EXTRUDER AND METHOD FOR PERFORMING A DIAGNOSTIC INVESTIGATION IN AN EXTRUDER

Abstract

An extruder for polymeric materials, includes: a hollow extrusion cylinder, having an inlet for receiving pellets of polymeric material, and an outlet for expelling molten polymeric material; an extruder screw connected to a motor to rotate inside the extrusion cylinder and to move the polymeric material from the inlet to the outlet; heaters coupled to the extrusion cylinder; a sensor system configured to measure values of a recipe parameter and of a monitoring parameter; a processing unit, programmed to store a target value for the recipe parameter and to perform a feedback control to bring the recipe parameter to the target value and to keep it at the target value.

Claims

1. An extruder for polymeric materials, comprising: a hollow extrusion cylinder, extending along a longitudinal direction and having an inlet for receiving pellets of polymeric material, and an outlet for expelling molten polymeric material; an extruder screw connected to a motor to rotate inside the extrusion cylinder and to move the polymeric material from the inlet to the outlet; heaters coupled to the extrusion cylinder; a sensor system configured to measure values of a recipe parameter and of a monitoring parameter; a processing unit, programmed to store a target value for the recipe parameter and to perform a feedback control on the heaters to bring the recipe parameter to the target value and to keep it there, wherein the processing unit is programmed to process a first value of the monitoring parameter, measured at a first time instant, and a second value of the monitoring parameter, measured at a second time instant, after the first time instant, and is programmed to generate alert data in response to a comparison between the first and the second value of the monitoring parameter.

2. The extruder according to claim 1, wherein the processing unit has access to a memory containing reference data representing an intensity of variation in the monitoring parameter and wherein the processing unit is programmed to generate the alert data in response to comparing the variation between the first and the second value of the monitoring parameter with the reference data.

3. The extruder according to claim 2, wherein the processing unit is programmed to detect variations in the target value for the recipe parameter and to generate alert data also as a function of an absence of variations in the target value for the recipe parameter between the first and the second time instant.

4. The extruder according to claim 1, wherein the processing unit is programmed to generate the alert data also as a function of a duration of the time interval between the first and the second time instant.

5. The extruder according to claim 1, wherein the processing unit is programmed to store a first succession of values for the monitoring parameter captured in succession one after the other and spaced by a first predetermined time interval, wherein the first value of the monitoring parameter and the second value of the monitoring parameter are selected from the values of the first succession.

6. The extruder according to claim 5, wherein the processing unit is programmed to derive, from the first succession of values, a second succession of values, spaced by a second predetermined time interval, wherein the second succession of values is a subset of the first succession of values and wherein the second predetermined time interval is greater than the first predetermined time interval.

7. The extruder according to claim 1, wherein the processing unit is programmed to process a plurality of different monitoring parameters and to generate the alert data in response to a corresponding plurality of comparisons performed for the respective monitoring parameters of the plurality of monitoring parameters.

8. The extruder according to claim 1, wherein the processing unit is programmed to save records to a database, wherein each record comprises the following information items: a time instant of capture; the value of the recipe parameter at the time instant of capture; the value of the monitoring parameter at the time instant of capture; data representing the type of polymeric material processed by the extruder at the time instant of capture.

9. The extruder according to claim 8, wherein the processing unit is programmed to receive a recipe which a user wishes to set, the recipe including data representing the type of polymeric material to be processed and a target value for the recipe parameter, query the database for identifying a record corresponding to the recipe to be set, compare a value of the monitoring parameter measured after setting the recipe, at the second time instant, with the value of the monitoring parameter contained in the record corresponding to the recipe, where the time instant of capturing the record constitutes the first time instant.

10. The extruder according to claim 1, wherein the monitoring parameter is based on one or more of the following quantities: pressure of the molten polymeric material measured downstream of the extruder screw; temperature of the molten polymeric material; absorbed power of the motor that turns the extruder screw; absorbed power of the heaters; temperature of the extrusion cylinder; speed of the extruder screw.

11. The extruder according to claim 1, wherein the recipe parameter is based on one or more of the following quantities: temperature of the extrusion cylinder; speed at which the polymeric material is moved out of the extruder screw; pressure measured at the outlet of the extrusion cylinder.

12. The extruder according to claim 1, comprising a pushing device, configured to move the molten polymeric material fed by the extruder screw, to make it available to a moulding machine for making polymeric objects, wherein one or more of the following conditions are true: i) the monitoring parameter is based on the pressure of the molten polymeric material measured downstream of the pushing device; ii) the recipe parameter is based on one or more of the following quantities: speed at which the pushing device moves the molten polymeric material; pressure measured at an inlet zone of the pushing device.

13. A method for performing a diagnostic investigation in an extruder for polymeric materials, wherein the extruder comprises: an extruder screw connected to a motor to rotate inside an extrusion cylinder provided with heaters and to move the polymeric material from an inlet to the outlet, causing the polymeric material to melt; a sensor system for measuring a recipe parameter; a processing unit, programmed to store a target value for the recipe parameter and to perform a feedback control on the heaters to bring the recipe parameter to the target value and to keep it there, the method comprising the following steps: measuring a monitoring parameter; processing a first value of the monitoring parameter, measured at a first time instant, and a second value of the monitoring parameter, measured at a second time instant, after the first time instant; generating alert data in response to a comparison between the first and the second value of the monitoring parameter.

14. The method according to claim 13, wherein the step of processing comprises making a comparison between an intensity of variation of the monitoring parameter from the first to the second value and reference data.

15. The method according to claim 14, wherein the step of generating alert data is also responsive to verifying the fact that the target value for the recipe parameter has remained unchanged between the first and the second time instant.

16. The method according to claim 13, wherein a plurality of monitoring parameters are measured and wherein the step of generating the alert data is responsive to a step of processing corresponding variations over time in the value of the monitoring parameters of the plurality of monitoring parameters, according to a predetermined logic.

17. The method according to claim 13, comprising a step of saving records to a database, wherein each record comprises one or more of the following information items: a time instant of capture; the value of the recipe parameter at the time instant of capture; the value of the monitoring parameter at the time instant of capture; data representing the type of polymeric material processed by the extruder at the time instant of capture.

18. The method according to claim 17, comprising a step of receiving a recipe which a user wishes to set, and which includes data representing the type of polymeric material to be processed and the target value for the recipe parameter, triggers a step of querying the database for a record corresponding to the recipe to be set, and wherein, in the case where such a record is found, the method includes a step of comparing a value of the monitoring parameter measured after setting the recipe, at the second time instant, with the value of the monitoring parameter contained in the record corresponding to the recipe selected from the database, where the time instant of capturing the record constitutes the first time instant, if no such record is found, the method triggers a step of self-learning in which it is made ready to update the database with a new record.

19. (canceled)

20. An extruder for polymeric materials, comprising: a hollow extrusion cylinder, extending along a longitudinal direction and having an inlet for receiving pellets of polymeric material, and an outlet for expelling molten polymeric material; an extruder screw connected to a motor to rotate inside the extrusion cylinder and to move the polymeric material from the inlet to the outlet; heaters coupled to the extrusion cylinder; a sensor system configured to measure values of a recipe parameter and of a monitoring parameter; a processing unit, programmed to store a target value for the recipe parameter and to perform a feedback control based on the recipe parameter, wherein the processing unit is programmed to process a first value of the monitoring parameter, measured at a first time instant, and a second value of the monitoring parameter, measured at a second time instant, after the first time instant, and is programmed to generate alert data in response to a comparison between the first and the second value of the monitoring parameter, and wherein the processing unit is programmed to store a first succession of values for the monitoring parameter captured one after the other and spaced by a first predetermined time interval, wherein the first value of the monitoring parameter and the second value of the monitoring parameter are selected from the values of the first succession.

21. The method according to claim 20, wherein consecutive values of the first succession of values for the monitoring parameter are spaced in time by a first predetermined time interval

Description

BRIEF DESCRIPTION OF DRAWINGS

[0080] These and other features will become more apparent from the following description of a preferred embodiment, illustrated by way of non-limiting example in the accompanying drawings, in which:

[0081] FIG. 1 illustrates an embodiment of the extruder of this disclosure, where the extruder is configured to feed molten thermoplastic material to a compression moulding machine;

[0082] FIG. 2 illustrates a further embodiment of the extruder of this disclosure, where the extruder is configured to feed molten thermoplastic material to an injection moulding machine, in an operating configuration in which the extruder screw is at the withdrawn position;

[0083] FIG. 3 illustrates the extruder of FIG. 2 in an operating configuration in which the extruder screw is at the advanced position;

[0084] FIG. 4 schematically illustrates a processing unit of the extruder of FIG. 1 or of FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0085] With reference to the accompanying drawings, the numeral 1 denotes an extruder. The extruder 1 comprises a hollow extrusion cylinder 2. The extrusion cylinder 2 extends in a longitudinal direction between an inlet 2A and an outlet 2B. The extrusion cylinder 2 is configured to receive pellets of polymeric material through the inlet 2A and to expel molten polymeric material through the outlet 2B.

[0086] The extruder 1 comprises a loading hopper 11, configured to feed pellets of polymeric material to the inlet 2A of the extrusion cylinder 2.

[0087] The extruder 1 also comprises an extruder screw 3; the extruder screw 3 is positioned inside the extrusion cylinder 2 and is rotatable relative thereto. The extruder screw 3 also extends in the longitudinal direction L. The extruder 1 comprises a motor 31 (preferably electric) configured to make the extruder screw 31 rotate on itself.

[0088] The extruder 1 comprises one or more heaters 4. The one or more heaters 4 are coupled to the extrusion cylinder 2. The extrusion cylinder 2 is made of a material with high thermal conductivity such as metal, for example, and specifically, steel; thus, the heaters 4 are configured to heat the material the extrusion cylinder 2 is made of, which in turn heats the thermoplastic material contained therein.

[0089] The extruder 1 also comprises a pushing device 5. The pushing device 5 is connected downstream of the extrusion cylinder 2 to move the material leaving the outlet 2B of the extrusion cylinder 2 and to expel it from the extruder 1. In an embodiment, the pushing device 5 includes a pump which is connected downstream of the outlet 2B of the extrusion cylinder 2. In this embodiment, the pushing device 5 is configured to move the thermoplastic or polymeric material leaving the extrusion cylinder 2 continuously; thus, the extruder screw 3 rotates continuously about the longitudinal axis L so that the extrusion cylinder 2 expels material through its outlet 2B continuously. This embodiment is used in extruders configured to feed compression moulding machines.

[0090] In an embodiment, the pushing device 5 includes a piston that moves with reciprocating motion inside a cylinder, from a withdrawn position to an advanced position. Inside the cylinder 2, the piston delimits an injection chamber which is in fluid connection with the outlet 2B of the extrusion cylinder 2. More specifically, the extruder includes a first duct that extends from the outlet 2B of the extrusion cylinder 2, and a second duct that extends from the injection chamber; the first and second ducts merge into an outlet duct configured to expel the molten polymeric material. The extruder screw 3 is rotatable inside the extrusion cylinder 2 about the longitudinal axis L and is also movable by translation along the longitudinal axis L, between a withdrawn position and an advanced position. Initially, the extruder screw 3 is at the withdrawn position and the piston of the pushing device 5 is at the advanced position. As the extruder screw 3 rotates the extruder screw 3 also moves along the longitudinal direction L from the withdrawn position to the advanced position and, at the same time, the piston of the pushing device 5 moves from the advanced position to the withdrawn position so the material leaving the outlet 2B of the extrusion cylinder 2 invades the injection chamber; at this stage, the material is prevented from flowing into the outlet duct by a valve which blocks its passage. After a predetermined length of time from when the extruder screw 3 starts rotating, the extruder screw 3 is stopped and the piston is moved from the withdrawn position to the advanced position by a specific motor; thus, as the piston moves to the advanced position, it pushes the molten material, which has in the meantime filled the injection chamber, into the outlet duct; at this stage, the valve has been opened and allows the material to flow into the outlet duct; while the piston is moving from the withdrawn position to the advanced position, the extruder screw 3 moves along the longitudinal axis from the advanced position to the withdrawn position; when all the molten material has been expelled, another cycle starts. This embodiment is used in extruders configured to feed injection moulding machines.

[0091] The extruder 1 also comprises a sensor system. The sensor system comprises one or more of the following sensors: [0092] Outlet pressure sensor 61, configured to measure the pressure of the thermoplastic material at the outlet of the pushing device 5; [0093] Screw power sensor 62, configured to measure the electric power absorbed by the electric motor 31 which drives the extruder screw 3; [0094] Screw speed sensor 63, configured to measure the rotation speed of the extruder screw 3; [0095] Heater power sensor 64, configured to measure the electric power absorbed by the heaters 4; [0096] Molten material temperature sensor 65, configured to measure the temperature of the molten polymeric material leaving the extruder; [0097] Pushing device power sensor 66, configured to measure the electric power absorbed by the pushing device 5; [0098] Cylinder temperature sensor 67, configured to measure the temperature of the extrusion cylinder 2; [0099] Pushing device speed sensor 68, configured to measure the speed of the pushing device 5; [0100] Inlet pressure sensor 69, configured to measure the pressure of the molten thermoplastic material at the inlet of the pushing device 5.

[0101] The outlet pressure sensor 61 is connected to an outlet duct which receives the molten material leaving the extrusion cylinder 2, downstream of the pushing device 5. The screw power sensor 62 is connected to the motor 31 that drives the extruder screw 3. The screw speed sensor 63 is connected to the extruder screw 3. The heater power sensor 64 is connected to the heaters 4. The molten material temperature sensor 65 is connected to an outlet duct which receives the molten material leaving the extrusion cylinder 2. The pushing device power sensor 66 is connected, in the case where the pushing device 5 comprises a pump, to the motor that drives the pump, and, in the case where the pushing device 5 comprises a piston movable inside a cylinder, to the motor that drives the piston. The cylinder temperature sensor 67 is connected to the cylinder 2. The pushing device speed sensor 68 is connected to the pump in the case where the pushing device 5 comprises a pump, and to the piston in the case where the pushing device 5 comprises a piston movable inside a cylinder. The inlet pressure sensor 69 is connected to a duct which receives the molten material from the outlet 2B of the cylinder 2, upstream of the pushing device 5 (that is, upstream of the pump, in the case where the pump is provided, or upstream of the point of connection between the first duct, connected to the outlet 2B, and the second duct, connected to the injection chamber, in the case where the piston slidable in the cylinder is provided).

[0102] The sensors 61, 62, 63, 64, 65, 66 are each configured to measure a respective monitoring parameter 72. More specifically, the outlet pressure sensor 61 is configured to measure a monitoring parameter 72 representing the quantity ‘p1’. The screw power sensor 62 is configured to measure a monitoring parameter 72 representing the quantity ‘p2’. The screw speed sensor 63 is configured to measure a monitoring parameter 72 representing the quantity ‘p3’. The heater power sensor 64 is configured to measure a monitoring parameter 72 representing the quantity ‘p4’. The molten material temperature sensor 65 is configured to measure a monitoring parameter 72 representing the quantity ‘p5’. The pushing device power sensor 66 is configured to measure a monitoring parameter 72 representing the quantity ‘p6’. Preferably, at least two of the sensors 61, 62, 63, 64, 65, 66 are provided, hence at least two monitoring parameters 72 are measured.

[0103] The sensors 67, 68, 69 are each configured to measure a respective recipe parameter 71. More specifically, the cylinder temperature sensor 67 is configured to measure a recipe parameter 71 representing the quantity ‘p7’. The pushing device speed sensor 68 is configured to measure a recipe parameter 71 representing the quantity ‘p8’. The inlet pressure sensor 69 is configured to measure a recipe parameter 71 representing the quantity ‘p9’.

[0104] The extruder 1 comprises a processing unit 7. The processing unit 7 is programmed to receive one or more recipe parameters 71 from the sensors 67, 68, 69. The extruder 1 also comprises a user interface 9, configured to allow a user to select a target value 70 for each recipe parameter 71. The processing unit 7 is connected to the user interface 9 to receive, for each recipe parameter 71, the respective target value 70 selected by the user.

[0105] The processing unit 7 is configured to compare the one or more recipe parameters 71 measured by the sensors 67, 68, 69 (or by one or more of them) with the corresponding target values 70 and to generate one or more feedback control signals 75 as a function of a difference between the one or more recipe parameters 71 measured and the corresponding target values 70. The processing unit 7 is configured to send the one or more feedback control signals 75 to one or more of the following components of the extruder: extruder screw 3, heaters 4, pushing device 5. More specifically, the processing unit 7 can send a feedback control signal 75 to the heaters 4 to vary the power absorbed by the heaters 4 (quantity ‘p4’); the processing unit 7 can send a feedback control signal 75 to the extruder screw 3, specifically to the electric motor 31, to vary the rotation speed of the extruder screw 3 (quantity ‘p3’); the processing unit 7 can send a feedback control signal 75 to the pushing device 5, specifically to the motor of the pushing device 5, to vary the power absorbed by the motor of the pushing device 5 (quantity ‘p6’). Thus, the quantities ‘p4’, ‘p3’ and ‘p5’ are read by the sensors 64, 63 and 65, respectively, and thus constitute monitoring parameters; at the same time, they can be controlled by feedback so that the one or more recipe parameters 71 remain equal or close to the respective target values 70.

[0106] The processing unit 7 is programmed to process values of each monitoring parameter 72 captured at successive time instants. More specifically, the processing unit 7 is configured to process a first value of each monitoring parameter 72, measured at a first time instant, and a second value of the same monitoring parameter 72, measured at a second time instant, after the first time instant. The processing unit 7 is programmed to generate alert data 73, in response to a comparison between the first and the second value of each monitoring parameter 72. In an embodiment, the processing unit 7 is configured to generate the alert data 73 if, for at least one monitoring parameter 72 (or, preferably for at least two monitoring parameters 72), there is a significant difference (greater than a predetermined tolerance threshold) between the first and the second value. The alert data 73 may indicate an anomaly in the operation of the extruder 1. In an embodiment, the extruder 1 comprises an alarm system (or output interface) 10 and the processing unit 7 is configured to send the alert data 73 to the alarm system 10.

[0107] In an embodiment, the processing unit 7 has access to a memory 8 (which may form part of the extruder 1 itself, or may be a remote memory); the memory 8 may contain reference data 74 representing an intensity of variation of each monitoring parameter 72 (that is, a tolerance threshold for the intensity of variation). The processing unit 7 is configured to receive the reference data 74 and to generate the alert data in response to a comparison between the variation of each monitoring parameter 72 from the first to the second value and the respective reference data 74.

[0108] It should be noted that in the case where the pushing device 5 comprises a reciprocating piston in a cylinder, some monitoring parameters 72, such as, for example, the pressure of the molten polymeric material measured downstream of the pushing device, have a cyclic trend; thus, the first and the second value are measured at corresponding time instants of different cycles; the reference data 74 are also referred to the cycle time instant at which the values of the monitoring parameters 72 are measured.