APPLICATION OF POWDER COATING TO INNER FACE OF CAST IRON TUBE

摘要

PROBLEM TO BE SOLVED: To provide a process for applying powder coating that has an excellent inhibition of the consumption of chlorine remaining in the service water, as the occurrence of pin holes is inhibited on the inner surface of the cast iron tubes and the basic performance such as corrosion resistance and water resistance are satisfied for a long period of time. SOLUTION: A cast iron tube is preheated up to 150-300 deg.C, coated with an epoxy powder coating containing a nitrogen-containing curing agent on its inner surface, then coated with a powder coating free from the nitrogen- connecting curing agent. The above-started nitrogen curing agent-containing epoxide coating is preferably an imidazoline and/or hydrazide curing agent- containing epoxy coating, while the nitrogen curing agent-free powder coating is preferably an acid anhydride curing agent-containing epoxy powdered coating or a polycarboxylic acid curing agent-containing acrylic powder coating, an acrylic-epoxy hybrid powder coating. These powder coatings all contain silica with an average particle size of 1-50μm and their gel time is adjusted to 10-200 seconds at 180 deg.C (according to the stringing method).