posted September 20, 2004 10:59 AM               

I would like to know if someone can suggest me the best screw type for producing blown film with a high molecular weight grade of HDPE.
melt index = 0.04
Density = 0.949
Melt temp = 215°C

posted September 20, 2004 03:59 PM               

A deeply cut screw will tend to out-pump the melting ability of the screw. Barrier type screw designs can be used to make sure the resin is properly melted while keeping the screw design deep cut.

Depending on the rheological characteristics of the material, narrow flight tips can reduce power consumption, and can long pitch flights.

Mechanical consideration come into play as deeply cut screws as the deeper the cut, the weaker the screw. At some point the power requirements will exceed the screw strength.

One odd aspect of some highly viscous resins is slip. The resin actually slips against the barrel wall instead if sticking to it like "Normal" resins. This dramatically alters the extrusion process for these materials. In fact some resins would not even be able to be processed without wall slip because the normal viscous heating would be so high.

Enter extrusion simulation; All of the competing extrusion process phenomena can be sorted out using a computer program rather than building screws and depending on trial and error and educated guesses.

Call me if you are interested in finding out more about simulation.