Post Re-Refractory Firing

Well, today I fired up the flowerpot furnace to get it ready for some smelting. A short while ago I repaired the furnace by fixing a couple of cracks in the lining and the terracotta pot. I needed to remake the furnace in preparation for some planned melting.
After adding refractory, it’s important to let the refractory lining cure (same as cement) so that it can dry out as much as possible. Next I needed to do a slow firing of the furnace to remove any pockets of moisture. You do this slowly so that the moisture isn’t turned to steam and then cause an explosion in the lining. If done right, the slow firing will do this admirably.

So I added some dry straw, wood shavings, small timber offcuts and some greenish apple wood and fired it up. Lots of smoke (cough) but eventually.

We have flames too. As I said … this is a slow firing process, I don’t want to get the furnace too hot too quickly, so let the fire take it’s course.
Adding more apple cuttings to the fire helps things along.
When the fire is going along well, and it has risen in temperature slowly, I connected the air supply to help the burn get hotter.

The vacuum was set to it’s lowest setting and started to fuel the burn nicely.

But I didn’t want to abuse the furnace too much, so I left the level of air pressure nice and low.
After a while, I turned the pressure up so that the furnace got up to a nice heat level.

Then I left the fire going until all of the fuel had pretty much burned out.
A crack opened up in the side of the furnace where I had repaired it, but this is OK, the crack is about 2mm wide at it’s widest and doesn’t go all the way through (it’s only in the terracotta) and, more importantly, it didn’t blow up.
With this furnace, I’m going to have to take it easy on the first couple of burns until the cracks settle into place. It will still be good for smelting aluminium and probably copper, but I won’t be using this furnace for anything of any significant heat. That’ll be the job of Furnace Mark II.
I also plan to operate this furnace in the lean-to attached to my workshop, rather than out in the open, so it shouldn’t suffer too much from the weather or rapid temperature changes.

Furnace Re-refractored

Well, I’ve relined the flowerpot furnace and fixed the major cracks. I’ll be giving the furnace a firing next weekend to finish the curing of the refractory and see if it blows up (there may … will … be air pockets in the refractory).

I am also planning to get a start on the mulling machine today (time and weather permitting). It’s only 9 degrees C here in sunny Hobart today, and the less time I spend out in the workshop, the better.

I have a bunch of 3 litre glass bottles that I am going to turn to glass sand when I have the mulling machine finished (or even only partly finished) and I’ll line the furnace with a glaze as well.

Part of the steel drum that I’m using for the mulling machine will be used to make a new furnace, so that’s a good thing (woot!). The new furnace will be about 2’ high and about 2’ diameter with an internal diameter of about 1’ x 16” high. Being a steel drum means that I can weld a lid onto the furnace so that I can better manage the heat in the furnace. Pictures will be posted, when I’ve done more.

Flowerpot Furnace

This is my first furnace. I have based the furnace design on the classic “Flowerpot” method described by Lionel Oliver on his excellent site (http://www.backyardmetalcasting.com/).

Basically, the furnace is a large terracotta pot that has been lined with a refractory. I searched online for a suitable mix and came up with 3 parts fire clay; 3 parts Portland cement; 1 part perlite. In retrospect, sand; Portland cement; fire clay and perlite would have been better … but … whatever.
I used a plastic flower pot to make the void in the middle where I will burn my fuel and a steel tube for the air intake.
I let the refractory cure for a week and then gave the furnace a test firing.

I dodgeyed up a connector for an old cheap vacuum cleaner for the fan and connected it to the furnace. The burn was pretty good. Initially, my crucible was a stainless steel pot that I bought from the tip shop. This gave me about half a kilo of aluminium, but the pot was a little thin, so it died after a few firings.

There are loads of resources out on the web for finding good recipes for refractory and cheap home-made furnaces. I suggest that you look far and wide and read as much as possible. Start small and have fun.

A View into Hades

The Flowerpot Furnace was my first smelting furnace. The melt in the furnace above is aluminium destined to become an unfortunate lump of ... aluminium. This was a pretty fun experiment and left me with the desire to melt stuff.

Since the first melt, I have indeed melted other stuff. including some old brass tap-ware. The furnace didn't like being cooled down rapidly in a Tasmanian downpour, however, so I need to repair my furnace.