I recently tried something I’ve never read about that works very well. When melting a crucible of maybe 50 or 60 pounds of iron, near the end of the melt I usually need to remove a fist-and-a-half volume of slag. Until the last few pours, I have always scooped this foamy mess out of the crucible. This involves some careful balancing of mushy chunks of slag on various skimming tools I’ve fabricated. I try to avoid dripping slag bits into my furnace throughout this process. On a whim not long ago, I tried using tongs made from repurposed pliers (and normally used to load pieces of scrap into the crucible) to grab a foamy squishy snowball of slag. Surprisingly it worked and worked very well. So, I picked out most of the slag with subsequent grabs. I feel like it provides more control doing it this way. And it makes handling the slag more positive. Sure, I have to use a traditional skim or two to finish the job. But pinching rather than scooping is my go to. Aluminum slag is so scant that this would not apply and simple light skimming seems simple and effective in my limited aluminum experience. Here are a couple pics of the tongs I use, though the specific design is not too important other than the need for opening of the prongs a few inches in order to grab decent-sized hunks of slag. Denis
Some follow up: here is a glob of slag I removed from an iron melt today. It is larger than usual as I melted a lot of small pieces. So, more than usual slag resulted. But, I was able to lift this chunk out as a single piece. It was almost the full diameter of the crucible. So, had it tried skimmers to remove it, I would have had to carefully break it up without slopping slag and lift out awkward chunks. Doing it with skimmers is not quick and not fun. But, instead, I grabbed it with my tongs and lifted it out as a single glob. I figure it measures about 4.5 inches as that is a 2 pound hammer for scale. Denis
I think Ammen mentions use of charcoal in crucibles for melting cast Iron. (Checks out, "complete handbook of sand casting," pg. 194: "the crucible is charged with alternate layers of charcoal and iron" He also mentions soda ash. Flux?) I thought the slag was predominantly iron oxide. Is it?
I can't speak for iron but I use crushed charcoal 'floaters' in aluminium and brass melts, mainly as a cover but it does seem to cling onto the dross (or the dross onto it) making the skim easier. Foseco make some powdered covers that are similar in behaviour. If your iron slag is clumping like that anyway it sounds like you've mastered a technique for lifting it.
“Mastered” may be a bit strong. I’d say I’ve made an improvement. But, I really do think it is an improvement. Vermiculite is something I’ve read about that I intend to try. Who knows, maybe charcoal can help too. Denis
I've been meaning to try some granulated limestone/marble to see if it neutralizes the acidic iron oxide slag and extends the crucible life a bit.
I recall mention of oyster shell, also. (Picked up some, took it to the further-away furnace for that reason...)
Hi ho ,I dont have a working Furness to play with(got a electric upright kiln but even that needs modding to hold my A4/A6 crucibles, ie adding more fire bricks n steel shell,& electric coils (I'v left a post on a great article/link for wireing electric kilns,with a working speadsheet u plug in u'r power supply volts amps n it will tell you how many coils u need to wind etc realy well done link from a blade making forum) but working toward it,& like to read about your try'els before I make noob mistakes.. So as a keen surf/rock fishing tween,I made my own surf rods,wich lead to casting my own lead sinkers - and the dross you get of oxidized lead was pretty thick,I hit on the idear of pouring the lead melt through normal rockwool, which filter out all said dross,& had nice clean lead castings..without skimming! The rockwool trapped all the crap & with welding cloves on you could feel the still hot liquid crap inside the wool.. My curant idear is to use high temp ceramic fiber as the slag /dross pour filter, I have seen cerramic cast/fired sponges(for wont of a better discdiscpition, but at a cost,) & rock wool is only recycled glass thats melted at round 800°c (1400°f) if that, so way under brass,bronze steel temps ..& maybe it would just tolerate alu wich leads to a 2nd idear of how to make silica Alu using my rockwool fiter? Is that possible? Would the alu melt dissolve enought of the glass fiber to get a better casting Alu mix? Did just learn from Melterselker's above post that alu isnt a big dross former, but still think if it heavily oxidized scrap or your using a a120 crucible.. as thats my largest crucible harhar my 1st crucible was a present & its only had one heat/pour !, then was use as a cigarette bin! its owner was unimpressed his factory worker using it as such & I was a crane truck driver doing a delivery n spotted this mad wast ! My xmass pressant came early that year! Its owner was impressed I knew what it was,I could bearly put it in the Kenworth, heavy bugger it is.. So I may still have dross problems way down the track with big pours.. so is anyone in a position to test out my idear or think it has merit?
I see you asked a question at the end of the post above. I got lost reading it. Could you boil it down to the essentials? Denis
Probably not, the rockwool we get around here is good to almost 1100°C well above the melting point of aluminium.
Thanks Ricco 1100°c ? Is that for Furness insulting or house roof type is what I ment,ie low grade float glass (800°c) bottle stuff,
Mmm,sorry Melterselllter,your post was/is as long as mine,U'rs just go's on n on about tongs.. n dross n a hammer I posted am a noob in the fine art of pours,& posted few questions & a backstory- is that why u got lost?
Over here it's a normal building insulation used the same way you'd use fiberglass batt insulation in walls, attics, etc.
Tar,Rocco,I'v been to a glass fiber melt plant & can say its all old beer bottles,jam jars,low grade bottle glass,I'll have to dr google what fiberglass is,even borasilacate = high temp *pryex is only 900°c I'v lost wax *cast it P.s is brass & bronze a heavy dros former,or is it down to aged oxide coating?
This looks like your metal was too cold (not the temperature shown in the picture but when you removed it from the crucible): the slag contains some slush. I had this experience as well. Heating up to above 1400 C (almost blinding yellow) might help. When the atmosphere inside the furnace (reducing) is OK as well, it should show a lustrous clean mirroring surface. In that case you barely have slag.
I suspect the metal in the pot was in the neighborhood of 2400F when I skimmed. The material removed, while fairly large in volume, is pretty frothy and only amounts to a pound or two of slag and a small amount of iron. I know from experience that it is true that waiting to skim until I was at pouring temp of 2550 would result less volume of slag as some probably burns off at higher temps and it may become less viscous. But, my goal is not to minimize slag volume or weight but rather to get my crucible up to the desired volume and at melting temperature as fast as possible. If I am filling the crucible to more than 3/4 capacity (which is almost always), I need to make room for added metal as early as possible so the added metal can start heating as early in the cycle as possible. This frothy slag will overflow the crucible if not removed prior to adding metal—-ugggh. It is indeed easier to let it cook down. But that just wastes fuel and time for me if I am going to fill my crucible to the usual 90 to 95% volume. By the way, included in that slag are 3 filters which were in the returns melted from prior pours. It is interesting how resistant to melting those silicon-carbide filters are. Denis
