The Shop > Metal Stuff
Oil fired crucible furnace
vtsteam:
Don, I think that for sure there is thinning on the inside, and especially visible at the top where hot metal and gas and slag all come together. I'm sure there is some erosion on the outside. But I just have a feeling that the significant part of it is occurring on the inside.
Now here's a couple statements to contemplate. One from BCS:
"These "A" shape crucibles are formed from what appears to be clay, fire clay grog and a smattering of silicon carbide particles. "
Yet these crucibles are identified as "Clay Graphite" crucibles. Why silicon carbide?
I should hasten to add I did not buy my crucibles (6years ago) from BCS. But I suspect they may be from the same source manufacturer.
And the second statement I have to find a source for, but I've seen it fairly commonly in a few references -- that silicon carbide is attacked by molten iron.
awemawson:
Steve,
Are you venting your moulds as well as giving them a riser and poring basin?
I used to insert a 'needle' made from 1.5mm gas welding rod on about a 1" matrix all over the pattern area. The trick is to push it in so it ALMOST touches the pattern. In fact if you do touch the pattern you just get little pips on the casting to file off.
This greatly helps with escaping gasses giving a free passage to atmosphere avoiding the metal.
Andrew
vtsteam:
Hi Andrew. Yes I have been venting all of them, and especially took pains on this last one. It got 30 vents with wire, Fifteen each side. And I even pushed them through to contact the pattern. The vents on the drag side left pips, those on the cope side did not. The cope is only 2" thick these days, so perhaps there was insufficient hydrostatic pressure to push it up the vents. It did rise up the riser however.
I don't believe these slag bubbles will dissipate through a vent however. They are hollow solids, not just gas pockets. That is why they collect at the bottom of the groove in the cope side of the casting, instead of dissipating, or rising to the higher edges and corners of the casting.
I cannot imagine permeability is the problem:
The cope is 2" thick, the sand is 60 mesh of good quality, the mold was vented 30 times, the moisture content was a measured 2.5% +- .05%, and the clay is quality bentonite (probably sodium type).
The only thing I can do at this point to increase permeability would be to reduce bentonite percentage -- which I have already initiated by mixing up new sand at 4% bentonite last night. I've given it overnight to age, but my impressions were that it was way under-bonded, and maybe unworkable even at 4% moisture -- at least yesterday -- we'll see how it feels today.
I really do not believe sand is the problem. But am trying to be open by trying this option. I think it is a slag problem, and that is where the solution is going to lie.
awemawson:
Personally I think you need to work on keeping the slag away from the mould! Can you form a pouring basin system that has a longish horizontal run before plunging into the mould with a skimmer bridging it to leave the slag behind. Or even decant the iron into a previously heated pourer.
I appreciate that you are working single handed - were you not your helper would need to hold the slag back as you pour. Can you devise some system a bit like a tea pot where the fluid leaves the pot from below the surface?
NeoTech:
with no idea about pouring melted iron.. but, have you tried those small nifty "mesh" thingys you see some people put in therem oulds.. like a small stainless mesh or something that sits in the inlet of the mould cavity supposedly to sort out the slag.. i imagine you conjour up one from fine mesh stainless.. Like those used in .. ehm ehm whats the word.. sand shaky sorting stuff thingymajigs.. you know.. ;)
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version