Mechanisation of the Grit Blasting Process for Thermal Spray Coating Applications

The bond strength between a thermal spray coating and substrate is critical for many applications and is dependent on good substrate surface preparation and optimised spray parameters. While spray parameters are usually carefully monitored and controlled, most surface preparation is carried out by manual grit blasting, with little or no calibration of blast parameters. Blasting is currently highly dependent on operator skill and often surface finish is only assessed visually, meaning a consistent, reproducible surface profile cannot be guaranteed. Mechanised blasting offers the promise of more tightly controlled surface preparation and presents an opportunity to improve coating adhesion. This paper presents investigations on the effect of blast parameters (including blast pressure, standoff distance, media feed rate, blast angle, traverse speed and media size) on surface profile for a range of metallic substrates using a mechanised, robotic blasting system. Substrates were characterised using contact profilometry and non-contact focus variation microscopy.