So we are working on a part that would be made from a 70D castable urethane. The problem is we are trying to get it as slippery as possible with various fillers. How much fill is too much for a resin to handle?
Side question: what fillers would you use (we have narrowed it down to 7 possibilities…still a little broad)?
little confused. You want the final product TO be 70D, or is it just originating from that material? What do you mean by slippery? Physical sliding and anti-friction? You can use PTFE, FEP or UHMWPE powder. Maybe even UHMWPE chopped fibers/staple.
as for how much it can handle? How much can YOU handle? Depending on the pot life, you can fill up the resin with fillers until you can’t mix it anymore, or get tired. Once you overfill the resin, while it will still cast with some effort, it might break down the properties and obviously make it harder than 70D.
It is just originating from that material…basically I want a castable UHMW. UHMW milled fiber sounds great but, apart from being nearly impossible to find, it seems like it would need to be treated prior. Any UHMW I have worked with needed corona and flame treatment prior to bonding. Also was going to use graphite powder.
Also, I did find a source for PTFE milled flock…the problem is that they say it is supplied untreated and the manufacturers that do use it get large batches sodium etched prior. This would be too costly at our volume, but UHMW would be better for our application anyway if we were able to get that to bond.
oooo…yeah, I forgot about treatment. However, there HAS to be a treated product out there. Or if you get a sample batch (normally 5 lbs) if that is enough. Kinnda wish producers and distros would sample more products. Come on, you are selling 5000lbs batches! scrap a little off the top!
kevlar fibers/pulp maybe?
I thought about kevlar pulp and talc. I know talc is used in other applications as a lubricant (but do I really need talc if I have graphite?). I know kevlar would help with the impact strength, like UHMW, but would it reduce the friction coef like UHMW (havent worked with kevlar a whole lot)? Riff, you seem to be helping me out in all kinds of threads right now!
I have experience with lots of random things 
Graphite might work as well. I would say do a test with several things. Graphite might not stick to the resin, and might mark any surface the part touches.
In the end, depends on if your part can handle a wet sloppy mess instead of something with more flow. Also, each material will sooner or later make the part brittle and just fall apart.