Presentation on theme: "Understanding Extrusion Chapters 2 and 3"— Presentation transcript:
1 Understanding Extrusion Chapters 2 and 3 Professor Joe GreeneCSU, CHICOMFGT 144
2 Chapter 2: Instrumentation and Control and Extrusion Lines One of the most essential elements of an extruderMeasure important process parametersWindow to the processEssential to troubleshoot problems
3 Instrumentation Most Important Parameters Temperature Control Melt PressurePressure TransducersTemperature MeasurementMelt Temperature MeasurementBarrel Temperature MeasurementTemperature ControlOn-Off ControlProportional ControlFuzzy Logic Control
4 Most Important Parameters Melt PressureDiehead pressure (pressure necessary to overcome resistance in die) determines the output of the extruder.When diehead pressure changes with time, the output changes as do the dimensions of the product.Pressure TransducersTemperature MeasurementMelt Temperature MeasurementBarrel Temperature Measurement
5 Most Important Parameters Melt PressureDiehead pressure (pressure necessary to overcome resistance in die) determines the output of the extruder.When diehead pressure changes with time, the output changes as do the dimensions of the product.Figure 2.1
6 Most Important Parameters Pressure TransducersStrain gauge and piezo-electric are most commonStrain gaugeCapillary or pushrod transducerTwo diaphragms, one in contact with the plastic melt and one some distance away (Fig 1.2). Connection is hydraulic in capillary and pushrod in the pushrod type.Strain gauge is attached to the second diaphragm to measure the deflection which is related to the pressure at the first point.
7 Most Important Parameters Temperature MeasurementMeasured with a thermocoupleType-Temp (TC)- when two dissimilar metals are connected there is a voltage generated between the metals.Resistance temperature detector (RTD)- Resistance of metals changes with temperature.Infrared detectors (IR)- objects emit radiation that changes with temperature. Used for surface temperature measurements.
8 Most Important Parameters Melt Temperature MeasurementMeasured with an immersion TC. Insulated probe protrudes into the melt andreads temperature at the point of the TC junction.Figure 2.4
9 Most Important Parameters Barrel Temperature MeasurementMeasured with TC or RTD Sensors pressed into barrelInfluenced by thickness of metal sheath. Can cause error as well as air currents around the extruderFigs. 2.5, 2.6, and 2.7
10 Most Important Parameters Temperature ControlMaintains temperature based upon as preset value and an actual readingOn-Off ControlPower is either on or off. Provides poor control,+/-20C, Fig 2.8Proportional ControlPower is proportional to the temperature within a certain temperature region called the proportional band. Fig 2.9Temperature can be kept steady with the power level adjusting to keep temperature very close to preset value.Proportional control (P-control) works well except when an upset occurs and the P-control is not able to change itProportional Control with Integrating Action (PI) can control itController integrates the difference between the actual temp and the setpoint and continues to act until the difference is zero.
11 Most Important Parameters Temperature ControlMaintains temperature based upon as preset value and an actual readingFuzzy Logic ControlNew method is fuzzy logic control (FLC).Artificial intelligence based technology designed to simulate human decision-making.Requires generation of a knowledge base which identifyProcess variables that are important in controlMembership functions for each variable, (H, M, L)Fuzzy rules which define the knowledge of what to do about an observation based upon previous operating experienceFLC is being applied a number of times in injection molding.FLC can outperform conventional PID control
12 Chap 3: Complete Extrusion Lines Tubing and Pipe LinesFilm and Sheet Lines using the Roll Stack ProcessFilm Lines Using Chill Roll CastingCombination of MaterialsCoextrusionExtrusion CoatingExtrusion LaminationBlown Film LinesExtrusion Compounding LinesProfile Extrusion Lines
13 Complete Extrusion Lines Tubing and Pipe LinesSmall diameter tubing (less than 10mm) is usually made with free extrusion process (No sizing unit)Gear Pump may be used depending upon the precisionInternal air pressure of the tubing is controlled to achieve proper diameters of the tubing.Diameter and wall thickness are functions ofextruder output, puller speed, and internal air pressure
14 Complete Extrusion Lines Film and Sheet Lines using the Roll Stack ProcessNo real difference between flat film and sheet extrusionCan be wither roll-upor roll down process
15 Complete Extrusion Lines Film and Sheet Lines using the Roll Stack Process
16 Complete Extrusion Lines Film and Sheet Lines using the Roll Stack Process
17 Complete Extrusion Lines Film Lines Using Chill Roll CastingThin films are often cast on a chill roll rather than extruded into a roll stack.Initial contact is established with the use of a air knife which produces a thin stream of high velocity air across the roll that pushes the film against the roll.Thickness gauge uses a scanning measurement head.Surface treatment (flame or corona discharge treatment) is done to improve adhesion for printing or laminating.
18 Complete Extrusion Lines Combination of MaterialsCoextrusionCombines two or more plastics through a single dieFeed block system- different plastics are combined in the feed blockSimple, inexpensive, and alloys many layers to be combined.The materials must have similar flow properties to avoid distortionMulti-manifold system- has own entrance and manifold in die and multiple melt streams combine just before they exit die.Plastics with widely different flow properties can be combined.Die design is more complicated and expensive.Fig 3.5 has 2 inlets, 2 manifolds, and single outlet. Flow of the upper layer can be adjusted by flexing the choker bar, using adjustments nuts. 2 plastics combine at the entrance to the land.Many multi-manifold dies are possible, ie, flat film and sheet, pipe, blown film, and profile dies
19 Complete Extrusion Lines Combination of MaterialsExtrusion Coating Fig 3.6Molten layer of plastic film is combined with a moving solid web or substrate, e.g., paper, paperboard, foil, plastic film, or fabric.
20 Complete Extrusion Lines Combination of MaterialsExtrusion Lamination (Fig 3.7)Involves two or more substrates, such as paper and aluminum foil, combined by using a plastic film as the adhesive.Extruded sheet or film can be laminated with a filmThe laminate is unrolled from a payoffAfter lamination the film is handled as a regular film
21 Complete Extrusion Lines Blown Film Lines (Fig 3.8)The tubular film is extruded upwards.Ratio of bubble diameter to the die diameter = blow up ratioTypical ratios for LDPE is 2.0 to 2.5:1Can produce tubular products as bags but also film via slit.
23 Complete Extrusion Lines Profile Extrusion LinesConsists of an extruder, die, calibrating unit, cooling unit, measurement unit, haul off, and coil or cutter or saw.Gear pump may be used if dimensional tolerance is small.Some lines a film or foil is laminated to the extruded profile.