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Precision machining a 7.4 tonne rotor for a gas turbine power plant

Precision machined 7.4 tonne rotor

Large and perfectly formed

Bearing surfaces on a massive 7.4 tonne rotor have been precision machined by BEP Surface Technologies – - in preparation for final turning operations by Boro Foundry who manufactured the shaft for energy conversion technology specialists Converteam.

Designed for use in a gas turbine power plant, the rotor is 5.6m long and has an outside diameter of 475mm. To facilitate the installation of vibration monitoring equipment BEP ground all the bearing diameters and thrust faces to 0.005mm TIR and ground the outside diameter to a surface finish < 16CLA.

Boro Foundry, a specialist manufacturer and supplier of a wide range of castings and machined parts, produced the rotor from a pre-machined forging supplied by Converteam. Machining operations included turning, milling, thread milling, milling keyways, drilling and boring to produce the finished shaft ready for the fixing of the ‘pole shoes’ and windings which were also subsequently machined. Turning operations were carried out on an 8m long Tuscan LL950 CNC lathe, the only one of its kind in the UK. Following grinding work by BEP, vibrator probe tracks with a surface finish > 0.063 RA, 0.025mm deep x 30mm wide were diamond burnished into the shaft at Boro Foundry’s Stourbridge, West Midlands factory.

Accuracy to these tolerances is essential to balance the shaft and to ensure it fits into a bearing that houses two vibration transducers. The probes read the highly polished surface of the shaft and take a reference that checks any movement which might affect electrical and mechanical characteristics and hence performance efficiency. Proximity probe transducers are widely used to measure shaft vibration, radial and axial shaft positions as well as differential expansion between case and rotor where they can detect shaft misalignment, rotor imbalance and abnormal bearing wear.

Handling items of this size and weight require especially robust lifting systems, suitably large turning and grinding equipment as well as engineers with expertise in working with large components. Machining to tight tolerances on this scale presents unique challenges. For example, even though the rotor is supported during machining it could not be left on the plant overnight as it would sag and this would alter the machine set up.

BEP has expertise in turning and grinding all kinds of large diameter, heavy rolls, cylinders and shafts to very fine tolerances. Its grinding machinery can handle steel mill rolls and large chill rolls up to 10 tonnes in weight. Diamond turning and polishing can be carried out on diameters up to 1100mm. In addition to the usual finishes on steel and cast and chilled irons, the company can grind copper, chrome, nickel and even rubber. Diamond grinding of plasma sprayed coatings such as tungsten carbide and ceramics can also be undertaken.

The completed rotor was shipped to a Converteam customer in the USA.


Caption to image ref: rotor shaft
Bearing surfaces on this 5.6 m long 7.4 tonne rotor for a gas turbine power plant have been precision machined by BEP Surface Technologies


Andrew McClusky
Sales & Marketing Director
BEP Surface Technologies Limited
Eton Hill Road
M26 2XT
Telephone +44(0)161-724 9090
Fax +44(0)161-725 9539