Plastics Extrusion - Pipe, Film & Profile worked example

Screen Pack Change Interval at 11% change interval safety allowance: a worked example

Suppose change interval safety allowance falls to 11%. This page works the full calculation at that level so you can see exactly which result moves and by how much. Estimate hours between screen pack changes from allowable contaminant loading, contamination rate, and a safety allowance.

The inputs for this scenario

  • Allowable screen pack contaminant loading: 45 lb equivalent (held at the documented default)
  • Contaminant loading rate: 5 lb equivalent / hr (held at the documented default)
  • Change interval safety allowance: 11 % (the input this scenario stresses; the baseline uses 15)

Working through the calculation

  • The calculation starts from the formula this tool documents: Base time = allowable screen loading รท contaminant loading rate.
  • Planned screen change interval works out to 9.99 hr at these inputs, and this is the headline figure for the scenario.
  • Base interval works out to 9 hr at these inputs.
  • Safety allowance applied works out to 11 % at these inputs.
  • Contaminant loading rate works out to 5 pieces / min at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where change interval safety allowance sits at 15% and the headline result is 10.35 hr, this scenario comes in 3.48% below the baseline at 9.99 hr.
  • It computes the planned hours between screen pack changes from allowable loading, contaminant loading rate, and a safety allowance. When the numbers land here, the stressed input is the lever to work; the walkthrough above shows exactly how much each output recovers as it climbs back toward the baseline.

Results at a glance

  • Planned screen change interval: 9.99 hr (headline result)
  • Base interval: 9 hr
  • Safety allowance applied: 11 %
  • Contaminant loading rate: 5 pieces / min

Run it with your numbers

  • To rerun this with your own numbers, open the live Screen Pack Change Interval calculator, set change interval safety allowance to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.