Extrusion

The extrusion process is basically designed to continuously convert a soft material into a particular form. The heart of this processing/fabrication machine is a screw conveyer. It carries the cold plastic material (in granular or powdered form) forward by the action of the screw and squeezes it, and, with heat from external heaters and the friction of viscous flow, changes it to a molten stream (refer to Figure 1). As it does this, it develops pressure on the material, which is highest right before the molten plastic enters the die. The screen pack, consisting of a number of fine or coarse mesh gauzes supported on a breaker plate and placed between the screw and the die, filter out dirt and unfused polymer lumps. The pressure on the molten plastic forces it through an adapter and into the die, which dictates the shape of the final extrudate.

Hot extrusion

Hot extrusion is a hot working process, which means it is done above the material’s recrystallization temperature to keep the material from work hardening and to make it easier to push the material through the die. Most hot extrusions are done on horizontal hydraulic presses that range from 230 to 11,000 metric tons . Pressures range from 30 to 700 MPa , therefore lubrication is required, which can be oil or graphite for lower temperature extrusions, or glass powder for higher temperature extrusions. The biggest disadvantage of this process is its cost for machinery and its upkeep.

Cold extrusion

Cold Extrusion is a push-through compressive forming process with the starting material (billet/slug) at room temperature. During the process, however, the deforming material undergoes deformation heating (conversion of deformation work to heat) to several hundred degrees. Typically, a punch is used to apply pressure to the billet enclosed, partially or completely, in a stationary die.

Advantages of Extrusion:

• Cost-effective for large-scale production with minimal waste.
• Versatile: Supports various materials and shapes.
• Customizable: Additives and design flexibility.
• Consistent quality and scalable production.
• Energy-efficient and integrates with other processes.

Disadvantages of  Extrusion:

• Material limitations: Not all polymers are suitable.
• High setup costs: Equipment and dies are expensive.
• Dimensional variability: Cooling shrinkage and die swell.
• Shape limitations: Intricate designs are challenging.
• Quality control issues: Surface defects and material inconsistencies.
• Post-processing needs: Cutting, finishing, or coating required.
• Environmental concerns: Energy use and plastic waste.

Application of extrusion

1.Construction Industry

• Pipes and tubing (e.g., PVC pipes, drainage systems).
• Window and door profiles (e.g., uPVC frames).
• Insulation materials (e.g., foam boards, weather seals).

2.Packaging Industry

• Plastic films and sheets (e.g., food packaging, shrink wraps).
• Containers and trays.

3.Automotive Industry

• Seals and gaskets.
• Wire and cable insulation.
• Interior trims and protective sheathing.

4.Consumer Goods

• Straws, ropes, and garden hoses.
• Plastic profiles for furniture or appliances.

5.Electrical and Electronics

• Wire and cable coatings.
• Conduits for electrical wiring.

6.Medical Field

• Catheters, tubing, and other medical-grade profiles.

7.Industrial Applications

• Conveyor belts and guides.
• Protective linings for machinery.

8.Agriculture

• Irrigation tubing and films.
• Greenhouse covers.

Polymer extrusion is versatile, making it crucial in industries requiring continuous, customizable plastic products.