How do you calculate demold time in rotational molding?

Divide the number of parts by the extraction rate for base hours, then multiply by (1 + allowance). With 120 parts at 12 per hour and a 10% allowance, base time is 10 hours and adjusted demold time is 11 hours.

What is a typical demold rate for rotomolded parts?

Easy open-top parts can hit 30-60 per hour, while deep tanks needing wedges or air assist drop to 6-15. The default 12 per hour reflects a moderately difficult part requiring some prying and inspection.

Why is rotomolding demold slower than injection molding ejection?

Rotomolds have no ejector pins or hydraulic knockout; the operator manually opens clamps, releases the part by hand, and often uses air or tools. Adhesion from worn release agent makes it slower still.

What increases rotomolding demold time?

Deep draw depth, undercuts, molded-in inserts, thin flexible walls, and degraded mold release all slow extraction. Poor release-agent maintenance is the single most common cause of creeping demold times.

How do I reduce demold time?

Reapply and rotate mold release on schedule, add draft to the tool, use air-assist ejection ports, and pre-position clamps for quick opening. These can move a 12-per-hour part toward 20-plus.

Demold time vs cooling time — are they the same?

No. Cooling time is the passive time the part sits before it is rigid enough to remove; demold time is the active operator labor to open the mold and extract it. Both occur at the cool station but only demold is direct labor.

Rotational Molding calculator

Demold Time Calculator

Demold time is the labor spent at the cool station opening the rotomold, breaking any part-to-tool adhesion, extracting the finished part, and clearing the cavity for the next shot. In rotational molding demolding can be surprisingly slow: thin-wall parts flex and stick, deep-draft tanks need air assist or wedges, and molded-in inserts create mechanical locks. Production supervisors and industrial engineers use this figure to staff the demold station and to keep the carousel indexing without a pile-up of cooled molds waiting for an operator. It is one of the most under-measured hidden costs in a rotomolding cell.

What this calculator does

Demold time is the labor spent at the cool station opening the rotomold, breaking any part-to-tool adhesion, extracting the finished part, and clearing the cavity for the next shot.
Use it when demold time in rotational molding is being added to next week's schedule and you need an honest hours estimate.
It computes total demold labor hours for a batch by dividing the number of parts to extract by the demold rate, then applying an allowance for sticking, cleaning, and fatigue.

Formula used

Base demold time time = required work ÷ processing rate
Adjusted time = base time × allowance factor

Inputs explained

Parts to demold this batch:
Parts extracted per operator-hour:
Sticking and cleanup allowance:

How to use the result

Use it when scheduling the cool-and-strip station or costing parts with deep draws, tight releases, or molded-in hardware that slows extraction.
It treats every part as equally easy to release; in practice release-agent condition, mold wear, and part geometry cause wide part-to-part variation not captured by a single rate.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 319.371 (BLS, May 2026), up 19.5% 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

How do you calculate demold time in rotational molding? Divide the number of parts by the extraction rate for base hours, then multiply by (1 + allowance). With 120 parts at 12 per hour and a 10% allowance, base time is 10 hours and adjusted demold time is 11 hours.
What is a typical demold rate for rotomolded parts? Easy open-top parts can hit 30-60 per hour, while deep tanks needing wedges or air assist drop to 6-15. The default 12 per hour reflects a moderately difficult part requiring some prying and inspection.
Why is rotomolding demold slower than injection molding ejection? Rotomolds have no ejector pins or hydraulic knockout; the operator manually opens clamps, releases the part by hand, and often uses air or tools. Adhesion from worn release agent makes it slower still.
What increases rotomolding demold time? Deep draw depth, undercuts, molded-in inserts, thin flexible walls, and degraded mold release all slow extraction. Poor release-agent maintenance is the single most common cause of creeping demold times.
How do I reduce demold time? Reapply and rotate mold release on schedule, add draft to the tool, use air-assist ejection ports, and pre-position clamps for quick opening. These can move a 12-per-hour part toward 20-plus.

Last reviewed 2026-05-12.