Hello, I’m looking for some advice on using TPU to make a replacement grommet for some wires to pass through a cover. It’s the alternator cover on a motorbike and it will be exposed to hot engine oil of about 80 deg. C. I tried making a mold and using red silicone gasket maker but the silicone doesn’t set completely even after a few days. We’ve used TPU 95A to make seals at work but have a problem with the layers separating after a while even with ambient temperatures. I’m worried the same thing will happen with the TPU in a hot engine.
Cheers
Mike
You can get high temperature silicone mastic, if you already have a useable mould. Amazon/elsewhere sell everbuild and others. Else, print the tpu at a higher temperature, so it fuses together better.
The layer adhesion issues are probably due to the settings I imagine, I haven’t had any TPU fall apart yet.
How fast and how hot do you print it? And what flow ratio and volumetric speed do you have set? Also what cooling settings are you using?
TPU needs a flow ratio of 1 and around 3mm3 for volumetric speeds. It also needs a high k value sometimes around 0.2 to 0.4 or more depending on brand so when you do your flow dynamics calibration take this into account. The Tinmorry TPU I use has a k of 0.189.
You will want to print it between 230-260c depending on brand. The part cooling maximum wants to be set to 50% because if it cools to fast you will get poor layer adhesion and you will want to slow the print speed down to around 80-100mms.
Steven from CNC Kitchen has some very good videos on YouTube about TPU that I highly recommend.
We only used the default settings from the slicer, thery looked good but fell apart about 6 months later. I’m really looking for confirmation that TPU will withstand the hot oil enviroment before I go ahead and make the part.
I think your best bet is to go back to your idea of using a mold (3D printed?) and red (high temp) silicone. You can solve the curing problem by adding corn flour (or finely ground corn meal) to the silicone to promote curing. I’ve also seen glycerin and acrylic paint used as additives for this purpose. If you want to spend more, you could get yourself some Smooth-On Mold Max 60 2-part high heat resistant silicone.
Hi Rowiac, I’ll give the corn flour a go as I was quite happy with the outside finish and strength of the red silicone. I am talking to someone locally about the smooth-on products as well.
Cheers
Mike
You can high temp RTV casting silicone…
Not sure about small quantities though.
Sets fully in a few hours.