Time required to heat dies

[SIzzleAndDoom]

Hi everyone,

I'm working on a project meant to come up with tentative preheat times for our forge shop's dies. I have all the necessary material properties of the dies (from the manufacturer). The dies are heated using several gas torches and heavy insulated blankets. All I'm missing are the mathematical relationships to make use of it all, and my knowledge of heat transfer is insufficient. At this point I'm not concerned with losses, only the equations needed. Can you all help me out?

Thanks,
Matt

 

[racookpe1978]

No.

Not to start from scratch and begin from no background info about your own training and the problem.

What do you know about heat transfer and transient heat transfer in particular?
What is the mass of the articles?
What area of the articles is heated, and how are they to be heated?
How are they supported while they heat?
Show a sketch of the proposed heating method, and show how YOU have begun YOUR calculations.
What is ambient temperature and what is final temperature and how long long do YOU think is the cycle time to heat the dies?

Otherwise, my answer is:
yes.
Heat them up.
Don't let them cool took much between heating and the die impact.
Don't heat too far or your dies will loose strength and be themselves deformed by the forming pressure, rather than restraining the forming pressure into the metal being pressed.
Don't heat them too little or the m,etal being formed will not mold and curve as you expect.

 

[gruntguru]

Q = M x Cp x (T2 - T1)

EXAMPLE (Replace the numbers with your own.)
Q = Heat input required
M = 1000kg
Cp(steel)= 0.49 kJ/kg.K
T1 = 20*C
T2 = 120*C
formula gives Q = 50,000 kJ (30 MJ)
heat output from gas torches = 600 MJ/hr (10 MJ/min)
Heating time = 30/10 = 3 minutes.
This neglects all losses - Loss through insulating blankets, heat loss from torch to air, etc etc. Losses might double the heating time so answer = 3 to 6 minutes. Do you need higher precision than that? If so, the calculations and (more importantly) the conditions and assumptions get more difficult.

je suis charlie