Pool-safe metal, coatings, and plastics

[Zymosis]

Hi all,

I'm currently about 10 months into a product development effort for a consumer exercise/training product that will sometimes be used in swimming pools. This means it needs to be able to handle pool water, which is approximately...

chlorine 1-3 ppm
bromine 3-5 ppm
PH 7.2-7.6
Alkalinity 80-120 ppm
Calcium hardness 200-350 ppm
Cyanuric acid 30-60 ppm
Salt 2700-3400 ppm

The product will primarily be used out of the water, but still needs to be able to handle frequent pool sessions. It's ok to ask owners to rinse the product after pool usage, but obviously we can't guarantee that they will do so.

The product itself is rather large (small ottoman sized) composed of thick-wall metal tubes, structural foam, injection molded plastic, and rubber/elastomeric parts. Basically... a structural component, some cosmetic skins, a rubber cover, some fasteners, and some legs.

I've been having trouble figuring out what materials make the most sense for this application.

For the plastic/foam parts, Delrin would a good fit were it not for chlorine compatibility issues. I need good strength/toughness, dimensional stability, low water absorption, lubriciousness for sliding surfaces. It seems like not too many reasonably priced structural plastics besides PVC can handle chlorine and bromine, but maybe there's a Delrin compound that could deal with them in low concentration?

For the metal legs, I was planning to use aluminum (6063 or 5086) with an electroless nickel coating. I need thick wall sections for features so stainless would end up too heavy. The outside of the legs act as a sliding surface so they need to be durable.

For the rubber... maybe butyl? Nominal thickness for rubber parts will be .125 - .250", injection or compression molded.

Those are just my best guesses at materials at this point. I would love to get some more insight from someone who knows more about corrosion-resistant materials than myself.

Thank you!

 

[TVP]

Electroless nickel over aluminum can have problems with localized corrosion if/when the EN layer has a defect, due to the adverse anode-to-cathode ratio. Hard anodizing with PTFE (most good anodizers offer this option) is a good way to improve the surface hardness and wear resistance without the corrosion issue of EN. For the polymer options, you may need to investigate some of the better engineering thermoplastics like polyphthalamide (PPA) or polyetheretherketone (PEEK). Maybe a polyester (PET or PBT) would have sufficient resistance, but I'm not an expert on those options, or elastomers.

 

[Zymosis]

Thanks for the help! I'd looked at hard anodizing but it wasn't clear to me that it would be better than EN. That sounds like it might be a good option.

PPA sounds like it could be a great option. I'm getting the impression that I need to start talking to a materials rep to get a better sense of what different formulations are available and at what pricepoints...