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MarkH

Open charcoal forge in shop?

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Hi, I'm new on the forum but not necessarily new to blade making. I'm currently in the process of getting a forge set up in my shop. I am looking for a pretty quick and dirty build just to get going. I have been bouncing back and forth between which fuels to use as that will seriously impact my design and how easily the forge is set up.

 

My main question is "What is the common opinion of little to no ventilation on forges, inside a sizable shop with air circulation?" I was assuming that a blown propane forge would be alright. But from recent searches I've been hearing that propane really needs to be ventilated. My next thought was charcoal, which I am very familiar with in a small forge. Would that cause many problems? Would some type of venting be needed? I know it burns clean, but clean enough to be open?

 

Just wondering everyone's opinion on the matter, especially from the ones with a safety minded approach. (my shop also happens to be my place of employment, don't want to get the boss in trouble)

 

I have another question, which may best be saved for another topic, but what design would someone recommend for a forge design capable of welding, heat treating, and shaping swords up to 40"? I work at Castille Armory, which is a sword maker on the U.S. west coast. Mostly stock removal on our blades. having the ability to forge would be a good asset to have for us.

 

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In any case you should have a carbon monoxide detector.

That charcole burns "cleaner" than coal does not mean no carbon monoxide.

The same is true of propane.. I run a Blown Forge with a Ribbon Burner inside my shop. It is 42' X 60' with 12' ceilings. I still have a carobon monoxide detector.

It does not go off even when I am running a reducing flame for fluxless welding.

 

Check out the attachments at the Forge Supplies page on my web-site.

 

Let me know if I can help you.

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All forges produce carbon monoxide. There are people just about every year who kill themselves buy trying to burn a charcoal grill inside their house or apartment. You will have to have good air exchange with any type of a forge. The carbon monoxide detector is a real good idea and in an industrial setting may well be OSHA required.

 

A solid fuel forge can handle irregular shaped pieces better than a gas forge because the solid fuel forge is open and a gas forge is a fire inside of a tube. However, it is easier to see the work inside of a gas forge and a gas forge is a lot cleaner to run.

 

Doug

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And for your other question, you should have (at least) 2 forges. One for shaping and welding, another for heat treat. You can only weld or shape so much metal at a time, so you don't want to be heating a whole sword sized forge when you only need 4 inches hot. And when you need to get the whole thing hot (heat treating) you don't need to get to welding temps. But surely you already have the means to HT the swords you're currently making, yes?

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I'd sayif you go with a charcoal forge you probably could get all the functions you need although it'll be a bit tricky. Also I would say you would need a hood for a charcoal or coal forge just for the smoke they initially put off at first. For a carcoal forge you could probably make a V channel long enough for heat treatment with a movable stop to shorten your forge for general work and welding with a tube running along the bottom with holes either with a twistable inner tube to again shorten the air flow to the fire size needed or more tedious multiple tubes that are easily interchangeable. I've done this with a 55 gallon drum lined with baked clay and some fire brick but mine was rudimentary and done when I first got into smithing anyway I hope this helps and definitely invest in a carbon monoxide detector always wanna be safe from a silent odorless killer.

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I really appreciate all of the input. I hadn't thought of a Carbon Monoxide detector, so that's a big step in the right direction.

 

To answer Jarrod; we have all of our heat treating done by a separate company to solid bars, which we then cut out the blade blanks with a water jet. This system suits our needs for making blades for sport, definitely not fully functional cutting blades.

 

At this point it is down to what regulations ill have to follow and how much extra mess my boss wants to deal with :rolleyes:. I have a few designs in my head I can make for a charcoal forges. I'm pretty much lost on propane.

Edited by MarkH

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The heat treating of a long blade is a different challenge than the HT of knives and it requires different (or at least larger) equipment. A gas forge is just a can, filled with a heat resistant material and a burner. If you have some fab skills, a forge is pretty simple.

 

This thread is one I wrote on a simple blown burner, and Chris Price wrote this one on building the forge.

 

I understand the allure of forging, it is certainly one my favorite things to do, but it's not the only way to skin the cat. If you are going to forge in a closed space, a forced air ventilation system is a good idea, just a big fan exchanging the air in the shop space with fresh. You don't want to kill yourself, and if you have anyone else in the building, you are putting them at risk as well.

 

As for shaping, welding, and heat treating, those are three vary different processes. I have three forges that I use to do them, a welding forge (horizontal, about 4 x 8 x 24), an every day forge (vertical about 2 x 4 x 6 hot area) and an 18" electric HT furnace. A lot of makers swear by salt pots, particularly for HT'ing the long stuff. You might also consider forging and grinding your blades and then sending them out to the guys you use for your other stuff to do the HT for you.

 

Geoff

Edited by Geoff Keyes

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Hi, I'm new on the forum but not necessarily new to blade making. I'm currently in the process of getting a forge set up in my shop. I am looking for a pretty quick and dirty build just to get going. I have been bouncing back and forth between which fuels to use as that will seriously impact my design and how easily the forge is set up.

 

My main question is "What is the common opinion of little to no ventilation on forges, inside a sizable shop with air circulation?" I was assuming that a blown propane forge would be alright. But from recent searches I've been hearing that propane really needs to be ventilated.

Propane forges have little risk in a shop large in size. Think about it, on Thanksgiving day, your mother just spent six hours standing in a kitchen with all four burners and the oven going away. If the forge is well tuned, all you're getting is carbon dioxide and water vapor. If poorly burning, mostly you're going to get some unburned propane, maybe a little carbon monoxide in the air, both of which can give you a headache. Of course carbon monoxide can kill, but find me the blacksmith that has died from using his propane forge. In other words, take care of your forge and you'll have no problems.

Edited by Gerald Boggs

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There are many more things going on in a gas forge than there are in a gas cooker and it is very dangerous to assume that a forge will be as safe as a cooker simply because both burn gas.

 

The "well-tuned" part is where most of the complexity comes in when referring to a gas forge.

 

For heating things with flames, the flame needs to be hotter than the thing that it is heating because heat transfers from areas of high temperature to areas of low temperature.

 

For cooking, the thing being heated (the food) tends not to need to reach a temperature much above about a couple of hundred degrees Centigrade; around 400 degrees Fahrenheit. None of the common fuel gases will sustain a flame at temperatures this low, so it's fair to assume that if there is a flame present, it is hot enough to cook with.

 

The steeper the temperature gradient, the faster the heat transfer, so higher flame temperatures are better for efficiency. The highest flame temperature for each of the common fuel gases tends to be at around the stoichiometric air:fuel ratio. This is the air:fuel ratio at which all the fuel and all the Oxygen are consumed with neither fuel nor Oxygen remaining.

 

Moving either side of the stoichiometric ratio, the flame temperature reduces because there is either excess air or excess gas to be heated to flame temperature and this takes some of the energy released during combustion.

 

If we have excess gas, we don't get complete combustion and produce some Carbon Monoxide, a toxic gas. If we have a small amount of excess air, the flame temperature is still very hot and there is enough energy to cause some of the excess Oxygen to combine with Nitrogen and form Oxides of Nitrogen, often abbreviated to NOX, which are toxic gases.

 

The OP lists auto racing and modifying among his interests, so he is probably somewhat familiar with some of this. An automotive exhaust Lambda sensor usually supplies a signal to the engine management system, which it uses to adjust the fuelling and maintain a Lambda value of 1. Lambda is just the scientific notation for the stoichiometric ratio. An exhaust reading below 1 is a rich mixture, above 1 is a lean mixture.

 

If the mixture is very lean, the flame temperature is much lower. There is not enough energy to react the excess Oxygen with Nitrogen and little or no NOX is formed. Carbon Monoxide will tend not be formed either.

 

The gas cooker will therefore be set up to burn very lean. That way there is minimal risk of causing large numbers of American mothers to keel over while cooking the thanksgiving turkey. The reduced heat transfer efficiency is generally felt to be an acceptable price to pay for this.

 

Wikipedia lists the CO concentration near properly-adjusted gas cookers as 5-15 PPM whilst OSHA place a long-term exposure limit of 50 PPM of Carbon Monoxide on workplaces.

 

We tend to need higher flame temperatures for forging than a very lean flame can provide. For welding, we tend to need temperatures that can only be reached with mixtures quite close to stoichiometric.

 

When we have Oxygen present and high temperatures at the surface of our steel, we get scaling and decarburization. We tend to consider this undesirable, so usually run our forges with excess gas instead.

 

This means that we are intentionally operating our forges to produce Carbon Monoxide.

 

Most of the Carbon Monoxide produced in the forge leaves the mouth of the forge and mixes with air, where it burns with Oxygen to produce Carbon Dioxide. This burning is often referred to as the dragons breath. Because the mixing is uncontrolled, parts of the mixture will cool before combustion is complete, so some of the Carbon Monoxide will not be burnt and will remain in the air.

 

I am less familiar with solid fuel combustion than I am with gaseous fuel combustion, but production of some level of Carbon Monoxide is pretty much inevitable when using a coal, coke or charcoal forge, or even when burning wood. Wikipedia lists the CO content of the exhaust from a typical home wood fire as 7000 PPM.

 

The received wisdom is to put forges outside.

 

If US workplace safety legislation is anything at all like ours in the UK, there will be an obligation on your employer to assess the risks and control them to an acceptable level: killing the workers is generally frowned on. I assume the OSHA workplace exposure limits will need to be met for all substances likely to be present, including Carbon Dioxide and Oxides of Nitrogen.

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Way too long for me to read, could you point out the number of times a gas forge has been the cause of poisoning? Because with thousands of folks doing something without having something bad happen, where is the risk? I've worked in a number of shops, and except for the summer to vent the heat, we never had the doors open or concerned ourselves with ventilation. The fire inspector's during their inspections didn't even address it as a safety concern. They did point out the need for quick releases on the fuel lines, so they were aware of the forges.

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Way too long for me to read, could you point out the number of times a gas forge has been the cause of poisoning? Because with thousands of folks doing something without having something bad happen, where is the risk? I've worked in a number of shops, and except for the summer to vent the heat, we never had the doors open or concerned ourselves with ventilation. The fire inspector's during their inspections didn't even address it as a safety concern. They did point out the need for quick releases on the fuel lines, so they were aware of the forges.

 

I would suggest that judging the inherently unsafe and un regulated actions. Of a lot of "by thier nature non risk adverse" blade smiths as proving that something is not risky? I find that a pretty odd conclusion.

 

No one had died yet that you know of? could well be. and I am glad of that if that is the case.

 

I have had my welding forge set off CO monitors when I used it in my closed off forge (with a man sized door open). I now open the vehicle sized door and have extraction.

 

If you take it wider then people die every year from CO from gas and from solid fuels, so the risk is real and its there and its probably small and its defiantly worth taking steps to avoid.....

 

Most of what we do is potentially lethal....just saying......the risk is there .

Edited by owen bush

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I have had my CO detector go off in the past. Depends on what you are doing, for how long, size of area,ventilation etc

One time was with a charcoal forge and two propane melters during a class. Improved ventilation took care of that in short order.

 

In fact I recall returning my first Monoxide unit a few weeks after purchasing it because it had gone off twice and thought it defective. It was not...my assumption of ventilation was the defective portion in the equation.

 

Ric

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Mark,

The problem with a question like this is , some will do it correctly and for many reasons, some will not. I have used a solid fuel Coke/charcoal forge inside for 37 years and my carbon monoxide alarm has never gone off. I use 14" diameter flue pipe in a metal building and a hood right over the fire. Due to a predictable wind and breeze direction ( around the building) the hood always draws the smoke from the fire area. The forge is made of steel and every leave of the room includes a check to make sure no combustable materials are left near the forge fire ( wire brushes or any other wooden handled tools). After every day of forge use I go into the forge after dinner and do a fire check before falling asleep.

 

I would look at some of the Japanese sword forging videos and estimate the size of their duct work. My guess is fire is equally as dangerous as CO.

Jan

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One one of these sites we did have a person that posted that he closed in his forge building for the winter. One day he went out to work in the forge and the next thing that he knew he was one the living room couch without his boots or glasses and feeling like hell. He found his glasses and his boots out in the forge. Evidently he was working and was overcome by carbon monoxide and removed them for some reason. Maybe to lay down on the floor. If so it it lucky for him that he decided to get up and move into the house or he could well have died. So much for the idea that one will notice symptoms of carbon monoxide poisoning as they happen. He sure didn't. The fact is that he came close to killing himself. It's something that you may only get to be wrong about once.

 

Doug

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I would look at some of the Japanese sword forging videos and estimate the size of their duct work. My guess is fire is equally as dangerous as CO.

Jan

 

I don't know if flue size on your forge will follow the same equation as the one we use for masonry fireplaces, (I can't imagine why not) but this is how the flue is sized for a solid fuel fireplace to make the drawing action work well for smoke and gasses. Take the area of the opening at the hearth and multiply by 10%-15%. That gives you the proper area of the flue pipe. Larger sizes let too much heat escape up the flue, smaller ones don't draw well.

So, if your forge has a full hood that extends down to the floor (where the fire is burning) and an opening for easy access to the fire, take ~12% of the area of that opening and you have the size for the flue pipe. A opening roughly 6 inches wide at the top, 15 inches wide at the base, and 18 inches tall is roughly 189 square inches.12% of that is ~23 square inches. 23=pi(r^2) tells you that the diameter of the flue pipe is about 7 inches. Using the 10%-15% rule says that any pipe from 6-9 inches will work.

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Joshua,

 

Thanks for bringing that up....but I am a simple guy and without specific examples and or diagrams I am a little lost.

Jan

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It seems to me that a coal/charcoal forge is most likely going to be ventilated with just an over-head hood (no side/back walls). The flare of the hood should be a little larger than the fire pot and that width is about the same as 'A' in the drawing. That flare leads to a chimney that has an area of 15% what the flare's/fire pot's area. Based on Joshua's post, I would think this is a likely design (about 1 minute in MS Paint, didn't think this required SolidWorks).

 

Forge_Flue.jpg

 

Please note that the equation on the right is for the areas, but the labels on the drawing looks like linear dimensions. As an example to (hopefully) help clarify things:

If your fire pot is 10" diameter, your flare could be 15" diameter. Flare area is therefore 3.14*(15/2)^2 = 177 in^2.

Your chimney thus needs to be about 177*0.15 = 26.5 in^2

3.14*(x/2)^2=26.5 ==> Chimney diameter would be 5.8"

So go get some 6" diameter pipe and enough sheet metal to cut and bend a flare.

 

Again, just trying to hopefully interpret Joshua's comment into a possible design. I very well might be wrong!

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You are! An open forge hood needs a much larger pipe than a mostly closed fireplace because that hood will try to suck all the entrained shop air along with the smoke. A 12" flue with a minimum 24" flare is normal for suspended hoods on coal forges. Charcoal does not smoke so much though, so a large roof vent could work fine as long as the sparks are not a problem.

 

You could also go with a side draft hood (Google the "super sucker" forge hood). I built a variant of one of those with a flattened expansion chamber to fit a narrow forge table. 8" x 10" fire pot, 10 x 10 hood opening, 30 gallon or so expansion chamber with a 12x16 exhaust into a 12x12 flue about 16 feet tall above the exhaust. Preheat the chamber with a sheet of newspaper and I get zero smoke in the shop even with green coal.

 

All that said, I strongly suspect OSHA and your insurance company are going to be the biggest problem in a commercial shop.

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Ah see! I took Joshua's closed off version and tried to apply it to an open version. It seemed too small to me, but I've only ever used dust extraction that was fan driven. I also know that distance away from the smoke source is going to be a big factor (2 feet above your fire is very different than 15).

 

But yeah, in a commercial shop OSHA (or OROSHA as you're in Oregon) will be the big concern. Fortunately they tend to be really nice about giving you the information if you ask ahead of time. Explain what you're wanting to put in and they should be able to tell you what you need to do for ventilation. Not design a system, but let you know about certifications and possibly recommend somebody that can help you meet their requirements.

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Thanks Jerrod,

 

I cannot imagine going with less than 14" in diameter..even at that I sometimes improvise a sheet metal curtain to avoid side drafts , temperature of the gasses is not that high.

 

Jan

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For clarification, I was thinking more along the lines of this type of hood/flue condition.

 

coal forge.jpg

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Do some searching for "Hofi forge hood".

 

I've heard good things and I'm going to try it when I rebuild.

 

If your forge is near an exterior wall, you don't have to cut a hole in your roof.

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If your forge is near an exterior wall, you don't have to cut a hole in your roof.

 

If you make it at 14" diameter plus, many of your solids in the flame will drop out in the horizontal section.

Jan

Edited by Jan Ysselstein

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CO gas is slightly lighter than air, but it diffuses in air, raising the amount of CO in the air. Because it is heated by the forge, it will accumulate at the highest point and fill down like an upside-down swimming pool.

Your body might be getting fresh air from having doors and windows open, but your head could be in this bubble of higher CO concentrated air. I don't like running a forge inside unless it's under a hood and properly designed, but with a propane forge a large vent fan that can suck air up and out of the shop is good to have. It should be able to clear a smoky shop in a few seconds.

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