Degassing Tablets

Where the metal submits. Metallurgy to Melt point.
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Harry
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Re: Degassing Tablets

Post by Harry »

Thanks for the feedback guys. HT, not sure which part you meant sounds complicated? The tool is simply a bell reducer (3/8" x 1/2") welded to the end of a piece of square tube. There is a shot of it in the video I posted in the Hybrid burner thread. The 3/8" pipe nipple I use to make the degasser packet, wrap a piece of foil around the outside with 1/2" or so hanging off the end. Twist it up then fill the nipple and slide it out so the degasser stay in the foil tube and twist the other end shut. This then stuffs into the bell reducer and is ready to plunge into the melt.

Will take a few pictures next time I am in the shop.

I do preheat my tool at the beginning of each casting session, in fact one time I tried to load it too quickly and set off the degasser. Have to let it cool back down before reloading but I usually have 20 minutes or so between each pour while I am making more molds up so that is no trouble. I make up a bunch of packets and and wait to load the tool right before I am ready to pour the next set of molds.

I might not be using quite enough of the degasser from the sounds of it. The packet I make is about 1/2" diameter and 1" long.

Once I get a chance to mill some more parts up that have been degassed I will report back on any differences I find. Whatever it takes to eliminate the very small porosity I am seeing I will do even if it ends up that I have to buy a tank for nitrogen and go that route. I am almost thinking that might be best in the long run anyhow for ease use and eliminating the noxious gasses.

The way my foundry is set up now I have pretty good ventilation with 2 18" and one 36" fans but if the wind is blowing the wrong way it can kind of mix up the air a little. Working on that now, I picked up some more OSB and 2 x 4s to close in the foundry area more which will make the fans draw better and have less chance of the fumes coming around the end of the wall and back into the foundry. Also thinking about taking the 42" barrel fan I put on my home made porta cool and putting it on my exhaust wall, that thing moves quite a lot of air.
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castaway
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Re: Degassing Tablets

Post by castaway »

I wonder if you need to find the cause before you get a cure. You and I have similar set ups with using good aluminum and petrobond sand. So why is it you have gas porosity and I don't. I gave up using degassing pellets years back mainly because of my enclosed set up and didn't want to deal with the chlorine gas but rather went with nitrogen being blown through the melt before the pours. 8-) Even this I don't do as much anymore since I haven't had gas problems and now just do it as a precaution on important pours.

The only thing that I would consider as a possible problem is I use NG and you use waste oil to heat with. So are you introducing in hydrocarbons during your melts because of a reduced burn setting at times. My NG produces almost no HC's so would it help if you could cover the crucible top with a refractory plate to limit any hydrocarbon exposure. The only other thing might be overheating of the melts which can add to Hydrogen gassing in the melts. :roll: Bob
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Harry
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Re: Degassing Tablets

Post by Harry »

Bob, sorry I missed this post until just now. I have something set wonky on the forum and every once in awhile a post gets marked needing approval so I didnt notice it.

Anyhow yes I do use good scrap to begin with but like you said I also use oil which is likely the culprit here. I dont think I am overheating and if anything underheating at times getting the occasional cold shunt on sections thick enough it should be no problem at all. I also hold the melt at times. Since I make molds while I am pouring sometimes a melt might be ready.

I think the lid idea sounds great and had talked about that before on the old forum but never got around to it. The only issue would be checking temperature but even that shouldnt be a problem with a tool to easily lift the lid.

What did you use for a lance for your nitrogen. This is the way I want to go eventually, need to get a bottle for it, actually two and they arent all that cheap. I live so far away from everything running out would be a pain so I would want a pair of decent sized bottles and I despise renting them.
I'd rather laugh with the sinners than cry with the saints the sinners are much more fun...
Muller
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