Nylon – chemically polyamide (PA, not to be confused with polyimide, PI) was invented in 1935 by DuPont’s Wallace Carothers (PA 6/6). Nylon 6 (PA 6, extruded), or polycaprolactam, was developed by Paul Schlack at IG Farben to reproduce the properties of nylon 6/6 without violating DuPont’s patent. Initially used in fibers to replace silk in parachutes, stockings etc, these resins established the basic principles of polymer chemistry that have made plastics such a ubiquitous part of our lives today. Nylon was also injection molded into components for the automotive market with varying degrees of success…people back then disliked nylon timing chain sprockets as they constantly stripped out!
(FUN FACT – “NYLON” was originally DuPont’s tradename, but DuPont didn’t protect it and it became so commonly used that they lost the right to it – today it is “ZYTEL®”)
Generally, nylon machined parts have a robust combination of properties, including high strength-to-weight ratio, toughness and inherent wear resistance. Stock shapes in 6/6 nylon are all extruded; in type 6, it can be either extruded (Europe) or cast (worldwide). While there are slight property differences, usually the decision between PA 6/6 and 6 involves either size and/or specifically modified version availabilities.
PA 6/6, sometimes referred to as Nylon 101 (old DuPont callout), is available in natural (off white), black, glass filled and specialty grades (low smoke, flame retardant, heat stabilized, impact modified). There are no enhanced wear resistant versions currently available.
NOTE: The crossover point [cost versus size] between unfilled extruded PA 6/6 and cast PA 6 is about 2.5” diameter rod, and .500” plate, over which cast PA 6 costs less to make.
PA 6 – in North America, 99+% of PA6 is cast, so we’ll stick to that technology. Cast nylon was first invented in Europe in the 1950’s and introduced in the US in the early 1960’s. Since it is made by combining two liquid feedstreams into a tool which react to become PA 6, additives are much easier to incorporate, and a wide range of sizes and shapes are readily available (from thin plate to custom castings weighing hundreds of pounds).
Here are the most popular grades of cast PA 6 currently available:
|Unfilled||Natural, black||General purpose|
|MoS2 filled||Grey, black||Higher crystallinity|
|Heat stabilized||Blue, black||Higher cont. Temp. Use|
|Oil-filled||Natural, green, others||High load / low speed|
|Oil & MoS2 filled||Dark blue, black||Crystallinity + lubricant|
|Solid lubricant filled||Red, grey, black||Highest PV rating|
|Solid lubricant filled||Purple||Lowest “stick-slip”|
|Impact modified||Blue, yellow||High impact resistance|
There are also alloys of PA 6, such as PA 6/12, which can offer lower moisture absorption and higher impact resistance.
Again, it is nylon’s combination of properties that make it so widely used. There are many applications that have 4 or 5 key property requirements, where nylon isn’t #1 on any of them but #2 on all of them!
Too many choices? No worries – the nylon experts at WS HAMPSHIRE can guide you through the selection process. You’re in the right place!
Tom Connelly is a self proclaimed “Street Engineer” with over 40 years in the plastics industry.