Larger Moya???

Just asking for a friend...how much for these plans?.

 

15 amps, wow! That guy pushes some serious air but I'll bet it's a screamer.
Might want to build a muffle box for that thing.

 

I just got the Notice that my blower has shipped, and yes I was harassing Kleerrite and all they would say is that it was backordered from the Manufacturer, 7+ weeks backorder.
You know what this means as soon as the furnace is running well, I will have to order a spare blower, can you imagine having to wait 8 weeks and not cast ??

Not this guy

V/r HT1

 

When providing air to a furnace there is a lot more to it. It is not just simply straightforward. There is a lot of static friction and a lot calculations and horsepower to overcome static friction.

Static friction gets more complicated with every bend in a pipe, or a corrugated pipe, length of pipe, diameter of pipe... And the list goes on, and on. Pressure or psi and ultimately CFM gets affected. The only way to alleviate this is to create more pressure (PSI) at the source or reduce static pressure.

Bigger burners can move a lot more air than smaller burners. Smaller can do the same job, but they need more pressure (psi) from the source. As well, the source needs to overcome the static pressure.

The easiest way I like to try to explain this is blow through McDonald's straw and then try to blow through 100 foot of 5/8" garden hose, using just your mouth. And try to fill up a balloon on the other end..... Most would think it would be easier using the garden hose,... But they would be wrong.

Both of my blowers for my furnace have over five psi delivery at the source. The trick is being able to have more than you need with a variable speed motor, or to be able to dump or restrict the air by adding more static friction (like using a ball valve or a dump ball valve).

The air or oxygen in the air is just as important as the delivery of the fuel for complete and uniform combustion.

One thing I definitely made a mistake on, is only making the exhaust vent only 3.5 inches for my 14 high and 12 inch diameter furnace using a A12 for aluminum. In the future I'm gonna try a A10 with copper. The scrap copper does not seem to dance as much in the air flow as aluminum. Big chunks of aluminum rims I can just drop in through the vent... Light weight pieces I have to be very careful with. It is a live in learn with what you got.

 

That’s one hell of a dissertation . In my mind it makes not a lot of sense... pressure is dependent on a close or restricted flow system. If you have an open system it’s very difficult to get any pressure... seems to me in a burner. Air flow would be the largest concern... that will be effected by friction losses... which I suppose could create a back pressure and potentially a reading in PSI.

I believe but cannot confirm that a slower moving volume of burning air/gas mixture spending more time in the furnace would transfer more heat to the interior of the furnace... so I’m trying to move my burner size up... I also think a thorough mixture of air fuel will help combustion. As always I look to the MIFCO furnaces for inspiration... as they are claiming melt times that very few have claimed to match... and no one has documented

But I welcome all input

it’s hard for hobbies to experiment. It’s too damn expensive

V/r HT1

 

You don't need high velocity air, and I agree completely the longer the hot gas stays in the furnace the the more heat it will give up to the furnace walls and crucible. A reverberatory furnace has a very long residence time of hot gasses with little or no flame in the melt chamber. That's efficient.

Fast melt times are not efficient. If you want to melt brass in 30 minutes you need to be very concerned about minimizing the furnace mass so it heats up quickly and can begin radiating heat to the crucible quicker.

You also need to be sure you have close to a neutral flame so you aren't heating fuel you aren't burning or heating air which is not being used. Your burner tube needs to be large enough to have the flame stay on the end and enough air velocity to avoid flashback into the burner while you are burning all the fuel you intend to burn. If you're putting so much air into the tube (and it doesn't matter whether it's coming from a hair dryer or a giant compressor) the flame is unstable and standing off the burner tube then your burner tube is too small. The area between the flame and the tuyere is a dark area and will detract from maximum heating. An attached or remote combustion chamber will speed melt times. I firmly believe the design with a doughnut shaped combustion chamber below the top of the plinth with a ring opening into the furnace is a great design. Probably not worth the extra effort though.

If the goal is a super fast melt time you must waste a lot of fuel because you are intending to heat the furnace quickly which means your flue temperature must be high. If you are absorbing much heat out of the gas you're wasting time. With a low mass furnace and four times the fuel you need for a reasonable melt time you'll melt quicker. You have to balance between speed and efficiency.

 

Ok the blower came in. The output is overwhelming...166 CFM is A LOT of air.

Let’s talk a little more about external combustion chambers. As that appeals to me

V/r HT1

 

I guess technically it's an Ursutz burner. I've never made one but built out of firebrick or refractory it should be robust and shoot a hot flame into the furnace. If you're burning motor oil you would need a good way to clean out the solids occasionally.

 

Clarke from Windy Hill Foundry mentions his furnace uses an oil pre combustion chamber in this video. Maybe he can provide some detail now he's doing maintenance on the furnace lining.

 

Pat G used to talk incessantly about Clarke's ursutz burner but I dont ever remember seeing its construction.
@HT1 What's the appeal?

 

It works reliably on oil fuel.

 

It also keeps all dark areas out of sight of the crucible. The crucible is heated by conduction from hot gas but primarily by radiation from the hot gas and hot furnace walls. Any dark area does not radiate but does absorb radiation so that slows heating of the crucible. Radiation within the ursutz chamber will also heat the gas more uniformly prior to entering the furnace. Don't discount the value of radiation in heating the crucible.

I'm considering a large tuyere with a cylindrical refractory chamber extending back from the furnace wall far enough that the combustion takes place in this cylinder with the burner stuck into the end, maybe a 3" ID cylinder about 6 inches long for a 2" burner.

I'm also considering a refractory disc a few inches above the flue opening to reflect radiant energy back into the furnace.

 

That's very similar to what Mark dropped on us many moons ago, and it is very compelling to me, , only question what should the angle of the cylinder be??? the correct angle would be more efficient




V/r HT1

 

That furnace drawing above is perfect for propane gas but will need more volume for oil firing as I found out with my copy.

I'm getting ready to trial some new modifications to my furnace in the hopes of reliably getting iron temps. I built something similar to the drawing above in a beer keg and I have direct experience of the original furnace in the drawing above running off propane which it does beautifully. My copy running oil can only get to bright orange heat/ barely brass temps. If I were to make a third furnace, I'd make the bore at least two inches larger and taller to slow the burning gas past the crucible walls and causing the cyclone on top of the crucible.

I've had a lot of delays in 2020 but I'm getting ready to do some more testing, I've had three really beautiful iron runs: yellow to white heat and several orange heat runs and I don't know why it won't get hotter. My latest theory is the original stainless steel cone air nozzle was getting red/orange hot and the fuel spray inside was hitting the hot inside of the cone and flashing off to gas and keeping the nozzle cool and burning quickly as gas rather than slower heating from droplet form.

 

That furnace has been relined many times over the years and the conical tuyere shown in the drawing has been a straight tube for ages (1980's) now.

 

I'm thinking a much longer external chamber, and larger in diameter, maybe 3" diameter by six inches inside.

 

Like this?: 4" bore x whatever length you attach to the flange.

 

i would have to assume there is a point of diminishing returns this long chamber adds thermal mass , that has to be heated


V/r HT1

 

It can help with tuning/timing by adding extra length to slower burning fuels to allow them to fully combust further inside the furnace...or at least that's my theory. It's proven hard to get stable combustion inside the tuyere so far and I can hear the combustion get a lot louder at the flame front moves around inside the furnace as I withdraw the fuel nozzle deeper down the tuyere pipe.

I built it with modification in mind: it's easier to narrow it down if needed but harder to bore out the furnace hole and make it larger. I don't know what makes a good oil furnace design so I can make modifications as needed. So far I've learnt that the airflow is too slow with a full 4" bore and the flames didn't evenly swirl: just travelled a short distance inside the furnace and did a 90 degree turn up one side of the crucible so one side was glowing and one side was cold. Necking the bore down with a sheet metal cone to 2.5" made the flames swirl 180 degrees round the crucible but it wasn't until I fitted a refractory disc on top of the plinth that I finally had flames running a full 360 degrees around the crucible. It could be considered a donut shaped/toroidal pre combustion chamber too. A 4" bore has an area of 12.5 square inches while a 2.5" bore has an area of 4.9 square inches so airflow speed is more than doubled which got rid of the lazy flame problem.


Also I can withdraw the brass fuel nozzle away from the furnace chamber on shutdown to prevent the nozzle from getting cooked by radiant heat when there's no airflow or fuel flow.

 

Exactly what I was thinking however with refractory lining.

I want to still use my drip burner with a pressurized fuel supply and I want my combustion to take place in the chamber so only hot gas goes into the furnace. Certainly the velocity of the gas entering the furnace determines the path it takes around the crucible. Currently with my leaf blower I get good swirl with the end of the burner in the furnace. I would expect that same volume of mixture to produce the same swirl, but need to think that through.