Application

Gravimetric Feeding in Plastics Compounding

Answer in brief

In compounding the recipe is made by the feeders, and the extruder only mixes what they deliver.

A filler feeder that drifts by a few percent changes the mechanical properties of the product, and nothing downstream corrects it.

Size each feeder for its own ingredient, not for a common standard.
Side feed fillers rather than dropping them into the throat.
Reconcile consumption against the recipe.

Reviewed October 21, 2026 · Updated October 21, 2026

The problem

Fillers aerate, fibres bridge and pellets flood, and the same line often feeds all three.

Dropping a light filler into the extruder throat entrains air and causes surging.

Desired outcome

A feeder that holds the set rate across the required turndown, with an inlet condition it can cope with and an installation that does not corrupt the weight signal.

Process approach

Twin screw feeders handle fillers and fibres, single screws suit pellets, and vibratory trays are used for fragile or flaky materials.

Side feeding introduces fillers into the melt rather than into the throat, which improves both rate stability and dispersion.

Refill from a conveying line is sequenced so that two feeders are not refilled at the same moment.

One feeder type per ingredient behavior, not one standard for all.
Side feeding for low density fillers.
Refill sequencing that avoids simultaneous disturbances.

Selection factors

Inclusion rate and tolerance for each ingredient.
Bulk density range, aerated and settled.
Fibre length or flake size where applicable.
Extruder feed point and whether side feeding is available.
Refill method and its timing.

Common failure modes

Light filler entrained with air at the extruder throat
Fibre bridging in a single screw feeder
Two feeders refilling simultaneously and disturbing the recipe
Accuracy accepted from the data sheet without in-service checks

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