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timgunn last won the day on May 19 2016

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About timgunn

  • Birthday 03/15/1962

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    Lancashire, UK
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    Tools, science, food, wine. Making things that "just work".

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  1. The length of the burner tube matters. There is a pressure loss (resistance to flow) associated with the length of the pipe and the flowrate. The maths gets pretty complex pretty quickly. The gas issuing from the jet generates a low-pressure zone around the gas stream that draws air in. The gas and air mix with the gas slowing down and the overall gas/air mixture retaining the momentum of the original gas flow. This effectively results in a (very) small overpressure that drives the turbulent mixture along the burner tube towards the forge. "Some" length of burner tube is necessary to get adequate mixing, but the longer the tube is, the greater the pressure loss along the tube. "About" 8 pipe diameters seems to be the length that most of the homebuilt NA burner designers have found works best. Elbows and other fittings offer a restriction to flow that can be expressed (for "simplicity", though that is a relative term) as an equivalent length of pipe. The combination of pipe lengths and the elbow looks, to my strictly inexpert eye, to be equivalent to about 5 or 6 times the "works best" value. The (fuel) gas pressure is so high that the gas will flow regardless. The extra resistance to flow will therefore affect the airflow almost exclusively, reducing the amount of air relative to fuel. Going to a smaller gas jet should help to get the mixture back towards a "good" mixture. If the resistance to flow in your long pipe is high, the mixture speed will be relatively slow. The mixture needs to move towards the forge faster than the flame-front can move through the mixture in the opposite direction. If the flamefront moves faster through the mixture, the flame will run back down the burner tube until it runs out of mixture to burn (somewhere near the gas jet, where the gas and air have not had the time/distance to form a flammable mixture). The flame will go out, mixture will start to flow. After a time, it will reach the hot forge chamber and ignite, whereupon the process will repeat. I am guessing this may be the pulse jet effect you mention.
  2. It would be nice to see the position of the gas jet relative to the end of the long threaded nipple with everything assembled. Looking at the photo, it seems that with the brass sleeve-thing inserted into the threaded nipple with enough sticking out at the back end to get the hose on, the jet will be somewhere close to flush with the end of the threaded nipple? I suspect that'll cause all kinds of turbulence right where you don't want it. I think you probably want the full length of the mig tip exposed to allow air to be drawn relatively smoothly into the low-pressure zone created by the gas coming out of the jet. Once you've got it something like, there are plenty of adjustments available with that design. If the installed burner is similar to the right-hand one in the first pic, there's a very long length (in total) of pipe on it plus an elbow. A screwed 90-degree elbow is usually considered to be equivalent to "about" 30 pipe diameters in terms of pressure loss IIRC. I think the left-hand one in the top pic is probably pretty close to convention at "about" 8 pipe diameters. The one on the right looks to be equivalent to perhaps 40-50 diameters.
  3. There was a group buy of 2" x 36" Multitool attachments on the now-defunct British Blades forum a few years ago. I think it was an importers stock clearance, but the price was a fraction of list (I think they were about 60 quid each). I bought 3 of them, and a 4" x 36. One of the guys on the forum came up with a kit to fit the MT to an IEC metric 80-frame foot-and-face-mount motor. It was a pretty simple kit: basically a few bits of plasma-cut 6mm plate, a few fasteners and a bit of 1mm shim stock to wrap round the 19mm motor shaft and adapt it to the 3/4" bore of the wheel. I bought 2 of them. They worked brilliantly, though the shim thing was a lot of faffing about and I just used Loctite on the second one I built. I used 0.75 kW (1 HP), 3-phase, 4-pole motors because I had a number of different VFDs available. If I was doing it again now, I would use a 1.1 kW (1.5 HP) 2-pole motor and a Sensorless Vector VFD. I mounted the third attachment to a really cheap, nasty 1/2 HP bench grinder. It beats the wotsits out of having no belt grinder, but is definitely underpowered. I had a try of one that someone had put on a 900-Watt bench grinder and that was a properly useful tool in a fab shop. The MT kits we had were for a 3/4" shaft with reducing bushes supplied to fit smaller sizes. I gather there have been other kits that will only go to a maximum 5/8" shaft, so cannot be readily used on an 80-frame motor. It's worth checking maximum shaft size on the one you are considering. In your shoes, I'd get the Multitool, mount it to a cheap/available bench grinder, then save for a motor and VFD. Have a think about making an adaptor plate in the meantime. That way, the only thing that you'd need to buy that wasn't on the direct upgrade path would be the cheap bench grinder. Even on a 1/2 HP bench grinder (a little under 3000 RPM, assuming you are on 50 Hz mains), it's able to stock-remove for knifemaking faster than most beginners can do with files. It does mean that you get to develop grinding skills, rather than filing skills.
  4. As mentioned, some systems have a built-in flow-limiting valve. It is broadly similar to the "air fuse" sometimes fitted to pneumatic systems before a hose. The idea being that if the hose gets cut, the air fuse will close and limit the airflow, so you are not having to deal with several yards of angry hose thrashing about and trying to beat you to death. It will limit the flow to some (fairly small) fraction of the maximum design flow and will automatically reset when the flow drops to zero (or near-zero). With a gas system, the potential is for several yards of angry hose with several feet of even angrier flame issuing from the end, so it's a pretty good safety feature really. If you have such a system in your cylinder, it will be designed to limit the flow once it gets over the maximum design flow for the cylinder. The supplier should be able to tell you what the maximum design flow is. You can then calculate what your burner takes at different pressures using the BTU calculator on Ron Reils site (other calculators are available) and see whether or not it'll do what you need. It is always a good idea to back off the regulator before closing the cylinder valve and to open the cylinder valve before increasing the pressure with the regulator. Opening the cylinder valve with the regulator turned up can cause an initial flow surge that may be enough to trigger such a safety system.
  5. The "Inverter duty and TENV motors" curve in Cody's second graph will almost certainly be for Non-Ventilated motors and for fan-cooled motors with a separately-powered cooling fan: effectively a mains-powered, fixed-speed fan which maintains the cooling airflow regardless of the motor speed.
  6. The VFD will effectively vary the Voltage and the Frequency together from minimum speed up to the rated speed of the motor. The maximum Current (in Amps) is whatever the motor is rated at, regardless of speed. Power can be thought of (in slighly oversimplified terms) as Volts times Amps. As the Volts go up, and the Amps stay the same, the power goes up. This is the "constant torque" part of the torque/speed/power diagram: Power is also Torque times RPM. Once the rated motor speed is reached, the rated Voltage is also reached. The VFD cannot increase Voltage beyond this, but can still increase the frequency. Power is again Volts times Amps. This is the "constant power" part of the torque/speed/power diagram. Power is Torque times RPM, so as the RPM increases, the torque must reduce. In real terms, the 1750 RPM 2 HP motor and the 3500 RPM 2 HP motor will both be giving 2 HP at 3500 RPM. Both will be giving the same torque because power is torque times RPM. Most of the heat generated within a motor is down to the Current (Amps) being drawn. At full Current (Amps), the heat generated will be broadly similar, whether the motor is running at maximum speed or at minimum speed. For TEFC motor, the cooling airflow moved by the cooling fan will vary with the speed of the shaft. At full rated speed, there is plenty of airflow and the motor can run at full-load continuously. As the speed reduces, the airflow reduces and the ability of the motor to cool itself reduces, such that the motor will need to be derated at lower speeds. Grinders tend not to be run at constant maximum torque, even at high speed, but particularly not at low speeds for a number of reasons: usually the operator has some degree of mechanical sympathy, workpieces get hot and need to be cooled down (during which the motor is under minimal load), belts get changed, etc, etc. This means that in "our" application, the derating usually happens without anyone needing to think about it.
  7. I think the consensus view on the internet (insofar as such a thing is possible) is 7 times the burner port area as the minimum for the combined openings. In most cases, the need to have an opening big enough to get the workpiece in and out will mean that the area of the openings comfortably exceeds this. Taking a worst-case scenario with a 3/4" burner: the thinnest wall, largest inside-diameter pipe anyone is likely to use is Schedule 5, which has 1.050" OD and .065" wall thickness for an ID of 0.92" and an area of 0.66 sq in. Multiply by 7 to get 4.7 sq in. A 2 1/2" x 2" opening will be enough, even with a 5/8" rebar handle in it. From the photo, it looks like the front hole you already have may be big enough, even if you close up the back hole when doing short stuff, and I'm guessing it'll need to be enlarged for workpiece access anyway?
  8. What sort of burner(s) are you thinking of? Naturally Aspirated, I'd go one (bigger) burner every day. It is much easier (and cheaper) to build a single adequate burner than it is to build two identical burners. I don't know what size your forge will be (I'm in the UK so "propane tank" is not a size I am necessarily familiar with), but for bladesmithing I'd guess you are looking at two 3/4" burners or one 1" burner. If you are going for blown, either one or two ports will work fine, so long as you keep everything downstream of the mixing point perfectly symmetrical. Ribbon burners are very good at keeping down the flame length. Whilst many swear by them, they are not exactly easy to get right (they look dead simple, but there is actually a lot going on and the opportunities to louse things up are much greater than most folk realise). I'd recommend starting with (a) more conventional burner(s) and only move onto a ribbon burner if your first 2 or 3 forges show you that you would benefit from a ribbon burner in your application. If you can get BSP fittings in your location, an Amal atmospheric injector from Burlen in the UK will form the basis of a very good burner indeed. The ones jetted for Butane work better than the ones jetted for Propane in "our" application. If you are building a burner to plans, make sure you follow the plans EXACTLY. If there are different jet sizes suggested for a NA burner, always start with the smallest: it will almost always get hotter and use less gas than the bigger one.
  9. When you “increased the pressure a little bit”, what was the proportion? It will need a big change in pressure to make a significant change in flow/mixture speed. If you poke out the gas jet, be very careful. The diameter, shape and surface finish of the jet are all important. If you change anything by poking it through with something inappropriate, you will alter the air:fuel ratio of the burner. I usually end up using Copper wire to poke out gas jets because it is soft enough not to scratch the bore but stiff enough to work.
  10. If you get the same with no wind, one thing you might try is increasing the gas pressure. Burnback is usually because the flamefront travels through the mixture faster than the mixture is moving through the burner tube in the opposite direction. Flame speed depends on several things: air:fuel ratio, pressure, temperature. Pressure in the burner tube is about atmospheric and you don't want to be messing with the air:fuel ratio if it's right. Initially, things are cold and the flame speed is slow. As the forge heats up, the flame speed increases. If the flame speed gets fast enough, it will travel back until it runs out of mixture and will go out. Fresh mixture will flow and will ignite when it reaches the hot forge. When the flame travels back along the tube, it heats the tube a little. Often there will be a burnback, followed a few seconds later by another, followed by more at reducing intervals as the tube heats, until the burn is just a rapid succession of burnback cycles (or sometimes the flame stabilizes within the burner tube). Increasing the gas pressure at the first sign of burnback might get the mixture speed up enough to prevent the problem. I would aim to double the pressure if tying this. Gas flow through a jet varies as the Square Root of the pressure difference across it, so doubling the pressure will give about a 41% increase in gas flow and therefore mixture flow.
  11. Rather than use gas, which as Alan says is relatively difficult to control because the temperatures needed are much lower than the flame temperature and the exhaust gases need to be able to get out, would you not be better off using Mineral Insulated Rod-type electrical elements and a PID controller? I'm pretty sure I could do it either way if I needed to, but I'd certainly be inclined to do it electrically because it's so much easier. The only reason I can think of to do it with gas would be because mains power is unavailable in the location. I would not try to partition the forge/oven for smaller items because the additional variables will be a pain to deal with. I have built electric HT ovens and gas HT "forges" for Austenitizing. I rather like the idea of using gas forges with a seriously reducing atmosphere for HT of Carbon steels (I'm pretty sure it can all-but-eliminate decarb), but it is not without its problems. The most serious of these is probably the massive levels of Carbon Monoxide produced: A perfectly tempered blade is good, but it tends to be better if the maker survives to do the other things that are needed to produce a finished article. I only ever use a gas HT forge outdoors. Search ebay for "6802 thermometer" and put the money saved towards a good thermocouple. The thermocouples supplied with the 6802s are often not much good for us at all. Sometimes you'll get a couple of PVC-insulated thermocouples which are only good to about boiling water temperatures. Sometimes you'll get glassfiber-insulated thermocouples that are good to about 400 degC/750 degF: useful for checking the temperature of a tempering setup. The ones pictured in the HF link look like the glassfiber ones. I would recommend an Omega KHXL-14U-RSC-24 thermocouple assembly. https://www.omega.com/en-us/sensors-and-sensing-equipment/temperature/sensors/thermocouple-probes/khxl-nhxl/p/KHXL-14U-RSC-24?searchterm=KHXL-14U-RSC-24 It is not cheap, but it's not very much more expensive than the HF pyrometer in the HF link. Because it comes with a fitted cable and plug, there is no chance of wiring it wrong. It is well worth making the time to talk to the technical sales guys at Omega and order by phone. They know their stuff and are helpful/patient, IME. If you need a bespoke thermocouple, they can supply and costs are very reasonable.
  12. The best hydraulic system I have ever seen for a limited-power forging press is the Anyang design, which uses a swash-plate pump with variable displacement. At low pressure, the pump is at full stroke and the ram moves fast. As the resistance increases, the pump stroke decreases, the ram speed decreases and the pressure developed increases. This means that the system is able to use the full power of the motor throughout the cycle. I think the 25-tonne Anyang press uses a motor that is either 4 HP (3 kW) or 4 kW. It is pretty impressive and I get the feeling it probably out-performs most 10 HP presses and many 15 HP forging presses (though I have to confess to pathetically little actual forging experience myself). All of the fixed-displacement-pump systems that I have seen move at a fixed speed and only use a fraction of the available motor power until the resistance is very close to maximum. 2HP is pitifully little power for a forging press. I would be looking for ways to increase the available power, rather than trying to build something that will work poorly, at best, on the power that you already have available. If a bigger electrical supply is out of the question, could you use a gas- or diesel-engined power pack for instance? Work is Force times Distance. Power is work per unit time. I struggle a little with US units, so we'll convert to units I understand. I think a US ton is 2000 Lb (as opposed to the 2240 Lb of the British ton or the 1000 kg of the Metric Tonne) 16 US tons is therefore 32000 Lb 32000 Lb is 14,545 kg and each kg of mass exerts a downward force of 9.8 Newtons at the surface of the Earth. 32000 lb (force) is therefore (14545 x 9.8) = 142545 Newtons 2 HP is 1500 Watts (as close as makes no difference). Power(Watts) is Work done(Joules) per unit time(seconds), so 2 HP(1500 Watts) is 1500 Joules/second. Distance is Work/force, so the distance over which 2 HP can exert 16 tons of force in one second is 1500/142545N = 0.0105 metres. That gives a speed of 10.5 mm/sec for a 16-ton ram driven by a PERFECTLY EFFICIENT system: about 0.4 inches/second. Perfectly efficient is unattainable. It's over 30 years since I played with Hydraulics as part of my job, but I don't ever recall them being particularly efficient. Even allowing for 30 years of development, I don't think there would be much chance of exceeding 1/4" per second with a real-world 2HP, 16-ton system. Hydraulics are usually used because they offer a convenient way to achieve a numerically large mechanical advantage. Levers are usually very efficient compared to Hydraulics, but trying to combine the two seems like adding a lot of complication. If you want to be able to keep the stroke short with different thicknesses of workpiece, you could use adjustable limit switches to limit the return stroke or, if you are using a very basic power pack with just a relief valve, threaded adjustable stops on the return stroke.
  13. First question is whether the motor is wired correctly? Over here, most small 3-phase motors are wound to be run at 230V in Delta or 400V in star (wye). Connecting a motor over here to 230V in Wye gives a similar problem to yours, easily sorted by reconnecting in Delta. I am in the UK and strongly advise you to avail yourself of local knowledge. I'm not sure whether the high Voltage being double the low Voltage on your nameplate means there are 2 sets of windings, to be wired in parallel for 230V or series for 460V. Check your wiring diagram. Are the PBxx settings correct for your motor?
  14. That looks old. I would not try running it on a VFD unless a Sine-Wave filter was used in the circuit. What follows is "as I understand things": somewhat oversimplified and perhaps not technically accurate, but close enough for me to get my head around. YMMV and it is worth researching things further if you are intending to go that way. Old motors often used a brittle Shellac-based impregnation material for the windings. I think some of the early synthetic impregnation materials were also rather brittle. Later polymeric resins are much "tougher". My rather limited experience is that post-1980-ish motors are no problem with VFDs. Pre-1960-ish motors are a problem and between 1960 and 1980, things are unclear. On a true sine wave supply (mains), the voltage rise is quite slow. As the current rises, the magnetic fields around each of the coils rise and interact with the other coils in the winding. I think they cause the windings to move towards each other, compressing the insulation, with each peak (positive and negative), causing the characteristic transformer hum tone. VFDs use PWM to switch a DC Voltage on and off very fast (most modern VFDs switch at 4 kHz and up), giving an almost instantaneous Voltage (and current) rise time. The force exerted is dependent on the rate-of-change-of-Current, so the mechanical forces on the insulation are very much higher than when run from "real" mains power. On a motor with brittle insulation, the forces are higher than the insulation can withstand and tiny cracks form. The upshot is that old motors tend to fail very quickly when run from VFDs. There are some other factors that come into play as well, but I can get my head around the one I've described and it has been sufficient to keep me from going down that particular rabbit-hole. A Sine-Wave filter can be fitted between the VFD and the motor to smooth out the high-frequency stuff and leave a sinusoidal waveform very similar to "true" mains (though still with the Variable Frequency that we want for speed control). These will often let you run an old motor on a VFD. Sinusoidal filters typically seem to cost "about" as much as the VFD with which they are used, so they are not cheap. If an old motor has been rewound, it will have been done with the materials used at the time, so a 1935 motor rewound in 1995 can be treated as a 1995 motor (unless it was specifically rewound with 1935 materials as a museum piece, for example).
  15. It's not entirely clear what you mean here. Do you mean the size of the hole through your "refractory" and into which you stick the torch, or the size of the gas jet in the torch? I once made a 2-brick forge and tapered the hole for the torch to go in. By moving the torch in and out of the tapered hole (wider at the outside), it was possible to vary the amount of air that was drawn in and thereby vary the temperature. (tip: in most cases, more air = hotter) The problem with using a torch, which is designed to work in open air and draw secondary air, is that it usually can't get enough secondary air to burn with the gas when used in a forge. If you open out the gas jet, you will almost certainly make things worse: even more gas and no more air producing an even richer burn and lower temperature.
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