1 Understanding Extrusion Chapters 2 and 3 Professor Joe Greene CSU, CHICO MFGT 144.
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1 Understanding Extrusion Chapters 2 and 3 Professor Joe Greene CSU, CHICO MFGT 144
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Transcript of 1 Understanding Extrusion Chapters 2 and 3 Professor Joe Greene CSU, CHICO MFGT 144.
1
Understanding ExtrusionChapters 2 and 3
Professor Joe Greene
CSU, CHICO
MFGT 144
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Chapter 2: Instrumentation and Control and Extrusion Lines
• Instrumentation– One of the most essential elements of an extruder– Measure important process parameters– Window to the process– Essential to troubleshoot problems
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Instrumentation• Most Important Parameters
– Melt Pressure– Pressure Transducers– Temperature Measurement– Melt Temperature Measurement– Barrel Temperature Measurement
• Temperature Control– On-Off Control– Proportional Control– Fuzzy Logic Control
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Most Important Parameters• Melt Pressure
– Diehead 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 Transducers
• Temperature Measurement
• Melt Temperature Measurement
• Barrel Temperature Measurement
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Most Important Parameters• Melt Pressure
– Diehead 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
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Most Important Parameters• Pressure Transducers
– Strain gauge and piezo-electric are most common– Strain gauge
• Capillary or pushrod transducer
• Two 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.
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Most Important Parameters• Temperature Measurement
– Measured with a thermocouple• Type-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.
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Most Important Parameters• Melt Temperature Measurement
– Measured with an immersion TC. Insulated probe protrudes into the melt andreads temperature at the point of the TC junction.
– Figure 2.4
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Most Important Parameters• Barrel Temperature Measurement
– Measured with TC or RTD Sensors pressed into barrel– Influenced by thickness of metal sheath. Can cause error
as well as air currents around the extruder– Figs. 2.5, 2.6, and 2.7
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Most Important Parameters• Temperature Control
• Maintains temperature based upon as preset value and an actual reading
– On-Off Control• Power is either on or off. Provides poor control,+/-20C, Fig 2.8
– Proportional Control• Power is proportional to the temperature within a certain temperature region
called the proportional band. Fig 2.9
• Temperature 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 it
• Proportional Control with Integrating Action (PI) can control it
• Controller integrates the difference between the actual temp and the setpoint and continues to act until the difference is zero.
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Most Important Parameters• Temperature Control
• Maintains temperature based upon as preset value and an actual reading
– Fuzzy Logic Control• New method is fuzzy logic control (FLC).
• Artificial intelligence based technology designed to simulate human decision-making.
• Requires generation of a knowledge base which identify– Process variables that are important in control
– Membership functions for each variable, (H, M, L)
– Fuzzy rules which define the knowledge of what to do about an observation based upon previous operating experience
• FLC is being applied a number of times in injection molding.
• FLC can outperform conventional PID control
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Chap 3: Complete Extrusion Lines• Tubing and Pipe Lines
• Film and Sheet Lines using the Roll Stack Process
• Film Lines Using Chill Roll Casting
• Combination of Materials– Coextrusion– Extrusion Coating– Extrusion Lamination
• Blown Film Lines
• Extrusion Compounding Lines
• Profile Extrusion Lines
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Complete Extrusion Lines• Tubing and Pipe Lines
– Small diameter tubing (less than 10mm) is usually made with free extrusion process (No sizing unit)
– Gear Pump may be used depending upon the precision– Internal air pressure of the tubing is controlled to achieve
proper diameters of the tubing.– Diameter and wall thickness are functions of
• extruder output, puller speed, and internal air pressure
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Complete Extrusion Lines• Film and Sheet Lines using the Roll Stack Process
– No real difference between flat film and sheet extrusion
Can be wither roll-up or roll down process
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Complete Extrusion Lines• Film and Sheet Lines using the Roll Stack Process
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Complete Extrusion Lines• Film and Sheet Lines using the Roll Stack Process
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Complete Extrusion Lines• Film Lines Using Chill Roll Casting
– Thin 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.
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Complete Extrusion Lines• Combination of Materials
– Coextrusion• Combines two or more plastics through a single die
– Feed block system- different plastics are combined in the feed block
» Simple, inexpensive, and alloys many layers to be combined.
» The materials must have similar flow properties to avoid distortion
– Multi-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
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Complete Extrusion Lines• Combination of Materials
– Extrusion Coating Fig 3.6• Molten layer of plastic film is combined with a moving solid
web or substrate, e.g., paper, paperboard, foil, plastic film, or fabric.
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Complete Extrusion Lines• Combination of Materials
– Extrusion 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 film
• The laminate is unrolled from a payoff
• After lamination the film is handled as a regular film
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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 ratio
• Typical ratios for LDPE is 2.0 to 2.5:1
• Can produce tubular products as bags but also film via slit.
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Complete Extrusion Lines• Extrusion Compounding Lines
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Complete Extrusion Lines• Profile Extrusion Lines
• Consists 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.
