Screw & Die Design Models

Published: December 06, 2011, By Tom Bezigian

I met with a couple of old friends this week, Dr. Natti Rao, who was visiting New York from Germany, and John Beaumont, a classmate from UMASS-Lowell.  It's always great to catch up with old friends, and even better when I can do that and talk about screw and die design modeling.  Wait... did I just say that?

Back in the day while I was at Cryovac, these models showed little more than a line graph with supporting calculations showing output, average melt temperature and shear rate.  Experience was more the guide than computer simulation back then... sometimes it worked, and sometimes it didn't.  Over the years, computers and programmers became more sophisticated, and the results became more visual and also more practical and more reliable.  

The folks at Crown Zellerbach in San Leandro were very advanced, and they developed models that showed gauge profile based on die design, melt temperature and rheology.  We used these programs and their visual aids in training operators and engineers by demonstrating the relationship between die gap and thickness.  Thickness at a certain point is a function of several variables, but is a cubic function of die gap.  Understanding this early in an operator's career will improve productivity and reduce waste, one of the main goals of operator training.

Fast forwarding to today, hardware and software advances have provided amazing visual graphics and calculations far beyond what was imagined when personal computers first came out some 35 years ago.  A good analogy would be to compare the graphics seen on the weather forecasts on television today compared to 35 years ago.  Back then, magnetic clouds were moved around by hand to show the current weather, whereas today beautiful 3D models depict the weather.  The same technology is available today to machine manufacturers and extrusion processors, whether the product is a flat film or sheet, a profile, or an injection molded part, at what I would call reasonable prices.  

Dr. Rao's program is less sophisticated than many of the higher-end programs available, but is easy to use and very accurate and have an extensive library of rheological data.  In the end, this is what engineers are looking for... accuracy and simplicity for a wide range of materials at a reasonable cost.  From my point of view, the price of his modeling software is about the price of just the rheological library, so it's almost a "no-brainer".  

Rao's program can be used to determine physical properties such as melt temperature and output (to name just a few) based on screw design, and then feed that information into the die and determine gauge profile based on melt temperature, rheological properties and die design.  It can also be used to determine the proper screw and die design to achieve the desired output, temperature and thickness requirements based on the material of your choice.

John Beaumont is president of Beaumont Technologies, in Erie, Pennsylvania.  His specialty is sophisticated mold design software that uses rheology as a friend so to speak.  I will expound on his specialty at a later time, but you can find his information at http://www.beaumontinc.com/

If you would like more information about Dr. Rao's modeling software, you can contact me and I will either direct you or try to answer your questions.  He will be at the NPE show in Orlando if you would like to meet with him.