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I'm hoping some kind person can tell me if I have this right or not. I swear this isn't a homework problem.

I'll be using a heated pneumatic press to heat seal lidding to plastic containers (imagine I'm sealing yogurt containers). I need to verify that the machine I'm looking at can deliver a certain psi at the interface of the plastic and the lidding. That interface has much less area than the total area of the heated platen applying the force.

From what I understand I take the pressure delivered to the machine, subtract the ambient air pressure, multiply by the surface area of the cylinder and then add the total weight of the platen to get the full downforce the machine is capable of. From there I divide that by the surface area of the contact between the object under the press and the platen.

Please enjoy my wonderful art below (these are just random numbers): psi diagram

So in this case the total downforce of the platen is: (100psi - 14.7psi) * 1 sq in + 10 lbs = 95.3 lbs

And the force experienced by the red object under the press is: 95.3lbs / 2 sq in = 47.65psi

I feel like that's right but all my attempts to google for this answer only lead me to finding the total downforce of the press and not the force experienced by a smaller object under the press. Do I have it right? Thanks!

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This looks right- but note the units of pressure (not force) experienced by the red object are pounds per square inch.

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  • $\begingroup$ Thanks man. It seemed like the only way that could work but I needed a sanity check. $\endgroup$ – Doug Henning Mar 14 at 18:11

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