Hey all, I just purchased a used Mankel Knifemaker forge - three burner propane variety. Nice unit but the first thing I notice is that the burners don't mix the gas and air very well. I get swirling orange flames racing around the chamber instead of a steady blue from the burners that I would expect from a well tuned burner. The result is that I have to burn a lot more fuel to get a good heat going. I played around with the pressure and air flow a bit but it didn's seem to do much for cleaning up the burn. In retrospect I should have tweaked with the volume at the needle valve... Might make a big difference. Anyway I was wondering if anybody here has experience with the Makel burners and what I should expect from them. Any suggestions on how to clean up the burn? Thanks!
Hey! I was starting to wonder if anybody else could see the message :-) I did a bit of googling and only found references to dealers. I guess I will have to ask them. I was kind of hoping sombody in the blacksmithing community had used one and could tell me what to expect from the burners. I'm not at all impressed with the air/fuel mixing in these things and have to believe it should be better than this. I opened them up as best I could and ran a wire around to knock any debris out that might have collected. The person I bought it from said they had it sitting in the shed for about a year. Still doesn't mix very well and doesn't heat up worth a darn. Just as an experiment I thought I'd stick my Rex burner in one end and see how well it heated with that. Never used a forge made with these kinds of refractory materials and burners so I really don't have a clue what it should look like if running correctly. I know it's supposed to get a lot hotter though ;-)
This is all IIRC, so apply the appropriate amount of sodium compounds....
The Whisper Momma I often use at Pennsic has a specific requirement for input gas pressure for the correct fuel-air mix, 13 psig I seem to recall.
It'll run at lower pressures, but doesn't get as hot and scales the steel more.
The Mankel forges seem to be of similar design and might have similar requirements for fuel-air mix.
I don't know how much experimentation you've already done, but, if you haven't already, try various gas pressures, up to pressures you might consider high. (13-15 psig)
Other possibilities are: the orifices are partially clogged or there's something inside the burner tubes beyond the bend where you might not be able to see. I sometimes get insect nests in my pipe forge if I leave it sit unused for too long. (and sometimes some really PO'd insects when I do start it up:)
Hi John, You know you might just have my problem right there... When I got it, the regulator was cranked up pretty high and I don't think I ever really played around with it at that range. At first I forgot to adjust to needle valve for volume and just played with the pressure (first time I've had a pressure valve to play with) and air. Wide open at a pressure over 10 psi freezes up the tank pretty quick but if I sqeeze back on the needle valve that just might do it. Figured I had to be doing something wrong. That sounds about like it. Thanks!
I hope it solves your problem with heat and scale. The needle valve reducing the volume could end up perpetuating the problem though.
Most of that type forges are designed to get pretty much the correct mixture at a certain pressure for the size orifices in the burners. If you reduce the amount of gas entering the burner with the needle valve, you accomplish the same thing as running at lower pressure, reduced gas flow. For using lower pressures or volumes of gas, you'll probably need to somehow "choke" the air inlets. Good ol' Duct Tape works pretty well for that, but sometimes you have to scrape it off as the burner tubes can heat up quite a bit.
(Did I write that right?:)
It's a balancing act and not necessarily intuitive. The perfect mixture burns all the gas using all the oxygen in the air mixed with it, creating a neutral (no excess gas or air) atmosphere inside the forge. With experience, you'll find you can tell the correct mixture by the color of the flames coming out of or around the door of the forge.
Of course, as soon as you bring any unfluxed hot steel out of the forge, it's going to scale up slightly just because it's now in an oxygen rich atmosphere.
Freezing up the tanks, especially the little 20-pounders is an occupational hazard. I use 50-pound tanks and I can freeze one of them up maintaining welding heat for a prolonged session. High gas flow reduces the temperature of the liquid in the tank causing it to boil off less readily. Result: freeze up and the gas don't flow.
I've had my regulator and the first few inches of the line frosted over, which is about when I decide to stop 'cause nuttin' more is likely to happen unless I change tanks. An "empty" tank often revives when allowed to warm up.
Another trick is to put the tank into a tub of water. If the tub isn't big enough, it can be hard to get the gas tank and the ice that's formed around it out of the tub. So use a tub with plenty of clearance around the tank.:)
Make sure to keep a sharp eye on the condition of your tanks if you do that. You'll probably have to clean and repaint the bottoms now and then to prevent rusting.
One thing using a gas forge will teach you is hammer control. A lot more steel gets hot in a gas forge and spot heating is pretty much impossible. You can compensate by quenching the part of a piece you don't want to move and using that area as a "handle" to do the work you want on the hot section.
Well, probably more than you wanted to know, and certainly more than you asked for, so I'll shut up now. :)
I didn't think the needle valve (located down stream of the regulator) would affect the pressure as much as the volume of gas allowed to flow in the line. Figured there is some crossover but that they were different effects?
I know there is a corrolation between the jet diameter and the optimum pressure. The jets have small breather holes just down stream from the jet and then the forced air kicks in downstream from this. Seems kind of strange since if the venturi on the jets was working well you wouldn't need the forced air and vice versa. If I can't make it work right I figured I'd try tapping in the fuel just below the fan and let it mix on the way to the burner.
Been doing some forge welding with a friend who built a forced air burner and forge. I've got a good idea of what it should look like running clean or a bit fuel rich. As it is, his home built works better than the Mankel and uses less fuel to get good and hot. My single T-Rex venturi burner works better than either one for range of operation if not top end (and I'm not so sure about that). I wanted the three burner thing for distribution of heat but if it comes down to it I think I can just poke the T-Rex in the small opening on the front end cover and open up the back end for work. I'd have to plug up the built in burner inlets though. I did some measurments on my Rex and cheap wool forge chamber setup and with the Rex cranked down as far as I could get it you could barely tell it was running and I still was getting 1650-1750F degrees in the chamber. This Mankel forge should theoretically blow these other setups away though. If I have to dump massive amounts of fuel into it though I really haven't gained anything.
Full tanks and a tub of water can go a long way to offset this when you want to crank it up. We've run my friends home made setup for three hours or so on one of the little tanks and had lots of fuel left over.
The problem with this is that the fuel output drops with the temperture and you start scaling up your work if you aren't paying close attention. I try to make sure I can always see a bit of flame shooting out the opening of the forge but no visible flame inside.
The cool thing about the little tanks is you can exchange them at wally world for a bit more than you might pay for the fuel alone. Reasonable considering. I took in an old piece of junk with an old style valve on it and payed an extra charge for the valve not being up to standard, but still got a decent tank and fuel for about 25 bucks.
My first forge design (god rest it's rainwashed soul) was set up so I could lay a blade across the opening with a fire brick wall behind it and heat up only about 6 inches of steel blade. Figured this out late into the forging of a Wakizashi I was getting frustrated trying to get straight. I'm planning to build a forge that I can just run a blade through and heat small sections. It's a lot smarter way to do big blades. The cool thing about inswool and the like is that you can wire wrap it into the shape you want for a cheap and dirty chamber. Makes it easy to play with designs. If you coat it with Satanite it will actually last a while as long as you don't get flux on it.
The result I've usually experienced with the needle valve on my forge has pretty much followed what I mentioned. I think reducing the gas flow while maintaining the velocity pretty much has the same effect as reducing pressure. The high velocity entrains more air and the burn goes oxidizing. But since I'm no burner engineer, I could be way off too.
Sorry for treating you as a complete newbie, BTW. I somehow didn't make the mental connection between Greyangel here and on the mailing lists. Most of my mental connections these days seem to be high-resistance. :)
No offense intended, guy.
You do realize, of course, that we're writing a halfway decent treatise on the wiles, ways, and vagaries of gas forges, eh? :)
I'm somewhat surprised the Mankel three-burner isn't giving you much better results. From what I've heard (no direct experience) they generally perform pretty well.
Best, John (suffering from high-resistance shorts in the neural network)
I certainly won't argue the point. I've been getting by on a needle valve and an air choke for a while now :-) This thing about having a regulator is new to me and I need to spend some time to guage the effect on known equipment as well as new.
None taken. I consider myself pretty wet behind the ears. I'm also Kyle J. depending on the forum in question. The handle is just an internet thing.
Overdue I'd say :-) Sombody needs to do it. Ron Reil's site is a great how to but those who have done this stuff for a while take a lot for granted. Most discussions of forges address materials, temperture, a bit about "rich" and "lean" - what ever that means. I usually qualify a statement like that as "fuel rich" or maybe "oxygen lean". Got to give Ron credit though, he really does have most everything you want to know on his site... Ya just got to find it first :-)
I'm pretty surprised myself. I haven't given up just yet. I still think I'm missing something but haven't had enough time to play with it to figure it out yet.
I keep telling myself that is just a natural occurence of age. At the rate I'm going I'll have all the symptomes of alhtzhimers by the time I hit 50.