Plastics Extrusion - Pipe, Film & Profile worked example

Screen Pack Change Interval at 17% change interval safety allowance: a worked example

What does the result look like when change interval safety allowance reaches 17%? The full calculation is worked below with real intermediate numbers. Use it when planning screen changes around pressure rise, gels, regrind use, or contaminated resin lots.

The inputs for this scenario

  • Allowable screen pack contaminant loading: 45 lb equivalent (unchanged)
  • Contaminant loading rate: 5 lb equivalent / hr (unchanged)
  • Change interval safety allowance: 17 % (raised for this scenario; the documented default is 15)

Working through the calculation

  • Applying the documented formula (Base time = allowable screen loading รท contaminant loading rate) to the inputs above produces each figure below.
  • At this operating point the engine returns 10.53 hr for planned screen change interval, the number this scenario is built around.
  • At this operating point the engine returns 9 hr for base interval.
  • At this operating point the engine returns 17 % for safety allowance applied.
  • At this operating point the engine returns 5 pieces / min for contaminant loading rate.

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 1.74% above the baseline at 10.53 hr.
  • A figure at this level is achievable when change interval safety allowance is genuinely sustained, not just peaked for a shift. It assumes a steady contaminant loading rate, but gel spikes, resin lot changes, or a slug of regrind can load a screen far faster than the average implies.

Results at a glance

  • Planned screen change interval: 10.53 hr (headline result)
  • Base interval: 9 hr
  • Safety allowance applied: 17 %
  • Contaminant loading rate: 5 pieces / min

Run it with your numbers

  • Every input above is editable in the live Screen Pack Change Interval calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.