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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. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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?
  7. 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).
  8. 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.
  9. Drop the Hz on the VFD to two-thirds of the frequency intended by the supplier (hopefully, that's the mains frequency where you are) to get the same speed as you'll get with the 6-pole motor and see how it goes.
  10. On a Venturi burner, knowing the pressure is useful, rather than essential, mainly to allow the operator to start the forge, set it to where it was last time it did the same job, and get on with something else while it gets to temperature. I always used to fit a gauge at the mixer (and still do when I want other folk to see what is happening with the burner), but now use plugged welding regulators on my forges. These have graduations marked on the body so that the skirt of the adjusting knob shows the pressure they are set to. They have the advantage of being built "industrial", with a nice big adjusting knob intended for use by someone wearing heavy welding gloves. It sounds like a pretty crude way of knowing the pressure, but there are not many gauges that provide significantly more accuracy/repeatability at reasonable cost. I like to keep all of my controls at the gas cylinder end: it's the direction I head if things start going wrong and I don't want to introduce the need to make an extra decision while the midden is hitting the windmill. I'm also not keen on adding weight to the end of the burner. There are various different gauges available. As said, very few will offer good accuracy at anything like reasonable cost. I tend to use glycerine-filled gauges with 1/4" bottom connections. These have stainless steel cases with sufficient structural integrity to contain the glycerine and the 1/4" connection is a lot harder to break than a 1/8" one. I have seen 1/8" back-entry gauges, salvaged from the regulators of old compressors, fitted on burners and try to keep my distance. If I *really* want to know what the pressure is doing, I use a 4-20 mA pressure transmitter and a datalogger, but I'm probably a little more anal than most smiths. It is worth pointing out that gas flow through a jet does not vary linearly with pressure, but as the square root of the pressure. If you want to double the gas flow, you need 4 times the pressure. Doubling the pressure will give 1.41 times the gas flow and halving it will give 0.707 times the gas flow. If you want to spend money to find out what is happening with your forge, you will almost certainly get more bang for your buck by investing it in a decent thermocouple and pyrometer.
  11. Ouch. What did it cost? I’ve been fortunate enough to salvage a few type S over the years. Even without having to consider the cost, their fragility is quite limiting.
  12. Wherever you buy your thermocouples should be able to supply them. Otherwise search for "thermowell". I'm the wrong side of the pond to recommend suppliers. Although they are used a lot in industry, they are not often the best solution in "our" applications. Thermowells tend to slow thermocouple response and tend to be very spendy in anything more exotic than 316 SS. Mineral Insulated thermocouple asssemblies are often a better option. I strongly recommend spending a few minutes scrutinising and understanding the process you are dealing with and the temperature you need to measure, before sitting down with a cup of coffee, notebook, pen and calling the technical sales folks at Omega to ask their advice. It is worth mentioning that bespoke thermocouples are pretty normal in industry, so the premium for non-standard is usually surprisingly small. It does mean dealing with a specialist temperature control business, rather than a box-shifter, but this gives you access to their technical knowledge and experience.
  13. 230V single phase at 50A is 11500 VA: There will be a power factor to consider, so probably not enough to run a 15 HP (11,250 W) motor via a VFD, but more than adequate for any motor/VFD you might fit to a 2" wide belt grinder.
  14. Dudley is actually in the "Black Country", west of Birmingham (England) and about 80 miles as the crow flies from Sheffield. This thread reminds me of the saying that to an American, 200 years is a long time and to an Englishman, 200 miles is a long way.
  15. I'm not sure whether it applies to your controller, but I've come across some that are initially set for 1 decimal place, limiting the maximum to 999.9 degrees. Changing to zero decimal places gives access to the full temperature range. Worth a try?
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