Saturday, October 29, 2011

Supercritical drying chamber for aerogel production

I built a pressure chamber from 2" pipe fittings and 1/8" brass valves to contain supercritical CO2 for drying applications. One project is to try aerogel production which generally requires that solvent be removed via supercritical drying. Normal evaporation would deform the aerogel structure as the surface tension of the solvent pulls the gel's structure tighter together and makes it dense. Since supercritical fluids have gaseous properties, they can diffuse out through the gel without affecting the structure the way that a liquid would.

Friday, October 21, 2011

Liquid lens video

Repost for new video on liquid lenses:

This is a project that I built a few years ago when I learned about liquid lenses. They are quite useful for optical paths with small diameters.

Thursday, October 20, 2011

Microstepping a stepper motor with the SLA7062

Stepper motors can be made to rotate more smoothly by providing simulated sine waves. The SLA7062 chip uses internal PWM to provide sinusoidal current waveforms to unipolar stepper motors. I have this working fairly well, but the PWM frequency is acoustically apparent and annoying.

Tuesday, October 4, 2011

How to TIG weld aluminum beverage cans together

I show how to weld aluminum cans together with a cheap import TIG welder. I am not a professional welder, so some of my advice may be unconventional or even wrong, but these methods work well for me. With a 3/32" electrode and large gas lens, I don't have to change the torch setup for nearly any kind of common welding. Let me know if you have any questions or would like me to make more welding videos.

Some things that I have learned:

Don't use pure tungsten electrodes. The new rare-earth blends work very well on nearly all metals.

Sharpen the electrode to a very fine point for low-current welding, and sharpen it like a pencil for higher (eg over 100A) welding.

Keep the electrode balance control electrode negative ("weld") and only shift toward electrode positive ("clean") when absolutely necessary.

The welder's pulse feature turned out to be not as useful as I originally thought. It just seems to complicate things. It's definitely possible to make great welds without it.

Use fat electrodes. Some people claim that using an electrode that is "too large" for the weld current will cause the arc to wander. Nope. Just grind it to a sharp point. Thin electrodes 1/16" and .040" overheat much too easily, and provide no apparent benefit. .040" electrodes are very frustrating.

Use thin filler rod. It's much easier to feed thin rod quickly than feed fat rod slowly. As I mentioned in the video, it's easier to sneak a thin filler rod into the puddle while keeping the torch close to the surface.

Saturday, October 1, 2011

Effect of long-term high pressure CO2 on acrylic

I left my supercritical CO2 chamber charged up with 750 psi liquid CO2 (not supercritical) for about a week. I then depressurized the chamber, and opened it. At first, the acrylic seemed fine with just minor surface crazing. After a few hours, I was surprised to find the acrylic had deformed in a major way and was full of CO2 bubbles. Weird!