Application

Loss-in-Weight Feeding of Fragile Materials

Answer in brief

Feed fragile materials with the gentlest device that meets the rate — vibratory trays or large, slow screws with generous clearances — run at the lowest workable speed, refilled by low-energy transfers, and verify attrition with sieve or dissolution tests at commissioning. Accuracy tuning comes second: broken product measured precisely is still broken product.

Reviewed August 14, 2026 · Updated August 14, 2026

The problem

Precision feeders earn their accuracy by moving material through screws, valves and drops — exactly the mechanical actions that grind agglomerates back to dust, crack coatings and shatter granules. Fragile products punish every unnecessary transfer: fines change bulk density and flow behavior mid-run, dissolution and dispersion properties degrade, and the downstream recipe receives a different material than the one that was specified.

Desired outcome

The feeding system should hold the target rate and tolerance while keeping particle attrition within a defined, measured budget. Product should reach the process with its granule structure, coating or instant properties intact, and the attrition level should be verified with sieve or dissolution tests at commissioning rather than assumed from catalog claims.

Process approach

Material enters the feeder hopper through low-drop, low-velocity refills — dense-phase conveying, gentle mechanical transfer or short gravity drops onto product rather than steel. Inside the feeder, large slow single screws, twin screws with generous clearances or vibratory trays move product with minimal shear; agitation is soft or replaced by mass-flow hopper geometry. The controller runs at the lowest speed that meets the rate, since attrition rises with tip speed. Discharge drops are cushioned and short, and every transfer in the chain is challenged: each one removed is attrition and segregation avoided.

Selection factors

Fragility mechanism: agglomerate breakage, coating damage, granule fracture or fines generation. Vibratory tray versus large slow screw versus twin screw with generous clearances. Hopper geometry and agitation that move product without kneading it. Refill path energy: drop heights, velocities and impact surfaces. Operating point: lowest screw speed that meets the rate, with headroom. Attrition verification: sieve analysis or dissolution testing before and after the feeder. Cleaning access where fines and breakage change over a campaign.

Common failure modes

Screw speed chosen for rate headroom grinds the product at the tip clearances.
Aggressive hopper agitation kneads agglomerates back into powder.
Refill drops accelerate product onto bare steel and shatter granules.
Fines from attrition change bulk density, so the volumetric bridge drifts over the campaign.
Dilute-phase refill conveying destroys the product before the feeder ever sees it.
Attrition is never measured, so the damage is discovered downstream as a quality complaint.

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Frequently asked questions

Which feeder type is gentlest for fragile products?

Vibratory tray feeders move product with almost no shear and suit granules and friable agglomerates best. Where screws are needed for rate or control, large slow single screws or twins with generous clearances beat small fast screws — attrition tracks tip speed and clearance pinch points.

How do I measure whether a feeder damages my product?

Sample before the feeder and after it, then compare: sieve analysis for size distribution and fines, dissolution or dispersion tests for instantized products. Run the comparison at commissioning across the operating range and write the acceptance numbers into the purchase.

Why do fragile products lose accuracy over a campaign?

Attrition creates fines, fines change bulk density and flow behavior, and the volumetric refill bridge drifts with them. Controlling breakage is therefore an accuracy measure, not just a quality one.

Does the refill path matter as much as the feeder?

Often more: a dilute-phase conveying line or a two-meter drop onto steel can destroy more granules than the feeder ever will. Dense-phase conveying, cushioned drops and product-on-product impact protect the material before it reaches the metering zone.

Coperion Loss-in-Weight Feeder Animation

The Coperion K-Tron animation shows a controller observing the decrease in combined hopper, feeder and material weight, comparing the measured rate with the setpoint and adjusting feeder output. It is evidence for gravimetric control only.

21 views

Volkmann GmbH

Product feeding of bagged goods (pellets)

Official Volkmann footage of bagged plastic pellets being fed into a vacuum conveying system. The clip documents one bag-feeding and vacuum-transfer boundary; suitability for a specific resin, additive package or receiving process must still be verified.

19 views

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