Reducing The Vibration Level Of The Blast Fan

Reducing the Vibration Level of the Reducing the Vibration Level of the Blast Fan of the Air-cooled Engine Blast Fan of the Air-cooled Engine

of a Volkswagen Beetleof a Volkswagen Beetle

Harland Emmanuel C. Machacon, M.Eng.Harland Emmanuel C. Machacon, M.Eng.Department of Mechanical-Industrial EngineeringDepartment of Mechanical-Industrial Engineering

College of Engineering, University of San CarlosCollege of Engineering, University of San Carlos

Vibration is practically the most Vibration is practically the most important indicator of the mechanical important indicator of the mechanical integrity of rotating machinery. Like the integrity of rotating machinery. Like the human heartbeat, vibration within rotating human heartbeat, vibration within rotating machinery tells a great deal about the health machinery tells a great deal about the health of that machinery. of that machinery.

This study focuses on a case of severe This study focuses on a case of severe mechanical vibration coming from the blast mechanical vibration coming from the blast fan assembly of the 1975 Model Volkswagen fan assembly of the 1975 Model Volkswagen Beetle owned by the author, identifying the Beetle owned by the author, identifying the root cause of such vibration and the root cause of such vibration and the corrective actions taken. corrective actions taken.

The Volkswagen BeetleThe Volkswagen Beetle

The Volkswagen Beetle was designed to be as simple as The Volkswagen Beetle was designed to be as simple as possible, thus making it reliable. Its air-cooled 1500cc 40 hp (25kW) possible, thus making it reliable. Its air-cooled 1500cc 40 hp (25kW) engine proved especially effective in actions of the German “engine proved especially effective in actions of the German “Afrika Afrika KorpsKorps” in Africa’s desert heat. This is due to the built in oil cooler.” in Africa’s desert heat. This is due to the built in oil cooler.

Possible Sources of Vibration in Possible Sources of Vibration in Volkswagen Beetle EnginesVolkswagen Beetle Engines

excitations that are inherent in the slider-excitations that are inherent in the slider-crank mechanism of the engine itself, crank mechanism of the engine itself,

vibrations coming from the mating phenolic vibrations coming from the mating phenolic gears that drive the valves, gears that drive the valves,

vibrations coming from the valve clearances vibrations coming from the valve clearances that may have been improperly set, that may have been improperly set,

vibrations caused by loosely mounted air vibrations caused by loosely mounted air cleaner assembly, and cleaner assembly, and

vibrations from the blast fan assembly. In vibrations from the blast fan assembly. In this study, the excessive vibration was this study, the excessive vibration was noticed at the blast fan even without taking noticed at the blast fan even without taking the readings.the readings.

The Rear-Mounted Engine of the The Rear-Mounted Engine of the Volkswagen BeetleVolkswagen Beetle

BLAST FAN SHROUD

ALTERNATOR

DRIVEN PULLEY

9.5x1175 V-BELT

DRIVE PULLEY

Schematic Diagram Showing the Schematic Diagram Showing the Alternator and the Blast FanAlternator and the Blast Fan

PULLEY

BLAST FAN

6202-2ZBALL BEARINGS

BEARING HOUSING

ALTERNATOR WINDINGS

BEARING HOUSING

Vibration Readings Against IEEE Vibration Readings Against IEEE Standard 1068 Paragraph 4.1.5.3Standard 1068 Paragraph 4.1.5.3

Vibration velocity readings are supposed to Vibration velocity readings are supposed to be taken on six directions on the alternator, three be taken on six directions on the alternator, three on the pulley side bearing location (vertical, on the pulley side bearing location (vertical, horizontal and axial directions) and similarly three horizontal and axial directions) and similarly three on the fan side bearing location using the on the fan side bearing location using the BALMAC 205 Digital Vibration Meter. However, BALMAC 205 Digital Vibration Meter. However, due to space limitations, only the vertical and due to space limitations, only the vertical and horizontal directions on each side are accessible. horizontal directions on each side are accessible.

Readings were taken at different engine Readings were taken at different engine speeds, the usual idle speed (1200rpm), speeds, the usual idle speed (1200rpm), 2000rpm, and 3000rpm. This was done by 2000rpm, and 3000rpm. This was done by manipulating the accelerator adjustment screw manipulating the accelerator adjustment screw until the desired engine speed is attained as until the desired engine speed is attained as displayed in the tachometer.displayed in the tachometer.

Average Vibration Velocity ReadingsAverage Vibration Velocity Readings((zero-to-peakzero-to-peak) of the Alternator at Engine speed ) of the Alternator at Engine speed

of 1200rpm (idling)of 1200rpm (idling)

LOCATIONLOCATION VERTVERT VERTVERT HORHOR HORHOR AXIALAXIAL AXIALAXIAL

SIDESIDE in/secin/sec mm/secmm/sec in/secin/sec mm/secmm/sec in/secin/sec mm/secmm/sec

PULLEYPULLEY 0.350.35 8.8908.890 0.410.41 10.41410.414 - - - - -- - - - - - - - - -- - - - -

FANFAN 0.440.44 11.17611.176 0.520.52 13.20813.208 - - - - -- - - - - - - - - -- - - - -


of 2000rpm of 2000rpm



PULLEYPULLEY 0.360.36 9.1449.144 0.400.40 10.16010.160 - - - - -- - - - - - - - - -- - - - -

FANFAN 0.420.42 10.66810.668 0.550.55 13.97013.970 - - - - -- - - - - - - - - -- - - - -


of 3000rpmof 3000rpm



PULLEYPULLEY 0.350.35 8.8908.890 0.420.42 10.66810.668 - - - - -- - - - - - - - - -- - - - -

FANFAN 0.450.45 11.43011.430 0.500.50 12.70012.700 - - - - -- - - - - - - - - -- - - - -

IEEE Standard 1068 Machinery Vibration IEEE Standard 1068 Machinery Vibration

Chart for Rotating EquipmentChart for Rotating Equipment

MACHINE SPEED MACHINE SPEED MAXIMUM DISPLACEMENTMAXIMUM DISPLACEMENT MAXIMUM VELOCITYMAXIMUM VELOCITY

(rpm)(rpm) (Peak-to-peak)(Peak-to-peak) (Zero-to-peak)(Zero-to-peak)

3000 and above3000 and above 0.001 inch0.001 inch 0.100 inch0.100 inch

1500-29991500-2999 0.100 inch0.100 inch

Small and Medium MachinesSmall and Medium Machines 0.0015 inch0.0015 inch

Large MachinesLarge Machines 0.002 inch0.002 inch

1000-14991000-1499 0.150 inch0.150 inch



999999 0.150 inch0.150 inch



IEEE Standards are good for a start until machine IEEE Standards are good for a start until machine history is developed. However, the most efficient and history is developed. However, the most efficient and reliable method for evaluating vibration severity is reliable method for evaluating vibration severity is comparing the most recent overall reading versus comparing the most recent overall reading versus previous readings for the same measurement. Once a previous readings for the same measurement. Once a history of readings is plotted out, a trend comparison history of readings is plotted out, a trend comparison between current and past readings are easier to analyze. between current and past readings are easier to analyze.

The actual vibration velocity values show higher The actual vibration velocity values show higher readings on the horizontal direction as compared to readings on the horizontal direction as compared to those on the vertical direction due to gravity. Both the those on the vertical direction due to gravity. Both the vertical and horizontal values are roughly in the level of vertical and horizontal values are roughly in the level of four to five times the IEEE standard. The vibration can four to five times the IEEE standard. The vibration can be ranked as severe as confirmed by the alternator be ranked as severe as confirmed by the alternator malfunction indicator lamp on the dashboard. This lamp malfunction indicator lamp on the dashboard. This lamp indicates that there is insufficient charging from the indicates that there is insufficient charging from the alternator.alternator.

Measuring Vibration Velocity on the Pulley Side Measuring Vibration Velocity on the Pulley Side of the Alternator in the Vertical Directionof the Alternator in the Vertical Direction

BALMAC 205VIBRATION METER

MAGNETIC PROBEVERTICAL MEASUREMENT

PULLEY SIDE

The Root Cause of the Severe The Root Cause of the Severe Mechanical Vibration on the AlternatorMechanical Vibration on the Alternator

Identifying the root cause of the vibration is easier Identifying the root cause of the vibration is easier using a Fast Fourier Transform analyzer such as the using a Fast Fourier Transform analyzer such as the SKF SKF MicrologMicrolog Vibration Analyzer. A Vibration Analyzer. A Fast Fourier Fast Fourier Transform analyzerTransform analyzer converts a vibration signal in time converts a vibration signal in time domain to a vibration signature in the frequency domain domain to a vibration signature in the frequency domain using algorithms. Since most of the machine vibration using algorithms. Since most of the machine vibration wave forms are close to sine waves, observing the wave forms are close to sine waves, observing the frequency at which the vibration occurs is an effective frequency at which the vibration occurs is an effective guide as to the cause of the excitation. guide as to the cause of the excitation.

Since only a digital vibration meter is available, we Since only a digital vibration meter is available, we are limited to trend plots and analysis will have to be are limited to trend plots and analysis will have to be through “through “Kepner-TregoeKepner-Tregoe” problem analysis tool and ” problem analysis tool and common sense. The simple design of the Volkswagen common sense. The simple design of the Volkswagen Beetle’s blast fan yields to the easy identification of the Beetle’s blast fan yields to the easy identification of the root cause.root cause.

The possible causes of excessive vibration in the The possible causes of excessive vibration in the blast fan assembly are unbalance, misalignment, bent blast fan assembly are unbalance, misalignment, bent shaft, mechanical looseness, and bearing defects. In shaft, mechanical looseness, and bearing defects. In identifying which of these factors is the contributor to the identifying which of these factors is the contributor to the vibration problem, a systematic tool of prioritizing based vibration problem, a systematic tool of prioritizing based on a risk priority number, which of the items are to be on a risk priority number, which of the items are to be verified first.verified first.

Prioritizing Among Which Possible Prioritizing Among Which Possible Cause of Vibration to CheckCause of Vibration to Check

POSSIBLE CAUSESPOSSIBLE CAUSES METRICSMETRICS SS OO DD RPNRPN REMARKSREMARKS

(SxO)(SxO)

UnbalanceUnbalance BalancingBalancing 77 22 22 1414 Unlikely to Unlikely to occuroccur

Visual CheckVisual Check

MisalignmentMisalignment VisualVisual

CheckCheck

77 77 88 4949 Easy to CheckEasy to Check

Bent ShaftBent Shaft Mount on lathe Mount on lathe 77 22 22 1414 Unlikely to Unlikely to occuroccur

Mechanical Mechanical LoosenessLooseness

MeasurementMeasurement 77 77 55 4949 Checked vs. Checked vs. bearingbearing

Bearing DefectsBearing Defects VisualVisual

CheckCheck

77 99 55 6363 Very likely to Very likely to occuroccur

where;where;MetricMetric – the test made to detect or measure the cause, – the test made to detect or measure the cause,

effect or effect or failure.failure.Severity (S)Severity (S) – an assessment of the seriousness of the – an assessment of the seriousness of the

effect effect related to a qualitative scale of 1 to 10.related to a qualitative scale of 1 to 10.Occurrence (O)Occurrence (O) – the likelihood that a specific cause exists. – the likelihood that a specific cause exists. Detection (D)Detection (D) – is the assessment of the ability of the – is the assessment of the ability of the

possible possible cause to be detected. cause to be detected. Risk Priority Number (RPN)Risk Priority Number (RPN) – the product of the severity – the product of the severity

and and occurrence rankings. The occurrence rankings. The RPNRPN can be used to can be used to compare overall risk.compare overall risk.

Although bearing defect has the highest Although bearing defect has the highest Risk Priority Risk Priority NumberNumber, the pulley alignment can be visually checked even before , the pulley alignment can be visually checked even before removing the bearings. Visual inspection confirmed that the pulleys removing the bearings. Visual inspection confirmed that the pulleys were well aligned. Meanwhile, mechanical looseness can be were well aligned. Meanwhile, mechanical looseness can be checked upon inspecting the bearings.checked upon inspecting the bearings.

The V-belt that drives the alternator was The V-belt that drives the alternator was removed. Inspection on the alternator without the removed. Inspection on the alternator without the belt revealed that there was considerable belt revealed that there was considerable mechanical looseness on the 6202-2Z deep-groove mechanical looseness on the 6202-2Z deep-groove ball bearing on the pulley side. It was also confirmed ball bearing on the pulley side. It was also confirmed later that the bearing on the fan side was also later that the bearing on the fan side was also defective. In fact, there are instances when the defective. In fact, there are instances when the alternator rotor rubs against some portions on the alternator rotor rubs against some portions on the stator when the shaft was turned by hand without stator when the shaft was turned by hand without the belt. This is the condition that restricts the the belt. This is the condition that restricts the motion of the alternator. The defective bearing is motion of the alternator. The defective bearing is only an effect of the root cause of the vibration only an effect of the root cause of the vibration

problem.problem.

Possible causes of bearing failure are Possible causes of bearing failure are ineffective lubrication, overloading, improper ineffective lubrication, overloading, improper installation, defective bearing seats on shaft and in installation, defective bearing seats on shaft and in housing, vibration while bearing is not rotating, and housing, vibration while bearing is not rotating, and passage of electric current through the bearing. passage of electric current through the bearing. Further inspection during the disassembly of the Further inspection during the disassembly of the alternator showed that the bearing seat on the alternator showed that the bearing seat on the stationary housing on both sides of the alternator is stationary housing on both sides of the alternator is defective. The bearing seat was already loose versus defective. The bearing seat was already loose versus the outer race of a new 6202-2Z ball bearing by as the outer race of a new 6202-2Z ball bearing by as much as much as 0.010”0.010” as measured by a micrometer. as measured by a micrometer.

Measurements on Actual Housing Fits on Measurements on Actual Housing Fits on the Alternator Bearings (6202-2Z)the Alternator Bearings (6202-2Z)

LOCATIONLOCATION HOUSINGHOUSING

BOREBORE

HOUSINGHOUSING

BOREBORE

SPECIFIEDSPECIFIED

BOREBORE

SPECIFIEDSPECIFIED

BOREBORE

REMARKSREMARKS

MinimumMinimum MaximumMaximum MinimumMinimum MaximumMaximum

InchesInches InchesInches InchesInches InchesInches

Pulley SidePulley Side 1.3781.378 1.3891.389 1.37801.3780 1.37861.3786 DefectiveDefective

FitFit

Fan SideFan Side 1.3781.378 1.3861.386 1.37801.3780 1.37861.3786 DefectiveDefective

FitFit

Measurements on Actual Shaft Fits on Measurements on Actual Shaft Fits on the Alternator Bearings (6202-2Z)the Alternator Bearings (6202-2Z)

LOCATIONLOCATION SHAFTSHAFT

DIAMETERDIAMETER

SHAFTSHAFT

DIAMETERDIAMETER

SPECIFIEDSPECIFIED

DIAMETERDIAMETER

SPECIFIEDSPECIFIED

DIAMETERDIAMETER

REMARKSREMARKS

MinimumMinimum MaximumMaximum MinimumMinimum MaximumMaximum

InchesInches InchesInches InchesInches InchesInches

Pulley SidePulley Side 0.59050.5905 0.59050.5905 0.59060.5906 0.59090.5909 AcceptableAcceptable

FitFit

Fan SideFan Side 0.5910.591 0.5910.591 0.59060.5906 0.59090.5909 AcceptableAcceptable

FitFit

Corrections Done on the Loose Bearing Corrections Done on the Loose Bearing Housing Fit of the AlternatorHousing Fit of the Alternator

The loose stationary housing bore was sent to the machine The loose stationary housing bore was sent to the machine shop for re-machining of the bore to oversize it to an inside diameter shop for re-machining of the bore to oversize it to an inside diameter of of 1.5001.500 to to 1.50051.5005 inches while maintaining its depth of inches while maintaining its depth of 0.4320.432 inch. inch. The step on the housing perimeter was made reference in locating The step on the housing perimeter was made reference in locating the exact center during the process of re-machining the bore in an the exact center during the process of re-machining the bore in an engine lathe.engine lathe.

An aluminum sleeve measuring An aluminum sleeve measuring 1.50001.5000 to to 1.50051.5005 inches inches outside diameter and outside diameter and 1.3780 1.3780 to to 1.37861.3786 inches inside diameter and inches inside diameter and 0.4320.432 wide was fabricated and then inserted into the re-machined wide was fabricated and then inserted into the re-machined housing bore. With the aluminum sleeve pressed into the oversized housing bore. With the aluminum sleeve pressed into the oversized bore, the resulting dimension was then in proper fit with the outside bore, the resulting dimension was then in proper fit with the outside diameter of the 6202 deep groove ball bearing.diameter of the 6202 deep groove ball bearing.

This was done to both stationary housing bores both on the This was done to both stationary housing bores both on the pulley and on the blast fan side. The defective 6202 ball bearings pulley and on the blast fan side. The defective 6202 ball bearings were replaced with new ones. The alternator was then were replaced with new ones. The alternator was then reassembled. reassembled.


of 1200rpm (idling)of 1200rpm (idling) after Correction after Correction



PULLEYPULLEY 0.0700.070 1.7781.778 0.0850.085 2.1592.159 - - - - -- - - - - - - - - -- - - - -

FANFAN 0.0650.065 1.6511.651 0.070.07 1.7781.778 - - - - -- - - - - - - - - -- - - - -


of 2000rpm of 2000rpm after Correctionafter Correction



PULLEYPULLEY 0.0600.060 1.5241.524 0.0650.065 1.6511.651 - - - - -- - - - - - - - - -- - - - -

FANFAN 0.0450.045 1.1431.143 0.0650.065 1.6511.651 - - - - -- - - - - - - - - -- - - - -


of 3000rpm of 3000rpm after Correctionafter Correction



PULLEYPULLEY 0.0650.065 1.6511.651 0.0700.070 1.7781.778 - - - - -- - - - - - - - - -- - - - -

FANFAN 0.0550.055 1.3791.379 0.0600.060 1.5241.524 - - - - -- - - - - - - - - -- - - - -

ConclusionsConclusions

Results show that after correcting the Results show that after correcting the mechanical looseness on the alternator mechanical looseness on the alternator bearings the vibration velocity readings bearings the vibration velocity readings reduced drastically. Now the readings were reduced drastically. Now the readings were within the acceptable levels of the IEEE within the acceptable levels of the IEEE Standard 1068. This means that dynamic Standard 1068. This means that dynamic balancing the blast fan impeller is no longer balancing the blast fan impeller is no longer necessary.necessary.

RecommendationRecommendation

A consistent condition monitoring of A consistent condition monitoring of the vibration readings can generate a trend the vibration readings can generate a trend plot showing the history of readings making plot showing the history of readings making this a convenient reference in predicting the this a convenient reference in predicting the health condition of this piece of rotating health condition of this piece of rotating machinery. A horizontal line with a machinery. A horizontal line with a magnitude of 1.5 times the recommended magnitude of 1.5 times the recommended zero-to-peak vibration velocity standard can zero-to-peak vibration velocity standard can be incorporated in such graph to represent be incorporated in such graph to represent the “warning” level. the “warning” level.

Documents

Reducing The Vibration Level Of The Blast Fan