Influence of Interfering Parameters in Electrospark Testing of Paint Coatings

Abstract

An analysis is made of interfering factors, such as base surface roughness and partial discharges, which can affect the process of continuity testing by the electrospark method, reducing the breakdown voltage of the interelectrode gap and leading to false alarms. To consider the influence of the coating base surface roughness, the distribution of the electric field in the system of two electrodes with a given roughness was constructed in the Ansys Electronics Desktop program. An experiment was carried out to determine the breakdown voltage of the air gap for different values of the surface roughness of one of the electrodes. A film 0.05 mm thick with a hole simulating a defect was placed on the roughness sample. An electrode was placed on the surface of the film in the region of the hole, to which a control voltage was applied. The voltage was increased to the value of the breakdown voltage and fixed. The experiment showed that the breakdown voltage of the interelectrode gap, simulating a through coating defect, practically does not change with a change in roughness. The process of electrospark testing can be affected by the waviness of the coating and the inhomogeneity of its thickness, which lead to the formation of air gaps between the electrode and the coating surface. It is shown that in this case the electric field intensity in the air gap will be higher than the field intensity in the dielectric coating, which, in turn, creates conditions for the formation of partial discharges in the interelectrode gap. Partial discharge creates a current pulse proportional to the capacitance of the air gap, which can be mistaken for the spark discharge current of the entire gap, and therefore as a defect, while the presence of a partial discharge does not mean the presence of a defect. Thus, it can be argued that partial discharges are an interfering parameter, the influence of which must be taken into account. Measures are proposed to reduce the influence of partial discharges on the continuity control process. To eliminate the possibility of false alarms from partial discharges, it is necessary to measure the parameters of the voltage pulse caused by the full discharge current and take them into account when making a decision about the presence of a defect.