Adhesion measurements for electrostatic powder coatings using a vertical drop test rig and LabVIEW software

Abstract

The total forces holding a layer of electrostatically charged powder onto a metal work piece results from the combination effect of an interfacial electrochemical phenomenon, an inter-particle/particle cohesive force and a bulk electrostatic image attractive force. An attempt has been made to obtain the total integrated effect by subjecting the powder coating to a mechanical impulsive force parallel to the metal substrate. This is a destructive measurement which is obtained by dropping the work piece down a vertical chute which incorporates an inductive charge pick up device to measure the charge of the powder coating during free fall. The sample is brought to rest at the bottom of the chute and dislodged powder is collected in a micro balance incorporated inside a Faraday cage. The exact charge/mass ratio of dislodged powder can be obtained and the technique enables the calibration of the inductive probe. All the measurements are taken with the powder layer before fusing. LabVIEW by National Instruments is a user friendly and powerful graphical development environment used for signal acquisition, measurement analysis, and data presentation. It is a package designed to acquire, analyse and present. Data acquired from the unit under test can be fed through DAQ cards, instruments or PXI systems and connected to a PC running LabVIEW for analysis. With multiple built-in functions and libraries that cover functions such as analysing and processing and also data visualization and report generation, LabVIEW is highly useful in this application.