Overview
ISO 6581:2018 specifies a comparative method to determine the fastness of coloured anodic oxidation coatings on aluminium and its alloys when exposed to ultraviolet (UV) light and heat. The procedure is intended for comparative assessments and rapid determination of light-fastness; it is not suitable for heat-sensitive coloured coatings. The test is severe compared with natural sunlight exposure and is designed for quality control, material selection and process validation.
Key Topics
- Principle: Expose test specimens and standard specimens to a UV light source and compare resulting colour changes.
- Apparatus: A heat-resistant, enclosed cabinet with an equidistant specimen arrangement and a medium-pressure mercury arc-lamp (silica envelope) is used. Lamp output varies with age; typical examples in the standard include a 400 W lamp with ~150 mm effective arc length placed at approximately 170 mm from specimens.
- Temperature control: Surface temperature of specimens shall not exceed 100 °C. Cooling (fans) and manufacturer guidance for lamp cooling should be followed to avoid affecting lamp arc.
- Specimen preparation: Samples should be taken from flat, representative surfaces (avoid edges), cleaned of contaminants, and typically larger than 150 mm × 70 mm.
- Ozone and safety: Some lamps produce ozone; forced ventilation and ducting may be necessary. The cabinet must prevent UV escape and include an interlock to switch off the lamp when opened.
- Result expression and reporting: Record exposure time to reach the agreed level of colour change or describe changes after an agreed exposure period. The test report must reference ISO 6581:2018 and include product identification, specimen colour/production method, apparatus details (lamp model, wattage, arc length, distance), exposure times, observed colour changes and any deviations from the procedure.
Applications
- Quality control: Rapid comparative screening of coloured anodized finishes for production batches.
- Material selection: Compare alternative anodizing processes, dyes or alloys for resistance to UV and heat.
- Process validation: Verify consistency of anodizing baths and finishing operations against standard specimens with known UV resistance.
Related Standards
- ISO 7583 - Terms and definitions for anodizing of aluminium and its alloys (referenced by ISO 6581:2018).
For laboratories and anodizers, ISO 6581:2018 provides a structured, repeatable comparative test to assess and report the UV and heat fastness of coloured anodic coatings, enabling informed decisions on coating selection and process control.
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