The L-705 and L-706 Bore Alignment Lasers are perfectly designed to perform alignment of gas (new) and steam turbine bores. The system uses a laser, reference target, measuring target, micrometer sweep device, and fixtures to hold the laser and targets. Since the laser beam is concentric to the OD of the L-705/706 housing to within .0005" (0.013 mm), it can serve as one reference target. This saves a lot of time during setup.

On most turbine alignments, the rotor bearing bores are used as the references. This means that fixtures that hold the laser and reference target must be placed precisely in these bores to the set points determined by the manufacturer of the turbine.






The fixtures (A-502A and A-502L) are hung in the bores using angle iron and special magnetic bases. Depending upon the size of the bore, either the large (A-501) or the small sweep unit (A-501A) is used to position the fixture so that the center is exactly on the reference points provided. The sweep unit is essentially an inside micrometer that allows the fixture to be placed to any points desired (for example, .000" left, .009" right and -.010" bottom).

Once both fixtures are swept in, the laser (L-705 for distances up to 50' (15 M) and the L-706 for distances from 50 to 110' or 15 M to 33 M) is placed in one reference fixture and a target (T-218T) is placed in the opposite reference fixture. The L-705 laser is manufactured so that the laser beam is concentric (centered to) to the housing's OD to within .0005" (0.013 mm). With the fixture "swept in," the laser is inserted into the fixture and is thus centered to the reference points. All that is needed now is to adjust the angle of the laser beam, using the two micrometers on the back of the L-705. These micrometers are adjusted until the reference target reads zero, both vertically and horizontally. The laser is now set up and ready for measurements.

For measuring an individual component, such as a diaphragm, there are two target choices. The first is the T-218T turbine target. The T-218T works much the same as the reference targets. The target fixture (A-502A) is swept into the center of the bore using the A-501(A) sweep unit, then the target is placed in the fixture and the reading is taken. A positive vertical reading means the diaphragm is higher than the reference bores. A positive horizontal reading means the diaphragm is to the right of the reference bores. Since the data is live, the diaphragm can be adjusted until the reading is zero (or to an offset determined by the engineers).

The second measuring target that can be used is the A-511 Wand Bore Target. Instead of using a fixture to "hang" a target in the center of the bore, the A-511 uses fixed-length legs that are approximately equal to the radius of the bore. Two legs are used, each 90 degrees from the other. One leg has a measuring tip on it and the other is used for support.

To take readings, the measuring leg and tip are placed horizontally on the left side of the bore and zeroed out (the right side can be used but it is important that the "zero" side be consistent throughout the measurements). Next, the tip is placed on the bottom of the bore and the vertical measurement is recorded by swinging the target axially (in the same direction of the laser beam) through the arc and noting the highest reading. The target-measuring tip is then placed on the right side of the bore and the horizontal measurement is recorded, again by sweeping the target axially through the arc, noting the highest reading. This "sweeping-through-the-arc" method is very similar to what is done using an inside micrometer and tight wire, and eliminates potential errors if the target is not at top-dead center.

Once all the measurements are recorded, they can then be entered into a spreadsheet to determine the component moves. After the moves have been determined, either the A-511 or the T-218T can be used to align the individual components to their calculated locations. Again, the laser and reference targets do not have to be repeatedly setup and taken down when moving or replacing turbine components.

Both A-511 and T-218T measuring targets are very repeatable (See A-511 Target Repeatability for details). However, in our experience, the A-511 is much faster at taking the measurements. To get the best repeatability, some mechanism should be employed to ensure that each point on the diaphragm or other component is marked and the measuring tip is placed exactly on the same point. Given that the surfaces inside a turbine are usually pitted and rough, a radius tip should be used. For new turbine installations, repeatability of .001" (0.025 mm) or better is easily achievable. However, for older turbines, it becomes increasing more difficult to hold .001" repeatability because of the high level of pitting and corrosion.