US Patent 7135052 Cassette filter

A cartridge filter includes a folded package including filter material and a frame holding the folded package. The frame includes a plurality of profiled strips having identical profiles, and each having two ends. The frame also includes a plurality of corner joints, each disposed at an end of a respective profiled strip. Each corner joint includes an end cap for engaging pair wise with an end cap of an adjacent one of the plurality of corner pieces.