Anodising

1.0 Scope

This specification defines the surface finish options and quality standards for anodised aluminum parts. It provides guidance on the visual inspection and assessment of significant surfaces with respect to defects unique to the anodising process.  Unless otherwise specified we would require any anodised parts to meet type II (Fractory B level).

2.0 Anodising Types

This section defines anodising service levels (Type II and Type III). More information can be found in the international standards referenced in the table below. Unless otherwise specified we would require Fractory Service Level B (Type 2 anodising)

4.0 Viewing Conditions

For all viewing situations a minimum of 1.0 metre shall apply provided that further distance be allowed commensurate with the use of the product and its in-situ viewing distances. Inspection shall be conducted using the unaided eye under 500 Lux lighting conditions.

4.1 Lux

A measurement of luminous intensity from a light source. The following table represents the illumination from common sources:

Illuminance Example

50 lux Family living room80 lux

320–500 lux Office lighting

400 lux Sunrise or sunset on a clear day.

1,000 lux Overcast day; typical TV studio lighting

10,000–25,000 lux Full daylight (not direct sun)

32,000–130,000 lux Direct sunlight

5.0 Anodising defects

This section defines common anodising defects to align expectations. Understandably the manufacturing partner, who provides coating, does not perform metalworking processes such as laser cutting, bending or machining - however, it remains the anodising partner's responsibility to notify Fractory if the parts received are in a condition that prevents a defect-free result. 

5.1 Anodising rack marks (contact points)

Anodising rack marks are small, unanodized areas or “contact points” created where the part is physically gripped by a conductive fixture during the anodising process. Because the rack blocks the chemical solution from reaching these locations, they appear as bare metal “shadows” or voids in the final finish. As rack marks cannot be completely avoided, they must be placed on non-visible surfaces. If visible and non-visible surfaces are not defined or if it is unclear which surfaces are cosmetic, additional clarification must be requested before processing. 

5.2 Color variation

Inconsistency in surface appearance or saturation across a single part or between batches, typically driven by fluctuations in bath temperature, chemical concentration or substrate metallurgy. Color variation is not allowed!

5.3 Handling-induced defects

Surface marks caused by skin oil transfers during handling (fingerprints), which act as a local resist to the anodizing process, leading to permanent, non-uniform patches or "ghosting" in the final finish. Handling/ fingerprint defects are not allowed!

5.4 Surface stickiness

Surface stickiness / tacky finish is a post-process defect where the anode layer feels adhesive to the touch, typically caused by over-concentration of sealing additives, improper pH levels in the seal tank or insufficient rinsing of the part. Tacky finish is not allowed and must be avoided!  

5.5 Bad material surface 

Anodizing is a conversion coating, meaning it transforms the surface of the metal rather than covering it up. As a result, it makes material surface flaws look even worse. Visible surface imperfections such as machining/cutting burrs, deep scratches and oxidation (rust) that were not removed during pre-treatment will be a visual defect after anodizing. Therefore material imperfections are not allowed and needs to be agreed before anodizing.

6.0 Masking (if requested)

Masking involves covering specific surface areas to prevent them from being anodized. This is essential for maintaining electrical conductivity, glue contact zones and mating surfaces, as well as ensuring critical dimensional tolerances remain unchanged. Masked areas must be clearly defined in the work input and ideally, specified on the technical drawing. If masking is requested, but not defined, please ask further information from Fractory account manager!