Latticino

Wrote a long involved response to this which unfortunately go lost to the posting gremlin. Don't have time or energy to repeat myself, sorry. Gist was that for a blown burner the mixing tube diameter is more a function of the blower selection than the forge size. The burner outlet is another case, as the diameter, or number of ports, or flame retention style nozzle needs to be able to operate at the correct velocity for the quantity of fuel/gas mixture you need to produce the heat. Bottom line, my recommendation is to take a good look at the simple Don Fogg design, use few long sweep elbows, add a normally closed solenoid valve if you ever plan on walking out of the room and leaving your forge on, use a multi-port (ribbon) burner head or some form of enlarged flame retention nozzle and the 1-1/2" or 2" mixing tube should be fine.

Alan, Honestly I've never fire cured my rigidizer, so can't comment on that. Since I only used one layer, the air cure worked fine for making it solid enough to support the inner liner of refractory. Then when I fired the refractory slowly I assumed that both layers got fired together. I expect that you could fire the first layer of rigidizer inside your shell with your burner. The underlying blanket does not need to be babied as far as heating rate goes (one of the big advantages of blanket).

Sounds to me like you are on a good path (provided you mean two 1" layers of refractory blanket). If you are concerned about longevity and cost tradeoffs I would certainly see if you can get the inner layer of blanket at 2600 degree rating and the outer layer at 2300 degree rating. It really only depends on what the inner face will be exposed to. The direct flame impact zone will be hottest (directly in front of the flame) and that could be up to 3000 deg, so I usually err on the side of caution and use the higher temp blanket for an inner layer. I also like to use some form of castable refractory as an inner liner; after the rigidizer and before the IR reflective kiln wash. I have used a number of different materials including MIzzou, high alumina refractory (like Greencast 97), and multiple layers of high temperature furnace cement. The first two do add more thermal mass to your forge, which is a mixed blessing (longer to heat, but holds heat better when the door gets opened or masses of metal get put in - kind of like a heat battery). I've never done two layers of blanket with rigidizer in between each layer. Not saying it is a bad idea, but not completely sure why it is a good one. As I understand it, the intent of the rigidizer is to capture the blanket fibers after they heat and become more friable as well as maintain the overall thickness of the blanket (from crushing) and the general shape of the forge chamber. Not sure how an intermediate layer helps there, but guess it could contribute to structure if nothing else. Hard brick splits are not the worst thing to use for a forge floor, provided that you put the same layer of insulation under them as you have in the forge walls. It is when you use them as a floor without any backing that they draw the heat right out of your forge. They won't have the same kind of resistance to flux damage that a high alumina kiln shelf does (check with a local potter, they may have broken shelves that are just the right size for you. Shelves can be cut with wet diamond wheel tile saws), but they are very cheap and can be replaced as a consumable. You can even give them a coating of Wayne's bubble alumina and they will last pretty well. I've had pretty good success with a loose casting of Mizzou for a floor that is pretty resistant to flux damage as well. Your forge shape as an oval sounds good to me. If you have concerns about odd shape forging you might want to consider designing a side door that will open to allow shapes like that to be heated. Good door design is tricky though and something I still struggle with. Just remember to put something directly opposite the burner outlet that can take the extreme heat of the flame.

My concern isn't just with turning the air on before the gas (which, of course is the correct policy, as is turning the gas off before the air). Even if you turn the air on first, if you happen to have a blower that is out of alignment, or has an arcing electric motor for some reason (say loose brushes) if the gas is introduced into the blower that spark might cause ignition inside the blower. Unlikely I agree, but I didn't expect the top to melt off my propane grille regulator either...

I'm planning on doing this with my updated gas forge as well. A couple of suggestions from my experience with using these thermocouples and covers in glass furnaces: Thermal expansion can be a problem. The metal will expand and shrink at a different rate than the ceramic sheath. Suggest you wrap the exterior of the sheath with refractory blanket and leave a reasonable gap between it and the metal tube holder. I'm not sure how well the sheath will respond to rapid thermal cycling. My glass furnace ran continuously and used to warm and cool over a period of days. Keep an eye on it and look out for cracks. Type K thermocouples aren't really rated for the high temperatures you will see in a forge used for forge welding (type R or S are better, but quite expensive). I'm not sure if mine degraded quickly due to the temperatures, but they certainly don't last long term. The thicker the thermocouple wire of the thermocouple itself the better. The tips start to look glassy when they are failing. You probably know this already, but you can't just wire it to the pyrometer with regular copper wire. It needs to be wired up with special thermocouple wire, as used for type K units. An inch or two inside the inner wall should work fine. You won't get a highly accurate reading, but you should get relative data that will be helpful (i.e. when the thermocouple reads 1500 deg. F the knife blank has just hit the transition zone, the blank might actually be at 1450, but it is all relative anyway) Good luck, post photos when you finish.

Frosty, If you are being conservative regarding safety, please don't suggest that the blower interior be used as a mixing chamber unless it is a piece of equipment specifically selected for this purpose (i.e. spark-proof construction and special motor). The typical Dayton squirrel cage blowers that many folks use certainly aren't, and I'm sure you would hate to hear about someone having their blower explode. I'm not saying that it is likely to happen, and the gas air mixing via the impeller is certainly an attractive option, just prefer to err on the side of caution. In my experience, with a multi port burner outlet (ribbon burner or the like) and a couple of pipe diameters for the mixing tube, there is more than adequate premix for these burners without having to resort to mixing in the blower.

Good one. Someday I'll have to write something up for forge blown burners specifically. Unfortunately the burner assemblies I have the most direct experience constructing and tuning were made with industrial components and might be a little prohibitive cost wise for the casual hobbyist. I was lucky enough to be onsite for a "dumpster dive" when a local university was upgrading their glass studio and got a lot of commercial grade equipment before it ended up being scrapped. Free is good! I reconfigured these components to build my own low pressure natural gas/ forced air burners, which included some that were PID controlled for full ramp and soak temperatures, with zero pressure regulators (for single point control of mixing range), high and low pressure gas safety valves, pilot burners and UV flame safety sensors. My current forge is a little less complicated, but the Eclipse components I'm using are still kind of pricey. I have also been responsible for upgrade and maintenance on a number of "home built" systems, but they weren't specifically my designs. These latter were the more conventional "Alfred" burners that utilized simple Tee fitting mixers with drilled orifices and squirrel cage blowers. There are great sketches of their construction in Dudley Giberson's glass facility design guide as well as Henry Halem's books (which I believe shows an enhanced design with things like zero pressure regulators and an idle circuit). I could scan and post them, but I'm not sure about the whole copyright issue involved and would prefer to err on the side of caution. I do have my own thoughts about things like blower selection and use as well as the relative ease in building and tuning a blown system. Hopefully I'll get a chance to share them with the group sometime in the future.

There are two conventional types of natural gas fired Makeup air units: direct fired and indirect fired. The former has the combustion operating right inside the breathable airstream while the latter has a heat exchanger where the essentially sealed combustion occurs outside the airstream and the heat gets transferred in through the metal walls of said exchanger. Needless to say the indirect unit is less efficient as well as being more costly and prone to failure. Because of this, many industrial facilities use a direct fired makeup air unit, but that is not the case in all locations. There are some drawbacks to the direct fired units, including adding the combustion products to the ventilation air as well as the associated water vapor (believe it or not some companies are more concerned with condensation on the walls of their insufficiently insulated buildings then their employee's potential breathing of combustion byproducts). Be that as it may, you are correct that the vast quantity of air being introduced by the direct fired makeup air unit far overshadows the relatively minor amount of combustion byproducts added to the space. You also have (or should have) additional general exhaust in your facility as well as specific vehicle exhaust (that connects right up to the vehicle exhaust pipe). As a reference the current International Mechanical Code requires a ventilation system that exhausts and makes up enough air so that the open side of a paint spray booth has a capture velocity of 100 ft/min. This means if the open side of your booth is 12' x 10' Hi you need 12,000 CFM of exhaust and makeup air during operation. If it is 0 degrees outside and the makeup air needs to enter the building at a minimum of 65 deg. F for comfort, this means the direct fired unit needs to add 842.4 MBH to the air. That sounds pretty substantial, but if you consider that an indirect system is likely only 80% efficient, that system will need an input of 1,053 MBH to deliver the same amount of heated air (with the associated ongoing cost). I'm not going to do the combustion calculations regarding the CO byproducts of burning 842 MBH of natural gas, but have been assured by manufacturers that the dilution factor takes care of it. Needless to say it is different if you have a (3) burner forge in a 20 x 20 shop with each burner outputting 70 MBH (like a T-rex at 30 psi say) and limited ventilation... Probably wish you hadn't asked this question now

No idea as yet what made it let go. Have to take a close look at it, but the whole top cap disappeared and there was a good 6" of flame shooting out of the top of it, roasting the interior of the grille compartment (of course the flame was around 50% yellow in color, so Mikey wouldn't rate it as an efficient burner at all . Fortunately I was nearby when it started and noticed the change in sound, or it could have been catastrophic. Still a lesson for propane forge builders to use a good quality regulator, not the garbage that is sold with a propane grille.

I was talking about ribbons. I've used multiport burners (ribbon or similar) on blown systems in the past and can certify that they are typically quieter than single port systems. Haven't used a multiport burner tip on an NA system yet, but know that Dudley Giberson has one and expect that it would be quieter as well. The back pressure of the multiport head may change the induction capacity of the NA burner, so further design development may be required. Don't get me wrong. I like the convenience of a NA burner, but I like the ease of not having to fill propane tanks and the relative cost differential of natural gas even more. I also had a propane tank regulator failure in my gas grille the other week with flames shooting out of the top of the regulator (no idea how that happened, but the plug looked like it blew right off) that scared me silly. Fortunately I was able to spray it down to keep it cool and get a high temp glove to shut off the main tap. Each to his own.

Or noise, or gas line pressure (say if you are running low pressure natural gas instead of bottled propane), or if your local requires a safety system with a purge function...

Couple of scratches here and there, but they are not obtrusive. Nice form, pattern and burl. Bet it sells for you.

Sounds like a great candidate for a low carbon body hammer with forge welded tool steel facing. Grab some truck leaf spring and go to town.

Unfortunately both have been used as a standard abbreviation. However, these days (as counterintuitive as it seems) MBTU typically refers to thousands of BTU and MMBTU refers to millions. Also I believe that typically burner ratings are in BTUH (BTU per hour) or MBH (thousand BTU per hour). If you are in contact with the company, I would ask them for clarification.

Alan, Actually I was quite impressed with the design and analysis you have come up with. I am also not a huge fan of in flue extractors (as you can see if you read my posts). I've been forced to employ them for some large boiler room systems I've designed and typically find them finicky, difficult to tune properly, prone to failure and sensitive to control drift. I try to avoid them whenever I can, and that is when they are expensive industrial systems with unitary computer controls. It appears that you also understand the different challenges for a smith as regards solid fuel fired forges (which typically include some sort of capture hood) and gas forges (which often do not). With a properly designed hood and stack I'm definitely in favor of the natural chimney exhaust and directed makeup air that you advocate (as noted in my fist response to the OP). However with forges that don't include decent capture hoods I think that powered exhaust is the best choice, at least for the budget hobby smiths that appear to be the bulk of the members online here. Of course you can still direct your makeup air to advantage. In my old glass studio I built an insulated enclosure that confined my furnace and glory hole with reasonably small door openings to access the working ports. That entire enclosure was exhausted and the makeup air for the shop came in from a window and cooler parts of the facility. The only studio I've been in that was more comfortable is the one down at Corning that is air conditioned. Proper location of makeup air openings can make your life a lot easier, and a fan to direct that air where it serves best certainly helps as well. I'm flirting with the idea of designing a combination door system and slot extractor hood for a typical gas forge. Just a pipe dream right now, but I think it could be an interesting option.

Well, I am a ventilation professional, for what that is worth. The positive pressure system has both benefits and drawbacks. The former you have described well. Note however, that overall facility smoke or fume purge is not the target use of a blacksmith shop ventilation system. If you get contaminated that far you presumably have other problems. The more standard exhaust system (which incidentally is also used for atrium smoke control, a similar high ceiling space) is designed to extract fumes before they reach the breathing zone. The air replacement is still with clean air (provided your air inlets are not set adjacent to your exhaust), as all the air exhausted must be replaced by something. The key advantage for an exhaust system is that you can target the location of the air being exhausted. This isn't as much an issue if your only building opening is the hood above your forge (where positive pressure will work as you have described), but if you have a gas forge (as the OP indicated) you may not have a hood at all. In that case I still recommend that the smithy be exhausted from a high point (the roof fan selected is a good option) and ventilation openings be brought in at the code required high and low position. Note that some engineers even have high and low fume extraction systems (common for car maintenance shops for instance), but in this case your fumes should all be hot and rise up to the smithy peak. Please note that in my original post I indicated that the exhaust fan system can interfere with the chimney effect in a hooded forge and needs to be used with care primarily as a supplement for heat control. In this case the building openings need to be large enough to ensure that the makeup air preferentially enters via these openings (low static loss across the openings) and the stack should be drawing strongly before the exhaust is turned on. Also note that the 10 ACH is a good rule of thumb for the minimum to provide adequate ventilation. It is not a caveat and the code minimums for your area as regards combustion equipment ratings and occupied space ventilation requirements should still be followed. I personally have on the order of 30 ACH in my shop, utilize a passive turbine vent year round and keep a CO monitor in my working area. For a sidewall exhaust there is minimal cost in adding excess ventilation, and plenty of side benefit. As far as being concerned about the quantity of air for a fan, they are sized with two parameters: airflow and external static pressure (i.e. 1,000 CFM at 0.25 inches WG). These are available in a fan chart or table for a specified fan. For a sidewall fan the static losses are minimal, and provided you have large unobstructed openings for makeup air (or can make them by opening windows and doors) you should be fine with something on the order of 0.15 to 0.3 inches of WG external static at the fan.

Nice art project. As a forging hammer I'd take a 2 lb. Harbor Freight drilling hammer or 3 lb. crosspeen with a wooden handle, 32 oz. ball peen or even a decent carpenter's framing hammer over that any day. Not completely sure where you got the idea that solid steel rod makes a good forging hammer handle. Perhaps you have put this in the wrong section of the forum and it belongs in the "Metal Sculpture" section. If so I think the second version that you have a photo of is headed more in the direction of the comic book version of the Mjolnir, if that is what you are after. As far as phone camera tech, some older phones need to be put into USB sharing mode (and the photos typically come up in a windows folder titled DCIM)

Personally for a very functional mini forge I used a standard 1 gallon paint can and lined it with 2" of high temperature ceramic blanket, rigidizer and a final inner layer of high temperature refractory cement (applied in several very thin layers). I then cobbled together a 1/2" Frosty T and it appears to work pretty well. Haven't got enough miles on it to be able to talk about longevity or ultimate temperature, as it is just prototyped at this point (need to finalize a stand, doors and burner support), but the whole thing must have run me under $30 as I had the scraps of wool, a regulator and hose laying around from another project. So far I think I have about 2 hrs. worth of assembly time in, so not sure if you could make a 2-brick faster (but if you do be sure to buy extra bricks).

IMHO forge efficiency is related to several variables: interior volume, insulation quality and door design. The first is a function of the size of work you want to do. The second is an interesting variable as better insulating quality (lower thermal conductivity) is often indirectly related to material density, but some material density is helpful if you are going to be working up to a significant thickness (as the mass of cold metal will significantly cool the forge interior every time you put it in). It becomes a trade off on whether you go with light weight high temperature insulating blanket material, medium weight insulating fire brick, or relatively heavy weight insulating castable material (not castable refractory, castable insulation). In my experience it is a good idea to combine these materials and use the appropriate ones for appropriate parts of the forge. I have found that insulating fire bricks don't hold up for me (my gas forge made with 2300 deg. F insulating bricks only lasted (4) firings). The surface doesn't do well with direct flame impingement, and they don't handle thermal shock well either. Perhaps on a smaller scale they would do better, or maybe the Atlas forge uses better bricks. I don't have the data handy right now, but if I recall correctly insulating brick doesn't have as low a thermal conductivity per inch thickness as blanket, though likely slightly better than most high temperature insulating castable. As far as door design, it doesn't look like the Atlas forge has any at all. Needless to say, door design can vary quite a bit if you have a NA or blown burner. The former doesn't use electricity, so you don't have energy loss there, but the latter can have a much smaller door opening, so you lose less heat. An idler circuit, or some kind of forge temperature control, will also save you gas, if that is your key criteria. Personally I think the time you use doing the forging is the most expensive commodity you spend, so I would say an efficient forge is one that allows you to work most effectively. If you get one of the Atlas forges I'd be interested in hearing your experience with it.

Wayne, Very curious why someone from NM would have any interest in a Mexican restaurant in middle Ohio... isn't that kind of like someone from Japan going into a sushi restaurant in North Dakota?

Heavy, yes. Potentially an interesting art piece, sure. Hand hammer??? There I have my doubts. What happened to the picture of your rebar hammer? Would love to see one of it on a scale with the weight showing as well as one showing you using it for forging.

Unfortunately this is an awful option. This same question has been asked many times. I urge youto read through the anvil forum to find much better alternatives.

Take care moving the rolled socket back out. Work at tool steel temperatures, just in case. Keep the blade side cool, if possible, re heat treat if not. Don't water quench, just in case is all high carbon. That's all I got, good luck.

Wet tile saw (diamond wheel) works great also if you have access.

Glad to help. Please post photo of repair when done.