Cascade mixing in the new TrueWeigh continuous gravimetric blender from Conair, Cranberry Township, Pa., is said to result in a more homogeneous blend, even when additives are dosed in very small quantities. This suits the unit to extrusion applications requiring a highly accurate blend of dissimilar ingredients. This is Conair’s first continuous-type gravimetric blender (as opposed to batch type) and is based on the same technology used in its TrueWeigh gravimetric extrusion control.
Two sizes of new blenders can handle up to six components with total throughput up to 700 lb/hr or up to 3000 lb/hr. Ingredient hoppers and dispensing augers can be sized to deliver as little as 0.25 lb/hr with metering accuracy within 0.5% of setpoint, depending on the material.
Unlike batch blenders, this unit dispenses all ingredients simultaneously at the desired rates, coming together in a “cascade.” The various ingredients flow together in out of the blender and into the extruder or a holding bin. In batch blenders, ingredients are typically dispensed one at a time into a mixing chamber, where they are combined by mechanical agitation before being dumped from the blender. This works quite well in applications involving similar materials (virgin and masterbatch pellets, for instance) and relatively large quantities of minor ingredients. However, when materials of different particle sizes and bulk densities are involved, and in small additive proportions, there is a limit to the uniformity achievable with mechanical agitation.
The two standard configurations are a stand-mounted unit that dispenses blended material into a holding bin, or a machine-mounted version.
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