This paper addresses a vexing problem that has plagued machine reliability decades. Despite the best efforts to precisely align rotating machinery shafts,.dynamic movement (mostly manifested by the thermal growth of the machine casings).has resulted in machines operating at less than optimum alignment conditions. | Dynamic Movement White Paper VibrAlign, Inc. 530G Southlake Blvd Richmond, VA 232326 © 2002 VibrAlign, Inc. Executive Summary This paper addresses a vexing problem that has plagued machine reliability professionals for decades. Despite the best efforts to precisely align rotating machinery shafts, dynamic movement (mostly manifested by the thermal growth of the machine casings) has resulted in machines operating at less than optimum alignment conditions. Take a look at this picture. They look like identical machines on the truck don’t they? Well they are identical machines. They actually have consecutive serial numbers. They were installed at the same time, right next to each other, and perform the same duty (hot air supply to the dryer section of a web process). These fans heat up in operation, so calculations were made to determine the running position (since the fan housing and supports would grow as the units went on-line). What was found is that the two identical fans did not grow identically? There was almost a 20mil difference in their on-line position. Why the drastic difference? The foundations were identical as were all the connections, ducting, etc. What this points to is the need to measure the actual position of machinery. Calculations of anticipated growth are a good starting point, but should not be the sole effort made. This paper will cover some fundamentals of precision alignment, as well as the methodology for calculating thermal growth. Then discuss and demonstrate the importance of field measurements of actual on-line positions. © 2002 VibrAlign, Inc. Some Basics What is shaft alignment? Shaft alignment is the positioning of the rotational centers of 2 or more shafts such that they are co-linear when the machines are under normal operating conditions. Proper shaft alignment is not dictated by the TIR of the coupling hubs or the shafts, but rather by the proper centers of rotation of the shaft .
