- Joined
- Sep 23, 2006
- Messages
- 366
Greetings.
I posted this over at SFI but got only one answer; downsize. Probably a good idea, but I was hoping for some more thoughts, so here goes:
I have two forges that I'm working with, both with forced air burner. One is a relatively small vertical forge that humms up to very high temperatures very quickly.
This little bitch gets hot enough that I melted the cast iron burner tip when I had it inserted too far once, and made a puddle of iron slag on the forge floor. She has no problem running just as hot as I want at something like .5 - 2 ish psi with a neutral or fuel rich flame. Even using the relatively small (one inch diameter) burner I built, the air intake valve is almost closed to run a neutral flame, and it can be a little tricky to get a rich flame without cutting air off completely. Overall, I'm happy with this forge, and it's quirks are few.
The larger one, that I eventually want to use for welding, is another matter.
I just can't seem to get this big ho up to temp, and the interior definitely doesn't heat anything close to evenly.
I have a bigger 1.5" burner for this thing. I've tried running the air intake full throttle (same blower though, which I move from one to the other) and adjusting gas pressure for flame. This blower will give me a neutral flame in this big mutha at around 3-4 is psi, I get small yellow flames coming out both front and back doors, but the interior liner is only glowing for a 6" or so stretch in front of the flame. There is a VERY noticeable vortex effect, you can look through the doors and see the yellowness swirl at a decent velocity front to back in a fairly even thickness...
I've gone so far as to hook up my sears shop vac (6 hp) in exhaust mode as the blower. This naturally requires that I close off that intake valve a bunch and adjust my flame slowly. I've gotten the gas up to 7 psi with a neutral and a sligthly rich flame. I'm not so sure I dare open up more than that, not that I really want to be burning gas this fast anyway!
A bit more info about the setup:
I am using a 100 pound tank with a medical grade 2 stage regulator. I get very even and controllable pressure. I have a gate valve for air intake control, and two ball valves for gas, one at the buner I use to fine tune volume of flow, and another at the regulator, as a secondary emergency shutoff. I prefer ball valves for gas lines so I can kill the gas in a hurry if I need to.
Gas is fed through a quarter inch hose into a t fitting plumbed into the airflow just prior to a double burner size expansion chamber. The nozzle is the same diameter as the main burner body, half the diameter of the mixing chamber.
The big forge I'm having problems with should be rediculously well insulated. I used a keg for the outer body so I would have lots of room inside to insulate. I only cut one end off the keg. The remaining wall is integral to the keg body. That back door has a 4 inch hole cut in the center for its door / exhaust.
Inside the outer keg is two one inch thick layers of 8lb density inswool. I used a 10" sauna tube as a casting form, and filled the gap between the inswool and the 10" diameter tube with mizzou castable. This left me a 1" (or maybe a bit less) thick layer of castable refractory for a liner which has a very regular, quite smooth 10" inner diameter. I propped it 1" from the bottom / back, and had a canister filling the back door, so the whole body and back wall are one peice.
I flame cured the mizzou three times, for about 5-10 minutes each, allowing it to cool and dry overnight between. Then I coated it with ITC-100. I flame cured the ITC and when it had cooled, re coated, and re cured with ITC again.
The front door is the end I cut off the keg. This one, unfortunately is less well insulated. It only has 1" of inswool and two layers of ITC. However, to try and make up for the heat loss through the lesser insulation, I used the 1.5" hole from removing the keg pump pickup as the window on this end. I figured if more heat were radiating out of this end, I could use a larger exhaust port to pull some of the heat to the other end helping even things out a bit.
I havn't even really finished building this forge, as initial testing was so disappointing. The door is still not attached in any meaningful way, and to close off the combination, I just sort of push it into place so that almost all of the flames stop shooting out of the joint, and prop it there for this burning session.
A few observations. When I'm burning in this forge at full throttle on the small blower, or at all with the shop vac, it takes only a couple of minutes for the outside of the keg to get too hot to touch. As stated, there is a noticeable vortex effect, with an almost completely transparent hole in the flame running the length of the interior, and a good yellowish flame swirling against the outer walls for pretty much the entire thing. There is a blueish flame several inches long coming from the burner running tangent to the forge body to achive this vortex effect. The area where this flame directly impinges on the interior of the forge, as well as like two or so inches next to, and six or seven inches beyond this area glow bright yellow like the whole interior of the smaller forge, but the rest jut looks gray. This does not appear at all to be an even heat, having a very hot spot right in the middle, across the top wall and down one side, the rest being significantly cooler.
I've heated some steel in it, and it takes noticeably longer for the same peice of metal to get up to forging temp in this big monstrosity than in the much smaller vertical forge.
So the question is, as all us parents evetually ask (I got three boys, and while my eldest is only seven, I'm beginning to ask already) where did I go wrong?
I figure a 10" diameter by 16" depth is big, but not outlandishly so for a good forced air forge. I have more than twice the insulation I've seen on many other well runnung forges. I can only think of two potential problems. One, the exhaust ports / windows may not be big enough. If I'm causing too much backpressure, am I restricting the amount of flame (burning, expanding gasses) I can viably force into the combustion area? Two, the mizzou has a pretty high thermal mass. Much higher than say straight inswool. Maybe It just needs a half hour to get up to temp because of the thermal mass? From the looks and feel of it, if that's the case, I'll probably scrap that liner in favor of more inswool and three layers of ITC. I liked the castable for its relative permanence and durability, as well as flux resistance. I had planned on using a stainless foil layer on the floor to help catch flux, and have an almost permanent forge, as the small one is only barely an improvement on the coffe can design, being built out of one of those big tins they sell flavored popcorn in, and having extra insulation and ITC-100.
Or maybe, this is just too big a forge body for one burner of this size, and a big, heavy honkin burnr with a serious blower, and some serious pressure is needed. Again, I would much rather not be burning propane at 7 psi full throttle, and would rather scrap the keg for a more reasonable forge if that turned out to be the case.
I posted this over at SFI but got only one answer; downsize. Probably a good idea, but I was hoping for some more thoughts, so here goes:
I have two forges that I'm working with, both with forced air burner. One is a relatively small vertical forge that humms up to very high temperatures very quickly.
This little bitch gets hot enough that I melted the cast iron burner tip when I had it inserted too far once, and made a puddle of iron slag on the forge floor. She has no problem running just as hot as I want at something like .5 - 2 ish psi with a neutral or fuel rich flame. Even using the relatively small (one inch diameter) burner I built, the air intake valve is almost closed to run a neutral flame, and it can be a little tricky to get a rich flame without cutting air off completely. Overall, I'm happy with this forge, and it's quirks are few.
The larger one, that I eventually want to use for welding, is another matter.
I just can't seem to get this big ho up to temp, and the interior definitely doesn't heat anything close to evenly.
I have a bigger 1.5" burner for this thing. I've tried running the air intake full throttle (same blower though, which I move from one to the other) and adjusting gas pressure for flame. This blower will give me a neutral flame in this big mutha at around 3-4 is psi, I get small yellow flames coming out both front and back doors, but the interior liner is only glowing for a 6" or so stretch in front of the flame. There is a VERY noticeable vortex effect, you can look through the doors and see the yellowness swirl at a decent velocity front to back in a fairly even thickness...
I've gone so far as to hook up my sears shop vac (6 hp) in exhaust mode as the blower. This naturally requires that I close off that intake valve a bunch and adjust my flame slowly. I've gotten the gas up to 7 psi with a neutral and a sligthly rich flame. I'm not so sure I dare open up more than that, not that I really want to be burning gas this fast anyway!
A bit more info about the setup:
I am using a 100 pound tank with a medical grade 2 stage regulator. I get very even and controllable pressure. I have a gate valve for air intake control, and two ball valves for gas, one at the buner I use to fine tune volume of flow, and another at the regulator, as a secondary emergency shutoff. I prefer ball valves for gas lines so I can kill the gas in a hurry if I need to.
Gas is fed through a quarter inch hose into a t fitting plumbed into the airflow just prior to a double burner size expansion chamber. The nozzle is the same diameter as the main burner body, half the diameter of the mixing chamber.
The big forge I'm having problems with should be rediculously well insulated. I used a keg for the outer body so I would have lots of room inside to insulate. I only cut one end off the keg. The remaining wall is integral to the keg body. That back door has a 4 inch hole cut in the center for its door / exhaust.
Inside the outer keg is two one inch thick layers of 8lb density inswool. I used a 10" sauna tube as a casting form, and filled the gap between the inswool and the 10" diameter tube with mizzou castable. This left me a 1" (or maybe a bit less) thick layer of castable refractory for a liner which has a very regular, quite smooth 10" inner diameter. I propped it 1" from the bottom / back, and had a canister filling the back door, so the whole body and back wall are one peice.
I flame cured the mizzou three times, for about 5-10 minutes each, allowing it to cool and dry overnight between. Then I coated it with ITC-100. I flame cured the ITC and when it had cooled, re coated, and re cured with ITC again.
The front door is the end I cut off the keg. This one, unfortunately is less well insulated. It only has 1" of inswool and two layers of ITC. However, to try and make up for the heat loss through the lesser insulation, I used the 1.5" hole from removing the keg pump pickup as the window on this end. I figured if more heat were radiating out of this end, I could use a larger exhaust port to pull some of the heat to the other end helping even things out a bit.
I havn't even really finished building this forge, as initial testing was so disappointing. The door is still not attached in any meaningful way, and to close off the combination, I just sort of push it into place so that almost all of the flames stop shooting out of the joint, and prop it there for this burning session.
A few observations. When I'm burning in this forge at full throttle on the small blower, or at all with the shop vac, it takes only a couple of minutes for the outside of the keg to get too hot to touch. As stated, there is a noticeable vortex effect, with an almost completely transparent hole in the flame running the length of the interior, and a good yellowish flame swirling against the outer walls for pretty much the entire thing. There is a blueish flame several inches long coming from the burner running tangent to the forge body to achive this vortex effect. The area where this flame directly impinges on the interior of the forge, as well as like two or so inches next to, and six or seven inches beyond this area glow bright yellow like the whole interior of the smaller forge, but the rest jut looks gray. This does not appear at all to be an even heat, having a very hot spot right in the middle, across the top wall and down one side, the rest being significantly cooler.
I've heated some steel in it, and it takes noticeably longer for the same peice of metal to get up to forging temp in this big monstrosity than in the much smaller vertical forge.
So the question is, as all us parents evetually ask (I got three boys, and while my eldest is only seven, I'm beginning to ask already) where did I go wrong?
I figure a 10" diameter by 16" depth is big, but not outlandishly so for a good forced air forge. I have more than twice the insulation I've seen on many other well runnung forges. I can only think of two potential problems. One, the exhaust ports / windows may not be big enough. If I'm causing too much backpressure, am I restricting the amount of flame (burning, expanding gasses) I can viably force into the combustion area? Two, the mizzou has a pretty high thermal mass. Much higher than say straight inswool. Maybe It just needs a half hour to get up to temp because of the thermal mass? From the looks and feel of it, if that's the case, I'll probably scrap that liner in favor of more inswool and three layers of ITC. I liked the castable for its relative permanence and durability, as well as flux resistance. I had planned on using a stainless foil layer on the floor to help catch flux, and have an almost permanent forge, as the small one is only barely an improvement on the coffe can design, being built out of one of those big tins they sell flavored popcorn in, and having extra insulation and ITC-100.
Or maybe, this is just too big a forge body for one burner of this size, and a big, heavy honkin burnr with a serious blower, and some serious pressure is needed. Again, I would much rather not be burning propane at 7 psi full throttle, and would rather scrap the keg for a more reasonable forge if that turned out to be the case.
