heat treatment furnace options/brands
Anybody have experience with automatic electric heat treatment furnaces?
I'm looking for something I can plug into a 50amp or better yet 30amp 3-phase outlet, program, load, and go.
Ideally could harden, then temper, in an efficient sequence (quenching of course is outside the furnace.)
Any particular suggestions of brands to buy? Not buy?
(Workpieces are likely to be short shafts, bearings, etc. Think bicycle parts, human powered boat parts, etc. So, maybe 1ft cube?)
I don't know of any single furnace that will "efficiently" harden AND temper. One reason is that there is approx 1000°F between typical hardening and tempering temperatures. Takes a while (hours even) for the furnace to cool down to tempering temps.
Since I don't do production work I have no problem hardening a small batch and then waiting. With the furnace door open I can be down to tempering temps in about two hours. I use a small table top muffler furnace. It is limited in size of work but effective.
I am interest in hearing about small furnaces that can do both also.
Interresting point about the temp change David.
I just decided to start looking for a furnace two nights ago and had not considered the fact that it can take a while to get back to drawing temp. I quite often hear that cracks are more common if the part is cooled completely before tempering. Seems as though only cooling it to 150° min is the general concensus. Since I have no furnace I have no first hand info though!
Here's your load and go furnace. That's the only spec of yours it meets. 30 amp draw is OK, that's doable with a small furnace. Programming is not a problem, it's the quench cycle that is hard to do. The only ones that I know of doing this are "vacumn" furnaces. We looked at an Ipesn/Abar Tiny Turbo for our quick loads. I don't remember price, but I think was over $100K.
BTW, that was with Super System Inc. controls
I have a book,whose title I cannot recall!!! A little blue soft cover book. It says to temper your parts when they've gotten just cool enough to hold in the hand (abt.130 deg.F.) He recommends a toaster oven with a decent high temp. thermometer. I have done this with a Brownell's 1000 degree dial thermometer with a long shank,sticking through a hole drilled in it,for drawing in the 400 degree range.
This need to draw at once is described as a "do or die" necessity for maximum tool life.
We used to have 2 furnaces at work,and after using the toaster oven for a time,just started keeping the 2nd. oven at tempering temp so it would be ready at once soon as the steel cooled enough to hold.
OK, well these folks http://www.knightsfurnace.com/ make a furnace with a fancy controller like used for pottery on it. (I suppose other folks do too.)
But when you think about it, you want to open the door at harden temp and then quench the part in whatever medium, tracking temp as you go. That will generally go pretty fast. (Quench is from, say 2000F to 150F as fast as, say, oil will allow. Right?)
So programming the furnace to drop to 150F as fast as it can go, which will be definition be pretty slow, won't work very well, because it will take much too long.
One could of course have two ovens, one for each temp. These folks make pre-configured units like that:
Pretty spendy, and would need a transformer. So maybe better to get two of the simpler furnaces?
Anybody ever by one of these things used and have it be OK?
before you jump into this, do yourself a favor and get Bill Bryson's book, _heat Treatment, Selection, and Application of Tool STeels_
Next, I wish I could tell you to start browsing the Crucible metal sites, but they are in bankruptcy, so who knows how long the links will be good. But you can search any steel you might use and they have complete sheets on every one.
Next best is to sign in the Carpenters site so you can use their professional advice and information. Their information is not as easy to use, and not as consistent but there's a lot there.
Every steel has a different heat treat schedule.
Each steel has several potential heat treat schedules depending on which features are most important to you. As a rough example, say I am using A2. A low austenizing temp with a long soak, fast air quench, and relatively high tempering temp followed by a second temper 50° lower will give me a very tough product at the given hardness. OTOH, hardening from the high end of the austenizing temp, and a low temper will bring out the most hardness possible in the steel. This is a generalization, for A2. If you have the charts for the steel, you can tailor the chracteristics to your product.
Your run of the mill furnaces are good for about 1800F
If you want to do HSS steels and some of the higher alloyed steels, you will need one that the elments can take 2200, or maybe higher for some of the older HSS steels like T-1.
It is possible to buy an older shop furnace, or say a school or lab furnace, and for a few hundred$ add a new controller.
Most steels require a ramp up to temp, with more or less brief soaks at one or more temperatures on the way up. If you might need to anneal, say, HSS, you will need a furnace that can ramp down over a very long period of 24 - 36 hours, at, say, 30°/hour or so.
I find that a contorller with 8 steps does most of what I need. Usually only 3 are used*. preheat to first set value, soak at set value for 8 - 15 mins (my parts are small), ramp up to austeniizing temp, soak for 1 to 2 hours, then I set a second temp 1° higher in case I don't get back to the furnace in time, when I see it, I know I'm past the soak time and can quench the tool.
You will prematurely age the elements in your furnace if you cool it fast enough from the hardening temperature to be ready to temper by the time the part is quenched, even if you use air hardening steel.
I have 2 furnaces, but most of the time just use the oven in the kitchen. It is a Bosch gas oven, and it is astoundingly accurate, better than my heat treat furnace, without a lot of diddling on the program. Of course a kitchen oven will only allow you to do lower temp steels like W, O-1 and the harder levels of A2 or S7 (down to about Rc56). If you plan on using HSS steels it might be better to get a second furnace. Some of those actually yield a harder product tempered from around 1000° than they do from, say 800°
Eurotherm makes excellent controls, but they can be spendy. My old control was that brand but ancient. The unit was like 6 x 12 x 6" deep and weighed maybe 8 lbs. But it sure was easy to use. It failed this year, & I got a tiny modern Fuji which works ok, drove me crazy programming it for 3 days, still overshoots until it learns a specific program, and is not as nice or intuitive to use as the old Eurotherm. Modern Eurotherm controls are similar in size now, but pricy. If they are as stable as the old ones, the extra cost would be worthwhile.
*What I actually do, is have steps 1 - 4 programmed for a ramp up/ie heat treat cycle, and can select "run only steps 1 thru 4". Steps 5 thru 8 are programmed with a ramp down, i.e annealing cycle. If I need to anneal, I choose "run only steps 5 thru 8". But 3 out of 4 or 8 steps would cover most steel heat treatment needs.
I didn't pick up on the "quench outside".
Here's what you need. There are a lot of job shops that run a set-up like this.
You could probably find a used pair, but will end up rebricking if you have them shipped very far.
Stephen Thomas (and others),
I follow the "do or die" rule of not letting the part get below 150°F on quench fro hardening. The book by Bryson you mention is quite good for recipes on treatment of just about any steel one is likely to heat treat. It was Bryson that suggests placing the the work on the top of the furnace to maintain 150+ °F until the furnace is at tempering temp.
For the HSMer, I like the suggestion of using a toaster oven for tempering if it can be controlled consistently. I have also used a single burner hotplate with a bunch of kiln bricks and connected to a process controller for tempering.
Somewhere on this forum I have posted a wiring diagram and parts list for the conversion I did to a muffler furnace.