timgunn1962

I don't want to seem overly negative, but the .pdf in the original post scares the wotsits out of me. I've only had dial-up speeds this week, so one of the links I've not followed may have mentioned this, but just in case: If I'm reading it correctly, the gas/air mixing is done prior to the plenum (big pipe) top right. The plenum and individual burner feeds are therefore, by design, filled with a flammable gas/air mixture during normal operation, with an ignition source (flame in the forge) at the end of the burner feeds. The only thing that can stop the mixture flashing back is the speed of the mixture down the burner feeds. As long as this is higher than the flame speed through the mixture, it should be safe, but as soon as the mixture speed drops, there will be a flashback into the plenum. The flame will start to move down the burner feed pipe, radiating heat into the mixture in front of it and generating pressure. As the pressure and heat build, the flame will accelerate, generating more pressure and radiating more heat, accelerating the flame and so on.This may or may not cause a major safety issue (eg, operator fatality). The pressure rise/flame front acceleration will stop either when the mixture runs out, or when the pressure has risen enough to overcome the forces constraining it (Translating from my native geek; the plenum explodes). It is certainly possible to engineer the plenum, burner feed pipe sizes, and so on to keep it safe, but the fact that you've asked the question on here tends to suggest that you aren't that familiar with the issues and that your time would be better spent on a design which eliminates the risk. It is the gas/air mixture that is the dangerous bit. Having it confined in the plenum is what gives rise to the explosion risk. If you just run air to the plenum and pipe gas to a separate nozzle near the outlet of each burner, there is only a gas/air mixture for the last bit of the burner feed pipe. Any flashback can only get as far as the gas nozzle, so it can't build the speed and pressure that would make it dangerous. I'll admit the chances of actually killing yourself with the original design are not particularly high, but assuming the plenum and pipework are built strong enough to contain things, the only route for the hot, high-pressure, gases to leave the plenum is via the burners. The risk of damage to the forge lining when this happens is quite high. Regards Tim

Gundog, the elements in your link look to me as if they may be difficult to use effectively. I have some of the 1200 W ones on order to play with, mostly because I want to build a couple of very small (folder-sized) HT ovens, but I expect to have to be a bit inventive.. The wire is rather thinner than I've used on the HT ovens I've built to date. It looks like the elements are simply cut from a continuous coil, so it doesn't look like there's any straight tail at each end to connect to. As you point out, the vendor seems to have no idea about them. To date, I've used 16 AWG Kanthal A1 elements for all my ovens. The 18" ovens have used a pair of 14A, 115V elements connected in series for use on 230V, using one element each side of the oven. Total power is about 3 kW. The 42" oven uses a 13A, 230V element on each side of the oven, and each element is powered from it's own 13A UK mains outlet. Total power is about 6 kW. I bought my elements from jrider12 on ebay. He was in Portland, Oregon IIRC, but seems to have dropped off the radar lately. Pmtoolco, also in Portland seems to sell similar elements on ebay. If you are following Andy Gacoigne's write-up from BritishBlades, it's worth noting that he also used two 110V elements connected in series. BCS now list 240V elements as well (they didn't when Andy built his). At least one builder has connected two of the 240V elements in series and found the oven won't reach temperature. There are cheap PID controllers on ebay that will switch Solid State Relays, which in turn switch the power to the elements. Again, these were not so readily available when Andy built his. I use a more expensive ramp/soak programmable controller myself, because I feel the extra cost is more than justified by the extra capability it provides. http://www.automationdirect.com/adc/Shopping/Catalog/Process_Control_-a-_Measurement/Temperature_-z-_Process_Controllers/1-z-16_DIN_Size_%28SL4848_Series%29/SL4848-VR Whatever controller you buy, make sure it has an online manual. That way you can call for help on the internet and someone can probably help. Without a link to a manual, you're on your own. Tim

I've not tried a burner of that design and want to learn a bit about them. In the bottom video, I assume you restricted the airflow at about 2 seconds, unrestricted it at about 3 seconds and it burnt ok until about 15 seconds? Did the flame travel back up the burner toward the jet when the noise changed at 15 sec?

The readout in Westernironworks' post #13 above works very well indeed. The thermocouple probe that comes with it is only really useful up to tempering temperatures though. It's a glass-fiber sheathed bead probe. The TM902C only reads in degC. I don't find it a problem, but some will, particularly West of the pond. I have had four of them so far. All give very good agreement with each other and with my other, much more expensive, instruments. As a probe for checking forge temperatures, I'd recommend an Omega KHXL-14G-RSC-24. Some details can be found here: http://www.omega.com/ppt/pptsc.asp?ref=KHXL_NHXL&Nav=tema06 My recommendation is based on my own experience; The KHXL part denotes a typeK thermocouple with a Mineral Insulated "Super Omegaclad XL" sheath, which is claimed to be good to 1335 degC (2440 degF). It certainly seems to survive much better above 1200 degC (2192 degF) than 310 Stainless steel, the only other MI sheath material I've used at high temperatures. The 14G denotes a 1/4" (possibly 6mm?) probe with a grounded junction. The 1/4" probe is rigid enough to allow it to be placed where it's wanted in the forge; helpful if you are trying to establish the temperature distribution. The grounded junction provides fast response and means that the measuring point is at the probe tip (Insulated junctions slow response and tend to average the temperature over the last couple of probe diameters: 1/2" or so on a 1/4" diameter probe). The 24 denotes 24" length. It's a fairly comfortable length for most of us. 18" is a bit too short for comfort once the tip is 12" into a forge at 1300 degC (2192 degF). The probe comes with a length of cable attached, ending in a miniature plug to suit the TM902C and most other handheld readouts. 1300 degC seems a pretty good temperature for pattern welding Carbon steels (I measured the forge temperature at a hammerin after 2 days of constant use making Damascus. The temperature was 1280-1310 degC. Nobody had even hinted that the temperature might not be right). The Omega probe will let you set your forge temperature to the right ball-park for this. It may be too low for comfortably welding mild or wrought, but it's pretty much the limit for base-metal thermocouples. The next step up is Platinum-based thermocouples with ceramic sheaths: very fragile and very expensive.. I feel the kiln-type fixed thermocouples are useful in kilns, or where it has been determined that the temperature at the probe tip is representative of the temperature of the entire working area. For HT they are great. For other things, I'm not so sure. Bear in mind that if the working area is small (eg a small hot-spot under the burner), it might not be desirable to block part of it with the thermocouple.

Usually, it's necessary to have a clean, oxide-free surface on each of the metals being joined. Aluminium is very reactive indeed, and almost instantly forms a stable oxide layer in contact with air. I don't think the charcoal-in-the-foil trick will work with Aluminium, which is much more reactive than carbon, so isn't likely to release the Oxygen from its Oxide layer to the carbon. As a result, it will be difficult to diffusion bond Aluminium to anything else with simple equipment of the sort available to the average enthusiast. I think the guys who do it use Argon to exclude air. It's probably better to try the technique with less reactive metals first, then progress to the more advanced combinations if you decide it's what you want to do. It's certainly worth researching it a bit first. There are good books by Ian Ferguson and Steve Midgett, both titled "Mokume Gane". I've not read Midgett's yet, but Ferguson's seems to give good technical information on the process (and is the cheaper of the two). Midgett is on my "must read" list.

I'm not sure on the "Z", but I think it refers to a non-slandard shaft. On fans, the shaft is often either reduced in diameter, increased in length or generally messed about with in some way. You'll probably need to measure it. I don't think you need to find an absolutely identical replacement. If you are on a speed controller, that may limit your choice of motor, but if you are throttling the inlet, or outlet, for flow control, you'll need something that physically fits (including, if I'm right, whatever is non-standard on the shaft), has 2 poles (3600 RPM or thereabouts) and has no less than the original power. A higher-rated motor is no problem; it will just run lightly loaded. Unless you have a massive impeller to accelerate to speed in yours, fans are about the lightest starting duty it's possible to get, so the motor doesn't need to be specced for high starting torque. It does no harm if it is though. Googling the Centaur PB50 shows an Aluminium impeller of fairly small diameter, so no problem there.

A smaller motor pulley, or even driving directly from the shaft, might help. Alternatively (or additionally) attaching a larger diameter to the drum and driving that? It would only need to be wood or MDF, and it looks like you could go at least 50% bigger than the present drum diameter without hitting the frame, giving a 50% torque increase. I can't make out the belt or pulley details. If you're limited on the small pulley size by the belt section, you could try a polyvee belt. They tend to be used a lot in tumble dryers over here. I think the automotive ones tend to be a larger section, so might not work as well on really small pulleys. If you can't do it on a single-step drive, an intermediate shaft is likely to prove cheaper and easier than a gearbox. It looks like you have a nice heavy axle for the drum, so driving it with a cement mixer gearbox might be worth considering. They seem to give around 30-50 RPM at the drum and are worm drive so I'd guess at a reduction of between 25:1 and 50:1.

I'd take on board Rich's electronic control suggestion and raise it to a ramp/soak (programmable) controller. Unfortunately, it tends to add quite a bit to the cost. There's generally quite a bit of fiddling about to get the temperature right with manual power controllers, and the oven temperature can still vary with ambient temperature. On a tight budget and with reasonably simple carbon steels, it'll certainly get the job done. For Stainless though, you'll struggle to find anyone who regrets paying the extra for a ramp/soak controller. If the initial cost really needs to be kept down, it's worth asking either the manufacturer, or whoever you are thinking of buying from, whether there's a retrofit kit available to upgrade from the manual system to programmable control. It's not difficult to source the controller and a contactor or SSR to do it yourself, but a properly-engineered, manufacturer-supported system has advantages. I've built 5 HT ovens. There's nothing particularly difficult or technically demanding about it and there's certainly no reason I can see for any company to make an oven that performs significantly less well than any of the big-name offerings. I'm pretty sure the thing that will make the difference between good and excellent is the controller. I don't know what your gas forge setup is like for HT, but I'd say a Don Fogg drum setup will perform about as well as an electric HT oven with manual control. If you are only going to use carbon steels, and cash is tight, it might be an option.

The 2 or 3 is for the tuning: fit one, try it, drill it out, try it again, see if it's better or worse Keep going 'til you've gone too far, then go back to the best size. It's easy drilling them out, but harder to put it back in, so you'll need a second undersized jet to open up to the right size. It's always good to have a spare in case you break a drill in one. For the tuning, you want the air fully open and the gas pressure at maximum. The temperature to aim for will be just a tad hotter than you feel you'll ever want to go. You can adjust the temperature down on temperature (edit; that should read air restriction) and pressure, so that way you get the maximum usable range. I've no pictures of Greenbeast's burner, I'm afraid. I sorted the bits and left him to do the hard work. The first iteration was with an M6-threaded MIG tip, so the easiest way to get smaller jets with what I had available was to use M6 brass setscrews and drill them in the lathe. If you don't have a lathe, you can do it in a drill press as long as you don't adjust the table: Locate a piece of scrap material and clamp it to the table. Drill it 5mm and tap it to M6 using the tap in the chuck. Screw your jet-to-be into the tapped hole and drill it. If you are testing somewhere nearby, you can drill to size. Greenbeast was 200 miles away, so I drilled undersize for him to open out by hand. I'm assuming you are somewhere metric from the reference to a 0.6mm mig tip. You'll need to use appropriate drill and tap sizes if you're not on M6 MIG tips.

Just realized I posted on IFI, not a knife forum. I think you'll need to go a fair bit leaner/hotter for welding mild steel or wrought iron.

Looks pretty good to me. I think there's a fair chance it'll be OK for forging temperatures as it is, and may manage to hold stable at HT temperatures once it's in a forge and has an air restrictor sleeve on it. What are you intending to use it for? If you are going to be trying for welding temperatures, You might be better off with a 0.6mm MIG tip to lean off the air:fuel ratio, as you suggest. If you can get an even smaller jet, preferably 2 or 3 of them, and a cheap set of drills in .05mm increments, you can tune it to near-perfection. I think we ended up with a 0.65mm drilled jet on Greenbeast's burner over on British Blades. That was a 3/4" pipe burner, albeit with a different mixer arrangement to yours. For the jets, we just used M6 brass screws, through-drilled to 0.55mm (because it was too small and I had lots of drills that size) in a lathe. Then it was a case of open out the hole by hand with a drill held in a pin-chuck until things got worse. Then just open out another one to the best size tried. I think the hole in the original 0.6mm Mig tip was about 0.73mm, and was too big. If I was to do it again, I might try hammering a .6mm MIG tip down onto .6mm MIG wire first.

The moving of the fuel to the jet isn't really much of a problem. The important thing is getting it atomized finely enough to give a consistent burn and this can be done with oil pressure (lots of it) or with air moving at high speed. One of the advantages of a syphon system is that the air that provides the atomization, also provides the motive force to get the oil to the nozzle. If the air stops, so does the oil. A pressurized oil feed with air atomization means that extra controls are necessary to cut the oil feed when the air stops, so the complexity increases.

Bentiron1946, that sounds intriguing. What fuel are you using to get 3,750F? And why do you pour the Bronze so hot?

I get a different weight, but I could be wrong. I think the numbering goes ; cwt, qrs, lb. Cwt is hundredweight and there are 112 lb in a cwt. A Cwt is made up of 8 stones, each of 14 lb, or four quarters, each of 28 lb. The odd pounds are just pounds. 1 cwt is 112 lb, 2 qr is 56 lb 4 lb is 4 lb Total 172 lb There are also 20 cwt in a ton, making a ton 2240 lb. The metric system was adopted here some time ago. Perhaps understandably.

Tidy job, Tim. I've not tried playing with oil burners, but it looks like fun. How easy are you finding it to vary temperature with the Babbington? And have you been able to get welding temperature out of it yet? I'd expect it to be easier to vary the mixture/temperature with the syphon system, once it arrives. My understanding of oil burners isn't great, but the Babbington seems to have a lot of things that aren't easy to adjust independently, yet need to be very close to optimum, in order to work even moderately well: a bit like a Venturi setup vs a blown burner on gas. As Ben says, it might not be ideal running a compressor all the time, but there'd be nothing really stopping you running Propane instead of air to atomize the oil. Most of the Babbington burners I know of, use tiny nozzles at around 0.25-0.3mm (.010-.012") for atomization. Because the gas- or air-flow varies with nozzle area, at any given pressure, they'd use around 10-15% of the gas that a 0.8mm (.032") MIG-tip burner would use, with the rest of the heat provided by the oil. It's still a worthwhile saving. Please let us know how you get on when the syphon setup arrives. Regards Tim