Induction vs Coal: forging a hardy tool 

Nice. Hopefully we'll run into each other at a Saltfork Craftsmen event!

I have a local smith friend who just got an induction forge and I'll be excited to see it work. But with a gas forge I can heat many pieces at the same time, moving them to the hot tter area of the forge sequentially. The induction forge may shine in many things, but there are advantages for the gas and coal forges. If I wee a younger smith doing a lot of production again I would add one of these to my shop for certain. Looks like an ideal way to heat the middle of a bar to upset or punch the bar in a short area. This is a great set of videos on beginning to use an induction forge.

:-) thx

An induction forge works quite nicely for knives. You'd want to make a few different coil shapes for it. Rectangular cross-section coils work better for flat stock that the circular ones.

@@ejoftheanvilThanks for the info.

@Rodney Langstroth: not easily. That size is barely possible. Taller stacks, nope. It's hard to bring a full billet to an even welding heat. You tend to burn some areas while others are still too cold. I have some ideas on that which I hope to try (and document with videos!) in the coming months.

@@ejoftheanvil I'm also very interested for a video about damascus and forge welding with induction forge as I'm curently in the market for this or a DIY propane forge and I'm sitting on the fence.

That's complicated. Rule-of-thumb for my unit: 200-600mm (about 8-24") coil length. But what it can actually drive depends not only on what material is currently in the coil, but also the temperature. I go into more detail in ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-XGGiGrkwXts.html .

Plug: I installed the same plug as my welder. I think the hard-wired thing is mostly for the 110v unit which would have to draw something like 70A.

@@ejoftheanvil thanks for the reply!

I believe the electronics can do 100% duty cycle with sufficient cooling. Unless you have better water cooling than I do, you will not reach anywhere close to 100% duty cycle. I have found that sheet metal work (which radiates tons of heat back into the coil) and long-duration heats of larger stock for my power hammer will trip the alarm and it will shut down even with what is probably

It's an LH-15a. I bought mine on ebay from zhuofei3371 (also joyfay.com). Search LH-15a induction heater. Don't get a 110v version!

Yes, that's a good summary of the conditions and how to work with them. However, you can get coal impurities on your work at any level of the fire. The coal I used for this project came (partly) from a literally dirty batch. The silicate impurities do drip down on the work and are very sticky and rather rougher on the surface than regular scale (iron oxides). In my case, I wasn't deep enough in the fire to get contaminated by the consolidated clinker (mostly the same silicates). In the case of such dirty coal, a vigorous brushing right out of the fire is helpful because the silicate goop comes off pretty easily then. As you point out, scale should be brushed off late in the heat. There's not much point when the metal is so hot that scale is forming very rapidly.

Just to be clear, I use bituminous reclaimed from a long abandoned Iron production related site, lots of little pieces of brick, chunks of coal with visible sulfur impurities, some white phosphorus, and most of the dust in mine is actually sand.

That would explain why you have so much expertise with this!

At $0.10 / kWh, it costs $3.00 to run the induction heater for 4 hours continuously at 100% power (so, 8 hour day at 50% heating time). I can get coal at $0.07 per pound (yes, quite cheap compared to most sources). That's about 42 lbs of coal. I'm pretty sure I'd use more in an 8 hour day. And, that doesn't include the cost and hassle of driving to get coal ... the electricity just shows up. That said, in a production environment, I'd still probably use propane since I could work multiple pieces at once. As a hobbyist, I'm completely sold on induction (especially since I can use it immediately unlike coal and propane). If I were a pro, I'd probably have one in addition to propane not only because of the convenience, but because certain operations are just faster with induction.

Induction is very good for heat treatment in most cases. You can make a coil that heats just the edge of the knife or hatchet. You can find them on ebay advertised as 15kW (they're not, they're 7.5kW) units. If you don't want to take the ebay risks: ussolid.com/u-s-solid-15-kw-high-frequency-induction-heater-30-80-khz-220v-or-110v.html You will also need a cooler. Larger TIG coolers will work.

You definitely want a good fit for the current size of your work. I have a video showing that effect: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-gzp4MvxLAag.html. However, you can't have more than about 600mm of coil. I show that mistake in ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-XGGiGrkwXts.html. I have a few more videos on the design of coils planned.

@@ejoftheanvil greatly greatly appreciated.

Yes, I think so.

That's great insight and a good way to think about forging. However, even if the force isn't concentrated, forging-heat metal wouldn't bounce like that. Not only am I striking very near visibly cool metal, but I suspect the core isn't very hot either. Cold metal doesn't yield like hot, so it's springy. For the taper I'm doing, I started with a blunt taper. This concentrates the blows on the end of the bar. The benefit from being near the edge is not hitting the anvil with the tilted hammer face. By 2:49, I'm actually extending the taper. If you look closely you will see that only the "peak" where the taper intersects the unforged bar is in contact with the anvil. The hammer is hitting opposite that on the other "peak" which is only a very small area of contact. For longer tapers or drawing out (say reducing 3/4" round to 3/8" for tong handles), the near or far edge can be used to great effect for reducing the contact patch. That approach wasn't needed to keep the contact small for this taper. As I said, great insight. If you ever decide to take up smithing, sounds like you'd do really well!

EJ of the Anvil I come from a science background. Thx for the very well explained reply ... will read fully on pc when I get home (on smartphone ATM). One brief thought ... your first para seemed to pose the possibility of an uneven heat in the cross section, which doesnt seem possible to me ... iron is more than sufficiently thermally conductive such that if it is red hot on the exterior, it will be red hot in the center as well ... the stock would probably need to be in excess of at least half foot in diameter (probably more) for a thermal gradient of that magnitude to occur, but I admit that's an educated guess with no practical experience behind it. The key point is that you're heating via EM Induction with a 360deg loop, not a traditional fire, and since EM flows freely through metal along field lines, the pattern of heating should be reasonanly uniform to match, whereas a coal fire heats by conduction (not induction) from the exterior inwards. Thus, if it could happen at all (re: cross sectional thermal gradient), it seems like it would occur in a stoked fire, rather than a 360 deg indiction coil, and even then only temporarily. Again, i am speculatong. Non sequitur question: I love the idea of using induction for fast and efficoent reheats like you do (if I were smithing i would doubtless do the same), but on a slightly negative note, doesnt this remove beneficial carbon introduction from the equation ? Repeated heatings in a real coal fire are almost certainly adding carbon to the iron as you work it, in order to improve the molecular syructure, in much the same way as flat strips in a charcoal fire absorb carbon ala the "blister steel" process. Induction is wonderfully fast, clean and efficient, but i cant help but think that you miss out on the ability to improve the carbon content as you work your steel. In other words, induction heating only helps you shape it, not improve its strength. Again, im just thinking aloud, and would appreciate any insights you care to share. I'd love to try smithing, but alas a torn rotator cuff says no. Anyway, cheers. Great channel - I look forward to learning by watching. 😊 P.s. BTW, one of my favorite smithing technique sites is joey van der steeg. He has some great technique vids.

Another non-sequitur: those coils definitely use a lot of power. I have no idea of the payback period, but with a pair of Tesla Powerwallls, you could buy all your power off peak (or store it if you have solar or micro-chp), and then run the forge off battery power. its an attractive daydreamy idea to pair electrically facilitated smithing with a residential co-generation and/or storage system.

Induction heating does have a skin effect. This is because the induced current produces opposing magnetic fields which repel the inducing fields. Watch starting 1:00. I pull it out about 2:24. At that point, you can still see that it's cooler in the center. Heat flows in steel, but not nearly like aluminum or copper. I held the bar in my bare hands for two heats before switching to tongs. The core isn't room temperature, but it's a few hundred degrees cooler. That has equalized quite a bit by the end of the second heat, so the bouncing pretty much goes away. I needed another 15-30s of heating on that first heat to both provide more heat and to let heat conduction do its job. As far as carburizing goes, it's a rather slow process and requires a carbon source. Blister steel takes hours at something like 1900°F and is done by packing the iron with powdered carbon. It can also be done with high heat and carbon monoxide. In a coal forge, low down it's hot but oxidizing (extra O2, some CO2, no CO), in the middle it's neutral (little O2, more CO2, no CO), beyond that is a little bit of reducing flame (less O2, same CO2, tiny bit of CO) but it's too cool to get the carbon to migrate into the iron. In practice, this means you actually lose a tiny bit of surface carbon with any heat source. It may be slightly more with induction, but either way it's negligible. Bummer on the injury :-(. Yeah, I've been watching Joey for years. Love his work.

EJ of the Anvil just watched the skin effect ... i learned something new today, which is always a good thing. Fascinating. Didnt realize induction has a pushback effect. Likewise on the carbeurizing processes you explained. Clearly my understanding earlier was faulty. 😀

Yes. But you can't work with it practically in a normal blacksmith's environment. For instance, at a reasonable forging temperature, it will melt your steel tongs.

Yes, you would have to expect the tools to be disposed of or used for scrap.

Why would you ever want to forge tungsten?

@GuardedDig2: Yes, good observation: an established coal fire heats about as fast (or even faster for large stock). I pay US$.07 per pound of coal. That may be cheaper than the electricity for induction heating, but not by much because the induction heater is basically only on when I'm heating. The real key for me is the convenience for short duration work. If I only have an hour or so, I lose almost all of it to the coal fire. I lose 60 seconds or so to putting the right coil on the induction heater.

EJ of the Anvil I will admit that’s convenient. It’s also clean so you wouldn’t get all dirty. For me I only get smithing when I have most of the day because I like to get a lot done. But I can see the appeal of an induction heater but it’s not for me. Would wrapping the coil in ceramic wool or fire brick help or make more efficient?

@@JustinTopp Generally no. You want the stock to nearly completely fill the coil to maximize energy transfer. However, it's a good thought and I think there are times where it might help. Like when you need an even and deep heat for a large forge weld. I plan to tinker with it at some time.

The "Brazeal" style of cutoff tool wedges itself in the hardie, due to the taper. It can also be used in different sized holes/anvils as well due to the taper, if long enough. Now that said, you wouldn't want a fullering tool or swage to be tapered due to the immense amount of pressure placed on it when forging, which could cause the hardie hole to spread or worse case, the heel of the anvil to crack off. BAAAAD times ! that's why they are always "loose" and bounce a bit. It's the nature of the beast. With a "Brazeal" hot cut tool, the hot material is soft enough and the curved shape of the cutting edge concentrates the pressure to a very small surface area of the stock. This allows little force to be applied to the hardie hole other than a minor amount needed to secure the wedge and provide ample resistance for cutting while driving all the residual pressure directly to the point of impact against the hot steel. Once you use this style of cutoff, you will never use another !

T. DesMarais Thank you. Hard to absorb this sort of thing by reading and video snippets - there is no substitite for hands on time.

One great solution for loose hardies is be to put a tang with a hole in it on the hardy shank, and use a weight or spring or wedge, etc. to retain the hardy, while still allowing it to load only the anvil face around the hole. One can use closer tolerance stock to fit their hole, if they can afford it, one problem is the prohibitive cost of a welder, the other is the effort needed to only upset the part you want to be thicker. My hardy tools are really weird, as having a 5' railroad track for an anvil means giant "staple" shaped pieces with forms/tools/swedges on top have to suffice for now.

RufusWolf Ah, clever ... a spring braced against the opposite end of the hardy hole that maintains constant pull from below on hardy tools.

As of May 2019, about US$700 for the induction heater and $3-400 for a cooler.