Five factors to consider when moulding PEEK

Are you a first-time moulder of PEEK? Or possibly you’ve tried moulding it and might be running into trouble? In this piece, we consider five factors in the injection moulding process that can help to avoid the need for troubleshooting when moulding PEEK polymer – and it can help to reach the full potential of this high-performing material.

Polyetheretherketone (PEEK) is an advanced high-performance thermoplastic that is widely used in demanding applications in the aerospace, automotive, energy, industrial, electronics, and medical industries. One of the benefits of this semi-crystalline plastic is that it offers exceptional mechanical properties, temperature performance, and chemical resistance.

Even though injection moulding PEEK may be seen as challenging, it can be moulded similarly to other high-performance thermoplastics. By focusing on some of PEEK’s unique processing requirements, one can prevent common challenges or pitfalls. Getting PEEK injection moulding right pays major dividends. Producing high-quality, defect-free PEEK components allows you to take full advantage of its excellent performance.

To realize PEEK’s benefits, every detail of the injection moulding process must be controlled and optimized. In this article, you will learn the five key factors to consider when moulding PEEK. By following the guidelines from ChengHe, you can prevent defects, reduce iterations, and accelerate proficiency with this high-performance material.

#1 Equipment: Standard Injection Moulding Machines

The first factor involves the equipment you use. PEEK can be moulded on standard injection moulding machines supplied by most well-known machine suppliers. Depending on the grade of PEEK you’ll be moulding, processing temperatures on your injection moulding barrel will be somewhere in the range of 350–400°C.

These temperatures can be reached on most standard injection moulders with cylinder heaters without the need for modifications. If modifications are required, these are usually for the heater bands or thermocouples/controllers. We suggest using ceramic heater bands as they provide the most consistent processing. Additionally, consider the use of barrel blankets as they provide heat insulation, with the benefit of energy cost savings.

A general-purpose screw is effective. Copper and copper alloys should be avoided in contact with the melt. All metallic components should be smooth and highly polished to prevent material hang-ups.

#2 The Importance of Drying PEEK Polymer

PEEK granules are supplied nominally dry but may absorb moisture from the atmosphere. In our technical data sheets and injection moulding guides, we provide specific guidance on drying. In short, we suggest drying the pellets on trays in circulating ovens for 2–3 hours at 150–160°C, or alternatively, overnight drying.

The aim should be to reduce the residual moisture content to <0.02%. Dehumidifying or desiccant dryers may also be used and must be capable of maintaining a dew point or saturation temperature of -40°C.

#3 Cleanliness is Key

Cleanliness is a non-negotiable requirement—keep it clean! Any contamination should be avoided when processing PEEK. Most other polymers will degrade at PEEK’s processing temperatures; therefore, it is imperative to start with clean drying ovens, hoppers, injection moulders, and any other containers used to hold runners or parts.

Pull the screws and properly clean and brush the barrel and screw before starting to mould PEEK. Check for hang-ups in hoppers. Regrind can be a major source of contamination, and we suggest that you use dedicated equipment for the regrinding of PEEK materials. Any contaminants during the injection moulding process will show up as black specs in your final component.

#4 Use the Biggest Gates Possible

Moving along the injection moulding process, we come to gate design—PEEK likes big gates. Gate size is dependent on the part volume, number of cavities, and component geometry. PEEK is a semi-crystalline polymer and exhibits much higher shrinkage compared to amorphous thermoplastics.

Moreover, cooling from a much higher processing temperature to ambient causes more shrinkage compared to lower-temperature processing polymers. Using the biggest gates possible will ensure that you fully pack out your component. At ChengHe, we follow a general "2/3rds rule" regarding the maximum section thickness of your component. Depending on the grade, this might be a minimum of 1mm for unfilled PEEK and 2mm for compounds. Gate designs such as tab, side, or fan gates are most commonly used. Submarine or tunnel gates can be considered for very thin walls or small parts but tend to lead to "freeze off" during the moulding of bigger parts.

#5 Good Temperature Control

Good temperature control on your mould is critical. The mould temperature is vital to obtaining a semi-crystalline component that can fully utilize PEEK’s unique set of properties. Without proper control, you may see a mix of brown (amorphous) and beige (semi-crystalline) sections on the same part.

To mould PEEK and its compounds successfully, one needs to be able to maintain mould temperatures between 170–200°C (to avoid quench-cooling into the amorphous state). It is important to note that this should not only be the set temperature on the mould, but the actual surface temperature of the mould. This can be achieved using electrical heaters for smaller parts and oil heaters with isolated flow lines for larger shot sizes or tools with deep cores. Consider using insulation boards between the mould and the machine platen to ensure uniform temperature distribution.

Summary

In summary, while many factors play a role in successful PEEK production, these five are essential for any high-performance project:

1. Standard Equipment: Most machines can handle PEEK with the right heater bands.

2. Proper Drying: Reduce moisture to <0.02% to prevent porosity.

3. Strict Cleanliness: Avoid black specs by eliminating cross-contamination.

4. Optimized Gating: Use larger gates to manage high shrinkage rates.

5. Thermal Management: Maintain 170–200°C mould temperatures for full crystallinity.

ChengHe’s technical service teams across the globe are available to support customers with any injection moulding questions. You can also download our Injection Moulding Guide and data sheets from our website or contact us through our official service channels.