Polymer and Plastics Extrusion Equipment
Diamond America has over 20 years of experience in custom extruder design for polymers and plastics, including expert 3D modeling and Finite Element Analysis (FEA) software systems to optimize die and extruder performance and quality.
Plastics extrusion equipment is used for continuous, high-volume manufacture of a wide range of final products that have constant cross section, such as plastic pipes, frames, sheeting and films.
Critical factors in the design of polymer extrusion equipment
The compression ratio is the ratio of the screw depth at the feed zone by the hopper, to its depth at the metering zone by the die.
Compression ratio varies greatly according to the polymer that is being processed. For example, where rigid PVC requires a compression ratio of around 2.3:1, polypropylene or a more slippery material requires a ratio of nearer 4:1.
The compression ratio is also impacted by the relationship of cross sectional areas at the screw feed and metering points. Finally, barrier designs, mixers, and variable lead screws affect not only the compression ratio, but the final screw output as well. The design of polymer extrusion equipment is indeed a very specialized process.
Due to the wide variety of products, ranging from plastic pipes to films, polymer extrusion die design is very diverse and complex and includes dies for:
- Blown Film extrusion
- Sheet and Film extrusion
- Tubing extrusion
- Over Jacketing extrusion
- Extrusion Coating
Dies have to be carefully designed to handle the specific behavior of plastic extrusion melts. Polymers consist of long chains of molecules which become aligned and oriented in a single direction when forced through a die. On release, they tend to diverge randomly when no longer constrained, causing a phenomenon known as ‘die swell’.
Prevention of die swell must be built into the die design by:
- Decreasing the extrusion rate
- Increasing the melt temperature, at constant extrusion rate
- Increasing the length of the die land
- Increasing the draw down rate without affecting output
(Draw down rate is the ratio of haul-off speed to natural extrusion speed)
Examples of polymer and plastic extrusion applications, materials and selection criteria:
|Building & Construction industry|
|Rainwater Pipes, Gutters||Rigid PVC||Strong, UV resistant, color fast|
|Soffits, Fascias||Compact/foamed PVC||UV resistant, color fast|
|Windows, Doors||Rigid PVC||Appearance, can be cut and welded|
|Door Seals||Co-extrusion||Dual properties in one molded profile|
|Garden Fencing||Polystyrene/polyethylene||Recycled material, does not require painting|
|Light Diffusers||Acrylic||Optical properties|
|Conduit and Cable Protectors||Rigid PVC||Tough, good insulator, chemically stable|
|Cable Harnesses||PTFE Filled PVC||Flexible, resistant to chaffing|
|Curtain Tracks||Rigid PVC||UV resistant, tough material, can be colored|
|Fridge Seals||Rubber, PVC and metal||Can be magnetized|
|Drip Tubes, Catheter Tubes||Plastic composites||High integrity, reinforced, can be sterilized|
|Aerosol and Spray Dip Tubes||Polyethylene||Transparent, stable, chemically resistant|
|Gas Pipes, Water Pipes||Polyethylene||Corrosion resistant, good integrity|
|Soil Pipes||Rigid PVC||Strong, can be joined using solvent cements|
Diamond America Extrusion Test Facility
Diamond America provides a fully equipped test facility for new product process and formulation testing for all applications.