Furnace Drain Holes---Procedure for use?

I have noticed several mentions of furnace drain holes placed in the base of melting furnaces. The idea makes sense. But I also note that the holes are usually plugged with blanket or compressed refractory board.

So, my question is: In the event of a crucible rupture that presumably dumps a fair bit of molten metal into the furnace, how do you locate and open the hole so the metal can drain out before it cools?

I am casting my furnace hotface sides tomorrow. I already drilled a 1" hole in the base of the hotface locating it off center about 4 inches which should clear the base of a plinth.

Melter.

 

This one almost deserves a poll. I have a hole, but keep it plugged with kaowool. I suppose if I had a breach, I could take a piece of rebar and stick it through the hole and push out the kaowool.
I can tell you, my next furnace build will not have a hole. If you ever have to question the integrity of your crucible, then you probably shouldn't be using it. Fair enough?

 

Thanks for the above replies:
The rebar and blind poking to open the hole is what I imagined, but that seemed like a chancy scenario. And just venting the hole seemed like an energy sink.

You can be sure that I do not intend to use a crucible if it's integrity is in doubt, but, then, I have heard of surprise failures. That's the point of this precaution, I suppose.

Given the high temperatures expected in a furnace interior how could aluminum foil not melt out with every use?

Melter

 

Yep, I'm another for drain holes.
Nope, no plug either.
I've never noticed any flames shooting out the hole either.

Murphy's Law!

When ever I do end up with a crucible failure in the future (and it will happen sooner or later) one less thing I have to worry about is cleaning the bottom of the furnace out and possibly replacing some of the refractory.

 

My small propane tank furnace started with a 3/4" offset drain plugged from the bottom with a wad of foil. Put to the test from clumsiness or too much degasser it clogged up. Note: if you clog your drain, poke it out while still hot and molten with a steel rod. So I bore the hole to 1" and put a layer of hd foil over the bottom of the drain tube. It melted from just normal use and a huge amount of fire shot out. Two layers did the trick. It melts when needed but not before. I use copper foil for melting brass and bronze.

 

How do you secure the foil/hold it in place? I'll be melting iron, so, likely copper foil will be the ticket. Where do you get it?

Melter

 

David has a Butt Plug he'd be more than happy to send ya.

Think it may have been used though before he got it.

 

Simple but effective.



I found this at an art supply store. It's used for embossing. This was the thinnest they had.

 

Lowe’s has really thin 6” x 6” sheets of copper and a few other metals in their hardware section.
It’s in the drawers where all the weird stuff is.

 

your furnace needs a drain or several inches of sand in the bottom, you are going to get metal in the bottom of your furnace sooner or later unless you are some sort extreme perfectionist. My current furnace probably has 10 Lbs of metal in the bottom that is never coming out just from splashes from overfilling and dropped slag from skimming .

V/r HT1

 

Thanks for the ideas. Good stuff.

I am thinking it might not be too hard to incorporate a "poker" on a lever that could pass under the furnace and could be used to pop up/out a plug or perforate copper foil should a spill occur. Sounds like it is worthwhile to figure something out.

Hope to cast my hot face sides tomorrow or early next week.

Denis

 

Pro drain here... Can't wrap my head around why someone wouldn't want to take the small amount of extra time during a furnace build to include it. I also don't plan on needing the safety provided by foundry PPE, but I wear it anyway. In my very short experience, my drain doesn't hinder my furnace's performance. That said, I don't have any numbers to back that up. Just the ability to melt everything I've tried thus far. If someone was struggling to reach an internal temp, then I could see a drain being a problem causer... but then you could still plug it up...lol. The one time you need it, you'll be thankful it's there.

The never mentioned benefit of the drain is being able to direct melt into ingot trays.

I use the tin foil ball thing mentioned earlier to seal it off. Not that you need to. Just the practice I follow. Spills would follow the channels within the floor, under the plinth, and melt the tinfoil plug out.

I used a piece of 1" pvc electrical conduit to form the drain. I'm going to guess that gives me a ~1.5 hole.

 

I tried the tin foil ball. Melted it. I find with the hole plugged, I get a more complete burn of my LIQUID! I wonder if this is a diesel/WMO vs propane thing. With my hole open, After 30mins or so, I end up with fluid on fire coming out that damn hole. With it plugged with kaowool, no more fluid, no more fire. After it's shut down, I lift up the plinth and everything is nice and dry.

As long as I burn oil, no hole. Mine was made with a 1in PVC pipe that I torched out when the refractor was dry. Stinky stinky, hate the smell of burning pvc.

 

I plan on burning propane/oil/diesel, shell without a drain. If a crucible fails, I would rather the contents remain inside the furnace body. To me it's more controlled.

 

I don't use drains in my furnaces.
If I ever spilled aluminum in a furnace, I would probably turn it on its side and train the burner into the interior to melt/drain it.

For an iron spill, I am not sure it would drain out the hole anyway; I guess it would if it were at pour temperature, but not all of it.

To prevent spills, I use quality crucibles (Morgan salamander super), use lifting tongs that have a stop on them so as to limit pressure on the sides of the crucible, and don't jam the metal into the crucible where it cannot expand when hot.

Before use, I tap on a crucible lightly to make sure it makes a ringing sound.
If it makes a dull sound, it may be cracked.