Extruder and method for performing a diagnostic investigation in an extruder

Abstract

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

Description

Technical Field

[0001] This invention relates to an extruder for polymer materials. This disclosure also relates to a method for performing diagnostic investigations in an extruder for polymer materials. This disclosure further relates to a method for extruding polymer materials. This disclosure also relates to a diagnostic system for an extruder.

[0002] Therefore, this disclosure relates to the field of extruders for polymer materials; more specifically, this disclosure relates to the field of extruders configured to feed materials into injection or compression molding machines. Background Technology

[0003] Such extruders are described, for example, in the applicant's patent document WO2018025150. Another extruder for polymer materials is described in the applicant's patent document WO2016181361A; the extruder described in this document includes one or more sensors configured to monitor the properties of the polymer material inside it.

[0004] Typically, extruders are supplied with plastic material (e.g., from silos or bags); in such cases, it is necessary to quickly identify malfunctions during material loading. For example, when a first load of material is completed, a second load of a different material may be mistakenly loaded. Therefore, it is necessary to identify unforeseen material variations. Furthermore, even if the material of the second load loaded when the first load is completed is the first material, its properties may differ from those of the first material in the first load; these differences may be due to, for example, the fact that the second load may come from a different manufacturer and / or manufacturing plant than the first load; or they may be due to contaminants or defects in the second load or due to unsuitable storage conditions (e.g., the second load may have been stored in an excessively humid environment). Therefore, it is necessary to identify unforeseen changes in material properties.

[0005] Therefore, in the extruder field, there is a need for rapid detection of unforeseen changes in materials or material properties. Furthermore, since the behavior of materials within the extruder is also affected by the wear condition of the extruder, another requirement is the ability to distinguish between behavioral changes caused by material properties and those caused by extruder wear. This allows for the detection of wear-related problems, enabling the planning of maintenance and replacement of worn components. Yet another requirement is the ability to detect other extruder problems, such as a broken mixer, allowing for targeted maintenance.

[0006] Examples of extruders are provided in the following patent documents: WO2016181361A1, DE102008019445A1, US5122315A, WO01 / 77206A1, WO2020 / 074743A1, and EP3210748A1. Additionally, information about extruders can be found in the following article: Hobson Wet et al., “What is your extruder trying to tell you?”, PTONLINE, XP055798505. Summary of the Invention

[0007] The purpose of this disclosure is to provide an extruder that overcomes one or more of the aforementioned disadvantages of the prior art and a method for performing diagnostic investigations in an extruder for polymer materials.

[0008] The above-mentioned objectives are fully achieved by the extruder according to the present disclosure and the method for conducting diagnostic investigations in an extruder for polymer materials, as characterized in the appended claims.

[0009] Therefore, this disclosure relates to an extruder for extruding polymeric materials or plastics. Examples of polymeric materials are polypropylene and polyethylene.

[0010] The extruder includes a hollow extrusion barrel. The hollow extrusion barrel has an inlet for receiving granules of polymer material and an outlet for discharging molten polymer material. The extrusion barrel extends elongated in the longitudinal direction. More specifically, the extrusion barrel extends elongated from the inlet to the outlet.

[0011] An extruder includes an extruder screw. The extruder screw is connected to a motor, which drives the extruder screw to rotate within the extrusion barrel, causing the polymer material to move from the inlet towards the outlet. Therefore, the rotation of the extruder screw causes the polymer material to move from the inlet towards the outlet.

[0012] The extruder includes a heater connected to the extrusion barrel. More specifically, the heater includes an electric heating element. The heater is configured to heat the polymer material within the extrusion barrel.

[0013] In one or more embodiments, the extruder includes a pushing device. The pushing device is configured to move molten polymer material conveyed by a screw so that the molten polymer material can be used in a molding machine for manufacturing polymer objects.

[0014] In one embodiment, the actuation device includes a pump; in this case, molten polymer material is continuously fed to a molding machine, preferably a compression molding machine. The function of the pump is to ensure that material is discharged from the extruder and delivered to the molding machine at a constant rate; in fact, without a pump, the flow rate of the material would fluctuate due to the inherent characteristics of the extruder; in some applications, such fluctuations are unacceptable, and therefore a pump is preferred.

[0015] In another embodiment, the actuation device includes an injection piston that is translatably movable within a chamber between a retracted position and an advanced position; in this case, molten polymer material is intermittently fed to a molding machine, preferably an injection molding machine. In either case, when a actuation device is provided, it includes a motor (preferably electric) configured to drive a pump or injection piston.

[0016] However, in one or more embodiments, no pusher is provided, and the molten material is directly conveyed from the extruder outlet to a machine that processes the material to manufacture objects or other products. If the downstream machine is a compression molding machine, the absence of a pusher results in lower dimensional accuracy of the manufactured objects; however, in some applications, this lower accuracy may be acceptable. In this case, if the downstream machine is an injection molding machine, the axial movement of the extruder screw may serve to push the material out of the extrusion barrel (rather than a pusher); in this case, after the dispensed dose of material is pushed out of the barrel, the screw must remain in the push position until the die is fully filled; this limits the machine speed, but is still acceptable in some cases.

[0017] Furthermore, even when the extruder is configured to deliver polymer material to the lining machine, a pusher is not necessary. The lining machine is a machine that produces a dosing dose of polymer material, which is then applied to the interior of a closure (e.g., a crown or can lid) to improve the seal. In these machines, fluctuations in the flow rate of the material delivered by the extruder are permissible. Such lining machines are described, for example, in patent documents WO2004080684, EP0838326, and WO2015092644, which are incorporated herein by reference.

[0018] This disclosure may also provide a system comprising an extruder and a machine configured to receive molten material from the extruder. The machine configured to receive molten material from the extruder may be a compression molding machine, an injection molding machine, an injection compression molding machine, or a lining machine.

[0019] The extruder includes a sensor system. The sensor system is configured to measure the value of at least one formulation parameter and the value of at least one monitoring parameter. It should be noted that the sensor system may be configured to measure the values ​​of multiple formulation parameters; the sensor system may be configured to measure the values ​​of multiple monitoring parameters.

[0020] An extruder includes a processing unit. This unit is programmed to store target values ​​for formulation parameters and to perform feedback control to bring the formulation parameters to and maintain those target values. Therefore, formulation parameters refer to parameters that can be set to target values ​​and must be maintained near or at those target values. On the other hand, monitoring parameters generally refer to parameters measured by a sensor system.

[0021] The processing unit is programmed to perform feedback control on (at least) the control parameters in order to maintain the formulation parameters at target values. In one embodiment, the control parameters are consistent with the monitoring parameters; in another embodiment, the control parameters are other than the monitoring parameters. The sensor system is preferably configured to also measure the control parameters.

[0022] The heater is connected to and controlled by the processing unit. The heater is configured to receive command signals from the processing unit. The control signals indicate the amount of heat to be transferred from the heater to the extruded material.

[0023] More specifically, in one embodiment, the processing unit is configured to control the heater via feedback to bring the recipe parameters to a target value and maintain those parameters at that target value. Therefore, in this embodiment, the control parameters are parameters related to the operation of the heater. As described below, other feedback controls (as a supplement or alternative to the control of the heater) may exist, acting on other control parameters, such as the power of the actuator motor and / or the rotational speed of the screw.

[0024] Specifically, in one example, the processing unit is configured to receive a control parameter as a control temperature, which represents the temperature of the extruded material. The processing unit is configured to compare the control temperature with a predetermined temperature value. The processing unit is configured to send a command signal to the heater based on the performed comparison. If the control temperature is lower than the predetermined value, the command signal commands the heater to increase the amount of heat transferred to the material; conversely, if the control temperature is higher than the predetermined value, the command signal commands to decrease the amount of heat transferred.

[0025] Preferably, the processing unit is programmed to process a first value of the monitoring parameter measured (or captured or exported) at a first moment and a second value of the monitoring parameter measured (or captured or exported) at a second moment after the first moment, and is programmed to generate alarm data in response to a comparison between the first and second monitoring parameter values. In one embodiment, the extruder includes an alarm system; the processing unit is configured to activate the alarm system based on the alarm data. The alarm system may include a siren, warning lights, and / or a video interface on which messages are displayed to the operator.

[0026] In one embodiment, the first value and the second value of the monitoring parameter are obtained by the processing unit by calculating a moving average; the moving average is the average of values ​​that can move over time within a predetermined time window (e.g., 60 seconds). Therefore, the first value is given by the average of the values ​​of the monitoring parameter calculated at the first moment and used in the time window immediately preceding the first moment; the second value is given by the average of the values ​​of the monitoring parameter calculated at the second moment and used in the time window immediately preceding the second moment.

[0027] Calculating moving averages has the advantage of reducing noise (i.e., minimizing random variations in the values ​​of monitored parameters that are not caused by factors such as material anomalies or wear; thus, variations caused by factors such as material anomalies or wear are more noticeable).

[0028] In one implementation, the processing unit can access a memory containing reference data representing the intensity (or degree) of changes in the monitored parameters. The processing unit is programmed to generate alarm data in response to a comparison of a change between a first value and a second value of the monitored parameters with the reference data. For example, the reference data may include the maximum permissible difference between the monitored parameters at a first time and at a second time; if the change in the monitored parameters exceeds the maximum permissible difference, the processing unit is configured to generate alarm data.

[0029] In one implementation, the processing unit is programmed to detect changes in the target value of the formulation parameter. For example, the formulation parameter may be set by the operator; a change in the formulation parameter might be due to the operator entering new formulation parameters when adding new material. The processing unit is also programmed to generate alarm data if the target value of the formulation parameter does not change between a first time point and a second time point. Therefore, if the monitored parameter changes between the first and second time points but the formulation parameter does not change, the processing unit generates alarm data. In reality, changes in the monitored parameter not caused by changes in the formulation parameter might be due to anomalies in the material (i.e., unexpected changes in the material or its properties).

[0030] In one embodiment, the processing unit is programmed to also generate alarm data based on the duration of the time interval between the first and second moments. More specifically, the processing unit is programmed to generate alarm data based on a comparison of the duration of the time interval between the first and second moments with a predetermined value (e.g., one week or one month). In practice, if the duration of the time interval between the first and second moments is less than the predetermined value, the processing unit is programmed to attribute the change in the monitored parameters (or multiple monitored parameters), if any, to an anomaly in the polymer material; conversely, if the duration of the time interval between the first and second moments is greater than the predetermined value, the processing unit is programmed to attribute the change in the monitored parameters (or multiple monitored parameters), if any, to extruder wear.

[0031] Preferably, the time interval between the first and second moments is less than 1 hour. More preferably, the time interval between the first and second moments is less than 30 minutes, 20 minutes, or 15 minutes. In practice, it should be noted that changes in the monitored parameters over long time intervals (e.g., weeks or months) may be due to causes other than anomalies in the material: for example, extruder wear, particularly screw wear. Therefore, the processing unit generates an alarm signal only when a (significant) change in the monitored parameter is detected within a time interval short enough to rule out wear as the cause.

[0032] In one embodiment, the processing unit is programmed to store a first series of values ​​for a monitoring parameter, captured sequentially and spaced at first predetermined time intervals. The first predetermined time interval is preferably less than or equal to 1 second. A first value and a second value (by the processing unit) of the monitoring parameter are selected from the first series of values. This allows for the identification of changes in the monitoring parameter that occur during a brief transition (approximately a few minutes) and last for a longer period (e.g., 10-15 minutes); for example, if the filling (or bag) of polymer material differs from the previous filling (or bag), the monitoring parameter changes from the first value to the second value over a transition period of a few minutes, and then remains approximately constant at the second value until the polymer material in the filling (or bag) is complete (e.g., 10-15 minutes).

[0033] The processing unit is programmed to derive a second series of values ​​from a first series of values ​​at second predetermined time intervals; the second series of values ​​is a subset of the first series of values, and the second predetermined time interval is greater than the first predetermined time interval. Preferably, the second predetermined time interval is greater than 5 or 10 minutes; for example, the second predetermined time interval could be 10 or 15 minutes. Therefore, the processing unit captures values ​​measured in the first (shorter) time interval, and if no significant change is detected, the processing unit can delete some data from the captured data and retain only some of these values ​​(specifically, those at the second predetermined time interval) in memory to obtain information about the trend of the monitored parameter. In practice, in one embodiment, the processing unit is configured to save the second series of values ​​of the monitored parameter (or multiple monitored parameters) to a database.

[0034] In one embodiment, the processing unit is programmed to process multiple different monitoring parameters. In this embodiment, the processing unit is configured to generate alarm data in response to multiple comparisons performed for a corresponding monitoring parameter among the multiple monitoring parameters. These monitoring parameters are measured by a sensor system; in this case, the sensor system includes multiple sensors, each configured to measure a corresponding monitoring parameter among the multiple monitoring parameters.

[0035] More specifically, the processing unit processes multiple monitoring parameters by comparing the value of each monitoring parameter at a first time point with its value at a second time point. It should be noted that the more monitoring parameters that change significantly between the first and second times (exceeding a certain tolerance), the greater the probability that an anomaly does exist in the material; therefore, the processing unit can generate alarm data including an alarm reliability level, which depends on the number of monitoring parameters whose changes between the first and second times are significant (i.e., greater than the corresponding tolerance threshold)—(the more monitoring parameters with significant changes, the higher the alarm reliability). More complex processing logic is also conceivable, where each monitoring parameter is assigned a corresponding (predetermined) weight, such that the alarm reliability is a function of the weighted average of the changes in the monitoring parameters between the first and second times.

[0036] More specifically, the monitoring parameters (or multiple monitoring parameters) may include and / or be based on one or more of the following quantities (e.g., according to a predetermined formula, it may include a combination of one or more of the following quantities):

[0037] p1) The pressure of the molten polymer material measured downstream of the actuating device;

[0038] p2) The power absorbed by the motor that makes the extruder screw rotate;

[0039] p3) Extruder screw speed;

[0040] p4) Absorbed power of the heater;

[0041] p5) Temperature of the molten polymer material;

[0042] p6) Electrical power absorbed by the motor of the driving device.

[0043] It should be noted here that the combinations of quantities 'p1', 'p2', 'p4', and 'p5' are particularly useful for detecting errors when adding thermoplastic materials; on the other hand, quantities 'p3' and 'p5' are particularly useful for detecting the wear condition of the extruder screw. Therefore, for example, if the processing unit detects unexpected changes in 'p5' and 'p3', the alarm data will include diagnostic information indicating possible wear of the extruder screw. Conversely, if the processing unit detects unexpected changes in one or more of the parameters 'p1', 'p2', 'p4', and 'p5', the alarm data will include diagnostic information indicating a possible abnormality in the material.

[0044] The processing unit can also be configured to detect faults in a mixer configured to mix molten materials when 'p1' and 'p6' undergo unexpected changes but other parameters (e.g., one or more of parameters 'p2-p5') do not change significantly.

[0045] It should be noted that the formulation parameters (or multiple formulation parameters) may include and / or be based on one or more of the following quantities (e.g., according to a predetermined formula, it may include a combination of one or more of the following quantities):

[0046] p7) Extrusion barrel temperature;

[0047] p8) The speed at which the device moves the molten polymer material;

[0048] p9) Pressure measured at the inlet area of ​​the actuating device.

[0049] More specifically, when the actuating device includes a pump, the speed at which the actuating device moves the molten polymer material represents the speed of the pump.

[0050] It should be noted that one or more monitoring parameters may be consistent with one or more control parameters. The processing unit acts on the control parameters through feedback control to bring the formulation parameters (or multiple formulation parameters) to a target value and maintain them at that target value. More specifically, the processing unit controls the speed of the extruder screw (amount 'p3') through feedback control to maintain the pressure (amount 'p9') measured at the inlet area of ​​the pusher at a corresponding target value. Alternatively or supplementarily, the processing unit may control the power absorbed by the heater (amount 'p4') through feedback control to maintain the temperature of the extruder barrel (amount 'p7') at a corresponding target value. Alternatively or supplementarily, the processing unit may control the electrical power absorbed by the pusher (amount 'p6') through feedback control to maintain the speed (p8) at which the pusher moves the molten polymer material at a corresponding target value.

[0051] It should be noted that, as described below with respect to the method (but this applies in the same way to the apparatus), parameters 'p7' to 'p9' can be used as monitoring parameters, and alternatively, parameters 'p1' to 'p6' can be used as formulation parameters.

[0052] In one implementation, the processing unit is programmed to save records to a database, where each record includes one or more of the following information items: capture time; value of formulation parameter (or combination of formulation parameters) at the capture time; value of monitoring parameter (or combination of monitoring parameters) at the capture time; and data indicating the type of polymer material processed by the extruder at the capture time. In this way, a database can be constructed in which each type of polymer material and each formulation parameter (or combination of formulation parameters) is associated with a corresponding monitoring parameter (or multiple monitoring parameters).

[0053] More specifically, the processing unit can be programmed to: receive a formulation that the user wishes to set, which includes data indicating the type of polymer material to be processed and target values ​​for formulation parameters; query a database to obtain a record corresponding to the formulation to be set; and (if such a record is found) compare the values ​​of monitoring parameters measured at a second time after setting the formulation with the values ​​of monitoring parameters contained in the record corresponding to the formulation, wherein the time at which the record is captured constitutes the first time. It should be noted here that extruders are typically used to process multiple different materials; therefore, they can process a first material (e.g., in the first week), then a second material (e.g., in the second week), and then the first material again (e.g., in the third week). When processing of the first material resumes at the beginning of the third week, it is useful to compare the monitoring parameters (or multiple monitoring parameters) measured at the beginning of the third week with the monitoring parameters (or multiple monitoring parameters) from the first week that are also related to the first material. For this purpose, it is useful to store in the database the values ​​of the monitoring parameters associated with data indicating the type of polymer material during the first week. Another useful feature is storing the moment the monitoring parameters were captured in the database, because the longer the time elapsed after the capture moment, the greater the wear on the extruder (in fact, wear can cause changes in monitoring parameters even without any anomalies in thermoplastic materials). The processing unit can also periodically save new records for each formulation set.

[0054] Therefore, in one embodiment, the values ​​of the monitoring parameters (or the vector values ​​of multiple monitoring parameters) are measured at predetermined intervals (e.g., every second) and stored in a backup memory connected to the processing unit. Thus, at each interval, the processing unit is able to calculate the (moving) average of the values ​​of the monitoring parameters taken over the time window preceding that interval. Furthermore, the processing unit may store the values ​​of the monitoring parameters or their moving averages calculated at each interval or at a subset of intervals.

[0055] In cases where the installed plastic bags or silos are incorrect, it has been observed that changes occur in the vector of one or more monitoring parameters during a transition period lasting several minutes (e.g., 5 minutes, 10 minutes, or longer). After this transition, the vector of one or more monitoring parameters remains constant for a duration sufficient to complete the incorrect bag or silo installation, and at the end of this duration, it returns to its initial value (again, through a transition period lasting several minutes).

[0056] Therefore, in one embodiment, the processing unit can periodically compare the moving average of the monitoring parameter calculated at a first time point with the moving average of the monitoring parameter calculated at a second time point (at each measurement, every minute, or every 5 minutes), where the second time point is the current time and the first time point is earlier than the second time point by a predetermined time length (e.g., 5 or 10 minutes). This comparison can be performed periodically while the same formula is being prepared.

[0057] When formulation production stops, the processing unit stores data in a database representing the values ​​of the monitored parameters (or multiple monitored parameters) during the period when the formulation was set to the current formulation setting. More specifically, if the monitored parameters have not changed significantly, the processing unit saves a subset of the values ​​(or moving averages) of the monitored parameters that were measured or calculated during formulation production and associated with the information item indicating the capture time to the database, and deletes other values ​​(because there has been no significant change); for example, it could save one value per formulation, one value per day, or one value per week. On the other hand, if the monitored parameters have changed significantly (e.g., if the monitored parameters have two distinctly different values), the processing unit can also save information representing these significant changes to the database (e.g., it could save two distinctly different values). Thus, the database contains a history of the values ​​adopted by the monitored parameters (or a vector of multiple monitored parameters); this data can be used for comparison with new monitored parameters that will be calculated the next time the same formulation is set (even if the extruder is used for other formulations simultaneously) and / or may be useful for detecting wear problems that have occurred since the last formulation setting. Furthermore, if values ​​are saved at predetermined time intervals (e.g., one value per day or one value per week), these values ​​allow for monitoring of the slow drift of parameters due to wear and tear.

[0058] In one implementation, the processing unit can also derive trends in the values ​​of monitoring parameters (or vectors of multiple monitoring parameters) measured or calculated sequentially (e.g., per second), and derive alarm data based on a function analysis of that trend. In this case, when recipe preparation stops, if there are no significant changes, the processing unit can also save a subset of the values ​​(or moving averages) of the monitoring parameters measured or calculated during recipe preparation and associated with the information item indicating the capture time to a database, and can delete other values.

[0059] In one implementation, there may be no formulation, and even the parameters based on quantities p7-p9 may be monitoring parameters measured by a sensor system. In this case, the processing unit can be configured to save records to a database, where each record includes the value of one or more monitoring parameters (i.e., vectors representing the monitoring parameters of quantities p1-p6 and / or 'p7-p9' listed above) that are associated with data representing the type of polymer material being processed at the capture time, as measured by the sensor system. Therefore, the database can contain unique markers for each type of polymer material and can be used to identify the type of polymer material being processed by the extruder (even if the monitoring parameters do not change between different times). In fact, if the processing unit knows the values ​​of one or more monitoring parameters representing quantities 'p1-p6' and / or 'p7-p9' as measured by the sensor system, the processing unit can identify the type of polymer material from the data stored in the database. This disclosure may also provide a method for deriving diagnostic information about the type of polymer material being processed by the extruder.

[0060] More specifically, the processing unit can be configured to operate in a self-learning mode, wherein, at multiple consecutive moments, the processing unit receives vectors of monitoring parameters measured by the sensor system, along with information about the type of material communicated by the user. Therefore, the processing unit can generate a relationship (or correlation) between the vectors of monitoring parameters and the type of material. This relationship can be derived by an artificial intelligence system integrated into the processing unit and including, for example, neural networks. Alternatively, this relationship can be obtained based on human knowledge according to rules communicated by the user. After constructing a self-learning database comprising the values ​​adopted by the vectors of monitoring parameters associated with a type of material over a specific time period, the processing unit can operate in an identification mode, in which the processing unit receives the vectors of monitoring parameters measured by the sensor system and can identify the type of material being processed. Identification can be based on calculations of the proximity between the measured values ​​of the vectors of monitoring parameters and the values ​​of the vectors of monitoring parameters stored in the self-learning database.

[0061] In one implementation, the processing unit can derive diagnostic information based on one or more pairs of monitoring parameters measured by the sensor system (i.e., by comparing the value of one parameter in a pair with the value of another parameter in the same pair). More specifically, the one or more pairs of monitoring parameters may include parameters representing the following paired quantities:

[0062] - The power absorbed by the motor that rotates the extruder screw ('p2') and the speed of the extruder screw ('p3');

[0063] - The absorbance power of the heater ('p4') and the temperature of the extruder barrel ('p7');

[0064] - The electrical power absorbed by the motor of the drive device ('p6') and the speed of the drive device ('p8').

[0065] It should be noted that the values ​​used for the monitoring parameters typically change during the start-up transition of the extruder; this start-up transition lasts for approximately 10-15 minutes from the moment of energization. In one embodiment, the processing unit can be configured to identify the type of polymer material being processed based on the changing trends of the monitoring parameters (or multiple monitoring parameters) at startup. More specifically, for each type of material, the database can contain multiple data points representing the changing trends of the monitoring parameters (or multiple monitoring parameters) at startup; based on a comparison between the measured monitoring parameters (or multiple monitoring parameters) and the data in the database, the control unit can identify the type of material being processed.

[0066] It should be noted that this disclosure also provides a diagnostic system for an extruder. The diagnostic system includes a processing unit according to one or more aspects of this disclosure. The diagnostic system may also include a sensor system according to one or more aspects of this disclosure that can be connected to an extruder according to one or more aspects of this disclosure.

[0067] This disclosure also relates to a method for performing diagnostic surveys in an extruder for polymer materials. The extruder is manufactured according to one or more aspects of this disclosure. The method for performing diagnostic surveys includes the step of capturing monitoring parameters.

[0068] The monitoring parameter may differ from the formulation parameter, but it may also be consistent with the formulation parameter. In the example embodiment, multiple monitoring parameters are used; multiple formulation parameters are also used. Preferably, at least one of the monitoring parameters differs from the parameter used as a formulation parameter; in one embodiment, all the monitoring parameters differ from the parameter used as a formulation parameter.

[0069] In one implementation, diagnostic information can be derived by analyzing the trends of one or more monitoring parameters that are also used as formulation parameters. Specifically, the processing unit captures the values ​​of the formulation parameters, compares them to corresponding target values, and if a significant difference is found, acts on at least one control parameter to, in turn, bring the formulation parameter closer to the corresponding target value (adding or subtracting a predetermined tolerance). From the moment the processing unit operates on the control parameter, a transition process for the formulation parameter to approach the corresponding target value is initiated. By analyzing the trend of the formulation parameter value during this transition process, diagnostic information can be derived, for example, to generate alarm data. Therefore, in this case, a single parameter can be used both as a monitoring parameter and as a formulation parameter.

[0070] The parameters (or parameters) to be used as monitoring parameters and the parameters (or parameters) to be used as formulation parameters can be selected according to several methods, which in principle can also be varied depending on the application (e.g., according to the type of machine connected to the extruder, i.e., according to the type of treatment applied to the plastic provided by the extruder) or even according to the formulation. Therefore, depending on the application, each of the above parameters 'p1'-'p9' can be used as a monitoring parameter, as a formulation parameter, or as both a monitoring parameter and a formulation parameter.

[0071] For example, if the extruder is used to supply molten material to a machine equipped with a pushing device, such as an injection or compression molding machine, then the parameters 'p1', 'p2', 'p3', 'p4', 'p5', and 'p6' above can be used as monitoring parameters, and the parameters 'p7', 'p8', and 'p9' above can be used as formulation parameters. Feedback control can be performed on parameters 'p4', 'p3', and 'p6', therefore, parameters 'p4', 'p3', and 'p6' are also used as control parameters.

[0072] In another embodiment, the extruder is used to convey molten material to a machine without a pusher (e.g., an injection or compression molding machine or a lining machine without a pusher). Parameter 'p1*' (representing the pressure of the molten polymer material measured downstream of the extruder) and parameters 'p2', 'p4', and 'p5' can be used as monitoring parameters, while parameters 'p3' and 'p7' can be used as formulation parameters. In this case, parameters 'p2' and 'p4' can be used as control parameters, and therefore can be used as both monitoring and control parameters. In this case, parameters 'p6' and 'p8' are absent, and parameters 'p1' and 'p9' are consistent (that is, they are a single parameter 'p1*').

[0073] The method includes capturing monitoring parameters at consecutive time points. To perform a diagnostic investigation, the method includes processing a first value of the monitoring parameter measured at a first time point and a second value of the monitoring parameter measured at a second time point after the first time point. To perform a diagnostic investigation, the method also includes generating alarm data in response to a comparison between the first and second values ​​of the monitoring parameter.

[0074] More specifically, the process may include comparing the intensity of the change in the monitored parameter from a first value to a second value with reference data.

[0075] Preferably, the step of generating alarm data also responds to verifying that the target value of the formulation parameter remains constant between the first and second time points. On the other hand, if the target value of the formulation parameter changes, the monitoring parameter will typically change.

[0076] In one or more embodiments, a plurality of monitoring parameters are measured; the step of generating alarm data is in response to a step of processing the corresponding changes in the values ​​of the monitoring parameters among the plurality of monitoring parameters over time according to predetermined logic.

[0077] To perform diagnostic investigations, the method, in its implementation, includes the step of saving records to a database, wherein each record includes one or more of the following information items: capture time; values ​​of formulation parameters at the capture time; values ​​of monitoring parameters at the capture time; and data indicating the type of polymer material processed by the extruder at the capture time.

[0078] In one implementation, receiving a recipe that a user wishes to set triggers a query to a database to obtain a record corresponding to the recipe to be set. More specifically, the recipe includes data indicating the type of polymer material to be processed and target values ​​for recipe parameters. If such a record is found, the method includes a step of comparing the value of a monitoring parameter (or multiple monitoring parameters) measured at a second time after setting the recipe with the value of a monitoring parameter (or multiple monitoring parameters) contained in a record corresponding to the recipe selected from the database; here, the time of recording constitutes the first time; therefore, the method includes generating alarm data if the measured monitoring parameter differs significantly from the stored value of the monitoring parameter. On the other hand, if no such record is found, the method triggers a self-learning step, in which the database is prepared to be updated with the new record.

[0079] This disclosure also provides a computer program including instructions executable by a processor to implement the steps of a method for performing a diagnostic investigation in an extruder for polymer materials according to this disclosure.

[0080] This disclosure provides a method for extruding polymer materials. The method includes the step of receiving granules of polymer material at the inlet of an extrusion barrel. The method includes the step of rotating an extruder screw within the extrusion barrel to move the polymer material from the inlet toward the outlet. The method includes the step of heating the polymer material within a hollow barrel while the material is moving from the inlet to the outlet. Heating is performed by a heater associated with the barrel. The method includes the step of discharging molten polymer material through the outlet of the barrel. The method includes moving the molten polymer material discharged through the outlet of the barrel (i.e., conveyed by the extruder screw)—making it usable in a molding machine for manufacturing polymer objects. The method includes the steps of capturing formulation parameters and monitoring parameters. The method further includes the step of performing feedback control on the heater (or more generally, on the control parameters of the extruder) to bring the formulation parameters to and maintain them at previously stored target values. The method includes one or more steps of a method for performing diagnostic investigations in an extruder according to one or more aspects of this disclosure.

[0081] This disclosure provides a method for extruding polymer material through an extrusion barrel that receives granules of polymer material through its inlet, and the extrusion barrel is provided with a heater, an extruder screw, and a pushing device. The extruder screw rotates within the extrusion barrel to move the polymer material from the inlet toward the outlet of the extrusion barrel. The pushing device is used to move the molten polymer material discharged through the outlet of the extrusion barrel and make it usable in a molding machine for manufacturing polymer objects. The method includes the following steps:

[0082] - Set the target values ​​for the recipe parameters;

[0083] - Capture the values ​​of recipe parameters (in real time);

[0084] - Perform feedback control on the heater (or more generally, on the control parameters of the extruder) so that the formulation parameters reach and remain at the previously stored target values;

[0085] - Capture and monitor parameters (preferably, different from formulation parameters);

[0086] -Process monitoring parameters;

[0087] - An alarm is generated in response to a comparison between the first and second values ​​of the monitored parameter.

[0088] In one implementation, processing the monitoring parameters includes processing a first value of the monitoring parameter measured at a first time point and a second value of the monitoring parameter measured at a second time point after the first time point. In another implementation, for example, the (first) value of the monitoring parameter (preferably measured in real time) is processed by comparing it with reference data contained in a knowledge base; in this case, it is preferable to process multiple monitoring parameters; furthermore, in an example implementation, the monitoring parameters (or multiple monitoring parameters) are processed together with the formulation parameters.

[0089] It should be noted that the steps of setting, capturing recipe parameters, and performing feedback control are performed by the processor in the processing unit; the processing and generation steps can be performed by the processor of the same processing unit or by another processor of another processing unit.

[0090] According to one aspect of this disclosure, a computer program is provided that includes instructions for performing the above-described steps of the method when executed on the aforementioned processor (or on the processor and on the other processor). Attached Figure Description

[0091] These and other features will become clearer from the following description of preferred embodiments illustrated by way of non-limiting example in the accompanying drawings:

[0092] - Figure 1 An embodiment of the extruder of this disclosure is shown, wherein the extruder is configured to convey molten thermoplastic material to a compression molding machine;

[0093] - Figure 2 Another embodiment of the operating configuration of the extruder of this disclosure with the extruder screw in the retracted position is shown, wherein the extruder is configured to deliver molten thermoplastic material to an injection molding machine;

[0094] - Figure 3 This illustrates the operating configuration with the extruder screw in the advance position. Figure 2 The extruder;

[0095] - Figure 4 Schematic illustration Figure 1 or Figure 2 The processing unit of the extruder. Detailed Implementation

[0096] Referring to the accompanying drawings, reference numeral 1 denotes an extruder. The extruder 1 includes a hollow extrusion cylinder 2. The extrusion cylinder 2 extends longitudinally between an inlet 2A and an outlet 2B. The extrusion cylinder 2 is configured to receive granules of polymer material through the inlet 2A and discharge molten polymer material through the outlet 2B.

[0097] The extruder 1 includes a hopper 11 configured to convey granules of polymer material to the inlet 2A of the extrusion barrel 2.

[0098] The extruder 1 also includes an extruder screw 3; the extruder screw 3 is positioned within the extrusion barrel 2 and is rotatable relative to the extrusion barrel 2. The extruder screw 3 also extends in the longitudinal direction L. The extruder 1 includes a motor 31 (preferably electric) configured to rotate the extruder screw 31 itself.

[0099] The extruder 1 includes one or more heaters 4. The one or more heaters 4 are connected to the extrusion barrel 2. The extrusion barrel 2 is made of a material with high thermal conductivity (e.g., metal, specifically steel); therefore, the heaters 4 are configured to heat the material that manufactures the extrusion barrel 2, which in turn heats the thermoplastic material contained therein.

[0100] The extruder 1 also includes a pushing device 5. The pushing device 5 is connected downstream of the extrusion barrel 2 to move material exiting the outlet 2B of the extrusion barrel 2 and discharge it from the extruder 1. In one embodiment, the pushing device 5 includes a pump connected downstream of the outlet 2B of the extrusion barrel 2. In this embodiment, the pushing device 5 is configured to continuously move thermoplastic or polymeric material exiting the extrusion barrel 2; therefore, the extruder screw 3 rotates continuously about the longitudinal axis L, causing the extrusion barrel 2 to continuously discharge material through its outlet 2B. This embodiment is used in an extruder configured to feed a compression molding machine.

[0101] In one embodiment, the actuating device 5 includes a piston that reciprocates within the barrel from a retracted position to an advanced position. Inside the barrel 2, the piston defines an injection chamber that is fluidly connected to the outlet 2B of the extrusion barrel 2. More specifically, the extruder includes a first conduit extending from the outlet 2B of the extrusion barrel 2 and a second conduit extending from the injection chamber; the first and second conduits merge into an outlet conduit configured to discharge molten polymer material. The extruder screw 3 is rotatable within the extrusion barrel 2 about a longitudinal axis L and is also capable of translating along the longitudinal axis L between a retracted position and an advanced position. Initially, the extruder screw 3 is in the retracted position, and the piston of the actuating device 5 is in the advanced position. As the extruder screw 3 rotates, it also moves along the longitudinal direction L from the retracted position to the advanced position, while the piston of the actuating device 5 moves from the advanced position to the retracted position, causing material exiting the outlet 2B of the extrusion barrel 2 to enter the injection chamber; during this stage, a valve blocking the material passage prevents material from flowing into the outlet conduit. After a predetermined time elapses since the extruder screw 3 begins to rotate, the extruder screw 3 stops, and a specific motor moves the piston from the retracted position to the advance position. Therefore, when the piston moves to the advance position, it pushes the molten material filling the injection chamber into the outlet pipe. During this stage, the valve is opened, allowing material to flow into the outlet pipe. When the piston moves from the retracted position to the advance position, the extruder screw 3 moves along the longitudinal axis from the advance position to the retracted position. When all the molten material has been discharged, another cycle begins. This embodiment is used for an extruder configured to feed an injection molding machine.

[0102] Extruder 1 also includes a sensor system. This sensor system includes one or more of the following sensors:

[0103] -Outlet pressure sensor 61, which is configured to measure the pressure of the thermoplastic material at the outlet of the pusher 5;

[0104] - Screw power sensor 62, which is configured to measure the electrical power absorbed by the motor 31 that drives the extruder screw 3;

[0105] - Screw speed sensor 63, which is configured to measure the rotational speed of extruder screw 3;

[0106] - Heater power sensor 64, which is configured to measure the electrical power absorbed by heater 4;

[0107] - Molten material temperature sensor 65, which is configured to measure the temperature of molten polymer material leaving the extruder;

[0108] - A power sensor 66 for the actuating device is configured to measure the electrical power absorbed by the actuating device 5;

[0109] - A barrel temperature sensor 67, which is configured to measure the temperature of the extrusion barrel 2;

[0110] - A propulsion device speed sensor 68, which is configured to measure the speed of the propulsion device 5;

[0111] -Inlet pressure sensor 69, which is configured to measure the pressure of the molten thermoplastic material at the inlet of the pusher 5.

[0112] An outlet pressure sensor 61 is connected to an outlet pipe that receives molten material exiting the extrusion barrel 2 downstream of the pusher 5. A screw power sensor 62 is connected to a motor 31 that drives the extruder screw 3. A screw speed sensor 63 is connected to the extruder screw 3. A heater power sensor 64 is connected to the heater 4. A molten material temperature sensor 65 is connected to an outlet pipe that receives molten material exiting the extrusion barrel 2. If the pusher 5 includes a pump, a pusher power sensor 66 is connected to a motor that drives the pump; if the pusher 5 includes a piston movable within the barrel, a pusher power sensor 66 is connected to a motor that drives the piston. A barrel temperature sensor 67 is connected to the barrel 2. If the pusher 5 includes a pump, a pusher speed sensor 68 is connected to the pump; if the pusher 5 includes a piston movable within the barrel, a pusher speed sensor 68 is connected to the piston. The inlet pressure sensor 69 is connected to a pipe that receives molten material from the outlet 2B of the cylinder 2. This pipe is upstream of the actuating device 5 (i.e., upstream of the pump if a pump is provided, or upstream of the connection point between the first pipe connected to the outlet 2B and the second pipe connected to the injection chamber if a piston that can slide in the cylinder is provided).

[0113] Sensors 61, 62, 63, 64, 65, and 66 are each configured to measure a corresponding monitoring parameter 72. More specifically, outlet pressure sensor 61 is configured to measure monitoring parameter 72 indicating quantity 'p1'. Screw power sensor 62 is configured to measure monitoring parameter 72 indicating quantity 'p2'. Screw speed sensor 63 is configured to measure monitoring parameter 72 indicating quantity 'p3'. Heater power sensor 64 is configured to measure monitoring parameter 72 indicating quantity 'p4'. Molten material temperature sensor 65 is configured to measure monitoring parameter 72 indicating quantity 'p5'. Actuator power sensor 66 is configured to measure monitoring parameter 72 indicating quantity 'p6'. Preferably, at least two of sensors 61, 62, 63, 64, 65, and 66 are provided, thus measuring at least two monitoring parameters 72.

[0114] Sensors 67, 68, and 69 are each configured to measure a corresponding recipe parameter 71. More specifically, cylinder temperature sensor 67 is configured to measure recipe parameter 71 with a value of 'p7'. Actuator speed sensor 68 is configured to measure recipe parameter 71 with a value of 'p8'. Inlet pressure sensor 69 is configured to measure recipe parameter 71 with a value of 'p9'.

[0115] The extruder 1 includes a processing unit 7. The processing unit 7 is programmed to receive one or more formulation parameters 71 from sensors 67, 68, and 69. The extruder 1 also includes a user interface 9 configured to allow a user to select a target value 70 for each formulation parameter 71. The processing unit 7 is connected to the user interface 9 to receive the corresponding target value 70 selected by the user for each formulation parameter 71.

[0116] Processing unit 7 is configured to compare one or more formulation parameters 71 measured by sensors 67, 68, 69 (or one or more of them) with corresponding target values ​​70, and generate one or more feedback control signals 75 based on the differences between the measured formulation parameters 71 and the corresponding target values ​​70. Processing unit 7 is configured to send one or more feedback control signals 75 to one or more of the following components of the extruder: extruder screw 3, heater 4, and pusher 5. More specifically, processing unit 7 may send feedback control signals 75 to heater 4 to change the power absorbed by heater 4 (amount 'p4'); processing unit 7 may send feedback control signals 75 to extruder screw 3, specifically to electric motor 31, to change the rotational speed of extruder screw 3 (amount 'p3'); processing unit 7 may send feedback control signals 75 to pusher 5, specifically to the motor of pusher 5, to change the power absorbed by the motor of pusher 5 (amount 'p6'). Therefore, the quantities 'p4', 'p3', and 'p5' are read by sensors 64, 63, and 65, respectively, thus constituting monitoring parameters; at the same time, they can be controlled by feedback to keep one or more formulation parameters 71 equal to or close to the corresponding target value 70.

[0117] Processing unit 7 is programmed to process the value of each monitoring parameter 72 captured at consecutive time points. More specifically, processing unit 7 is configured to process a first value of each monitoring parameter 72 measured at a first time point and a second value of the same monitoring parameter 72 measured at a second time point after the first time point. Processing unit 7 is programmed to generate alarm data 73 in response to a comparison between the first and second values ​​of each monitoring parameter 72. In one embodiment, processing unit 7 is configured to generate alarm data 73 if a significant difference (greater than a predetermined tolerance threshold) exists between the first and second values ​​for at least one monitoring parameter 72 (or, preferably, for at least two monitoring parameters 72). Alarm data 73 can indicate an anomaly in the operation of extruder 1. In one embodiment, extruder 1 includes an alarm system (or output interface) 10, and processing unit 7 is configured to send alarm data 73 to alarm system 10.

[0118] In one embodiment, the processing unit 7 has access to a memory 8 (which may be part of the extruder 1 itself or may be a remote memory); the memory 8 may contain reference data 74 representing the intensity of change of each monitoring parameter 72 (i.e., a tolerance threshold for the intensity of change). The processing unit 7 is configured to receive the reference data 74 and generate alarm data in response to a comparison between the change of each monitoring parameter 72 from a first value to a second value and the corresponding reference data 74.

[0119] It should be noted that in the case where the pushing device 5 includes a reciprocating piston in the cylinder, some monitoring parameters 72 (e.g., the pressure of the molten polymer material measured downstream of the pushing device) have a cyclical trend; therefore, the first and second values ​​are measured at corresponding moments of different cycles; the reference data 74 is also referred to as the cycle time point for measuring the value of the monitoring parameter 72.

Claims

1. An extruder for polymeric material, the extruder comprising: - a hollow extrusion barrel extending along a longitudinal direction and having an inlet for receiving pellets of polymeric material and an outlet for discharging molten polymeric material; - an extruder screw connected with a motor for rotating within the extrusion barrel and moving the polymeric material from the inlet to the outlet; - a heater coupled with the extrusion barrel; - a sensor system configured for measuring a value of a recipe parameter and a value of a monitoring parameter; - a processing unit programmed to store a target value of the recipe parameter and to perform feedback control on the heater to bring the recipe parameter to the target value and to keep the recipe parameter at the target value, 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 to generate alarm data in response to a comparison between the first value and the second value of the monitoring parameter, wherein the monitoring parameter is based on the following quantities: - a pressure of the molten polymeric material measured downstream of the extruder screw; - a temperature of the molten polymeric material, wherein the alarm data comprise a diagnostic information item indicative of whether an anomaly is present in the material.

2. The extruder of claim 1, wherein the processing unit has access to a memory containing reference data representative of a strength of variation of the monitoring parameter, and wherein the processing unit is programmed to generate the alarm data in response to a comparison between the variation of the first value and the second value of the monitoring parameter and the reference data.

3. The extruder of claim 2, wherein the processing unit is programmed to detect a variation of the target value of the recipe parameter, and to generate alarm data also in dependence on an absence of variation of the target value of the recipe parameter between the first time instant and the second time instant.

4. The extruder of any one of claims 1 to 3, wherein the processing unit is programmed to generate the alarm data also in dependence on a duration of a time interval between the first time instant and the second time instant.

5. The extruder of any one of claims 1 to 3, wherein the processing unit is programmed to store a first series of values of the monitoring parameter captured consecutively 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 first series of values.

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

7. The extruder of any one of claims 1 to 3, wherein the processing unit is programmed to process different pluralities of monitoring parameters and to generate the alarm data in response to a corresponding plurality of comparisons performed for respective ones of the pluralities of monitoring parameters.

8. The extruder of any one of claims 1 to 3, wherein the processing unit is programmed to save records to a database, wherein each record comprises the following items of information: - a capture instant; - values of the recipe parameters at the capture instant; - values of the monitoring parameters at the capture instant; - data indicative of the type of polymeric material processed by the extruder at the capture instant.

9. The extruder of claim 8, wherein the processing unit is programmed to: receive a recipe that a user wishes to set, the recipe comprising data indicative of the type of polymeric material to be processed and target values of the recipe parameters, query the database to identify a record corresponding to the recipe to be set, compare the values of the monitoring parameters measured at the second instant after setting the recipe with the values of the monitoring parameters contained in the record corresponding to the recipe, wherein the instant at which the record was captured constitutes the first instant.

10. The extruder of any one of claims 1 to 3, wherein the monitoring parameters are based on one or more of the following quantities: - absorbed power of the motor turning the extruder screw; - absorbed power of the heater; - temperature of the extrusion barrel; - speed of the extruder screw.

11. The extruder of any one of claims 1 to 3, wherein the recipe parameters are based on one or more of the following quantities: - temperature of the extrusion barrel; - speed of the polymeric material moving out of the extruder screw; - pressure measured at the outlet of the extrusion barrel.

12. The extruder of any one of claims 1 to 3, comprising a pushing device configured to move the molten polymeric material conveyed by the extruder screw so that it is available to a forming machine for manufacturing polymeric objects, wherein one or more of the following is applicable: i) the monitoring parameters are based on a pressure of the molten polymeric material measured downstream of the pushing device; ii) the recipe parameters are based on one or more of the following quantities: - speed of the pushing device moving the molten polymeric material; - pressure measured at an inlet region of the pushing device.

13. The extruder of claim 1, wherein the processing unit is programmed to generate the alarm data also as a function of the duration of the time interval between the first instant and the second instant, wherein the monitoring parameters are based on the speed of the extruder screw, and wherein the alarm data comprise an item of diagnostic information indicative of whether the extruder screw is worn.

14. A method for performing a diagnostic investigation in an extruder for polymeric material, wherein the extruder comprises: - an extruder screw connected to a motor to rotate inside an extruder barrel provided with heaters and to move the polymeric material from an inlet to an outlet, thereby melting the polymeric material; - a sensor system for measuring a recipe parameter; - a processing unit programmed to store a target value of the recipe parameter and to perform feedback control on the heaters to bring the recipe parameter to the target value and to keep the recipe parameter at the target value, the method comprising the steps of: - 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 subsequent to the first time instant; - generating alarm data in response to a comparison between the first value and the second value of the monitoring parameter, wherein the monitoring parameter is based on the following quantities: - a pressure of the molten polymeric material measured downstream of the extruder screw; - a temperature of the molten polymeric material, wherein the alarm data comprise a diagnostic information item indicative of the presence or absence of an anomaly in the material.

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

16. The method according to claim 15, wherein the step of generating alarm data is further in response to verifying the fact that the target value of the recipe parameter remains unchanged between the first time instant and the second time instant.

17. The method according to any one of claims 14 to 16, wherein a plurality of monitoring parameters is measured, and wherein the step of generating the alarm data is in response to a step of processing the corresponding changes over time of the values of the monitoring parameters of the plurality of monitoring parameters according to a predetermined logic.

18. The method according to any one of claims 14 to 16, comprising a step of saving records to a database, wherein each record comprises one or more of the following information items: - a capture time instant; - a value of the recipe parameter at the capture time instant; - a value of the monitoring parameter at the capture time instant; - data indicative of the type of polymeric material processed by the extruder at the capture time instant.

19. The method according to claim 18, comprising a step of receiving a recipe that a user wishes to set, which comprises data indicative of the type of polymeric material to be processed and the target value of the recipe parameter, and wherein, in the event that such a record is found, the method comprises a step of comparing the value of the monitoring parameter measured at the second time instant after setting the recipe with the value of the monitoring parameter contained in the record selected from the database corresponding to the recipe, wherein the time instant at which the record was captured constitutes the first time instant, if no such record is found, the method triggers a self-learning step in which it is prepared to update the database with a new record, if no such record is found, the method triggers a self-learning step in which it is prepared to update the database with a new record. ​ 20. A computer program product comprising instructions executable by a processor to implement the steps of the method of any one of claims 14 to 16.

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