I have found the best way to remove paint without chemicals is a ScotchBrite disc in my 4.5" angle grinder. It cuts right thru the paint and is not agressivbe enough to cut the underlying metal, it only polishes the metal to a near mirror finish. I get my discs at a local industrial supply house for about $3 each.
I am modding an old kart and used this method to selectively remove paint in areas I want to weld something to. Only takes a minute to remove the Imron paint and primer from 6" of structural tube. It also automatically feathers the edges making it easier when prepping for new paint later.