Film extrusion is a process used to create plastic films

Film extrusion is a process used to create plastic films that are used for various applications such as packaging, insulation, and construction materials. The process involves melting plastic pellets or granules and forcing the molten material through a die to form a thin, continuous film.

Screw barrels play a crucial role in film extrusion as they are responsible for melting and conveying the plastic material. The mechanics of screw barrels in film extrusion can be described in the following steps:

1. Material feeding: Plastic pellets or granules are fed into the hopper located at the rear of the extruder. The feed section of the screw barrel contains a feed throat, which is the entry point for the plastic material.

2. Melting: As the plastic material is fed into the extruder, it moves forward along the screw flight, also known as the helix, due to the rotation of the screw. The screw barrel is heated using various heating elements such as electric heaters or oil circulation systems. The heat generated by these elements melts the plastic material as it moves along the screw barrel.

3. Conveying: As the plastic material melts, it becomes a viscous fluid. The screw flight pushes the molten material forward towards the die, while constantly mixing and homogenizing it. The screw flight consists of different sections with varying flight depths and geometries to provide optimal conveying and mixing capabilities. The flights are designed to create pressure and shear forces on the molten plastic, ensuring uniform melting and mixing.

4. Pressure buildup: As the molten plastic material moves forward, pressure builds up within the screw barrel. This pressure is essential for achieving a continuous flow of the molten material through the die. The screw design, including the compression ratio, flight depth, and channel geometry, is optimized to create the desired pressure profile.

5. Die flow: Once the molten plastic reaches the end of the screw barrel, it enters the die. The die forms the shape and thickness of the film by controlling the flow of the molten material. The die consists of a narrow channel with a specific shape and dimensions. The pressure generated by the screw barrel forces the molten plastic through the die, where it is rapidly cooled and solidifies into a continuous film.

6. Film winding: After the film is formed, it is usually wound onto a roll for further processing or use. Winding systems are typically located downstream of the die and can be designed to accommodate different film thicknesses and widths.
Screw barrel for extrusion of film blowing