Furnace design

Yes, I have been working out the measurements and angles the last few nights in my garage. I hit a little snag in that I forgot to account for the bulge in the gear oil drum when designing the wheeled base, so I had to factor in an additional spacer piece to push the 4 arms out about 1" on each side for clearance.

 

Thanks Andrew, hope you get it working soon and post some pictures of it running in all of its glory!

What is in your hopper for casting projects?

 

I have multiple parts for my lathe project that need to be cast, as well as melting down a large amount of scrap that I have.

 

We had a 70 degree day today so even though the lifting mechanism isn't done, I got out the furnace to test out if the burner will fire up on diesel without propane preheat. It sputtered alot with the fuel at the same level as the burner but even raising the container up by a foot smoothed things out as long as I had the blower running. I do have to find a different blower though, my wife frowned on the fact I used her hairdryer as the blower. Would an old automotive blower motor work if an appropriate enclosure was fabricated or do they not have enough output. It seems like they could be a good choice due to the fact that they are designed to be run at varying speeds.

 

Leaf blowers work great and yard sale season is coming up. There are a number of ways to throttle them including using a router speed controller. I’ve been told those bucket vacuums from Home Depot work well too but I’ve never used one. They’re about $30.
You could buy your bride a new hair dryer. They’re usually down with that, but it’s probably not enough volume for your furnace (although Jason is using a fan from a microwave successfully somehow). I use a hairdryer on my propane burner which is primarily used for preheating, but I have a leaf blower for the oil burner.
You definitely want to elevate your oil tank if you are using unpressurized or unpumped oil. Those siphon nozzles work fine per their specs when being used for their intended purpose, but of course we are not doing that. Higher is better, but make sure that thing is secure or you will be sorry. Simply setting it on top of a step ladder is a really bad idea. (The bucket didn’t fall off. The ladder tipped over. What a mess.)
I would stick with straight diesel for now until you get your sea legs. The thinner your fuel is the better. The amount of air you need for atomization will affect your air/fuel combustion balance and using straight diesel will at least eliminate the variable of inconsistent viscosity.
I used the siphon-only scenario with a .75gph nozzle for a couple of years with pretty good results and then went to a pressurized oil tank and a 1.0gph nozzle. Although it’s still a siphon nozzle (which is a misnomer btw), the “siphon” action becomes moot, so the compressor-blower-fuel-flow balancing act becomes more controllable.

Pete

 

Pete nailed it above. I throttle my leaf blower using a simple blast gate. It is another alternative to the router control.
Denis

 

I was planning on sticking with straight diesel for the long term, with the possibility of mixing in small amounts of waste oil when I have some, such as after changing the oil on my lawnmower and snowblower. It is just easier for me to run down to the gas station to get a couple of gallons of diesel. I built the burner with the capability to burn waste oil in case I decided to do so in the future, but as you said, diesel flows easier, especially as the weather gets colder here in the fall.

 

I finally got around to actually assembling the lid lifting mechanism on my furnace. My welds aren't great, but test-fitting all of the pieces together proves that it works. I am not satisfied that the lid won't always return to rest on the same spot, so I am going to add 2 locating tabs on the backside of the lid so that as I close it, they will re-center the lid on the body. The next tasks will be to figure out how I want the handles to function, add some reinforcements and the rest for the lid when it is open, and painting everything with a high-temp paint.

 

Looks good!, you'll be able to leave ingots/scrap etc. on top to preheat and still be be able to open and close it. I haven't seen too many (if any) earlier parallelogram lids out there.


P.S. Keep in mind the crucible lifter may need some thicker steel to resist heat soak. I can't tell from your photos but it looks like the vertical strips joining the curved strips in contact with the crucible are 1/8" or 3.2mm flat steel bar which is thin enough to possibly soften from heat during crucible lifting. Some square bar say 12mm or more would be slower to heat at it's core and take a bit longer to soften

 

So when your lid is open, will it be parked horizontal and over the burn tube etc? That looks like how it may function based on the single photo provided. If so, the underside of the lid will be radiating a lot of heat down onto whatever is below it. On my furnace the open lid will ignite wood on the ground in 30 secs or so.

Denis

 

You are correct, it is 1/8" and were the first ones i made for the cheap Amazon crucible I had. I am trying to plan a design specifically for my A6 crucible but also be scalable for an A8 or A10 in the future.

 

That's going to be an issue, I have my tuyere and fuel system at 90 degrees to the opening axis, either a heat shield will be needed or rotate the lid opening direction 90 degrees.

I've seen a small handheld locking crucible lifter made from 1/2" square hollow tube and it has to be used quickly to get the crucible onto the pouring shank in a matter of seconds or it will loosen it's grip.

 

The idea was to have the very edge of the lid sitting about a half inch above the middle of the opposite wall of the furnace when it is parked in the open position.

The furnace body is still rotatable and not set in a final position thankfully, as issues arose during prior run tests of the furnace. My original intention was to have the furnace set up like it is in the pic, but the couple of uses I had done with it just by lifting the lid off by hand, I noticed issues relating to the layout of the wheeled base and with the blower I now have, the original design won't allow for the air supply tube from the blower to the burner to fit. The burner will be offset from the lid path by about 60 degrees for clearance. I will check what the radiant heat is like at a 60 degree offset and rotate further if needed to help keep the burner cool.

 

I think you are going to need a reflective heat shield above the burner even at a 60 or even 90 deg offset. That should be very easy to install. I would make sure that if access to the burner is needed as the melt progresses, it is made to easily move momentarily out of the way when you want to adust your fuel or air to the burner. (I would also make sure that it is not easy to forget to return it to position. I have learned it is quite possible to be distracted by other issues and forget pretty simple steps while a melt proceeds. So, I try to engineer easily made errors out to the process.)

Denis

 

I ran a test run today and the furnace very quickly hit over 2000 degrees which satisfies me just fine, as that will be enough for what I am planning to melt. I did rig a heatshield to cover the burner when the lid is open and it seems to work quite well, at about 110 degrees underneath with an ambient temp of 90 degrees today. I had issues keeping the burner lit while transferring from propane/diesel mix to straight diesel, but I tried backing off the air pressure from 30 psi to 25 and that did the trick. I ended up using about a half gallon of fuel per hour, which is what my nozzle is rated at, so I am pretty happy with those results as well. Now to make an appropriate set of tongs and a pouring shank as well as seasoning my new crucible and I should be ready to get back to actual casting.