Mig gas for degassing

[mite5255]

Has anyone tried bubbling mig gas through the melt for degassing and if so was it successful

Mike

[dallen]

there has been some discussions of that very thing on other threads in other boards. some say that they have done it and that it works, problem I see is that of regulating the gas flow in a small crucible and getting the bubble size down to some thing thing that would resemble the flow from an aquarium bubblier, and for it to work you have to or need to do this for 5 to 10 minutes.

I don't have a mig so no gas bottle, only have ones for my oxy/acetylene and a paint gun co2 tank that is empty and I'm to stingy to buy the gas to drive the 6 mile round trip to fill it. So I haven't tried it. I did order some new degasser that I have yet to try in my fluxing / degas wand that I made off of whats posted on BCS. weld a pipe nipple crossways onto a flat bar handle roll up chemicals in paper plumge to bottom of pot give stir like ole mom cooking stew, hold breath while facing into the wind.

[mite5255]

I'm having a few issues with porosity in the sump extensions that I'm making and was going to give it a try tomorrow. I tried degassing tablets that I got off Harry which worked but I was thinking bubbling an inert gas through the melt might be just as effective

Mike

[dallen]

it would have to be a gas that will grab onto the hydrogen gas that has been absorbed into the aluminum. have you tried melting just enough metal to fill the molt with sprue and risers with a cover on the crucible and not doing anything to the melt untill just before you pour cleaning the dross of the top.

The more you agitate the melt the more gas it will absorb, also running your furnace with it fuel rich will help to keep gas out, but will do nothing for oxide inclusion's which can also cause porosity.

What type of metal are you melting, run of the mill scrape aluminum, engine parts, or car wheel's, I find that with car wheels that on the first go round I have a lot more gas porosity then on melts after it has beem already melted once to get rid of all the finish.

How are you using the Tablets that you got from Harry, I crush them up and put them into my fluxing tool, which is a short 1.5 inch long .5 inch diameter stainless steel tube welded to a 1/4 " rod that I put a bit of paper in one end then fill with the powder from the crushed tablet. then plunge it to the bottom of the crucible so that the gas generated has to pass thru the melt picking up the hydrogen as it does so, also helps to float out the oxides.

Please post any results of your inert gas purging, so others may benefit from your trials.

Those tablets from harry are for a 100 pound melt, so for them to be effective you would need to weigh one then break it down into percentage of chemical to use for your much smaller melt amounts.

[HT1]

the gas method i'm familiar with , is to cover the melt in a layer of inert gas during melting, normally argon, or nitrogen, this prevents any gas ever being generated at all. this method is used in magnesium, and other very reactive metals. pure copper is another place it used to be required, I think there has been a chemical degasser developed, but I'm not up to date on all that new techniques

[mite5255]

Wellll the mig gas appears to work but my sand was a bit damn and guess which f$%king d$%klhead did't vent the moulds , so the count so far is 8 sump extensions that are no good. Just had a mother's and I'm heading out to try again

Mike

[Harry]

The more you agitate the melt the more gas it will absorb, also running your furnace with it fuel rich will help to keep gas out, but will do nothing for oxide inclusion's which can also cause porosity.

That should be fuel lean for aluminum shouldnt it? I have always read the aluminum like to absorb hydrogen and brass/bronze like to absorb oxygen. That is why you use a charcoal cover over brass but not aluminum. I run very lean with aluminum and have very few gas issues. I have noticed on some stuff I have been milling though that there are sometimes some very tiny inclusions near the surface so I am going to do some testing with degassing.

From what I have seen on using an inert gas you do want as fine of bubbles as you can get, plunge to the bottom and stir then skim and pour.

[HT1]

Wellll the mig gas appears to work but my sand was a bit damn Mike

I know it is a ten cent question, but you are face heating those green sand molds??? to drive the moisture off, and closing them, JUST prior to pouring? that really helps with gas issues, and moisture problems in green sand.
Venting just should not be that big of a deal... I shouldn't say that without seeing the project.

[mite5255]

Wellll the mig gas appears to work but my sand was a bit damn Mike

I know it is a ten cent question, but you are face heating those green sand molds??? to drive the moisture off, and closing them, JUST prior to pouring? that really helps with gas issues, and moisture problems in green sand.
Venting just should not be that big of a deal... I shouldn't say that without seeing the project.

Ummmmm short answer no, but will next time, i have done that in the past , why did't I think of doing it this time ah well life's one big learning experence

Mike

[dallen]

The more you agitate the melt the more gas it will absorb, also running your furnace with it fuel rich will help to keep gas out, but will do nothing for oxide inclusion's which can also cause porosity.

That should be fuel lean for aluminum shouldnt it? I have always read the aluminum like to absorb hydrogen and brass/bronze like to absorb oxygen. That is why you use a charcoal cover over brass but not aluminum. I run very lean with aluminum and have very few gas issues. I have noticed on some stuff I have been milling though that there are sometimes some very tiny inclusions near the surface so I am going to do some testing with degassing.

From what I have seen on using an inert gas you do want as fine of bubbles as you can get, plunge to the bottom and stir then skim and pour.

I have always had problems with aluminum with porosity in aluminum, some of it I have narrowed down to using car wheel without first melting them into ingots, the other is that when I first got into this hobby I wasn't using any type of chemicals for gas or dross. and now I think some of it may be from having the burner on propane. I will have to figure out a way to throw together a 1.250 diameter oil burner.

since I started degassing every melt I have noticed that the porosity has almost disappeared, but its still there. theres too many ways for to to happen to say which is causing it till I eliminate them one at a time. or just start my whole process over from start. but when I only have two pounds to melt it seems kinda dumb to fire up a furnace that will melt a hundred pounds of iron. So I guess I will have to stick with some of the processes I have in place and just be more careful in my procedures.

.