I need to form a seal between a solid and an elastomer. So far I’ve not had success. What I’m building is a diaphragm pump. The check valves are silicone inserts from minivalve.com 12. They fit into a counterbore hole.
I’m trying to figure out which approach to try next.
TPE’s I’ve tried so far are Flexible PLA and PCTPE (flexible nylon). I just received ninjaflex today. I’m most optimistic about the ninjaflex since it can stretch, so I could design the elastomer part to stretch over the solid, and hopefully that would help in forming a seal.
I think the main problem right now is the rough surface finish. The only way I know to print a smooth surface is to vapor treat ABS, which I’ve never done before (I also don’t have any ABS yet, but I could get some in a pinch).
I see that ABS and ninjaflex can work well together, especially when printed together. Stan from Fenner Drives writes:
Start with either Gorilla Glue or Loctite Vinyl, Fabric and plastic adhesive.
If you have a way of coextruding with ABS, NinjaFlex actually bonds well to ABS after extrusion.
Stan
NinjaFlex Engineer
So one approach I’m considering is adding a bowden extruder to my i3 Hephestos for the ABS, and run the ninjaflex through the stock direct drive extruder.
You could use a soldering iron at 240-250c to weld ABS and Ninjaflex together. Same goes for PET or XT with Ninjaflex, that bond is fairly strong too, just make sure, that the contacting area is large. You could modify the geometry to a wavy contact surface instead of a straight one, that could increase the strength. If you want to modify your i3, make sure, that all components can handle dual extrusion, you need another hotend, preferably the Chimera, also maybe new electronics etc. Cheers, Marius Breuer
I’ve been designing my parts with a dedicated fit, and seems I forgot about the possibility of clamps. I used to work in a shop and used pipe clamps all the time, but now I’m working with parts which I can design however I want and suddenly I forget some of the most basic solutions!
Designing the contact area to be melted together is probably my favorite idea. Hopefully this can be done while still keeping some aesthetic appeal. Obviously, clamps are good to keep parts replaceable, and I can heat weld them on more final versions.
Someone on IRC said silicone sealant would work, so I got this stuff: http://www.loctiteproducts.com/img/products/big/cntct\_silicone.png, which seems to be working. What my air bubble test revealed is that the top layer of my ninjaflex part is leaking in a couple specific spots (bottom layer has no leaks, only the top layer has leaks), even though the floor and ceiling of my part are considerably thicker than the sidewalls. I have my infill at 80% and the top/bottom layer thickness was at 0.6mm. Obviously I can increase that layer thickness. I could also change infill to 100%, but I might not be happy with the stiffness that will add.
If you have ever soldered anything you can use the same technique with ninjaflex or nearly any other thermoplastic. Place your Ninjaflex print on the table and secure it, so that it doesn’t come loose quickly. Next heat your soldering iron to 250C and get a small string of Ninjaflex filament. Now place the tip of the filament on one hole and push it down with the soldering iron. It’s very easy to solder (or technically correct “weld”) thermoplastics, just test it on a wasted ninjaflex print and experiment with the temperature, for me usually 20C above the printing temperature works fine, lower temperatures maybe require you to hold on the same spot longer, higher temperatures can make the Ninjaflex too runny, but maybe the sealing will be stronger. PS: If you have the choise use a flat, large soldering tip. Cheers, Marius Breuer
