We just bought a used HT oven for $60. It has about a 1.5 cubic foot interior and goes up to 2kF. It has an analog temp meter and a rheostat that controls the on/off ratio instead of a temp dial setting. I forget the name but one of the guys says it's a better but older make and model.
I doubt it'll save us money on heat treating but it'll be fun and the guys have a new toy...very important for morale. My question is: How hot and how long to do a steak in there? Crusty on the outside and red in the middle! Mmmmmm!
Not really a rheostat (which is a variable series resistance), but rather a duty-cycle control.
Possibly Blue-M? I've worked with one about that size.
Certainly. I would suggest replacing the duty cycle controller with an electronic one -- Omega makes nice ones. Gunner has some of some other brand used I believe. The duty-cycle type keeps inserting that off cycle even when you are barely on the way up to temperature. The electronic one (based on the behavior of my Omega which I fitted to a smaller oven which I got with *no* controller) is that it will stay on full time until it reaches about 75% of the set point temperature, then it will turn off for a while and observe the overshoot, then it will go back full on until it gets close to the setpoint and start cycling just right to have perhaps a 1 degree F overshoot at 1850 F. Even with this, it takes about an hour to get to set point. I'm not sure how long it would take with the duty cycle controller -- I wasn't after as great an accuracy back then. :-)
Hmm ... fifteen seconds perhaps? 0.0625" thick black outside, and the rest red and jucy. :-)
Of course, it depends on how hot you get it first. (There is also the trick of how you will get it back out if you don't have proper heat treating gloves. :-)
I did such a retrofit on a similar oven. The issue was to ensure that the plastic controller and solid-state relay didn't overheat when the oven was at full temperature. The smell of boiled plastic will totally destroy the flavor of the steak.
Anyway, the thread on my retrofit is titled "Old Vigor Burnout Furnace adapted to heat treating" and was posted in August 2008 to RCM.
The problem with *my* oven at least with that kind of cycle would be just how fast does the temperature need to fall vs how fast will it *really* fall with the existing oven. Faster with the oven door open and a fan blowing into it, but no way to be sure just what the cooling rate of the workpiece vs the theromcouple.
Of course, my (older) Omega controller has the disadvantage of having a single set point. But it has the advantage of a low voltage DC output to feed to a solid state relay to control the power to the heating element, so it is reliable and quiet as it cycles. :-)
Gunner Asch on Sat, 08 Jan 2011 01:07:50 -0800 typed in rec.crafts.metalworking the following:
4x4 - that much farther to walk, once you get it stuck. And on slick roads, the difference is the number of tires uselessly spinning.
Driving to church Saturday evening, taking my lady friend after the "Christmas Dinner" - it is the big fat flakes zooming at you which make the trip so exhausting. Good thing I know the road, but still, ... "lost the road! .... found it!" "Good to hear."