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EMAIL TIPS Volume 84 May 2012

White Papers Available

Current Readers of Email Tips will discover that in addition to the monthly installments in the new magazine format, past articles and instructional papers are available. The current library includes articles on Piping Vibration, Acoustics, Resonance and Transient Test Methods.

Printing This Email Tip

1. Select the “Print” Icon 2. Select “Print Publication” 3. Select “Save File” and “OK” Email Tip will Download as a PDF and be Ready for Printing. Easy as 1, 2, 3.

This Month’s Features:

Field Testing Tip – Sometimes “luck” is our best friend. Field testing insights

The Frequency Spectrum – Similar Spectrum signatures: Fluting vs. Barring.

Definitions : The Bearing Cage, Fit Function and Frequency

Product Review: Computer Aided Engineering (CAE) company generates some nice animations of a Rolling Element Bearing.

2012 Training Schedules Core Training Courses:

• Intro (IVA) – VAI – VAII – VAIII

Concentrated Training Courses: • TWF – Spectrum – Phase – Bearings

Specialty Training Courses:

• ODS/Modal – Precision Balancing

Cover:

Sometimes you get lucky. The cover this month shows just that. Rarely does the field analyst get this close to a wind turbine blade without a visit to the manufacturing facility. As it turns out, we hit the tri-fecta (literally). The three blade and hub assembly shown on the cover and below provided nearly perfect boundary conditions for Impulse Natural Frequency testing. The 120 foot blades were a convenient distance off the ground for transducer placement and measurement mapping.

When Opportunity Knocks…….. be ready.

In Situ Field Testing Tip: Recently Full Spectrum Diagnostics performed a modal analysis on a wind turbine blade at a customer site. This testing shed some light on aerodynamic problems occurring at that time that were suspected to be the root of blade cracking issues. This example is used in training courses to explore the ins and outs of field testing. Typical questions include:

Is this a real blade or some sub-scale model?

How can you test a blade this size in the field?

How was the blade mounted?

Did you need a crane?

What did you use to excite the blade?

How was the transducer mounted?

As we review the particulars of this test, ever-present potential of luck and opportunity are discussed. The data was taken on-site as the unit was being assembled. The truth is that I happened to be in the right place at the right time. The assembly on this unit had been halted due to problems with some of the tower bolts. The turbine blades were mounted on the hub and were ready to be hoisted into place. The blade assembly was resting on a wood pallet next to the tower. The boundary conditions could not have been closer to the final assembly, save the horizontal direction of the cantilevered blades. In fact when blades are tested for natural frequency in the manufacturing facilities they are typically mounted one at a time to a “hub” fixture or supported (free-free) by bungy-cords.

I would contend that this in-situ test lent itself better to the real thing than the standard laboratory test. I even had “real” weather conditions, it was snowing! Which brings me to the “luck” factor. The adverse weather conditions restricted me from testing an operating unit on-site that day. Being idle allowed me a window to test the blade.

The excitation method was an Impulse Hammer at a fixed reference location with two roving tri-axial transducer responses (mounted with double-sided tape). The two rows of tri-axial response locations, included approximately 126 FRF measurements, took about an hour to collect. The results were surprisingly good.

Confidentiality agreements restrict me from disclosing the OEM, details of the problem or the final resolution. The teachable moment here focuses around making sure your field test replicates real life operational conditions as close as possible. I would suggest a sub-assembly test of this sort for any vendor to verify the blade integrity (frequency, damping & mode shape) and sub-assembly conditions prior to the final installation. Otherwise, once to hub is installed on the tower at a couple hundred feet in the air the ability to perform a test of this sort is a logistical nightmare.

Figure 1.0

Wind Turbine Blade First Easy-wise Bending Mode

Figure 2.0

Wind Turbine Blade Second Torsional Mode

Figure 3.0 Blade Frequency Response Functions (FRF’s)

Spectrum Analysis Tip:

The last issue of Email Tips included a summary of a “Fluting” or “Electro-Erosion” problem in rolling element bearings subject to improper grounding or stray electrical currents discharging across the raceways. This Spectrum Tip includes a somewhat similar issue (spectral signature) in the paper, steel, and non-woven industries when product calendaring is performed.

The calendaring process includes the removal of moisture, imprinting of a pattern, of somehow changing the properties of the material that is directed between two closely spaced rolls that are in “nip”, or pressure loaded together.

A problem with the nip process is the appearance of “barring” or “corrugation” which leaves marks or defects on one or both rolls, or the sheet being processed. The repetitive pattern can be caused by many problems or variations in the nip load, alignment, run-out, or eccentricity.

The similarity to fluting problems is in the spectrum signature. Fluting creates “regularly” spaced pits in the bearing raceway. The spectrum signature produces a series of high frequency modulated peaks that are spaced at the ball passing rate (inner or outer). The ripple of energy as the rolling elements impact the eroded stripes excites one or more structural natural frequencies that act as a carrier frequency for the fault. The frequency “haystack” includes the “ripple-rate” or the period of the multiple impacts, i.e., the (non-synchronous) bearing fault frequency rate.

Barring creates a similar pattern as one of the nipped rolls bounces on the other at the rotational rate of one of the rolls. In this case the (synchronous) impact energy excites one or more structural natural frequencies that when excited create a “regularly” spaced pattern of “flat spots” on the roll or the sheet. Again, the natural frequency creates the carrier frequency and the regular impacting rate at a multiple of roll speed. The modulation in the high frequency range is spaced at 1x RPM of the roll with the barring pattern.

A similar “haystack” signature is found in the frequency spectrum. In the Fluting case, the spacing is non-synchronous. In the Barring case, the spacing is synchronous. It’s important to think about the underlying source of the vibration. The sideband spacing is a fundamental clue. One may also look to the time waveform for beating or pulsation response.

Figure 4.0 Fluting Spectrum Modulation [BPFO Spacing]

Figure 5.0 Barring Spectrum Modulation [1xRPM spacing]

Figure 6.0 Barring Spectrum Modulation [1xRPM spacing]

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REMAINING: 2012 CORE VIBRATION TRAINING SCHEDULE IMPLEMENTING A SUCCESSFUL PdM PROGRAM JUN 19-20 Cameron, WI 2012-PdM-01 Tuition: $ 945.00 / 2-day Format Proficiency Test: Included INTRODUCTION TO VIBRATION ANALYSIS IN-PLANT COURSES AVAILABLE Tuition: $ 945.00 / 2-day Format Proficiency Test: Included VIBRATION ANALYSIS I SEP 11-14 Chicago, IL 2012-VA1-04 DEC 11-14 Charlotte, NC 2012-VA1-05 DEC 18-21 New Orleans, LA 2012-VA1-06 Tuition: $ 1,295.00 / 3-day Format Certification Exam: $ 200.00 VIBRATION ANLAYSIS II MAY 08-11 Chicago, IL 2012-VA2-03 MAY 22-25 Cumming, GA 2012-VA2-04 JUL 10-13 St. Paul, MN 2012-VA2-05 SEP 25-28 Cedar Rapids, IA 2012-VA2-06 Tuition: $ 1,395.00 / 3-day Format Certification Exam: $ 200.00 VIBRATION ANALYSIS IIIa OCT 23-26 Leesport, PA 2012-VA3-01 Tuition: $ 1,595.00 / 4-day Format Certification Exam: $ 200.00 PRACTICAL VIBREATION ANALYSIS IIIb AUG 21-24 St. Paul, MN 2012-PVA-01 Tuition: $ 1,595.00 / 4-day Format Certification Exam: $ 200.00

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JUN 26-27 Brookfield, WI 2012-CSA-01 JUL 17-18 Davenport, IA 2012-CSA-02 OCT 02-03 St. Paul, MN 2012-CSA-03

Tuition: $ 945.00 / 2-day Format Proficiency Test: Included CONCENTRATED PHASE ANALYSIS SEP 18-19 Davenport, IA 2012-CPA-01 Tuition: $ 945.00 / 2-day Format Hands-on Exercises: Included CONCENTRATED RE BEARING & GEAR ANLAYSIS OCT 16-17 Cedar Rapids, IA 2012-BGA-01 Tuition: $ 945.00 / 2-day Format Proficiency Test: Included VIBRATION ANALYSIS FOR MOTOR SHOPS AUG 28-30 Charlotte, NC 2012-VAM-01 DEC 04-06 St. Paul, MN 2012-VAM-02 Tuition: $ 1,295.00 / 3-day Format Hands-on Exercises: Included PRECISION BALANCING !!! NEW !!! AUG 07-08 Brookfield, WI 2012-BAL-03 NOV 13-14 Wheeling, WV 2012-BAL-04 Tuition: $ 945.00 / 2-day Format Hands-on Exercises: Included

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 sized at 3” x 6”, it easily fits in your pocket for everyday use!

Designed for the Vibration Analyst

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. These groupings by frequency content and direction allow the analyst to “narrow-down” the potential faults and zero-in on current vibration problem. The Wall Chart is the ultimate companion to the Vibration Fault Guide and the Vibration Techniques Guide references. Order now at: Http://www.fullspec.net/store.html Or by Phone @ (763) 577-9959 BULK DISCOUNTS & BUNDLE PACKAGES AVAILABLE!

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 BULK DISCOUNTS & BUNDLE PACKAGES AVAILABLE!

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.

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

ModalGuy@aol.com

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.

LpagL@aol.com