MIRROR BORING MACHINE
SITUATION: Couplings which transmit torque between turbines and generators over time experience wear in the bolt holes. The repair of couplings must take place during an outage when the turbine and generator are offline. The typical repair process involves assessing the worst case out-of-round bolt hole and then oversizing the bore diameter for all the bolt holes in both coupling halves.
PROBLEM: The current practice was to match machine the couplings while they were on the shafts of the turbine and generator, meaning this repair process was in the critical path of the outage. Therefore any delays in this repair process could cause a delay of the entire project, exposing GE to potential liability and costs.
SOLUTION: The Mirror Bore machine enabled the boring of both the turbine half and the generator half of the coupling independent of the turbine and generator shafts. This change in the process removed the coupling machining from the critical path and reduced the outage time for GE and its customers.
The Mirror Boring Machine is a precision machine tool that attaches to the front face of turbine coupling with an electromagnetic chuck and precisely bores the bolt holes.
To achieve proper centering and leveling of the boring machine, a fixture plate with holes (2.75” or 4.25” diameter) matching the hole pattern of the coupling is machined flat within specifications. These holes allow the boring machine to quickly align itself. A centering pilot ring, either 2.75” or 4.25” diameter is attached to the machine’s electromagnetic chuck. A particular feature of the Model 5380-S1 is a specially designed lifting arm that maintains the balance of the machine throughout its operational cycle.