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#1 Guest_Tai_*

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Posted 20 August 2003 - 09:29 AM

I think it works best to saturate the wool rather than coating it. I make a thin slip and work the wool through it, then ring out the excess. The inside surfaces automatically glaze over when fired, creating a thin hard inner shell that won't sag at welding heat.

#2 davidmorganesq

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Posted 21 August 2003 - 06:27 AM

Mike, could you give some details on how you did the double lining for your forge? I was thinking of relining my bucket forge, or making a larger, more evenly heating one for heat treating.  I'm using homemade castable, 1 part portland cement, one part sand, one part horticultural perlite, basically perlite concrete, and it's pretty tough stuff.  My thought was that I could adjust the quantity of perlite; higher for a weaker but better insulating mix, lower for a tough inner layer.

Cheers,

David


#3 Joe W.

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Posted 21 August 2003 - 10:37 PM

Yeah, but does it get hot? :o
It looks like you could melt fire in that thing! The firebrick to make an adjustable front is a great idea. Time to build another forge...I'm jealous!


#4 davidmorganesq

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Posted 23 August 2003 - 03:37 PM

Thanks for the details Mike.  I'm unclear on how the burner/nozzle is constructed, i.e., what is inside the sticky-out trapezoid bit?  Any details would be welcome.

thanks,

David.


#5 DFogg

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Posted 25 August 2003 - 05:32 AM

Tim Zowada's forges are the first I saw that used a tangential burn. It does burn more evenly and efficiently than a straight in burner.

Some commercial horizontal forges with the burners coming straight down from the top the flame will not reach complete combustion until the flame has bounced up off the floor. It will leave a dark spot as it is heating up. Working in that type of fire is like working inside the cone on a torch, it is not the hottest nor the cleanest part of the flame.

Don Fogg


#6 davidmorganesq

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Posted 26 August 2003 - 05:40 AM

Hi Guys.  Just fired up my new forge, and it seems to be doing what I want it to, an even heat over most of the forge interior.  I need to do some more tinkering with gas pressure and the like and there's still moisture being driven out, but it looks like this one's a keeper.

Thanks to Mike for the details on his forge.

Cheers,

David.


#7 DFogg

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Posted 28 August 2003 - 07:29 AM

A positive pressure blower pushes air under pressure. Probably the most common positive pressure blower is a vacuum cleaner. In that case it is using the intake side to do the work. The squirrel cage type blowers move air, but not under pressure so any constriction in the line will reduce the air flow.

If you think about venturi burners they aspirate enough air to run properly. Adding a blower creates a power burner, but it doesn't require that much air flow to make a big difference in capacity. For instance, I have a 9 cfm blower on the burner that I use to fire the 55 gallon drum forge. It will hold a constant 1650F running wide open.

A positive pressure blower provides a 1000 times more air than you need. It is noisy and it needs an additional and expensive gate valve to reduce the air flow. It is the wrong blower. If you were trying to push air through a solid fuel like coal or charcoal it would be the only way to go, but for gas it creates more problems than it solves.

I use magnetic vinyl for the flap and it never moves. They sell it at building supply for covering floor registers or magnetic signs.

Don Fogg


#8 Antoine

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Posted 20 August 2003 - 07:33 AM

Hi!
I've started building a small gas forge using ceramic fiber for insulation.
Ceramic fiber is quite fragile so many people recommend coating it with ITC100 to protect it and improved insulation.
I was wondering if you could coat the ceramic with a layer of refractory cement ( let say 1/2 inch) to make it solid, then with itc100? Or even just with cement?

Would this cause problems to reach welding temperature? Do you think the cement would stick well to the fiber?
Thank's!


#9 Antoine

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Posted 20 August 2003 - 07:21 PM

Thanks for the advices!

The hard floor is a good idea,Thinking of casting a piece of refractory cement that follows the curve of the forge trapping the flux at it's bottom. The rest being wool.

Tai, your post made me think ot high temperature clay. I have some grey/blue clay around where I live. Do you know what type of clay resist the best real high temps? I've heard of kaolin, but can't remember if it was in relation to high firing clay, any idea??

Thank's for the help!


#10 Antoine

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Posted 21 August 2003 - 08:07 AM

Fantastic stuff Don!
Does it have a certain shelf life?


#11 Guest_Tai_*

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Posted 21 August 2003 - 09:37 AM

I just use a porcelain clay slip.

#12 Mike Blue

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Posted 22 August 2003 - 07:45 AM

:D

It gets hot enough to melt the firebrick doors and the refractory inside gets very soft and runny sometimes when I'm working on wrought iron/nickel welding.  

The burner is a stainless nozzle.  It's oxidized over the years and the oxides have drooped over the burner opening to interfere with the fire.  

This picture shows that the burner chamber is a trapezoid.  There is a one inch thick space in the center that spreads the fire out like the paint burner flares used on propane torches.  The fire comes in on a tangent to the circumference.  

My first real shop had a wood floor.  One of the first times I had this thing up to welding heat I kept smelling wood burning.  I'm pretty careful.  I looked all around for tell tale smoke and couldn't see anything.  The smell kept persisting.  

What happened was the borax flux was running out the small back hole and solidifying into glass.  Like a hot stalagtite it kept getting longer and longer until it finally reached the floor and warmed up the wood.  I quit working to look for the source of the heat, the glass cools, no more burn.  I'd spray the floor with water to make sure nothing was on fire.  I'd go back to work, more glass, more heat etc.  I chased this thing for two days until I finally looked behind the fire and saw the glass thread.  Strange things happen to smiths.  

Things do get hot enough to run out of this firepot.  It uses propane fairly cheaply, but I'm sure its not as cost effective as the venturi type forges.  Those seem downright miserly.  

For all the work I've got done with this forge, I'm ever grateful to Alfred and Howard for their ideas about how a forge should work.  

And, it's a very cool fire to just sit and stare into....

There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves. Will Rogers

#13 John Frankl

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Posted 24 August 2003 - 01:30 AM

The trapezoid appears to be a "pre-burner" to insure complete mixing and combustion.

Are you piping in propane through a needle valve or a standard gate valve?

On castable refractories, I have been told that the higher the temp. rating the more durable the material, but the lower the insulating capacity. IOW, the high alumina is rated to 3,000 degrees and is nearly buttet proof, but it sucks up a lot of heat and gives very little back. A standard castable rated to 2,300 degrees insulates much better, but it is somewhat fragile (not like kaowool, but relative to the high alumina). 2,500-2,700 is a compromise in terms of durability and insulation--Does this concur with other peoples' understanding of castable refractories?

Thanks,

John


#14 davidmorganesq

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Posted 25 August 2003 - 09:13 AM

I think that this may depend on the type of burner.  The venturi I am using produces a tight, contained flame, wheras I get the impression that blown burners produce a wider, 'softer' flame, although I've never seen a blown burner working outside a forge.  If the gasses are exiting a burner at a lower velocity, my guess would be that they have more time to spread out and billow about before loosing some of their energy to the general forge environment.  Also, there is a lower limit to the space you can heat with a single burner when using venturis- if you want to heat a longer length, you have to reduce the diameter of the chamber, which will bring the burner closer to metal being heated, again increasing the difference between the heat close the burner, and the ends of the forge.  I figured that by using a tangental flame distributor type arrangement I can keep the overall volume of the forge small, and therefore more efficent and economical.  I'll let you know how it works.

#15 DFogg

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Posted 26 August 2003 - 07:17 AM

Use a needle valve for the propane, gate valve has comparitively no control. You can use a gate valve for a shut off if it is rated for gas, but ball valve is better.

The gate valve for the air is an expensive and to my mind unnecessary addition unless you are using a positive pressure blower. In that case, you have the wrong blower and would need the gate valve to be able to reduce the air enough to get it to work.

Don Fogg


#16 John Frankl

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Posted 29 August 2003 - 12:56 PM

Don,

Thanks. That helps alot. I am not all that mechanically oriented--though I am happy to say that knifemaking has led to knowledge in a variety of fields I would otherwise know nothing about .... usually through the generosity of folks like you and the others on this forum.

Thanks all,

John


#17 Mike Blue

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Posted 20 August 2003 - 08:09 AM

Part of the benefit from any ceramic fiber is the "loft" in the insulation.  The dead air space inside the wool is what gives it the insulating ability.  Putting something heavy, as in refractory castible or rammable, together with the wool will collapse the air space and negate the insulating quality of the fiber material.  

It's even a risk to put the ITC100 or similar compounds directly on the wool for the same reason.  Although that would be a lighter coating and less prone to air cell collapse, I'd think the effect would be the same.  Talking to one of the local refractory experts, the infrared compounds work a little better, in her opinion, when painted on hard refractory.  I think if I was going to use soft walls, I'd coat one layer of kaowool with ITC or Macote and have one full lofted thickness layer behind that.  

Up to this point in my shop I've used only hard cast refractory insulators and hot face.  I think the ideal forge (of horizontal tube type) would have a hard castible floor and insulating wool upper.  It would be more complex in assembly that way than casting tubes.  

For simplicity, the next one I put together will likely be a castible tube, inside a light steel shell with the wool blanket draped over the top.  I think that combination is the ultimate in simplicity minimizing potential damage to the expensive wool.  But, exposed wool loft also degrades over time due to the accumulation of shop dirt.  It seems less so than burning it up in the forge.  

The times when other smiths have brought their new baby forges to my shop, or to local guild meetings, for show and tell, the majority of the time they don't get to welding heat is because of the lack of effective insulation.  The radiant loss through the side walls exceeds the forge's ability to retain heat.

Although I've read about Don's vertical forge, I am not qualified to comment on anyone's experience with that design.  Their comments would add much to this discussion.

There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves. Will Rogers

#18 Mike Blue

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Posted 21 August 2003 - 12:54 AM

Don,

Oh no, I'm a very big fan of insulation.  Howard helped me build the big burner I've used since 1988 or so.  It's based on a Pendray style blown noisy dragon's breath type.  14 inch diameter 3/16 inch thick cold water casing with 3 inches of 2700 degree castible insulator next to the metal jacket and 3 inches of castible hot face on the inside.  About 8 inches of usable tube, but over the past six months things are sagging and bubbling a bit.  I'm getting my mind around building something new with venturis.

Still, it's been a workhorse.  It takes about 30 minutes to get to welding heat.  The thermal mass is what I like.  I can throw a cold ten-fifteen pound billet into the fire whole and not pull the heat down very much at all.  

I used to have some old kaowool blanket laying over the top to trap more heat.  I haven't noticed any change in the outer casing.  If I take it apart, I'll look for degradation.

There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves. Will Rogers

#19 DFogg

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Posted 21 August 2003 - 10:51 AM

The ramable is premixed and comes wrapped in a plastic bag, but once you open the bag it can dry out. The best way to use it is to share it with someone. One block is enough to do several forges.

Don Fogg


#20 Billybob

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Posted 22 August 2003 - 09:36 AM

hey, this is just a thing i have done to put ITC100 or stainite in a forge.. i make a thin mix and spray in in the forge with cheap sand blaster..just blast it on the kowool,,




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