Calulate Pressure of extruder based on force November 22, 2018 04:58PM Registered: 8 years ago Posts: 19
Is it easy to calculate the pressure that can be generated by the cold end of an extrusion system which is then available for the hotend?

I refer to this simple article

https://www.dummies.com/education/science/physics/how-to-calculate-force-based-on-pressure/

Which states : Pressure = Force/Area

Can you then work out - Pressure = What your extrusion system can lift (say 4 kg's before failing) / surface area of filament (A=π x 1.75 squared)

As with most things with physics I am probably missing something - any ideas.
 Re: Calulate Pressure of extruder based on force November 22, 2018 06:25PM Registered: 9 years ago Posts: 465
For correctness, 1.75mm is the nominal diameter of the filament. 0.875mm is the radius of the filament. (Surface area then is about 2.405mm^2)

However, what you've calculated there is the amount of pressure that there will be in the nozzle if the nozzle is blocked to the point where it can no longer extrude. Any pressure above that point will be lost when the plastic flows out of the nozzle. However, if what you're interested in is the maximum that the system can exert, then in that case, you take the rated motor torque, (Nm) multiply by the radius of your extruder and any gear reduction that your extruder has (This ignored friction losses, but...) and you will get N of force, which you then divide by 2.405mm^2 in order to get pressure (N/mm^2) If your filament does not flow at this pressure, your extruder will stall.

Actual pressure in the melt chamber will be dependent on the viscosity of the melted filament, as to what makes it flow through the surface area of the nozzle, so you will have lower pressure in the melt chamber with a larger nozzle than you would with a smaller one, and greater pressure at lower temperature than at higher temperature.

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