During the course of a major alternator rotor re-wind programme situated at a large nuclear power station in the Ukraine, In-Situ Machining Solutions (UK) Ltd have been involved in the orbital or planetary on-site machining project involving the repair of a damaged coupling locating taper at the drive end of a 1000 megawatt x 14 metre long x 65,000 kg alternator/generator rotor.
The taper turning work had to carried out on site and in place due to the sheer size of the component and it’s geographical location. Transporting the component off site to a machine shop was not an option, machining the taper on-site, was the only solution open to the power station management.
In-situ machining Solutions (UK) Ltd is known around the world for it’s expertise in the field of orbital or planetary machining of stationary journals. For this particular project a special taper turning machine was designed, produced in-house to suit the dimensions of the alternator shaft drive end taper, Ø816mm at the small end of the taper and Ø820mm at the large end over a distance of 760mm. 0.5mm was machined from the existing damaged taper to accommodate the new pre-machined bore of the huge 1800mm diameter coupling.
Such was the accuracy requirement of the taper it’s fit with the mating coupling bore, special gauges had to be produced for checking the dimensions at 25mm intervals along the full 760mm length of the taper. On completion of the machining work the taper was measured by our customer’s inspection department and sizes taken, these were within the +/- 0.02mm of theoretical design dimensions in terms of physical size and roundness.
Large ball end outside micrometers were used to measure the taper, flatness was checked using straight edge and engineer’s blue compound, all calibrated prior to the start of the job.
Accurate setting of this particular orbital turning machining was carried out by a laser alignment technique using an adjacent inboard diameter of the alternator shaft and a fixture plate on the outboard end of the shaft to attain the very high concentricity requirements (0.03mm) to the bearing journal diameter of the alternator rotor shaft.
Surface finish was achieved by means of an initial single point turning operation and a subsequent superfinishing/polishing technique to gain the desired 0.6 µm surface finish required in readiness for the induction heated fitting of the new coupling. This extremely accurate on-site machining work was completed within the allotted programme and to the complete satisfaction of our customer who credited the efforts of the In-Situ Machining engineering team in attaining their company’s exacting requirements.
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