Size a drying hopper around the resin grade and the amount your process actually consumes per hour. The hopper needs enough usable material inventory for the required drying time, but a calculated inventory is only a starting point. Nominal loading capacity in kilograms, actual usable inventory and throughput in kilograms per hour are three different quantities.
Estimate the inventory and usable volume
For a steady production rate, multiply hourly consumption by the drying time specified for the exact resin grade: M = q × t. Then divide that mass by the material's bulk density, ρ: V = M ÷ ρ. Use the specified time together with its temperature and air conditions; include startup pre-drying in the operating plan. Use the density of the actual material batch and compare the result with the hopper's effective material volume, rather than assuming its total geometric volume can all be used as inventory.
| Assumed input or result | Value |
|---|---|
| Hourly consumption, q | 40 kg/h |
| Required time, t | 3 h |
| Bulk density | 0.60 kg/L |
| Estimated inventory | 40 kg/h × 3 h = 120 kg |
| Estimated usable material volume | 120 kg ÷ 0.60 kg/L = 200 L |
The 40 kg/h rate, 3 h time and 0.60 kg/L density are hypothetical inputs. The 120 kg and 200 L results are an inventory and volume estimate, not a drying recommendation for a resin or a machine guarantee. If actual consumption or density changes, recalculate with the new values. Conair's explanation of bulk density describes why mass and occupied volume are related; see also our guide to bulk density of plastic regrind.
Inventory coverage is not proof of drying
Dividing inventory by the consumption rate gives nominal coverage time. It does not prove that every pellet stays in the hopper for the required period, or that the resin reaches its specified moisture condition. Material level changes during refilling and consumption, and flow can give different portions of material different residence times. Check the usable level range, replenishment pattern and material flow as part of the proposed installation. Conair's DH hopper information illustrates why material flow and air distribution are design considerations; its construction should not be assumed for another hopper.
Allow for pre-drying at startup and check the highest production demand, not only an average rate. Temperature, airflow and air treatment must suit the resin supplier's requirements as well. A larger inventory alone cannot replace the specified drying conditions. For the distinction between process-air readings and the material's actual condition, see dryer dew point versus resin moisture.
Read equipment capacity in context
A hopper's nominal kilogram rating is a loading figure, not a guaranteed hourly throughput. Actual loading depends on bulk density and usable volume. RHONG's hopper dryer uses hot air; it should not be treated as equivalent to a dehumidifying dryer. Choose the air treatment required by the grade and process before selecting a configuration. Machine tonnage alone is not enough to size the hopper, and the example above does not select a model.
For a configuration discussion, send the resin grade, production demand, feeding pattern and material form. Include the actual bulk density and the resin supplier's specified drying conditions for the capacity estimate.