Most powders are milled to a median size of around 30 to 45 microns. The finest fraction gets carried off by booth airflow, slips past cyclones and accumulates in reclaim, where it clogs hoppers, packs in hoses and causes spitting and impact fusion. A high fines content also hurts transfer efficiency. Shops control fines by blending reclaim with fresh powder and checking particle size when problems start.
Reclaim's all fines now, the hopper won't fluidize and the guns are spitting every few minutes.
If the hopper stops fluidizing evenly after a long run on reclaim, add fresh powder before touching the gun settings.
Also heard as
- dust
- fine fraction
Related terms
Reclaim
Oversprayed powder collected from the booth and fed back into the system for reuse.
Spitting
Powder bursting out of the gun in clumps, leaving lumps and heavy spots on the part.
Cyclone
A cone-shaped separator that spins booth exhaust so the powder drops out for reclaim and the air goes to filters.
Feed hopper
The fluidized container that holds powder and supplies it to the gun pumps.
Same word, different worlds
Powder particles smaller than the specified size range, which cause buildup, spitting and poor flow.
Refractories & Furnace LiningsSmallest particle fraction of a refractory mix, which fills the gaps between coarse grains and forms the bond.
Paper Optics & TestingFiber fragments and small particles that pass a fine screen and have an outsized effect on sheet optics.
Asphalt PavingThe dust-sized part of the aggregate passing the No. 200 sieve, which stiffens the binder into a mastic.