Most extruders are single-screw—about 90% is my best estimate. But that is misleading, because the twins are concentrated in two market areas—rigid PVC and compounding—and the twins for one application are very different from the other.
When an extrusion system is taken apart, there is a lot of sticky stuff, and it seems logical to remove it. Here are some techniques and tools you may want to consider using to do that; under certain circumstances, though, you may want to do nothing at all.
Equipment is a minor expense compared with materials, as articulated in the 6-1-2-1 rule of cost distribution: 60% materials, 10% equipment, 20% direct labor and 10% everything else, including power, packaging and insurance.
Allan Griff has been an indefatigable instructor of extrusion-related matters for decades. In this column, he recounts how the technology has evolved even as the fundamentals continue to apply. A summary of extrusion learning opportunities is included.
The show was too big to cover—"seeing it all” is as impossible as conversing with those talking mice that run rampant just a few miles from the convention center—but the event is unrivaled for meeting people and connecting with companies that make what we want to buy, or buy what we make.
The added cost of gear pumps can be justified by savings of material because aim thickness can be lower. Another benefit is reducing the load on the extruder, which may include pushing the melt through a static mixer to improve appearance, properties and maybe production rate.
Allan Griff started attending NPE back when it was held in the Chicago Stockyards exhibition area. A lot has changed since then, but the essentials remain the same.
Screw design is important but it’s not the only factor, as mixing can also be promoted by static mixers, water-cooled screws and wise selection of ingredients.
