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Pyrometer purchasing/use suggestions


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Hey everyone,

I've only made one knife at a local forge and am getting everything together for my own home forge. I would like to get a Pyrometer to help me better understand the different shade temps at least for the first little bit. I have heard that many people (if not all) get to the point where they don't need one, but I would like to use it to help me along the way in the beginning. 

 

Can anyone post some suggestions of which ones to buy, or at least things to look for when buying one? Also, any tips on how to use one would be much appreciated as well.

 

Thanks in advance!

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If all you want is to determine the proper temperature for quenching carbon steel, you can watch for decalescence.  A search for that term on this forum will tell you quite a lot.  

 

An actual pyrometer is not cheap.  Harbor Freight used to sell one for around $35, but now they don't.  I was asking a similar question a while back in this thread: 

Keep in mind you need two things: the reader and the probe.  The Auber unit mentioned early in that thread(https://www.auberins.com/index.php?main_page=product_info&cPath=17&products_id=199) is nice, but I went with a dual-input mini-model from Omega, this one: https://www.omega.com/en-us/temperature-measurement/temperature-and-humidity-and-dew-point-meters/p/HH307-308

 

I needed a long probe, so I got the one Tim recommended in that thread: https://www.omega.com/en-us/temperature-measurement/temperature-probes/handheld-probes/p/KHXL-NHXL

 

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Posted (edited)
8 hours ago, Alan Longmire said:

If all you want is to determine the proper temperature for quenching carbon steel, you can watch for decalescence.  A search for that term on this forum will tell you quite a lot.  

 

An actual pyrometer is not cheap.  Harbor Freight used to sell one for around $35, but now they don't.  I was asking a similar question a while back in this thread: 

Keep in mind you need two things: the reader and the probe.  The Auber unit mentioned early in that thread(https://www.auberins.com/index.php?main_page=product_info&cPath=17&products_id=199) is nice, but I went with a dual-input mini-model from Omega, this one: https://www.omega.com/en-us/temperature-measurement/temperature-and-humidity-and-dew-point-meters/p/HH307-308

 

I needed a long probe, so I got the one Tim recommended in that thread: https://www.omega.com/en-us/temperature-measurement/temperature-probes/handheld-probes/p/KHXL-NHXL

 

Thanks Alan, I expected a good quality pyrometer to cost a bit so I'm not turned off by the price of the units you pointed out. I didn't realize that I needed both the probe and the reader. 

 

Any advice on how to use one? I've heard everything from punching a hole in your forge and having the probe stick into the middle of the open space of the forge to just laying the probe on the bottom of the forge floor and putting the metal you're wanting to measure on top of the probe in the forge. 

 

Thanks again, I really appreciate the info!

Edited by brendon.davies
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Since I got the 24" probe with built-in handle, I just wait until the temperature in the forge has equalized, then stick the tip of the probe where I want to measure the temperature, usually just above the floor.  It takes a few minutes to get there and settle in.  I then adjust the forge until it's hitting the temperature I want.  

 

If you want constant measurement, you'll want to get a thermowell to put a probe in.  This is just an inconel sheath that you stick through a hole in the forge as a semi-permanent place to measure temperature.  You can just use a probe, but the well helps things last longer.  If you're not worried about accidentally hitting the probe, you can install one of the potter's kiln- type ceramic covered probes. They last well in the heat, but if you smack one with a billet it will fall apart.

 

Oh yeah, one more thing: You want a type K thermocouple probe, and the reader has to be able to read type K.  

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One thing to look at when buying a pyrometer is to look at the rating of the accompanying thermocouple.  A lost of times they are rated at temperatures lower than most forges run at.  What you want is a ceramic shielded thermocouple.

 

Doug

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2 hours ago, Doug Lester said:

ceramic shielded thermocouple

 

Actually, no, he doesn't. Type K, inconel sheath. Ceramic ones are too fragile for forge use.

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There are whole books about temperature measurement with thermocouples. It would be a trifle naive to expect a forum post to condense it all into a few sentences. 

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Don't forget to purchase and use the correct type of thermocouple wire as well.  Using regular copper wire can throw off your readings,  Note that type R or S thermocouples are also good for forge temperatures, just stupid expensive...

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Here's one I used for several years, it has both the 1300C probe and a battery powered reader for about $50: https://www.amazon.com/gp/product/B01DMQOWD4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

Or you can build your own, eBay has type 1300C K probes for 20$: https://www.ebay.com/itm/112652921112 (no affiliation, this is just the last listing I bought one of these from). You can use a PID controller as a reader, even if you don't plan on controlling anything with it, they go for $10 to $20 (https://www.ebay.com/sch/i.html?_nkw=pid+controller&_sacat=0&_sop=155). Nice thing about this setup is that you can later add a solenoid valve to a gas forge idler, and use it to control your forge temperature.

 

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4 hours ago, Jesse Lange said:

I have been very impressed by/ happy with this one, and the price isn't too bad either: 

 

https://www.amazon.com/dp/B079HHSHLQ/ref=cm_sw_r_cp_apip_eQtyqOb4AXk3C

 

I've also seen it used by some of the pros in their videos (I forget who, but maybe Steve Schwarzer). 

 

Hey Jesse,

Interesting that you posted about that IR thermometer, I read that the IR ones get kinda flaky when the temps get hotter than 1000 F. How long have you used it for and how accurate has it been for you? I would love to use an IR one if it works good, really interested in your feedback on it. 

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In my experience with IR, you get what you pay for.  I've used units that worked fairly well on liquid steel, but get rather finicky when slag got in the way due to extremely different emissivity constants.  It is also very important to be aware of how they work, especially in regards to the emissivity constants and the cone for measurement area (30:1 in the one linked above).  You will want to figure out the emissivity constant for your refractory and always point at that, not your steel as the reading area will be bigger than your steel at most distances.  I definitely prefer K-type thermocouples (or R or S, depending on application), but the IR technology is definitely getting way better as time goes on, so hopefully some day the IR options will be good enough at a cost that makes them worth while.  

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Interestingly, emissivity can just stop being an issue if the measurement is taken from a hole that is at least 6 diameters deep. Oversimplifying somewhat, the general idea is that anything emitted will reflect around within the hole before coming out and the effective emissivity within the hole will be very close to 1.

 

In many cases, a forge is very similar to a hole and an IR temperature measurement taken through the mouth of the forge can be quite accurate. Obviously it will only work if there is not a rear opening to confuse things and the distance-to-spot ratio needs to be sufficient to get the whole measuring spot within the forge without melting the instrument.  

 

IR units are already cheaper than type R and S thermocouples in many cases.  They are becoming cost-comparable with "proper industrial" type K and N thermocouples, over which they have some advantages. Admittedly they have some disadvantages as well.

 

 

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I tend to regard a long hand-held Mineral Insulated type K thermocouple with a high-temperature sheath material as the first step. This can be moved about in the forge to establish where the hot zone is. If it is big enough and reaches the lining (which is primarily what will emit the IR), the thermocouple can be kept in the working zone while an IR reading is taken. If the IR and thermocouple agree, the IR measurement can be used for subsequent measurements.  

 

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40 minutes ago, timgunn said:

IR units are already cheaper than type R and S thermocouples in many cases. 

I have tried several "top of the line" units to replace our S types and they were not at all adequate.  If you know of one that can give accurate readings through the smoke and slag in an induction furnace and/or ladle for reading molten steel and irons I would love to know of one.  The last one I played with required emissivity adjustments based on alloy group (stainless and low alloy were different, for example) and the slag was an issue at all times.  We were able to find adequate angles to keep the unit away from the heat, but it did get pretty awkward due to the distance-to-spot ratio.  If we could get one for $2k or so I think we could be cost effective, but they would have to be pretty solid units that don't die after a year or two in the foundry.  

 

Sorry for the slight de-rail.  I think it is definitely doable in a forge, and Tim's second post it pretty much exactly what I had in mind earlier.  

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I think there are probably ways of using IR to replace R and S in certain production applications, but only if all the other variables can be eliminated. That ain't gonna happen in many of "our" applications. It doesn't seem likely it could happen in yours.

 

The only smith I know who seems to have used one effectively just used it to check his billet temperatures were consistent coming out of the forge, before sticking them under the power hammer. He always measured straight from the forge and didn't care what temperature was read, as long as it was the same temperature every time. The main reason he used the IR was that the light in the shop was very variable throughout the day, making it very hard to judge temperature consistently by eye. Once the billet was hit and the scale came off, emissivity changed dramatically and the IR pyrometer was useless.

 

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On 4/27/2021 at 11:42 AM, brendon.davies said:

 

Hey Jesse,

Interesting that you posted about that IR thermometer, I read that the IR ones get kinda flaky when the temps get hotter than 1000 F. How long have you used it for and how accurate has it been for you? I would love to use an IR one if it works good, really interested in your feedback on it. 

 

Take my response w/ a grain of salt as I am relatively new to this (started last fall, took a 2 week ABS intro to Bladesmithing class about a month ago). 

I've been very happy with the IR thermometer. When I've used it to check temp for normalization and hardening, I've ended up with really tight silky grain structure. I've also used it to check temp in my forge and I've been able to get readings upwards of 2400 degrees. When I've soaked bar stock and checked temp of forge and then pulled out the stock and checked, the temp has been consistent, so I have decent confidence in the accuracy. 

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