MFV "multi-flighted vent"
The MFV is a self-cleaning vent design that is more efficient in removing moisture and volatiles than conventional vent designs. These conventional vent designs that are single-flighted accumulate a large “glob” of polymer from the first stage that at best can remove gasses that are not trapped in the "glob." Also, flow on the trailing side of the channel is less, providing an area for polymer to hang-up and degrade.
How it Works
The MFV concept is simple – the greater number of flights, and unique channel design, separates the flow from the first stage mixer into "rope-like" strands that are smaller in size and have greater surface area that allows for greater volatile and moisture removal.
Vented operation in two-stage screw designs first requires complete melting of the polymer in the first stage. This is accomplished by a mixing devise that completes the melting and connects to the MFV (multi-flighted vent). The mixing device provides a “rope-like’’stream of polymer to the MFV section.
Unlike conventional vent designs, the MFV has no areas of low flow where material can hang-up and degrade, as the MFV is self-cleaning. The increased surface area of the polymer greatly improves volatile and moisture removal, improving stability and overall part quality.
The MFV has also been used in numerous side feeding operations since 1989. The concept is to allow more uniform distribution of the given additive (glass, mineral, etc.) to the polymer. These screw designs are normally (3) stage with a second MFV located at the end of the second stage.