I worked on maintenance for a short while in an animal feed mill in Blandford, Dorset, that was flat out 24/7 from the first frost of winter to half past April.
Everything ran until it stopped or broke, then you fixed it with one of the numerous back up spares.
One night I ended welding up the discharge chute on 'pony nuts'which had worn through on a sharp bend, the foreman wouldn't stop the line so I wedged a sheet of 10 gauge - around 2mm - steel across the whole width of the chute and set to. after a couple of tacks the molasses coating the inside started to burn, I stopped and the the foreman said 'Keep going Stef, the next batch thro' will damp it down'.
The whole room filled with smoke but as he said, every couple of minutes a ton or so of pony nuts hurtling past kept the chute cool.
The whole system was known as 'Breakdown Maintenance', as opposed to 'Prophylactic Maintainance'. It's not stupid as it would seem, instead of changing out a motor with a 500 hour scheduled working life, for rebuild, the same motor might well run for 2000 hours and then be total scrap. However the cost per hour run would be comparable.
Cheers
Stef