well...... congrats on the oven, first off. Sounds like somebody's stepping up into the world. As far as the different masses on ferrous and non-ferrous metals and core temperatures, I can bore you for hours on theoretical and proven times for heat conductivity. Let's go this route instead,shall we?
Aluminum heats faster than steel. This is fact. Therefore the aluminum piece would take less time than the steel even if greater mass (up to a point). Assuming you are NOT doing this in a kitchen type oven, one would coat the steel first, hang it in a cold oven and turn it on. Heat it up to temperature and wait until it starts to get that "melt" about it. Keep checking by cracking the door and looking in with a flashlight ( I told you all we were gonna stay away from the technical stuff,lol). When your part is _just_ cured....take it out and hang in a spot where it can cool down by itself easily enough via air reduction. THEN you put in your aluminum part. When that has cured sufficiently (part metal temperature as indicated by your directions) only then can you open the oven doors slightly, turn the heat off and leave the fan on. The fan will help cool everything down and both pieces will be coated using the most cost effective method. Steel can take a long time to heat up and it can go along for the ride in your oven when coming up to speed (which you were going to turn on anyways). The steel will retain heat longer, so basically you've got to get it out of there toot sweet. Aluminum conducts heat faster, therefore able to take that quick heat up and cool-down in the oven. So basically....there ya go. Both parts done and no oven time ($money$) wasted.
Of course...you listed extreme weights for examples. What would you do in a real world situation where the parts were within like masses? Easy.....coat them all, put in a cold oven. Shut the doors and turn the oven on to temperature. repeat the process for aluminum as stated above. If near same weights and masses, the parts will basically "act" the same in that method. If near same mass (within 5 pounds of one another maybe?) you can heat the oven up and hold at a temperature below the lowest cure ( say maybe 325?) for a while then boost the temp. up to final cure range. You'll note that most thermoset plastics (what you guys use) have a 100% over-cure range in them. Meaning....if your aluminum part is fully cured and the steel is just getting there....and will be done let's say 8 minutes later? It's ok. Your "window" is set nicely so that you can do this. Just work slowly and don't rush,k? It's easier to re-coat or even re-prep whatever your doing than burning/blasting the part off and reworking it,lol. Especially a 50lb hunk of aluminum,right?
That's it in a nutshell, folks. Sorry that I drone on and on at times. But then again...... you guys all ask good questions that need some explanation at times,lol. Take care all..... Russ
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