Materials with extreme chemical resistance

[SophBayliss 0]

Hi,

 

I am working on a project testing material resistance to aviation hydraulic fluid (Skydrol/Hyjet V).

 

I am looking for recommendations of materials which may have some resistance to such a chemical.

 

I know that GF30-PA6 fairs well when exposed to these chemicals but equally that materials such as ABS and PLA degrade extremely quickly.

 

Any material suggestions or data sources would be greatly appreciated.

 

Many thanks,

Soph

[geert_2 551]

Most bottles for chemical products are made from PE, both HDPE and LDPE, or PP, so these have a reasonable chemical resistance. For use on the ground, maybe this could be an option, if they meet your strength-requirements?

 

However, for use in airplanes, I doubt if they meet the temperature range? Especially PP might become very brittle when well below freezing temperatures. Also, they degrade quite fast in strong UV-light, so not very suitable for outside applications, especially not at 30000ft. Impact-resistance of PP is lower than PE, this could also be a factor.

 

I have no experience with printing them, so I don't know about layer-bonding, warping, settings, etc.

 

Maybe another option might be to design and 3D-print a mould, and then cast a suitable material in it? Maybe PU-rubber, or hard PU (whatever you need)? Probably not silicone rubber: silicone is water-tight because it repels it. And it is chemically quite resistant. But it is for sure *not* oil-tight, and not solvent-tight. I found out after a full cup of liquid parafine leaked through it overnight... After cooling down, the whole silicone cup was impregnated with parafine too, opaque white instead of transparent yellowish. That is why it is a good idea to thoroughly impregnate silicone moulds with silicon oil, prior to casting solvent-like composites: this saturates the mould with silicon oil, and reduces the amount of solvents that can seep in and destroy that mould by curing in the silicone itself.

 

I often make PLA moulds for casting silicone models. Or silicone moulds, around a PLA- or plasticine model, to cast PMMA epoxies.

 

If you would go the moulding way, make sure to follow classic design and moulding rules: no undercuts, drafts, pouring openings, venting openings, etc... Print the mould very fine, and then smooth it by sanding or chemical smoothing (dichloromethane). If well done, you can make multiple casts from one mould.

 

[SophBayliss 0]

Thanks!

 

At the moment i am just looking at non-flying parts such as tooling which often gets the chemicals spilled on it and is currently metal but could be cheaper to 3D print and lighter so less of an ergonomic issue.

 

HDPE is most likely a good option I hadn't thought of!

 

Thanks again for the advice with moldings, that's something I am looking into in another project.

[geert_2 551]

When making a mould, include holes in the seam-line for a compressed-air pistol, so you can blow air between both mould halves. Also provide slots to insert a screw driver to pry both parts apart. This will greatly help you in demolding. Otherwise it could be a nightmare: silicone casts tend to suck vacuum very strongly, like a suction cup.

 

You see both features here. This is a mould in PLA, for casting soft silicones. The round conic openings for the air pistol do not go into the silicone cast itself. They stop short of it, and are only to blow air in-between both mould halves.

 

In this mould I have no pouring openings and no venting openings. I pour the silicone in one half of the mould, and then close it, and the superfluous silicone is pushed-out via the seams. It is too thick and cures too fast for pouring into tiny openings. I can't show the inside, but it also contains alignment features, and it makes sure no air is entrapped. Clamping is done with clamps on the outside, but depending on the size and design, you might need to design dedicated clamping areas and flanges as well.

 

Round holes for inserting a compressed-air pistol, and rectangular slots for inserting a screw driver. First blow air, to separate the silicone from the mould, then pry both parts open with the screw driver. This works very well.