All about Plastic Extrusion and Helpful Tips for Buying ...

Plastic extrusion is a continuous manufacturing method used for producing high volumes of products by converting thermoplastic materials such as pellets, powder, or granulates into desired shapes through melting and shaping processes.

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In this process, molten plastic is directed into rotating molds through screws, allowing it to pass through a die that imparts the desired shape, resulting in a product referred to as extrudate.

A typical plastic extruder will consist of 4 zones:

1. Feed zone

This zone maintains a constant flight depth, which is defined as the distance from the main to the minor diameter of the screw within the flight.

2. Transition zone/compression zone

In this area, the flight depth decreases, causing the thermoplastic material to be crushed and begin the plasticization process.

3. Mixing zone

Here, the flight depth remains constant, often utilizing a specific mixing device to ensure the material is completely melted and blended uniformly.

4. Metering zone

This zone features a lower flight depth compared to the mixing zone but remains constant, with pressure propelling the melt through the shaping die.

What can be created by using plastic extrusion?

Plastic extrusion allows for the shaping of molten plastic into tubes and profiles, making it an essential process for creating a vast range of products and components for various applications.

Thermoplastics, notably polypropylene and PVC, are ideal materials for this process. Here are several applications of plastic extrusion:

1. Tubing

Extrusion is commonly used to create diverse pipes and tubes for transporting liquids or gases, such as water and sewage. Additionally, smaller diameter tubes are produced for products like medical tubing and straws.

The flexibility or rigidity of extruded tubes can be tailored based on the type of plastic used, making them suitable for different applications such as plumbing supplies or medical uses.

2. Profiles

Plastic extrusion can produce a variety of cross-sectional shapes suited to design requirements, used in applications like rain gutters, railings, and window seals. Profiles can include co-extruded elements, enhancing functionality by combining materials.

3. Solid extrusions

Extrusions can also result in solid shapes, including plastic planks, decking, and various bar shapes for industrial or automotive applications. Solid plastic is favored for outdoor furniture due to its durability and weather resistance.

4. Insulation

Extrusion is utilized to create insulation for electrical cables by enclosing wires in plastic, providing waterproofing and resistance against corrosion and abrasion.

5. Sheets and film

Extruded sheets and films serve as protective screens, components of window glass, or in plastic packaging solutions like blister packs.

Few Different types of plastic extrusion lines

Various extruder designs are available to meet different production needs. Here are some noteworthy types:

1. Single screw extruders

These are the most common in the polymer extrusion industry, favored for their cost-effectiveness and reliability. Standard designs incorporate three key zones: feed, metering, and transition/compression zones.

2. Twin-screw extruders

These extruders consist of two Archimedean screws, allowing for various configurations, including intermeshing and non-intermeshing types. The ability to adjust parameters adds versatility.

3. Tubing extrusion

This extrusion method produces tubes and pipes while employing air pressure for shaping. After exiting the die, these products typically enter a cooling tank.

4. Blow film extrusion

By continuously forming plastics, this method creates tubes that are then blown to achieve the desired thickness, commonly used for items like shopping bags.

5. Sheet film extrusion

Plastic sheets or thicker films are extruded, with subsequent cooling processes ensuring controlled thickness.

6. Over jacket extrusion

This extrusion method effectively coats wires with molten plastic, ensuring adhesion when necessary.

How to select a plastic extruder?

To make an informed decision when choosing a plastic extruder, consider the following factors:

1. Track record of success

Look for manufacturers with a proven history of reliability and industry experience to ensure ongoing support throughout the extruder’s lifecycle.

2. Quality of components

Select manufacturers using high-quality components from recognized brands, facilitating easier sourcing of spare parts in the future.

3. Quality of service and support

Evaluate the overall customer service experience, from initial purchase support to future assistance, to ensure a cooperative relationship.

Nanjing Cowin Extrusion Machinery Company Ltd stands out for its specialization in polymer processing equipment, offering high-quality extruders and reliable customer support.

Extruder dimensioning & screw diameter - Extrusion Training