Oil furnace build

[Pete O]

I mentioned in the 'Today's Project' thread the other day that I was building a furnace. I'll try and remember to take photos as I go and we'll see how this progresses.
I feel I should mention at the outset that I have never built a furnace before. In fact I have never operated a furnace. Indeed, I have never even seen a furnace operating! Just seemed like a good idea to be able to produce my own castings and lumps of metal.
Given my absolute ignorance, I will be deriving the entire design from this book, purchased online about 12 months ago:
   

I will certainly be open to any suggestions for improvements or alterations as I go, so if you know a better way please chime in, otherwise it will be very closely based on Colin's book.

The author's furnace is unashamedly rough-and-ready in it's construction, to the extent that he does all his metal cutting with an arc welder cranked up hot! I guess it's not meant to be a showpiece, and it certainly melts some metal. Hopefully mine will too.

The furnace has 3 concentric metal tubes: the outer skin, outer former and inner former. The space between the inner and outer formers is filled with castable refractory, and the inner former removed once the refractory has set. The space between the outer former and the outer skin is to be filled with insulation. I'd waited too long to find a suitable treasure trove of tubes and drums to make the 3 required tubes from, so I got some 2mm sheet cut and rolled by the local guys I buy most of my metal from. I then welded the seams of the 2 main tubes, the skin and the outer former, and rolled the inner former to shape around 3 250mm plywood discs that will maintain it's shape while ramming the refractory.
   
The extra ring is for the lid, same diameter as the outer skin.

Today's progress involved getting the base frame cut and welded up, so the outer former sits on the flat of the angles:
   


   

Then cutting slots into the bottom of the outer skin so it sits down over the angle iron frame.
   

I couldn't bring myself to use the arc welder to do the cutting, so I used a holesaw to cut holes for the tap hole through the skin and outer former; this is for tapping off metal melted directly in the base of the furnace, i.e. without a crucible. It is angled up into the centre. I had to cut-and-shut a short offcut of exhaust tubing to the desired diameter for the tap-hole former; I'll weld this in place after all the basic setting out is done
   

I then started nutting out the location of the big hole business for the air blower inlet and the preheater outlet; I was part way through roughly sketching this out on the outer skin when my good lady called me for the evening repast. I had promised to spend the evening indoors after dinner, so that's it for today.
   

[Mayhem]

Thanks for posting this Pete - I'm looking forward to watching this build.

[Swede56]

Keep the pictures coming if I get the time after I retire I would like to make one.
I used to do some casting in High School back in 1971 or 1972 it was fun.

[RobWilson]

Looks like your off to a cracking start Pete 


Rob 

[Pete O]

A little more progress this afternoon, night shift tonight so I had to pick a job that I could get done between sleeping in and going to work.

Colin describes a geometric method called 'parallel line development' for marking out the cut shape of the inlet port tube. I haven't come across this before, it was kind of fun and the result was a very nicely fitted 3" pipe that intersects the 10" furnace bore at the perimeter.

Marking out the pattern:
   
   
The pattern is then cut out and wrapped around the pipe
   
a line is traced onto the pipe around the edge of the pattern, about 90 seconds work with the 5" angle grinder and the result is a very nice fit
   
   

The 3" pipe will stay in place in the furnace, forming a port for the 2 1/2" inlet tube.
I decided to do this job before cutting the hole that I was marking out the other night, as my inlet pipe is larger than the author's design (he recommends the increased size) and I've found it will require moving the inlet hole opening around the corner about 20 degrees or so to avoid conflict with the lid lifting arrangement. I got the opening marked out on the outer skin ready to cut out when I get back to it.

I may be a little distracted in getting back to this after my night shifts, as I have a new toy to bring home...

[Pete O]

Finally made a little more progress on the furnace today, it's amazing how distracted one can be just by buying a new machine. Not to mention having to work for a living.
Anyway, some pics of today's efforts;
Got the formers for the air inlet and preheater ports welded in between the two layers of steel tube;
   
Also the tubular former for the pouring spout. The astute observer will also notice it is now on wheels- used the last of a batch of damaged casters I picked up form ebay,
   

Made a start on the lid lifting business; welded the tube on the side of the furnace and bent up the handle/lifting frame- had to butt weld the light RHS to use up some offcuts.
   

I also picked up my 3 bags of refractory. I don't know what's in this stuff, but for the size of the bags they seem much heavier than eexpected.
   

I also made a source of scrap cast iron; my faithful old vice broke in half during the course of today's proceedings.
   

This is the 6mm plate I had planned to use for the base; I retrieved it for the woodshed and was a bit dismayed to see how badly it has corroded in the 16 years since I dismantled the brick barbeque it was on; I'm open to suggestions as to how best to clean it up
   

[oldgoaly]

what is the rating on the refractory? 3000* F ?

[Pete O]

The refractory is 1650 celsius (centigrade), which according to one online calculator is 3002 farenheit, so I guess you're close enough oldgoaly!

Made some more progress today, so again with some photos:
Got the lid lifting business finished, except for the pedal arrangement- can't do that until I have the base plate sorted and for now I have a temporary plywood base in place for pouring the refractory
   

I used some of my bolt collection to make a sort of spoke arrangement which I hope will hold the disc of refractory lid from falling out of the ring
   

The only bit of suitable material that I had on hand for the upright part of the lid lifting arrangement was galvanised RHS, the small amount of gal welding left me with a headache for the rest of the day, horrible stuff. Can't even use a fan for the fumes when using the mig. Serves me right for being too lazy to switch to the stick welder and set up a fan, was such a small amount of gal welding I didn't think it was worth it. Hope this doesn't fume me every time I do a melt with the thing.
   

Set up the lid frame on some plywood ready to take the refractory, the tin for the exhaust port is sitting over 4 nails to keep it central
   

A few more tins for plinths
   

The plan is to cast the refractory tomorrow, I have a promise of help from the wife to lend a hand with holding the formers for the inlet, preheater and tap hole while I ram the refractory up. Left it all set up ready to go (I hope)
   

If those of you with experience of this stuff spot some problems, please speak up before I start wetting the refractory tomorrow. I'm particularly keen for opinions on whether the bolts poking in from the rim of the lid will be enough to hold the refractory without causing cracks, this seemed like a reasonable way to go but I have not used the stuff before.

[dallen]

exhaust hole it too small, it needs to be at least 4 inches in diameter, or for those that use the metric system 101.6 MM
larger if your going to be using large scrap. you can always block it off with a brick.

But it needs to be large enough that you can put metal to be melted into the crucible without opening the lid.

for the headache from welding on the zink, drink milk.

[Pete O]

Thanks Dallen, I'll put one of the 4" tins in place for the exhaust hole. Colin's design says 3" but like you say I can always choke it off. I guess I could make the hole even bigger and cast a few rings with various size centre holes for chokes, also useable as plinths. I'll see what tins and stuff I have around. Sure I have some 5" pvc pipe somewhere.