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timgunn

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timgunn last won the day on August 29 2020

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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. I know it's probably not necessary, but I'll say it anyway: dry it out properly before you fire it up. Depending on the "refractory paste" you have used, this can take from "a bit longer than you'd expect" to near-geological time. The worst stuff I used was a readily-available "refractory cement", which I assume was actually clay-based. After a couple of days I thought it was dry enough, but it wasn't. On first firing, the surface dried out pretty much instantly, the moisture behind it flashed to steam and lifted the surface as bubbles. These broke and flakes fell off, then the pro
  2. Looks good Jaro. The 3-port diverter should work too, but I think the porting on these is usually set up to keep the combined area of the port openings fairly constant, which might limit the ability to throttle the flow and increase the backpressure. I don't really have much experience of those valves though.
  3. Sorry: fat fingers. The bleed-off-excess-air method will work fine though. It just "feels wrong" bleeding off the majority of the air that you are compressing without doing anything useful with it (which is why I mentioned the air curtain). I don't think I've seen a real gas forge actually using more than about 18 CFM of air, which, if my calculations are somewhere near the mark, corresponds to between 5.5 lb/hr and 8 lb/hr of Propane use, though I'm sure some of the guys with big power hammers exceed this.
  4. If it's 3-phase, and particularly if it can run on 230V 3-phase (where is Hobbit country by the way?), I'd be inclined to run it on a VFD. I tend to build my VFDs into IP65 enclosures with sockets on for things to plug into, so one VFD can run several different machines simply by plugging the appropriate one in. The controls are on a long cable, so I can move it to the appropriate machine. It doesn't make the VFD any cheaper, but it's a lot easier to justify the expense if it's something you can use for multiple purposes. The
  5. It's a side-channel blower (aka regenerative blower). I love them. I feel they are an order of magnitude "better" for forges than most conventional centrifugal blowers. However, the Pressure:flow curve is unusual. Without seeing the curve for the actual blower you have, my guess would be that the blower can do 85 CFM at zero pressure (about 144 M3/hr), 150 mbar (60" WC, about 2.2 PSI?) at zero flow and that it will follow a curve between these 2 endpoints. If you try to throttle it to get down to the flow you need, you will very probably (perhaps almost certainly, depen
  6. I quite like rigidizer. It does have fairly limited benefits though. There are several different reasons for using it and different people will have different priorities. I don't expect rigidizer alone to immobilize fibres. I have at least a slight suspicion that rigidizing Low Body Persistence fibres will increase their body persistence. I don't see a convincing safety argument for either applying rigidizer or for not applying rigidizer. I tend to view the rigidizer as something to stiffen up the insulating layer that supports the hard refractory coating us
  7. It's worth mentioning that "Kast-O-Lite" is a trade-name used for a series of Insulating Castables with a range of temperature ratings. Usually Kast-O-Lite is followed by a number, which denotes the rated temperature in hundreds of degF. For welding forges, Kast-O-Lite 30 (3000 degF) is the stuff to use. Also seen as Kast-O-Lite 30 LI, the LI stands for Low Iron: this may not matter much to "us", but there are some applications where the LI is important.
  8. The biggest issue is the thread type. If the imports are specced as NPT and you are in the US, there is unlikely to be any tangible difference between import and domestic. If they are BSP threads. you may have trouble mating them with NPT threads. The civilized world (defined as the part that includes me) tends to use BSP threads, which have a Whitworth, 55-degree, threadform, as opposed to the (uncivilized heathen) American, 60-degree threadform. There are some differences in thread pitch between BSP and NPT at many sizes, but 1/2" and 3/4" use the same TPI.
  9. Drilled-bar burners are used in Propane BBQs and the like, where the chamber being heated is relatively cool. I seem to recall from school that Radiative heat transfer increases as the 4th power of the temperature difference (though I have a nagging feeling it may be a bit more complicated than that). At forging temperatures, the heat transfer is MUCH higher than at BBQ temperatures and Jaro is right about the effect. To overcome this, a ceramic, insulating version of the drilled-bar is needed to reduce the heat flow and keep the inside surface of the plenum below auto-ignition temperature: he
  10. I think there are probably ways of using IR to replace R and S in certain production applications, but only if all the other variables can be eliminated. That ain't gonna happen in many of "our" applications. It doesn't seem likely it could happen in yours. The only smith I know who seems to have used one effectively just used it to check his billet temperatures were consistent coming out of the forge, before sticking them under the power hammer. He always measured straight from the forge and didn't care what temperature was read, as long as it was the same temperature every time.
  11. I tend to regard a long hand-held Mineral Insulated type K thermocouple with a high-temperature sheath material as the first step. This can be moved about in the forge to establish where the hot zone is. If it is big enough and reaches the lining (which is primarily what will emit the IR), the thermocouple can be kept in the working zone while an IR reading is taken. If the IR and thermocouple agree, the IR measurement can be used for subsequent measurements.
  12. Interestingly, emissivity can just stop being an issue if the measurement is taken from a hole that is at least 6 diameters deep. Oversimplifying somewhat, the general idea is that anything emitted will reflect around within the hole before coming out and the effective emissivity within the hole will be very close to 1. In many cases, a forge is very similar to a hole and an IR temperature measurement taken through the mouth of the forge can be quite accurate. Obviously it will only work if there is not a rear opening to confuse things and the distance-to-spot ratio needs to be suf
  13. There are whole books about temperature measurement with thermocouples. It would be a trifle naive to expect a forum post to condense it all into a few sentences.
  14. On a single burner forge, a small leak is not usually a significant problem. On a double-burner, it may be. The gas leaving the jet at high speed is what causes the air to be entrained. Gas from the leak is relatively slow and effectively non-directional, so doesn't help to induce air itself and just mixes with the air going past. This means that the "air", induced by the gas leaving the jet as intended, is actually a (lean) gas/air mixture and the overall mixture will be richer than that from an otherwise identical, but leak-free, burner. Flame temperature
  15. When I built my first HT oven, I made an angle-iron frame, put everything together and test-ran it. I was intending to clad the outside in sheet metal, but had no idea how hot it would get until I tested it. The available choices seemed to be plastic-coated steel, Aluminium or Stainless Steel, in increasing order of cost. In the event, I found the surface temperature reached about 135 degC, 275 degF, but that the IFB provided such poor heat transfer to human skin that it seemed safer without a metal cladding. I am aware that knifemakers in general tend to cluster towa
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