Voids in Ecoat on Castings
How do we fix cracks in the castings?
Q. We electrocoat small gray iron castings for a third party company. Sometimes the castings have small cracks and voids that fill up with liquids and create visual electrocoat paint defects. We have tried increasing the film thickness and degassing the castings before ecoat, but we don't see much improvement. Do you have any suggestions?—J.W.
A. Since there are no pictures of what you refer to as “small cracks and voids,” it is hard to gage the size, occurrence and frequency of the casting defects.
For workable sized crack and voids, you can try filling them with a suitable casting filler or putty. Since you will be electrocoating the casting, it is necessary that a conductive filler or putty be used, or it will not be electrocoated. Also, the putty must be capable of withstanding typical electrocoating cure temperatures of 350-400°F.
Conductive putties typically contain high levels of zinc or aluminum powder particles mixed in with epoxy or acrylic resin materials that can make them cure and harden.
One thing to mention is that unless fully cured, the putty can leach unwanted chemicals into your critical pretreatment or electrocoat tank, interfere with pretreatment or ecoat stages or lose hardening performance.
You should ask your pretreatment and electrocoat suppliers for recommendations on putty or filler products they have experience working with, and are known to be compatible with your process and their materials.
Question: I am responding to the article in the January 2001 issue regarding the comparison between powder coat and electrocoat performance.
The main task of this work was to study the influence of the different parameters on the electrolytic coloring process for aluminum.
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