During powder coating production, cast aluminum and cast iron parts are prone to surface defects such as pinholes, bubbles, and craters. These defects are not always caused by powder quality or curing parameters. In many cases, they are closely related to substrate outgassing.

Main Causes of Outgassing

Cast aluminum and cast iron typically contain microscopic pores that can retain air, moisture, oil, and other volatile substances during casting, processing, transportation, and storage.

During curing, the workpiece heats up and the trapped gases expand and escape from the pores. If the powder coating has already melted and formed a film, the gases may become trapped beneath the coating, resulting in pinholes, bubbles, and crater-like defects.

Solutions for Cast Part Outgassing

Pre-Baking for Degassing

Pre-baking the cast parts before powder coating allows trapped air, moisture, and volatile substances to escape in advance. After pre-baking, the parts can proceed to coating and curing, helping reduce outgassing-related defects.

Use Anti-Outgassing Primers

For porous castings or applications with high surface-quality requirements, an anti-outgassing primer or suitable primer powder system can help improve the substrate surface and reduce the impact of internal gas release on the coating.

Conclusion

Pinholes, bubbles, and craters on cast parts are often associated with a combination of substrate porosity, pretreatment, heating rate, and curing conditions.

By combining pre-baking, anti-outgassing primers, and proper process control, manufacturers can effectively reduce outgassing defects and improve the appearance and consistency of powder-coated cast aluminum and cast iron parts.https://www.powdercoating.org/ https://www.eupia.org/ https://www.iso.org/home.html https://www.lekamaterial.com/news/