Spitting
Spitting turns up in 3 fields: thermal spray, powder coating, boilers. Here is what it means to the people in each one.
Spitting in thermal spray
A gun shedding blobs of molten buildup into the coating, leaving lumps known as spits.
Intermittent release of material that has built up on the nozzle bore, injector tip or HVOF barrel, which breaks loose and lands on the part as large semi-molten nodules called spits. Spits are weak spots and surface lumps that may need grinding out or a strip and respray. Common causes are fines in the powder, worn hardware, injection set too close to the plasma, and running too hot.
"Gun's spitting every couple of minutes, I can hear it pop, stop and clean the injector."
Spitting in powder coating
Powder bursting out of the gun in clumps, leaving lumps and heavy spots on the part.
Spitting usually comes from powder fused onto worn pump throats, hoses or the gun deflector, called impact fusion, which builds up and then breaks loose. Damp powder, too many fines, kinked hoses and low air also cause it. The result is blobs that cure as raised dots or runs. Fixes are cleaning or replacing wear parts, checking air, and cutting fines in the reclaim.
"Gun three is spitting again, pull the venturi insert, I bet it's coated with fused powder."
Spitting in boilers
Describes a steam radiator vent that throws out water and steam instead of just air.
A spitting vent usually means water is reaching it: the radiator is pitched wrong and holding condensate, the boiler pressure is set too high, or the boiler is surging and sending wet steam up the risers because of oil or dirt in the water. A failed vent float can spit as well. Replacing the vent without fixing the cause just gives a new vent that spits.
"Vents are spitting on every floor since the new boiler went in, skim the oil off it and drop the pressuretrol to 1.5."