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Material Properties of Thermoplastic PEEK

Material Properties of Thermoplastic PEEK

What is PEEK

First developed by ICI ( Imperial Chemical Industries) in the UK, PEEK material is one of today’s most popular high-performance engineering plastics and is known by its academic name, polyether ether ketone. 

What is PEEK

The material is obtained by polymerization of 4,4′-difluorobenzophenone with hydroquinone as a potassium salt. It is a new type of colorless semi-crystalline aromatic engineering plastic.

which can be used in a wide variety of applications, including CNC plastic machining. Polyether ether ketone is characterized by its high-temperature resistance, high strength, and excellent physical and mechanical properties. 

Material Properties of Peek

PEEK has a density of 1320 kg/m3 with water absorption of 0.1 % over 24 hours. It has a melting point of 343 °C that qualifies it for the classification of high heat engineering material as it retains its mechanical properties over elevated temperatures.

Young’s modulus of PEEK is 3.6 GPa and tensile strength of 90 to 100 MPa with a thermal conductivity value of 0.25 W/m.K. The strength-to-weight ratio of PEEK is comparable with that of stainless steel. As a result, PEEK is used extensively as a replacement for metals.

The glass transition temp for PEEK material is 143 °C. Certain grades of PEEK material can have a useful operating temperature of up to 250 °C. 

PEEK is available in different grades including industrial grade and medical grade. However, the specific properties of these grades of PEEK vary from manufacturer to manufacturer.

Different grades of PEEK are available in filament form, granular form, or solid form for further processing through different manufacturing processes.

In terms of chemical properties, PEEK material is highly resistant to degradation by organic and aqueous environments. However, PEEK is soluble in sulphuric acid even at room temperature.

It is also resistant to biodegradation. There are some medical grades of PEEK that can be implanted in the human body for 30 days.

Different medical grades can be implanted for longer periods in the body. Some grades of PEEK are radiation-resistant as well. These radiation-resistant grades of PEEK are used in space applications.

PEEK can also be used widely in electrical applications due to its desirable electrical insulation properties. 

The Applications of Peek Material

As PEEK ( polyether ether ketone) plastic material resin has many of the above advantages, it has been widely used in the petrochemical, electrical and electronic, instrumentation, machinery automotive, medical and health, aerospace, military nuclear energy, and many other fields.

It is also widely used in china CNC machining parts. Peek can be machined to close tolerances and has a low coefficient of friction, making it ideal for wear-resistant applications. 

(1) The applications in the automotive industry

PEEK has excellent fatigue and chemical resistance properties, so it can be used in automotive fuel management systems.

Due to its lightweight, it is replacing a variety of reactive metal or aluminum components used in transmission, braking, and air conditioning systems, including piston units, seals, gaskets, or bearings, which can lead to significant reductions in vehicle weight and noise.

PEEK has the following main applications in the automotive industry:

  1. Seals and thrust washers: used in the sealing of gearboxes and clutches in automobiles.
  2. Worm gears: mainly used in automotive seat adjusters.
  3. Vacuum pump spinners: mainly for use in power-assisted braking systems in automobiles.
  4. ABS cams and ABS spools: mainly for use in braking systems in automobiles.
  5. Bushings and plain bearings: mainly for window crank motors and wiper motors and sunroof motors in automobiles.
  6. Limit pegs and limit spacers: mainly used in the crank window motor and wiper motor and sunroof motor of automobiles, etc.

The applications in the automotive industry

(2) The applications in the aviation industry

With low density and good processing performance, PEEK can be directly processed into the required precision parts. And its good hydrolysis resistance and corrosion resistance can be used to make aircraft external parts, the excellent flame retardancy is commonly used to do the internal parts of the aircraft.

PEEK is used in aircraft for specific components: 

  1. Engines: The main performance of PEEK in most engine applications is resistance to high temperatures and the frictional effects of contact with lubricated materials. PEEK materials are used at long-term temperatures of 260 degrees and can withstand localized engine overheating conditions.
  2. Aircraft Exterior Components: The wear resistance of jet aircraft exterior components depends on the impact of the material surface on atmospheric raindrops or microlithic materials. Test surfaces of PEEK have good resistance to rain. 
  3. Aircraft interiors: PEEK’s outstanding flame retardancy, mechanical properties, creep resistance, and fatigue resistance are demonstrated by the requirements of airline transport applications for the manufacture of transformer housings, battery racks, and fuel line brackets. 
  1. Engine fairings: Finishing covers on the wings to streamline the airflow around the intertwining strut assembly of a painted engine. 

(3) The applications in the medical industry

In the medical field, PEEK offers innovative and economical components with excellent wear, heat, electrical and chemical resistance.

Its applications in healthcare include dental instruments, endoscopes, dialyzers, etc., mainly for orthopedics.

(4) Electrical and electronic fields

PEEK is a Class C insulating material that guarantees excellent insulation properties in environments such as high temperature, high pressure, and high humidity, as well as wave-transparent, dimensionally stable, and self-lubricating properties, with very low dielectric constants and loss factors at all frequencies.

Modified anti-static grades/insulation grades/static shielding grades of PEEK are available to meet the different needs of the electrical and electronic industry.

Limitations of PEEK Material Processing

PEEK is a special engineering plastic with excellent performance and has many significant advantages over other special engineering plastics.

It has high-temperature resistance, excellent mechanical properties, good self-lubrication, chemical resistance, flame retardancy, peel resistance, irradiation resistance, stable insulation, hydrolysis resistance, and easy processing. 

But PEEK also has processing limitations, PEEK materials are molded and processed in a variety of ways, including injection molding, extrusion, blow molding, pressing, and mechanical processing.

The applications in the automotive industry

The mechanical processing of which there is no small difference in thermal expansion, heat dissipation properties, elasticity, wear resistance, and other aspects of metal materials and general engineering plastics.

if not given sufficient attention, improper operation will produce blow-ups and even damage to processing equipment and other situations.

Causes of material blowing up during processing: 

(1) Blow-ups occur during processing because the stress in the blank itself has not been completely removed.

(2) Cracking occurs when machining with excessive tool draft.

(3) Direct drilling with a larger drill bit, due to the large cutting force is very easy to squeeze fried.

(4) Machining deep holes without repeatedly backing off the drill to discharge chips, chips are not fully discharged, and extrusion is caused by cracking.

(5) Inadequate cooling, drilling cooling is not sufficient due to the cutting heat generated and the cutting force being too high, which will also blow up.

(6) The feed rate is too fast, which will increase the stress inside the PEEK bar to produce a blowout.

(7) Due to the wear-resistant PEEK material, the cutting edge of the drill bit will soon wear out when drilling, and if the drill bit is not re-sharpened in time, hard drilling will also produce a blow-out. 

So, if the rough machining of the part is large, the heat generated will inevitably lead to the release of internal stresses, resulting in the deformation of the part.

In particular, parts with high dimensional requirements are subject to an annealing process after rough machining and then finishing to dimensional requirements.

The main role of carrying out heat treatment annealing is to improve the crystallinity of the part, thus increasing its strength and chemical resistance, reducing the internal stresses generated during extrusion and machining, and improving dimensional stability over a wider temperature range.



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