Unmelts
Lab shorthand for particles that hit the surface without fully melting and kept their round shape.
Particles that arrived solid or only partly molten, so in a cross section they show as round or angular grains among the flattened splats. They bond poorly to surrounding material, weaken the coating and often sit beside pores. Causes include particles too large for the parameters, low power, wrong carrier gas, short dwell time or a gun running cold, and specs often limit unmelts by count or area.
Top coat has unmelts all through it, the coarse end of that powder never saw the hot core.
Unmelts and oxides in the same mount usually point to injection rather than power: some particles miss the hot core while others overheat.
Also heard as
- unmelted particles
- unmelted
- partially melted particles
Related terms
Carrier gas
The gas stream, usually argon, that carries powder from the feeder through the hose into the spray jet.
Running hot
Booth talk for parameters that are overheating the particles or part; running cold is the opposite.
Porosity
The fraction of a coating's volume made of voids between and within splats, usually reported in percent.
Cut
Shop word for a powder's particle size range, such as minus 45 plus 15 micrometers.