CED recess coating: Strong fixes for poor e-coat coverage

Summary for ced recess coating Discussion

Need uniform ED coat in CED process is the core issue here: the questioner reports poor e-coat deposition and rust in non-coverage recess areas of a car sill outer panel, while panels with wax holes do not show the defect. He lists bath conditions and asks whether increasing %NVM or inlet voltage will solve the problem, noting that changing inlet voltage causes hash marks. Dinesh Maurya advises first adjusting bath conductivity down into the 1200–1300 range and says the binder-pigment ratio is too high, suggesting it should be closer to 0.13 for a 6th-generation product. Ravish Singh adds practical process-side suggestions: increase the number of anodes if possible and increase the solvent content of the bath. The thread does not give a single confirmed fix, but points toward bath chemistry and anode coverage rather than simply raising voltage.

Hello sirs I humbly feel that it’s really a great time to interact with you wizards. in our CED

⇦ huh? process, we are encountering a major paint problem poor E’coat deposition (dipping process) defect in the sill outer panel of the car body because of “rust” in the non-coverage area of coating. this is not occurring in the sill outer panels we use which are provided with wax holes.

I’m really baffled whether the problem is with the process parameter settings or the mechanical alignment or settings .

the process parameters settings we use in our CED process are :

%NVM = 18.7
pH = 5.94
CONDUCTIVITY = 1827 uS
P/B RATIO = 0.16-0.25
BATH TEMPERATURE = 30.7
APPLIED VOLTAGE = INLET POINT = 0 V
OUTLET VOLTAGE = 100 V
MAIN BUS = 235 V
CURRENT = INLET = 0/350 amps
MAIN = 950 amps

when we change the inlet voltage, paint defect “hash marks” start appearing in the car bodies . we are planning to increase the %NVM or the inlet voltage , WILL IT SOLVE THE PROBLEM !
generously give me your valuable suggestions .

ACRONYMS:

ED = electrodeposition [“e-coating”, “electropainting”]

CED = cathodic electrodeposition

NVM = non-volatile material

P/B ratio = binder-pigment ratio

C Nanda Kumar
graduate engineer – Chennai, India
2005

A. TRY TO ADJUST THE CONDUCTIVITY IN RANGE OF 1200 ~1300. P/B RATIO IS IN MUCH HIGHER RANGE IF You HAVE 6TH GENERATION PRODUCT THEN THIS SHOULD BE IN LOWER RANGE AS NEAR BY .13.

DINESH MAURYA
– jamshedpur, India
April 12, 2009

1. If possible try to increase the number of anodes
2. increase the solvent content of bath.

Ravish Singh
– New Delhi, India
July 10, 2010