Hot-dip Galvanising Line Troubleshooting: Causes & Fixes

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Problems on this page:

Bare spots on the coating Coating too thick Rough coating, ash or dross inclusions Zinc splashing or explosions at the bath Zinc bath temperature unstable High zinc consumption Pre-treatment baths exhausted early Crane and jig problems

Bare spots on the coating

Hits OEE: Quality

Symptoms: Galvanised parts show uncoated areas after dipping.

Degreasing or pickling incomplete

Check the degreasing and pickling bath strength, temperature and time for the steel being run.

Flux bath weak or contaminated

Check the flux concentration, iron content and temperature.

Paint, weld slag or marking ink on the steel

Inspect incoming work and remove contaminants that the chemical pre-treatment cannot.

Air trapped by the part shape

Check the venting and draining holes in the fabrication.

Prevention: Coating inspected visually on every load before dispatch.

Coating too thick

Hits OEE: Quality

Symptoms: Coating thickness is above what the steel needs, using zinc and causing rough or brittle coatings.

Steel chemistry reactive (silicon or phosphorus content)

Check the steel certificates and adjust the dipping time and bath temperature for reactive steel.

Immersion time too long

Check the dipping time against the plan for the steel thickness.

Withdrawal speed too slow or drainage poor

Check the withdrawal speed and how the work hangs.

Bath temperature too high

Check the zinc bath temperature control.

Prevention: Coating thickness measured on samples from each load.

Rough coating, ash or dross inclusions

Hits OEE: Quality

Symptoms: The coating is lumpy or carries ash or dross particles.

Ash not skimmed from the bath surface before withdrawal

Skim the bath surface before every withdrawal.

Dross level in the bath too high

Remove dross on the set schedule.

Flux carried over in excess

Check the drying of fluxed work before dipping.

Iron build-up in pre-treatment tanks

Check iron levels in the pickling and flux tanks.

Prevention: Surface checked on every load.

Zinc splashing or explosions at the bath

Hits OEE: Availability

Symptoms: Molten zinc splashes or erupts when work is lowered into the bath.

Wet work or trapped water in closed sections

Check that work is dry and that closed sections are vented; trapped moisture turns to steam in the bath and is a serious hazard.

Flux not dried

Check the drying oven before the bath.

Work lowered too fast

Lower work at the speed the procedure sets.

Tools or scrap added wet

Dry anything added to the bath.

Prevention: Venting and drying checked on every load; the exclusion zone around the bath is kept during dipping.

Zinc bath temperature unstable

Hits OEE: Quality

Symptoms: The bath temperature drifts and coating quality changes.

Burner or heating fault

Check the furnace burners or electric heating and their control.

Thermocouple drifting

Check the bath thermocouples against a reference.

Heavy loads dipped too close together

Space heavy loads so the bath recovers its temperature.

Kettle wall heating uneven

Check the furnace heat distribution around the kettle.

Prevention: Bath temperature logged continuously and reviewed each shift.

High zinc consumption

Hits OEE: Performance

Symptoms: Zinc used per tonne of steel is above the normal level.

Coatings thicker than needed

Work through the coating thickness causes.

Too much dross and ash produced

Check the bath temperature and the flux carry-over.

Poor drainage leaving runs and drips

Check the hanging of the work and the withdrawal speed.

Excess zinc removed and lost

Check how drips and runs are removed and recovered.

Prevention: Zinc use per tonne recorded weekly.

Pre-treatment baths exhausted early

Hits OEE: Performance

Symptoms: Degreasing, pickling or flux baths need replacing sooner than planned.

Drag-out from poor draining

Drain work above each tank for the set time.

Rinse tanks not used or contaminated

Check the rinse tanks between baths.

Heavy oil or rust on incoming steel

Agree incoming steel condition with customers.

Bath analysis not done on schedule

Analyse the baths on the set schedule and correct them in time.

Prevention: Bath analysis results logged.

Crane and jig problems

Hits OEE: Availability

Symptoms: Cranes, jigs or wire hangers cause delays, drops or damaged work.

Crane faults or slow travel

Check the crane drives and brakes on the maintenance plan.

Jigs and hooks worn or coated with zinc

Strip and inspect jigs and hooks on a schedule.

Work hung badly for draining

Train the jigging team on hanging for venting and drainage.

Not enough jigs for the work mix

Plan jig capacity for the work mix.

Prevention: Crane faults and jig condition recorded.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: shot blast machine · overhead crane · electroplating line · dust collector · powder coating system

Stop the same fault coming back

Recurring hot-dip galvanising line stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover