Melt time?

Hadn't thought of that, but you're exactly right. Any need to refill mid-melt means a shutdown.

My tank holds 11 gallons, though. If I manage to go through that much in a session, I'm probably going to want a break anyway. Your observation makes the point of verifying that it's full (ish, at least) before starting.

I'm pretty happy with the way this is running. One thing I need to do is find a bigazz pipe wrench to tighten down the fill cap. That's a 3" NPT fitting, and tightening it by hand (along with a TON of teflon tape) got it close to air tight, but it still leaks a little.

Here's the setup in action:



I took Denis' advice and ran this richer than I have before. Previously, I tried to keep any visible flame from licking out the top. This time I ran it about like you see in that video. I think that is a big part of why the melt went faster.

At this point, based on that one session anyway, it seems like I can get all the fuel I need into the furnace. I set the pressure coming out of the compressor at just under 20#. The way this setup was put together, that's the same pressure going to the air port on the nozzle. I've got needle valves on both the fuel and the air as they go into the burner. I had the fuel set pretty low (like about 1/4 turn away from closed) and the air set to pretty much wide open.

Point being, I think I am now air limited, not fuel limited, assuming I want to pump more BTUs through this thing.

I see two options for getting more air: Re-plumb my fuel pressurizer so I can run higher pressure on the air into the nozzle, or upgrade my blower motor. My current blower is 60CFM.

Which way would you go? More compressed air, or a bigger blower fan?

 

Both. The tank functions as a tee: 20# air goes in, and 20# air and 20# fuel go out. The pressurized air and pressurized fuel flow into the Delvan style 0.75 GPH nozzle.

 

Personally, I have separate regulators for the air for my fuel tank and air to nozzle (I just have a T in the air hose). I set the air pressure to the fuel tank to deliver the qty of fuel I want to supply (I tested the best I could). I set the air pressure for the nozzle to atomize that qty/type of fuel. I do not have a single needle valve in my setup, only 1/4 turns that are either on or off. I rely on the pressure gauges, they are a better measuring tool than say ... opening a needle valve say 19/32 of a turn. All of that said, I am using diesel ... its always consistent.

In another year or two (when I REALLY have more time for melting) I may go Denis' route with a flow meter. At that point, since the flow meter becomes the measurement tool, I would add in a needle valve for fine tuning the measured flow.

Something else to think about, compressed gas that suddenly expands to atmosphere is cold (I think) and also moisture laden (ever try to sandblast without adequate dryer/separators in place?). Maybe its not enough to make a difference ... but I would rather get as much ambient dry air as possible from my blower vs my compressor.

 

That's kind of my thought.

I don't know much about these nozzles. I assume they are mostly used for oil fired heating furnaces and such. Is that right?

I guess what I wonder is the purpose of the compressed air in the nozzle in those heating furnaces. Is it just for drawing and atomizing the oil, or is it intended as a primary source of combustion air? Do those systems have a separate source for combustion air?

 

I also have a regulator that tees off the junction of airline and the oil (air) pressure regulator as Mr Ed describes. It's not shown in my pictures on page 1 as I added it later. I have it set at 10psi for waste oil. When my mix is thinner, like when I've added alot of diesel, I turn it down a few lbs.i keep the oil at 20 and meter it with the needle valve at the burner. I dont dry my air. Maybe I should, but moderating that atomizing air to a reasonable minimum is probably ok in terms of moisture. I figure if I utilize that air for atomizing and use my blower for combustion then I minimize the variables.
Try sticking your leaf blower on there, just temporarily. Some sort of air dump or else a router speed controller from Harbor Freight for volume control. That will at least answer the question. I've used extra atomizing air pressure to augment an inadequate blower on occasion, but that's been rare.
Another consideration for your fuel tank is adding a petcock or some other means to tap off water in the tank. An inline oil filter is also a good idea.

Pete

 

The compressed air is for siphoning and atomizing. I think the compressed air is just a fraction of the combustion air volume. Don’t be surprised if significantly increasing combustion air and fuel results in a colder furnace. There is a sweet spot as far as how much fuel you can burn INSIDE your furnace. Blasting fuel/ air into the furnace will result lots of heat generated, but a lot of that heat may be released after the exhaust exits the furnace. For my medium/large furnace .19L/min is optimal.

I meter my fuel flow so that I can hit that number.

I would underline Pete’s fuel filter suggestion. The last thing my fuel sees before entering the furnace is a small inexpensive automotive fuel filter. It is surprising (sort of) how much crud it picks up. Prior to the filter I had mysterious fall-offs in performance at times. Now I know that was partial plugging of the nozzle. With the filter everything works reliably every time. Actually I filter my fuel twice—-once just before the meter as dirt messes it up and then again at the furnace as there is a quick connect (dirt) between the meter and the furnace. Both filters show plenty of trapped dirt.

Denis

 

Just finished a pour.

To test the idea of the setup being combustion air limited, I took about a half a roll of duct tape and fed my shopvac into the system.

Holy hell, that thing was a madman! From dead cold to pour in under 1.5 hours. By far my fastest melt yet, 18# of bronze. The hardest part was keeping it under control.

The shopvac was way too much. I ended up putting tape over about 3/4 of it's air intake just to throttle it back.

Again, can't express my thanks to this forum enough. It is incredibly helpful getting advice from you guys!

 

Sounds like you've made sopme real progress. I use a 4 dollar blast gate to control my blower air.



It is nice because I mark it to show where I run my furnace at optimal airflow. So, I set fuel flow rate and then open the gate to the mark and tune it by tiny increments (1/8 to 1/16" changes) up or down until the flame looks right. In fact, if for some reason the flame changes while I am melting I look for fuel flow issues, outlet obstruction, atomization issues (all are very infrequent) if the air setting is correct.

In time I think you will be melting that 18 pounds of bronze in around 1 hour times.

Denis

 

If you restrict the airflow in a vacuum cleaner it will make the electric motor overheat so it will have a short life. There are two ways throttle back air using a vacuum cleaner, use a tee fitting to divert air from your furnace burner or use a electronic speed controller. I have used both but I found the electronic speed controller works for me the best.

 

Many (I think akmost all) modern vacuum cleaners use a separate fan to cool their motors. Older style ones did rely on suction air to cool their motors. But that had obvious weaknesses. In wet/dry vacs using suction air would be an immediate problem when used for sucking up water.

https://blog.ametekdfs.com/oem-air-moving-blog/blower-airflow-separation-where-are-bypass-blowers-useful-2

Denis

 

I hope I dont steal this thread,
But I use a similiar blast gate on my super insane overpowered furnace, and it seems the blower (again super insane overpowered) just forces the air through anyway

thoughts???

Admin if you want to move this to my furnace thread Please do

V/r HT1

 

It is hard to imagine how the air would just blow through the gate. Some small percentage should get through due to leakage. I guess if your blower is producing very high (should not be needed) pressure it would be possible for it to bend the gate and allow large-volume bypass. But, used as intended with "ordinary" pressure it works fine and allows very small incremental changes in air flow and is very reproducible with a marked setting allowing a predictable air flow matched to fuel flow from one session to the next.

There are sturdier gates available for 4 times the money from places like Lee Valley Tool. This one is of steel and aluminum construction:



It should withstand significant pressures.

Denis

 

FWIW, the shopvac was mostly for test purposes. I wanted to see if stuffing more air into the system would make the difference.

That question has been answered with an emphatic "yes". Next step is working out a permanent solution. I might stick with the shopvac, but I'll need to work out some piping and gating on that. Like I said, as it is, that thing puts out way, way more air than the furnace can handle. I need to sort out a system to either blow some of the excess air off, or find a less powerful blower.

Here's a question: When I had the air from the shopvac cranked up, I ended up getting quite a bit of flame blowing out between the base and the lid. Need to come up with something to seal that. My first thought is this stuff: https://www.amazon.com/Lynn-Manufacturing-Strip-Superwool-Blanket/dp/B008HQ79DK/

Any thoughts on that? Anyone got any better ideas?

 

I'd wait till you tame your air volume/pressure before worrying too much about it. I have very little visible leakage when my combustion is dialed it, but when I go off the rails for whatever reason (blower quits, etc) I get flame shooting out everywhere! I understand the concern from a safety standpoint, but you made the observation under conditions that were exceptional.
The ceramic fiber you linked to would be short-lived. I believe HT1 posted a similar thread recently.

Pete

 

I just cut a 1” wide strip from a full blanket of wool. I glue it down to the top of the furnace with a thin coat of Satanite. Some people worry about the fibers released from the wool. Outdoors I do not. But spraying some rigidizer on the wool causes a sort of thin cohesive layer on the surface of the wool. I do coat the edge of the wool exposed to the flame with a thin layer of Satanite. I end up replacing the wool after a half dozen or so melts.

I do not worry about a small amount of leakage of vapor around my burner tube or the occasional gentle “open-air”burning of poorly vaporized oil there. But, you sure do not want tongues of high-temp flame leaking out between your lid and furnace body. That will heat up and burn the metal parts of the lid exposed to such flame. If I see such a leak develop mid-melt, I just stuff the leaking area with wool. Maintaining a good gasket of wool prevents this for the most part. I tried wood-stove gasket material with poor results.

Some guys report making a good enough seal between lid and body using Satanite and a sort of lapping technique. That would be a very nice solution. My furnace does not lend itself well to such.

Our combustion furnaces are pressurized, so leaks do have to be addressed.

Denis

 

if your blower is positive displacement, and the system is airtight, throttling the output with a gate (orifice) will just increase the velocity of the outbound air, I'm using a router control to control the blower speed, which I don't like, it's finicky, I want solid repeatable numbers

 

My gate, like all gates, is located a good distance upstream on the combustion air tube—-4 feet upstream on a 4” tube in my particular case. No doubt, right as the air passes through the gate there is an increase in velocity as that is the narrow point of the flowing stream of air. But beyond that as the tube goes back to its 4” diameter it slows back down (right at the gate it is also very turbulent because of the short distance of sudden velocity change). So, whether 20 gallons per minute (made up number) flows out the tube due to an upstream gate or due to a slowed blower motor the velocity as it enters the burner tube is the same. If the gate were right at the entry into the furnace, velocity would be increased at that point, but my plastic gate (or an aluminum one) likely would not survive more than a few seconds.

So, gates don’t accelerate air flow except at the gate itself.

Denis

 

velocity is not the issue it's the volume of air (with a positive displacement blower ) it really doesn't matter if you choke the output, the blower will (to it's capacity) force the same volume of air through the orafice (a gate in our case) only at a higher pressure /speed , if you are running a squirrel cage or similar blower, the pressure will "leak" around the blower , so a gate is an acceptable way to throttle the air flow,
I would have to vent some of the discharge air off from my blower, and I cannot think of a reliable, repeatable way to do that


V/r HT1