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Problems of painting on aluminium gravity die cast items

We are into gravity die casting of Aluminium Alloy. We finish our products with the help of Emery papers. In the pin holes/blow holes we apply Arreldite mixed with talcum powder and finish it
We do Black Colour (Stoving Enamel) but we don't get good coating and finishing after colouring is very bad.
We request you to suggest what can be done to overcome this problem.

Thanks and Regards,

Srujal Shah
Business Man - Ahmedabad, Gujarat, India
April 9, 2008

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In initial stage of cooling gases escape from the aluminium casting leaving very small tubes (you see the top as a pinhole) - these are called capillaries. When cold, air enters until it is either replaced by a fluid or pushed out by heat. Sealing the air in, is not the best of methods to use because when the top coat is applied followed by baking, the entrapped air expands and causes the defects you are seeing.
Try this ˜ when the aluminium item is ready for painting (no filler) but a clean ready to paint, heat the item to a temperature of 80-100°C ˜ hold for 30 mins at that temperature. Allow to cool to warm to the touch and apply paint and bake as normal. Method 2 ˜ purchase some etch/wash primer, clean item and heat as before. Apply primer, allow to air dry apply paint and bake.
Please inform us of the results obtained.

Terry Hickling
Birmingham, United Kingdom
April 10, 2008