BS/EN 4868-2019 pdf download.Aerospace series-Anodic electrodeposition of hexavalent chromium free primer.
4.1 General
This specification establishes the requirements for a waterborne, hexavalent chromium free corrosion inhibiting, chemical and solvent resistant, anodic electrodeposition of organic coating capable of curing atllO°Cto 120°C.
The ariodic electrodeposition process applies a protective coating with uniform film thickness control, complete coverage of recessed areas, minimal surface defects and high transfer efficiency. Once the film is deposited on the substrate, a thermal cure is required to achieve the final properties of the coated parts.
4.2 ApplicabilIty
It can be used as a protection against corrosion, as a painting primer before top coating application, for electrical insulation, and as a masking before anodizing and/or conversion.
4.3 LimitatIons
4.3.1 All processes that can compromise the anodic electrodeposition film (e.g. forming, blasting, shot peening,, heat-treatment) shall be performed prior to surface preparation of the parts to be coated).
4.3.2 Anodic electrodeposition shall not be applied:
• in areas where electrical conductivity is required;
• for high temperature applications (> 180 eC);
• for components which can permanently entrap treatment solutions, except components that can be adequately masked;
• for assemblies with overlap areas (e.g. spot-welded and riveted parts) containing tight tolerances that cannot provide adequate pre-treatment and/or coating penetration between the overlap area.
5 Protection system classification
Coating layer is classified by the three following types:
• Type A: thin layer thicknesses (4pm to 12pm);
• Type B: medium layer thicknesses (12 pm to 30 pm);
• Type C: thick layer thicknesses (> 30 pm).
• electrical contact points or areas where these are inadmissible;
• specification for testing parts and/or samples.
6.2 Condition of parts prior to the treatment
All prior operations such as welding, soldering/brazing, blasting, shot peening,. machining and heat
treatments shall have been completed.
• the parts shall be free of oil. grease, marking inks and other surface contaminations;
• if needed/required, mechanically disturbed layer shall be removed either by mechanical or chemical processes;
• surface treatments prior electrodeposition process are possible. In case of anodic electrodeposition rework, all organic coatings residues from the previous coating shall be completely removed.
6.3 Process conditions
6.3.1 Tooling
The tools, bars, electrical contact systems, and metal masking tooling shall be free of corrosion or any other damage which may be detrimental to the treatment during use, The part racks and tools must be designed and set up in such a manner as to:
• avoid any retention of air or treatment solution in the parts;
• facilitate neutralization and removal of solutions during rinsing operations;
• the electrical contacts shall be kept in good condition for the correct flow of the current;
• electrical contact point locations should be defined between purchaser and processor, avoid any accidental contact between the parts to be treated and the tank equipment or electrodes, and between the different parts during all the process;
• the contact is preferably achieved at several points in order to ensure better current distribution. Contacts shall be cleaned before each treatment;
• the tlxturing tools (e.g. in aluminium alloy, titanium, stainless steel) shall provide effective electrical contact with the parts.
6.3.2 Masking
The parts shall be at least degreased prior to masking.
Component areas which shall not be coated shall be masked with suitable material compatible with curing coating temperature (120 °C maximum) and treatment baths.
6.3.3 Surface pre-treatment
Surface preparation means any method able to completely eliminate all surface contaminations.
In case of soda etching, the final step prior to anodic electrodeposition shall be chromate-free acidic pickling.
The rinsing shall be carried out in order to avoid acid residues. it shall be carried out as quickly as possible after pickling in running water at room temperature. The water used for final rinsing is recommended to have a conductivity less than 20 itS/cm.
6.3.4 Anodic electrodeposltion
During the electrodeposition process:
• distance between parts and electrodes shall be defined to avoid electrical arcing,
• the process parameters (temperature, voltage, time) shall be adapted to the material and in accordance with the customer requirements.
6.3.5 Anodic electrodeposltion post treatments After the electrodeposition process:
• parts have to be adequately rinsed according to 6.4 or in ultra-filtrate (a double-rinsing is recommended);
• afterwards, the parts shall be cured (a previous air drying before curing is allowed);
• after curing, a final top coat could be applied.
6.4 Water quality
The water shall comply with the following requirements:BS/EN 4868-2019 pdf download.