Rotating machine primer

Electrical Apparatus, Nov 2004 by Nailen, Richard L

Rotating machine primer

Rotating Machinery: Practical Solutions to Unbalance and Misalignment. By R.B. McMillan. Fairmont Press, 700 Indian Trail, Lilburn, Ga. 30047; (770) 925-9558. $98 (hardbound). 227 pages.

Author McMillan, a professional engineer with 30 years of industrial maintenance experience, has written a handy primer for those new to the mechanical problems of most concern to anyone dealing with rotating machinery-principally electric motors and their connected loads of fans and pumps.

Beginning with the principles of sinusoidal oscillations, spring mass system behavior, and the simple trigonometry needed to deal with vibrations, McMillan explores resonance, beat frequency, and the types of unbalance (e.g., static versus dynamic) before outlining the methods of field balancing. Although most practical literature deals with the two-plane method, because of the high length-to-diameter ratio of rotors, this author includes a chapter on single-plane balancing, useful in dealing with fans.

The treatment of alignment begins with Chapter 7. Topics include the types of misalignment, alignment of belt drives, and the detailed procedures of both the reverse indicator and the rim-and-face methods. Graphical and calculator methods are covered in detail, using examples. That's a sound approach; although the ease and speed of use have converted many operators to laser alignment tools, everyone can benefit from a thorough understanding of the fundamentals upon which newer technologies are based.

One of the most misunderstood alignment topics is "soft foot." McMillan does explain how to compensate for it, although unfortunately never actually defining it (as a condition in which all of a machine's foot mounting surfaces do not lie in a single plane).

The book concludes with several useful appendices including trig tables, suggested forms for recording alignment and soft foot correction steps, metric conversion factors, some material properties, and a series of sample step-by-step procedures for aligning and balancing complete cooling tower fan drives.-RLN