Casting a metal (Enthelpy of Fusion Question)

In summary, the conversation discusses the process of pouring liquid aluminum at 700oC into a steel mold starting at 20oC. The goal is to find the final temperatures of the aluminum and steel. The calculations involve the mass, specific heat, and melting point of aluminum and steel. The equation is set up with the variable Tf representing the final temperature, and the goal is achieved through goal seek at 94.77oC. The conversation also mentions the potential reactions that can occur between molten aluminum and stainless steel.
  • #1
360modina
7
0
I want to take a liquid metal, Aluminum at 700oC and pour it into a steel mold starting at 20oC. For the purpose of the question let’s say that the heat transfer is 100% with no losses to the surroundings.

Here are some numbers:

Al
Mass = 200 g = 0.2 Kg
Ti, Al = 700oC
Cp = 900 J/Kg-K
ΔHf = 10.67 kJ/mol
Melting point of Al = 660oC

Steel
Mass = 3Kg
Ti, st = 20oC

So the liquid aluminum will cool once it hits 660, but the steel mold should never change state due to its higher melting point.

At this point I want to find the final temperatures of the Aluminum and the Steel mold.

Here's what I have so far can someone please check my theory/number placement:

(900 J/Kg-K)(0.2Kg)(700oC-660oC)+(200g)(1 mol/26.96g) + (900 J/Kg-K)(0.2Kg)(Tf, Al - 20oC)

= (486 J/Kg-K)(3Kg)(Tf, St - 20oC)

So my guess is both final temperatures will be the same, I just wanted to know if this work looks correct or if I need to change/move some numbers.
 
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  • #2
This part (900 J/Kg-K)(0.2Kg)(Tf, Al - 20oC) is not correct. One is still cooling from Tmelt to Tf. The Al decreases in temperature while the Fe heats up.

At equilibrium Tf(Al) = Tf(Fe)
 
  • #3
That's actually why I posted this, I had a feeling that using the 20oC on the Aluminum side didn't make sense, so I think the left hand side should be changed to (900 J/Kg-K)(0.2Kg)(Tf, Al - 660oC).

Is that correct, or am I still missing something else?
 
  • #4
Try (660°C-Tf(Al)). The Al is cooling from 660°C to Tf, 660°C > Tf.
 
  • #5
Ok, I reworked it again let me know what you link:

LHS (Aluminum)
(900 J/Kg-K)(0.2Kg)(700oC-660oC)+(200g)(1 mol/26.96g)(10.67 kJ/mol)+(900J/Kg-K)(0.2Kg)(660oC - Tf)

RHS (Steel)
(486 J/Kg-K)(3Kg)(Tf - 20oC)

I took the sum of the LHS and the RHS and put them both into excel

I set Tf as my variable on both sides of the equation and used goal seek to find Tf = 94.77oC

With that LHS=RHS=109019.9
 
  • #6
It is my experience that molten Al can do nasty things to Stainless. Even though you are well below SS melting point reactions can still occur. The fact that your steel is cool should help.

Good luck and dry molds.
 

1. What is the enthalpy of fusion and why is it important in casting a metal?

The enthalpy of fusion is the amount of energy required to melt a solid metal into a liquid state. In casting, this is important because it determines the temperature at which the metal will melt and become fluid enough to be molded into the desired shape.

2. How does the enthalpy of fusion affect the casting process?

The enthalpy of fusion affects the casting process in several ways. It determines the melting temperature of the metal, the amount of energy needed to melt it, and the cooling rate required for solidification. It also affects the shrinkage and density of the final cast metal.

3. What factors can influence the enthalpy of fusion in casting a metal?

The composition and purity of the metal, as well as its crystal structure and grain size, can influence the enthalpy of fusion. Other factors such as the heating and cooling rates, pressure, and presence of impurities can also affect the enthalpy of fusion.

4. How is the enthalpy of fusion determined for a particular metal?

The enthalpy of fusion can be determined experimentally by measuring the heat flow during the melting process using techniques such as differential scanning calorimetry. It can also be calculated using thermodynamic data and equations for the specific metal.

5. How can the enthalpy of fusion be optimized for a specific casting process?

The enthalpy of fusion can be optimized by selecting the appropriate metal alloy, controlling the heating and cooling rates, and ensuring the purity and homogeneity of the metal. The use of additives or alloying elements can also help to adjust the enthalpy of fusion for a specific casting process.

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