I was wondering if abrasive coal slag can be used as an ingredient in any refractory product.  What else (other than an abrasive) could it be used for surrounding foundry work?

Welcome aboard from 7500' in SE Wyoming.  Glad to have you.

If you put your general location in your profile we will be able to give better answers to some of your queries.  This is a world wide forum and as far as we know you could be in Lapland, Kansas or Tasmania.

Coal slag/clinker is basically impure glass because the commonest impurity in the swamps when the coal was being laid down was sand and silt which was washed in.  So, any use of coal slag would be about the same as ground up glass.  It will melt at about the same temperature and will abrade anything softer than itself.  Because the melting point is fairly low, it did melt when the coal was burned, I don't see much use for it as a refactory product which would be exposed to higher temperatures than its melting point.

Ground up to about pea gravel size slag is an excellent medium for traction in ice and snow.  Anyone who lives in snow country and has access to slag/clinker should carry a container of it in their vehicle.  And give it as a strange but very useful gift to friends and family.  It works much better than sand or cat litter because it is sharper and more "grabby" and is a good size (sand is often too fine).  Back in the day before road salt was a thing cities would spread crushed coal clinker on the icy streets for traction for horses, wagons, and pedestrians.

"By hammer and hand all arts do stand."

PS  In my experience "slag" are the molten impurities which accumulate on the top of liquid metal when refining ore, e.g. iron, and are poured off and discarded.  "Clinker" is the unburned residue remaining after coal is burned.  They are close to interchangable but IMO not quite.  One implies a refining process while the other refers to a residue which is similar to ash when burning wood.  My 2 cents.

Welcome aboard Dave, glad to have you. Ditto George about your general location, you'll have a much better chance of meeting members living within visiting distance. 

Clinker makes excellent traction on ice, some of the best. Most kitty litter is bentonite clay and if you use much it actually becomes more slippery than ice when it gets wet. Clinker makes decent fill and a bit in the garden provides nutrients.

About the only place I can think of clinker would be useful in a foundry would be as a bed to pour over. Small scale, hobby, foundries set molds on a DRY sand or gravel bed to pour so any spills are trapped safely. Clinker could maybe used in the sand bed but a HOT melt spill could cause smoking.

Frosty The Lucky.

Thanks guys !  Glad to be here and excited to learn.

Some of the homemade foundry refractories use various types of grog - fired ceramics ground up or crushed silicates that melt down to glass. The old backyard metalcasting site had one that used perlite, a volcanic glass, for that purpose. The basic idea is that it adds porosity and also changes the plasticity so that the mix doesn't tend to crack through expansion or contraction as the water content changes.

I've used some of the recipes; they're cheap and somewhat effective, if not as high a refractive value by far, as the real thing. They also tend to eventually vitrify or crack and need repair or replacement. I wouldn't want to play with clinker for that purpose when there are established recipes. I'd keep it for traction or to sell as "dragon poop" instead.

Also, be careful ramming homemade refractories for foundries - they're prone to steam explosions if not dried fully and brought to heat slowly on the first firing, or if you leave a void when you ram it into the shell (it pools water in the void). It's exciting, but nothing you would want to volunteer for.

I use mine to fill in the areas next to my drive way where my truck makes ruts in the yard. Either that or i use it around the foundation of my barn as filler for where the rain makes trenches. 

A bit late to the party on this thread but currently researching the same thing, using coal slag as a portion of refractory mix. My recipe is using coarse grade blasting media, roughly 1/16” particle size. Still in the mixing formula phase but so far I’ve found it to be a good mix in for the wet consistency I look for. I’m also using zircopax plus, perlite, calcined alumina, alumina hydroxide, dry sodium metasilicate, magnesium oxide that I calcine myself from magnesium sulphate, bentonite clay, and calcium-aluminate cement binder. So far it has been a mix of great and awful. Some mixes set too fast to work. Some take too much water to make workable. A few have held up really well. One puck (3” diameter by 1/2” thick) I was able to make glow white with an acetylene torch and it vitrified down 1/8” ish but no further after about 5 minutes. After cooling it was very hard to break by hand. Most of the other recipes failed my expectations. Two exploded which I’m chalking up to retained water even though they got dried in an air fryer for a couple hrs.

I’m mostly doing this for fun but also so I can stop melting down my forge. It’s the third rebuild, last one I coated in a mix of zircopax and kastolite-97l which was decent.

Hello ZebraPaste and welcome!

I'm no expert on refractories so I'll leave the suggestions to someone else.  I hope you're documenting your experiments and will post your most  successful recipe here.

Please read the "Read this First" article that is pinned at the top of the page.  Also this is a worldwide forum and it would be great if you'd edit your header to show us where in the world you are.  

Hi Brian thanks for the heads up about the header info. I’m testing a new puck tomorrow so I’ll update with what happens. From what I’ve gathered, a forge liner has slightly different needs for the roof, sides, and bottom (if the burner is blasting directly down) or whatever the direct flame contact face is. I spoke with some sales reps from the companies that make the available products and a few raw material producers to get some data. My goal for tomorrow’s test is can I get this puck to heal itself with each thermal cycle. Basically I’m going to heat it to bright yellow and let it air cool. Then heat it again and throw it in water. Then dry it out, heat it again and let it cool in a slow controlled environment to see if it deals with thermal shock. Last time the puck stayed whole but I was able to snap it with my hands. So this one has the added coal slag to see if a lower melting point aggregate can act as a binder since the calcium aluminate cement is probably being calcined again at those temperatures.

Update to coal slag puck: calling this one a failure. Didn’t break from the thermal shock testing but lost strength and I broke it with a slight smack from a steel bar. Next puck will use phosphate bonded alumina binder.

Update to the aluminum phosphate binder. One test (filled a steel bottle cap) turned out successful. No shrinkage cracks, thermal shock test passed, harder than expected (used it like a sharpening stone on a scalpel I made from L6 scrap). Can’t get it work work again, must have some contamination or something.

If it won’t repeat, contamination or slight ratio/moisture changes seem likely