Getting the melt out of the die may look like the main objective in extrusion, but it’s just the first half. Plenty of teams go into halftime with a lead, only to lose it in the second half. Avoid this by paying as much attention to the shaping and cooling phases as to the heating and mixing stages.
There is always an issue of contamination with recycling. Contaminants can be removed by filtration (screening), and the technology is well ahead of most of our needs. The hard part is estimating the commercial significance of the contamination to justify the cost of finer screening.
This is the traditional time of year for us to look at the past, present and future . . . by learning from the past, thinking in the present and planning for the future. We call them resolutions, and they are often promises to do something we haven’t done well or at all in the past.
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.