#1 Each scenario calls for a different approach.
perhaps;
Hit them w/ PB Blaster for DAYS prior to attempt to remove.
Use a
PROPERLY SIZED screwdriver tip.
Seat driver tip and smack it w/ a hammer WHILE you are turning counterclockwise
AFTER YOU HAVE CLEANED TEH SLOTS OF PAINT AND RUST ETC,
keeping screwdriver perfectly aligned in slots all the while pushing REALLY HARD
to keep screwdriver in slot. It is hard to do, eye-hand coordination is a must.
Tap while trying to unscrew while pushing HARD
If it moves a smidge hit it w/ PB Blaster and wait more then repeat the above.
Or drill jus the heads off JUST ENOUGH to get the hinges off then
try to grab the shaft of the screw w/ vise grips, but AFTER you
hit it w/ PB Blaster and WAIT.
If they are a lost cause, cut the FLAT and flush.
Get a sharp center punch and dead center tap a point.
Drill thru and attempt to tap.
See note #1
On larger screws sometimes you can weld a bolt to the head and you have a better
head to grab onto and unscrew.
Or cut a slot for a flathead screwdriver.
If it is mission critical there are companies that specialize in broken bolt
removal. They have a zapper gun deal that will blow a hole thru the offending
screw and then they have a lot of different tricks to get the guts out.
You have to use a proper approach for THAT particular scenario.
CLICK HERE and I have used
THIS MAN in the past always w/ success.