If you don't want to take the flanges off the roll you can use some
fine sand paper.  I did this for one of my roll that had excessive
rust and if worked just fine, only some parts of the flange are now
extra shiny.  :-)

If you want to take off the flanges you can use some naval jelly to
remove the rust.  But after all that trouble you might as well just
replace the flanges.

Ray Finch
Albuquerque, NM, USA