The Shop > Metal Stuff

Oil fired crucible furnace

<< < (22/46) > >>

vtsteam:
So where do they come from?

Well one likely possibility is of course the metal scrap. And thin radiator metal has a lot of surface area, with rust and maybe even some sand inclusions from coring inside. So it could generate a lot of slag -- being thin it also could oxidize badly in the furnace atmosphere. .

But now we get to an interesting distinction between the two different pours with the same patterns. The first one was poured with thin radiator scrap, but the second one was poured with only five chunky pieces of thick cast iron with very little rust. That metal melted quickly and was skimmed three times -- twice in the furnace and once outside just before the pour. So you would expect clean metal.

But something I noticed this time is another clue. There was a lot of slag the first two skimmings. And it was the old pasty frothy thick kind I'd had with the thin radiator metal. But that was odd, because the prior melt, with the very same kind of metal, in the very same crucible poured with no slag.

So what's the difference?

Well one thing was different.

The crucible was new last time.

vtsteam:
Suppose the crucible itself was generating the slag. A particularly sticky frothy hard to remove cottage cheesy slag.

That might make sense because a crucible is supposedly made of refractory materials. If they melt, or even more interestingly chemically react with molten iron, you'd expect it to be a pretty nasty type of slag -- almost a solid, not fluid at all, since it is close to its solid temperature. It's not like glass or something else with a lower melting point. And a chemical reaction between the iron and the cruciblecould produce a frothy gassy quality. It would also mean that there was an afiinity between the iron and the slag. They might be hard to separate from eachother. Mingle.

If you think about it, where did the crucible substance go, as these got thinner and thinner each melt? Was it really that they sloughed off on the outside where the heat was greatest. Where the flame was?

Or were they dissolving into the iron melt?

vtsteam:
Let's take a look at an earlier photo of two of the crucibles:

dsquire:
Steve

I'm wondering if there is any way to measure the crucibles to determine if they are getting thinner on the inside or the outside?

I know I'm not saying much but I am following every post. Keep up the good work.  :D :D

Cheers  :beer:

Don

vtsteam:
The one on the left is the first one I tried, the one that got leathery on the last pour and distorted. On the right is the second crucible I tried. I's had one pour, which I believe had no flux. They both show some surface pitting, and a spill of slag down the sides. But no sign of the refractory actually fusing or melting. No sags or hot spots. You can tell by the way that neither had the flame directly playing on them -- no local discoloration. The flame swirls around the crucibles in the furnace, as it should.

The main difference between the two crucibles, is that the one on the left was fluxed with sodium carbonate - soda ash - and on its last pour it received a fair handful of that. The soda ash was quite effective at dissolving the slag in the melt, despite the fact that it received only thin radiator metal. In fact that flux was so effective that in truly liquified the slag into a syrup consistency -- the only time this has ever happened in all of the melts I've done.

So it is a powerful flux, capable of liquifying the really difficult slag I've had. It also coincidentally affected the whole crucible, made it soft.

But was that a coincidence. Or were both the slag and the crucible the same substance?

Navigation

[0] Message Index

[#] Next page

[*] Previous page