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I would like to build a 2ft x 2ft x approximately 1.5" heat press consisting of 2 heated plates, a PID controller with thermostor, and a hydraulic press. The plates will need to maintain 60-80c as evenly as possible. I don't have much electrical experience but have been researching this for a week or so now. It seems the ideal thing would be to use a thin insulated nichrome, machine out a piece of aluminum that is 22" x 22" x .5", run the nichrome back and forth as many times as possible, and embed the aluminum in a 2ft x 2ft x 1.5" piece of steel.

The more nichrome with lower amps running through the plates the more even the heat but I run into insane voltage requirements the longer I stretch it.

Is there a way around needing thousands of volts to run 40awg nichrome 100 or more feet? Does someone have a link to a prefabricated version of these plates that would be cheaper than building them? Not an electrical engineering question, but would these plates stand up to a 20 ton press?

Any design input, helpful equations, or other advice is greatly appreciated!

-Mac

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  • \$\begingroup\$ Yes, using thicker wire with lower resistance. But putting things into 20 ton press, think is a bad idea, there is also HF heating if your material can heat under HF. \$\endgroup\$ Dec 5, 2015 at 16:52

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Based merely on your questions I'd suggest you buy, rather than make, a heated platen. Or at least the heating part.

If making, you cut the 100 feet of wire (a resistor) into short enough sections (many parallel resistors) that a more suitable voltage drives it - or you choose something more appropriate for the task than 40 AWG nichrome. Industrial heating elements come in many flavors, lots of which work fine off 240 VAC.

schematic

simulate this circuit – Schematic created using CircuitLab

Dunno about 20 tons, but a dry-mount press is a stock off the shelf (or off the used product) item with a large heated platen, for instance.

Silicone pad heaters are one stock item that would appear to work fine for your proposed use. Not associated with or even a customer of the place I found a picture of them... Watlo pad heaters

If you heat by clamping them to the backside of the thick steel platen, 4 common 240VAC electric stove elements (per plate) will probably get the job done perfectly well - ("as evenly as possible" is taken care of by 1.5 inches of steel.) You can also drill lots of holes and insert lots of cartridge heaters.

Be sure to carefully and throughly ground all parts of the press, especially if you home-brew the element. If something fails, you want the breaker to blow, not to electrocute someone.

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  • \$\begingroup\$ Agreed. For industrial heat presses 'pencil' or 'cartridge' heaters are a standard solution. They're available in a range of lengths and power densities. You'll need to drill long holes for your application. Set them back from the working face and the temperature will even out in the metal. \$\endgroup\$
    – Transistor
    Dec 5, 2015 at 18:15
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You'll need to calculate the power requirement. This approach may help.

$$P = \frac{{m}.{\Delta T}.{SHC}}{t}$$

Where P = power (kW), m = mass (kg), ΔT = change in temperature, SHC = specific heat capacity of your metal and t = time.

So, if your press was a 15 kg steel block (SHC = 0.45 kJ/kg.K, and you want it to get from 20°C to 80°C in 5 minutes:

$$P = \frac{{15}.{(80 - 20)}.{0.45}}{5(60)} = 1.35 kW$$

Once it gets there the controller would reduce power and static power would depend on heat loss to the environment.

You now need to figure out how much heat will be transferred to the object being squished and how often per unit time. It may cause you to increase the power of the assembly.

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