughput parameter (M.sub.i(t.sub.Wn)) of the current recipe identifier, so that a second estimated throughput parameter (M.sub.i(t.sub.Wn)) is obtained, and (d) when the second estimated throughput parameter lies below the threshold throughput parameter (M.sub.j(t.sub.p)) of the future material (20) with the future recipe identifier (R.sub.j), emitting an alarm.

7. The method according to claim 1, further comprising the steps: (a) for at least one predetermined recipe identifier (R.sub.1) determining the throughput parameter (M.sub.1(t)) as a function of time (t), and also from throughput parameters on extruding of materials (20) with other recipe identifiers (R.sub.2, R.sub.3, . . . ), and (b) calculating an error time estimated value (t.sub.P,est) at which the minimum throughput parameter (M.sub.1,min) for the predetermined recipe identifier would fall below the minimum throughput parameter (M.sub.z,min), which is assigned to the recipe identifier (R.sub.z), by extrapolating the throughput parameter (M.sub.1(t)).

8. The method according to claim 7, further comprising the step: (a) for a predetermined amount of recipes fitting a parameterised model function to the measured throughput parameters (M.sub.i(t.sub.W)), so that fit parameters are obtained, (b) wherein the extrapolating of the throughput parameter (M.sub.1(t)) takes place by means of the model function with the fit parameters.

9. A method for operating an extruder (12), which has a screw (14), with the steps: (a) detecting a recipe identifier (R.sub.i) which is assigned to material (20) which is to be extruded and encodes at least one parameter, from which a target screw rotational frequency (f.sub.i) of the screw (14), which is to be preset at the extrusion, is able to be determined, (b) time-dependent detecting of a throughput parameter (M.sub.i(t)), from which a conclusion can be drawn regarding a throughput (m) of the extruder (12), comprising a throughput per revolution of the screw (14), (c) at a change time (t.sub.W1) changing the material (20) to be extruded to a material (20) with a second recipe identifier (R.sub.j), (d) detecting a throughput parameter (M.sub.i(t.sub.W1)) for the material (20) with the first recipe identifier (R.sub.i) at the change time (t.sub.W1) or a change time (t.sub.W1,e) equivalent thereto, which lies within an equal wear interval (I.sub.e), about the change time (t.sub.W1), (e) detecting the throughput parameter (M.sub.j(t.sub.W1)) for the material (20) with the second recipe identifier (R.sub.j) at the change time (t.sub.W1) or a change time (t.sub.W1,e) equivalent thereto, which lies within the equal wear interval (I.sub.e) about the change time (t.sub.W1), (f) storing an equivalent throughput characteristic diagram (K), which links the throughput parameter (M.sub.i(t.sub.W1)) for the material (20) with the first recipe identifier (R.sub.i) at the change time (t.sub.W1) or the equivalent change time (t.sub.W1,e) with the throughput parameter (M.sub.j(t.sub.W1)) for the material (20) with the second recipe identifier (R.sub.j) at the change time (t.sub.W1,e).

10. The method according to claim 9, further comprising the steps: (a) determining a recipe identifier as reference recipe identifier, and (b) determining the equal wear intervals I.sub.e(t.sub.Wk) from the change times (t.sub.Wk) of the reference recipe identifier.

11. The method according to claim 9, further comprising the steps: (a) detecting an error time (t.sub.P) at which the extruder (12), owing to too great a wear, is no longer able to be operated with the target screw rotational frequency (f.sub.i,soll) (because otherwise the required quality of the product is no longer guaranteed), (b) determining the throughput parameter (M.sub.i(t.sub.P)) at a time (t.sub.P) in the equal wear interval (I.sub.e), (c) determining the minimum throughput parameter (M.sub.i,min) from this throughput parameter (M.sub.i(t.sub.P)), by equalizing of minimum throughput parameter (M.sub.i,min) and throughput parameter (M.sub.i(t.sub.P)).

12. A method for operating an extrusion system (10), which has (a) a first extruder (12.1) and (b) a second extruder (12.2) and (c) at least a third extruder (12.3), with the steps: (d) carrying out a method according to claim 1 for the majority of the extruders.

13. An extruder (12) with (a) a cylinder (16), (b) at least one screw (14), which runs in the cylinder (16), and (c) a control unit (24), wherein (d) the control unit (24) is arranged to automatically carry out a method according to claim 1.

14. An extrusion system (10) with (a) a first extruder (12.1) with a first screw (14.1), (b) a second extruder (12.2) with a second screw (14.2) and (c) at least a third extruder (12.3) with a third screw (14.3), (d) at least one control unit (24), which is arranged to automatically carry out the method according to claim 1.

Description

[0049] The invention is explained further below with the aid of the enclosed drawings. There are shown here

[0050] FIG. 1 an extrusion system according to the invention, with extruders according to the invention for carrying out a method according to the invention,

[0051] FIG. 2 a diagram, in which the progression of the throughput parameters for several recipe identifiers is recorded schematically over time,

[0052] FIG. 3 a comparable diagram to that according to FIG. 2, wherein the time over which a recipe is respectively processed, is shorter than in the case of FIG. 2.

[0053] FIG. 1 shows an extrusion system 10 according to the invention with a first extruder 12.1, a second extruder 12.2 and a third extruder 12.3. The first extruder has a first screw 14.1, which runs in a cylinder 16.1. By means of a material feed 18.1, material 20.1 to be extruded is fed to the extruder 12.1.

[0054] The extruder 12.1 has a drive 22.1 in the form of an electric motor for rotating the screw 14.1. A control unit 24.1 controls the drive 22.1 so that the latter brings about a predetermined screw rotational frequency f. The control unit 24.1 can communicate with a central computer 26. It is possible that in addition an intermediate computer 28 is used. The control unit 24 comprises a digital memory in which a program is stored which, during operating, brings it about that the method described below is implemented.

[0055] Firstly, a recipe identifier R.sub.i of material which is to be extruded is detected. The index i is a running index, which could also be designated as a recipe index, because thereby the different recipes are numbered consecutively. A recipe contains for example an indication of the components of the material 20.1 which is fed to the extruder 14.1.

[0056] The recipe R.sub.i comprises in addition an indication of a target screw rotational frequency f.sub.i,soll, which is to be preset at the extrusion of the material 20.1. Generally, this target screw rotational frequency f.sub.i,soll refers to a predetermined throughput m, which refers to the quantity of material which is delivered by the extruder 12.1 per revolution of the screw 14.1. From the throughput m and the screw rotational frequency f.sub.i therefore a mass throughput can be calculated which is measured in kilograms per unit of time and indicates how many kilograms of extruded material are delivered by the extruder 12.1 per unit of time.

[0057] The extruder 12.1 delivers the extruded material to an injection head 32 via a line 30.1. The remaining extruders of the extrusion system 10, in the present case therefore the extruders 12.2 and 12.3, deliver respectively extruded material via corresponding lines 30.2, 30.3 to the injection head 32, where a profile 34 is injected from the combined streams of material. The profile 34 runs on a conveyor 36, for example a conveyor belt, for further processing.

[0058] A scales 38 determines the weight of a portion of the profile 34, so that a section weight G, which is also designated as a metre weight, of the profile 34 can be determined. As the portion of the material which comes from a specific extruder is known in the profile, from this information and from the measured metre weight and from a speed at which the profile 34 is moving, the throughput in kilograms per unit of time of all extruders can be determined. The speed at which the profile 34 is moving is likewise measured, for example by measuring a rotational speed of a roll over which the profile 34 rolls. The extruders 12.2 and 12.3 and any further extruders which are present are respectively constructed identically, however it is also possible that they differ in their type of construction. The essential characteristics of the extruders which are relevant for the invention are, however, those described above.

[0059] The respective control units 24 (reference numbers without numerical index refer respectively to all corresponding objects) detect the respective screw rotational frequency f.sub.i. As generally the throughput is indicated in mass per unit of time and according to a preferred embodiment is part of the recipe, from the screw rotational frequency f.sub.i the throughput per screw revolution can be calculated, namely as a quotient of throughput in weight or mass per unit of time with the target throughput according to the recipe. The target throughput is indicated in mass or weight per minute. When wear occurs, then the screw rotational frequency f.sub.i must be increased, in order to achieve the target throughput. This generally takes place manually, but can also take place automatically.

[0060] FIG. 2 shows diagrammatically that the throughput parameter M decreases with the time t, which is measured in operating hours. At the start of the observation, in particular after the installation of a screw into the extruder, firstly material is extruded with the recipe identifier R.sub.1. It can be seen that the target throughput lies just below 500 grams per screw revolution.

[0061] This recipe identifier is detected by the control unit 24 for example in that it is inputted by an operator via an operator interface. From the recipe identifier R.sub.1, the control unit 24 determines the screw rotational frequency f.sub.1 which is firstly to be selected. During the extruding, the throughput parameter M is detected continuously in the form of the mass throughput per screw revolution, for example once per second or once per 10 seconds.

[0062] At a change time t.sub.W1 firstly the respectively current throughput parameter M.sub.1(t.sub.W1) is stored. Thereafter, the material is processed according to a second recipe identifier R.sub.2. At the start of the processing, the throughput parameter M.sub.2(t.sub.W1) is determined. The same takes place at a time t.sub.W2 on a change from the material with the second recipe identifier to the material with the third recipe identifier R.sub.3.

[0063] At a time t.sub.W5, at which the material is processed according to the second recipe identifier R.sub.2, the screw rotational frequency f.sub.2 would have to be selected to be so high, in order to achieve the predetermined target throughput, that too intensive a heating of the material to be extruded, and local complete vulcanization would occur. The throughput parameter M at this time is M.sub.2(t.sub.P). It is stored as threshold throughput parameter. For a later recurring processing of the material according to the recipe identifier R.sub.2 it is known from then that it must be ensured that the throughput parameter M.sub.2 always lies above this threshold throughput parameter M.sub.2,min.

[0064] In FIG. 1 the case is shown in which the materials are exchanged with respect to the corresponding recipe identifiers so rarely that the wear during processing of only one material already clearly progresses. However, the case occurs more frequently in which different materials with different recipe identifiers are changed so frequently that the wear during the processing of the material with a particular recipe identifier is small. This case is indicated schematically in the diagram according to FIG. 3. It can be seen that during an equal wear interval I.sub.e, the wear decreases only so little that it can be regarded as constant. For this reason, in good approximation the throughput parameters M.sub.3,eq (t.sub.P), M.sub.2(t.sub.P), M.sub.4,eq(t.sub.P) can be regarded as belonging to the same wear state.

[0065] If for example at a distinctly later time t.sub.W9 a change is made from the material with the recipe identifier R.sub.3 to the recipe identifier R.sub.4, then in an approximation it can be assumed that a difference M=M.sub.3(t.sub.Wn)M.sub.4(t.sub.Wn) has remained the same. Therefore this difference, which in this case is regarded as wear progress summand, is added to the throughput parameter M.sub.4(T.sub.W9). If it should transpire that the value thus obtained lies below the threshold parameter M.sub.3,min for the recipe production R.sub.3, which is charted schematically, then an alarm is emitted.

[0066] Alternatively, it is possible that instead of the difference, the quotient is formed from the throughput parameters, in the present case this would be M.sub.3(t.sub.Wn)/M.sub.4(t.sub.Wn) When material with a recipe identifier is used particularly frequently, it is expedient to regard this recipe identifier as reference recipe identifier.

[0067] In FIG. 2, the measurement points are indicated schematically at which at least for the recipe with the recipe identifier R.sub.2 the throughput parameters are determined. When a plurality of these parameters exists, then the wear curve can be adapted with a model curve which in the present case is drawn in dashed lines. For example, as in the case shown in FIG. 2, this is a straight line. With sufficiently many measurement points, the parameters of the model function can be selected so that the model function is adapted optimally to the measurement data. This curve fitting belongs to the prior art and is therefore not described further.

[0068] Through the adapting to the model function, fit parameters are obtained which describe the chronological development of the throughput parameter M.sub.4 for the material with the recipe identifier R.sub.i. As soon as these are obtained, the time at which the specified or determined minimum throughput parameter M.sub.i,min would be fallen below can be determined therefrom. This value can be interrogated in an automated manner or in response to a corresponding enquiry by the user via the user interface of the respective control unit 24 or via the intermediate computer 28 or through the central computer 26.

LIST OF REFERENCE NUMBERS

[0069] 10 extrusion system [0070] 12 extruder [0071] 14 screw [0072] 16 cylinder [0073] 18 material feed [0074] 20 material [0075] 22 drive [0076] 24 control unit [0077] 26 central computer [0078] 28 intermediate computer [0079] 30 line [0080] 32 injection head [0081] 34 profile [0082] 36 conveyor [0083] 38 scales [0084] f.sub.i,soll target screw rotational frequency [0085] f.sub.i screw rotational frequency [0086] G metre weight [0087] i recipe index [0088] m throughput (Kg/R) [0089] M material flow direction [0090] R recipe