Metal Temp vs. Time

[zoomer]

Please help me before I actually test this out with an infared thermometer.

I'd like to chart the temperature drop per second for:

8 lbs. of Aluminum (A380 specifically) in a ladle container where the top is exposed but heat will radiate from sides.
1250F starting metal temp.
72F ambient air replenished so 72F always.

For every second, the temperature will be: _____F?

 

[IRstuff]

Is this for school?

TTFN

FAQ731-376

 

[zoomer]

Not for school...it's so I can expand my duties and responsibilities at work for the same pay.

I work for a die caster and they don't have the answer.
I can use an infared thermometer but it only goes up to 950F...so, my knowledge of thermo and transfer doesn't give up the answer.

Seems easy right? Hot metal in a container losing heat to the surrounding air at a rate of X degrees per second.

 

[IRstuff]

Unfortunately for you, it's not "easy." Radiated loss is proportional to absolute temperture to the 4th power, so it's nowhere linear. Even convective loss is nonlinearly dependent on temperature. Since it's nonlinear with temperature, you'd need to crank some finite difference equations to get tolerably meaningful results. 8 lbs of aluminum is massive enough that you also need to have a decent idea of what the thermal conductivity and specific heat are at different temperatures, assuming that there's some temperature dependence.

Alternately, you might look into some material that you can place in front of your pyrometer to reduce the flux to the detector, to capture the initial temperature behavior, but you'd need to have a good idea of how the device actually works. You might get some help from the manufacturer of the device.

TTFN

FAQ731-376

 

[zekeman]

"Alternately, you might look into some material that you can place in front of your pyrometer to reduce the flux to the detector, to capture the initial temperature behavior, but you'd need to have a good idea of how the device actually works. You might get some help from the manufacturer of the device.""

Good idea, but it can easily be done be reducing the view factor to the IR detector.or equivalently reduce the solid angle.

 

[corus]

A ladle is typically lined with refractory and so heat conducts through the lining to the outer shell before losing heat via natural convection and radiation. At the upper surface, heat radiates away dependent upon its view to the ambient. This will give rise to a temperature distribution through the aluminium. You really need to use a 2D finite element program to work out the temperature within the aluminium with all the temperature dependent thermal properties of the metal, lining, and ladle. The change in temperature will also be dependent upon the time so there is no simple answer as the heat loss will be so many degrees per second.

Tata

 

[zekeman]

"Good idea, but it can easily be done be reducing the view factor to the IR detector.or equivalently reduce the solid angle."

Correction, not valid for a IR thermometer, but for a naked detector.

Zoomer,

Many of the IR detectors have thermocouple atachments for the higher temp measurements. If so, then get your company to get one at modest cost. Doing this analytically is not a good idea if you have the testing means.

 

[CastMetal]

What exactly are you looking for this data to provide you with? Time to solidification? Temperature of the metal as it enters the cavity?

The reason I ask is even with a thermocouple the variations in temperature throughout a 8 lb mass will be significant, Making it difficult to accurately measure repeatedly.

And as stated above this isn't a linear answer. If you just want a ballpark number relative to that specific temperature range use a thermocouple with a repeatable positioning setup relative to the ladle for a few samples and plug data into excel for a linear fit t vs deg F.

 

[zoomer]

The die cast manager doesn't know their pour temperature.
I know that letting the ladle dwell for X seconds will reduce the temperature down to ___F.

X is 30 seconds
T1 is 1250F metal start temperature
T2 is ____F after 30 seconds.

I'd like to say: T2 = 1200F, you lost 50F by not pouring on time. Or, you lost 200F by not pouring on time.

Introducing the plant to engineering principles.

I have an old graph for ferrous metal but not for Aluminum.
This type of data doesn't exist, but I'd like to plug and chug.

 

[CastMetal]

Its going to be easiest to just find it empirically with a thermocouple. But if you want a ballpark number 20deg/min is a rough starting point.