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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. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. 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?
  9. It'll almost certainly be Auber Instruments. Auber tend to be highly rated in America. They don't have a presence in Europe so I have not used them myself. I use Omega or Automation Direct for the ramp/soak controllers on my HT ovens. Both seem to be US companies with a presence in the UK. Both have knowledgeable and patient technical support staff. I gather Auber also have knowledgeable and patient support staff. The best advice I can give to anyone on controllers, VFDs and other electronic gizmos is as follows: Shop around. Read the specs carefully and list the "possibles". Find the manuals online and download them. Read them. Properly. This is likely to mean printing hard copy and making notes. If you are more together than me, it'll probably involve multi-coloured highlighters. If you don't understand at least most of what is in the manual, cross it off your possibles list. If you cannot download the manual from a readily accessible website without signing up to being spammed, cross it off your possibles list. Read any reviews you can find on your possibles list. Narrow down your buying choices so that you can make an informed decision. There are some geeky folk on the forums (I count myself among them) who have some general experience of PID controllers, VFDs and the sort of stuff "we" might find useful. If you run into a problem and need to ask for help online, there's a pretty good chance one of these geeky types can help, but only if they can access the manual. A link to the manual gives you a good chance of assistance. No link to a manual means you are on your own. Manuals are expensive things: paying a specialist writer-of-manuals to write a manual (in their own language) does not come cheap. Keep this in mind.
  10. My recommendation would be to build a completely separate control box: Preferably a metal enclosure (to help with cooling the SSR) fitted with cable and plug to plug it into a mains socket, power to the PID controller taken from inside the box and the PID controller output switching an SSR, which switches the power to a power socket on the front of the box. I fit a miniature thermocouple socket to the front of the box so that the thermocouple just plugs in. The one in the photo is larger and much fancier than necessary, having been assembled for a 28"-long HT oven I built. Once built, it can be used to control pretty much anything: Austenitizing HT oven, tempering oven, salt pot, electric crucible furnace.
  11. Looks pretty reasonable so far. It looks like you are using the terminals on the PID controller to carry the full element power with 2 wires in each? If so, I would suggest a minor wiring change to keep the big currents off the PID terminals: incoming power directly to the SSR and a second small wire in the SSR terminal to take power down to the PID controller. It's probably easiest to use a big terminal block to join the power wires on the other leg, with a small wire from that terminal to the other PID power terminal. The PID controller terminals are unlikely to be rated for high current and they can get pretty warm once serious Amps start flowing. It's not unknown for them to get hot enough to melt the plastic and lunch the PID controller. The DC to the input side of the SSR only needs little wires and they don't get hot (switching the SSR usually takes about 30 mA max at 3-32V). I usually try to use obviously-different wire for mains and low-Voltage control circuits in any enclosure. My experience is that stuff usually goes wrong when I'm tired and anything that might help me to avoid confusion and a mains jolt seems like a good idea. Caveat: American wiring is something of a mystery to me. I've built about 8 HT ovens so far, but they have been on European 230V mains supplies with one 230VAC hot leg and a Neutral at Earth (Ground) Potential.
  12. I don't know how much you've played with the burners yet, but it's worth choosing a fixed value for the gas pressure, letting the forge get to temperature, then making adjustments to the choke to see how that affects the temperature. Adjusting the choke should adjust the air:fuel ratio and with it the flame temperature. Adjusting the pressure should adjust the amount of flame you have. You'll adjust both in normal use, but it's worth spending half an hour or so early on just getting a feel for what does what. Maximum flame temperature is reached at an air:fuel ratio that is close to stoichiometric. It's hotter than we usually want/need (well above the melting point of Iron) and "we" tend to run more fuel-rich and cooler. Running fuel-rich means that there is a reducing atmosphere in the forge that tends to grab any Oxygen before it can react with the workpiece to form scale. The partially-burned gases finish burning when they reach Oxygen in the air outside the forge and this is what gives the Dragons Breath. It looks like you have a fair amount of adjustment available both ways. Opening the chokes should get the forge hotter, closing the chokes should make it cooler. A hotter flame should also get it to any given temperature faster.
  13. "The reason for the 5 HP is because running a 3 phase motor on a VFD you only get 2/3 the rated HP just like running a static phase converter." That's news to me. What is your source for this information? I'm pretty sure it's wrong generally, though there may be specific circumstances under which it is the case. The only one I can think of offhand is when the supply Voltage is less than the motor rated Voltage, but I'm sure there are others. I've been using VFDs for over 30 years and I've never been told by a motor- or drive-supplier that I need to derate a motor by 1/3rd in order to run it from a VFD.
  14. “Venturi” is the term used to describe the shape of the classical Naturally-Aspirated mixer. It tends to get used (incorrectly) for any Naturally Aspirated burner: one which does not use an air blower to provide the air. Get the back-pressure down by reducing the restriction on the openings and see if it improves. If you still can’t get it hot enough, have Dragons Breath and the gas jets are changeable, fitting the next size down jets will probably get the temperature significantly higher.
  15. Looks like it's a high-speed drill press from a quick google: possibly 1500-10000 RPM, though the one in the link below looks to be 3-phase and is in Europe. If the pulleys and motor pole count are the same, it'll be around 1800-12000 RPM on 60 Hz mains. A bargain if that's what you need, but not really a general-purpose tool. http://unimachines.at/tischbohrmaschine-super-valmer-model-6-1970-14105.html
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