Slag and cast iron

[kelvin2164]

I do a few cast iron castings for the model steam trains that I make and I find that the slag that floats on the top is rather difficult to remove. sometimes I pour the molten metal and the slag blocks the runners. Is there a flux or something that makes the slag removal easier.

 

[Herbiev]

Redux EF40 flux

 

[Wizard69]

I'm not familiar with Iron casting all that much but I did work in Zinc die casting for a few years. There we skimmed the dross in the case off the top of the pots. In those machines Zinc is pumped from the bottom of the pot. Obviously pumping Iron, at least outside of a gym, isn't possible.

Interestingly I did visit Cornwall Furnace in PA last year. This problem is basically as old as the Iron Age. If I understood the tour guide right, when the dross or slag levels got high enough the slag was drained off of the top of the melt. When it came time to tap the furnace for good iron that was done from a lower position on the furnace.

This probably doesn't apply to you as I imagine you are melting in a crucible. I suspect you are stuck with some sort of flux and skim routine. The other option would be to filter during the pour.

 

[kelvin2164]

I am using a crucible and trying to skim it off the top, like with aluminium. However it is very 'sticky'. Sticks to the side of the pot when trying to scoop it out, etc. Herbiev recomended Redux EF40. I cant find that anywhere. I was wondering if something simple like borax would do the trick.

 

[fltenwheeler]

The foundry that I use for my iron castings uses a filter to keep the Slag out of the part.

Tim

 

[seadragonfoundry]

IMHO you are pouring too cold. Bring it up to melting point so that a rod poked into the melt shows it is all liquid, skim and give it a few minutes to superheat, add ferro silicon, lift out, a quick skim and pour. I use a foundry assistant first class (my bride) to hold back the light amount of slag that is left with a sacrificial serving spoon or block of wood as I pour. I have tried filters and they do work to some extent but if you are pouring cold, they block up and you pour short Best to pour hot. I use an A12 crucible and pour 14 kg of iron which is enough for me to handle.

 

[abby]

Although I cast cuprous alloys flux inclusions can still be a problem especially with investment castings .
I have found a good solution is to arrange the sprues so that the metal is introduced at the bottom of the casting and flows up and out through a well sited riser.
Any flux , oxide and bits of broken off investment are usually flushed through or float to a high area.

I can appreciate that this method of sprueing is easier with lost wax investment than green sand castings but the principle should still apply.
Dan.

 

[kelvin2164]

I'm still learning and identified 4 problems with my 'only half full" casting. 1. The gate into the mould was too small and I think the slag blocked this. 2. It was too cold, as there was a thick layer of iron left around the inside of the crucible. 3. The sand was too wet, I think this sucked out a lot of heat. 4. Slag inclusions. I now use a row of 3" nails across the inlet to filter the pour.
On the subject of risers. I tried all size risers and settled on a lot of 3mm dia vents made by pushing a steel rod through the sand. This seemed to help with my shrinkage problems, but obvious;y doesnt allow impurities to float off. My castings had a very deep recess in the top from shrinkage and the thinner risers seemed to help with this. I dont know. It's all black magic to me.

 

[Wizard69]

Although I cast cuprous alloys flux inclusions can still be a problem especially with investment castings .
I have found a good solution is to arrange the sprues so that the metal is introduced at the bottom of the casting and flows up and out through a well sited riser.
Any flux , oxide and bits of broken off investment are usually flushed through or float to a high area.

I can appreciate that this method of sprueing is easier with lost wax investment than green sand castings but the principle should still apply.
Dan.

Interestingly there is a video of frying pans casting technique with what appears to be the bottom up approach. I'm not sure if that was on Lodges web site or someplace else. It does appear to complicate things and in this case the processes automated.

 

[abby]

Kelvin what you describe are vents rather than risers , your casting needs to be "fed" as it cools to minimise shrinkage.
This is done by arranging a reservoir of molten metal that acts as a "feeder" , this feeder remains molten longer than the casting so that as the casting cools it draws metal from the reservoir.
Shrinkage can also be controlled by "chills" , these are metal inserts which cool the casting at various points causing preferential solidification.
Foundry work is a very involved practice but well worth the effort.

 

[seadragonfoundry]

With all due respect, there is a lot to learn. Could I recommend any post by 100model on HMEM. He also has many videos on YouTube and debunks a lot of myths about metal casting, especially cast iron, on which, IMHO he is an expert.
When I first started pouring metal the mantra was vent,vent,vent! What a load of crap. If your sand is right ,this is unnecessary unless it is a really thin casting that has to run a long way. Myths about sand bombs, molten metal flying everywhere unless you vent, bull****. There are a number of books by C.W.Ammen which are invaluable, in your case, "Casting Iron" would be appropriate .Most of the old skills have been lost and are then re invented as new skills. Really, it is not rocket science.