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help regulating forge temp


gmerrell
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all I'm have a problem maintaining my
forge temp while also keeping a reducing atmosphere.


Fist I'm in Colorado at about 9500 feet

so the O2 is thin. I'm also using an old Kerby vacuum as my blower
with a dimmer switch to control the speed (I know red neck city) I
also have a dust collector blast gate on the output to restrict the
air flow going to the burner. The air that doesn't go to the burner
goes through a Y to a pipe at the front of the forge to push the
flame up away from the opening.


My forge has about 4" of kwool on all sides, and once I get up to 2200-2300°F

I can't keep the temp down and keep a reducing atmosphere in the
forge. If I turn the air flow way down and still keep an orange flam
coming out the forge the temp creeps up >2400. If I turn the air
up so the temp goes down then I lose the orange. I usually end up
with the propane pressure around 0.5psi and the air barely on. Then
turn the needle valve for the propane to get the reducing atmosphere
then turn the gas off when I pull the billet out of the forge so it
cools down.

 

Any help? I tried turning the gas pressure up to 7psi with the needle
valve almost closed and the air way down and that kinda helps?

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I assume, from what you've said, that you are trying to weld up PW billets in this forge. If you are trying to just forge mono-steel, then you are way too hot, by 400-500 degrees. It sounds like you've got plenty of air, and plenty of gas. Can I see a picture of your burner, please?

 

I don't understand why the temp should keep climbing. My first impulse is to change out the vac for a smaller fan, like a bathroom vent fan with about 50-75 CFM output. What I like to see is a soft, billowy greenish flame out the door, that tells me that all of the air is being used in the combustion chamber and the remaining gas is igniting when it finds free O2.

 

With your current setup, as an experiment, do this. Get the forge going, so that it is hot enough to auto start. Cut the air down to a whisper and then try to control the state of the burn with just the needle valve. What you are looking for is a combination of air and gas where the needle valve is open about half way, the air is wherever it lands and you have a bit of flame out the door.

 

On my HT forge I can set the line pressure from the tank at about 6-10 PSI, set the air intake about 70% closed and just barely open the needle valves (there are two) and hold the temp at 1500F. With a single burner and the same gas setting my welding forge runs with the air about 50% and the gas about 50% and I get a stable 2400F. I should note that I am only about 700 feet above sea level.

 

Post a pic of you setup and hopefully someone else has some thoughts.

 

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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Since we are talking about Forge Temp. I have a question.. Where can I find a good/not to much money Pyrometer ?? I got my forge going but I have no idea what the temp is.. I'm pretty sure I am going to have to redo it because the only way it works well is with the air at full blast and the propane cut way back.. Plus I don't like the pin valve I got because it's not working that well.. Thanks

Thanks Glendon

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I'm using one of these, and it works fine for me. However, digital pyrometers are easier to read and can be had fairly cheap. I found this one on Ebay. Be aware, these are not PID's, they won't control the forge, they just tell you the temperature.

 

Geoff

 

PS

 

I use these needle valves on my forges. I bought 6 the last time, so I would have some when I need them. They work fine for me.

 

Geoff

Edited by Geoff Keyes

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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Since we are talking about Forge Temp. I have a question.. Where can I find a good/not to much money Pyrometer ?? I got my forge going but I have no idea what the temp is.. I'm pretty sure I am going to have to redo it because the only way it works well is with the air at full blast and the propane cut way back.. Plus I don't like the pin valve I got because it's not working that well.. Thanks

 

The pyrometer itself, or at least the readout, is the cheap and easy part. I use a TM902C bought off ebay; a search will find these at 5 or 6 bucks, delivered from China. They take a type K thermocouple input and have a miniature (flat-pin) socket. Too cheap not to have IMO. Slight downside for those that think in Fahrenheit is that they only read in Centigrade. Those I've had all read to 1365 degC (2489 degF), despite being marked 750 degC or 1300 degC.

 

You will need to spend considerably more on the thermocouple.

 

I use Mineral-Insulated thermocouples of 6mm (1/4") diameter and 600mm (24") length with a plastic handle and curly cable, ending in a miniature plug to suit the TM902C and my other (much more expensive but no more accurate) instruments.

 

I also have a couple of longer 6mm MI type K transition joint thermocouples. These also work well and are off-the-shelf items, just needing the plug fitting. The sheaths on those I have are type 310 stainless steel, rated for 1100 degC (1202 degF), but they seem to work fine up to the 1365 degC maximum for the sort of timescales they see when used for checking/adjusting my forge.

 

There are cheaper unsheathed thermocouples intended for fixed installations. They need a sheath if they are going to be in a forge for long and ceramic sheaths are available for this.These are good if you can put them in the right location to measure the temperature that you are interested in. Most of the forges I have had any dealings with have had temperature variations throughout the internal space. A long handheld probe will let you measure and understand the variations, helping to find a useful location for the fixed thermocouple if that is the way you intend to go. The ceramic sheaths are pretty good insulators and therefore slow the response to temperature changes. This means they tend to damp out fluctuations and can make a forge appear much more stable than it really is. It's one of the reasons I like to check the temperature stability and distribution before going that route.

 

Most thermocouples are made to order. I try to specify "Grounded junctions" for the handled ones. This reduces the response time significantly when compared with "insulated junctions", but does have minor disadvantages in other areas.

 

If you are in an industrial area, there is a good chance there will be a thermocouple supplier fairly near. If not, Omega are about the biggest name in temperature control and it's worth talking to them (www.omega.com) if you need to order with shipping. They have knowledgable technical support and I like their Omegaclad XL sheath material. Either way, I'd strongly recommend talking to the technical guru at whichever supplier you use and listening to their advise.

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I don't see why that should give you any trouble, except perhaps for pipe size. You might try reducing the injector to 1".

 

I still think it's a problem with too much air, though the blast gate ought to fix that. Once you cut the air down, I think you'll find that the burner is too large in diameter. Keep me informed on any changes you make, I'll be interested to see what the solution ultimately is.

 

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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