The black dust comes from the metal carriage traveling back and forth on the metal rail of the garage door opener. This creates metal shavings that drop on your door as the door travels.
Properly lubricating the rail and carriage assemblies periodically will allow the parts to glide and not grind.
We recommend lithium grease for most units. Be careful not to overdo it if you are doing it yourself.
If you over-lubricate it will end up dripping on your car, your floor, and your garage door.
If you need your garage door serviced, give us a call at (513) 821-5095.