Email Tips Volume 85 June 2012

85

EM MAIIL TIP T PS A Learn ning Publicaation from Full Spectrrum Diagno ostics

Vo ol. 85 June 2012

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EM MA AIL TIP T PS Volume 85 June 20 012 4

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2012 2 Trainin ng Sche edules

Currentt Readers off Email Tips will discover that in addition n to the mon nthly installm ments in the new n magaziine format, past p articles and instructtional papers are availablle. The currrent library in ncludes articles on Piping Vibration, V Ac coustics, Ressonance ansient Test Methods. and Tra

CORE E TRAINING SERIES: • Intro (IV VA) – VAI – VAII – VAIIII CONC CENTRATED D TRAINING G TRACK: • TWF – Spectrum – Phase – Be earings SPECIALTY & AD DVANCED TRAINING T • ODS/M Modal – Preccision Balanccing • On-site e Mentoring

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s Featurres: This Month’s Oil Whirl Instabilitty in the Tim me Waveform m g – Using a Flat Top Wiindow for Signal Processing Displaccement meassurements Definitions : The Oil Film Bas sics ct Review: Machinery M Trainers T for Vibration, V Produc Alignme ent, and Dia agnostics.

The journal bearin ng shown on the cover iss a pressu ure dam type e design. Th he “fixed” ge eometry journal bearing is designed d to produce sig gnificant pressu ure spike on the journal which w induces greater operattional stabilitty in the bea aring. A tape ered pockett is milled intto the upperr (unloaded) half of the bearing. The tape er cut-out ends in an abrrupt ledge or “dam m” that produces the pre essure change from fluid in nertial effectss. The dam design limits the rotor operattion to a sing gle rotational direction.

Time Waveform Tip: The time signature for a journal bearing Oil Whirl Instability problem includes a combination of a synchronous waveform (1x RPM) and a subsynchronous waveform.

The sub-synchronous waveform is created from a non-synchronous response in the speed range of 0.38-0.49x RPM. The unique feature of this waveform, as with any synchronous / non-synchronous combination of frequencies, is a changing waveform pattern each shaft revolution. In this case, the lower amplitude rotor speed (1x RPM) component appears to “ride” on the higher amplitude whirl frequency component.

Three samples of this type journal bearing instability are found in the figure to the right. The shorter period is created by the rotor turning speed. The longer period that occurs (nearly) every other cycle in the waveform is the whirl instability. The instability in this case was 0.47x fraction of rotor speed.

An interesting twist on the time waveform is found when the x and y directional components are combined in an Orbit diagram.

The subsynchronous component can create an internal loop that “rides” the larger synchronous component. The best viewing is a “live” orbit over multiple shaft revolutions.

Figure 1.0 TWF Samples of Oil Whirl Instability

FLAT TOP WINDOW FUNCTION

Signal Processing Tip: Journal type bearings are most commonly monitored with shaft “Proximity” or “Eddy Current” probes.

These transducers are designed to measure displacement vibratory response via fluctuations in a magnetic field produced in a coil at the tip of the probe.

For journal bearing applications the amplitudes of interest are on the order of the internal radial clearances between the rotor and stator.

Depending on the bearing design (size, speed, etc.), this can be in a range of 0.25 – 5 mils peakpeak (0.00025 – 0.005 in.).

The small values of interest require signal processing designed for amplitude accuracy. The window function typically used for displacement probe analysis is the Flat Top window. This window sacrifices frequency accuracy for amplitude detection with a pass band shape that varies less than 1% in a given line of resolution.

HANNING WINDOW FUNCTION

Figure 2.0 Flat Top vs. Hanning Window Functions

When compared to the Hanning (Hann) window (offering better frequency response) having a pass band shape that can induce an amplitude variation of up to 16%, the importance of selecting the proper windowing function is realized.

Definitions: Fluid Film Mathematics Journal bearings are designed to operate at a specific internal clearance (eccentricity) between the spinning rotor and the static stator. Oil is entrained by the journal creating a thin wedgeshaped film between the journal & the bearing surface. Hydrodynamic pressure is created in the film, which effectively “floats” the journal & carries any loads applied to it. The internal clearances for creating a successful film also create an operational boundary or “threshold of instability”.

When speeds, loads, film properties, or babbitt wear conditions create a change in internal clearances, this “threshold” may be exceeded.

In this condition the rotor may Oil start to orbit or “whirl” about the about the static eccentricity point.

The vibration analyst will see this instability as an excessive subsynchronous peak in a 0.38x - 0.49x RPM range in the frequency spectrum.

The unstable whirl motion can be rapid in its onset and when the whirl amplitude exceeds the internal clearances of the bearing, rotor/stator contact can result where a “wipe” or smear of the Babbitt material occurs.

The diagram to the right shows the orientation and reaction loads of a journal bearing during operation.

Note the radius of the bearing “R”, and the radius of the rotor “r”. The distance between the center of the bearing and the center of the shaft is the bearing eccentricity. When loaded properly “W”, the rotor will spin (without whirl) on the thin film “Ho”.

When the wear or film properties change, in addition to the spin, a dynamic whirl component can develop.

The whirl is limited to the internal clearances of the bearing (eccentricity, film thickness) prior to rotor contact with the stator (wipe). When a journal bearing wipes, the unstable operation is unpredictable and often catastrophic.

Figure 3.0 Journal Bearing Load diagram

Product / Literature Reviews: BARRY CONTROLS: Vibration Isolation Primer If the reader is interested in a solid summary of Vibration Isolation terms, theory, and applicable examples; the link below will be an excellent starting point. I’ve consulted this article numerous times in the last 20 years as a refresher and guide to numerous isolation applications. The 16 page article packs-in significant theory and applicable equations, but is written with the novice in mind.

The examples will allow the reader to choose the appropriate isolation system himself, or simply provide enough information to ask intelligent questions when seeking the advice of professionals (always a good idea). http://www.barrycontrols.com/UserFiles/File/Engineeri ng/iso_select.pdf Full Spectrum Diagnostics has no financial connection with any of the books, papers, reference materials, or application notes reviewed in this newsletter. All of the reviews of these materials are first-hand opinions of Full Spectrum Diagnostics’ analysts and instructors.

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THE VIBRATION FAULT GUIDE The Vibration Fault Guide is a 110-page indispensable asset for every vibration analyst, as well as a helpful tool to bridge the gap between the analyst and his management staff.

Some 45 Rotating Machinery Faults are Identified and defined. Conveniently designed at 3” x 6”, it easily fits in your pocket for everyday use!

GUÍA DE FALLAS DE VIBRACIÓN Este manual consta de 110 páginas y fue compilado por Full Spectrum Diagnostics como referencia rápida para la industria de Mantenimiento Predictivo y Monitoreo de Condición. La guía incluye ejemplos de espectros, formas de onda, definiciones de fallos y reglasde análisis de fase para aproximadamente unos 45 problemas que se pueden presentar en maquinaria rotativa.

También incluimos varios estándares de especificaciones de vibración, guías para definición de bandas de alarmas, fórmulas y definiciones de Procesamiento de Señales. Es suficientemente pequeño como para llevarlo en la bolsa de su camisa ( 3.5” X 6.0”), pero su contenido es tan grande que podría ser considerado como una guía de referencia esencial para la industria del Monitoreo de Condición.

THE VIBRATION TECHNIQUES GUIDE The Vibration Analysis Techniques Guide is a 108-page pocket sized information treasure trove.

Information on dozens of analysis techniques, specifications and data presentation formats are included.

If you liked the Vibration Fault Guide, your next educational step should be the Vibration Analysis Techniques Guide get yours now at:

Order now at: http://www.fullspec.net/store.html Or by Phone @ (763) 577-9959

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THE VIBRATION ANALYSIS WALL CHART The Vibration Analysis Wall Chart is a 46” x 36” Full-Color Laminated Reference for your drab office wall. The overall Alarm charts in the center of the chart are surrounded by groupings of over 40 dominant rotating machinery faults. The fault groupings include frequency content and dominant directional response that effectively allow the analyst to “narrow-down” the potential sources and zero-in on current vibration problem.

When combined with the Vibration Fault Guide, the Vibration Analysis Wall Chart completes the diagnostic analysis loop. Weather you require one chart or a need to wall-paper your office, we can help!

Order now at: Http://www.fullspec.net/store.html Or by Phone @ (763) 577-9959

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THE VIBRATION ANALYSIS PERIODIC TABLE This Full Color Laminated 8 ½ x 11 inch card-stock table provides a “quick-look” method of distinguishing one machinery fault from another and suggests Diagnostic Tests or formula that may be used to build a case and make the call!

This Chart is a “Logical” analysis tool that classifies vibration problems

by Frequency Content and Directional Response. The potential vibration sources are instantly reduced based on the analyst’s current measurement data. The Table “forces” the user to think logically and classify faults accordingly.

Individual Faults are Foot Note Referenced to the Vibration Fault Guide for a more detailed review. If you think the Vibration Fault Guide is valuable, your next educational step should be the Vibration Analysis Periodic Table!

Get yours now at: www.fullspec.net, or by phone at 763-577-9959

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INSTRUCTORS:

Full Spectrum Diagnostics’ Lead Instructor & Seminar Author is Dan Ambre. Dan is a graduate of The University of Iowa with a Bachelor’s degree in Mechanical Engineering, and has completed additional graduate level course work in Engineering Dynamics from The University of Illinois at Chicago, and Florida Atlantic University.

Dan is a Certified Vibration Analysis Level III Instructor with over 16 years of Vibration Training and Certification Experience.

Dan’s 25+ years of vibration experience in the Aviation & Aerospace Industries comes from positions at Sundstrand Aviation Corporation and Pratt & Whitney (United Technologies Corporation).

This fieldwork includes Vibration & Acoustic testing, Rotor Dynamics analysis of high speed Rotor Systems, Experimental Modal, and Finite Element Analysis.

His consulting experience base comes from positions at Technical Associates and Full Spectrum Diagnostics, which he founded in June of 2000. He is a Registered Professional Engineer in the States of North Carolina and Minnesota.

Since 2002, after years of close association, Louis G. Pagliaro joined Full Spectrum Diagnostics. Lou fulfills multiple roles as our Seminar Sales Coordinator, Senior Instructor and course content co-author.

Lou is a certified Level III Vibration Analyst (since 1996) and was recently re-certified by American Society of Nondestructive Testing as an ASNT PdM Level III in Vibration Analysis.

He has over 30 years of varied industrial experience, including Maintenance Management, Vibration Analysis, Vibration Training, Certification, and course development in areas of Noise Control, Precision Maintenance, Precision Alignment, Preventive Maintenance, and Maintenance Skills Enhancement.

His worldwide teaching credentials include instruction of TAC, Update International, CSI, Entek and SKF customers in eight countries. Louis is a graduate of Niagara College in Welland, Canada.

Lou can be contacted by phone at (704) 577-3953, or via Email at Lpagl@aol.com.

Dan can be contacted by phone at (612) 875-9959, or via Email at ModalGuy@aol.com

ModalGuy@aol.com

LpagL@aol.com