Hard colour anodising

[blackburn mark]

i was tempted to inject liquid butane into a part to keep the temperature low enough for hard anodising, not a wise option at all considering a slight knock on the hanger wires would blow the roof off the shed.... but perfectly ok for mad science purposes :)

[m_c]

Mark, have you got any guides to Hard Annodising?

I only had a quick search when I was looking last week, but it would be interesting to know what's actually required.

[blackburn mark]

its been ages since I researched it, I pieced it together from various sights but most of it escapes me now.
me and another member (happy chris) had a go at the standard anodising, he was over the moon with it, I'm surprised he didn't try anodising the dog :)

I think (if may memory serves) for hard anodising you need to keep the temperature at 5*c or lower which is a tad difficult if your hammering it with a higher voltage (30v ish?)
I was after making ball sockets 50mm diameter, my thinking was to keep the bath very small, just big enough to fit the ball in and the liquid butane would cool the ball and the ball would in turn cool the acid
you could do with a none flammable to cool it but i'm not sure what?
or maybe have a closed (ish) system that exhausts the expanded gas outside?
or do some magic with an old fridge :)

[Jonathan]

I'd try petiers for cooling the tank as they're pretty cheap on eBay. For testing you could just put the tank in a bigger tank full of ice, or just freeze some bottles of water etc, can't be that hard. Only guessing, but I expect a bigger tank is better as the current density will be more even.

[m_c]

For cooling, I was thinking more of a coolant loop/heat exchanger running through a freezer with a thermostatic flow control.

However, the big issue seems to be finding out exact details. I've done a couple quick searches, and not really found anything definitive. I'm sure more searching will turn up more info, however it's not really a priority for me right now, and I was just wondering if anybody had any useful links/guides for future reference.