Plastic Materials and Processing - Theory
This section of the course will concentrate on the theory of extrusion and plastic materials, including:
Where plastics come from ·
How material structures determine mechanical and other properties such as tensile and burst strength, heat ageing, etc
Why do you need to dry plastic materials?
Regrind vs. virgin material, amorphous vs. crystalline, thermoplastics vs. thermosets, additives, etc.
Molecular weight, MFI test vs. flow
The Extrusion Process
Theory Session covering:
Typical process parameters and areas to consider for safety and quality reasons
Extrusion Process Overview - Construction of an extrusion line and machine design
Explanation of all components in an extrusion line:
- Dies, breaker plates, screen packs
- Pipe die vs. profile die design
- The Cooling Bath
- vacuum principles and temperature ranges
- Screw Cooling (where used), importance of coolant temperature and flow control
Handling tooling and cleaning tooling – importance of clean sealing surfaces
Start up and shut down procedures
Tooling for Tube/Sheet Extrusion
A practical session - choosing and assembling/ disassembling extrusion tooling:
Pin and bush (cone and die) selection, draw down ratio, draw down balance and reversion
Dies and spacer ring sizes/ sealing surfaces/ hang-up areas
Breaker plates and Screen Pack selection
Bolts, Thread types and Torque required
When to tighten – Cold or Hot?
What to tighten first – Clamp or Face plate?
Using steel on tooling and how it can damage the tooling (hang-ups, degradation, die lines, etc)
Achieving the correct wall thickness, and Centring the die for uniform wall thickness
Knowing what production orders will follow and arranging tooling to suit (set-up for multiple runs, etc)
Setting up and preparing for Set-up
A detailed practical set-up the line:
Line Pre-start checks and component selection
Tools required
Stripping and easy cleaning of the die and Breaker plate while hot
Reassembly, wiring up and testing the die
Fitting the die and tightening procedure
Setting up ancillaries
The correct extruder start-up procedure
Setting the bath coolant flow rate/ temperature
Calibrator sizing and water set-up
Stringing up the line.
Achieving part specifications
Condition v quality trial
Process Parameters
How Process Parameters interact, how to choose parameters for a particular set-up
Heater bands and Thermocouples - effect of die temps on tubing/ sheet specifications
Forward or reverse barrel temp profile, PID control and Troubleshooting.
Effects of breaker plate and filter pack on back-pressure and melt strength/ output
Effects of changing the screw cooling flow rate
Effects of changing the bath temperatures
For this training, we use the facilities of the CNMR centre.The centre has the following extrusion equipment:
Sheet Extrusion - Width<600mm - Thickness <700mm
Cast Film - Width <600mm - Thickness>30um
Pilot Blown Film - Layflat <50mm - Thickness 50 - 250um
Compounding - 50mm single screw - 19mm twin screw
Tube & Profile
Where possible we restrict extrusion course numbers to just six places. Our courses can be run in-company if required, or we can modify any course to your needs.
Who Should Attend?
Technicians, Operators, Supervisors, Engineers that need to understand how to select extrusion tooling and run/ optimise the process. |
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