For the demanding task of admixing small amounts of low viscosity additives or melted pigment concentrations, the use of static SMX mixers is steadily on the rise. These mixing devices display a range of advantages over dynamic systems (such as extrusion systems) through a substantially lower energy consumption, less shear rates on the polymer (typical shear velocities lie in the range 2-25 sec-1) and a very narrow residence time distribution. This greatly diminishes the risk of degradation of the polymer during mixing procedures. At the same time, there is a notable reduction in the amount o transitional output fractions outside specifications, which occur as a result of change-overs in concentration or type of additive as well as of the master batch. In addition, the costs for static mixers in comparison to extruders is substantially lower, and the maintenance effort practically nil.
The energy needed for the mixing process is drawn from the melt flow and is manifested by an increased pressure drop in relation to an empty pipe configuration. The pressure loss has to be compensated for by the drive, mostly a gear-type pump, and amounts to between about 30 to 100 bar depending upon operational conditions of the process and the corresponding configuration of the mixer employed. In relation to the particular mixing task, the necessary mixer lengths can vary substantially. The relative mixer length L/D (length to pipe diameter ratio) is as follows:
Koch-Glitsch Mixing & Reaction Technology, 4111 East 37th St. North, Wichita, KS 67220. Tel: 316-828-4145; Fax: 316-828-4444.