Forges 101

[VainEnd84]

I have a question about volume displacement of large stock in propane forges, and designing a forge for a specific task.

I have been asked to make 3 30lb sledgehammers where the length of the head from face to face not exceed 8" which means the dimensions will be about 4.25"x8" which has a volume of 113.5 cubic inches.

My question is how large of a forge would I need for this size of steel to not have a large negative effect on the function of the forge?

[Mikey98118]

It depends somewhat on the forge shape. I would go with a box shape forge, with maybe a third larger capacity than the work. Whats more I would make it a brick pile forge, which is usually the best solution of for short runs of special work pieces.

[VainEnd84]

Cheers mikey, another question, I already have a large amount of ceramic fiber blanket, ridgidizer , and castable refractory, could it be possible to make a form and make "bricks" my self? Or should I just spend the $15/brick?

[Mikey98118]

6 hours ago, VainEnd84 said:

$15/brick?!? You"re being robbed!

There are a few guys on eBay selling K26 brick, dirt cheap, with shipping charges even cheaper. Two or three years back Frosty and I were discussing building our own tough super insulting bricks for making brick pile forges; they would not have been anywhere near as good as K26, and nowhere near as economical. This is why it frustrates me to have to bring this new brick back to people's attention over and over. Its kind of like the joke about a guy who discovers a money tree and says "I'll pluck you tomorrow. I ain't gonna work my first day in Chicago."

 

[Mikey98118]

"he last widely-adapted innovation with farrier forges came with the introduction of portable gas models."

This is the opening statement in an article from Farrier Magazine. When applied to gas forges in general, this statement is hilariously wrong. Even as regards commercial forges it can't stand up. Chile forge is quite up to date, as are about half of the available import forges. It does apply to most well known forge models, unfortunately. Then, the article goes on to quote one manufacturer as stating that 2400 F is as high as gas forges get; maybe his do, but I've had two different people tell me that they read their forges temperatures at 2750 F before they had to remove their damaged probes from  them; that was while burning propane; propylene burns much hotter. When listening to 'experts' its always a good idea consider the source!

 

[Frosty]

1 hour ago, Mikey98118 said:

"he last widely-adapted innovation with farrier forges came with the introduction of portable gas models."

Did the article mention WHEN portable gas forges were introduced? When the internet was new to us non college folk I used to spend endlessly entertaining hours surfing the patent servers. In part I was looking into propane forge burners, between fascinating distractions that is. The earliest patent for a portable propane burner regards jets to make the older ones burning brown gas run neutrally on propane. The Brown gas farrier's forge was patented not long after the Civil war. Until then gas forges were only useful as shop forges where gas was piped in. Of course you had to compress your own gas and there were patents for those as well. Of course you could use an acetylene reactor but they weren't nearly as portable as a compressed gas cylinder.

And "experts" say Salt is bad for you, keep plenty of grains close. Always. 

K 26 brick in Anchorage shipping included runs about $4.00 ea. I've been thinking about not using ceramic blanket anymore and I get it free from the trimmings headed for the dumpster.

Were I heating a .25 x 8" cylinder of steel I think I'd do it standing on end on a plinth in a vertical cylinder just like I were melting. It'd need to be large enough I could lay it flat later in the forging if I were making a shaped pein. 

Frosty The Lucky.

[Mikey98118]

Propane became widely available back in the early fifties, and butane even earlier. So it would be a safe guess that commercial gas forges that would have been classified as "portable" would go back that far. I would put significant changes in commercial gas forges as coming along yearly nowadays. What the comment points to is the closed minds of so many manufacturers. "Innovation; whats that?" Oh, I know; it must mean using replacing heat resist paint with a fancy finish that will burn off in no time at all; yeah, that's what innovation means!

[VainEnd84]

Yeah I always figured $15/brick to be horrible which is why I never entertained the idea of a brick pile for before. And I'm always hesitant to buy off of Ebay because getting some of there things into canada can be a nightmare, customs her is horrible for destroying unusual items, but I'll look into it, thanks as always for your help!

[Frosty]

Try contacting a HVAC service company and find out where they buy. I'd be very surprised if folk in the boiler business were still using old soft fire brick seeing as there's a much better product available for less $. If they don't sell they'll know who does. 

Try Amazon, I don't do Ebay either. Amazon has a rep to maintain and the legal department to make things stick. 

Frosty The Lucky.

[VainEnd84]

I have gone to HVAC companies, that's where I got my hook up about ceramic blanket, but they only know where to get 2300degree rated soft brick, the only people locally that sell 2600degree soft brick are pottery places, and they prefer to sell by the case lot (their cases for some reason have 36 bricks in them) but I will try amazon.

[Mikey98118]

Forget about using Amazon. I just looked; their brick is ridiculously overpriced fireplace and stove bricks (rated as light or medium duty). They are not the safest source for products (it's pretty much buyer beware all the way), but eBay is often the only source for goods at reasonable prices.

[Frosty]

Things change, it wasn't long ago Amazon was THE place to get K 26 for decent and E bay was iffy. Darn stuff keeps changing and nobody asks me first. <sigh>

Frosty The Lucky.

[Mikey98118]

For the last two decades I have been forced to spend more times researching parts markets then designing burners and forges. You're right, Frosty; they keep on changing

[Mikey98118]

The 0386-0403 STK-9 TurboTorch for mini-forges

 

Building miniature burners are only fun for diehard enthusiasts. Furthermore, once you get down to a 1/4” burner size, low cost propane torches can match their output for about the same money that you would spend on building materials. So as air/fuel hand torches, home built burners make little sense.

    Until recently, canister-mount torches didn’t get mini forges and casting furnaces hot enough; the problem was that their brass flame tips had to remain outside the equipment portal to keep from being melted. Stainless steel tips have been appearing on some canister-mount air/fuel torches in recent years, so that they were able to also burn propylene fuel safely (since the Canadian plant was switched over to it in 2008, all so called MAPP fuel is actually propylene). This stainless steel nozzle also allows, “dual fuel” torches to heat miniature forges and casting furnaces (coffee-can size and smaller) efficiently, through a burner portal exactly like a commercial or homemade propane burner; this also holds true for “two brick” miniature forges.

    The 0386-0403 STK-9 TurboTorch has a stainless steel nozzle, along with a goose-neck gas tube that can be positioned through 360 degrees, so that it can be aimed downward into a forge body, while the fuel canister remains upright; it can also be aimed horizontally into the side of a casting furnace while the canister remains upright.  

[Exo313]

Thoughts on the RP3T3 by Uniweld? Looks similar, but a triple nozzle?

 

[Frosty]

I took a look at their web site and I'm not clear on a few things. "Triple Twist" could mean a couple things, but I THINK the triple nozzle means there are 3 nozzles in the set. I could sure be wrong though.

I don't see why it wouldn't work, though we'll need to hear from someone who's used one for anything meaningful.

I picked up a Turbotorch set at a yard sale a couple years ago and have no doubt it'd heat a good sized forge. I have a few tips, one really small one, the medium one is what I'd call a pencil flame, the next one up would be a fine soldering/brazing tip and the large heater/ rosebud is a beast. 

I wonder how the rosebud would work in a multiple outlet burner. . . Hmmmmm. I'd hate to burn it up though, a replacement is more than $100.

Frosty The Lucky.

[Mikey98118]

Exo313,

I have seen double, and even triple tube, air/fuel torches; so long as their flame tubes (this is only one of the various names manufacturers hang on the combination mixing tube and flame nozzle their air fuel torches use) are stainless steel, they should work okay inside miniature forges and casting furnaces. But, even when their flame tubes are made from stainless steel, things "ain't no slam dunk." My torch has a single single stainless steel flame tube, which has an internal fin for helping to mix the fuel air mixture; it appears to also be stainless steel, but it could have been made of brass in a cheaper torch.

A double or triple flame tube isn't going to be easy to mount in a burner portal opening. More than one flame tube is going to be hard or even impossible to fit up with a doubling tube. My burner's flame tube is only about .030" thick. When mounted in a forge or casting furnace, even stainless steel tubing will oxidize away. Without a thicker walled doubling tube, that torch won't last very long. Also a doubling tube allows us to use thumbscrews in the portal tube to securely hold the torch in place.

What it boils down to is that "just because we can do a thing doesn't necessarily mean we should." We can get away with using a solid brass air/fuel torch mounted outside of a burner portal, instead of inside of it, by substituting more expensive propylene fuel gas for propane. We get by with one-third the cost for our torch by spending three times the cost of fuel.

We can get buy with using bottle-mount torches or bottle-mount homemade burner to run miniature forges or casting furnaces, buy being careful not to run them too long at a time, and over heating the fuel canister. But adding a hose kit so that we can run the equipment from a refillable propane cylinder, instead of exchanging propane or propylene canister for prolonged use does more than save money; it guards our safety.

So, when we burn hotter and/or longer, we want to burn carefuller

[Frosty]

Here's a thought for you Mike, maybe should present it on the side but there are other folk in the PAC NW and heck it might not be available anymore. Boeing used to have one of the most cool used and decommissioned stuff shop. Last time I dropped by there were racks and bins of construction metal drops for sale at scrap prices. 

A forge burner WILL burn the output nozzle off given time unless you use jet or rocket engine alloys. See Boeing or another aerospace company's used and rem sales outlet.

Dad and I used to shop at one in Burbank Cal. It was one of the coolest scrap/wrecking yards I've ever seen in my life, there were reject space capsules I could crawl around in. Wicked cool doesn't cover the place.

Enough side tracking, it might be worth making a call or two. Hmmmm?

Frosty The Lucky.

[Mikey98118]

Boeing Surplus was a great scrapyard, but like every other Mikey shopping heaven in and around Seattle, it closed down years ago. The land just got too valuable. This was actually a blessing in disguise (honestly); it forced me to use sources that everybody else could; that's progress, good buddy. Growing up and "flying right" just sucks  

[ThomasPowers]

Hmm my local scrapyard has a small pile of jet engine parts, I wonder if I could find any nozzle materials...Unfortunately they are probably closed over the Christmas/New Year break.

[Mikey98118]

That's just mean Thomas. Go ahead and hit me square in the scrapyard envy, you dirty rat

[ThomasPowers]

I can send you some vanes if that would help?  It's a nice small family run place but being near the small engineering University they get a lot of weird stuff at times, I'll have to post a picture of the slab of steel with a hole blown through it courtesy of the explosives program at the University...

[Mikey98118]

 Drain holes

Forges mostly come with steel shells, with the single exception of brick pile types. Most forges also have a seal coating, or solid refractory surfaces on their interiors. Rigidizer is highly recommended on ceramic fiber insulation. And rigidizer contains a lot of water, which turns to steam during heat curing. 

Drilling a little hole (1/8" to 3/16") in the bottom of the forge for some of the steam (that turns back into water) to run out of is a big help, both when cure firing the insulation, and during the years to follow. Otherwise, moisture from the air can accumulate in the insulation layers, and turn to steam when the forge is run, with no safe path to leave without damaging seal coatings, etc.

 

Well, can't that steam escape through the same little cracks and screw penetrations it used to find its way into that insulation? Water vapor can in the atmosphere can penetrate through very tiny openings over long periods in idle equipment; gradually wetting a lot of ceramic fiber surface. But steam will rapidly expand a fairly minor amount of water, with mere minuets in which to be expended before causing damage; give it a path to leave, instead.

 

A sensible box forge

So when might a steel shell amount to silliness on a forge? Let' talk  some about the w-h-y of box forges. Assuming that box forges started out as a way to accommodate straight refractory products like bricks, ceramic fiber board, and high alumina kiln shelf, Coming up with a box shape is no great stretch, right?

And most of us don't want such expensive materials wrecked, so steel comes first to mind. If you're running a busy shop that makes sense, but if that new forge is going to live in your garage or studio, I would recommend just keeping gorilla types outside of locked doors; this will save a lot of other equipment to. Just post a sign saying "no brats allowed". Keep a whip and a chair handy; brats don't go quietly.

Which brings us to what should sensibly follow in typical box forge construction:

(1) For most forge sizes: K26 bricks for floor, walls, and ceiling.

(2) A pail of refractory cement to glue the ceiling into one piece, the floor into one piece, and each wall into one piece (six parts in all).

(3) The thinnest high alumina kiln shelf you can find to cover the brick floor.

(4)   four sections of angle, and four sections of all-thread, with matching nuts and flat washers to  allow the angle to keep the floor, ceiling and walls together.

(5) a floor flange, pipe nipple, six thumb screws to make a burner port to mount on the top side of the ceiling, and hold the burner.

(6) A good burner, with valves, regulator, hose, and fuel cylinder.

(7) Four extra bricks (minus whatever bricks you left out of one wall to leave an exhaust opening in the front of the forge.

Beyond these items there can be a long list if you like, but it will all be add-ons This list is all you need to construct a basically sound box forge.

[VainEnd84]

I know that the go to soft fire brick, in terms of cost, durability, and ease of access is the k26 fire brick, bit is it actually good enough and If so why? I've been doing some research into soft fire bricks and have learned some interesting things about them recently.

The most important thing I have learned is that the temperature rating (k26 or 2600 degree rating for instance) is actually the max "short run" temperature load (short run varies by manufacturer but always seems to be less than an hour). So a k26 fire brick will start to thermally decay at temperatures at or above 2600 degrees F fairly quickly. Most seem to have a sustained thermal load capacity of about 200-300 degrees F less, which means that a k26 fire brick will only be sustainable long term for temperatures around 2300-2400 degrees F.

This turnes out not to matter in forges as much because the fire bricks start to degrade from thermal cycling before the thermal decay has much effect.

There are 4 other types of commonly available fire bricks, k23, k28, hard fire bricks, and medium duty fire bricks (in talking with some suppliers I have learned that new manufacturing techniques and materials are resulting in stronger and better insulating bricks to be available in the next few years). We can toss out the medium duty fire bricks for use in forges because they generally have a max load of 1800-2000 degrees F and are meant for things like fire places. We can likewise toss out using k23 fire bricks as a max thermal load of 2300 F and a sustained load of 2100 F they will start to thermally decay much too soon. And hard fire bricks have almost no insulating capacity so there is little point in using them either.

That brings us to the k28 fire bricks. With a max thermal load of 2800 F and a sustained thermal load of 2500-2600 F they are one of the better insulators available as far as bricks are concerned . Their biggest down fall is that they are extremely fragile and are hugely susceptible to thermal cycling. So unless you plan to rarely if ever turn off your forge (not recommended outside of industrial/production line forges) they will fail much too soon.

In the end we really are best off to use k26 fire bricks for the time being. 

Can anything be done about thermal cycling degrading fire bricks? I'm happy to say yes, there most certainly is. I had an enlightening conversation with a thermal engineer who works for a local company that deals in refractory materials. The big thing is that soft fire bricks are not actually designed to be brought up to their max temperature and cooled to room temperature more than 6 or 7 times in their life. So how can we counter act that? It's actually very simple:

1. Make them smaller, you cut the brick in half, take a 4.5"x9"x2.5" and make it in to 2 of 4.5"x4.5"x2.5"

2. Rough fit them to your final shape, in otherwise fit them to the inside of your forge shell but leave a bit of a gap between all of the bricks about 3/16"

3. Use the dreaded high temperature cement to cement the bricks together

4. Coat in a castable refractory and if you like coat with an IR reradiotor

While all of this will help the longevity of the bricks they will still eventually fracture due to thermal cycling.

[Another FrankenBurner]

Thank you for that.  I used a k23 brick as a baffle wall for about a month before it turned into a pile of rubble.  I am now using k26 bricks.  I armored one with metrikote and another with kast o lite.  I have not been using them long enough to say anything about them other then they are still currently intact with no cracks.  I have had a hard time finding them affordably.