Laser Optics Align Turbine Housing

Ismaning, Germany- Many machines feature bearing housings or other parts with semi-circular reference surfaces. Alignment via traditional taut-wire techniques and precision-ground shafts works for conventional applications. But such methods are labor intensive, and may fall short on jobs that demand extra accuracy.

That's why the Gorlitz facility of Siemens AG recently opted for the CentralignTM laser system when aligning the diaphragms, bearing pockets, glands and sealing rings of steam turbines. Developed by PRUFTECHNIK AG, the centerline measurement system includes a laser emitter, a receiver unit and a dedicated computer. The receiver features two position detectors with built-in inclinometer, and mounts onto a sliding magnetic bracket that contacts the inside surface of the part measured.

During operation, the emitter directs the visible laser to the receiver's position detectors, located one behind the other. This "reference beam" describes the turbine's approximate centerline; half-silvered optics split the beam so that it strikes both position detectors. Each detector comprises a square resistive surface subjected to two voltages, one biased along the X axis, the other along the Y axis.

When the laser strikes the detector surface, it alters the X and Y voltages proportional to beam displacement from the detector's center. "The signal from each position detector," explains Paul Glatt, PRUFTECHNIK training manager, "consists of a pair of voltages corresponding to the X-Y position of the laser beam to the nearest micron."

Measurements are taken in several different angular positions as the bracket moves along the inner surface of the diaphragm. Misalignment causes the laser beam to describe an ellipse in the position detectors. This behavior, in turn, allows calculation of the diaphragm's true centerline.

Readings from the position detectors pass through an A/D converter and are transmitted via infrared signals to a computer that utilizes a proprietary operating system. The computer measures offsets between the individual arc-shaped diaphragm segments, and allows on-screen adjustments of the desired centerline.

Time to complete the job? "Measurements on 23 planes took about three hours," reports Glatt. Traditional methods, he says, would require a full day or more.

Additional details, Europe...Contact PRUFTECHNIK AG, P.O. Box 1263, D-85730 Ismaning, Germany, Tel: +49 89-99616-0.

Additional details, U.S...Contact Ludeca Inc., 1527 NW 89^th Court, Miami, FL 33172, Tel: (305) 591-8935.