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I Forge Iron


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About timgunn1962

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    Lancashire, England

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  1. Are they Devil Forge burners? I would replace the worm-drive hose clips with 2-eared "O" clips. I am slightly (?) anal about it and use 2 of them at 90-degrees to each other. You squeeze up the ears on the O-clips with end-nips. The worm drive ones tend to drag the hose to a sort of D-shape and are more prone to leakage at the corners of the D in my experience (and yes I did use the recommended size). If you are using parallel-threaded fittings, use a good anaerobic pipe seal. As said above, you may need quite a lot more pressure to overcome burn-back up the burner tube. Moreso when you open up the chokes for higher flame temperatures.
  2. If you are only heat-treating, you will not need a 3/4" burner. A 1/2" NA burner with fine adjustment of the airflow can easily heat a much bigger volume than that. I have built a few small HT forges using a burner based on a 1/2" Amal atmospheric injector. Intended as a cheap way to get good temperature control for a knifemaker on a budget. I used a 20" piece of 10" pipe, lined with 1" of blanket and with disks of 1" board for the ends, giving around 900 cu in. Everything got a wash of china clay in a solution of Sodium Silicate and water because it was cheap, immobilized the surface fibres and the forge was not going to get hot enough to melt the Sodium Silicate (it melts at about 1100 degC-ish, around 2000 degF). It will hold HT temperatures to within a couple of degrees for plenty long enough to soak O1 and similar steels once it is adjusted. The adjustment is by the knurled portion which is threaded into the injector body and has a pipe thread the same size as the burner tube. This gives superfine adjustment of the mixture and therefore the temperature. The burner has a flame retention cup made from a short (1") length of 3/4" pipe welded flush with the end of the 1/2" pipe and a 3" length of 1" pipe slid on and welded to it. Target temperature when the photo was taken was 800 degC (1472 degF). It was actually running at 801 degC (1474 degF). I was trying to make a smaller version of the Don Fogg 55-gallon drum HT forge. It wouldn't work for me at all until I turned it over, putting the burner port at the top and the work/exhaust port at the bottom.
  3. What is the smallest burner tube diameter and how many burners/ports? There is little point in jumping through hoops to get a blast gate in a 3” line if you are going to be reducing to a 1 1/2” burner with only a quarter of the area further down the line.
  4. One factor in attainable thickness that I've noticed is the size of the grog/aggregate used. It's not really practical to cast a 1/4" thick wall if the lumps are over 1/2". Sieving it can overcome this, but may make it more crack-prone due to lack of reinforcement. These castables are/were formulated by competent folk who do/did it for a living. Generally speaking, I find it is best to read the manufacturers spec sheets and use a product suited to the task in hand, unless you are fortunate enough to have access to one of the technical guys who genuinely knows how far outside the published spec a product will go while still getting the job done AND who is properly familiar with the finer details of the process.
  5. I can't think where I've seen it, but I have a feeling that Devil Forge may use a MegaPascal-marked gauge, though I would imagine this may vary by destination. The cylinder fittings vary by country and, IME, regulators usually come with gauges marked in the customary units for the country/region they fit. .1 MPa is 1 bar or 15 PSI.
  6. The highest I have measured in a Propane forge was 1556 degC (2833 degF) and still rising. I didn't want to risk the $400+ typeS thermocouple, so didn't wait to see what it would top out at. I measured a forge at a hammerin a few years ago. It was being used for pattern-welding blade steels and was right around 1300 degC (2372 degF). As I understand things, it had been adjusted to give a temperature suitable for "anyone" to weld in and I regard 1300 degC as a good target temperature for a (bladesmiths) welding forge. The more experienced pattern welders tend to use a lower temperature (probably around 1200 degC) because it gives crisper contrast between the different-coloured layers. One caveat is that High-Carbon blade steels tend to need lower temperatures than lower-Carbon steels or Wrought Iron. However, if you are getting 1400 degC and have Dragons Breath (The DB is a sign of a reducing atmosphere: a secondary burn that takes place when hot, partially-burned gases reach fresh air containing enough Oxygen to complete the burn), you should be ok for welding pretty much anything.
  7. I do not fit ball valves on my burners. My rationale is as follows: In normal operation, all adjustment and on/off control is done from the regulator, which is at the cylinder. It is where I habitually go to adjust or stop the gas. It is at the upstream end of the relatively fragile hose and it is reasonably well away from the hot bits. If the midden hits the windmill, I do not want options. I do not want to have to spend any time at all, however brief, assessing the situation and deciding whether to use the "safety shutoff valve" that may have been provided in the hot area where things are going wrong, or the cylinder valve in the relatively safe location. I will go to where I habitually go and do what I habitually do to shut things down and that is at the cylinder. It is the safer place to be. I will close the cylinder valve. Admittedly it will take a fraction of a second longer than closing a ball valve, but I will have saved that fraction of a second, and more, by not having to make a choice earlier. Others may feel differently. As a general rule, I'd rather not share a shop with those who do.
  8. You are right and I am wrong. Thanks for correcting me.
  9. The pressure in a Naturally Aspirated burner is needed to impart speed to the gas issuing from the jet. There is some quite complex, and not particularly intuitive, Physics going on, but basically there is a conservation of momentum thing happening which draws in air and mixes it with the gas. In a blown burner, the air is forced in, rather than being drawn in by the fast-moving gas stream, so there is no need to have high pressure and a high-speed gas stream. A bigger jet will give a lower speed for a given gas flow and the lower speed is obtained with a lower pressure. High speeds tend to be associated with laminar flow, while low speeds tend to be associated with turbulent flow. Turbulence is needed to mix the gas and air effectively, so lower gas speeds are preferable where high speed is not needed to get the air in the first place. Flow through a jet varies as the square root of the pressure: half the flow needs a quarter of the pressure. Double the flow needs 4 times the pressure. If you are going to use a “jet”, it and regulate the gas flow on pressure, the “jet” needs to be sized to give a useful range of flows across the pressure range you can set with your regulator. Finding an appropriate jet size for a NA burner is the difficult part. Not needing to do it for a blown burner is probably the main reason blown burners are usually considered easier to build. If you use a needle valve (which can be thought of as an adjustable-area “jet”) to control gas flow, you don’t need to worry about regulator pressure overmuch.
  10. 1mm gas jet on a blown burner seems very small. Are you getting any Dragons Breath? If not, You are probably running too lean and would benefit from a bigger gas “jet”. A small jet and high pressure are needed in NA burners because the gas velocity needs to be high to entrain air. Blown burners have the blower for the air and gas velocity is not needed.
  11. I had an IR thermometer, good to 1600 degC. Pretty close to useless for most smiths. It ended up with a guy who makes some nice kitchen knives. He uses it to check for consistent temperatures when taking billets from the forge as they come out. Once he’s got the first one or two working right, he doesn’t care what temperature value he is reading, just that the reading is the same each time. When the steel is in the forge, it scales to some extent. When it comes out into the air, it scales some more. When it gets hit, the scale gets knocked off and immediately starts reforming. The emissivity changes with every process and every second that passes. There is no one value that will give accurate temperature readings.
  12. I did a bit of playing with jet sizes and found the Butane jetting to work very well on Propane forges. I think the factory jetting is intended for “normal” heating applications which use both primary and secondary air. For Propane forges, there is usually no secondary air so the Propane jetting runs pretty rich and not quite hot enough for welding. The Butane jetting is smaller, so runs less rich and a bit hotter when burning Propane: certainly hot enough for welding bladesmithing steels, though I don’t know whether it will manage WI welding temperature. It’s still rich enough to limit scaling in the forge, so there’s some scope for reducing the jet size further to get even higher temperatures if needed. The Amal jets are available in closely-spaced increments and the sizing is pretty intuitive.
  13. Try increasing the size of the hoses. If you can double the diameter of the long section, the area will increase by a factor of 4 and the pressure loss will go down dramatically (the physics gets complicated, but a first approximation is that the pressure loss varies as the square of the velocity, so you'd get something of the order of one sixteenth of the pressure loss along the same length at the same flowrate). Shorten the hose and the pressure loss will vary with the length (as a first approximation). Ten feet of 1 1/2" hose will give "about" one fortieth of the pressure loss of your twenty-five feet of 3/4" hose. If you go for 1 1/2" hose upstream of the tee, get the tee as close as possible to the burners and use the 3/4" hose (that you already have) between the tee and the burners, things will probably get a lot more manageable.
  14. It sounds to me like you probably don't understand the physics well enough to be asking the right questions. The lines between blowers and pumps can be blurry at best.It's certainly not as simple as changing from one to the other at a defined pressure. "200-300 CFM" is a very wide range when considering the pressures needed to drive flow through a tube. I'd suggest an online search to find the catalog for "Rotron Regenerative Blowers" and read the technical stuff near the back. It'll either give you some answers or will give you a better idea of the appropriate questions. There is a "friction loss per foot of tubing" chart that should prove particularly instructive.
  15. Can you buy jets for the burner separately? If it needs secondary air as it stands, with the choke fully open, to get the maximum temperature that you need, fitting a smaller gas jet will increase the primary air:fuel ratio and reduce or eliminate the secondary air requirement. I would find out what jets are available, if any, and how fast you can get them, before butchering the burner mountings. That way you can see what you get and decide whether to try different jets or cut-and-shut if it does not do what you want.
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