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I Forge Iron

timgunn1962

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  1. When you look up the feeds and speeds for drilling, there are both values, feed and speed, given. "We" can usually take the speed with a pinch of salt and run a lot slower, as the values are given for production scenarios in which time is money. It is certainly unwise to run faster. The feed is important for work-hardening materials. Each pass of the cutting edge does work as it cuts and leaves a thin work-hardened layer on the workpiece. If the feed is correct, the next pass of the cutting edge will get below this thin work-hardened layer and cut the un-work-hardened material beneath. Turning slow and feeding hard with a drill-press is the best approach for most of us. Using a hand-held drill, it can be hard to maintain enough pressure to get the feed necessary. If the drill stops cutting, even momentarily, it will skate on the previously-cut surface with the feed pressure spread over a tiny area at, and just behind, the cutting edge. This high-pressure contact will cause further work-hardening and the problem will swiftly escalate. Many of us are impatient, bloody-minded types and will persist in trying to drill after the drill stops cutting. If you have no option but to use a hand-held drill, use the slowest speed you can, watch the swarf and IMMEDIATELY stop if the drill stops cutting. Either sharpen the drill (a skill that is well worth acquiring) or replace it with a new one, then start again. IME, the only "better"/harder drills that work well in a handheld drill are TCT drills intended for use on Stainless Steels (which work-harden very readily) or Hard Plate (here in the UK, I've bought them from locksmiths when I've run into the problem when out on sites, but they really know how to charge). Cobalt drills do work a little better than vanilla HSS, but they also tend to be more brittle. The improvement is significant in a rigid setup, but there is a high probability you'll just break them in a handheld drill. Solid Carbide is even worse for breaking when used in a handheld drill (though truly superb in a rigid setup). The TCT ones have the hard tip, but a tough shank and flutes, so are a good choice in a handheld drill.
  2. Although the "obvious" thing to do is to look for "better"/harder drill bits, the problem is not usually with the drill bit, but with the rest of the setup, In My (limited) Experience. Very few handheld drills run slowly enough for drilling hard steels. The hardness problem is not usually "just" the hardness of the steel that is about to be drilled. Work-hardening often enters into the equation as well.
  3. I think the way that the IFBs fail in a forge is down to the extreme temperature gradient when the forge starts. I think the hot face gets hot fast and expands, putting the cooler material behind it under tension and starting cracks. When the forge stops, the "hot" face cools quickly, contracting while leaving the warmer material behind it expanded. This puts the cooler material under tension and the cracks propagate from within the IFB material to the surface. In industrial kilns, the rate at which the temperature rises is much lower, the temperature gradient is much less and the cracking problem doesn't really arise. Because IFBs are intended for industrial applications, there is no information provided by the manufacturers on their resistance to rapid thermal cycling. The only information "we" tend to get is anecdotal from others of "us". Unless you have another, better, use for the bricks, I'd say use them for a forge and report back on how well they work.
  4. It is certainly burning. It looks rich: there is a lot of secondary flame, but that should be adjustable once it's in a forge. Do you know what is causing the flame length variation that is apparent in the video?
  5. Perspective doesn't help, but are the chokes in both burners set the same? Second pic, it looks like the right-hand burner might have more choke opening?
  6. Personally, I'd go for Kanthal A1 or equivalent, rather than Nichrome, though that is primarily because it's what I've used in the past for Heat Treat ovens/furnaces and a couple of little crucible furnaces. There are several grades/compositions of Nichrome with differing maximum temperature ratings. I seem to recall the rating for Kanthal A1 being higher than for any of the available Nichrome alloys when I last looked. It's not simply a case of being able to take Bronze melting temperatures. The element will need to take Bronze pouring temperature (around 1150 degC, 2100 degF? but very dependent on which Bronxe alloy, alloy, thickness of casting and many other variables) plus whatever additional element temperature (delta T) is necessary to drive the heat output into the surroundings while those surroundings are at that pouring temperature.
  7. What are you doing in a forge that needs hotter than Propane can get? I know that a Naturally Aspirated Propane forge can get hot enough to melt Wrought/Pure Iron, because I've done it, albeit unintentionally. Oxygen injection can increase the flame temperature by reducing the proportion of Nitrogen that gets dragged along for the ride. Burning a cubic foot of acetylene in air releases exactly the same amount of heat as burning a cubic foot of acetylene in Oxygen. It's just that burning it with Oxygen, those BTUs are just heating the products of combustion, whereas burning in air, they are heating the products of combustion plus the Nitrogen (and trivial amounts of one or two other gases) that makes up the rest of the air. Sorry, fat-fingered. Oxy-Acetylene is used when really high temperatures are needed, such as when welding. We don't normally need the sort of temperatures in forges that are only available using expensive Oxygen, so it makes more sense to expend a bit of effort, rather than money, tuning the burner to get the temperature we want. This is generally a case of getting the appropriate air:fuel ratio.
  8. How much Lime are you adding? I was under the impression that Calcium Hydroxide melted at about 600 degC (Wikipedia tells me 580 degC, 1076 degF). Having experimented unsuccessfully with Waterglass (Sodium Silicate) as a rigidizer for blanket and as a binder for Zircopax, I have experienced the instant conversion from rigidizer to lubricant at around the melting point of the Waterglass ("about" 1100 degC, 2000 degF). The blanket just moves away from where the flame hits it and the Zircopax/Waterglass becomes a dribbly mess. It may well be that you are seeing the same effect from the lime?
  9. Old thread on what appears to be the same grinder.
  10. 2 bar, 30 PSI is usually fine. The square law for pressure vs flow through a jet in compressible fluids (gases) holds until the flow "chokes": the speed through the jet reaches the local speed of sound. This happens somewhere "around" 30 PSI for Propane. Going from 2 bar to 4 bar (30 PSI to 60 PSI) will therefore get you less than the 41% increase in gas flow that you'd expect to get if the flow didn't choke. There's no cost difference between a 0-2 bar and a 0-4 bar reg, and there's no noticeable difference in adjustability with the welding regs, so I tend to buy 4-bar for the "free" little extra at the top end. A 4-bar reg is nice to have, but doesn't give you much over a 2-bar in the real world. I think you'll find the 0-2-bar will be fine.
  11. I'm pretty sure that's a 0.5 bar to 4 bar regulator; about 8 to 60 PSI. There are lots of them on ebay in the UK and they are complete dog-toffee IMO/E. I had a couple of them, tried one, threw both away. The 8 PSI minimum tends to make lighting the forge unnecessarily exciting and there's obviously no control at the lower end of what would normally be the working range. The best regulators I have found tend to be plugged (no gauge) 0-4 bar Propane regulators from welding suppliers. These usually have a scale showing the (approximate) pressure setting on the side of the body, where the skirt of the adjusting knob indicates the setting. It's usually not much less accurate than a cheap gauge and is considerably more rugged than any gauge. The regulator is designed for industrial use and fine adjustment by less-than-delicate individuals wearing welding gloves. About twice the price of the 0.5-4 bar cheapies on ebay UK and, I feel, considerably better value.
  12. As Latticino says, this is (often?) caused by the speed of the flame-front moving through the mixture faster than the mixture is moving in the opposite direction. It usually starts when the forge gets fairly hot because the flame speed increases as the temperature rises. The flame will run back along the burner tube until it runs out of mixture (Propane will not burn unless it is mixed with air (or another Oxidising agent). The flame goes out. The gas keeps flowing, draws in air and mixes with it. The mixture reaches the hot forge and ignites. The process repeats. Every time the flame-front moves along the burner tube, it heats it a bit, making the flame speed even faster. If you can catch it quickly and turn up the pressure, you can often get the mixture speed faster than the flame speed and stop the problem. You have to be pretty quick to stay ahead of the burner tube heating up. You also need a big increase in pressure. The gas speed varies as the square root of the pressure, so doubling the pressure will only give a 41% increase in mixture speed. To double the mixture speed you need 4 times the pressure. Pussy-foot about giving it one or two extra PSI and you've got no chance.
  13. To get from your hose to the BSP inlet (presumably 3/8" BSP), it is best to buy suitable fittings. Over here, NPT is the PITA and NPT-BSP adaptor fittings are available at decent pneumatic/hydraulic suppliers. In a pinch, I have been known to run a tap down the existing threads (BSP tap and NPT thread in my case) and fit a "local" fitting with plenty of anaerobic pipe seal, though not, as yet, with gas pipework. I think that the pipe nipple will probably screw in relatively easily, at least in the 3/4" size (1/2" and 3/4" have the same thread pitch in both NP and BSP). I always use an excessive amount of PTFE tape here anyway (BSP into BSP) to protect the female thread in the injector, and hand-tighten only. The PTFE tape is for padding only, not for sealing in this case, so there's no need to get too concerned about whether it's rated for gas. The clever bit about the Amal injector is the super-fine adjustment provided by the screwed choke and you really don't want to louse up the threads that provide this. I also dry-lube the thread further down to ensure it will adjust freely: Dry Molybdenum Disulfide, Dry PTFE, Graphite or some combination thereof. Grease tends to pick up dust and grit, making things worse, so I don't use it.
  14. Twaddell units are a hydrometer density scale: the higher the number, the greater the density. Both are solutions of Sodium Silicate in water, as far as I can tell. Either will do the job: you'll (almost certainly) dilute it with water. I think I used the 140 Twaddell and it was seriously thick and viscous as it came. It's probably "about" twice as concentrated as the 75 Twaddell. Be careful with Sodium Silicate. It seems to melt somewhere around 1100 degC, 2000 degF. Used as a rigidizer for blanket, it is ok up to its melting point, but then it becomes a lubricant for the fibres allowing them to flow away from where the flame impinges on the blanket. It might work ok in a forge design that doesn't involve the flame impinging on the blanket. I gather a Bentonite/Zircopax (Zirconium Silicate) mixture has been successful for one or two folk. My limited experience of Bentonite in other fields causes me to feel it's not something I wish to experiment with. I would expect massive shrinkage on drying and I'd expect it to take a long time to dry (though I'm in the wet bit just North of Manchester, England and don't have a climate that's particularly conducive to drying: YMMV). I seem to recall posts on its use by someone who already had experience with pottery/ceramics and it's my guess that they'd already traversed that particular learning curve. I also have a vague recollection of them using Veegum/Bentone, rather than Bentonite, though I'll confess I have no real knowledge of the differences. I have used Zircopax/China Clay without much success (largely due to shrinkage on drying) and commercial Rigidizer/Zircopax, which was more successful: it dried without cracking, albeit slowly, and held up to welding temperature pretty well. I used a fairly thin mix of Zircopax in rigidizer, sloshed it on liberally so the rigidizer soaked into the blanket carrying some of the solids in to a depth of maybe 1/8"-1/4", but leaving most of the solids as a surface coating maybe 1/8" thick. I let it dry slowly for 3 or 4 weeks (in a Lancashire summer) before sticking the whole thing in a slow oven for a morning, turning it up in stages over an afternoon before removing it and carefully cleaning the oven before the wife came home in the evening. Commercial Rigidizer is usually a suspension of fumed Silica in water (there are also Alumina rigidizers). There are probably wetting agents and something to modify the pH (it felt like it might be mildly alkaline when I got it on my hands and washed them off, not unlike washing soda), but the main factor in determining how much Silica can be held in suspension seems to be the particle size. The commercial rigidizer will use the "best" particle size for creating a high-concentration suspension. Other uses of fumed silica include as a thickening agent for epoxy resins, and it seems reasonable to assume that these will use the best particle size for thickening resin. I tried using resin thickener to make rigidizer and the best I could manage was a Specific Gravity of 1.015 against a commercial rigidizer measured at 1.08. Clearly the Silica concentration was much lower and I surmise the particle size was different. I know others have used Silica suspension with Zircopax successfully. I think Tinkertim used a Silica investment binder (Morisol), rather than a proprietary rigidizer, and posted on here.
  15. There are many variables and it's a really good idea to sit down and work out exactly what you need to do and what you have to do it with BEFORE you start building. Some of the stuff I can infer from the information provided: You have a 220V supply available. What current (amps) can it provide? I am in the UK, where the domestic outlets are 230V nominal and are rated for 13A, limiting me to 3 Kw in round figures (If I need to, I can go to 16A or 32A, but it means the user needs to have non-standard, industrial, sockets to feed the oven). I'm assuming the 1500-2000 degrees is Fahrenheit? The length certainly seems to suggest Carbon steel temperatures. That is much easier than needing higher temperatures for Stainless steels. Realistically, you don't really want to be getting too hung up about the stuff you cannot reasonably change, like the Voltage, the length of work you need to HT, etc. Watts per cubic foot or watts per square foot are not particularly useful unless you have all the information to hand and can deal with the math involved in calculating heat transfer rates. Understanding just enough to know when you are doing something different to established practice, and not deviating far from something you know works very well, is the path that most homebuilders of HT ovens take. Generally, it works pretty ok. You have obviously done quite a lot of the build already. My general impression is that you've almost certainly not loused it up beyond recovery. I've not used coils with diameters as large as yours, so don't have a feel for what will work: You may be completely golden. If you've not already done so, Google "Kanthal Handbook .pdf" and try to get your head around as much of it as you can. My most recent builds have been 27" long, 7" wide and 6" high internally, using 3 kW of elements, and have managed 1300 degC, 2372 degF, during testing, so I don't think you'll have any problem reaching Carbon Steel temperatures on your dimensions, unless the IFBs you have used are really lousy insulators (by IFB standards), or you have significantly less power available than I do. If you can let us know what power supply is available, we can work out the element power and resistance needed. Then we can calculate the surface loading. If you have any details on your IFBs that would be helpful too. I used 16AWG Kanthal A1 on my first few builds (I've built 8 or 9 to date) and some of the guys who use them professionally experienced element burnouts. I went to 1.6mm Kanthal A1 for the 3 most recent builds and, as far as I know, they have held up well for nearly 4 years. I have always tried to maximize the available groove length, in part because I'm middle-aged and grumpy and find it easier to get the staples in to retain the coils in the grooves if I stretch the elements to the longer end of the recommended range. I run 4 lengths of the sidewalls as a rule. My elements are about 3/8" OD and the grooves are cut with a 10mm bit in a router. The 7" width of my build has been largely dictated by the need to bridge the roof with a single brick. I build without mortar because I just don't have the knack of using the accursed stuff. I did build one quick-and-dirty 42" oven, 9" wide, that used a 3 kW element each side. That used Ceramic Fiber Board for the roof and solved the issue of bridging the 9" gap. The last 2 ovens I built were 6 brick-widths long (27") and the 1" blanket I use as a door gasket compresses down to 1/2" in use, adding another inch for 28" total internal length (because some bloody irritating bladesmith had suggested, in passing, that it might be a good idea to build two ovens that could be joined together to make one for long stuff, they got built with removable backs with blanket gaskets too. I anticipated some other bladesmith telling me that a mere 56" of combined length is too short, so built the doors and roof from Ceramic Fiber Board with the facility to add layers to the door and middle for more length)
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