Oil fired crucible furnace

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Harold_V
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Oil fired crucible furnace

Post by Harold_V » Tue Aug 31, 2021 1:55 am

Hey, guys!
I plan to build a melting furnace for aluminum and copper alloys. I have several #16 and #20 crucibles, along with some handling tools. That isn't much of a concern for me, but the energy source I must use is. I'm used to having natural gas, and have built several furnaces in my years, but now I have to consider using heating oil, as there is no natural gas at my disposal. I prefer to stay away from propane, although it might be a choice if I can't solve the riddle of burner design.

I obtained a burner from an oil fired furnace. It produces not only air, but the high pressure required to atomize the oil. They provide a respectable amount of air, and the nozzle can be changed to increase BTU's, but the principles are somewhat different in a melting furnace as opposed to a hot water boiler. I suspect that I'll need higher velocity, and I'll probably have to relocate the nozzle. What I've considered is reducing the 4" discharge down to 1½" stainless pipe via a funnel shaped reducer, with the nozzle located near the small end. I can retain the spark ignition with this design, and use a spark plug if necessary.

Before I spend a lot of time trying to re-invent the wheel, is there anyone who has some experience with oil fired melting furnaces who is willing to share burner design with me? Any comments would be appreciated.

H
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liveaboard
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Re: Oil fired crucible furnace

Post by liveaboard » Tue Aug 31, 2021 7:12 am

I built burners from scratch for a ceramic kiln in India.
These worked by preheating the fuel and burning the vapor, and the third generation worked very well. The energy output was around 50kw each, or 2800btu per minute at full power.
I could get the large oven to 1050C with ease.

The fuel was under pressure (the entire tank) , air was drawn by convection.
I doubt you want to use this design, but you might want to look for educational purposes.
I made this webpage about it a while back;

https://www.amsterdamhouseboats.nl/pres ... burner.htm

rrnut-2
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Re: Oil fired crucible furnace

Post by rrnut-2 » Tue Aug 31, 2021 9:36 am

An induction furnace will melt those alloys as well. I have no experience with it, but I have seen aluminum foundry's using them.

Jim B

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ChipsAhoy
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Re: Oil fired crucible furnace

Post by ChipsAhoy » Tue Aug 31, 2021 12:42 pm

20210831_103124.jpg
Harold:
I have this 85 page book that is destined for Sally Anne, but will gladly give it to you if you PM me your mailing address.
He may have gone where you are going to go.
I purchase this with the dream of melting Cast Iron some day..... after digging through this .... ain't happening.
Scotty

Harold_V
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Re: Oil fired crucible furnace

Post by Harold_V » Wed Sep 01, 2021 3:20 am

liveaboard wrote:
Tue Aug 31, 2021 7:12 am
I built burners from scratch for a ceramic kiln in India.
Nice design!
I'd like to avoid pressurizing the fuel source, however. The burner I have has a high pressure pump that atomizes the heating oil quite nicely. I'm in hopes that I can modify the output of the burner so it is compatible with the design of the furnace I will build.

Thanks for your contribution.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

Harold_V
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Re: Oil fired crucible furnace

Post by Harold_V » Wed Sep 01, 2021 3:23 am

rrnut-2 wrote:
Tue Aug 31, 2021 9:36 am
An induction furnace will melt those alloys as well. I have no experience with it, but I have seen aluminum foundry's using them.

Jim B
Hey, Jim!
Because I have only the two furnaces, I'm not keen on the idea of using induction. By using a crucible furnace, I'll be able to melt any non-ferrous alloy without concern of contamination, so it will increase the possibilities instead of limit me to one alloy.

I appreciate your thoughts.

H
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Harold_V
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Re: Oil fired crucible furnace

Post by Harold_V » Wed Sep 01, 2021 3:38 am

ChipsAhoy wrote:
Tue Aug 31, 2021 12:42 pm
20210831_103124.jpg
Harold:
I have this 85 page book that is destined for Sally Anne, but will gladly give it to you if you PM me your mailing address.
He may have gone where you are going to go.
Thanks for the offer, Scotty. Unfortunately, the design in question isn't in keeping with my intentions.
I purchase this with the dream of melting Cast Iron some day..... after digging through this .... ain't happening.
Trust me, I understand. Fact is, today (my today, your yesterday), after years of effort, I poured my first casting in gray iron. I'm melting with the induction furnace mentioned, above. So many issues to overcome. The cost and effort has been staggering, so I'm well pleased to finally achieve some degree of success.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

Russ Hanscom
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Re: Oil fired crucible furnace

Post by Russ Hanscom » Wed Sep 01, 2021 9:42 am

Any chance you could set a second crucible inside the induction one?

I have a suspicion that necking a 4" burner output down to 1 1/2" is not going to have produce results. You might be able to change to shape to say a rectangular output but reducing the flow area significantly is going to make the blower unhappy and probably throw off the air/fuel ratio.

Harold_V
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Re: Oil fired crucible furnace

Post by Harold_V » Wed Sep 01, 2021 3:50 pm

Russ Hanscom wrote:
Wed Sep 01, 2021 9:42 am
Any chance you could set a second crucible inside the induction one?
Unfortunately, that's not an option. The chamber of induction furnaces is quite small in diameter, but deep. The smaller furnace I have is only 5" diameter, while the larger one is 6-5/8" diameter. This condition is a function of the coil diameter and can not be altered appreciably.
I have a suspicion that necking a 4" burner output down to 1 1/2" is not going to have produce results. You might be able to change to shape to say a rectangular output but reducing the flow area significantly is going to make the blower unhappy and probably throw off the air/fuel ratio.
That's one of the issues I'm grappling with. I made a plywood adapter so I could try the smaller diameter. It does seem to function, although the atomisation was somewhat compromised. That would be addressed by relocating the nozzle to the end of the reducing pipe, however.

If push gets to shove, I have a Rotron blower that would not bog down with the restricted nozzle size. The blower in the burner assembly I have is just a squirrel cage, and is easy to bog down, as you suggested. The blower motor also powers the pressure pump, so I'd have to run dual motors, but that isn't an issue. The Rotron blower has 1" female pipe threads, so adapting it would be dead easy. I would be able to control air flow with a gate valve (typical construction for natural gas fired furnaces).

H
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John Hasler
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Re: Oil fired crucible furnace

Post by John Hasler » Wed Sep 01, 2021 4:07 pm

Other things being equal dropping the nozzle diameter from 4" to 1.5" will give you 7 times the nozzle velocity. The flame wants to burn at the point where the flow velocity equals the flame front velocity (a constant, more or less). If you don't reduce flow the flame may lift or blow out. If you do, since velocity is lower back inside your necked-down tube you may get blowback.

Why not just fabricate a suitable burner?

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Re: Oil fired crucible furnace

Post by Harold_V » Thu Sep 02, 2021 1:07 am

John Hasler wrote:
Wed Sep 01, 2021 4:07 pm
Other things being equal dropping the nozzle diameter from 4" to 1.5" will give you 7 times the nozzle velocity. The flame wants to burn at the point where the flow velocity equals the flame front velocity (a constant, more or less). If you don't reduce flow the flame may lift or blow out. If you do, since velocity is lower back inside your necked-down tube you may get blowback.
Not quite sure I understand this, so please elaborate. One thing you should know is that the nozzle will be at the end of the necked down tube, so there shouldn't be any combustion behind the nozzle. The length of the reduced tube would be about 3". I suspect, from your comment, that the pressure behind the nozzle would be lower, so that might cause the flame to push behind the nozzle. Is that correct?

One of the things I may do is include a gate valve to control air flow. It most likely won't be needed with the squirrel cage blower, but it would be invaluable if I use the Rotron as an air source. That's the common method of controlling both air and gas for the furnaces I've built in the past.
Why not just fabricate a suitable burner?
Chuckle!

That's what I hope to do. I'll use as much or as little (or none) of the existing burner assembly as I can or must. I'm not beyond building one outright, but I have no clue what would work. That's why I was asking here. Do you have anything to offer in the way of guidance?

H
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John Hasler
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Re: Oil fired crucible furnace

Post by John Hasler » Thu Sep 02, 2021 7:26 am

>One thing you should know is that the nozzle will be at the end of the necked down tube, so there shouldn't be any combustion behind the nozzle.

I'm assuming, perhaps incorrectly, that the mixture of air and atomized oil enters the fat end of the tapered tube. If so you have a blowback hazard because the flow rate (not the pressure) toward the fat end may be low enough to support combustion.

Do you have some drawings or photos? I'm havig trouble visualizing this.

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