It is not part of the sink. Use either a blow dryer on hot or a propane torch to loosen the old flange. BE CAREFUL! Most all disposer sink drains are held in by a mounting collar & three screws going up through the disposer unit mounting ring. The sink flange/drain is screwed into the mounting collar from inside the sink,, which is mounted under the sink. I always run @ a half inch round bead of plumbers putty just under the sink flange where the brand name is stamped. Do not use a rubber ring in sink. Remove excess putty after tightening. Good luck. Always run water with unit on for a few seconds after food is down the drain to rinse out any acidic food residue.

I had a problem with that before. I just ask for help with the garbage collector to know what to do with it.