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Model Forum / General / Models / December 2006Tiny Furnace Success
Thought I would share a small success with you. About a month ago I decided to sort myself out a little furnace for annealing or hardening tools or small lumps of scrap metal I want to re-use, and today I am chuffed to have run it up to 850C for well under my £200 budget (should go over 1000C if I need it). I bought one of those Efco 150 efforts from Germany via eBay. Very small but no controller. £131 inc P&P. Hole in the back for a thermocouple. Then I bought a tiny new PID controller and huge (40A) solid state relay (SSR) - via eBay from the States, and they threw in a type K thermocouple. That was under £50 collected from the local post office, though it took nearly 3 weeks to get to me. Last night I wired up the controller, SSR, some idiot lights in a nice box, and thermocouple and bingo, it all works (and yes it works in Celsius, and on UK voltage). The controller is PID with self tuning, and once tuned it seems to go to and hold a temperature accurately. So what I am saying is that converting a simple hobby kiln with no temperature control to single-phase SSR with accurate control can be pretty cheap. Maybe even cheaper if I had got the controller from where it was originally made - Hong Kong ! Now I need some tongs....and maybe some Kasenit..... Steve > and maybe some Kasenit..... Don't use Kasenit in the kiln! Or your heating elements will end like mine. It will be eaten up. You need carburizing powder (but I don't know the name). Like this: <http://www.angele-shop.com/catalog/product_info.php?pName=carburizing-powder-box -05-kg&cName=auxiliaries-hardening> That's what I read somewhere. Nick  Signature*********************************** *** Available now in NZ and AUS *** *********************************** <http://www.yadro.de> > Don't use Kasenit in the kiln! > Or your heating elements will end like mine. It will be eaten up. You need > carburizing powder (but I don't know the name). > Nick Hi Nick, I have been following your thread with interest, but kept quiet about my SSR experiment in case I found it didn't work ! I bought a book on electric-kilns and it says that Kanthal elements have big trouble with reducing atmospheres as they rely on aluminium in the alloy to form a thin protective film, and the reducing atmosphere removes it. Kanthal can be used up to 1200C. It doesn't give the same warning for Nichrome elements - which can be used to 1050C. So I was thinking it might depend which elements you have. Is this something you have explore in detail ? I don't know how to tell which type I have, except I know the kiln is rated for 1050C. Steve > I have been following your thread with interest, but kept quiet about > my SSR experiment in case I found it didn't work ! Coward! ;-) If my mercury switch would not have worked, I would have installed a PID and SSR. But the mechanical(!) regulator keeps the temperature quite close (looks like better than 7°C). > I bought a book on electric-kilns and it says that Kanthal elements > have big trouble with reducing atmospheres as they rely on aluminium in > the alloy to form a thin protective film, and the reducing atmosphere > removes it. Seems that it isn't that simple. Kanthal says, that the Kanthal AF I am using is better for carbonizing and sulphoric atmospheres and the oxide is very resistant to diffusion. And they last about 3 times longer than the Nikrothal. For Nikrothal, they say it has a higher resistance to corrosion compared to a *non*-corroded Kanthal. But the Kanthal gets the corrosion layer during the first heating up (which has to be done with an empty kiln). Now which one is better? I think the Kanthal, because all use them. :-) Also, Kanthal suggested the A1 when I phoned them. As I didn't get the A1, I took the AF which is quite the same. > Kanthal can be used up to 1200C. It doesn't give the same > warning for Nichrome elements - which can be used to 1050C. Now if I know what Kasenit is made of. Certainly something with carbon. :-) > I don't know how to tell which type I have, > except I know the kiln is rated for 1050C. This _might_ be Nikrothal. Nick Signature*********************************** *** Available now in NZ and AUS *** *********************************** <http://www.yadro.de> > If my mercury switch would not have worked, I would have installed a PID and > SSR. But the mechanical(!) regulator keeps the temperature quite close > (looks like better than 7°C). I bought two controllers and two SSRs - let me know if your switch packs up. > Now if I know what Kasenit is made of. Certainly something with carbon. :-) I think it is mainly carbon with 10% barium carbonate - but don't know where I read that. Pack carburising should be done in a tin with a lid, and a bit of fireclay round the join might help. Keep the carbon where it is needed and away from the rest of the furnace - also it will be CO in there - so probably an extract over the top and maybe even a CO detector. I think all these element types ending in ..al have a small amount of aluminium in them to help protect the surface. In pottery they sometimes have reducing conditions due to carbon, and they say you can get away with it to some extent providing the next few firings are oxidising. Also I don't have exposed elements, they are the other side of the lining (does that make it a muffle?), so maybe that helps too. But I am trying to find what element types I have first, then we shall see. At least I can now anneal and temper...though I need some tongs to do the quench part. Steve >> If my mercury switch would not have worked, I would have installed a PID and >> SSR. But the mechanical(!) regulator keeps the temperature quite close [quoted text clipped - 7 lines] >I think it is mainly carbon with 10% barium carbonate - but don't know >where I read that. <snip> I would assume some sodium/potassium hexacyanoferrate as well. Mark Rand RTFM > >> If my mercury switch would not have worked, I would have installed a PID and > >> SSR. But the mechanical(!) regulator keeps the temperature quite close [quoted text clipped - 14 lines] > Mark Rand > RTFM http://www.martellabs.com/msds/80349.txt Tom SignaturePosted via a free Usenet account from http://www.teranews.com >> >> If my mercury switch would not have worked, I would have installed a PID and >> >> SSR. But the mechanical(!) regulator keeps the temperature quite close [quoted text clipped - 18 lines] > >Tom IIRC that's the stuff. Mark Rand RTFM > http://www.martellabs.com/msds/80349.txt Aha - so Kasenit is american - no wonder my searches for Kasenit and Carburising come to nowt (in america they spell it carburizing). From the MSDS it looks like it is entirely potassium ferrocyanide, so they hope to get some of nitrogen into the case as well - at the expense of having some HCN floating around in the air as well as CO. I think I may go for the old fashioned route - as a rule I don't have things around with cyanide in the name. When I worked at a heat treatment plant as a student we had a molten salt CN bath and one of the night shift felt a bit queasy, went to the loo, and was found dead there. Like being bitten by a dog at a tender age I have always kept away from it since. Anyone got old Model Engineering mags Vol 2611 Novices Corner has a section "Simple Methods of Case Hardening" Vol 2835 Experts Workshop "Case Hardening Tools". Vol 2855 Experts Workshop "Case-Hardening in the Workshop" Vol 2867 Beginners Workshop "Case Hardening" Vol 3124 For the Schools "Case-Hardening with Bone Dust" Vol 3148 For the Schools "Case-Hardening without Scale" Vol 3167 Trade "Case Hardening" Vol 3299 For the Schools "Case Hardening" Vol 3659 Workshop "Case Hardening" Tubal Cain Vol 3661 Workshop "Case Hardening contd." Maybe I should pop this request up as another thread ? Steve > I think I may go for the old fashioned route - as a rule I don't have > things around with cyanide in the name. That triggered my alarm-bells as well! But the MSDS reads not so alarming (to me). But I'm not an expert in reading them; due to language problems, legalese and lack of chemical competence. Comments of enlightened people would be great. Nick Signature*********************************** *** Available now in NZ and AUS *** *********************************** <http://www.yadro.de> >> http://www.martellabs.com/msds/80349.txt > [quoted text clipped - 10 lines] >there. Like being bitten by a dog at a tender age I have always kept >away from it since. Note that potassium ferrocyanide (potassium hexa-cyanoferrate) is used as an anti-caking agent in ordinary table salt. At normal temperatures it's rather benign. Once stuff is at red heat, a little bit of CO and HCN from the Kasenit is the least of your safety concerns. Mark Rand RTFM > Note that potassium ferrocyanide (potassium hexa-cyanoferrate) is used as an > anti-caking agent in ordinary table salt. At normal temperatures it's rather > benign. Once stuff is at red heat, a little bit of CO and HCN from the Kasenit > is the least of your safety concerns. Ooer - ferrocyanide in my salt (disguised as hexa-cyanoferrate). So maybe I should go back to worrying about the mercury in my fillings. So where do you get the Kasenit stuff in the UK ? I see its $12.95 a pound in the US, so seems cheap enough - but a quick search didn't locate it. However I am still tempted to make my own mixture with charcoal, barium carbonate and ground bones. After all, metallurgy needs to retain a little magic - just look at the enormous thread that exploded when someone mentioned j-p-nese sw-rds ! Steve > > http://www.martellabs.com/msds/80349.txt > [quoted text clipped - 10 lines] > there. Like being bitten by a dog at a tender age I have always kept > away from it since. > Steve Actually Kasenit was invented in Britain and the original company was British. BTW its been around for over 70 years. Are you toying with the idea of packing your components in leather? That would be considered "old fashioned". :-) Tom SignaturePosted via a free Usenet account from http://www.teranews.com > Actually Kasenit was invented in Britain and the original > company was British. BTW its been around for over 70 years. > Are you toying with the idea of packing your components in > leather? That would be considered "old fashioned". :-) > > Tom Sounds good to me - just like GB390162 from 1933 (is this the invention you refer to?) A hardening-bath for iron and steel tools comprises one-eighth of a litre of water, 250 gms. coal dust, 75 gms. potassium p ferrocyanide, 1/2 litre of oil, to which is added 250 gms. of pulverized slate. To case-harden the tools, the latter are heated to 600-700 DEG C., sprinkled with potassium ferrocyanide, heated again to 800-900 DEG C., and cooled in the hardening-bath. Woops - can't be that one - the author is German GB141802 is UK and 1920 District Chemical Co., and Hoblyn, J. B. Jan. 20, 1919. Case-hardening.-Oxalates are contained in carburizing-mixtures in addition to other ingredients, such as charcoal, barium carbonate, sodium chloride, potassium ferrocyanide, and organic nitrogen compound such as amines. The oxalates used are preferably those of the alkali and alkaline-earth metals, and the quantity varies from 2 to 20 per cent. The aromatic amines preferred are those of the type diphenylamine and a and # naphthylamine. I like this one too from Moss Gear Co Ltd Abstract of GB425724 1935 A case-hardening composition comprises pulverized coal 10 lbs., caustic soda 1 lb., barium carbonate 1 lb. and water 12 lbs. The ingredients are mixed together with water to the consistency of treacle and the articles to be hardened are dipped into the viscous compound and the coated articles are then packed into boxes and heated in a muffle or placed direct in the furnace which is then heated to about 900 DEG C. As you can tell, the novelty of being able to search old patents still hasn't worn off !! Those boys must have had loads of fun experimenting with different concoctions. Steve > > Actually Kasenit was invented in Britain and the original > > company was British. BTW its been around for over 70 years. [quoted text clipped - 42 lines] > > Steve Ever heard of KISS Steve? Try searching for Kasenit as the applicant. Tom SignaturePosted via a free Usenet account from http://www.teranews.com > Try searching for Kasenit as the applicant. > > Tom Aha, you mean this one with all the cookery ingredients - its the best one of the lot. Though the potassium ferrocyanide apppears to be an optional extra. Thanks. Abstract of GB412173 of 1934 In the case-hardening of iron or steel articles, the articles or parts to be treated are coated with a pasty mixture, preferably of a honey-like consistency, containing farinaceous material such as flour or rice and heated to 900-950 DEG C. The grains of farinaceous material are preferably ground whole to include the nitrogenous matter of the skins or husks and is mixed with a binder such as a mixture of starch, water or sugary substance and, one or more energizers such as an alkaline earth carbonate, hydrate or alkali. One or more adhesives or moisture retaining substances such as gum and glycerine and fillers such as slate powder, gypsum barytes or iron oxide may also be added as well as densifying matter such as pumice powder or ground coke. The mixture may also contain potassium or sodium ferrocyanides. In an example, the mixture comprises 31 per cent of ground rice, 21 of barium carbonate, 1 of sodium hydrate, 5 of glucose, 3 of silica and 39 of water. Take 3 times a day with meals (or instead of meals) Steve > > Try searching for Kasenit as the applicant. > > [quoted text clipped - 24 lines] > Take 3 times a day with meals (or instead of meals) > Steve Now would you be rather spoon fed, or drip fed? :-) Tom SignaturePosted via a free Usenet account from http://www.teranews.com >>> If my mercury switch would not have worked, I would have installed a PID and >>> SSR. But the mechanical(!) regulator keeps the temperature quite close [quoted text clipped - 12 lines] > Mark Rand > RTFM x-posted to them as knows. SignatureBigEgg Hack to size. Hammer to fit. Weld to join. Grind to shape. Paint to cover. http://www.workshop-projects.com - Plans and free books - *Now with forum* > I bought two controllers and two SSRs - let me know if your switch > packs up. The controller would be interesting. Got a link to a description? > I think all these element types ending in ..al have a small amount of > aluminium in them to help protect the surface. Nikrothal doesn't have Al in it. <wild guessing> I _guess_ that Kanthal is a Swedish city. They sometimes like to name their companies that way (Husaberg (= "house-mountain"), Husqvarna (="house-river")) and the ending "thal" might mean valley (Tal in German). But I might be _completely_ wrong. </wild guessing> > Also I don't have exposed elements, they are the other side of the > lining (does that make it a muffle?), I think so. > At least I can now anneal and temper... That's what we all want to do. > though I need some tongs to do the quench part. Maybe quite a good idea. :-) They are easily made out of some round bar, hammered flat where rivet is going through. Nick Signature*********************************** *** Available now in NZ and AUS *** *********************************** <http://www.yadro.de> > > I bought two controllers and two SSRs - let me know if your switch > > packs up. > > The controller would be interesting. Got a link to a description? Look on eBay for 190061305421. They are VERY small - 48mm by 48mm face - so they fit in the palm of you hand. The top display is the current temperature, and the bottom one is the target temperature (C or F according to preference). They have output to 2 relays plus an SSR output (which I think is better). They accept a wide range of TCs and they throw in a type K. These are simple units, no computer interface, no ability to program time cycles. You can manually set the PID controls so I suppose you might be able to control heating rate a little, or you can just set it to auto-tune the PID. Not much use for the pottery market without more control, but good enough for me and cheap as chips (plus they also do SSRs). Steve |
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