How to prevent paint chip off at the countersink & what is the cause?

[S3ssion]

I have experienced the paint chipped off at the upper edge of countersink of Alu. enclosure after few times screw & unscrew during installation. The metals were with fine brushing & clear iridite treated before painting process, and the paint was cured at 140 Celsius then fine textured, the final cure at 160 Celsius for 8 min. Great appreciate if any one point out the major factors which cause the paint chip off. Thanks.

Harry

 

[CoryPad]

There is a shear stress acting on the coating due to the screw rotating under pressure against the countersink. The coating may not have sufficient shear strength to resist this shear stress.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[S3ssion]

Thanks, Cory! I will measure how much torque force applied to the screw to reduce the shearing force. Thank you again.

Harry