At a mine in Texas, unacceptably high vibration levels and high bearing temperatures were observed on an 1800 RPM Marathon electric motor coupled to a Lufkin gearbox needed to drive the world’s second-longest conveyor system (21 miles). Good shaft alignment is crucial. Obviously, the alignment has to be done uncoupled since the gearbox shaft cannot be rotated manually. Alignment was originally attempted with dial indicators; however,  the shaft and coupling surfaces where the indicators could mount were not in the best condition and this was causing significant repeatability problems with the alignment readings.
Uncoupled Alignment

Fig 1: Rotalign mounted on uncoupled shafts

Their main issue was that the gearbox could not be rotated by hand. We suggested to the customer that he use a ROTALIGN® ULTRA system,  taking advantage of the Pass Mode measurement capability. The customer purchased the ROTALIGN ULTRA and a specially designed ALI 2.230 magnetic sliding bracket. Readings were taken in pass mode as suggested. In this mode, hundreds of readings are taken at many different shaft rotational positions, hence improving the chances of getting repeatable readings. The excellent repeatability obtained can be seen in the ROTALIGN’s Measurement table in Figure 2 below.
Uncoupled Alignment Measurement Table

Fig. 2: ROTALIGN Measurement Table

Another huge advantage of using the ROTALIGN ULTRA in the Pass Mode mode is that thanks to the standard deviation value obtained from the readings a very clear picture emerges of the quality of the data obtained while taking the readings. Any rogue measurements caused by surface imperfections in the gearbox coupling can be eliminated without compromising otherwise good data. The ROTALIGN ULTRA’s Technical Note # 12 – for Non- Rotating Shafts was provided to the customer to better guide the process.

Accurate readings were obtained quickly and efficiently, resulting in many man-hours saved on this critical alignment job. By achieving good alignment the customer was able to solve both the vibration and bearing temperatures issues and was henceforth able to move the desired amount of coal from the mine to the power plant 21 miles away.

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, by Pedro Casanova CRL