I'm rewatching some olfoundryman videos on YouTube and am wondering about the powder he spoons onto the tops of the risers after he fills the mold. Is this common practice? I'm guessing it's some sort of phosphor that ignites and keeps the metal liquid for as long as possible. Is that right? Where would I get it?
Yes it's exothermic hot topping and does what you speculated. Well, foundry suppliers like FOSECO and others, but doubtful they would sell to anyone but a commercial foundry. Also likely to be a significant minimum buy and hazmat transport fees. Best, Kelly
I've wondered if one could use a propane torch to add supplemental heat to the riser when casting aluminum.
I looked around and the only supplier who mentions anything about minimum order says "drum quantity" so that's out. I wonder what the stuff actually is...
I looked at sds for one of these hot topping compounds and they appear to be quite similar to thermite.
There are many other practical things that could be done instead of Exo Topping. Just make the riser large enough to do the job it's intended to. Make it a blind riser that is merely vented but not exposed to minimize heat loss. Use and insulating sleeve on the riser. Change your casting design so it doesn't require such a massive riser. Production foundries may use such to minimize remelt or simply because they don't have the space on the tooling, or the ability to change or justify the effort to change the tooling to remedy a problem. Best, Kelly
If my memory serves correctly hot toping is basically thermite with a certain % of baking soda added. It's used to slow the reaction so you get a longer more consistent heat. I was surprised to find out it's used in fireworks as a delay.
