Page 42 - CFCM Nov-Dec-2020 Final_Neat

BRUSH PLATING

In brush electroplating, localized areas or entire parts
can be plated using a brush saturated with plating solution.
The operator can move the plating tool over the area to be
plated or the part can rotate with the plating tool stationary.
In either case, operator experience is important.
Brush electroplating has several advantages over tank
plating, including portability, ability to plate items that can-
not be tank plated, low or no masking requirements, com-
paratively low plating solution volume requirements and
being able to repair components in-place. A disadvantage
compared to tank plating is the need for greater operator
involvement, which makes the success of the process de-
pendent on the skill of the operator. Brush plating is also
limited in thickness by the time the operator can spend
plating; tank plating (especially hard chromium plating) is
Figure 3: Typical on-aircraft brush plating showing frequently done over plating times of 24 hours, with mini-
set-up for masking and runoff control. mal attention.
Brush electroplating is now specified by manufacturers
• A second cable (positive charge) connects to the and OEMs alike. Brush plating is used in several industrial
plating tool (making it the anode). sectors such as:
• The anode (plating tool) is wrapped in an absorbent • Transportation (Aircraft, Marine, Rail, Automotive)
material which holds the plating solution between the • Electrical (Power Generation, Motors)
anode and the cathode and also prevents direct con- • Industrial (Moulds and Dies, Hydraulics,)
tact with the item being plated. • Printing (Cylinders, Bearing Journals, Housings)
• Electrical current travels from the anode (plating tool) • Resources (Mining, Pulp and Paper, Petroleum,
through the plating solution to the work area Refineries)
(cathode). • Food (Pharmaceutical, Mixers)
• Plating occurs where the wrapped plating tool contacts
the work piece. This process can also be used for Brush Anodizing es-
• The plating tool is replenished (with plating solution) pecially in the aerospace industry. In Brush Anodizing, the
by dipping the tool in the plating solution. same mechanics of applying the solution pertain however
• The plating tool is moved continually over the the polarity of plating tool and part are reversed so that the
surface of the part to achieve an even distribution of part is the anode. Brush anodizing is finding increasing
plating material. use in aerospace repair.
• Upon completion the plated part is then rinsed off The two main sectors using Brush Plating and Brush
and sent for further inspection. Anodizing are the aerospace and nuclear industry where it
is used for salvage and repair of parts in situ.

DISADvAnTAGES OF bRuSH PLATInG/AnODIzInG
For conventional Brush Plating/Anodizing applications on
horizontal surfaces (involving the plating tool being dipped
in the solution and transferred to the part and then dipped
in solution to replenish the brush again and then applied
to the part, etc.) there are few issues with the process. It is
really akin to “painting with conventional paint”.
However, for vertical or inclined surfaces, brush plating
can become a little complicated as the plating tool and so-
lution have to work against gravity.
Figure 1 shows the Poseidon P-8 (based on the Boeing
737-800) which is used in maritime patrol and is subject to
corrosion from proximity to the ocean as well as low altitude
flying (60 m above sea level). Brush anodizing is used to re-
pair areas of corrosion on the aircraft as shown in the figure.
Figure 2: Non-drip selective plating system and closed-loop circuit. In situ repairs on inclined or vertical surfaces (and de-

42 CAnADIAn FInISHInG & COATInGS MAnuFACTuRInG nOvEMbER/DECEMbER 2020