Polymer extrusion mixing problem (blue/white resin)

Mike Mousakas's $500 student-contest puzzle: blue resin starts in the center of an extrusion and ends up on the outside. Mousakas (chemical engineer) explained it as a boundary-layer problem; Tom solved it in five minutes as inhomogeneous flow (white sticks to the wall, blue noses forward and folds over). Used to close the lecture on the theme that engineers from different disciplines describe the same phenomenon in different vocabularies. ## Figures referenced (recurring numeric anchors)

The last thing we'll do is talk about Stamixco, which we were talking about with some people before class. If you're doing polymer extrusion — an injection molding press — it's like a great big toothpaste tube. It might be 30 feet long, made out of steel three inches thick, but it's just a toothpaste tube. You're going to squirt polymer out and extrude it into something. Part of the problem is, a lot of times it's like a two-part epoxy — you want to mix two polymers together. If they're very thick, it's hard to get them mixed well. So this is what they call a static mixer. That's where the name Stamixco comes from. Pretty simple tool, but there's some technology in the design.