Avoid Salt Water Corrosion with Plastics Parts

Marine Plastics Acetal Roller

Marine Plastics Grade – Acetal Roller

Aluminum is a very popular and reliable material used in many marine related applications because it offers light weight and corrosion resistant properties. Aluminum also provides an excellent  strength-to-weight ratio but what it does not offer is a low coefficient of friction. If your application requires sliding abrasion or rotational wear resistance you need some plastic at the helm.
A great place to start your material selection process is UHMW which is a good all-purpose wear surface material. Old-timers tend to call the UHMW the “poor man’s Teflon” because it is so slippery. UHMW also has great impact strength and near-zero moisture absorption. It is also light weight and machinable. UHMW has been used for dock fenders for decades in demanding areas such as major ports and harbors down to municipal and private marinas.
Now,  one should anticipate any mating metal surface getting very rough from salt and rust corrosion. In that case, a harder material may be better so that particulate doesn’t get embedded in the surface of the plastic material.
Cast Nylon  would help eliminate this problem and it won’t corrode in the saltwater environment. Cast Nylon also provides extreme durability, is self-lubricating and offers a very low coefficient of friction. The primary caution with nylon is that it does absorb moisture up to 7% by weight. This can result in a dimensional change up to 2%, but if you incorporate this into your design it will work great for years. Proper design techniques can frequently compensate for this factor.
For improved strength and stiffness capability you can jump to the filled Nylatron products. Here the harder Nylatron GSM will offer improved wear and increased hardness when compared to non-filled grades.
If you have an application that requires more structural stability you can look to acetal.  The acetal materials offer high strength and stiffness coupled with that reliable corrosion resistance.  Although not as good as the cast nylons, the acetal will still provide a low coefficient of friction and good wear properties.  It also absorbs minimal amounts of moisture and as such would be a better fit for tighter tolerance mating parts.  Manufacturers research actually demonstrates that acetal bearings will outperform nylon in a fully submerged application 4 to 1.  Acetal is very commonly used for rope sheaves  because of its high strength and durability coupled with the self-lubricating properties and low moisture absorption.  As a result of this combination of desirable properties, the acetal sheaves require not metal bearing and can rotate on the bore with long service lives.
If you would like to discuss your marine application (or any plastic application) with our plastic materials expert just send an e-mail to shawn.lynam@metalpress.onlinemetals.com or call Shawn at (206)285-7836.