IR thermometer

[HSC ///]

thinking I want an IR thermometer, high temp

I prefer buy once, cry once,
I prefer not to goto Harbor Freight
I'm good at finding deals for quality used

what do you guys use and recommend?

thanks

 

[JTknives]

no no NO these don't work for what we need.
Even high end IR temp guns are not as accurate as we want. There are lots of variables with these temp sensors be as thy just read the IR emmited. Different materials emit different amounts of IR even at the same temp. I'm hoping Stacy will pop in and expound on this.

 

[timgunn1962]

I'd recommend a thermocouple over IR.

IR can work if the application is appropriate, but the changes that need to be made to make the application appropriate are usually much more onerous than using something else. It is not a magic bullet for measuring temperature.

The biggest problem with IR is emissivity. This is a value which quantifies how closely the emission of IR from a surface equates to that of an ideal "black body", which would have an emissivity of 1.

There's a pretty good explanation of the emissivity issue at:

http://www.reliableplant.com/Read/1...-difference-between-apparent,-actual-ir-temps

From our point of view, the Oxide layer can be thought of as behaving in a similar way to black paint. In the forge, it will reach a thickness. As soon as the hot metal reaches open air, the metal will Oxidize and the Oxide layer will thicken, most likely increasing emissivity and apparent temperature as it does so. Then it gets worked, spalling off the Oxide layer (scale), reducing the emissivity and apparent temperature, before re-Oxidizing.

 

[knarfeng]

The problem with IR thermometers is that they look at an area instead of one spot. So it's hard to be certain if the item in question is at that temp, or if something next to it is. I don't permit the use of IR thermometers in my curing specifications.

 

[HSC ///]

Ok ok
I have an omega t/c
There are other uses for an ir

Quench oil
Water quench
Parkerize tank


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[Stacy E. Apelt - Bladesmith]

Agreed, I have a $1500 lab IR gun that I still wouldn't trust on reading hot steel for HT. It is far too complicated to adjust for emittance, and even then you are guessing at the degree of it. An 8 gauge TC and a good reader will tell more accurately what the blade is while in the forge. I use it to check how hot the outside of a HT oven gets, and to check the quench oil tank.

The place that many go wrong in using a TC is that they just stick it in the forge and take a reading. They usually get a number much higher than the blade. The ways to get a more precise reading are:
1) Don't read while the flame is on if possible. Set the TC in the forge right next to the blade and turn off the flame. the blade will not cool much in the few seconds it takes to take the reading.
2) If using the TC while the forge is running ( as in HT), place the TC in a ceramic sleeve. This keeps the direct flames off the TC and simulates an object roughly similar to the blade. Place it next to the blade if possible, or at least in the same part of the forge as the blade. Sheathed TCs read a bit slower to temperature changes, but are more accurate in readings.
3) Use a heavy gauge TC - 8 gauge ( 1/8") is what you need. If using an unsheathed TC, a stainless clad one will last longer.
4) Soak the forge well before taking any readings. Run your forge at a consistent temperature for 15 minutes ( or longer) before taking readings or doing HT. The whole interior of the forge needs to be at the same temperature for an accurate reading - blade, TC, refractory. Until they are all fully soaked to equalization, you are reading whichever is the highest. Once fully soaked and the flame adjusted for maintaining a steady temperature, the sheathed TC will be reading the same as the blade within a few degrees. Flipping the flame off for 10-15 seconds will not make much change, as the entire chamber is maintaining the heat.

 

[Karl B. Andersen]

I use a high temp one to check my quench oil. It matches a thermometer exactly.
And when shooting a blade in the Evenheat oven, it matches the readout exactly. I've used it in the past to see how long it takes a blade to come up to heat.

Of course you can't use one for a forge as it's reading the dragons breath OUTSIDE the forge, which is far cooler than the inside.

 

[braillediver]

We used Thermocouples for technical applications and always attached them to a mass that was given time to stabilize before taking a reading.

 

[Drew Riley]

thinking I want an IR thermometer, high temp

I prefer buy once, cry once,
I prefer not to goto Harbor Freight
I'm good at finding deals for quality used

what do you guys use and recommend?

thanks

What are your intended uses for an IR gun? There are a lot more options now days than there used to be, and you can get a "decent" gun for well under $100 that's good for quick reference.

If you want accuracy (especially high temp) you'll want a thermocouple set up.

 

[HSC ///]

What are your intended uses for an IR gun? There are a lot more options now days than there used to be, and you can get a "decent" gun for well under $100 that's good for quick reference.

If you want accuracy (especially high temp) you'll want a thermocouple set up.

Thank u
See post #5 above.


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[Drew Riley]

Thank u
See post #5 above.


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Ah, I overlooked that one. Any of those should be fine enough for an IR. Check out Amazon, Ebay, or even the sale papers at some of the big supply houses (McMaster, MSC/Enco, Grainger, Northern Tool, etc....)