Variable-Depth Channel Aids Barrier-Screw Mixing.

Better mixing is said to result from a patent-pending modification of the solids channel in the barrier section of the DSBV screw from Davis-Standard Corp., Pawcatuck, Conn. It reportedly promotes earlier melting, mixes as it melts, and raises output slightly above that of a conventional barrier screw, according to a paper by John Christiano and Michael Thompson at the recent SPE ANTEC 2000 Conference in Orlando, Fla.

In the conventional rectangular solids channel of a barrier screw, the mass of pellets is pushed forward as a plug, which melts on the surface next to the barrel. Davis-Standard's new design has two separate solids channels that alternate in depth, but in an opposing manner. That is, one channel gets shallower while the other gets deeper. This repeatedly deforms and kneads the solid bed and causes earlier melting and mixing in the barrier section of the screw, the authors say.