Temp display for forge

B

BD Blades

Well-Known Member
This may be a silly question but I will ask.

I am new to forging and currently only have a small home built forge. I am hoping to buy or build a bigger one. I was wondering if anyone uses a temacuople and temperature display for thir forge. If forging at the right temprature and keeping grain size small and so on is so important I can't see why this would not help. I know nothing about what would be involved to set something like that up and it may not be cost effective. Just curious.
 
Yes, I and others do use thermocouples with pyrometer to help regulate our forge temperatures. I know that I payed less than $100 for mine and not long ago someone posted a link to a add on Amazon.com that was selling one for $40 that measured up to around 2200-2400 degrees. I stuck my probe through the side wall of my heat treating/welding forge. It had been through the back until I cut a pass-through port in the back. I don't run one on the small forge, 7" fire chamber, that I only use for forging. Going by the color of the steel is good enough for that operation.

It does help in heat treating to be able to cut the heat back so that I can soak the blade without having to worry as much about overheating the thinner parts like the edge and point. Especially if I have to heat treat a hypereutictic (>77 points carbon) where I have to try to hold it between the upper and lower critical points for 5-10 minutes to dissolve the carbon out of the carbides without growing the grain. Hypoeutictic (<77 points of carbon) can be soaked at a slightly higher temperature and only long enough to make sure that the steel is heated all the way through, though reducing the heat helps prevent overheating here too. It also helps if you can learn to spot decalcience (sp). That is a play of shadow that passes across the steel as the iron crystals in it change phase. The steel actually starts to brighten, then becomes a duller red or orange, then brightens again. Always back up that observation by testing with a magnet. Recalcience (sp) is the same thing but as the steel cools. It took me several months to spot this after I first heard about it.

Doug
 
Thanks for the quick reply Doug.

I guess to refine my question more, I can certaily see why you would use the pyrometer for the HT and welding, but is it just not necessary for forging. I may be getting out there on this, but if keeping grain growth down is very important and maybe you did not have such a trained eye wouldln't the pyrometer help with temp control. Or can what little growth you have be fixed in normalizing and heat treating.
 
Measuring temperature certainly lets you sidestep a big chunk of the learning curve, and whilst a cheapish thermocouple and readout won't be any better than a good smiths eyeball at getting repeatable temperatures, it won't be any worse either.

If you are self taught and/or still learning, a good smiths eyeball won't be available until you are pretty good. Even then it's nice to check its calibration every so often, especially if the lighting conditions change.

For the cheapest setup I can find that does the job well, I suggest the following:

Get on ebay and buy a TM902C readout for under $10. The probe that comes with it isn't much use to us, but you can stick it in your quench tank for checking the temperature. I can't be sure, but it might even be glass-fiber insulated and good to tempering temperatures, so you can check your oven. It certainly won't do forging temperatures. NOTE: The TM902C only reads in degC, to 1300 degC (2372 degF) so if you only think in degF, either sort yourself out a conversion chart or buy a different readout. Despite the price, my TM902C is accurate. It agrees with my more expensive readouts and it's the one I tend to use most, just because it's cheap and foolproof.

Then go to www.Omega.com and get a KHXL-14G-RSC-24

The KHXL page is at http://www.omega.com/ppt/pptsc.asp?ref=KHXL_NHXL&Nav=tema06

For some reason the 24" probe doesn't show, but put "KHXL-14G-RSC-24" in the search box and it'll give you a price. Looks to me around $60 shipped in the US, but I'm not familiar with any sales taxes, etc in the US and could be wrong.

KHXL-14G-RSC-24 breaks down as; Type K Mineral Insulated thermocouple with a "Super Omegaclad" sheath, usable up to 1335 degC (2440 degF) for short periods (this is vague, I know, but think in terms of hours or days, rather than weeks or months). 1/4" (6mm) diameter (rigid enough to be able to place the tip where you want it when it's 2 feet away from the handle) with a grounded junction (this gives fast response and means that it measures right at the tip). It's 24" long (enough that you won't burn your hand or melt the handle unless you are pretty careless) with a plastic handle, curly cable and a miniature plug to fit the TM902C (or most other typeK readouts you may come across).
 
For general forging I would not worry about measuring temperature. Use your eye and your hammer to tell you whether or not the steel is at the right heat to move. Don't be overly worried about grain growth during forging but do be worried about getting the steel so hot that it decarberizes on you, but that's not going to happen unless you get to a bright yellow. Grain growth can be corrected by triple normalization during heat treating, though I usually do at least one normalization after I forge the knife or stop forging on it for the day just to relieve the stress caused by forging.

Doug
 
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