Painting - painting old head registers

Am re-painting the heat registers in my daughter's
old apartment block. These are the big, cast-iron
vertical kind.

The silver paint is peeling off them. Can I just scrape
the flakes off with a steel brush and re-paint?
Do I use a primer? What kind of paint is best?
What kind of brush works best?

many thanks,
Lulubells

The 'silver' paint may be aluminum, so to be safe, wear an appropriate mask to avoid inhaling the dust. Now, if you are down to bare cast iron, ideally it should be primed before using an easy topcoat like a latex. This means added time that some people don't want to invest in rads because they're fiddly to paint. You could paint them directly with a rust paint like Tremclad, spray (put a large sheet of cardboard behind the register and beneath it first) but be careful of the overspray and mist. If you wanted the latex alternative, prime with a rust resistant oil primer first, then paint with latex. There are specialized 'Rad brushes' out there, bent at an angle, flexible metal handles and such, or you can simply brush it on. It's an ugly job but someone has to do it. :D