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Masking E-coat parts that have already been E-coated

An aluminum housing is E-coated black and then assembled onto an engine (large volume assembly line) that gets E-coated yellow. The customer wants the housing to remain black but it is picking up yellow paint during the 2nd E-coat process. It is thought this is due to the difference in paint film thickness between the peaks and valleys on the rough aluminum surface.

Is there a way (chemical spray, film, tape, etc?) to mask the black housing during the 2nd yellow E-coat? Ideally the masking technique would not be affected by the pretreatment process of the 2nd E-coat and not interfere with the coating process itself.

(Improving the aluminum surface finish helps but does not solve the problem, and is not cost effective)

Any ideas?
thanks in advance,

Greg Potts
Construction OEM - East Peoria, Illinois, USA
2006

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Hello Mr Greg P;

Sorry for asking, but I'm sure you have considered assembling the yellow part after the black e-coat was completed? It may be easier to mask the black part.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2006

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