Machining PET

PET belongs to the polyesters – thermoplastics with ester bonds in the molecular chain. For machined parts, the semi-crystalline variant (PET-C) is extruded as semi-finished stock; it is stiffer, harder and more dimensionally stable than the well-known transparent bottle PET. PET absorbs only little moisture (about 0.3 %), is dimensionally stable and largely retains its dimensions even under changing climate. It is hard and stiff, yet comparatively notch- and impact-sensitive.

PET machines excellently – turning, milling, drilling and sawing produce clean, dimensionally accurate results. Thanks to low moisture absorption and low thermal expansion, tight tolerances are reliably maintained. Because of its notch sensitivity, we use sharp tools and adapted cutting parameters and avoid sharp internal corners. This is how we reliably produce precision and wear parts – from single pieces to series production.

PET is worthwhile whenever dimensional stability, stiffness and wear resistance are required – for example:

• Precision parts with tight tolerances and high dimensional stability
• Sliding and wear parts such as bearings, bushings, guides and wear strips
• Components for food processing (FDA-compliant, food-safe)
• Components for conveyor technology and automation
• Electrically insulating components with high stiffness

PET is priced in the mid-range of engineering plastics – usually somewhat above POM, but considerably below high-performance plastics such as PVDF or PEEK. As a rough guide, semi-finished stock prices are in the range of about 8–20 €/kg. The component price is determined mainly by the semi-finished shape and dimension, material utilisation (offcut), machining effort and lot size. We are happy to quote binding prices on request based on your drawing.

Equally important are the limits of the material:

• Applications with high impact/shock loading – PET is brittle and notch-sensitive; use POM or PA instead
• Continuous contact with hot water or steam above about 60 °C (hydrolysis)
• Contact with strong acids and alkalis
• Components with fire-safety requirements – PET only reaches UL 94 HB; use PA 6 FR or PVDF
• Continuous service above about 115 °C – then PVDF or PEEK are options

An honest assessment – and how the disadvantages can be mitigated in practice: Advantages:

Disadvantages:

Practical tip: PET plays to its strengths wherever dimensional stability, hardness and wear resistance matter – for example in precision and sliding parts in food and conveyor technology. Where impact strength is the priority, we recommend the tougher POM or PA; for fire-safety requirements PA 6 FR or PVDF, and for higher temperatures PVDF or PEEK.

• High stiffness, hardness and dimensional stability
• Low moisture absorption, very good dimensional accuracy
• Good sliding, wear and creep properties
• Suitable for food contact (FDA-compliant)
• Very good, precise machinability
• Brittle and notch-sensitive – low impact strength
• Not resistant to hot water/steam (hydrolysis) and strong acids/alkalis
• Only UL 94 HB – not flame-retardant
• Continuous service limited to about 115 °C