I am getting some conflicting answer and some questions I cant seem to find answer about crucibles. 1) Do you need to glaze\season a graphite crucible with borax? All the video I see seem to be people glazing their smaller jewelry ceramic crucibles with borax. I have seen a few people post videos on glazing their graphite crucibles, but these videos really seem like they are just doing it because they saw someone else do it. 2) Is degassing and fluxing the same thing? 3) Is it necessary to degas and\or flux your metal before you pour? I know its not necessary, but do you really see a benefit from this? I have come across a handful of videos that people have said they just dont see any benefit. This is mainly with the salt. I see a handful of commercial fluxs that have borax as a base ingredient and am guessing this is why everyone seems to be using the 12 mule borax. 4) What is the best product to use to degas\flux your metal? I have seen salt, lite salt, borax, and wax...but cant really find solid answer on which is better or why use one over another. I have seen wax for lead, and the other three for aluminum, but then I have read that adding these chemicals will change the properties of different metals and people have stopped using them because they have start to decompose (for lack of a better word). Thanks for any info you can supply...my head is spinning trying to google search this any longer.
#1 no but check with the crucible mfg #2 no #3 mixed opinions, your better off not degassing in most cases. Flux can really help in some cases, but hurt you in others. Just starting out I'd recommend doing nothing. #4. There are different fluxes for different materials. Again for starters do nothing.
+ 1 But # 3 depends entirely upon your metal, try and cast a Tin bronze without degassing, you will get swiss cheeze looking Bronze, Sil Bronze and yellow Brass require no Degassing , Aluminum Pouring Sawdust atop the molten metal degasses it perfectly(I still have trouble believing that one) V/r HT1
it was a discussion over at AA where I first heard it, thought t was hooy, then a Foundryman 30 years my senior mentioned it to me, he had absolutely no reason to lie, so I tried it , multiple times with ZERO issues, get a coffe can of dry sawdust, most any variety, pour it on top of the heat immediately before pouring, let it burn down to ash, I leave my furnace running, but with the lid open it takes 30-40 seconds for the sawdust to burn off ( also a surprise) I assume, the sawdust Burning draws the Hydrogen to the top and burns it off , I was using pool shock and was getting horribly brittle aluminum, once I switched to the sawdust I saw immediate improvement with the exact same metal , not brittle, finer grain structure V/r HT1
Never heard of saw dust on aluminum (lead yes) but have heard many people claim they get poor results with pool shock.....so maybe eliminating that was a contributing factor? Depends on the metal to a certain extent but I would say degassing and fluxing aren't the same thing, especially in aluminum. Fluxes generally concentrate oxides and other undesirable elements, making them clump so they are more easily skimmed. Then there are cover fluxes that do just the opposite and create a barrier between the metal and air so it cannot react usually with the oxygen in the air. Degassing is most common in aluminum because hydrogen gas is soluble in molten aluminum and comes out of solution when the metal solidifies and creates porosity. The industry standard for addressing this is rotary degassing with Argon. The best advice for a beginner casting aluminum, use metal sourced from scrap castings (not extrusion, wrought, cans etc), use clean metal, and a lean/oxidizing flame in your furnace (unless you are electric then you're naturally fine). If you use oily or painted melting stock, that creates a lot of H2 when it burns off and also a lot of dross. Leave the dross/oxide layer on the top of the melt until just before you are ready to pour. It actually can be a barrier to more H2 dissolving into the melt. Then there are all kinds of things that aren't fluxes at all that can be added to modify the metal properties like grain refiners and modifiers for aluminum or ferrosilicon/inoculants for iron...etc. Best, Kelly
