The spray stream is fundamental to understanding thermal spray coatings. Spray processes involve accelerating particulate matter in a cold to molten or semi-molten state toward a substrate to form a coating. Particle trajectory, temperature, and velocity at any moment in time in the gas stream constitute the spray stream or pattern.
To understand what is happening in a hot jet stream, refer to the figure which shows particle trajectories in a plasma jet. While the figure shows particles entering the gas stream radially, they could just as well be introduced along the centerline of the jet or generated by atomization, as in wire flame spray or electric arc spray.
Some particles travel along the jet centerline, others take an intermediate position, and still others ride along the periphery of the jet. Fine particles riding the periphery may, in fact, never enter the main jet, and coarse particles may pass through the jet and take an outside position on the opposite side to their injection point. On impact with the substrate, particles impacting virtually simultaneously make up the spray pattern.
Image – Particle trajectories in a typical plasma spray stream
This information is from ASM Handbooks Online, Vol. 5A: Thermal Spray Technology, Coating Structures, Properties, and Materials. To find this information (subscription required), click on the link below and scroll down to Figure 12.
https://dl.asminternational.org/handbooks/book/12/chapter/134972/Introduction-to-Coating-Design-and-Processing
