Injection Molding worked example

Hopper Residence Time with drying hopper holding capacity of 25 kg: a worked example in injection molding

Here is what the math looks like when conditions slip. We hold every other input steady and drop drying hopper holding capacity to 25 kg, then walk the calculation through step by step. Calculate how long resin stays in the drying hopper to verify it meets minimum residence time requirements for proper moisture removal.

The inputs for this scenario

  • Drying hopper holding capacity: 25 kg (the input this scenario stresses; the baseline uses 50)
  • Press resin consumption rate: 15 kg/hr (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Residence time = Hopper capacity / Press consumption rate.
  • Ratio works out to 1.67 hrs at these inputs, and this is the headline figure for the scenario.
  • Raw ratio works out to 1.67 value at these inputs.
  • Conversion factor works out to 1 x at these inputs.
  • Denominator works out to 15 value at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where drying hopper holding capacity sits at 50 kg and the headline result is 3.33 hrs, this scenario comes in 50% below the baseline at 1.67 hrs.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to drying hopper holding capacity, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. It assumes ideal plug flow; real hoppers can channel or short-circuit, so actual minimum residence time for the fastest-moving resin may be shorter than this average.

Results at a glance

  • Ratio: 1.67 hrs (headline result)
  • Raw ratio: 1.67 value
  • Conversion factor: 1 x
  • Denominator: 15 value

Run it with your numbers

  • To rerun this with your own numbers, open the live Hopper Residence Time calculator, set drying hopper holding capacity to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.