I have yet to find anything on this topic, and while I have another post going, this one I want to keep simple:
If 4000 watts is applied to a plate, of volume V and Area A, in a steady state temperature of T, how hot can it get, and over what period of time?
Sorry, I'm probably doing a poor job of describing it. I'm going to assume the temperature of air stays the same, so Tair=80F for example. if the plate has a surface area of 2ft^2, and a mass of 35lbs, and other constants, what would the temperature of the plate be if given a heat flow of 4000Watts? I've been using the Thermal Wizard website, but I haven't found a good solution yet. I was hoping to graph the temperature of the plate over time.
You are expending considerable energy in solving the wrong part of the problem (as stated in other post). You are interested in providing sufficient thermal energy to melt plastic on demand. What are the constraints for the melting process, such as: mass flow rate of plastic; mass flow rate of substrate on which the plastic is placed (in case the platen needs to warm the substrate); softening temperature of plastic; initial temperature of plastic pellets, film, etc? Steady-state temperature of the plate will cause you grief. You need to provide the correct temperature and heat flux to sustain the melting process. The plastic is going to pull heat out of the plate and then the process won't maintain itself. The plate temperature is not the problem to solve: the total system is the problem to solve.
Advice: quit trying to find an online calculator and get out a heat transfer book and run some calculations. If you don't understand the calculations then you shouldn't try to solve this online. You will never know if the solution is correct, or even close. Part of the issue with internet calculators and help forums such as this, is that you are still responsible for the solution in spite of the advice received.
Alternate solution: run an experiment. 4kW of heaters are cheap and so is 35 lbs of plate.