jwmelvin

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About jwmelvin

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    Northern Virginia
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    performance driving; fabrication

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  1. jwmelvin

    Forges 101

    Vibrating worked great for me, with 3 mm cores. The refractory sunk in like magic. I used an offset weight on an angle grinder to vibrate, so pretty high frequency. I wasn't using Kast-o-lite though, I used Wayne's refractory #2, which doesn't have the fibers or large particles of KOL.
  2. AFB, thanks for continuing your work and posting about it. Seeing the venturi tube made me think. I'm still not clear as to the role of the throat, in that it accelerates the flow but then expands the flow right after that; such an action will lose energy compared to just flowing through a fixed diameter, so there must be a point. Perhaps the reduced pressure at the throat is what induces more air flow from the ambient pressure around the entrance. Or maybe there is something about a reduced diameter that allows the gas jet to impart more momentum to the induced air flow. Anyhow, I did a bit of reading and came across this study, which seems pretty relevant to our purposes. Have you seen it? One point I found interesting is that the optimum inducer nozzle design depends on the configuration of outlet ports (i.e., the back pressure created by an array of outlets, which we call a ribbon burner). So I will probably work on inducer design more now that I have settled on an outlet block that I like.
  3. I soldered some brass fittings with plumbing solder and it has been working fine. But if another option is easier, I’m all for it.
  4. Thanks. I did order the flux and solder AFB recommended. I was trying to figure out the difference from my plumbing solder, which has silver (1-5% I think?).
  5. Is the idea of brazing rather than soldering that you benefit from the higher strength? Or the higher temperature capacity?
  6. Aerodynamicist commonly use 6° expansion as the limit, which is a little more aggressive than 1:12. But in that range. https://www.grc.nasa.gov/www/k-12/WindTunnel/windtunnel_report.html Look at figure 9 here (5-6° for optimal pressure recovery); pretty interesting study: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720020645.pdf
  7. Yea, my folks live in Hawaii, on the dry end of Molokai, and the giant centipedes are an interesting aspect of life there. They are fast.
  8. Good point, thanks. I put the thermocouple in because it seemed like it would possibly give useful info, so if it can help me repeat conditions that's great. I've been a little tentative to run more than 10 psi so far, but I will do so next time I fire it up and see how things go.
  9. Thanks. Knowing that your forge takes something like 20 psi is helpful; I didn't figure you would be able to tell me what I will need in my forge. I have never forge welded so that's (a big) part of the problem. I've only had my forge hot a few times. While I have a thermocouple, it seems to take a while to equalize in temperature and I'm not sure how much to trust it. It would be super helpful to work with someone in person; I will try to get to a local meeting to make some contacts.
  10. I welded my plenum together, which seems to help it maintain a stronger flame (no leaks): Here is the ~6.5 psi startup flame: Once warm, a 10psi flame burns a bit off the block: There were no issues running at ~2psi. Oh, I'm curious about what I might expect for being able to get to welding temperature. My forge volume is ~300 in^3, and I'm using something like a 3/4" burner (the mixing tube is larger ID than a traditional 3/4" pipe). Any thoughts as to pressure I might have to run at the gas jet? I.e., is 10 psi typically enough for this sort of thing, or would you generally expect to go higher? I know each burner-forge setup is different so what my setup needs will be different from yours, but having some examples and ballpark ideas would really help.
  11. I ran my forge for a few hours yesterday to see how the ribbon burner did. It worked, though still needs some tweaking. I assembled the tongs that I had started the other day and used them to play with an old rasp to get to know the process for shaping a blade. It is definitely going to take some time to develop the necessary skills. :) Oh, you can just barely see how I radiused the edges of the anvil next to the step, for about 5-6" towards the heel.
  12. I rotated the forge a bit so that the burner enters at an upward angle, to help keep heat off the plastic inducer. It seems to work fine that way, as the mixing tube did not heat up at all during operation over a couple hours. The ribbon nozzle certainly works but I'm not sure it's working as well as it could. I was seeing ~1700 ºF while running at ~7-8 psi. The flames were generally pretty short and there was a lot of secondary flame, so I guess rich. At times the flames lengthened out to how I've seen them before. I think my taped-together plenum is leaking so I need to work on that. I will probably just go ahead and weld it together. It seems tough to get sharp pictures from my phone but here's one of the flame size and one of the secondary flame: I should add that there were no issues with backfiring, but I didn't try to run it down to super low pressures either.
  13. Yes there are plenty of pictures of it running a jet nozzle. It seems to work fine but I have no comparison really. I’ve been thinking to build a different style inducer for comparison.
  14. Ah, got it; handheld cylinder. A needle valve modifies pressure, but does so as a function of flow rate. So it may be valid to approximate the jet pressure as the cylinder pressure when one uses such a small orifice and runs the needle valve fully open.
  15. I was just curious why you would be discussing full cylinder pressure.