I am interested to cool the melt from high to low or from 1200 to 800 C in just 6 seconds.
It is very difficult proposition to adhere to cooling rate of 50C/s without doing proper FEM modelling. You have to improvise some method, but before I tell anything two more things are required to know -
1. Material (which alloy? Al/ Mg based etc.)
2. At 500C will it still be liquid?
Once these answers are known we can discuss further.
The casting temperature is between 800 to 1200C. The concept is to cool as-cast as fast as possible. In high pressure gas quenching, distortion maybe the issue. The economic feasibility of gas quenching too is quite low.
From the above discussions I understand the following -
You are trying to cast liquid Al-alloy into a mold to obtain tensile specimen and you want to cool the liquid metal to 500C as fast as possible.
If the above is correct then the solution given by Xu Wang is correct. Considering that you are using metallic mold (steel), use heat balance equation and mass of mold and cast alloy to determine the preheating temperature of mold.
Cp(alloy) * mass of alloy * (liquid T - 500) = Cp(steel) * mass of mold * (500- mold preheating T)
Please confirm:
How to estimate values of specific heat ?
Lastly, what is your opinion over salt bath?
How can you pour liquid metal in a salt bath to obtain a regular sized tensile specimen? If you do not worry about the final shape then salt bath is perfect.
The heat balance equation is just a rough approximation and never meant to gave you a precise cooling rate. Just to extimate the mold preheating T, Cp values at RT is just fine. Before pouring actual alloy you can test with a dummy alloy and thermocouple to measure the actual cooling rate.
In order to acheive proper cooling rate one has to treat this as transient heat trasfer problem, either analytically or by FEM methods.
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