T burner tuning

[Jbradshaw]

fI built a 3/4" Frosty T burner that I am using in a brick pile forge. I have a coupler on the end as a flare because I had already drilled the hole In the brick for it when I read that a flare was not needed. It fires up with no problem and I have not had any trouble getting 5/8" coil spring to forging heat with it. I have not tried to get it to forge welding heat yet, so am I not sure how it would perform for that task. The thing I have noticed that makes me wonder if it is tuned correctly is that I am getting absolutely no scale when I forge in it. 

Below is an image of the flame. There is some dragons breath, but it was too light to capture it. Since i am not sure what I am looking at I thought I would ask before starting to trim the MIG tip (it has not been trimmed at all at this point). 

 

 

 

[Frosty]

The flame looks pretty good. You have two other problems. First you have ONE 3/4" burner in a 9"x9"x9" = 730 cu/in chamber with a huge, wide open doorway. A well tuned 3/4" burner is good to bring 300-350 cu/in to welding temperature.  The huge wide open doorway is letting the heat radiate to the room rather than concentrate INSIDE the forge.

The second problem being you built it from hard fire brick which has a nominal R value of 1 and it has a high specific heat. This means it isn't insulating worth spit and it's a major heat sink. This is costing you fuel to warm it up and keep it hot.

You can do a couple things, make another 3/4" burner Or replace that one with a 1" burner and close up the doorway. It'll get hot but it's still going to be a fuel hog and take time heating up.

You can remove a layer of brick, cutting the volume in half and close up the door for the same effect as above.

If you rebuild a smaller volume with soft, insulating fire brick it'll get hotter and faster gut soft brick doesn't like thermal cycling and tends to break up between expanding and contracting as it heats and cools. A gas forge heats and cools pretty quickly, soft brick rarely lasts  more than 3 firings in mine.

There are a number of threads about building gas forges in the gas forge section. The general consensus between folk who've been building and using the things for years is sort of evolving but runs like this. In general terms. 2 layers of 1" 8lb. Kaowool or equivalent ceramic wool refractory as the outer liner. The inside or flame contact layer being a high alumina 3,000f castable refractory or kiln wash mixed to a plaster consistency and applied between 1/4" to 1" thick. The inner layer or kiln wash having an IR reflective component is a good thing. Lastly a kiln shelf floor also kiln washed.

Forge liners are wear items, they will wear out but there are methods to make them last longer, not permanently but longer. Floors especially take a beating from mechanical abrasion from being scuffed and gouged by steel to flux dripping on it. It's only good sense to make floors easy and inexpensive to replace.

Like I say, there are some darned good discussions on the topic in the gas forge section.

Frosty The Lucky.

[Jbradshaw]

Thanks for the feedback Frosty. The picture is misleading regarding the internal volume of this forge. What you are seeing are the bricks I have closing up the opening. So 4.5" high by however wide I spread them at the moment. The actual internal measurements are 6.75x4.5x9= 273 cubic inches by my calculation. I was concerned that what I had might be hard firebrick instead of soft. The supplier I picked it up at said they had never heard of hard or soft firebrick and what they sold is just called firebrick. A local blacksmith told me that he buys his at a pottery supply (they were out when I was looking for bricks and the place I got the brick I have was only a couple of blocks away).  The size of the opening is also misleading in the photo. I have three pieces of brick stacked in front of the chamber opening (one on each side and one as a bridge between them). I can close it up completely with these and usually only have enough open to get access to the piece I'm working on.

I am using the firebrick forge because I didn't know if I was going to want to stick with using gas (I started forging last summer using lump charcoal.), so I didn't want to invest the time and money to make something more permanent. I like the fact that I can fire it up at will and don't need to worry about putting a fire out at the end of my session. I will be building something more permanent.

So for the short term, I will replace this brick with soft brick until I obtain the things I need to build a new forge. If my flame is good why am I not getting any scale? Not that I want scale, but I thought gas forges produced a lot of it.

[Frosty]

Well, you asked ME about the flame and MY preference is for a flame that's a little rich, carburizing to prevent scale production in the forge. It will produce more CO than a neutral flame but both are demon CO producers so take precautions. CO alarm, good ventilation, etc.

If you steel isn't scaling when you take it out of the forge then it's NOT STEEL! Hot steel will scale when exposed to open air, If it isn't then it's some alloy we don't know of and at high temperatures what you don't know CAN hurt you.

I take it you bought your fire brick at a building supplier. They don't deal with supplying HVAC guys who deal with furnaces and the like. Do a little yellow pages walking. (much better than the internet for this kind of search.) Look for HVAC or furnace suppliers, if you can't fine one listed call a HVAC service company and ask where they buy their refractories. Don't get too specific about what you're looking for unless they tell you they sell it. You really don't want to confuse issues, all you want is refractories. HVAC guys tend to get their knickers tied in knots when someone starts talking about home made propane fired appliances. Thoughts of litigation start dancing in their heads like ferrets on pixy stix.

The HVAC service guys use a lot of refractories of all kinds, just depends on the furnace. Most oil fired use 3,000f hard fire brick on the contact layer and the exchange tubes and hard brick are backed by ceramic blanket Oh, on and on. A ceramics or pottery supply is a good place if more expensive than a good HVAC supplier. We are lucky enough to have EJ Bartells in Anchorage, they're an industrial HVAC service and supply outfit and carry just about everything a boy needs to build wicked HOT stuff.

Frosty The Lucky.

[DavidTodtman]

Very helpful, Frosty. Thanks.

 

[Jbradshaw]

Thanks for the heads up on tracking down refractory. Do you think HVAC suppliers  are likely to have the kaowool too?

Saying "absolutely no scale" was a bit of an exaggeration. But I am not getting the same amount of scale as I did with lump charcoal. And I'm getting nothing like what I see coming off guys work on YouTube when they're using a gas forge, which is what I thought a well tuned gas forge should do. I am not looking to get more scale. I just thought it could be an indicator that my burner was not functioning optimally. But if I am understanding correctly, the excessive scale I see on YouTube is caused by a burner running lean. Eventually I will learn to recognize flame types, but physical changes are more obvious to me.

Most of my steel is new from a supplier. I mentioned the coil spring because I think it is the largest cross section I have heated in it. And because I was making punches from it this weekend so it is fresh in my mind.

The forge is set up in my garage. I do have a CO/gas detector. I always have at least one door and one window open. During heats I will periodically open the other door to get more of a cross draft. I would prefer to open the car bay door, but it lets in too much light during the day.

[Frosty]

Yes, HVAC suppliers carry ceramic blanket refractories, it's more common in most modern boilers than hard refractories.

A perfectly neutral flame will hardly scale at all in the forge but often circulation patterns will draw fresh air in the door and you can get scaling in different areas. I tune mine to be a little rich so any air drawn in the door has enough hot fuel waiting to be consumed.

A lot of what you see on Youtube is good examples of the old saw, "Anything can be MADE to work." There are some really poor burner build videos and though they may melt aluminum they're really just rust machines in a forge.

You can crack the vehicle door and let fresh air in the bottom without affecting ambient light too much. It's better to adjust to judging temperature in brighter light than needing to spend tie in a hyperbaric chamber to flush the CO from your blood. Is it an attached garage? If so putting a window fan in blowing into the rest of the house will keep it's pressure higher than the garage and minimize the chance of CO migrating into the living space.

Frosty The Lucky.