Extruder and method for performing a diagnostic investigation in an extruder

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,
• storing 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, and
• deriving, 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.

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 in succession 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,
• wherein the processing unit is programmed to derive a second succession of values, spaced by a second predetermined time interval, and wherein the second predetermined time interval is greater than the first predetermined time interval.