March 15, 2012
Measuring Thermal Growth Targets using the XA Pro w/OL2R
By Brad Case
Previous blogs have defined thermal growth of rotating equipment and discussed several different methods to calculate the cold (ambient) alignment targets to compensate for thermal growth. The OL2R program (Off Line to Running) of the Fixturlaser XA Pro allows the aligner to easily measure thermal growth (dynamic movement) and determine the correct cold alignment targets for a machine set. The OL2R program is used in conjunction with the OL2R brackets. The benefit of using the OL2R method to measure thermal growth is that the growth or dynamic movement of the machines due to both the temperature change and the process influences are measured and displayed for both the vertical and horizontal planes. The hot (on line) measurements are taken while the machines are operating.
How is the thermal growth measured while the machine is running? The answer is in the brackets that are mounted to the machine frames which set up a virtual rotational centerline for each machine. As the machine frames change position due to the dynamic movement so does the virtual rotational centerlines.
The OJT portion of a recent training class involved mounting the OL2R brackets to an electric motor and hot process pump at a petrochemical facility then gathering the OL2R measurements of the ambient (cold) position and the online (hot & running) position.
Each machine was drilled and tapped to accept the tooling ball mounts of the OL2R brackets, then the brackets installed and “roughed in” to each other using the aiming lasers on the brackets. Note the coupling guard remains in place.
The electric motor and pump were placed in operation and allowed to reach operating temperature. It is not necessary to leave the XA Pro sensors installed on the OL2R brackets while the machines reach operating temperature. The sensors can be removed and the XA Pro used for other alignments during this time. However, the OL2R brackets must remain in place until the running (hot) measurements are taken.
Once both machines reach operating temperature, the sensors were replaced and the OL2R program selected. The cold measurements were retrieved (from the XA display unit) then the hot measurements were taken and saved.
The hot measurements show the growth or change in position of the machines from the initial cold position. With all the information collected, one button press calculates the new target values. The targets are saved to the XA to be used for future alignments.
In this case, the majority of the thermal growth occurs at the bowl end of the centrifugal overhung pump. This in turn drives the pump shaft downward at the coupling end. Looking at the vertical coupling target values, this uneven growth causes the pump shaft at the coupling to drop below the electric motor shaft so the target values for future “cold” alignments are to set this electric motor (movable machine) low and at an angle of -4.2mil/1” angularity, and -53.0 mil offset at the coupling. There is also a small amount of compensation for dynamic movement in the horizontal plane. Pretty cool, huh?
There might be some terms you’re not familiar with in this post–look them up in our new Glossary of Shaft Alignment Terms.