What Cure Data Actually Means
A moving die rheometer or oscillating disc rheometer test, run per ASTM D5289 or D2084, produces a cure curve with scorch time (ts2), optimum cure time (t90), minimum and maximum torque. Scorch tells you how long compound can flow before it begins to set, which matters for preform life and mold fill. T90 is the baseline for cure time at a given temperature.
Thick parts need longer than t90 suggests because heat takes time to reach the core. Compounds vary lot to lot, so a lot with a longer t90 can quietly add minutes per cycle across a month.
- ts2 scorch time sets handling and fill window
- t90 sets baseline cure time at mold temperature
- Cross-section thickness adds heat-up time on top of t90
- Lot-to-lot cure drift changes real cycle time
Setting Cure Standards per Part and Mold
Store a cure time standard on each routing operation by part number and mold, plus the temperature and pressure it assumes. Validate with first article runs: cure a few shots at stepped times and check durometer, compression set and physical properties as required. Record the final setting and who approved it.
When you change compounds, polymer suppliers or mold design, re-validate. Without a documented standard, operators adjust timers by feel, which hides capacity loss and invites under-cure risk.
Capturing Actual Cycle Times
Press controllers and PLCs can report cycle counts and times. Where that is unavailable, operators log start and stop with barcode scans on the job traveler. Compare actual cycle time to the standard by mold, compound lot and operator.
Large gaps point to temperature loss in a platen, worn heaters, mold cleaning needs or operators extending cure to avoid undercure scrap. Tracking this gives maintenance a prioritized list and gives estimators true cure time for future quotes.
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Injection Molding Cooling Time Calculator
Estimate the cooling time of a molded part from wall thickness, resin thermal diffusivity, melt, mold and ejection temperatures, and see how it drives total cycle time.
Scheduling Presses Around Cure and Changeovers
Press capacity in rubber is cycles per hour times cavities, minus changeover. Mold changes on hot presses take time and cause scrap on start-up, so sequence jobs by compound family and temperature to avoid unnecessary changes. Schedule post cure oven loads separately, because post cure for FKM or silicone can take hours and becomes a hidden bottleneck.
Preforms have a life, so cut them close to when the press needs them. Respect operator constraints, since multi-cavity hand-loaded molds may need two people.
When Spreadsheets and Whiteboards Are Fine
A shop with fewer than a dozen presses and stable repeat work can often run a disciplined schedule board with cure standards on the traveler. The case for ERP-based finite scheduling grows with job count, mold-to-press constraints and delivery pressure. Even then, start by cleaning up standards, since a finite schedule built on bad cure times only produces wrong dates faster.
Frequently asked questions
How do you determine cure time for a rubber part?
Start from the compound t90 at mold temperature from a rheometer test, then adjust for part thickness and heat transfer, and confirm with trial cures checked against physical property requirements. Document the validated time on the routing and re-validate when compound or mold changes.
What is scorch time in rubber?
Scorch time is how long uncured rubber can be heated before it starts to cross-link and lose flow. It is often reported as ts2 on a rheometer or as a Mooney scorch value. It limits preform handling time and affects mold fill.
Why do actual rubber cycle times exceed standard?
Common reasons include lower real platen temperature, longer loading and unloading, compound lots with slower cure, operator extension of cure time to avoid undercure, and mold issues. Logging actual times by mold and lot helps separate those causes.
Netray can compare standard and actual cure and cycle time from your ERP and press data, and highlight molds and lots where the schedule is quietly drifting.