Closure leakage / poor seal

What you will see

Application torque below SKU minimum. Symptoms: caps unscrew under shipping vibration, bottles leak in warehouse, consumer pre-opening risk. For CSD: CO2 retention loss > 17% over shelf life. Often confused with closure quality issue — but if cap quality is good and torque is low, capper is the problem. CROSS-COMPONENT NOTE: insufficient torque AND low preform neck wall thickness produce identical symptoms (loose-feeling caps, CO2 loss) — diagnose by measuring both torque AND preform wall thickness before assuming the capper is at fault.

Likely causes

• Capper torque setpoint too low (operator override, or program error)
• Magnetic clutch slipping too early (worn out)
• Pneumatic torque control insufficient air pressure
• Operator reduced torque to "prevent breakage" when real issue was over-torque (corrected wrong way)
• Preform neck wall too thin — neck flexes under cap, effective seal compression drops even when measured torque is in-spec

Do this first

Measure break-torque on 10 applied closures. If consistently < SKU min, increase setpoint. Re-verify by re-measuring 10. CROSS-COMPONENT: if torque is in-spec but caps still feel loose, measure preform neck wall thickness (see neck_wall_thickness_undersize in preform tree).

How to diagnose it

1. Break-torque on 10 closures
2. Compare to SKU min (PCO 1881: 14 in-lbs minimum)
3. Verify capper program SKU code
4. Check air pressure (90 PSI typical at capper)
5. CROSS-COMPONENT CO2 retention test: 30 bottles, 24h + 7d measurement; if loss > spec AND torque was in-window → preform-side or angle-side cause
6. CROSS-COMPONENT: section 5 preforms and measure neck wall thickness at sealing area

How to fix it

1. Increase torque to SKU min + 4 in-lbs (mid-window)
2. Re-validate with 10-bottle break-torque
3. If clutch worn, service before next shift
4. If torque is correct but CO2 retention still fails → run cross-component diagnosis (see co2_retention_failure entry)

What you will see

The horizontal sealing surface (where closure meets bottle neck top) has scratches, sink marks, or pits. STATION 05 (sealing surface) IMD catches this. Causes leakers in service — even microscopic defects (~0.05mm depth) can leak under CSD pressure. CROSS-COMPONENT NOTE: Sealing-surface leakers can originate from EITHER side of the seal interface — the closure liner/seal-land defect, OR the preform top sealing surface (see seal_land_damage in the preform defect tree). Diagnose by switching to a different closure lot OR a different preform lot to isolate.

Likely causes

• Mold cavity seal-land surface polish worn (closure-side)
• Sink marks from excessive cooling (thicker section pulls inward)
• Damage from capper chuck (chuck face contacts seal land during application)
• Storage damage (closures dragged against rough surfaces during transit)
• Preform sealing land damaged — see seal_land_damage entry in preform tree

Do this first

Inspect 30 closures with bright angled light specifically on the sealing surface (inverted view). Mark any with visible scratches/marks. Functional test: cap onto pressure-tested bottles and leak-test. CROSS-COMPONENT: also invert 30 preforms and inspect the bottle finish top sealing surface — preform-side damage produces identical leaker symptoms.

How to diagnose it

1. Invert closures and inspect seal land under angled light
2. Photograph 5 worst examples
3. For CSD: apply to pressurized bottle, submerge, check for bubbles
4. For water: 10 closures on water bottles, store inverted 24h, check for leaks
5. CROSS-COMPONENT isolation: switch to a different closure lot from the same SKU. If leakers persist with new closures → preform-side. If leakers stop → closure-side confirmed
6. CROSS-COMPONENT: invert 10 preforms and inspect bottle finish top sealing surface under angled light for scratches/nicks/sink marks

How to fix it

1. Functional leak test confirms severity
2. If >1% leak rate AND closure-side root cause confirmed, quarantine lot, contact Delta with leak-test data
3. Delta cavity inspection (seal land polish) — refurb if needed
4. Inspect capper chuck — does it contact seal land? Should not for CSD closures (chuck grips OD only)
5. If preform-side cause confirmed → reference preform tree seal_land_damage entry; contact Delta for preform CAPA