I’m trying to determine which material would best meet my current needs for an elastic resin. I need to print some grommets that interface/cushion between a plastic screen and mounting screw. These grommets will be exposed to UV quite often (motorcycle windscreen).
In the past, I used Black Prusa Flex80, which did well, however typically it tore when taking the components apart after some time under compression and my stock is getting close to running out and I need to run another production.
Hilariously, these are $25 a piece from Harley-Davidson, and only a few cents on an SLA printer. They are a custom size and not something that can be purchased off the shelf or through a distributor like Amazon.
looks as though 40a is susceptible to UV exposure, and i assume elastic and flex. seems casting molds with a 2 part silicone might be the best route for my needs
I checked out the white paper on silicone right after submitting this, and it read that silicone 40a would degrade with UV exposure, so I’m not sure it’s the best option for this purpose. Although I am already using a flexible resin from another manufacturer, so it may not make that big of a difference.
I wonder if you can use a hybrid arrangement here. My impression is that the compressibility of the grommet is useful to transfer loads to the screen without creating point stresses, and probably some other factors I’m not aware of. My assumption is that thread locker is what prevents the threaded fasteners from loosening, rather than any locking characteristics of the compressible grommet.
I wonder if you can use Tough resin for the main grommet and create load spreading features on its contact surface with the screen. Or recess it and use an O-ring to transfer the load from grommet to screen.
I have looked at the silicone recently (online, not purchased yet but will) and get the impression that it’s too soft for this kind of application. I think you might see it squishing out of the way as you tighten the fasteners.
I agree that 40a may be too soft/spongy for this particular application, and elastic 80 may be better suited. The screw that mounts here has a surface that mates directly to the grommet, so it’s to prevent cracking from pressure between two hard points. I do have a need for gaskets for other components, which is why I was also leaning towards 40A, but it seems that perhaps 80flexible is what I need. And considering what I was using before has a shoreness of 80, it may the best fit.
In that case indeed the Silicone 40 may not be the best choice.
It would be nice to know the level of degradation tho, as a vast majority of polymer degrade with UV but not always at the same rate. If it stay usable and in good shape for 2 / 3 years outside it may still be interesting considering the OEM prices.
With that said if the Elastic 80 is more UV resistant and the same shoreness as the OEM part if may be better suited !
Sadly, all photopolymer resins will degrade with UV exposure over time unless coated or sealed with something, which makes long-term outdoor use a challenge.
At this scale, I’d personally recommend printing a negative mold in something like Clear V5 and casting with a two-part silicone instead. It’s a bit more work up front, but gives you more material flexibility and long-term durability, and lowers the cost even more for future castings.
Do you have suggestions for what we can use to seal? I’m thinking more about the tough resins than the flexibles now. For example, I recently had some success dying Grey V5 in IPA+ alcohol ink baths. Are there UV-stabilieing substances we can get soaked into the outer layers of a print?
We don’t have any official documentation or recommended methods for soaking in UV stabilizers as far as I know.
That said, there are a bunch of spray-on UV-resistant coatings that people use to protect printed parts. The off-the-shelf cheap option I keep on hand and use for personal stuff is just a standard UV-resistant clear coat from Rust-Oleum or Krylon. It’s easy to find, gives some decent protection, and works well for most small projects.
For more special projects, automotive 2K clear coats offer much better durability and UV protection. The only downside is they’re expensive and sometimes comes in those cans with a button on the bottom to activate them, which starts a chemical reaction and gives you only about 24 hours before the whole can cures. So they’re not ideal unless you’re sealing a bunch of parts at once or a large project
For flexible materials, I haven’t dug into the TDS to fully verify compatibility, but I’ve personally used flexible Plasti Dip spray on parts that needed to retain their softness and it worked totally fine. It will be black though, and definitely won’t retain any clarity or translucency if you’re coating Flexible or Elastic resin. But it’s worked good enough for me.
