Oh, nylon…the material of choice for so many. Chemists at Dupont developed it in the early 1930’s. This trusty polymer is an excellent material for a wide variety of applications. For many customers new to the vast world of plastics it tends to be the default choice. Nylon may seem like a safe multipurpose material pick. However, one must always carefully consider the requirements of a project when considering a material for plastic fasteners.
WHEN NOT TO CHOOSE NYLON
Even the popular nylon has weaknesses. The polymer cannot withstand extreme high temperatures and long-term contact with water and many organic solvents. Nylon fasteners also do not perform well in applications that require low out-gassing, ultra-high strength, or clean and easy machining. The polymer also does not cut crisply so there is a need for extensive deburring. As a condensation polymer, nylon fasteners cannot be left in water. The parts are highly absorbent even from just moisture in the air.
SO WHY NYLON?
With all these issues, where did this material’s reputation as a top all-around plastic material come from? Well, for one thing, it’s cheap! Consider PEEK, a plastic that is much more chemical and heat resistant than nylon. PEEK fasteners can tolerate temperatures almost as high as 500° F. However Nylon fasteners can handle only around 300°F for short periods of time. PEEK costs around $50 per pound while nylon only costs around $3.00. Polyphenylsulfide (PPS) can also withstand high temperatures and only costs $10 per pound but is extremely brittle, even when reinforced. For projects that do not require high levels of temperature and chemical resistance, nylon fasteners are the cost effective choice.
Nylon also has certain useful chemical properties. Fasteners made from this polymer are relatively easy to glue and can be colored almost any hue simply by using fabric dyes dissolved in hot water. It can be permanently immersed in gasoline or motor oil without fear of corrosion, as it is excellent in and around many petroleum-based materials.
There are also many special-use nylons which use a wide variety of processes and additives to alter and improve nylon’s natural properties. For example, fasteners made from this plastic can be made fire-resistant to the extent that they get a UL rating of 94-V0. Its can also be modified to extend its continuous use temperature range.
Also, nylon is fairly strong. And with the addition of fibers such as carbon, glass and metal it can be made even stronger . These fibers add strength and dimensional stability.
EASY TO MOLD
Nylon is also very easy to mold. It becomes water-like when heated in a plastics extruder or injection molding machine. This melting property has the benefit of letting the material be pushed into very small spaces. The minimum annular distance between two plates for Delrin is forty thousandths. However the minimum distance for nylon is only fifteen thousandths.
All of these properties make this material an alluring and cost-effective choice for the novice engineer. Even when a few of the comparative factors are examined, there are still unique properties that make nylon fasteners competitive with respect to fasteners made out of other plastics. Yet it is important to always pick your material to fit your project. No single plastic can fit all applications.