ASTM D4145 is offered by Micom as part of its coating testing services. ASTM D4145—Standard test method for coating flexibility of prepainted sheet—describes a procedure which allows to assess the flexibility and adhesion of organic coatings on metal sheets after they have been bent progressively. Following each bending, the panels are examined with a low magnification tool as a means to detect slits on the film. As for the adhesion, it is measured by applying and removing a pressure-sensitive tape over the bend. Thus, this current practice relies on the principles stated in the ASTM D3359 standard. Typically, ASTM D4145 is employed after a weathering process such as: UV testing, salt spray testing or accelerated aging testing.
Coating flexibility of prepainted sheets:
The goal of ASTM D4145 is to assess the ability of a coating system to withstand strains of fabrication through the use of a T-bend test. In other words, this test characterizes the flexibility and adhesion of the coating after it had been subjected to a bending stress and it is through the use of the T-bend rating that it is possible to evaluate those attributes. In fact, by curving a coated metal foil around itself or around a die, it is possible to study the behavior of the coating towards curving stress which can occur during the manufacturing process of the metal sheet. More particularly, this test consists of monitoring, for each bend performed, the presence of cracks and pickoffs of the coating of the specimen through the use of a magnification tool and of a pressure-sensitive tape as a means to determine the T-bent rating. The latter corresponds to the amount of metal necessary to attain no slit, nor removal of the coating on the bent specimen. More precisely, if the specimen is bent around itself, the rating is defined as the minimum number of thicknesses of metal required to observe the previously stated criteria, however if the sample is bent around a die, the rating corresponds to the metal equivalent of the diameter of the die used to witness the enounced criteria. Lastly, this procedure is a means to verify if the coating can endure a manufacturing process that may contain various deformation processes.
The main factors that have to be considered when running this test are: the axis of bending, the temperature of the specimen and the rolling diameter of the metal.
Typical experimental parameters for ASTM D4145:
The number of samples required is one and its size is of 2 by 6 in (50 by 150 mm). The bending process may occur around a die or around the sample itself and precautions have to be made in order to ensure that this operation is executed in a smooth and uniform manner.
Other test methods related to ASTM D4145 please see: ASTM D522