New oil burning furnace build

What a mess. I'm glad it wasn't worse.

 

Well the tree trunk is mostly cleared up now, took 30 wheelbarrow loads to get things cleared away. I was all set to cast a concrete base today to sit the furnace on, when I noticed the stack of manhole covers and rings..... I'll pile up some of my water damaged green sand and sit a manhole cover on top as the base would rock (cover underside isn't flat) and put the furnace on top of all that allowing it to be levelled while still keeping it off the ground to some extent and slowing the thin steel furnace base from rusting. I may be able to get some zinc paint on it too. So I have the air blower motor rebuilt from flood damage, the fuel pump motor is rebuilt too and the fuel plumbing could do with a backflush and clean. I'll overhaul the butterfly valve for the air while I'm at it.

 

The old furnace fuel pump needed checking since it went under in the December 2023 flood, so it was pulled apart and I was able to simplify some of the plumbing by directly connecting the ball valve to the needle valve with a 1/4" BSP to 1/2" BSP adapter, after the needle valve I replaced the Ryco Z168 final filter with a new one. The exit hose barb turned out to be full of mud wasp larvae so it was a good idea to check everything after sitting for 18 months or more. The pump and motor are on a new galvanized steel base and there's a vertical aluminium sheet in tasteful anodized gold to give the plumbing some mechanical support. It's all topped off with a new pressure gauge for the pressure regulator hidden behind the gauge. The butterfly valve was in a bad state, I could salvage the aluminium butterfly but the shaft and body were toast so it now has a 5/8" aluminium shaft and a new PVC body. All the fuel hoses are clear reinforced clear PVC tube good to 250 PSI and 60 degrees C which is the oil temperature when in use. I'll test it all on some diesel and make sure everything works as it should.

 

You hear of people building a plane or a yacht in their basement without a way to get the project out..... I kind of had similar feelings today as I moved the furnace into it's final location in the backyard. A bit of discussion with a friend and we'd come up with a way using stuff lying around: I have some 150mm C section purlins that are two metres long, made of a fairly heavy gauge. I used them as rails from the back of the workshop to the final resting place with three pipe rollers and a timber wedge as a brake. This was all done solo, moving down and up gentle slopes with a furnace I estimate weighs 150Kg or 325 pounds based on the 120Kg of dense refractory used. I had a timber wedge that I used to keep rollers in position and as a brake to wedge the furnace after every 30cm or so and it was definitely needed to prevent runaway of the furnace down a slope while positioning rollers. The final resting place is a pedestal made from coarse sieved sand capped by a scrap manhole cover. All the jockeying into position ruined the level but I'll use some timber wedges to get it back to level again. I'll make a weather cover from some heavy duty plastic cloth for the time being to keep it dry and also run the hot air gun before use to make sure it's dry.


Easing it off two concrete blocks and onto the rollers:



Wood wedge for brakes (needed)


Almost there, the work went fast, maybe half an hour.



Manhole cover for the base of the furnace:



In position, fairly smooth and stress free operation.

 

Today I used a kaolin clay slurry to roller paint on a couple of coats of clay on the inside of the furnace. I'm hoping it'll vitrify and give some iron slag protection, it's the same stuff I use to patch cracks in the refractory. I have the hot air gun drying it out on low setting which reaches boiling point. I did a stocktake of all the air plumbing and found a missing coupling so everything needed to run the furnace is now ready....time to bite the bullet and fire it up and see what it can do, maybe cast some ingots or similar.

 

Thanks Kelly, last night I set up all the plumbing as it's been a while and covered it all up. By early morning it started raining and hasn't eased up yet, I'll use the time to make some sand moulds and try for some usable castings.

 

After a couple of rain aborts, I fired the furnace up this morning. It starts fairly easily on straight diesel with no preheat with some burning newspaper to ignite the flame and ran with a much more even spiral flame that circled the crucible compared to the older narrow gap furnace. Performance wise:


.........................Time.......Temperature.......Fuel Used........Load
Old furnace:..........77 mins......1350+ deg C............30 litres...............A8 full of iron
New furnace:........40 mins.......1380 deg C..............14 litres...............A25 40% full of copper

Both ran the same fuel pump system and air blower and both were adjusted for a smoke free flame just a bit rich as that gave the fastest temperature rate of rise. The top ring cracked and opened 4mm or 3/32" where flame escaped due to a gap, the kaolin mostly stuck but some bits peeled in thin sheets and the refractory liner cylinder is miraculously crack free. So the efficiency is much better with twice the chamber volume for roughly the same amount of refractory weight, with half the fuel consumption all other things being equal like the blower and fuel system. I'm only using two of the four spray nozzle positions so I'll experiment with three fuel nozzles and chase even higher temperatures. It did run with the needle valve wide open but seemed to starve for fuel a bit.

I melted maybe 10 kilos of copper and I could see it was nice and hot for once, skimmed it and plunged a home made capsule of phos copper shot to the bottom of the melt where it melted instantly and skimmed the melt and removed it from the furnace. I had it sitting on half a brick to give enough height for the crucible lifter to clear the pouring shank ring and the crucible fell over, fortunately away from me and I had to pour the remainder into an ingot mould. There were fine bright beads of copper shot everywhere on the ground a bit like some old time "salted" gold mine.

Note the crack on the right hand side of the ring under the lid.



On the way to 1380 deg C with the pink S type thermocouple



Spilled copper off the ground, lots of fine bright granules everywhere.

 

Ran the furnace for the second time, with a large piston machined flat and covered in sand to rest the crucible on this time. The furnace ran really well with fuel flow set to less than the usual 20 litres per hour. The thermocouple is located 3/4 of a turn from the tuyere air intake and fuel nozzles and temperature rise is very rapid, I may have it in a hot spot hit by direct flames. The thermocouple is vital to getting the fuel air mix set right for fastest temperature rise as small airflow changes either way cause the temp to plateau or even drop. I can recommend having the thermocouple for easy tuning.

I made two copper castings, discs of 6 and seven inches diameter which looked great initially apart from the sand fused to them, on rough machining, several bubbles 3-4mm were revealed. There must have been entrained air during the pour which was a thin narrow stream of metal down about a 3/4 hole cut in the sand with similar size hole as a vent and feeder. The phos copper did it's job and there was a fair bit of contraction as the metal cooled which you can see in the photo. I'm going to have to re-design the runners to get a sound casting so if anyone has ideas on how to go about it I'd appreciate it. My first thought would be to incline the mould about 30 degrees from horizontal so it fills from the bottom working up to disc cavity.


The first charge of copper in the crucible was molten by now so I added some more and ran to about the 35 minute mark.


The top left and bottom right holes were where I poured the copper


Looks great but several hidden bubbles under the surface.

 

Thanks Kelly, yes the sprues are vertical and they were a hard target to hit, so pouring speed was slower than ideal, so a cup is a good idea. I'll try some incline along with a square sprue and a resin sand pouring cup: that treated copper flows like water and is easy to spill.

The new furnace heats up rapidly compared to the old one, it's ready in 2/3rd the time so it uses 1/2 to 2/3rd the fuel. I'd say it's more efficient and a bit hotter, but it remains to be seen if iron temps can be reached reliably, say 1500 deg C/2732 deg F. It's getting close to that goal at 1432 deg C!.