sheet metal
鈑 centers on metal in flat, thin form: sheet metal. The meaning is narrow and concrete, referring to a manufactured metal plate.
鈑 combines 金 (metal) with 反, which likely contributes the sound and may relate to the idea of a flat, spread-out surface. The exact historical development is uncertain.
The metal radical 金 on the left and 反 on the right suggest a metal sheet that can be bent back and forth. Picture a thin, shiny sheet of metal being folded: 鈑 is sheet metal.
For バン, imagine a metal band wrapping around a sheet of metal: band -> バン, and the metal sheet is held in place.