What it is and why it matters
First-hour yield (FHY) is the percentage of good ware produced in the first 60 minutes after a changeover or restart. It is the cleanest single measure of how well your forming, forehearth and line coordination handled a transition. A fast changeover with 55% FHY is often worse than a longer changeover with 90% FHY — and most plants we visit cannot tell you which they have.
Why it gets ignored
FHY falls into a measurement blind spot. Minutes-to-complete is easy — a stopwatch does it. Yield is harder — it requires classification, counting, and discipline in a window when the crew is under pressure to stabilise. So plants track changeover time, announce it proudly, and quietly watch pallet rejection trends two days later without connecting the two.
What good looks like
- Median FHY > 90%. Steady, consistent across crews and products.
- P10 FHY > 80%. Even the worst changeover should clear 80%. If your P10 is 55%, you have a systemic issue, not a bad-luck issue.
- Defect mix stable. A flat top-5 defect pareto that does not reshape every changeover is a sign of healthy standard work.
How to measure it, practically
- Define the window. 60 minutes from first gob post-changeover. Be strict.
- Count ware produced and ware accepted in that window. Cold-end data is fine; do not demand hot-end counting heroics.
- Tag defects by mode. Stuck ware, check, blister, stone, finish defect — whatever your top 5 are.
- Post daily. If the crew cannot see it on the huddle board, it is not a KPI, it is a statistic.
What moves it
- Forehearth pre-tuning. Getting setpoints to the incoming product's window before restart, not during.
- Mould conditioning standard. Pre-heat cycles done on schedule, not by feel.
- Operator checklist for first 20 minutes. The most common FHY killers are avoidable with a 3-item checklist.
- Feedback loop to changeover standard. Every sub-90% FHY event becomes a standard-work revision candidate.
One warning
Do not incentivise FHY in isolation. Paired with changeover time, it is powerful. Alone, it creates slow changeovers that look good on the yield dashboard. We build the two into a combined index and review them side by side — never apart.