1. Understanding Extrusion Chapters 2 and 3
Professor Joe Greene
CSU, CHICO
MFGT 144

2. Chapter 2: Instrumentation and Control and Extrusion Lines
One of the most essential elements of an extruder
Measure important process parameters
Window to the process
Essential to troubleshoot problems

3. Instrumentation Most Important Parameters Temperature Control
Melt Pressure
Pressure Transducers
Temperature Measurement
Melt Temperature Measurement
Barrel Temperature Measurement
Temperature Control
On-Off Control
Proportional Control
Fuzzy Logic Control

4. 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

5. 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

6. 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.

7. 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.

8. 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

9. 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

10. 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.

11. 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

12. 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

13. 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

14. 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

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 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.

18. 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

19. 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.

20. 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

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 ratio
Typical ratios for LDPE is 2.0 to 2.5:1
Can produce tubular products as bags but also film via slit.

22. Complete Extrusion Lines
Extrusion Compounding Lines

23. 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.