Size range of a powder, written as an upper and lower screen or micrometer limit and spoken as minus 45 plus 15, meaning particles pass a 45 micrometer screen and the fraction under 15 has been classified out. Each process favors a cut: fine cuts for gas-fuel HVOF and many plasma ceramics, coarser cuts for liquid-fuel HVOF, flame and some abradables. The wrong cut for a gun gives unmelts, spits or low deposition efficiency.
That's the 45/15 cut, it's for the gas gun, the liquid-fuel gun wants the 53/20.
Never top off the hopper with a different powder lot mid-job; a shifted size distribution changes the coating even at identical settings.
Also heard as
- size cut
- size range
- powder size
Related terms
Fines
Powder particles smaller than the specified size range, which cause buildup, spitting and poor flow.
Feedstock
The raw coating material fed into a thermal spray gun, as powder, wire, rod, cord or liquid suspension.
Deposition efficiency
The percentage of the feedstock sprayed that actually ends up as coating on the part.
Unmelts
Lab shorthand for particles that hit the surface without fully melting and kept their round shape.