Milacron Injection Molding & Extrusion helps its customers tackle challenging plastics processing applications through extending their exclusive partnership to offer screw designs by Robert Barr, Inc. Barr ET and VBET screws are available on new Milacron machines, or as aftermarket products from Milacron’s ServTek business.
Barr Screws
The ET (Energy Transfer) screw has a patented low-shear solid/melt mixing section that provides faster melting and better energy efficiency. The patented newer VBET (Variable-Barrier Energy Transfer) screw has a much longer solid/melt mixing zone, to significantly increase energy efficiency, eliminate hot spots, and produce an exceptional, uniform melt.
Barr VBET Screw
Faster, more efficient melting is achievable using the Barr VBET (Variable Barrier Energy Transfer) screw – available exclusively from Milacron. For even the most challenging applications, the companys team customizes a solution that yields better mixing and melting, lower energy costs and processing productivity improvements of up to 50 percent.
The Barr VBET Difference
Typical barrier screws largely keep the unmelted and melted resin separated, with a narrow barrier flight. This design generates higher melt temperatures and requires additional cooling of the molten polymer downstream. The Barr VBET keeps the unmelted pellets mixing with fresh melt, yielding significantly higher melting rates because its surface area for unmelted pellets far exceeds the solid bed surface area of a conventional screw.
How the Barr VBET Works
The Barr VBET screw channel is divided into two sub-channels. The unmelted pellets continuously shift their positions as they circulate from one sub-channel into another sub-channel along the screw. A pellet in the surface layer of one sub-channel ends up in the center layer of the other sub-channel. This Solid/Melt Flow mechanism gives uniform melt quality and uniform melt temperature by continuously mixing the melt and eliminating undesirable hot spots inside the screw channel.
Additional Barr VBET Advantages:
- Unique, low-shear design geometry. Nearly half of the screw’s length functions as an energy transfer section, providing an increase in conduction melting by 30 to 50%.
- Reduced heat loss and lower melt temperature. The Barr VBET energy transfer section melts 30 to 50% of the polymer by conducting heat from the previously melted polymer, reducing the time for downstream cooling.
- Uniform melt quality and temperature. The Barr VBET screw channel is divided into two sub-channels. The pellets continuously change their positions as they flow from one sub-channel into another along the screw. This solid/melt flow mechanism continuously mixes the melt, eliminating undesirable hot spots.
- Substantially higher processing power. The mixing/melting section of the Barr VBET Screw is 30-50% longer than a regular screw. The conductive melting capacity of the Barr VBET Screw can process a wider variety of resins, including high-viscosity materials (including PVC) and high melt-flow rate materials.
