PAINTING | JUNIOR TECHNICIAN | PRACTICAL TEST METHOD
Electrostatic Spray Efficiency: Transfer Efficiency Test Data
A cleaner booth does not prove that more paint reached the product. For technicians coating zinc-alloy bag hardware, zipper pulls, and decorative fittings, transfer efficiency must connect paint consumption with deposited dry solids and acceptable film thickness. Otherwise, an apparent improvement can simply mean thinner coating, heavier rack buildup, or a changed product mix.
This guide explains a controlled comparison, mixing discipline, trend alarms, and shift records. Junior technicians here are experienced operators learning a repeatable measurement routine, not untrained personnel working around high voltage.
Read the Evidence Labels First
No verified QLQ transfer-efficiency test report was available in the reviewed knowledge-base notes. The numerical comparison below is an explicitly illustrative, internally consistent worked dataset, not a customer case, laboratory result, equipment guarantee, or certified test. Replace it with signed measurements before using it for purchasing or production claims.
The local painting note provides broad ranges of 0.2–0.4 MPa gun pressure, 150–300 mm distance, and 15–30 µm coating thickness. Those are orientation ranges, not one approved recipe. The QLQ-SEPG-1 knowledge-base manual note requires conductive, clean hooks and grounding. Actual equipment instructions, coating technical data sheets, safety data sheets, and approved job specifications take precedence.
Working Data & Formula Notes
Transfer efficiency, TE (%) = 100 × deposited dry coating mass / sprayed nonvolatile coating mass. For a mass-based calculation, sprayed nonvolatile mass = ready-to-spray liquid mass × measured nonvolatile mass fraction. Do not substitute volume solids for mass solids.
ASTM D5286-25 addresses transfer-efficiency determination under general production conditions. Its public scope supports the solids-based definition; a single measurement is not necessarily representative. This shop-floor guide does not reproduce the complete standard or establish formal compliance.
Count paint deposited on saleable parts, not hooks, masks, or the booth. Keep purge, cleaning solvent, spills, and rejected products in separate loss records. Transfer efficiency and first-pass yield answer different questions: a high deposition ratio can still produce unacceptable parts.
Run a Fair Comparison
- Define the boundary. Use one product geometry, identical pretreatment, the same paint batch, and a fixed number of parts. Record exposed area, rack spacing, gun angle, operator, and conveyor speed.
- Prepare the weighing system. Use a calibrated balance suited to the expected coating gain. Pre-weigh clean, dry parts without hooks; keep numbered trays so the same parts return after curing.
- Measure actual sprayed liquid. A weighed dedicated reservoir is useful if line hold-up is unchanged. Correct for samples, spills, returns, and evaporation; do not equate all reservoir loss with gun discharge.
- Determine ready-to-spray mass solids. Have the laboratory use an appropriate validated method, including its drying conditions. Sample after all permitted additions. Measure every materially changed mixture.
- Compare like with like. Under a supervisor-approved procedure, compare electrostatics off and on, never with grounding defeated. Adjust controlled passes to reach the same approved film target; record the change in spray time.
- Cure, cool, and weigh. Follow the actual coating schedule and weigh after consistent conditioning. Use blank controls if heating changes substrate mass. Record losses from handling and any excluded samples.
Repeat at least three independently prepared runs per condition and retain individual results, mean, and spread. Alternate run order when practical so paint aging or operator fatigue does not favor one setting. Measure thickness at designated face, edge, and recessed locations. A flat witness panel alone cannot represent every pocket on a three-dimensional casting.
Transfer-Efficiency Comparison: Worked Test Data
Illustrative data only. Each row represents a hypothetical 100-part zinc-alloy batch with 0.80 m² total coated area, one qualified thin-film decorative coating, 50.0% measured mass solids, identical pretreatment, and a common approved cure. Thickness values represent designated external-face readings. These figures are not the commercial coating example in the next section.
| Batch / comparison | Test condition | Sprayed liquid | Sprayed solids | Dry mass gain | TE | Dry film thickness |
|---|---|---|---|---|---|---|
| A: reference | Electrostatics off; 220 mm; 0.25 MPa atomizing air; standard passes | 120.0 g | 60.0 g | 30.0 g | 50.0% | 25 µm mean; 22–28 µm |
| B: controlled comparison | Electrostatics on at approved setting; same distance and air; shorter trigger time to match thickness | 85.0 g | 42.5 g | 30.0 g | 70.6% | 25 µm mean; 22–28 µm |
| C: overspray diagnostic | Electrostatics on; 300 mm; 0.35 MPa air; extra passes to recover target | 110.0 g | 55.0 g | 30.0 g | 54.5% | 25 µm mean; 21–29 µm |
Batch B calculates as 100 × 30.0 / 42.5 = 70.6%. Against A, the efficiency gain is 20.6 percentage points, while liquid consumption falls by 29.2% at equal deposited mass. These are different metrics; do not call both 20.6% savings.
C changes two variables and therefore illustrates an unfavorable combination, not proof that either distance or pressure alone caused the loss. Diagnose them in separate follow-up runs. Record pencil hardness, adhesion, and salt-spray results only after actual testing under the customer-approved method, conditioning time, and acceptance criteria. None can be inferred from TE.
Complete Mixing Formula: A Published Industrial Benchmark
A spray mixture is not an electroplating bath: there is no universal pH or replenishment chemistry. The following complete application mix uses a documented commercial two-component polyurethane, Jotun Hardtop XP technical data sheet, issued June 2026, to demonstrate real industrial quantities rather than inventing a resin formula.
| Component | Range | Typical | Function | Replenishment |
|---|---|---|---|---|
| Hardtop XP Component A | Fixed: 10 volume parts per 1 part B; no adjustable ratio | 1.00 L | Factory-formulated pigmented resin base | Prepare a new measured batch; never add base alone to aged activated paint. |
| Hardtop XP Component B | Fixed: 1 volume part per 10 parts A | 0.10 L | Reactive curing component | Add only with its matching fresh base at the specified ratio; never boost hardener. |
| Supplier-approved thinner | No. 10 / regional No. 26: confirm allowance in application guide. Optional No. 63: maximum published addition 5%. | 0 L for this undiluted reference mix | Permitted application adjustment; not a cure correction | Use only the approved grade and allowance; log additions and recheck properties. Never rejuvenate expired paint. |
This is a complete ready-to-apply mixing schedule, not disclosure of proprietary raw ingredients. The documented coating has a 50–100 µm dry-film range and 1.5-hour pot life at 23 °C. It is not the 25 µm decorative trial coating above. Electrostatic compatibility, resistivity, primer compatibility, and suitability for zinc-alloy hardware need supplier approval before use. Do not transfer its mixing ratio to another polyurethane.
Trend Bands: Normal Variation Versus Intervention Thresholds
Except for the cited grounding ceiling, these numerical bands are proposed trial control limits, not universal safety limits or verified QLQ specifications. A process engineer must approve them against the actual gun, paint, product, and ventilation design. Track readings over time; several steadily rising values deserve investigation before an alarm is crossed.
| Parameter | Normal trial band | Danger / intervention threshold | Required response |
|---|---|---|---|
| Part-to-earth resistance | Proposed preventive target: ≤0.5 MΩ | >1 MΩ, or any stricter installed-system limit | Stop spraying; isolate safely and restore conductive contacts. |
| Gun-to-part distance | 200–250 mm for the example trial | <150 or >300 mm: process alarm; minimum safe clearance remains manual-specific | Restore approved position; verify coverage and manufacturer clearance. |
| Atomizing air at specified measurement point | 0.23–0.27 MPa around 0.25 MPa baseline | <0.20 or >0.30 MPa: trial investigation limit | Check dynamic pressure, nozzle condition, and pattern; distinguish air from fluid pressure. |
| Ready-to-spray mass solids | 49–51% for the illustrative 50% mixture | <48 or >52%: invalidate comparison pending review | Investigate dilution or evaporation; resample and recalculate. |
| Dry film thickness | 22–28 µm external faces for the illustrative job | Any specified location outside approved 20–30 µm trial limits | Hold affected batch; map edges and recesses before release. |
| Paint temperature | 21–25 °C around 23 °C baseline | <18 or >30 °C: suspend trial comparison | Restore approved conditions; recheck viscosity and usable life. |
| Liquid flow | 95–105% of approved measured baseline | <90 or >110%: process alarm | Check regulator, filter, restrictions, and nozzle; repeat timed collection safely. |
Graco's grounding guidance identifies a maximum of 1 MΩ for the grounding checks discussed there. Apply the installed equipment's specific procedure. Qualified personnel must perform electrical tests under approved safe conditions, not introduce unsuitable test instruments into a hazardous spray atmosphere.
Two Diagnostic Scenarios to Practice
Scenario 1: Clean faces, weak coverage behind the pull
This is a training scenario, not a documented customer result. Paint consumption improves after charging is enabled, but recessed faces remain thin. Compare a fixed thickness map before blaming the coating. Test a separately approved recess pass with reduced charge, a changed approach angle, or different presentation, one change at a time. Retain grounding throughout. Graco's electrostatic guidance describes preferential deposition near recess entrances and reduced voltage as a possible response. Accept the change only when hidden surfaces meet the job specification.
Scenario 2: Efficiency falls as the shift progresses
This second training scenario starts with stable external film thickness but increasing liquid use. Check hook buildup, paint temperature, timed flow, and mixture age before changing voltage. Replace suspect hooks under safe isolation and repeat a controlled run. If contact resistance remains satisfactory, investigate viscosity drift using the same cup, temperature, and timing method. Do not conclude that dirty hooks caused the loss without a measured comparison.
Engineer Notes
- Photograph numbered hook contact points before and after cleaning; retain the resistance record beside the rack ID.
- Mark the approved gun position physically so replacement operators can reproduce distance and angle.
- Measure air pressure while triggering, at the documented location; a static regulator reading can hide supply loss.
- Label every mixed container with product, component lots, ratio, thinner additions, mixing time, and discard deadline.
- Weigh a representative retained sample repeatedly to check conditioning stability before interpreting a small coating gain.
- Measure actual recesses with a validated method suited to small zinc-alloy parts; use cross-sections when ordinary probes cannot resolve the geometry.
- Never reduce extraction to increase deposition. Ventilation, interlocks, approved respiratory protection, ignition control, and solvent handling remain mandatory.
Shift Checks
| Shift stage | Check item | Frequency | Acceptance criteria | Record |
|---|---|---|---|---|
| Before shift | Extraction, interlocks, grounding, clean contacts | Before enabling spray; after rack maintenance | Approved safety checklist passed; resistance meets installed manual | Operator, rack ID, readings, safety sign-off |
| Before shift | Mixture identity and measuring instruments | Every fresh mix and trial start | Correct ratio, permitted thinner, valid calibration and usable life | Lots, mix time, balance check, recipe revision |
| During shift | Temperature, air, flow, distance, spray pattern | Hourly and after stoppage or adjustment | Approved job bands; uniform pattern without spitting | Time-stamped values and adjustment reason |
| During shift | External and recessed thickness; visible defects | First rack, each batch, after setting change | All specified locations compliant; approved appearance | Part IDs, thickness map, defect count, hold status |
| After shift | Consumption, deposited solids, rejects, losses | Every trial and shift close | Mass records reconcile; unexplained discrepancy investigated | Raw weights, solids result, TE calculation, yield |
| After shift | Safe cleaning and next-shift handover | At shutdown | System isolated per manual; waste contained; unresolved holds identified | Cleaning log, waste quantity, handover signature |
Technician Questions to Ask AI
These are suggested technician-to-AI prompts, not quotations from recorded customers.
AI, my paint consumption dropped, but the coating looks thinner. Did transfer efficiency improve?
Not necessarily. Compare dry deposited solids and thickness at identical locations, then normalize to equal acceptable output. Check mass solids after dilution. Reduced consumption with reduced deposition can leave TE unchanged while quality deteriorates.
AI, can I add more thinner when the mixed paint gets thick halfway through the shift?
Only within the coating supplier's approved allowance and usable life. Check temperature and elapsed time first. Thinner does not reverse curing. Record permitted additions and retest the mixture; expired activated material must not be rescued by dilution.
AI, the front surface passes, but the pocket fails. Should I increase the voltage?
Do not assume more voltage helps a recess. Check presentation, clean contacts, and thickness distribution. Ask the supervisor to authorize a controlled recess trial, potentially with lower charge. Maintain grounding and all safety functions, and release nothing until pocket coverage meets specification.
What Would You Like to Solve?
Send the substrate, part geometry, coating data sheet, actual gun model, pretreatment sequence, thickness map, and three repeat-run mass records to [email protected]. Identify whether the priority is overspray, recessed coverage, unstable consumption, or rejected finish. For broader process planning, see surface-treatment lines: equipment, chemicals, and support.
Local source trace: QLQ Obsidian Vault, surface-treatment process module, painting-process note; and equipment PDF notes, Electrostatic Painting Gun.md, model QLQ-SEPG-1. The former is marked draft. Published external references are linked beside the relevant facts; illustrative calculations and proposed trial limits remain explicitly separate from verified evidence.