Machining PA 6 G

PA 6 G (cast polyamide 6, also cast nylon) is a semi-crystalline engineering thermoplastic of the polyamide family. Chemically it is PA 6, but it is not extruded – it is cast directly in a mould. This results in a particularly high degree of crystallinity and thus higher stiffness, hardness, heat deflection temperature and dimensional stability, as well as a very low-stress material. Like all polyamides, PA 6 G absorbs moisture.

PA 6 G machines excellently – turning, milling, drilling and sawing produce clean results with a good surface finish. Thanks to the low-stress cast structure it is particularly suitable for dimensionally accurate large parts. Because of the moisture absorption and thermal expansion, for tight tolerances we take the swelling and shrinkage behaviour into account and condition the stock if required. This lets us reliably produce precision and large parts – from single parts to series production.

PA 6 G pays off when large, stiff and wear-resistant parts are required – for example:

• Large gears, pinions, chain and rope wheels
• Large idler, deflection and rope rollers
• Thick-walled plates and large castings (near-net-shape)
• Sliding and wear parts with high surface pressure
• Components for offshore, subsea, wind power and conveyor technology

PA 6 G is somewhat more expensive than extruded PA 6, as casting is more elaborate. As a rough guide, semi-finished stock (natural rod/plate) ranges from about 8–20 €/kg; oil- or MoS₂-filled and coloured grades are higher. The part price is mainly determined by grade, stock form and dimension, material utilisation (waste), machining effort and batch size. We are happy to quote binding prices on request based on your drawing.

Just as important are the limits of the material:

• Highest dimensional accuracy under changing humidity – POM is often the better choice here
• Permanent contact with hot water/steam or strong acids (hydrolysis/attack)
• Continuous use above approx. 110 °C or requirements for flame retardancy (only UL 94 HB)
• Very high chemical or temperature requirements – then PVDF, PPS or PEEK
• Small, simple parts in standard dimensions – extruded PA 6 is more economical here

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

Disadvantages:

Practical tip: for large, stiff and dimensionally stable parts PA 6 G is the first choice; for small standard parts we use the more economical extruded PA 6. Where the highest dimensional accuracy under humidity is required we recommend POM, and for aggressive chemistry or high temperatures PVDF, PPS or PEEK.

• Higher stiffness, hardness and dimensional stability than extruded PA 6
• Low stress, available in very large/thick-walled dimensions
• High abrasion and wear resistance, good sliding properties
• Good machinability and weldability
• Good resistance to oils, greases and fuels
• Absorbs moisture – dimensional and property changes
• Not resistant to strong acids and hot water (hydrolysis)
• Not flame retardant (UL 94 HB), limited to approx. 110 °C continuous use
• Somewhat more expensive than extruded PA 6