H.D.Plastics specializes in both Rigid and Flexible Custom Plastic Extrusion Products and plastic tubing extrusion products. We utilize our long years of extrusion expertise by our twin screw extruder to produce almost any co-extruded plastic shapes and components suitable for your specific engineering project.

How to define the proper screw extruder machines?

Screw extrusion profiles uses one (single screw) or two (twin screw) screws to transport the thermal plastics material. Screw extruders are preferred over ram extruders since they provide more shear and intense mixing, resulting in better homogeneity and temperature uniformity.

The single screw extruder is the most widely used extrusion system in the plastics industry, while twin-screw extruders are preferred for some special applications, since it provides intensive mixing and ensures almost complete emptying of the extruder, minimizing loss of highly valuable product. These extruders operate by a first in–first out principle and minimize the non‐motion, thus preventing localized overheating of materials within the extruder.

twin-screw-extruder

The three basic functional screw element types are classified as forwarding, mixing and zoning. Forwarding elements are usually flighted. They convey material away from the feed opening towards the die. Mixing elements can be dispersive or distributive.

Based on design and function of the screws an extruder is typically divided into three sections along its length. In the feeding section the material will be transferred from the hopper to the barrel. Once the material enters the compression section it will begin to soften or melt. The temperature of this section is normally set at 30–60°C above the glass transition temperature (Tg) of amorphous polymers or the melting point of a semi‐crystalline polymer.

Especially in co‐extrusion it is important to make sure that the design of the screws is ensuring a stable throughput. Sometimes a melt pump is used to reduce the pressure and throughput instability.

Apart from this technological solution, melt pulsation can also be prevented by constructional screw and barrel adaptations such as changing the length, diameter and pitch of the screws.

The benefits of Co-extrusion Profiles by twin-extruder processing

Highly skilled engineering on Co-extrusion dies design. It will benefit the construction of the co-extrusion profiles and enable the molten plastic to evenly flows from a cylindrical profile to the profile shape of the product required. By combining several materials together, we can deliver one unique product with new and exciting characteristics, it can maximum save your cost and multi-function features.