Continuous mixer takes on performance, serviceability challenge.
Harrison initially favored the design advantages of twin-screw turbo head mixers because of their record of excellent sand mix quality combined with easy cleaning and low wear. The new requirement, however, necessitated more frequent changes from silica to zircon to chromite sand for numerous mold-facing and backing-sand formulations. This type of mixing application traditionally had been handled using zero retention single-screw mixers, which accommodate quick changes of mixed sand formulas. However, in the past, easy cleaning and low wear frequently were given lower priority in order to achieve faster change of sand formulation.
Harrison was unwilling to compromise its objective and began discussions with engineers at Dependable Foundry Equipment Co., Tualatin, Ore. Dependable manufactures both twin-screw turbo head mixers and zero-retention single-screw mixers in addition to mixers of other designs.
Harrison wanted a mixer that achieved "the best of both worlds," namely fast sand formulation changes using aggregates of dissimilar density plus excellent sand mix quality, low wear and easy cleaning. The two companies studied the Dependable Pacemaster twin-screw continuous mixers to try to find a way to accomplish faster sand formulation changes.
Dependable and Harrison recognized that zero-retention mixers need more time to restart after stopping for hand tucking or other tasks that require a pause in mixer discharge. Twin-screw mixers do not have this delay and instead offer easy turbo head cleaning and low wear. Equally important, they are well-known for good first/middle/ last sand mix quality, even with materials of dissimilar density.
Additionally, by establishing a programmable logic controller (PLC) job record for each mold, twin-screw mixer controls became workable with new programming techniques to anticipate desired sand formulation changes. Thus, pre-reloading the sand conveyor belt in the mixer primary arm eliminates objectionable delays and wasted sand.
Select No. 002 at www.moderncasting.com/info
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|Title Annotation:||Case History|
|Date:||Oct 1, 2005|
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