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Jan Ysselstein

Fuel consumption of a forge or crucible furnace.

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http://www.exothink.com/Pages/btu.html

 

Working with my propane supplier ( I am a portable tank schlepper ) has made me more aware of fuel consumption rates for forges and crucible furnaces. I typically get 3 crucible runs from a 10 Gallon tank. say 3 gallons per run of about 1.5 hrs or 2 gallons per hour. ( 360 inches cubed = volume) 180,000 BTu/hr

 

My forge is the same furnace probably running a little slower, say at 1.5 gallons per hour.....I can run the forge at a much lower rate but the 1.5 is typical.( 360 inches cubed = volume). 135,000 BTu/hr

 

NOw I am sizing a forge to heat blooms at about 720 inches cubed of internal volume...? Does that suggest a 135,000 x 720/360 or 270,000 BTu's/hr or is there something I am missing.

 

The frequent crucible runs scheduled for this winter will provide me with an opportunity to verify or compare the effectiveness of forge coatings, including some of the products frequently mentioned here. If any one has a recommended experiment to run ...put it out there and we will probe it. I don't think you would want to be stuck with my suggestion

All experiment have some implicit criteria ...such as it has to repeatable by another person and the information needs to be numerical not anecdotal and so on and so on.

 

Jan

Edited by Jan Ysselstein

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hmm

 

I must start by staying I run coal here as my primary, although I do have a good number of propane forges of various builds and sizes.

 

I think the best you can do is get some rough estimate at best. The individual burners make more difference for fuel consumpton and top temperature as anything else.

 

Heat loss from the containment is a function of surface (square) while your interior space is volume (cube). This suggests the effect of heat lost is reduced for larger forges?

 

Just as important might be the time to temperature of the metal itself. Penetration into the centre is another volume over surface ratio - but this time working the opposite direction (volume increasing far faster than the surface area where the heat can be absorbed). You may have the number of BTU available, but its just going to take a lot longer to get that bloom mass hot enough. Consumption per hour may be fixed, but heating time is greatly increased.

 

You run 10 lb tanks? I'm using 40 lb ones here and need three of them to keep an ample supply on hand.

Admittedly my forges are home builts (and thus not the best in terms of burn effeciency!). I get about 12 - 14 hours out of a single 40 lb, giving me just into a yellow, with my two burner (with about a 12 x 12 x 5 inch interior). Delivery pressure on that one set about 6 psi (although that number might not mean much specifically)

 

Be interested in any actual numbers you generate.

I do have a digital pyrometer here, next time I fire the propane forge (today a day off for me). I will get some accurate temperature numbers on my unit for comparison.

 

They have been talking about starting a user carbon tax here in Ontario - and in Canada generally. Of course right now this is too vague to really mean much, but it would likely increase my costs at each purchase.

The blacksmithing coal we use here already is shipped by truck from the USA (Penn. / WV). Right now it runs roughly $50 CDN for a single 75 lb bag (closer to $35 with bulk purchase).

I had looked into *carbon* use for my full time operation here in Ontario back in 2008, when the concept of a carbon user tax was first proposed here:

 

http://warehamforgeblog.blogspot.ca/2008/07/carbon-and-forge.html

 

The currious thing was that *coal* turned out to be the *smallest* carbon foot use - at least based on my use.

(I freely admit that this did not take into account production or transport carbon generation.)

 

Darrell

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In my chilli 2 burner, I can forge all day at bloom welding heat, with my 30lb tank. Like 11-4:30

That is running at about 20 psi all day. Sometimes more. The temp is HOT. Bloom welding temps.

 

I use about 2 full bags of chopped charcoal in that same amount of time, welding bloom. So the cost, for me is about half as much with the gas. But I have a good deal on gas, as we have a big tank at work, and I can get it near cost.

 

If I'm playing with modern steel, a 30lb tank would last about 2.5 times as long, of at least 2 long days of forging.

 

Mark

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Darrell, Mark,

 

I will start keeping a log on weight of propane used , forge volume, approximate operating temperature. By the way that is ( I use) about a 10 Gallon tank weighing about 40 lbs. ( I do use smaller tanks as back-ups ).

 

I do have access to a low pressure line which will only supply about 200,000 BTu's/per hour ( or 2.2 gallons liquid equivalent or 9.5 lbs )..I will soon find out if that is enough.

 

The effectiveness of the forge coatings will be measured by drilling a hole into the center of the plinth and measuring the time required for the center to get to a given temperature . An effective reflective coating should slow that process way down. We will start by doing a couple of heats without any coating on the rammed refractory plinth.

 

The PSI numbers are all relative to the burner, so me at 11" of water pressure and a blown burner may be delivering more fuel than another person at 10 psi and a small orifice injection burner.

 

 

 

 

 

 

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That's for sure !! With a ribbon burner, you can run 5 psi, and melt your forge !! :)

 

So, the burner makes a big difference. Make a forced air burner, and that 9.5 psi should be plenty.

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Do they make an accurate fuel gauge for portable propane tanks?

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Nope. A flow meter is the best way to measure consumption outside of weighing the tank, but try finding one rated (or calibrated) for propane.

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I have found that the age of the forge lining is almost as important as the exact design when it comes to efficiency. We build all of our own forges and we tend to use them pretty hard, but I always notice a distinct decline in performance as the fresh insulation and coating begin to degrade. We go with 2" of Inswool with a thin coating of refractory over that for protection, and this heats up very quickly and gets very hot...until we bang something into it or poke a sword point through the lining by accident. Each round of repairs to the refractory shell improves matters a bit, but never back to the original performance.

 

We run 100 pound tanks, and they last very different amounts of time depending on the type and amount of hot work getting done. Two of my partners were recently working on Viking-style pattern-welded swords, and all that forge-welding ran through an amazing amount of propane.

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For charcoal, all I can say is that it is worth talking to a few suppliers/distributors and letting them know of your interest. When Jesus Hernandez was coming up to do a smelt at our Hammer-In last year we managed to pick up an enormous amount of good quality charcoal at $5/bag (20 pound bags), including shipping. The price was so low because the lump size on this particular batch didn't meet the standards the distributor wanted, but what did we care that the lumps ranged from 1" to 4" rather than being almost entirely 4"? This particular distributor sold the remaining 7 tons (!) to a farmer in Idaho who spread it on his fields as a source of carbon.

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Hello Peter,

 

Thanks for piping in, since starting the post I have given the coatings experiment some more thought and am considering making a refractory sphere maybe 4"- 6" in diameter. I will make a mold and force some rammed refractory into it , drill it and dry it ( by fire) then use it for testing. I want to stay within the suggested guidelines of:

 

"All experiment have some implicit criteria ...such as, it has to repeatable by another person and the information needs to be numerical not anecdotal and so on and so on."

 

So, if someone makes a claim regarding the performance ( or lack of performance ) of a given material, another party should be able to verify it.

Jan

 

My gut feeling is we may have to look a little closer at the emissivity definition to see how all that applies to us in particular.

 

I am trying to use my homemade charcoal for making iron and trying to use propane almost exclusively for welding and forging. I do use some fines with coke in the Murray Carter style forge, the charcoal bits keep the fire active during my long lunch breaks.

 

Jan

Edited by Jan Ysselstein

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I think that your experiment will need to involve a few parameters:

 

-forge temp that needs to be achieved and a thermocouple to measure it

-forging temp that needs to be achieved, which I guess will need to be ascertained by eye

-standard bar size to heat so others can repeat the experiment

 

For each forge design, burner type, lining, and coating there will be a lower limit of propane consumption below which the forge simply won't reach the required temperature. Measuring the time-to-temp at various pressures (flow rates) would establish the initial down time, while the time to heat a specific bar to the required temp would establish the rate at which work could be achieved.

 

The standard bar size could be a 4" length of 1" square welded onto a 1/2 RD handle. I think using three of these in the experiment would be appropriate. The basic procedure could be a start from dead-cold on the forge and bars. The timer is started when the fire is lit, and a note is made when the forge first reaches temp. The first bar is then added, and then the time is noted when that reaches temp and is removed and set aside. The second bar is then added, etc. The experiment ends when the third bar reaches the required temperature.

 

The most accurate way to measure the gas consumption would probably be with a scale, assuming that you have an accurate scale for the size of tank you are using. Gas consumed/time elapsed would be the output of the experiment, and this could then be further compared with the amount of useful work that heating the three bars represents. The equivalent experiment with charcoal would be to weigh the charcoal before and after...though this would require some way to extinguish the fire that wouldn't damage the forge.

 

In the case of some of the coatings, I think the experiment would need to be performed once when the coating has just been applied and then a second time after a week or two of reasonable use. My experience in the past has been that the coatings are very effective for a while and then the effect tapers off, I assume due to chemical reactions between the forge atmosphere and the coating material. If you are able to find a coating that is effective and cheap, then re-coating periodically would be no problem. The one time I tried ITC-100 I was very happy with the initial results, but then sorely disappointed by the cost over time as the coating degraded.

 

My last few forges have just been Inswool painted with Kaolin slip, and that has worked quite well from an efficiency standpoint...but it doesn't hold up well to abuse. Adding Kyanite (mullite) to the slip should reduce the crazing of the surface, and adding Alumina should theoretically improve the IR reflectivity. EPK and Kyanite are both readily available and quite cheap. I'm not so sure about the alumina.

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Peter,

Peter, it is "our experiment ."

 

I think changing the design to a forge heating rate rather rather than an object heating rate is a good idea. I have ordered enough 8"x8"x3/4" kiln shelves to make a couple of simple forges. The forges will consist of 6 shelves forming a cube, the front shelf will be drilled for an air/LPgas inlet, an exhaust and a hole for a thermocouple. I will hold off on the heating of specific steel stock as it will become a source of probable inconsistency in testing. The ceramic shelf box will be covered with a layer of Inswool and all will be contained in a 5 sided box....the front panel or 6th side will be temporarily tacked/wired in place.

I am hoping to avoid a condition where the energy input to the furnace is so low, the heating of a load ( steel ) would be too slow. I have some constant volume blowers, if they do not work I will rig a flow meter/valve to the air supply of another fixed volume blower with a larger capacity .

So the assumptions are forge temp = forging temp and no we will make other holes in the furnace to keep things simple.

 

I should have it set up this week , assuming I do not have to order more wool.

Jan

Edited by Jan Ysselstein

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Jan,

 

I got started off on a tangent of forge and burner design versus the coatings experiment that you were originally discussing. To test the coatings I think you are right that a time-to-temp measurement would be sufficient.

 

Someday I would love to see the forge liner debate of "thermal mass" versus "insulating value" finally resolved, but that will be another day. I barely have time to keep up with the things I actually have to do, let alone start working on things that I simply want to do.

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Peter,

That thermal mass question includes safety and hours of operation. All the materials are here , I need to cut some sheet steel panels and figure out how I will assemble the refractories...pinned or glued or ?..

 

The air/Lp gas inlet and the thermo couple inlet will both be sealed from the atmosphere with a Sairset/clay type mix.

I am hoping to get some suggestions from forge users as to what to test.

 

Jan

DSCN2886.jpg

Edited by Jan Ysselstein

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Furnace performance tracking math.

This should apply to any furnace in any condition. A baseline is established, prior to doing repairs and/or coating .
You will need a fixed blower rate and a fixed gas rate and a fixed furnace exhaust hole size for all the runs comparing that furnace to itself.
You will need a thermocouple ( type K), a digital volt meter , a digital temperature readout like the ones on a PID controller. A chart showing the thermocouple voltage at each temperature
Example. At a fixed air and propane flow rate it takes a furnace 45 minutes to increase 1000 Deg C in temperature ( from 100 Deg C to 1100 Deg C )
For this furnace run , we take 1000 Deg C/ 45 minites = 22 deg/min ,
Assuming this was done prior to improvements this will be the highest value seen 22 deg C/min
After patching and coating, the same furnace is tested again and this time it only took 18 minutes to go from 110 Deg C to 1100 Deg C
The old furnace in the condition where 22 Deg C heating rate existed was running at about 3 gallons/hr at $3.30 per gallon or $10.00 per hour
A possible guess ( extrapolation) would be the repaired furnace is now capable of running at 18/22 x3gallons or 2.45 gallons per hour or $8.08 per hour.
At a savings of $2.00 per hour that repair may have been worth it.
This may not reflect exactly how a furnace will perform but it is a step away from anecdotal chatter into a numerial way of comparing one's furnace before and after repairs.
I am going through the ( temporary) expense of making this little box furnace for reasons I will explain as we get into testing. I use these 8" tiles any way, as bottoms in my welding furnace, they dissolve fairly quickly..I just cut another 2" strip and replace it and so on. The kaowool under that strip area never gets whetted by flux.
Edited by Jan Ysselstein

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