Foundry Furnace for the Tiny Shop

[Manxmodder]

Great results for little outlay,can't ask for better than that  well done.

I'll be really interested to see how well it melts brass on a charcoal firing  ....OZ.

[RobWilson]

I would say well done that man  , dam fine result  for $20     


 only a Yorkshire man would want it done for 10 cents cheaper 


Rob ( running away ) 

[awemawson]

I would say well done that man  , dam fine result  for $20     


 only a Yorkshire man would want it done for 10 cents cheaper 


Rob ( running away ) 

Oi !

Andrew (Yorkshireman   )

[vtsteam]

$20? Wasteful luxury! Why, when we were kids we used to melt titanium in a carboard box lined with horse manure and consider ourselves-ill used to escape ten cents the poorer........

[awemawson]

Steve, I do believe we've converted you to British humour 

[tom osselton]

Lucky ba**ard we never had a box!   

[Will_D]

Ehh! you were lucky:

Titanium:

We had to scrounge the wires from the young ladies bras' to aquire enough "Tit-ane-er-ium" to melt down to cast 'owt useful from that imaginatively named metal 

[vtsteam]

Looked up this old thread because I'm finally rebuilding -- or relining the tiny furnace. Not because of any defect from heats, but because the lining got wet and stayed that way all winter this year -- I hadn't noticed, since the lid was on. The lining went soft and crumbly -- maybe the multiple freezes and thaws had a hand. Anyway, the price of plaster of paris is now up $2 I noticed. Bought one for the refurb.

This evening before dinner, I chopped and scraped out all the old lining, ready for renewal. Read this thread over to see what I'd done 3 years ago...oh, also restored all my photos in it after, you know, the Photobucket fiasco.

I'll try to get pix of the relining process.

(all this is in preparation to resuming casting for the headstock cap on my uhhhhh "new" lathe build).

[vtsteam]

After work today, I took a wire brush to the inside of the old furnace shell:

[vtsteam]

Nice to be working on grass again instead of snow, or later, mud. The bit of lawn above wasn't green three days ago. Spring happens fast here when it decides to!

I found a piece of Sonotube (cardboard concrete form) in the big shed that was close to the ~8" OD I wanted. It was 8-5/8", so I cut a strip out 1-1/2" wide.

[vtsteam]

And then taped it back together.

[vtsteam]

These are the ingredients for the lining renewal: some water, sand, and plaster of Paris, plus the Sonotube and shell.

I taped a bit of PVC pipe in the Tuyere opening to serve as a plug. I stuffed both ends of the pipe with paper towels to prevent the liquid lining pouring out before it set.

[vtsteam]

You can see the Tuyere plug here, set at an angle to give a tangential flow for the blower (charcoal) or burner (propane).

I taped around the outside of the plug also, to prevent leaks.

[vtsteam]

The shell is 12" in diameter, and with an 8" form, I should end up with 2" of lining.

Plaster of Paris is quite a good insulator. It's used as sprue and riser liners in big time iron casting for this reason. My guess is that the insulative quality is partly a result it being quite porous when cured. To be honest I was surprised to first learn that plaster was used in iron work at all. Bronze statuary, yes. Anyway reading that was one of the reasons I thought it might work out long term for this non-iron melter.

This originally experimental furnace really did live up to the hope -- and if I hadn't let it sit wet over this last winter, the first lining would still be giving good use. I've easily melted brass in it, as well as the lower temp aluminum and zinc castings for my "new" lathe.

Anyway, here's the first pour of plaster and sand mix. This forms the bottom, and I waited for it to set up before putting the Sonotube form in.

[vtsteam]

I mixed plaster of Paris by filling half a gallon bucket with cold (not warm) water. Then I poured plaster in to the center slowly until it took no more and formed a lasting "island" in the middle of the water, without collapsing. Like in the photo below. That's the normal mix rate.

Then I mix by hand. Literally. You put your hand in and stir and squeeze out all the lumps. Trust me, a spoon or any other utensil will not work as well, and you will get lumps.

Then sand is added. I just added hand fulls to roughly what felt right. I'd guess about the same amount as I'd added plaster. Again, the hand stirring and lump dispersal method is best.

Then just pour.

Plaster of Paris will take anywhere from 3 to 20 minutes to begin setting up, depending on temperature, quantity mixed, and what it's mixed with. Sand, temperature, and volume of mix all accelerate it. So cool temps, mixing no more than 2 quarts (liters) of water, and stirring and pouring quickly all help.

I've had it go off in summer in 3 minutes, which isn't even enough time to clean out your container. It cures by exothermic reaction -- in other words it generates heat in curing -- a bigger volume generates more heat more quickly.

[vtsteam]

Second pour, with the form in place:

[vtsteam]

Again I waited until the plaster started to feel firm. And then made the third pour.  I'd done that before placing the Sonotube, too. Otherwise it would have embedded into the bottom, and been hard to remove.

[vtsteam]

Lasxt pour. This time I added extra sand to make it a bit firmer so it wouldn't overflow the lip of the shell. I wanted to build the height up a small amount towards the cardboard form. That can be abraded back down to fit the lid -- but if the top is left with hollows, then it will leak rather than forcing the exhaust through the flue hole. A slightly thickened mixture allows that little bit of slope from the tube down to the shell edge, without runoff.

[vtsteam]

Letting it cure for about an hour, I stripped out the cardboard form by collapsing the seam edge inwards.

It probably only took 2 hours total to renew the lining, and the cost was $16 worth of plaster of Paris -- the sand water and Sonotube, were already on hand.

I didn't have time to do the lid -- have to leave something for tomorrow..... 

[awemawson]

Great work Steve, and also great to see you back doing things

I'm amazed that the P.O.P. lining stands up to iron temperatures even with the addition of the sand. When I was doing lost wax casting it was OK for aluminium but brass, bronze and copper needed a special high temperature version. For iron I used a hybrid of lost wax to form the cavity, and sodium silicate for the bond with dry silver sand - worked pretty well.

I'm no chemist, but as I understand it, the high temperatures decompose the P.O.P. by reversing the hydration reaction. 

[vtsteam]

Andrew thanks! 

also, re poP and iron, according to Steve Chastain, plaster of Paris is used commercially for insulative sprue and riser liners for iron, not iron foundry furnace linings. I wasn't suggesting that. I assume those are single use applications.

Iron melting wasn't the intention from the start with this furnace -- non ferrous melting was the spec. Worked fine for that. I have my other furnace for iron.

[vtsteam]

And Andrew, as for melting brass, see here and next few posts in this same poP furnace lining thread:

https://madmodder.net/index.php/topic,10482.msg121017.html#msg121017

[vtsteam]

I poured the lid today the same way. I used a 3" shampoo bottle to make the vent hole form. It fit the metal lid perfectly.

[vtsteam]

Form removed, lid is done.

[vtsteam]

And the shell given a new coat of paint: