Quality control
Every batch is checked at three points: raw materials in, semi-finished goods during production, and finished goods before release. The tests and limits are set out below.
Incoming raw materials
- Granularity
- Moisture
- Purity
Semi-finished goods
- Granularity
- Acid and alkali resistance
- Glossiness
- Transparence
- Hiding power
- Viscosity
Finished goods
| Test | Method | Limit |
|---|---|---|
| Granularity | 0.5 g of powder is taken from a 100 g sample, dispersed with detergent, and measured on a particle size analyser. Against standard: △D90 ≤ 1 µm, D100 ≤ 25 µm. | △D90 ≤ 1 µm, D100 ≤ 25 µm |
| Moisture | 5–10 g of powder is tested in a moisture analyser to two decimal places at 130 ℃. | ≤ 0.40% |
| Colour | A test sample and the standard sample are mixed with the same percentage of varnish, screen-printed on the same glass and fired, then measured on a colour analyser under C light at 2°. △E = √(△L² + △a² + △b²), where L is lightness, a is red–green and b is yellow–blue. | △E ≤ 1.0 (visual match) |
| Pb and Cd dissolution | After firing, the sample is tested by atomic absorption spectroscopy in 4% acetic acid for 24 hours at 22 ± 2 ℃, to GB 3534. | Pb ≤ 10 mg/dm², Cd ≤ 1.5 mg/dm² |
| Acid resistance | To ASTM C724-1991: soaked in 3.5% HCl for 15 minutes, then graded one to six. | Grade four or better |
| Alkali resistance | To ASTM C675-1991: soaked in 9.1% NaOH + 0.9% Na₃PO₄ at 88 ± 2 ℃ for 2 hours; the loss is measured against standard. | △g ≤ 0.0020 g/cm² |
| Mar resistance | Three 20 × 20 cm colour-glaze glass panels are scraped 20 times, smeared with ink, left 10 minutes and cleaned with quartz powder. | No ink trace |
| Anti-shock | A 1,040 g metal ball is dropped from 1 m onto tempered glass whose glazed area is less than 30%, more than eight times. | No breakage |
| Viscosity | Solid content measured at 25 ℃ on an NDJ-79 viscometer. | Solid ≥ 80%; 160–170 Pa·s static, 60–70 Pa·s dynamic |
Acid resistance grades
Acid resistance (ASTM C724-1991) is graded one to six:
- No obvious corrosive trace.
- Obvious trace at a 45° angle of view, none at less than 30°.
- Trace at less than 30°, no effect on reflection.
- Trace at less than 30°, effect on reflection.
- Surface not smooth.
- No decoration left.
We require grade four or better for the enamel to pass.
QC objectives
- First-pass yield of at least 99.7% on a single test.
- No justified customer complaint.
- Returns no more than 0.20%.
- Customer satisfaction index reaching 90%.
- 100% pass rate for incoming raw materials.
- Income from new products at least 10% of total income.
Ask for test data on a grade
Tell us the product, the application and the quantity, and we will reply by email. For a colour match, send a fired sample or the target reference.