I have single screw extruders that are melt fed with LDPE and LLDPE products. I would like to know if anyone can provide a calculation (formula) for calculating the expected power required. This is a very simple screw design that is primarily a melt conveying screw. The screw is has a short mixing section at the end of the screw and is used to pressurize the product through a pelletizing die plate.

One of the formulas that I am using at present is:

m*Lc*(pi()D)^(n+2)*N^(n+1)/H^n

Where (all in metric units),

m = consistancy factor
Lc = Length of screw Channel (unravelled)
D = Outside Diameter of the screw
n = Powerlaw factor
N = Screw Speed (revs/sec)
H = Height of screw channel

The problem I'm having is that this formula is predicting ~30% higher power than what we actually see. If someone has a better formula for predicting power, I would certainly appreciate it.

Thanks.