What a Real Hot End Audit Covers (and What Most Miss)

It's 02:30 on a Wednesday morning. Section nine on line four has been producing choked necks for 45 minutes, and the hot-end superintendent is standing at the section with a forming card that doesn't match what's actually running.

That's not a forming problem. That's a documentation and handover problem sitting on top of a recipe management failure. A genuine hot end audit finds both. Most don't.

Most audits stop where the problems are visible

An OEM-affiliated consultancy comes in, walks the IS machine floor, watches the gob fall, checks reject rates, and writes a report about plunger timing. That covers roughly 20% of what actually drives pack-to-melt. The other 80% lives upstream, downstream, and in the shift-to-shift gaps nobody photographs.

I sat through a post-audit debrief at a two-furnace, six-line plant in the US Midwest where the report ran to 48 slides and never once mentioned forehearth profile variance. The plant was running ±7°C across the five working zones when the target was ±2°C. Every cord and settle wave they were chasing had a forehearth fingerprint, but the audit stopped at the machine.

A forehearth running out of spec doesn't just affect glass quality. It destabilises gob weight, which cascades into section timing, which shows up in ware dimensions, which ends up as a quality hold at the cold end. That chain is familiar to anyone who's actually stood on the hot end for a full shift.

Gob delivery is a system, not a component check

Gob weight CV is the number I look at first on any site visit. Target: ≤0.4% across a production run. I've walked into plants where crews couldn't pull that data quickly and had never trended it against reject rate. At a mid-size container glass plant in regional Victoria I audited two years ago, gob weight CV was running at 1.1% on two of their five lines. The team was attributing pack variance to blank mould wear. The moulds were fine. The shear timing was drifting.

Gob delivery is a system. The feeder spout, needle and tube, shear mechanism, and gob chute all interact with each other and with the thermal condition of the glass arriving from the forehearth. Pull them apart individually and you miss the relationships. The hot end audit Lean Glass runs treats this as a delivery chain, not a collection of isolated components.

Swabbing discipline sits in this same territory and most audit reports skip it entirely. Swab burn shows up fast when you're watching, but the chronic version is slower and harder to catch. Swabbing frequency, compound type, and who on the shift owns the swabbing record all matter. At most plants I visit, the 0600 handover misses the night-shift swabbing data at least 60% of the time. The incoming superintendent can't read the section behaviour correctly because they don't know what the last four hours looked like.

The defect you're chasing at the cold end almost always has its birth certificate somewhere on the hot end. The problem is that most audits never go back far enough to find it.

Hot coating and ware handling: where ownership breaks down

Hot coating is an afterthought on a lot of sites. The hot-end superintendent owns the IS machine. The quality team owns the cold end. Ware handling and coating sits between them and often belongs to nobody. That gap is exactly where leaners, scratching, and coverage failures breed.

Hot coating application, typically tin oxide or titanium tetrachloride, is sensitive to glass surface temperature. Running at the wrong belt speed, or with a coating hood that hasn't been calibrated since the last job change, means your coating weight wanders. You won't see it immediately. You'll see it three weeks later when customers start calling about scratching in the distribution chain.

Ware handling from the dead plate through the lehr conveyor introduces variables most hot end audits don't touch. Belt gap settings, pusher timing, the condition of the star wheel and cross conveyor. These are all measurable. A worn pusher pad consistently misplacing ware by 8mm doesn't sound critical until you're seeing thermal non-uniformity from the lehr and struggling to explain your annealing reject rate.

What a complete hot end review actually covers

A thorough hot end audit in container glass covers eight domains: IS machine condition and settings, gob delivery performance, forehearth thermal profile, swabbing programme and records, hot coating application, ware handling from dead plate to lehr, shift handover quality, and recipe management discipline. Each domain has hard metrics and observational checks.

The forming side alone includes:

• Plunger position and stroke verified against the live recipe card, not the posted spec sheet
• Baffle alignment checked with a centring tool. Baffle marks almost always trace back to alignment drift before anything else
• Section timing variance reviewed over a 24-hour trend, pass threshold ±10ms
• Mould preheat curve confirmed at 480°C ±10°C at the time of first ware

Lean Glass is vendor-neutral. We don't represent machine manufacturers and we don't have a financial stake in what you replace or retrofit. That matters when findings point at equipment the site has a long relationship with. The report has to tell the truth, not protect a supply agreement.

Across the plants I've run and audited, closing the gaps a proper hot end audit surfaces typically returns +3 to +5 OEE points within 90 days. That's not a projection. That's the range I've seen consistently on four-to-eight line plants where the fundamentals had drifted but the equipment was serviceable. If your pack-to-melt has been soft for two quarters and you can't point to a root cause, start with the hot end. Download the 30-point audit checklist to see what a structured review looks at before you bring anyone on site.