blade footings instead of milling them, as grinding these components involves a fraction of the tooling costs. The size of the ring surface at the outlet from the last stage has a crucial influence on the efficiency of the whole installation. Therefore the longer the last stage blade, the more efficiently the plant runs.
Rotor blades spin at around 3,000 to 3,600rpm and have to withstand high centrifugal forces. For example, the force exerted on a blade in the last stage of a turbine measuring 1.4m long and weighing about 50kg is equivalent to a weight of more than 500 tons. The blade footings must absorb these forces and transmit them to the rotor. To transmit the forces as uniformly as possible over all the material of the blade footing, the footing has tight tolerances for dimensional accuracy.
Developed for such particular applications, the MGC-L-260.75.90 grinding centre from Mägerle achieves high metal removal rates with great accuracy thanks to an extremely rigid structure. The water cooled 75kW motor provides the required drive and combined with the high autonomy of the grinding centre, ensures that machining times are kept to a minimum. The machine is based on Mägerle's travelling column principle, with frictionless, hydrostatic wraparound guide ways in X and Y.
This all ensures a very smooth running, stable machine with vibration damping and high table loading capacity. The console is mounted onto the machine bed and takes the clamping equipment for the blades that are to be machined. An additional rotary B-axis can be mounted onto the console if desired. This axis, used with the automatically changeable measuring probes, enables the blade set-up to be automated with a considerable reduction in set-up time.
The coolant nozzle built onto the grinding spindle can be programmed to move into any desired radial position so that the coolant is ready for use in the right place every time. In addition, the machine has an automatic balancing system integrated into the flange.
A rapid four compartment magazine for grinding wheels and measuring probes ensures short machining times and permits unsupervised operation. The ability to change wheels quickly and easily also provides the versatility needed for machining different profile geometries. This is a distinct advantage, for example where internal and external profiles do not match each other.
Mägerle is exhibiting at MACH under the stand of parent company Körber Schleifring.
Körber Schleifring
www.schleifring.net
Hall 5 Stand 5485
