Inspecting for Porosity with a Microscope

Flux, I should be able to remember that. I don't use it, but know I've seen it recommended to degas, but hot aluminum stripping oxygen out makes sense.

 

How do you degas aluminum then? Isn't it some kind of welding rod that gets dunked in before pouring?

 

I don't know. I don't degas, I rely on quick melt and pour and assume captured gas will escape when the scrap melts. I guess a flux should protect the molten surface from picking up gas.

 

Yeah that's what I was thinking of. Phosphor rod. Not sure what rod that actually is though. Like do the welding shop guys know what phosphor rod is if I said that to them?

Argon bubbled in doesn't sound too hard... I have argon for welding and a regulator and needle valve. All I'd need is a hollow carbon rod and I'd be good to go. But does that actually get rid of bubbles?

 

I'm thinking the big turbulence in your design is happening where the runner meets the blind riser. If the runner area expands out to maybe 3x berfore entering the blind riser, the speed should reduce to below critical velocity. Maybe set the blind riser on a 1/4" disk of a slightly larger diameter.

What I'm gathering so far from reading John Cambell's book is if you can see defects it means you have a problem with the pouring system, i.e. air is being entrained somewhere. The hydrogen porosity is more on a microscopic level. I wonder if Amazon has x-ray wi-fi xray devices?

The other thing I've gathered from Campbell's book is that the bifilms never go away. They are in the crucible, somewhat intact but strung out like really thin confettii, and they float up and down in the crucible depending on whether they are absorbing oxygen or hydrogen or neither. So, degasing may or may not help; it depends on the moon phase I think.

 

How exactly do we know any of this is really what's going on? Bifilms?

 

This an area where John Cambell says more research needs to be performed.

 

I suppose its a religion kinda thing. Personally, I've seen things that are well explained by this theory. Miricales, you might say, or not.

 

I buy a de-gasser from a supplier; no idea what the compound is but it works very well bringing the dross to the surface as well as the gas. They are designed to be plunged to the bottom of the melt.
http://www.mathews.com.au/laboratory.htm These guys supplied the de-gassing tablets.

Years ago I was using a cast-iron plumber's pot and was told by the instructor that a steel pot was no good, because it released hydrogen into the melt. Years later I forgot his advice and made a steel pot and found out that he was correct. So I built a new furnace and bought a graphite crucible and no more gas problems for me,

Cheers Charlie

 

Are those chlorine degassing tablets?

 

No idea, unfortunately. They came in a plain bag with no Safety Data Sheet, so I always wear a respirator whenever I use them,

Cheers Charlie

 

Made a little video of using my microscope, if there's any interest.

 

Nicely demonstrated! Thank you. Using the DRO for measuring was an excellent idea.

D