I don't know if you noticed, but the plastics industry is enjoying a particularly fertile period for innovation in design of mixing screws--single screws, that is. Uncovering the proliferation of new single-screw designs was a pleasant surprise to Senior Editor Jan Schut in researching her feature for this issue, "Single-Screw Compounding Is Learning New Tricks". One surprise, as Jan found out, is that you won't hear much about these new mixing screws by talking to compounders. That's because most of the initial applications are in injection molding, blow molding, and sheet extrusion. After so many years of hearing that injection molding screw design was a "neglected" science, it's refreshing to see renewed vitality in this area.
For most of the past two decades, single-screw compounding technology has been pushed out of the limelight by twin-screws. When I first learned about compounding back in the 1970s, single-screws predominated and only a lucky few compounding entrepreneurs could afford to buy even a second-hand twin-screw machine. Then in the 1980s, some major color-concentrate houses made a big break with tradition and switched to twin-screws. Today, most compounders are firmly wedded to twins, even if they keep running single-screws for certain jobs. It's not yet clear whether the new advances in mixing screws will affect future machinery choices by commercial compounders. But improved single-screws certainly are making a difference for other processors who need better dispersive mixing.