plate
鉼 centers on a flat, thin piece of metal: a plate. The meaning is specific to a metal sheet or platter.
鉼 combines 金 (metal) with 并, which likely contributes the sound and may relate to the idea of joining or flatness, but the exact historical development is uncertain.
The left side is metal 金, and the right side 并 looks like a flat, joined surface. Imagine a metal plate made by joining two sheets together.
For ヘイ, picture a heavy metal plate: heavy -> ヘイ, and the plate is so heavy you need help to lift it.