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Practical Solutions to Machinery and Maintenance Vibration Problems

Chapter 7, Misalignment

Section 2, Most Usual Sources for Misalignment Errors

1. Bases not properly prepared.

2. Machinery soft feet not determined and corrected.

3. Failure to compensate for indicator bar sag of alignment fixture. Sag is not negligible.

4. Failure to check stability repeatability of fixtures by rotating shaft and fixtures 360°.

5. Technicians who do not really accept modern alignment techniques, primarily because they do not fully understand them. Proper and practical training can change this.

6. Failure to follow dial indicator directions (clockwise or counterclockwise) during full rotation of fixtures and shafts. (Sometimes dial starts out in one direction and then reverses.)

7. Misconceptions about how much misalignment is truly acceptable with so called flexible couplings. (The coupling will accept misalignment and still function but the misalignment too often still creates vibration, resulting in machinery wear.)

8. No uniform idea of proper alignment tolerances. (Suggestion: ask several technicians for their idea of alignment tolerances. Note the wide variations and how many do not ask for the operating conditions such as rpm, machine criticality, etc.)

9. Failure to determine and compensate for thermal growth. Most technicians (and engineers) assume that the thermal growth will be as determined by the machinery manufacturer (too often wrong). For 95 percent of all machinery, growth calculations are very easy. Or, if growth calculations are calculated and the machines offset accordingly, no attempt is made to determine the machine's final true operating temperatures.

10. Pipe strain is not removed before or checked after alignment.

11. Proper and accurate alignment tools are not provided by the company. If the technicians provide their own alignment tools, there is too high a chance that they will be inaccurate.

12. Various unknowns. Not all the reasons are presently understood. Don't blame the technician if the company has not provided adequate practical training on the latest alignment methods, including reverse indicator method of alignment, laser method, proper tolerances, proper follow up and "expectancy" from supervisors and so on.

 

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