What barrel inventory factor should I use?

Use 2 unless you have better data; DuPont approximates resin in the cylinder as twice the maximum screw stroke. Routsis estimates 2 to 4 cycles of residence at 50% barrel use, a factor of 1 to 2.

Where do I find my resin's residence limit?

In the resin supplier's molding guide for your grade. DuPont, for example, allows 10 minutes for pigmented Delrin and 20 minutes for natural standard grades under normal molding conditions.

Can residence time be too short?

Yes. DuPont notes that below 3 minutes, Delrin may need higher than normal cylinder settings. Preheating pellets can also help small injection units reach a homogeneous melt.

Does a bigger shot on the same press shorten residence?

Yes, in proportion. Doubling shot weight halves shots held and halves residence time, so adding cavities cuts residence without touching temperatures. A smaller barrel does the same for an unchanged shot.

Injection Molding calculator

Barrel Residence Time Calculator

Estimate how long melt sits in the barrel at your shot weight and cycle, and compare it with the resin's limit before you schedule the job. You need the barrel's shot volume, melt density and cycle time.

What this calculator does

Average time melt spends in the barrel at your shot and cycle, checked against the resin's residence limit.

Formula used

Resin held (g) = barrel inventory factor × barrel shot capacity × melt density
Shots held = resin held ÷ actual shot weight
Average residence time (min) = shots held × cycle time ÷ 60
Barrel use = actual shot weight ÷ (barrel shot capacity × melt density) × 100
Longest cycle = limit × 60 ÷ shots held; smallest shot = resin held × cycle time ÷ (limit × 60)

Inputs explained

Barrel Shot Capacity: Theoretical shot volume from the press spec sheet.
Resin Melt Density: Melt, not solid, density from the resin supplier's flow data.
Actual Shot Weight per Cycle: Weigh a full shot: all parts plus runner and sprue.
Cycle Time: Measured from one mold close to the next.
Barrel Inventory Factor: Resin in screw and barrel ÷ shot capacity; DuPont estimates 2.
Resin Residence Limit: Maximum residence time from the resin supplier's molding guide.

How to use the result

Best suited to scheduling heat-sensitive resin onto a large press, diagnosing splay and black specks, planning cycles for insert-loaded jobs.
Melt clinging to the check ring, nozzle and hot runner walls stays far longer than the average. Hot runner manifold volume is not counted.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 280.569 (BLS, Aug 2026), up 6.6% from a year earlier. Quotes priced off last quarter's material cost miss this move.
The U.S. has 9,635 plastics product manufacturing establishments employing about 677,302 workers (Census County Business Patterns, 2023).

Common questions

What barrel inventory factor should I use? Use 2 unless you have better data; DuPont approximates resin in the cylinder as twice the maximum screw stroke. Routsis estimates 2 to 4 cycles of residence at 50% barrel use, a factor of 1 to 2.
Where do I find my resin's residence limit? In the resin supplier's molding guide for your grade. DuPont, for example, allows 10 minutes for pigmented Delrin and 20 minutes for natural standard grades under normal molding conditions.
Can residence time be too short? Yes. DuPont notes that below 3 minutes, Delrin may need higher than normal cylinder settings. Preheating pellets can also help small injection units reach a homogeneous melt.
Does a bigger shot on the same press shorten residence? Yes, in proportion. Doubling shot weight halves shots held and halves residence time, so adding cavities cuts residence without touching temperatures. A smaller barrel does the same for an unchanged shot.

Last reviewed 2026-10-01.