Hygroscopic nature of ASA
I intend to print some relatively large (200 mm x 200 mm x 60 mm) objects out of ASA, for use outdoors. They will be standing in water. Do I need to worry about the apparently hygroscopic nature of ASA?
RE:
In my experience, you don't need to worry, depending on the application. Yes, ASA, ABS, and Nylon will lose a bit of stiffness when wet, but they gain a slight bit of flexibility, and they might slightly grow in size. This is not unlike a part being in the sun and being heated. Plastics do change when exposed to water or heat, but for the most part, if you are not pushing them to their limits, you probably won't notice.
RE: Hygroscopic nature of ASA
Excellent, thanks for the advice.
RE: Hygroscopic nature of ASA
A note: I had ABS parts of a pond filtering system, plates of about 2 mm thick, that after 15+ years of immersion in running fresh water developed 2-3 mm 'bulbs', distributed randomly on the surface. I think this may be connected with water absorption around surface defects. Water in defect makes ABS swell, which may give larger opening, etc. The parts in question are formed by injection moulding. 3D printed parts have more surface defects than injection moulded parts. It may help to smoothen the parts and seal the surface in aceton.
Also be sure the immersed parts are solid, or the infill area may fill up with water. Last but not least beware of frost, which makes any water soaked into the material rise in volume and crack the material, brittle at low temperature.
RE: Hygroscopic nature of ASA
Interesting: printing solid parts is likely to be problematic as the warping powers of ASA even at 25% in-fill are extreme (the ASA pulls the flexible metal plate away from the magnetic base). I could increase the wall thickness I guess.
RE: Hygroscopic nature of ASA
ASA is touted as having less warp than ABS, but I haven't fount that to be true. If the plate is pulling off the magnets you have good adhesion, which is tricky with ASA. Other than a heated chamber, which is mandatory for larger parts, you can add intentional splits in your part to relieve internal tension, depending on the application.
PET also works good in water and doesn't warp much.
RE: Hygroscopic nature of ASA
Interesting: printing solid parts is likely to be problematic as the warping powers of ASA even at 25% in-fill are extreme (the ASA pulls the flexible metal plate away from the magnetic base). I could increase the wall thickness I guess.
So for underwater work, use grids and/or hollow shapes with a drain. Open-ended pipes instead of cylinders, boxes instead of cubes.
RE: Hygroscopic nature of ASA
Combining these two replies I guess the answer could be to make a shape that is open at one end and has internal breaks which don't make it to the outside (this is a scale model so the outside, representing stone, is fixed). I _might_ also try switching to printing a mould and pouring grout, which I do for other parts of the same structure, just was afraid grout might let water in and crack but, given a coat of polyurethane and a strategy that allows me to replace degraded sections, it might work and look more sympathetic.