Properties of powder coatings in load carrying construction

The present study describes the mechanical behavior of powder coatings used under very high compressive loads in clamping force joints. Carboxyl functional polyester powder coatings cured with hydroxyl functional β-hydroxyalkylamides with variations in coating thickness and amount and type of filler, have been studied. The coatings were subjected to conventional tests for coatings and polymers and also to specially designed tests developed to study the behavior of powder coatings in clamping force joints. The specially designed tests were used to study the coatings under compressive loads, and the relation between the results from these test methods and from conventional tests is discussed. The results show the importance of coating thickness in order to achieve the desired mechanical properties of a coating when used under high compressive loads. These loads put high demands on the stability of the coating, and the defects must be kept to a minimum. Increased thickness will give rise to more defects in the coating, especially voids and blisters due to the evaporation of water formed during the curing of the polyester powder coating. The surface roughness of the coating is also affected by the coating thickness, but the main influence originates from the type and amount of filler used. A rough surface will give rise to stress concentrations and increased plastic deformations in the coating, impairing the properties of the clamping force joint.