Page 161 - Root Cause Failure Analysis

Mixers and Agitators 149

Figure ZZ-3 Mixer can use eitherpropellers or paddles to provide agitation (Thomas Regis-
ter 1995).

propellers are used for medium- to high-speed applications where the viscosity is rel-
atively low. Paddles are used in low-speed, high-viscosity applications.

screw
The screw mixer uses a single- or dual-screw arrangement to mix liquids, solids, or a
combination of both. It comes in two basic configurations: batch and combination
mixer-extruder.

Butch

Figure 114 illustrates a typical batch-type screw mixer. This unit consists of a mix-
ing drum or cylinder, a single- or dual-screw mixer, and a power supply.

The screw configuration normally is either a ribbon-type helical screw or a series of
paddles mounted on a common shaft. Materials of construction are selected based on
the specific application and materials to be mixed. Vpically, the screws are either
steel or stainless steel, but other materials are available.

Combination Mixer-Extruder
The mixer-extruder combination unit shown in Figure 11-5 combines the functions of
a mixer and a screw conveyor. This type of mixer is used for mixing viscous products.