At the beginning of the 19th century, studies began into the potential of plastic materials, paving the way for an evolution that would profoundly transform the world of manufacturing. Among the techniques developed was plastic extrusion, which has established itself over time as one of the most important and versatile processing methods. Today, extrusion is considered a key process in industry, used to transform raw plastic into objects with a continuous profile, in various shapes and sizes.
How does plastic extrusion work?
Extrusion is carried out using special plastic extruders, which are machines capable of using heat and pressure to shape raw plastic and transform it into profiles of the desired shape. These systems are composed of a series of carefully designed components, each of which plays a specific role.
The process begins in the hopper, where the plastic granules, called pellets, are loaded. From here, the material is directed to the feed throat, which efficiently conveys the granules to the heated cylinder. Inside the latter, the hot walls bring the plastic almost to the melting point, while a rotating screw pushes the softened material forward.
The plastic then passes through the filter plate, which retains any impurities and ensures constant pressure in the system. At this point, the material reaches the mold, the element that gives the plastic its desired shape by forcing it through a shaped die. The molten plastic is guided along the path by a feed tube, which ensures a continuous and regular flow towards the final stage.
Finally, the newly formed profile enters the cooling tank, where it is rapidly cooled and solidified. This step allows the new shape of the material to stabilize and ensures the quality of the final product.
What are the most suitable materials for extrusion?
There are many plastic materials suitable for extrusion. To choose the right one, it is necessary to consider primarily the functional properties and performance that the final product must guarantee. Factors to be evaluated include mechanical strength, elasticity, surface appearance, ability to withstand different temperatures, and chemical compatibility with the environment or other substances. In any case, among the most commonly used are:
Polyethylene (PE): one of the most versatile and widely used materials for extrusion is polyethylene, known for its extraordinary flexibility, resistance to chemicals, and ability to maintain its integrity even at low temperatures. PE is particularly used to produce packaging films, pipes, containers, and coatings. It is also perfect for outdoor applications;
Polyamide (PA): nylon, or polyamide, is a strong and durable plastic known for its good mechanical properties. It is used in various industries thanks to its strength and flexibility. For example, it is often found in the textile industry, but also in the automotive industry, where it is used to make sturdy parts. In short, it is suitable for many applications that require strong but lightweight materials;
Acrylonitrile Butadiene Styrene (ABS): this thermoplastic material combines strength and hardness with high thermal resistance. It also stands out for its smooth, shiny surface, an important feature for products that require an attractive appearance (such as components for consumer electronics, toys, and automotive parts);
Polypropylene (PP): is particularly valued for its high resistance to chemicals, traction, and abrasion. It also boasts excellent resistance to repeated bending cycles and good workability at low temperatures. Polypropylene is widely used in various fields, including food packaging, automotive, and medical device manufacturing;
Polyvinyl chloride (PVC): this polymer offers excellent resistance to impact, light, and atmospheric agents, and is also economical compared to many other materials. PVC is available in two variants, rigid and flexible. The former is ideal for construction, window frames, panels, and pipes, while the latter is used in electrical cables, sheaths, and coatings.
Polycarbonate (PC): polycarbonate is valued for its transparency and high impact resistance, characteristics that make it perfect for applications where visibility and strength are essential. Thanks to its durability and ability to work at different temperatures, it is used in sectors such as automotive and electronics. Its color versatility also makes it ideal for solutions that combine aesthetics and functionality;
Polystyrene (PS): this is a rigid but lightweight material, widely used to make packaging, disposable products, food containers, and insulation. Although less impact-resistant than other polymers, it is easy to process and offers good value for money for simple applications.
The advantages of extrusion
Extrusion is a process that offers numerous advantages, including versatility. This technique allows for the creation of a wide range of products, from continuous profiles such as tubes and bars to flat sheets or custom shapes, easily adapting to the needs of different industrial sectors.
Another reason why extrusion is so popular is its cost-effectiveness. Unlike other plastic processing techniques, it does not require particularly expensive equipment, thus keeping production costs low. This makes the process extremely convenient, even for large-scale production, without sacrificing the quality of the final product. In addition, extruded plastic remains malleable and modifiable after processing, allowing for waste reduction through subsequent adjustments.
Furthermore, extrusion ensures a high production rate. The machines used can operate without interruption, ensuring a continuous and regular flow of finished products. This simplifies the management of the production chain, allowing companies to respond quickly to market changes and maintain a competitive advantage. In short, extrusion is a versatile, economical, and highly productive technique capable of ensuring quality and efficiency at every stage of plastic object production.
Difference between extrusion and coextrusion
In addition to traditional extrusion, there is also coextrusion, a similar but more advanced process. In classic extrusion, a single material is used, which is melted and pushed through a mold to create continuous objects such as tubes or sheets. Co-extrusion, on the other hand, involves the use of several extruders working simultaneously with different materials, which are joined during the process to form a single product composed of several layers.
This approach allows objects with combined characteristics to be obtained, for example by combining a rigid core that guarantees structural strength with a soft, flexible or waterproof outer coating that protects the product from moisture and atmospheric agents. Thanks to its versatility, coextrusion is used in many sectors. In the food industry, for example, it allows the production of multilayer packaging that better protects products and extends their shelf life, while in the pharmaceutical sector it is ideal for the production of flexible yet resistant and durable tubes, such as those used for creams and ointments.