Anyone use a noncontact thermometer?

[uncledeck]

I have used these at work for monitoring surface temps on solid material and have generally been impressed. I wondered if anyone has used them when smelting or casting?

http://www.harborfreight.com/cpi/cta...emnumber=96451

[zardoz]

I have used infrared thermometers for a couple of decades in the aluminum die casting business, and they have some limitations when trying to measure molten metal.

The problem is emissivity. Most infrared (non-contact) thermometers use a default emissivity of .95. A perfect 1.0 is a so called "black body" of perfect emissivity.

The highly reflective surface of molten metals like aluminum, or lead will not give an accurate reading, being off by several hundred degrees in some cases. I have a Raytek professional model at work, and I vaguely remember having to adjust emissivity to about 0.2 to 0.25 to match a reading I was getting off of an immersion type thermometer. Most of the ones, like at Harbor Freight, are fixed at 0.95.

The default 0.95 works well for about 99% of things you would want to measure, but if it is like a mirror surface, it does not work so well.

Just my experience there.

[snaggdit]

How about if you had a layer of kitty litter on top? Would it read the clay temp more accurately? Going by Harbor freight on Thursday.

[Bret4207]

The kitty litter is going to insulate the melt, I don't think it would be all that accurate. I could be dead wrong. A submersion thermometer will work in all cases. In my mind where an infrared would be handy is for measuring MOULD temp.

[OLPDon]

Not sure were I read it but it was mentioned that is you float a penny on the melt you could get a reading. But I would think a simple therm. would be best and surly it saves the $$$$.
Don

[montana_charlie]

If you cast with a dipper and keep it in the pot, it stays pretty close to the temperature of your alloy.
You could shoot it with your infrared thermometer...
CM

[twopatch]

Not sure were I read it but it was mentioned that is you float a penny on the melt you could get a reading. But I would think a simple therm. would be best and surly it saves the $$$$.
Don

You know pennys are made out of zink these days.

[snaggdit]

You know pennys are made out of zink these days.

Good call! An older penny, maybe. When did they change, last year wasn't it?

[454PB]

If you don't have an old copper penny, use a large gas check. It takes a minute or so, but either a penny or GC will turn nearly black from the heat.

[Willbird]

I have a craftsman multimeter which has a built in IR thermometer, it does not work well on Lee mold blocks either unless you smoke a spot to measure temp.

Bill

[leftiye]

Another good reason not to use Lee Molds.

[454PB]

On Lee moulds, use the sprue plate as a target.

[Willbird]

On Lee moulds, use the sprue plate as a target.

Well the sprue plate does not tell me what temperature the mold body is

Bill

[JIMinPHX]

An IR gizmo will give you a reading that is off when measuring this stuff, but it will do so consistently. If you get your pot up to a temperature that works well & the gizmo reads 354, which you know is wrong, so what. Just remember to get it back up to where the gizmo reads the same again next time & you are all set.

[Willbird]

Well on a shiny surface the gizmo tells you the surface is 55 degrees

Bill

[Charlie Sometimes]

Pennies went from copper to a zinc mixture about 1982, if I remember correctly- so anything before 1980 should be okay. Shot a 1982 with my rifle once on a real cold day, and it broke into pieces rather than punctured- still have the pieces somewhere.

[Willbird]

The newer pennies are copper clad zinc, I never put one in a lead pot to see what happens, it might not burst open for all I know.

Bill

[454PB]

Shooting the temperature on the sprue plate of a Lee mould will actually show a slightly higher temperature than the blocks themselves. Steel disperses heat more slowly than aluminum, and heat rises, so the sprue plate will be a little warmer than the blocks. Use a sharpie to apply a dark surface on the side of the blocks, then compare the temperature between the blocks and sprue plate.

The actual temperature is really only a reference, as long as I know all my aluminum mould cast best at say 400 degrees, then I know what temperature to strive for. Without lab grade test equipment, who knows what the temperature really is?