Why doesn't the molten plastic mix in the feedblock?

The flex lip adjusting mechanism is effective as a stand alone adjustment to correct flow imbalnace only if the due opening is less than about 0.040 inches. Larger openings require the addition of a restrictor bar (sometimes referred to as a choke bar) to balance flow.

The restrictor bar is a narrow bar about 1 inch wide that is positioned inside the die across the entire width of the die. It includes a series of adjustment screws that push and pull the bar for opening and closing the slot of material flow passing under it. This opening and closing of the flow passage across the die width conventionally used in conjunection with a flex lip as an additional and finer adjustment.

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