Anodizing Plant Division
Electrochemical Brightening
Electrobrightening tank for architectural profiles
Electrobrigthening can give a high degree of “polishing” or more correctly “smoothing”, i.e. removal of surface roughness such as scratches or light machining marks. With slight changes in operating conditions, it can be used for bright finish. Its main drawback is the relatively high capital cost of plant due mainly to cost of rectifiers. The standard of finish obtained is very high and a wide range of alloys and components can be satisfactorily processed by electro brightening.
The mechanism of electro brightening has been the subject of academic research for many years. A simple all-embracing mechanism has not been developed so far. However, there are some important similarities between the electrolytic and chemical processes. The electrolytic processes can be placed into two broad categories: 1) electro brightening and 2) electro brightening /levelling processes. The former are essentially micro smoothing and the latter produce macro smoothing.
ELECTROBRIGHTENING PRACTICE
Before electro brightening the work should be thoroughly cleaned, the cleaning treatment being selected to suit the contamination on the surface. A cleaner having a mild etching action has no detrimental effect on the final appearance. After cleaning and rinsing a desmut treatment followed by further rinsing is recommended.
The work is then transferred to the electro brightening bath and firmly fixed to the cathode work-rail. The current is then switched on and the motor moving the work rail is also started up. For best results, it is necessary to know with reasonable accuracy the area of work being polished since electro brightening current density is the main parameter controlling the standard of finish produced. In general pure aluminium and high-purity aluminium and aluminiummagnesium alloys give good electro brightening at 5-11 A/dm2 .
The more difficult high strength aluminiumcopper and other complex alloys require higher current density. Time of polishing depends partly on the alloy but mainly on the surface condition, polishing times normally ranging between 2 and 10 minutes. The best combination of current density and time must be established for any given component, but experience with the various alloys enables a suitable current density to be selected with a minimum of experiment. Aluminium-silicon alloys are very difficult to electrobrighten and are usually avoided. The main check then in any trial is on the time needed to achieve an adequate standard of finish.
Generally this processing will remove 12-50 µm with metal removal at the rate of 25 µm per 100 amp. minutes.
Far detailed information about equipment, rectifier and chemical needed ask Italtecno technical office.
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