Rotational Molding worked example

Venting Allowance with vent area provided of 63 units: a worked example

This worked example runs the venting allowance numbers for a tougher week than the baseline: vent area provided of 63 units instead of the typical 125 units. Venting Allowance checks whether a rotomolding mold has enough vent capacity to relieve the pressure swings that build as air heats in the oven and contracts during cooling.

The inputs for this scenario

  • Vent area provided: 63 units (the input this scenario stresses; the baseline uses 125)
  • Vent area required for the part: 100 units (held at the documented default)
  • Reference vent area for percentage: 100 units (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Venting Allowance margin = available value - required value.
  • Margin works out to -37 % at these inputs, and this is the headline figure for the scenario.
  • Absolute margin works out to -37 value at these inputs.
  • Available amount works out to 63 value at these inputs.
  • Required amount works out to 100 value at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where vent area provided sits at 125 units and the headline result is 25 %, this scenario comes in 248% below the baseline at -37 %.
  • Use it when designing a mold's vent or diagnosing pressure-related defects like blowholes or warp. A result at this level usually justifies acting on the stressed input before touching anything else, because every other figure in the table is downstream of it.

Results at a glance

  • Margin: -37 % (headline result)
  • Absolute margin: -37 value
  • Available amount: 63 value
  • Required amount: 100 value

Run it with your numbers

  • To rerun this with your own numbers, open the live Venting Allowance calculator, set vent area provided to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.