The Highest-Risk Block in the Factory

Plating is where a zipper factory touches the most regulated chemistry, generates the most hazardous waste, and creates the defect that is hardest to see at final inspection. A slider can look perfect on the day of shipment and fail a salt spray test three weeks later. That gap between appearance and performance is why plating deserves a dedicated audit rather than a paragraph in a general factory assessment.

The audit has two halves that are usually treated separately and should not be: process control, which decides whether the coating meets specification, and environmental control, which decides whether the factory will still be operating in three years.

What to Look at on the Line

Walk the line in process order and stop at every tank. The physical condition of the line tells you more than the logbook.

  • Tank sequence and identification, matching the process card for the part being run.
  • Racking and jig condition: contact points cleaned, no build-up, parts not touching.
  • Rinse stages: number of rinses, water flow, and whether counterflow is actually running.
  • Drag-out control between tanks, and whether drip time is specified.
  • Extraction and fume hoods operating over heated and acidic tanks.
  • Floor condition, bunding around tanks, and spill kit location.
  • Operator PPE: gloves, apron, face protection, and whether they are actually worn.

Ask for the process card for the current lot and compare it with the tank sequence in front of you. Any difference needs an explanation before the audit continues.

Bath Chemistry and Analysis Frequency

Ask for the analysis records, then ask who performs the analysis and how often the analytical methods are checked.

  • Which parameters are analysed: metal concentration, pH, temperature, additives, impurities.
  • Analysis frequency per tank, written into a schedule rather than decided by feel.
  • Who performs the analysis: in-house laboratory, or an external laboratory with reports on file.
  • Corrective action when a bath is out of range, with the addition calculated and recorded.
  • Bath life and replacement criteria, including impurity limits.
  • Temperature control: whether heaters are calibrated and whether the reading is recorded.

A passing answer shows a trend chart per tank with control limits and a note for every excursion. A failing answer is a folder of analysis reports with no corrective entries, which usually means the reports are filed rather than read.

Thickness, Adhesion and Corrosion

Coating performance is a specification, and specifications need numbers. Ask for the values and the method used to obtain them.

  • Coating thickness: target range, measurement method, and measurement locations on the part.
  • Adhesion test method and acceptance criteria, with results per lot.
  • Salt spray or equivalent corrosion test: duration, conditions, acceptance criteria and frequency.
  • Whether testing is in-house or outsourced, and how long results take.
  • What happens to a lot that has shipped before the corrosion result is available.

That last question is the important one. Many factories release on thickness alone and treat corrosion testing as a periodic check. If that is the practice, the audit should record it as a risk rather than a defect, because the exposure is batch-wide.

Wastewater and Discharge Records

Ask for the last twelve months of wastewater test reports from an accredited laboratory, then ask how the sampling point is chosen and who witnesses sampling.

  • Discharge volume per day, and whether it is metered.
  • Treatment process: neutralisation, precipitation, filtration, ion exchange, or transfer to a licensed contractor.
  • Test parameters covered, and whether they match the local discharge requirements for the receiving system.
  • Sampling point location, with a photograph and a description.
  • Any exceedance in the last twelve months, with the cause and the corrective action.
  • Sludge handling: quantity, storage, and the licence of the disposal contractor.

Do not ask whether the factory "complies". Ask what the last test result was, what the limit was, and what happened the last time a result exceeded it. Compliance is a series of events, not a status.

Air, Chemicals and Worker Protection

Environmental compliance is not only about what leaves in pipes. It is also about what stays in the building.

  • Local exhaust ventilation on every tank that generates mist or fume, with a record of airflow checks.
  • Chemical storage: segregated by compatibility, bunded, labelled, with safety data sheets available in the local language.
  • Eyewash and emergency shower within reach of the line, tested and logged.
  • Air monitoring results for the plating area, if required locally, with the testing body identified.
  • Training records for plating operators, including emergency response.

Restricted Substances and Customer Requirements

Ask for the declaration file for the finishes used on the parts you buy. Do not accept a general statement that the factory "meets requirements".

  • Substance declarations for each plating chemistry, current and signed.
  • Test reports from a recognised laboratory, with the part and finish identified on the report.
  • Change control: how the factory notifies customers when a chemical supplier or process changes.
  • Subcontractor plating, if any, with the same evidence set for the subcontractor.

The Actionable Audit Checklist

  • Tank sequence matches the process card for the running lot.
  • Bath analysis is performed on a written schedule, not on request.
  • Every out-of-range analysis has a recorded corrective addition.
  • Coating thickness is measured per lot, with locations defined.
  • Corrosion testing has a defined frequency and acceptance criterion.
  • Wastewater is metered and tested by an accredited laboratory.
  • Exceedances are logged with cause and corrective action.
  • Sludge disposal is documented with a licensed contractor.
  • Local exhaust ventilation is present and checked.
  • Chemical storage is segregated, bunded and labelled.
  • Emergency shower and eyewash are tested and logged.
  • Restricted substance declarations are current and part-specific.

What a Passing Answer Looks Like

Passing sounds like this: "Nickel was low on tank three on the ninth; we added two kilos, re-analysed after thirty minutes, and the lot was held until the result came back inside range." That answer shows a number, a decision and a hold. A factory that can produce that sentence under questioning is controlling its plating line. A factory that answers with a certificate is hoping the audit will stop there.

Donglong treats plating evidence as a gating item for approval, because a finish that fails in the field cannot be recovered by any amount of final inspection.