Tuesday, January 04, 2011

Extruder Philosophy

Extruders come in quite a range of configurations (single screw, twin screw, octascrews of all types...), an even larger range of geometries (L/D's all over the map, intermeshing twin screws, non-intermeshing twin screws...), all of which have a purpose.

The puzzle to me that I've noticed over my career and client visits is that companies tend to fixate on using just one type. Some companies only use single screws ("twin screws are too expensive and we can modify the screw to do what we need") while others use only twin screws ("can't do a blasted thing with a single screw"). And then at that, they only seem to run in a single dirction, either counter- or co-rotating, but not both. What is really funny is that I've seen "twin-screw companies", when they do have a single screw, run it like it's a twin-screw: starve-fed, instead of flooded as is typical for single screws.

I can understand a company locking into a business model and following it religously, but extruders?


孙尉翔 said...

So what were your suggestions and how did they appreciate them? I mean, did they really care?

John said...

The only time I tried to change a fixed philosophy is when I tried to get a "twin-screw" company to flood feed one of the few single screws that they had. It never went anywhere, but then again, they had a lot more problems with their set-up than just that. For instance, they had 3 pressure taps along the capillary die. They measured P1-P2, P2-P3 and then took the average! I tried to tell them to disconnect P2 as it was superfluous (simple algebraic manipulation shows that the average of the two pressure drops is simply P1-P3), but that didn't go anywhere either. Oh well.