infrared thermometer

[tommag]

I bought one of those infra-red/laser thermometers from Napa. I used it to check against my casting thermo. and it showed realistic temps when aimed at the cast iron pot. When I aimed it at the surface of the melt, it only showed temps in the 300-400 degree range. What do you figure is going on here?
Tom

[Edward429451]

Not deep enough in the melt to get an accurate reading. My digital thermometer with probe does the same thing when I get lower than 1/2 pot.

[floodgate]

The IR thermometers assume that they are looking at a "black" surface (rough, dark gray, etc., but NOT reflective). Non-black surfaces will read low.

floodgate

[tommag]

Floodgate, now that you mention shiny surfaces, I remember reading that in the instructions. DOH!
Kinda like Fishhawk says, as well. Edward, that makes sense, too.
Thanks as usual, guys.

[AZ-Stew]

If you're using a bottom pour pot where you won't be interfering with a ladle, you might consider floating a small piece of strap steel, such as that found at the home centers, in the pot as a non-reflective thermometer target. I don't know whether or not it would work, but you might give it a try.

You'll be measuring the surface temperature, rather than the temp of the melt near the pour spout, so take this into account.

Regards,

Stew

[montana_charlie]

Will your infrared thermometer read as high as the temperature of your alloy?
Mine only goes up to 500 degrees.
CM

[tommag]

Charlie, mine is advertised as 750, but doesn't blank out until about 770.
Good idea, Stew. I'm using a ladle, but in my smelting pot, a small peice of flat bar wouldn't get in the way.

[Sundogg1911]

If it is a good quality IR Thermometer there will be a setting to allow for reflection of different things. I have a 3M IR Thermometer (It was $600 new, but that was a while ago....I got it free from work When they got new ones) :-D If I adjust my setting for lead my readings are dead on. I saw a cheaper one (About $60) it had no adjustments. It's fine for engine block temperature or non reflective temps, but you wont be getting a good reading directly on the melted alloy. Just hit the edge of the pot close to the lead, that's probably as close as you will get.

[454PB]

A gas check (or a penny) floating on the surface will darken and allow accurate readings.

[Namerifrats]

I have a $60 one from Harbor Freight, goes up to 1100 degrees. Works fine for me, I notice a big difference when hitting the shiny alloy it shows to be alot cooler. Aim the beam on a little of the dross left on top of the alloy. I bottom pour so leaving a little dross doesn't get in the way.