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The plastic profile production process

Being a leading plastic extrusion company with more than 60 years of experience, Primo is supplying market leading industries with state-of-the art  technologies in plastic extrusion. When you engage in corporation with us, you will experience high flexibility that meets the requirements for your unique solution.

What is plastic extrusion?

Plastic extrusion is a high-volume manufacturing process in which raw plastic is melted and formed into a continuous profile. At Primo, we have been extruding plastic profiles since 1959. Both extruders and the process itself have undergone significant progress over the years.

A specialised production setup

Today, advanced technology and digital monitoring ensure high-quality and cost-saving processes for the benefit of a wide range of industries and numerous applications at our highly efficient and automated production plants in Europe and in China. 

In plastic extrusion, the heated plastic mass is put under pressure by a screw and is pressed through a die (the tool). The profile is then cooled down and hardens into its final solid state. This way, a profile can be produced in any length, which is an advantage, for example, when producing parts for cables that are rolled directly onto cable reels.

Plastic profiles for all kinds of purposes

Extrusion is a widely used method to shape plastic materials, but it is also used for other materials. For instance, the technique is used to a great extent in the food industry in which products like minced meat, pasta, and even cheese puffs are made by extrusion.

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Plastic extrusion is polymer extrusion

It is a frequently asked question  - and a fairly good one - whether plastics and polymer are the same.

The short answer is no. Plastic is a polymer, but polymer is not necessarily plastic.

Plastic belongs to the polymer family

A polymer is a macromolecule composed of many similar building blocks. Plastic belongs to the family of polymeric materials. The individual types of plastic are therefore also often called polymers.

The term is derived from the Greek "polymeros", which can be translated into poly = many and meros = parts. A polymer is therefore a very large molecule - a so-called macromolecule - composed of many similar building blocks. These building blocks are called monomers.

What are plastics?

Plastics are organic materials, just like wood, paper or wool. The raw material is first and foremost crude oil. In addition, cellulose, coal, natural gas and salt are included. Crude oil is a mixture of thousands of different substances, and in order to utilize them, the oil must be refined in large plants.

5 percent of the world's oil consumption goes to plastic; the majority is used for transport.

European plastic manufacturers are organised in Plastics Europe; here you can learn a lot more about plastics


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Extrusion technology

Extrusion is usually a fully automated process with continuous dimension checks and automatic machine adjustment. This makes it possible to manufacture a wide variety of products from simple tubes and rods to extremely complex window profiles. The extrusion also enables the manufacturing of very large products or practically endless profiles for use in for instance off-shore cables.  

A process with indefinite possibilities

The success of the process depends on several factors in which the temperature plays a critical role. The input consists of plastics in the shape of pellets, granulates, flakes, or powder which turns into a homogenous mass when heated. Often various ingredients are mixed to obtain particular properties, such as plasticity, colour, strength, etc.

The temperature needs to be measured carefully, as well as the pressure that the screw puts on the plastic mass relative to the given plastic material and the size of the tool. Too high, too low, or too much variation in the pressure can cause tension in the final result. The stress can lead to unwanted twists in the profiles or destroy their strength.

The specific plastic type and the design of the profile also play a major role in the properties of the final solution. 

The plastic extrusion process for manufacturing state of the art plastic profiles

The extrusion process

1. Storage and drying. The raw materials are stored in silos and flexible bulk containers. Before the process is initiated, the raw materials are dried according to the manufacturer’s instructions. Depending on the requirements for the end product, the materials are picked among a collection of more than 40 traceable polymer types from licensed suppliers. The range includes recycled materials.

2. Dosing. The raw materials are dosed into the extruder using a gravimetric scale. So-called masterbatches (for example, coloured polymers) can be added to the raw materials to meet customer requirements of particular properties, such as durability, flexibility, colour, etc.

3. The Extruder. The cylinder’s zone-based electric heaters and screw heat the raw plastic material to a temperature between 110 and 260 degrees Celsius and melt it into a homogenous mass. A custom-designed screw pushes the solid mass towards the die with steady pressure. At this stage, more processes can be integrated to ease the fitting or in other ways strengthen the end product, for example, through co-, triple- or quad-extrusion or a combination of these.

4. The die. The pressure pushes the hot mass through the die, which shapes the profile. The profile can be up to 25 cm wide and 15 cm tall. In preparation of this phase, and in developing the tools, Primo continues to aim at improving the functionality and certain characteristics of the end product. The production of the tools is a decisive phase of great importance for the finished profile.

5. Calibration and cooling. The calibrator cools the profile and shapes its final form using vacuum and water or air. A precise calibration and cooling help ensure that the end product has the desired surface and correct dimensions.

6. Haul-off unit. Two opposing belts which rotate at a uniform speed keep the process going. During this part of the process, inkjet marking is applied to the profile to ensure production data and traceability of the final product.

7. Inline-machining (optional). Final assembly can be simplified for the customer by cutting holes or specific edges on the profile. It is also in this part of the process that the profile can be sealed or that adhesives can be added to the profile.

8. Cutting. The profile is cut into the desired length (min. 0.02 m, max. 16 m). The cutting method is selected according to the shape of the profile and the raw material and can be done using, for example, a circular saw, a guillotine, or a hot knife. At this stage, an anti-static coating can also be applied to the profile, and profiles can be welded together.

9. Packaging. The packaging is designed for each individual type of profile. Typically, the profiles are packed in cardboard boxes or wooden crates to ensure adequate protection of the profiles and to ease further handling and unloading. Primo can also store the profiles in warehouses to ensure quick delivery and strengthen the supply chain.

Plastic extrusion - a complex process with numerous options 

Some plastic products require more properties than a single extrusion can deliver. In these cases, co-extrusion can be an option. Co-extrusion is the process of extruding two types of plastic simultaneously through the same tool as two layers, that are fused by the influence of heat.

Co-extruding is a complex process that puts great demands on the machinery and dosage of materials from both sources. The benefit however is that single plastic profiles can have a number of properties. For instance: a rigid side for montage and a softer plastic type for airtight sealing. 

Co-extrusion - and even quad-extrusion

In some cases, triple- and quad-extrusion can be applied. These methods require even higher degrees of precision and expertise in the dealings with the materials. Experienced extrusion companies offer such advanced production methods.

The extrusion process can also include an inlet process combining two processes in one; for instance the extruded plastic profile with a metal wire.

Additional operations in  plastic extrusion manufacturing to ease the process

When the profile is cooled, further adjustments will often be made. At this point, it is possible to drill holes, add coating, and a batch number. The batch number is a quality control measure that makes it possible to go back and find details about the production conditions at a given time.

Ideal materials for plastic extrusion profiles

The most common types of plastics that are extruded today are polyethylene (PE), polypropylene, acetals, acrylic, nylon (polyamides), polystyrene, PVC (polyvinyl chloride), ABS (acrylonitrile, butadiene, and styrene), TPE (thermoplastic elastomers), and polycarbonate.  See all material types.

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Kristoffer Buhl Larsen

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