Predicting excessive wear
To a degree, the wear characteristic of a specific extruder configuration processing a given formulation can be predictable and render indicators that will alert the operator of impending excessive wear. These possible indicators include:
Excessive wear on the components will hinder the process from obtaining a proper steady-state of processing. Worn components take longer to generate the energy and heat than non-worn components. This in turn generates more waste, which increases cost of production.
When a product plugs the barrel and extends back into the steam injection zone, the steam pressure is typically not high enough to overcome the product pressure, causing the steam injection to fall.
When a product plugs the barrel and extends back into the steam injection zone, the steam pressure is typically not high enough to overcome the product pressure, causing the steam injection to fall. This event can
easily become cyclic, rendering an unstable process that generates excessive amounts of wasted product.
Because the components are worn, they will not be able to efficiently convey the product through the barrel. This will cause the overall product rate (lbs/hr) to be reduced and possibly cause the product to back up into the inlet.
Other, more product specific, indications of excessive component wear include:
■ Higher extruder motor amperages;
■ Product surging;
■ Unpredictable extruder shaft lock-ups with products that have high
specific mechanical energy; ■ Loss of density control for specific products; ■ Uneven die pressure producing varying pellet sizes; and ■ Loss of starch gelatinization and product expansion. ■
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