Cage
Cage turns up in 2 fields: powder coating, valves. Here is what it means to the people in each one.
Cage in powder coating
Shop shorthand for a recess resisting powder because of Faraday cage effect.
Sprayers say a part cages, or is caging, when powder piles on the outside edges and refuses to go into a corner, slot or deep pocket. It names the problem without the physics and usually comes with a request to drop the kV, switch nozzles or grab the tribo gun. The noun cage also names the trouble spot itself.
"Bottom of that U-channel cages every time, give it a shot at 30 kV before the auto guns hit it."
Cage in valves
A slotted or drilled sleeve around a control valve plug that guides it and shapes how flow changes with travel.
As the plug lifts, it uncovers windows or holes in the cage wall, and the shape of those openings sets the flow characteristic. Cage guiding keeps the plug stable against side loads, and multi-hole or stacked-disc cages split the pressure drop into many small jets to cut noise and cavitation damage. Swapping cages is a standard way to change characteristic or capacity.
"Cage on the letdown valve is eroded around the bottom holes, that's why we can't get it to shut off."