Process for applying high application-temperature coating to heat-sensitive aluminum alloys

Abstract

A process is provided for coating a given surface of a heat sensitive metal article (e.g., thermally massive aluminum) with a high-cure-temperature-coating-forming-powder. A first oven heating step elevates the metal article's temperature to a predetermined preheat cycle high-limit-of-heat-load-temperature. After a first predetermined period of time, the metal alloy article is withdrawn from the oven. A high-cure-temperature-coating-forming-powder is then sprayed onto the given surface of the metal article. The spraying, comprising first and second spray sequences, is initiated essentially immediately after withdrawal of the metal article from the oven. The first spray sequence is a single group of spray passes that applies a coating layer to fill the pores in the given surface with heat melted high-cure-temperature-coating-forming-powder. The second spray sequence builds up the total thickness of coating. A second oven heating step elevates the metal article's temperature to a predetermined cure cycle high-limit-of-heat-load-temperature for a second predetermined period of time.

What is claimed is: 
     
       1. A process of coating a given surface of a heat sensitive metal article with a curable powder coating, comprising the steps: elevating the metal article's temperature in an oven to a selected temperature;   maintaining the metal article at approximately said selected temperature for a first period of time:   withdrawing the metal article from the oven;   spraying said curable powder coating onto said given surface of the metal article, said spraying being initiated essentially immediately after withdrawal of the metal article from the oven, said spraying comprising first and second spray sequences, said first spray sequence applying a coating layer having a thickness chosen to be adequate to fill pores in said given surface with said curable powder coating, said second spray sequence building up a total thickness of said curable powder coating resulting from both the first and second spray sequence to a total coating thickness over said given surface of the metal article;   re-elevating the metal article's temperature in said oven to said selected temperature;   maintaining the metal article at approximately said selected temperature for a second period of time;   said selected temperature, said first period of time, and said second period of time being chosen based upon experimentally determined data which defines a curve plotting temperature versus time of heating for which the metal article retains a percentage of its nonheated tensile and yield strength characteristics after undergoing a plurality of heating/cooling processes involved in at least two individual instant processes of coating:   said selected temperature being chosen as a temperature value on said curve; and   the first and second periods of time being so chosen that the cumulative time consisting of said first and second periods of time does not exceed the time of heating on said curve corresponding to said selected temperature.