Problem Overview
A customer approached LUDECA with a machine train alignment consisting of a fan coupled to a fluid drive coupled to a motor. This particular machine train had limited movement/adjustment available (See Figure 1).
Due to the nature and geometry of the machinery,  the fan on the left was stationary, and both the fluid coupling and motor were movable machines. Additionally, the fan could not be rotated. With these limitations and constraints, very careful planning was needed.

Upon arrival at the site, the LUDECA Field Service Engineer and site personnel began to analyze the situation and figure out the most efficient way to align the machine train. Using the advanced functionality of the Rotalign® ULTRA, uncoupled readings were taken across the fan and fluid coupling, and coupled readings were taken across the fluid coupling and motor. The “As Found” results can be seen in Figure 2.
As Found Results
Per the request of the customer, the alignment was to meet “Short-Flex” Tolerance requirements, even though the coupling was in fact a large gear coupling whose flex planes (points of power transmission) were 13 inches apart. Upon performing the horizontal correction of the motor it became bolt-bound, which prevented further movement in the required direction, New readings were taken and the misalignment is shown below in Figure 3.

Due to the Short-Flex tolerance requirement, the motor needed to move further on both the inboard and outboard feet than was possible. To achieve the Short-Flex tolerances would require very tedious corrections, involving additional movement of both the motor and fluid coupling, or in a more extreme case, re-machining of the bolt holes in the motor feet to allow for more movement. The LUDECA Field Service Engineer suggested that Spacer Tolerances be used. With Spacer Tolerances, the large axial distance between flex planes is taken into account in such a way that the angle at each flex plane is examined individually. This can be done by examining these angles directly in mils per inch, or as the projected offsets of the machine centerlines to each flex plane across the distance between them. With the tolerances set to the spacer-type coupling, the results were viewed once again and it was discovered that the alignment was, in fact, within proper tolerances (See Figure 4).  By changing the coupling type from Short-Flex to Spacer, what would have been a tedious and time-consuming task was found to be unnecessary, and was instantly resolved by entering the appropriate coupling type, in this case, spacer coupling.  The spacer-type coupling takes into consideration the distance between flex planes, whereas short flex-type ignores it.

Filed under:
, by Ana Maria Delgado, CRL