I actually do know how long it takes to change the the brushes on an electric motor but who cares? Neither of us knows how long it takes to change the electrodes in a plasma torch but I suspect the process might be, if it takes more time than optimum, have a hot swappable ready to replace the first torch needing replacement, replace the electrodes and hot swap that reconditioned torch into the next torch needing new electrodes... 

Did you forget you posted an article on the cement industry.. sparky?