How do flange bearings work?

I am asking because I want to mount a flange bearing to a heavy surface and then mount a heavy circular disk on top of the bearing. I figured that I would have the flange bearing mounted on the bottom, then a steel pipe leading to a pipe flange and then the top flange is bolted onto the disc. Sorry for my ignorance but I have never inspected one close up before and have no clue how the flange bearing connects to a pipe and allows its to spin freely without scraping whatever the flange bearing is mounted to.