Plastic Extrusion Technology Overview

This article will unravel the intricate aspects of the plastic extrusion process, from its foundational principles to its widespread applications.
White plastic windowsill

Plastic extrusion is a foundational manufacturing process in the plastics industry. This method transforms raw plastic material into a continuous profile, achieving various shapes and sizes to meet diverse applications.

Historically, this technology has played a pivotal role in bolstering the plastics sector, driving innovation and scalability. Its origins date back to the early 19th century when innovators began exploring the potential of reshaping plastic materials. Nowadays, plastic extrusion remains an effective high-volume manufacturing process for plastic products such as conduits, pipes and trims. 

What Is Plastic Extrusion?

At its core, plastic extrusion is a manufacturing method that yields consistent products with even cross-sections. Plastic extruders can form into various open and closed shapes. The most common shape used is a simple annulus or square profile used in tube and piping applications, typically designed to meet specific industry standards to make the tube compatible with fittings and other components.

Through heat and pressure, thermoplastic materials transform into specific shapes, all made possible by a system of meticulously designed components:

  • Hopper: Acting as the starting point, the hopper holds plastic granulates, staging them for the processing journey ahead. 
  • Feed throat: This component efficiently channels plastic from the hopper, directing it to the heated barrel awaiting further action.
  • Barrel: Within the heated confines of the barrel, the plastic edges closer to its melting point. Here, a rotating screw propels the softening material towards the feed pipe.
  • Breaker plate: The breaker plate strategically filters materials from the barrel. Besides its filtering role, it’s essential for preserving the requisite pressure within the system.
  • Die: The die stands as the defining component of the process. The molten plastic takes on the die’s shape, transforming into the desired profile.
  • Feed pipe: This element serves a fundamental purpose, functioning as a pathway for the nearly liquefied plastic exiting the barrel.
  • Cooling tank: This final phase is crucial. The freshly shaped plastic undergoes a rapid cooling system, solidifying and retaining its new form.
Plastic extrusion continuous process explained
Plastic extrusion continuous process explained

How Does Plastic Extrusion Work?

The plastic extrusion process works as follows: 

  1. Material preparation: Raw plastic, predominantly in granules or pellets, sets the stage for the plastic extrusion process. Typically housed within a hopper, this plastic is funnelled into the plastic extruder through an inlet. As these pellets meet the screw inside, their transformation begins, gradually becoming molten.
  2. Melting and conveying: Within the confines of the extruder, comprising a heated chamber and an ever-rotating screw, the plastic undergoes significant alterations. This rotating screw, though precisely controlled, can achieve speeds up to 120 rpm. Its rotation transports the plastic beads and subjects them to the chamber’s heat. Consequently, the mix of this heat and the friction from the screw’s action liquefy the plastic, with temperatures often ranging between 200 to 275 °C. Post this, the molten plastic encounters a filtering system, expunging impurities, supported by a breaker plate that stands firm even under pressures crossing 34 MPa.
  3. Extrusion process: Post the rigorous melting and mixing, the molten plastic finds its way through a tailored die or mould at the end of the extruder. This pivotal step imparts the desired die shape or mould shape to the plastic, finalising its dimensions.
  4. Cooling and sizing: Exiting the die, the plastic finds itself in a cooling tank. Here, air or water systems intervene, drawing heat away and rendering the plastic solid in its new form. Ensuring the perfection of its shape, sizing equipment might be brought into play, confirming the adherence to specific dimensions.
  5. Hauling and cutting: Rollers or equivalent mechanisms “haul” or pull the transformed plastic, ensuring its unhindered movement at the correct pace and tension throughout the process. The extruded profile is then segmented into precise lengths, with cutting tools or saws executing this task.
  6. Further processing: Beyond the core stages, some extruded products demand extra attention. These enhancements could encompass surface treatments or the fusion of additional components to the extruded shape.
  7. Inspection and quality control: At this stage, the extruded plastic profiles undergo a meticulous examination. Here, any abnormalities, deviations in dimensions, or other quality parameters are examined carefully.
Extruder machine for extrusion of plastic material
Extruder machine for extrusion of plastic material

Plastic Extrusion Materials

The choice of material crucially hinges on the desired attributes of the end product, whether it be strength, hue, elasticity, or others. The most commonly used materials are as follows: 

Acrylonitrile Butadiene Styrene (ABS)

The formation of ABS involves polymerisation techniques that fill it with toughness, surpassing Polystyrene. Its unique blend provides it with a waterproof sheen, ensuring temperature resilience. Due to its durability and aesthetic appeal, ABS is universal in consumer electronics and automotive components.

Polyethylene (PE)

A highly valued thermoplastic, Polyethylene offers flexibility coupled with remarkable chemical resistance. Notably utilised in creating containers, pipes, and packaging films, it provides an impressive blend of colour adaptability, strength, and resilience in colder climates.

Polypropylene (PP)

Esteemed for its chemical resistance, Polypropylene finds vast applications, ranging from automotive components to packaging. It boasts a harmonious balance between colour versatility, impact endurance, and performance at reduced temperatures.

Polyvinyl Chloride (PVC)

PVC stands out due to its vast application range and cost-effective nature. While flexible PVC champions adaptability and weather resistance, its rigid counterpart excels in stability and impact endurance, making it an excellent substitute for traditional materials like wood and metal in products like windows or refrigeration units.

Polystyrene (PS)

Known for its rigidity and lightweight nature, Polystyrene remains the preferred choice for insulation, packaging essentials, and disposable tableware.

Polyamide (PA or Nylon)

Nylon, a robust thermoplastic, prides itself on its mechanical prowess. Xometry has often highlighted its vast applications, from textiles to intricate automotive components.

Polycarbonate (PC)

Polycarbonate’s transparency and impact resistance position it as a material of choice in industries valuing optical clarity. Besides its durability and colour flexibility, it thrives under varied temperatures, making its presence felt in sectors like automotive and electronics.

Polyethylene Terephthalate (PET)

Predominantly seen in the food and beverage sector, PET’s primary application revolves around packaging. However, its versatility doesn’t end there; it extends to textiles and certain engineering facets.

Polymer for pipes
Polymer for pipes

Comparison Table

Material Name Heat Stability Chemical Resistance UV Resistance Rigidity Cost
ABS Fair Poor Poor High Medium
PVC Poor Poor Poor Varies Medium
Low Density Polyethylene (LDPE) Poor Good Poor Poor Low
High Density Polyethylene (HDPE) Fair Excellent Fair High Low
PET Poor Good Good Medium Medium
UHMW PE Poor Good Poor Medium Low
Polypropylene (PP) Excellent Excellent Poor High High
Nylon (PA) Excellent Excellent Fair High High
Polycarbonate (PC) Excellent Fair Excellent High High

Types of Plastic Extrusion Processes

Tubing Extrusion

Tubing extrusion process
Tubing extrusion process (Source: researchgate.net)

Tubing extrusion is dedicated to the formation of tubes or elongated hollow items. However, the technique remains consistent up to the die.  At this critical stage, a strategic application of internal positive pressure ensures a smooth process, thereby overcoming the typical energy demands linked with hollow items.

Blow Film Extrusion

Blow film extrusion process
Blow film extrusion process (Source: europlas.com.vn)

Central to producing items like shopping bags and certain packaging materials, blow film extrusion stands distinct. While the initial stages mirror typical extrusion patterns, differentiation arises at the die. 

The extruded material forms a tube, which is then inflated using air to create a bubble. This bubble is carefully stretched and cooled, resulting in a continuous and thin plastic film. The film then travels between nip rollers that apply a controlled pressure, ensuring uniform thickness and aiding in the cooling process. This technique is confined to slender plastic films, implying that thicker sheets demand alternative processes.

Sheet Film Extrusion

Sheet film extrusion process
Sheet film extrusion process (Source: shop71003.sosoutremer.org)

Often seen as a sibling process to blow film extrusion, sheet film extrusion focuses on workpieces that exceed the thickness apt for blowing. This process is well-suited for flat plastic sheets with a wide range of applications.

The raw material, in pellet form, is melted and then forced through a flat, slit-shaped die. The extruded plastic takes the form of a continuous sheet, which is then cooled and solidified. The cooling process often involves passing the sheet through a series of cooling rolls. Upon exiting the die, the material undergoes a meticulous pulling and rolling process. 

This action imparts the desired form and facilitates cooling, resulting in permanent solidification. The resulting plastic sheet can be further processed or cut into various shapes for applications such as packaging, signage, and construction materials.

Advantages of Plastic Extrusion

  • Cost efficiency: Plastic extrusion stands out predominantly due to its cost-effectiveness. When placed side by side with other manufacturing techniques, especially injection moulding, extrusion demonstrates a clear economic edge. The simplicity of the extrusion process, without any intricate tooling needs, translates to tangible cost reductions. Additionally, the capability of extrusion machines to function uninterruptedly ensures consistent production. 
  • Flexibility: The versatility that extrusion offers is truly unparalleled. The process can seamlessly mould plastic into various shapes and profiles so long as a uniform cross-section is maintained. This means a vast array of products, from complex shapes to standard sheets and pipes, can be efficiently manufactured using this method. Such freedom empowers industries to innovate and customise as per evolving market demands.
  • High production rate: The absence of breaks in machine operation ensures a steady flow of products, efficiently catering to high-volume demands. This continuous production model aids businesses in maintaining a consistent supply chain, addressing both immediate and future market requirements.
  • Material conservation: The malleability of hot plastic before cooling is a pivotal advantage. This intrinsic property permits additional shaping and resizing operations, ensuring optimal material utilisation and minimal wastage. Such an approach boasts production efficiency and resonates with sustainability and resource conservation.
Workshop with extruders for producing polypropylene pipes
Workshop with extruders for producing polypropylene pipes

Limitations of Plastic Extrusion

While plastic extrusion boasts numerous advantages, it’s essential to consider the following limitations:

  • Design restrictions: A significant drawback of plastic extrusion is the unpredictability of the post-extrusion expansion, commonly known as ‘die swell’. This unpredictable expansion can sometimes compromise the accuracy of the end product, requiring further rectifications and adjustments.
  • Material limitations: Although plastic extrusion accommodates the use of recycled materials, this option isn’t without its complications. Recycled plastics often bring along impurities and present inconsistent attributes. Such inconsistencies can affect the overall quality of the final product.
  • Setup costs: Initiating a plastic extrusion setup demands substantial capital investment. The associated costs of procuring dies, extruders, and other essential equipment, especially for specialised applications, can be steep.
  • Finish and tolerances: While plastic extrusion is versatile, the technique imposes certain restrictions on the range of products one can craft. It’s essential to research meticulously and possibly consult experts to identify the most suitable extrusion equipment tailored to your project’s specific requirements.

Applications of Plastic Extrusion

Packaging

Plastic extrusion dominates the packaging sector, primarily in the form of pipes and tubes. A typical example includes the PVC pipes. These pipes, shaped using a basic cylindrical profile die, are a testament to the widespread use of the extrusion process in packaging.

Construction

Extruded plastics find extensive application in constructing durable window and door frames. The long-lasting nature and inherent UV radiation resistance make materials like PVC a preferred choice. Beyond frames, even blinds and shades frequently incorporate extruded components. For instance, the famous faux-wooden appearance in many blinds is often achieved using extruded polystyrene.

Automotive

Wire insulation in vehicles largely relies on plastic extrusion, attributed to plastics’ intrinsic electric insulation capabilities. Plastics’ thermal stability and flexibility further make them ideal for safeguarding live wires, ensuring a durable and secure fit. In the automotive sector, the longevity and reliability of extruded jacketing and insulation are paramount.

Consumer Goods

The spectrum of consumer goods benefitting from plastic extrusion is vast. Consider the field of cleaning equipment: tools like wipers and squeegees, which people use daily, often incorporate handles made from extruded plastics. Some even boast a rubberised plastic finish, enhancing their cleaning efficacy, a testament to the versatility of the extrusion process.

Extruder for the production of polyethylene pipes
Extruder for the production of polyethylene pipes

Plastic Extrusion vs. Injection Moulding

Plastic extrusion and injection moulding are primary methods in the plastics industry, each offering unique advantages.

Plastic extrusion excels in producing continuous profiles with a consistent cross-section. Typical outputs include pipes, tubes, and sheets. This method is favoured for its simplicity, ability to run continuously, and cost-effectiveness, especially for high-volume outputs.

Conversely, injection moulding injects molten plastic into a mould, which cools and solidifies. This process is ideal for producing discrete items, often with intricate details. Its strengths lie in precision, using multiple materials simultaneously, and producing high-quality, repeatable components.

Injection Moulding Plastic Extrusion
Quantity range 50 – 1,000,000 > 1
Sample 1 month+ 2 weeks +
Prototyping
High-volume production
Functional
Aesthetic
Complex geometries
Coloured parts

In choosing between these methods, consider the production volume, part complexity, and product type.

Make Production Orders with Plastic Extrusion at Xometry

With its array of benefits, the extrusion process is revolutionising the plastic manufacturing sector. It strikes a harmonious balance between economic viability, design versatility, production efficiency, and sustainable practices, establishing itself as an asset for modern industries.

For businesses seeking reliable solutions for low and mid-volume production, Xometry offers top-notch plastic extrusion services.

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