Hydrofluoric Acid

["The Honjos" <fm7m-hnjy@asahi-net.or.jp>]

This is a chemistry question.

I picked up a bottle of chrome wire wheel cleaner and noticed that 
they contained phosphoric acid and hydrofluoric acid.  In fact, I 
realize that most CWW cleaners have it.  Now the phosphoric acid I 
understand -- it's a rust remover, and also provides a skin on top 
after the rust is removed.  What does the hydrofluoric acid do?

Regards
Makoto Honjo
Phone/Fax +81-3-3473-1848