Furnace build 1.0 - Zapins

This is a reposted thread of my original furnace build from 2013. Alloyavenue forum died so I want a record of my build for future help. Original thread here: http://www.alloyavenue.com/vb/archive/index.php/t-9501.html

Here is another more refined furnace build I did for a friend using the same general design: http://forums.thehomefoundry.org/index.php?threads/furnace-wax-burnout-3-0-zapins.317/

Here are some modifications to this furnace design including a proper swivel lid and increased height on furnace body for larger crucibles: http://forums.thehomefoundry.org/index.php?threads/furnace-modifications-furnace-2-1-zapins.192/

More furnace modifications to this design including self-pouring attachment: http://forums.thehomefoundry.org/index.php?threads/furnace-modifications-furnace-2-2-zapins.723/

This is the furnace 8 years later. The high temperature engine paint (2000F paint) has been burned and I added an extension to the top of the furnace to make it taller and hold a larger crucible and a swivel lid hinge rather than a door hinge for the lid. And a steel tube T for the blower. It is in good condition and lasted many melts! The refractory inside is perfect, just like the day I made it.


This is the furnace when I originally made it in 2013 with a smaller height and a stupid flip lid design using a door hinge. Look at that nice new engine paint! Check that classy PVC plastic T pipe out as well. Hmm nothing but quality here people.



Here are some videos of the furnace running under different conditions to help you fine tune your burner:

This is when I first start it up and the furnace is cold with very low amount of gas and no blower on. Watch how the flames spiral around the walls and encase the crucible on all sides.





Here are 2 videos of propane furnaces at melting temp.





Having a high pressure regulator let's you dump a huge amount of gas into the furnace fast and let's you properly fill the space with flames. If your pressure drops in the tank as it freezes up or your regulator can't supply it then your melting temp drops dramatically.

I'd also recommend learning this stuff at night when it is dark and you can better see what the flames are doing. It's very difficult during the day to learn these things.

 

Start of original thread: 2013

Success! My girlfriend found a scrap yard that sells to the public (a rarity these days). So we nipped down there and I found several water heaters. I had a look at a 40g one but it seemed too tall, and the 30g had the same width but was shorter and fit neatly in my car trunk. It was 50 cents / pound, so I paid $41, a bit pricey perhaps but at this point it could be another couple of months if I wait for one of the scrappers to call me back. The tank is from 1996, and a little rusted on the bottom, but the inner shell looks solid from what I can see.

It looks like this heater has the fiber glass insulation, so I won't have to remove foam from the inner shell. Lucky me.

I'll be chopping it up later tonight or tomorrow and will post more pictures soon.



I did a bit of work on the furnace shell today. I started off by using a hammer to pry/bash open the seam of the outer shell.



Once the shell was off, I discovered it was foam insulation - not fiberglass like I had thought from looking at the bottom of the tank.


I found that the foam comes off very easily using a wood chisel.


Tank all cleaned off, some small spots of rust here and there, and quite a bit of rust on the part that touched the floor.


Here the shell is after the rusted skirt at the bottom of the tank was cut off (using a hack saw and pliers).


I started to use an angle grinder to remove the rust. Lucky it was mostly surface rust and didn't go too deep.


This is the bottom of the furnace where the burner used to be when it was still functional. Lots of rust here, and strangely there is a tube that runs the entire length of the furnace inside it (a chimney I think?).


Here are some of my plans and calculations for the furnace. I think I should have just enough if my walls are 3" thick and the floor is 2" thick. This should give me 10 inches of internal room for the crucible. The crucible is 5" across, so I'll have 2.5" of room on either side. I think this might be too much space, but luckily I can always slather a good 0.5 inches of high temperature refractory on the inside if I need to, in order to bring the space down to 2 inches around the side of the crucible.

The height of the internal chamber should be 9" in total. I'll have a 2" plinth, and the crucible is 6" tall, which leaves me 1" of room on the top between the lid and crucible.


I'm using 3000F castable refractory. The guy I bought it from told me he advises 110 lbs / cubic foot of cast material, but the manufacturer apparently says it is 130 lbs/cubic foot. I've got 3 bags, which weigh 165 lbs in total, so I think I'll have just barely enough with about 80 something cubic inches left over.


I've got all the cage material so I can weld on a frame and wheels/etc. The one thing I'm still trying to figure out is how to attach the pipe to the outside for the burner to fit into. It is made of black water pipe which I think is terrible for welding. So I think it will have to be screwed in/cemented in place? Hmm. Will have to think on that.

 

I am also a little confused about the density part. The guy said he usually recommends 110 lb/cuft which apparently works out. I found the original manufacturing specs and there are two different density quotes.

Bought a chop saw and cut the tank open. I'm taking a break waiting for the stupid battery drill to charge because someone moved the corded drill...



Managed to cut the inner tube out of the furnace body with an angle grinder (for the lid) and then a jigsaw.



Looking down inside the furnace body. Pity about the nick in the side. I couldn't get through the metal any other way.


Cut the tube out of the inside of the lid and ground it down with an angle grinder.


Here it is, the new furnace with both halves together.


Then I used the angle grinder to polish the outside up. I got rid of the rust and paint (or galvanized coating?). Tomorrow I'll chop up the frame and then perhaps if there is time I'll take the tank to my local mechanic and have him weld it all up. I still need to get a 220v plug in the garage so I can use my arc welder...


I cut up some metal for a frame with my new chop saw.


I cut the burner hole and the burner tube. It was a little harder than I thought since the hole had to be more of an oval than a circle for the tuber to be angled correctly.


Here is the inside of the furnace with the tube in place. I think it will line up nicely once the refractory is in place.


Here are all the parts nicely ground down, chopped up and ready to be welded. Tomorrow I'll see if the mechanic can weld them all for me. Not sure if he will be willing to do it all though since there is a fair bit of it to do.


The prep work took me ages, at least 16-20 hrs. This is definitely not a project I'd like to repeat in the near future.

Here is the finished frame. I've just got to bolt the hinge and the wheels on and then pour the refractory. Shouldn't be too long now until the first firing, maybe two-three weeks tops since I've got a few different medical school interviews coming up.

I found a local guy to weld my furnace for me. Really nice guy, used to weld nuclear power plants and other stuff like that but is retired now, took us about an hour and a half and only cost me $40. A good deal I think.

 

02-13-2014, 03:30 AM
I've got to say this furnace has taken a lot more time than I thought it would. I think I've spent at least 24 hours on it so far including all the driving to get refractory, and prep work. Probably will take a total of 30-35 hours to completely finish it, so I'm nearly there!

No idea how long it will take to dry, but I finished the lining, my girlfriend helped a lot. Looks like I calculated the amount of refractory needed very well. I've got half a bag of refractory left for the floor and a plinth.

Made a burner tube through the refractory.


Tube in place.


Inside taped up.


Core weighed down with 80 lbs of granite slabs.

Refractory mixed and compacted.


Walls.


Walls look ok.


Lid done too, I used wetter refractory to ensure it bonded well.


Here are a few more pics after I removed the core.



Inner part where the flames will come in:


Here is the lid with the pot removed. The refractory is quite hard now, I'll probably put in a light bulb after I pour the floor of the furnace.



And as usual its not a real project unless someone shed a little blood. Gotten while pulling out the cardboard in the burner slot.


Yes, wheels and a hinge for the lid are next on the list of things to do, right after I line the base of the furnace with refractory and make the plinth. Then its due for a paint job and some unnecessary decals that will likely burn off.

It is odd because the refractory feels completely dry and not even cool to the touch. I was actually expecting it to take a long time to dry. I don't know if it truly is dry, but I won't be firing it for another week or two so I suspect it should be ready by then.

The good news is the hinge and lid fit PERFECTLY, so all I have to do is drill a few holes and attach the hinge, then bolt it in. The bad news is I welded the metal wheel pads up too high. So only 2 out of 4 screw holes line up with the support. Maybe I can take it back to the welder guy and ask him to weld on another two metal plates lower down to give the wheels full support, or maybe just weld the wheels directly onto the frame...

Well, the furnace floor is done.


This is the inside of the burner tube. I'm a little worried about the space with no refractory on it to the left. That dark stuff is the inside of the steel furnace shell. I think the incoming blower air might keep that area cool enough though and there should be no direct flame there so who knows, it might not need any extra refractory.


And here are the two plinths. One is drying and the other I'll leave in the bucket I made it in. I've still got about 8-10 lbs of refractory left so I suppose I can make more in the future if I want or use it to repair anything if it breaks.

 

Entire furnace with burner attached:


Hinge mechanism. It works well enough, it is easy to use, but I think I'll need to weld some braces onto the sides of the hinge to hold it steady. I noticed that at melting temperature the metal shell is a little more flexible than I had though and it wobbles when I open the hinge up.


Wheels on the back. I need to weld these to lock them in this position. They want to swivel around when I try rock the furnace back onto them.


Picture of the inside of the burner tube-patched so no metal is bare to the inside of the furnace.


A bit of metal missed the crucible... grr well she didn't stay pretty for long!


Here is the first firing of it. Video taken as I was still ramping up the temperature before I added my air blower so it is running pretty rich and at low pressure (be sure to watch it on HD for the full detail!). It spirals well, and the burner tube is adjustable so it can be pulled back or pushed into the furnace a few inches in order to get the optimal burning.



The furnace was getting pretty rusty without any paint, so I spent a few hours de-rusting the thing and then I painted it with 2000F resistant engine paint. Would have chosen black if they had sold it, but red works just as well for keeping rust at bay.


Here it is freshly painted.


Fired it up to cure the paint. Still seems a little bit gummy. Hopefully it will harden over night, though it is still pretty cold outside (23F now, and the directions said to paint when the temperature is between 60-90).


And furnace 8 years later with updated swivel hinge rather than door hinge design:
I also added another couple inches of height to the furnace to accommodate an A16 crucible (more details in this thread: http://forums.thehomefoundry.org/index.php?threads/furnace-modifications-furnace-2-1-zapins.192/)

 

How did your little metal tabs on that lid hold up? I welded a 2inch wide ring around mine and it's about had it.

 

They seem to be holding up ok. Not a lot of flame gets out at that point so no great erosion happening.