Smaller heater – part I

Having a major success with our BIG tubes, we decided that we’ll prepare tubes for a whole frame. While Serge inclined to use our current technology for the rest, I already had a plan to repeat our production process and get some light and awesome ~25mm ones.

When planning ahead, in February 2023 I reached to Vilem and he checked for us on Aluminum tubes available through his sources. Following options came up:

.. then situation somehow changed and apparently we ended up with these:

The idea here is that we’ll use an inner tube with a heater rod to expand another (external tube), which will be used as a mould for our CF tape, so we have an option to contract it and extract the tube after curing. Vili sourced tubes in a perfect condition.

They are awesome! Thank you Vildo!!!

Then I asked Serge to help us with cutting the external one.

Excellent job Serge, as always. A tiny test shown how cool it is.

Well, that inner tube sit in there too well! Testing this with Serge, he mentioned that once we’ll wrap it with CF, friction will be so high that we won’t be able to pull it out. That would be a not good at all. Checking what’s going on I reached to the Engineering ToolBox – (Resources, Tools and Basic Information for Engineering and Design of Technical Applications) and Serge was right!

The value 1 here is pretty bad (e.g. teflon on teflon is 0.04) – it actually is one of the worst values in that table! Apparently this is because Aluminum surface oxidises very rapidly under the atmospheric conditions, and Al2O3 has quite different properties from elemental Aluminum.

Anyway, there are thoughts how to solve this, but that’s for another day. Let’s move to our new … heater! Serge came with an awesome idea to use a Stove Cooktop Burner Element – straighten it and use it as substitute for our heating coil.

Serge did an excellent job and we ended up with this (first picture next to our Alu tubes):

Running ideas on how to actually use it through Richard, while he raised more then few exclamation marks on connecting this straight into 240V mains.

Crunching this for a while I picked a safe way to use our welder again to power this contraption. Testing it clearly shown that Risa’s worries were well in place.

One last question remained – how to keep our heating rod straight in a middle of our inner tube. Brainstorming it with Serge he suggested some high-temperature silicon. Google then came with JB Weld Muffler Seal, 340g from Super Cheap Auto, which apparently withstand temperatures up to 850F (450C) which we assumed to be enough to do the job.

So we ended up applying this muffler cement in rings on the rod, hoping this will do the job.

Finally we couldn’t resist and connected our welder to see what happens and ended up reaching nice 94C while running it on a lowest settings for about 5 minutes.

We’ve run out of time to wait for cement to cure properly, so a proper test will have to wait for another day. Anyway whole this exercise actually worked out well so I am positive this will do the job and we’ll see some tube prototypes in next few days. Stay tuned!