MECHANICALVIBRATIONS MANUALS / B-TECH / MECHANICAL / KUK

EXPERIMENT NO. - 1

AIM: TO STUDY THE FORCED VIBRATION OF THE BEAM FOR DIFFERENT DAMPING.

DESCRIPTION: IN THIS EXPERIMENT, A SLIGHTLY HEAVY RECTANGULAR SECTION BAR THAN USED IN EXPT. NO. 10 IS SUPPORTED AT BOTH ENDS IN TRUINION FITTINGS. EXCITER UNIT WITH THE WEIGHT PLATFORM CAN BE CLAMPED AT ANY CONVENTIONAL POSITION ALONG THE BEAM. EXCITER UNIT IS CONNECTED TO THE DAMPER. WHICH PROVIDES THE NECESSARY DAMPING?

DAMPING ARRANGMENT:

1. CLOSE THE ONE HOLE OF DAMPER FOR LIGHT DAMPING.
2. CLOSE THE TWO HOLES OF DAMPER FOR MEDIUM DAMPING.
3. CLOSE ALL THE THREE HOLES OF DAMPER FOR HEAVY DAMPING.

EXPERIMENTAL PROCEDURE:

1. ARRANGE THE SETUP AS SHOWN IN FIG. 11.
2. CONNECT THE EXCITER MOTOR TO CONTROL PANEL.
3. START THE MOTOR AND ALLOW THE SYSTEM TO VIBRATE.
4. WAIT FOR 5 MINUTES FOR AMPLITUDE TO BUILD UP FOR PARTICULAR FORCING FREQUENCY.
5. ADJUST THE POSITION OF STRIP CHART RECORDER. TAKE THE RECORDER OF AMPLITUDE VS. TIME ON STRIP CHART RECORDER BY STARTING RECORDER MOTOR.
6. TAKE RECORD BY CHANGING FORCING FREQUENCY FOR EACH DAMPING.
7. REPEAT THE EXPERIMENT FOR DIFFERENT DAMPING.

OBSERVATION TABLE:

S. NO.	FORCING FREQUENCY	AMPLITUDE
1.
2.

PRECAUTIONS:

1. DO NOT RUN THE MOTOR AT LOW VOLTAGE I.E. LESS THAN 180 VOLTS.
2. DO NOT INCREASE THE SPEED AT ONCE.
3. DAMPER IS ALWAYS IN PERPENDICULAR DIRECTION.
4. A MOTOR BOLTS IS PROPERLY TIGHTLY WITH WEIGHT.
5. A BEAM IS PROPER TIGHT IN BEARING WITH BOLT.
6. ALWAYS KEEP THE APPARATUS FREE FROM DUST.

TROUBLE SHOOTING:

1. THE MAIN LIGHT IS NOT ON CHECK THE MAIN SWITCH.
2. THE MOTOR IS NOT WORKING CHECK THE ROTARY SWITCH.

THE SENSOR IS NOT WORKING CHECK THE SENSOR SOCKET

EXPERIMENT NO. - 2

AIM: TO STUDY THE FORCED DAMPED VIBRATION OF EQUIPMENT SPRING MASS SYSTEM.

DESCRIPTION: IT IS EXCITER UNIT IS COUPLED TO D.C.VARIABLE SPEED MOTOR.RPM OF MOTOR CAN BE VARIED WITH SPEED OF ROTATION CAN KNOWN FROM THE RPM INDICATOR ON CONTROL PANEL. IT IS NECESSARY TO CONNECT THE DAMPER UNIT TO THE EXCITER. AMPLITUDE OF VIBRATION CAN BE RECORDED ON STRIP CHART RECORDER.

DAMPING ARRANGEMENT:

1. CLOSE THE ONE HOLE OF DAMPER FOR LIGHT DAMPING.

2. CLOSE THE TWO HOLES OF DAMPER FOR MEDIUM DAMPING.

3. CLOSE ALL THE THREE HOLES OF DAMPER FOR HEAVY DAMPING.

EXPERIMENTAL PROCEDURE:

1. START THE MOTOR AND ALLOW THE SYSTEM TO VIBRATE.

2. WAIT FOR 1 TO 2 MINUTES FOR AMPLITUDE TO BUILT THE PARTICULAR FORCING FREQUENCY.

3. ADJUST THE POSITION OF STRIP CHART RECORDER .TAKE THE AMPLITUDE VS. TIME ON STRIP CHART RECORDER BY STARTING RECORDER MOTOR. PRESS RECORDER PLATFORM ON THE PEN GENTALLY. AVOID EXCESSIVE PRESSURE TO GET GOOD RESULT.

4. TAKE RECORD BY CHANGING FORCING FREQUENCIES.

5. REPEAT THE EXPERIMENT BY ADJUSTING THE HOLES ON THE PISTON OF DAMPER CAN CHANGE DIFFERENT DAMPING.

6. PLOT THE GRAPH OF AMPLITUDE VS. FREQUENCIES FOR EACH DAMPING CONDITION.

OBSERVATION TABLE:

	FORCING FREQUENCIES(HZ)	AMPLITUDE(MM)
1.	4.0 MM	900 MM
2.	4.7 MM	900 MM

END FIXING ARRANGEMENT

AT MOTOR END AS WELL AS TAIL END DIFFERENT END CONDITIONS CAN BE DEVELOPED BY MAKING USE OF DIFFERENT FIXING BLOCKS.

1. SUPPORTED END CONDITIONS - MAKE USE OF END BLOCK WITH SINGLE SELF ALIGNING BEARINGS.

FIXED END CONDITION - MAKE USE OF END BLOCK WITH DOUBLE BEARING

GUARDS D1 AND D2:

THE GUARDS D1 AND D2 CAN BE FIXED AT ANY POSITION ON THE SUPPORTING BAR FRAME WHICH FITS ON SIDE SUPPORTS F. ROTATING SHAFTS ARE TO BE FITTED IN BLOCKS IN A AND B STANDS.

SPEED CONTROL OF DRIVING MOTOR:

THE DRIVING MOTOR IS 230V, DC 1/6 HP, 3000 RPM, UNIVERSAL MOTOR AND SPEED CONTROL UNIT IS A DIMMER STATE OF 240V, 2 AMPS, 50 C/S.

MEASUREMENT OF SPEED:

TO MEASURE THE SPEED OF THE ROTATING SHAFT A SIMPLE TACHOMETER MAY BE USED ON THE OPPOSITE SIDE OF THE SHAFT EXTENSION OF THE MOTOR.

WHIRLING OF ELASTIC SHAFTS:

IF L = LENGTH OF THE SHAFT IN CMS.

E = YOUNG’S MODULE KG/CM² 2.060 X 106

I = 2^ND MOMENT OF INERTIA OF THE SHAFT CM⁴

W = WEIGHT OF THE SHAFT PER UNIT LENGTH KG/CM.

G = ACCELERATION DUE TO GRAVITY OF CMS/SEC²

= 981

THEN THE FREQUENCY OF VIBRATION FOR THE VARIOUS MODES IS GIVEN BY THE EQUATION :

E.I.G

F = K X --------

W.L.⁴

END CONDITION	VALUE OF K
	1ST MODE	2ND MODE
FIXED , SUPPORTED FIXED , FIXED	1.47 1.57	2.56 2.46

DATA:

SHAFT DIA	I = CM4	W = KG/CM
3.8 MM 5.0 MM	X 10-4 X 10-4	0.15 X 10-2 0.28 X 10-2

PRECAUTIONS TO BE OBSERVED IN EXPERIMENTS:

1. IF THE REVOLUTIONS OF AN UNLOADED SHAFT ARE GRADUALLY INCREASED IT WILL BE FOUND THAT A CERTAIN SPEED WILL BE REACHED AT WHICH VIOLENT INSTABILITY WILL OCCUR, THE SHAFT DEFLECTING INTO A SINGLE BOW AND WHIRLING ROUND LIKE A SKIPPING ROPE. IF THIS SPEED IS MAINTAINED THE DEFLECTION, BUT IF THIS SPEED IS QUICKLY RUN THROUGH THE SHAFT WILL BECOME STRAIGHT AGAIN AND RUN TRUE UNTIL AT ANOTHER HIGHER SPEED THE SAME PHENOMENON WILL OCCUR, THE DEFLECTION NOW, HOWEVER BEING IN A DOUBLE BOW AND SO ON. SUCH SPEEDS ARE CALLED CRITICAL SPEED OF WHIRLING.

2. IT IS ADVISED TO INCREASE THE SPEED OF SHAFT RAPIDLY AND PASS THROUGH THE CRITICAL SPEEDS FIRST RATHER THAN OBSERVING THE 1^ST CRITICAL SPEED WHICH INCREASES THE SPEED OF ROTATION THAT THE AMPLITUDE OF VIBRATION WILL INCREASE SUDDENLY BRINGING THE FAILURE OF THE SHAFT. IF HOWEVER, THE SHAFT IS TAKEN TO MAXIMUM FIRST AND THEN SLOWLY REDUCED, HIGHER MODE WILL BE OBSERVED FIRST AND THE CORRESPONDING SPEED NOTED AND THEN BY REDUCING THE SPEED FURTHER THE NEXT MODE OF LOWER FREQUENCY CAN BE OBSERVED WITHOUT ANY DANGER OF RISE IN AMPLITUDE AS THE SPEED IS BEING DECREASED AND THE INERTIA FORCES ARE SMALLER IN COMPARISON WITH THE BENDING SPRING FORCES HENCE POSSIBILITY OF BUILD-UP OF DANGEROUS AMPLITUDES AT RESONANCE OR NEAR RESONANCE IS AVOIDED.
3. THUS IT CAN BE SEEN THAT IT IS A DESTRUCTIVE TEST OF SHAFT AND IT IS OBSERVED THAT THE ELASTIC BEHAVIOR OF THE SHAFT MATERIAL CHANGES A LITTLE AFTER TESTING IT FOR A NEW TIMES AND IT IS ADVISABLE THEREFORE, TO USE FRESH SHAFT SAMPLES AFTERWARDS.
4. FIX THE APPARATUS FIRMLY ON THE SUITABLY FOUNDATION.

TYPICAL TEST OBSERVATION:

a) BOTH ENDS OF SHAFTS FREE (SUPPORTED) 1^ST AND 2^ND MODE OF VIBRATION CAN BE OBSERVED OF SHAFTS WITH 3/16” DIA AND ¼” DIA.

b) ONE END OF SHAFT FIXED AND THE OTHER FREE; 1^ST AND 2^ND MODE OF VIBRATION CAN BE OBSERVED ON SHAFT WITH 3/16” DIA.

BOTH ENDS OF SHAFT FIXED- 2^ND MODE OF VIBRATION CANNOT BE OBSERVED ON ANY OF THE SHAFTS AS THE SPEEDS ARE VERY HIGH AND HENCE BEYOND THE RANGE OF THE APPARATUS.

FIXED – FIXED

DIAMETER OF BRASS ROD = 0.4 CM

WEIGHT = 150 GRM = KG/CM = 0.0015

YOUNG MODULUS E = 2.06 X 10⁶

S.NO.	SPEED RPM 1ST MODE	VALUE OF K	I=(ΠD4)/64	WEIGHT IN GRAMS	FTH = K.(EIG)/W	FACT = RPM/TIME
1
2

DIAMETER OF BRASS ROD = 0.47 CM

WEIGHT = 190 GRAM = KG/CM = 0.0019

YOUNG MODULUS E = 2.06 X 10⁶

S.NO.	SPEED RPM 2ND MODE	VALUE OF K	I=(ΠD4)/64	WEIGHT IN GRAMS	FTH = K.(EIG)/W
1
2

SUPPORTED – FIXED

DIAMETER OF BRASS ROD = 0.4 CM

WEIGHT = 190 GRAM = KG/CM = 0.0019

YOUNG MODULUS E = 2.06 X 10⁶

S.NO.	SPEED RPM 1ST MODE	SPEED RPM 2ND MODE	VALUE OF K	VALUE OF K	I=(ΠD4)/64	WEIGHT IN GRAMS	FTH = K.(EIG)/WL4	FTH = K.(EIG)/WL4	FACT= RPM/TIME	FACT= RPM/TIME
1.
2.

DIAMETER OF BRASS ROD = 0.47 CM

WEIGHT = 140 GRAM = KG/CM = 0.0014

YOUNG MODULUS E = 2.06 X 10⁶

S.NO.	SPEED RPM 1ST MODE	SPEED RPM 2ND MODE	VALUE OF K	VALUE OF K	I=(ΠD4)/64	WT. IN GRAMS	FTH = K.(EIG)/WL4	FTH = K.(EIG)/WL4	FACT= RPM/TIME	FACT= RPM/TIME
1.
2.

EXPERIMENT NO. - 3

AIM: TO DETERMINE THE RADIUS OF GYRATION ‘K’ OF A GIVEN COMPOUND PENDULUM.

TO VERIFY THE RELATION OF COMPOUND PENDULUM:-

T=2Π√ {K²+ (OG) ² /G*(OG)}

WHERE

T=PERIODIC TIME IN SEC.

K=RADIUS OF GYRATION ABOUT C.G. IN CM.

OG= DISTANCE OF C.G. OF THE ROD FROM SUPPORT.

L= LENGTH OF SUSPENDED PENDULUM.

DESCRIPTION:

THE COMPOUND PENDULUM CONSISTS OF A STEEL BAR. THE BAR IS SUPPORTED BY KNIFE EDGE.

TWO PENDULUMS OF DIFFERENT LENGTHS ARE PROVIDED WITH THE SETUP.

PROCEDURE:

1. SUPPORT THE ROD ON KNIFE EDGE.
2. NOTE THE LENGTH OF SUSPENDED PENDULUM AND DETERMINE OG.
3. ALLOW THE BAR TO OSCILLATE AND DETERMINE T BY KNOWING THE TIME FOR 10 OSCILLATIONS.
4. REPEAT THE EXPERIMENT WITH DIFFERENT LENGTH OF SUSPENSION.
5. COMPLETE THE OBSERVATION TABLE GIVEN BELLOW.

FORMULAE:

1. TIME PERIOD ACTUAL

T_ACTUAL = T/N SEC

2. ACTUAL RADIUS OF GYRATION, K_ACT

T_ACTUAL = 2Π√ {K_ACT²+ (OG) ² /G*(OG)}

3. THEORETICAL RADIUS OF GYRATION, K_THEO

K_THEO = L/2√3

OBSERVATION & CALCULATION TABLE:

S.NO.	L CM.	OG	NO. OF OSC. N	TIME FOR OSC.	TACT	KACT	KTHEO
1. 2. 3.

NOMENCLATURE:

K_ACT = RADIUS OF GYRATION ABOUT CE IN CM.

K_THEO = RADIUS OF GYRATION ABOUT CG IN CM.

L = LENGTH OF SUSPENDED PENDULUM.

N = NO. OF OSCILLATIONS.

OG = DISTANCE OF C.G. OF THE ROD FROM SUPPORT.

T_THEO = THEORETICAL PERIODIC TIME IN SEC.

T_ACT = ACTUAL TIME PERIOD.

T = TIME REQUIRED FOR 10 OSCILLATIONS.

EXPERIMENT NO. - 4

AIM: TO DETERMINE THE RADIUS OF GYRATION OF TRIFILAR SUSPENSION.

EQUIPMENTS: TRIFILAR SUSPENSION.

INTRODUCTION: TRIFILAR SUSPENSION IS A DISC OF MASS M (WEIGHT W) SUSPENDED BY THREE VERTICAL CORDS, EACH OF LENGTH L, FROM A FIXED SUPPORT. EACH CORD IS SYMMETRICALLY ATTACHED TO THE DISC AT THE SAME DISTANCE R FROM THE MASS OF THE DISC.

THEORY: THE DISC IS NOW TURNED THROUGH A SMALL ANGLE ITS VERTICAL AXIS, THE CORDS BECOMES INCLINED. ONE BEING RELEASED THE DISC WILL PERFORM OSCILLATIONS ABOUT THE VERTICAL AXIS. AT ANY INSTANT

LET: Ѳ = ANGULAR DISPLACEMENT OF THE DISC

F = TENSION IN EACH CORD =W/3

INERTIA TORQUE = I × Ѳ

RESTORING TORQUE = 3 × HORIZONTAL COMPONENT FORCES OF EACH STRING × R

INERTIA TORQUE = RESTORING TORQUE

DESCRIPTION: A UNIFORM CIRCULAR DISC IS SUSPENDED FROM THE PENDULUM SUPPORT FRAME BY THREE PARALLEL CORDS. TOP ENDS OF THE CORDS PASS THROUGH THE THREE SMALL CHUCKS FITTED AT THE TOP. OTHER ENDS ARESECUERED IN THE TRIFIELER DISC. IT IS POSSIBLE TO ADJUST THE LENGTH OF THE CHORD BY LOOSENING THE CHUCKS.

UTILITIES REQUIRED:

FLOOR AREA REQUIRED: .5 M × .5 M

1. ALLOW THE DISC TO OSCILLATE ABOUT THE VERTICAL AXIS PASSING THROUGH CENTRE

2. MEASURE THE OSCILLATION WITH TIME.

3. REPEAT THE EXPERIMENT FOR DIFFERENT LENGTHS & DIFFERENT RADIUS.

OBSERVATION & CALCULATION:

S.NO.	L,M	R,M	N	T,SEC

T= T/N, SEC

F= 1/T , SEC-1

K = 1/2ΠF × ∫GR2/L,

NOMENCLATURE:

R = RADIUS

N = NUMBER OF OSCILLATION.

T = TIME FOR N OSCILLATION, SEC.

T = TIME PERIOD OF OSCILLATION, SEC

F = FREQUENCY OF OSCILLATION, SEC-1

L = LENGTH OF THE CORD, M

K = RADIUS OF GYRATION, M

PRECAUTIONS & MAINTENANCE INSTRUCTIONS:

1. TIGHT THE DRILL CHUCKS PROPERLY.

2. LENGTH OF EACH CORD SHOULD BE EQUAL.

EXPERIMENT NO. - 5

AIM: TO DETERMINE THE RADIUS OF GYRATION OF GIVEN BAR USING BI-FILLER SUSPENSION.

DESCRIPTION: A UNIFORM RECTANGULAR SECTION BAR IS SUSPENDED FROM THE PENDULUM SUPPORT FRAME BY

TWO PARALLEL CORDS. TOP ENDS OF THE CORDS PASS THROUGH THE TWO SMALL CHUCKS FITTED AT THE TOP. OTHER ENDS ARE SECURED IN THE BI-FILLER BAR. IT IS POSSIBLE TO ADJUST THE LENGTH OF THE CORD BY LOOSENING THE CHUCKS.

THE SUSPENSION MAY BE USED TO DETERMINE THE RADIUS OF GYRATION OF ANY BODY. IN THIS CASE, THE BODY UNDER INVESTIGATION IS BOLTED TO THE CENTER. RADIUS OF GYRATION OF THE COMBINED BAR AND BODY IS THEN DETERMINED.

EXPERIMENTAL PROCEDURES:

1 SUSPEND THE BAR FROM CHUCK, AND ADJUST THE LENGTH OF THE CORD ‘L’ CONVENIENTLY. NOTE THAT THE SUSPENSION LENGTH OF EACH CORD MUST BE SAME.

2 ALLOW THE BAR TO OSCILLATE THE VERTICAL AXIS PASSING THROUGH THE CENTER AND MEASURE PERIODIC TIME T BY KNOWING THE TIME FOR SAY 10 OSCILLATIONS.

3 REPEAT THE EXPERIMENT BY MOUNTING THE WEIGHTS AT EQUAL DISTANCE FROM CENTER.

4 COMPLETE THE OBSERVATION TABLE BELOW.

FORMULE:

1 ACTUAL TIME PERIOD

TACT = T/N SEC

2 ACTUAL RADIUS OF GYRATION , K ACT FROM EQUATION

TACT = 2Π*KACT/A* √L/G

3 THEORETICAL RADIUS OF GYRATION

KTHEO = L/2√3

OBSERVATION & CALCULATION TABLE:

S . NO.	L CM	A CM	NO. OF SOCIAL	TIME FOR N SOCIAL	TACT	KACT	KTHEO
1
2

NOMENCLATURE:

2A = DISTANCE BETWEEN THE TWO STRING, G = ACCELERATION DUE TO GRAVITY

KACT= ACTUAL RADIUS OF GYRATION OF BI- FILLER SUSPENSION

KTHEO= THEORETICAL RADIUS OF GYRATION OF BI-FILLER SUSPENSION

L = LENGTH OF SUSPENDED STRING

N = NOS. OF OSCILLATION, N = NUMBER OF OSCILLATIONS

EXPERIMENT NO. - 6

AIM: TO VERIFY THE DUNKER LAY’S RULE VIZ.

1/F²=1/F_L²+1/F_B²

WHERE:-

F=NATURAL FREQUENCY OF GIVEN BEAM (CONSIDERING THE WEIGHT OF BEAM) WITH CENTRAL LOAD W.

F_L=NATURAL FREQUENCY OF GIVEN BEAM (NEGLECTING THE WEIGHT OF BEAM) WITH CENTRAL LOAD W.

F_L=1/2Π√ (48E.I.G/L³W)

FIB=NATURAL FREQUENCY OF THE BEAM.

DESCRIPTION:

AT RECTANGULAR BAR IS SUPPORTED IN TRUNION FITTING AT EACH END. EACH TRUNION IS PROVIDED

IN A BALL BEARING CARRIED IN HOUSING. EACH BEARING HOUSING IS FIXED TO THE VERTICAL

FRAME MEMBER. THE BEAM CARRIES A WEIGHT PLATFORM.

EXPERIMENTAL PROCEDURE:

1. ARRANGE THE SET-UP AS SHUN IN FIG.10 WITH SOME WT. W CLAMPED TO WT PLATFORM.

2. PULL THE PLATFORM S RELEASE IT TO SET THE SYSTEM IN TO NATURAL VIBRATION.

3. FIND THE PLATFORM TIME T S FREQUENCY OF VIBRATION F BY MEASURING TIME FOR SOME OSCILLATION

4. REPEAT EXPERIMENT BY PUTTING ADDIONAL MASSES ON WEIGHT PLATFORM.

5. PLOT GRAPH OF 1/F2 VS.

FORMULA:

1. FREQUENCY OF BEAM,

FL=1/2Π√ (48EIG/L³W)

2. NATURAL FREQUENCY

F_B=Π/2√ (G.E.I/WL⁴)

3. MOMENT OF INERTIA OF BEAM SECTION

I=BH³/12

4. ACTUAL TIME PERIOD,

TACT=T/N

5. ACTUAL FREQUENCY,

FACT=1/TACT

OBSERVATION & CALCULATION TABLE:

S NO.	WT. ATTACHED W KG.	NO. OF OSC N	TIME FOR N OSC. ‘T	TACT=T/N (SEC)	FREQUENCY FACT.(HZ)

NOMANCATURE:

B=WIDTH OF BEAM

E= MODULUS OF ELASTICITY OF BEAM MATERIAL

FL= FREQUENCY OF BEAM

FB= NATURAL FREQUENCY OF BEAM

FACT=ACTUAL FREQUENCY

G=ACCELERATION DUE TO GRAVITY..

H=THICKNESS OF BEAM

I=MOMENT OF INERTIA

L=LENGTH OF THE BEAM

N=NUMBER OF OSCILLATIONS

T=TIME TAKEN FOR N OSCILLATION

TACT=ACTUAL TIME PERIOD

W=WEIGHT OF BEAM PER UNIT LENGTH

W=CENTRAL LOAD OF THE BEAM, OR WEIGHT ATTACHED.

EXPERIMENT NO. - 7

AIM: TO STUDY THE UNDAMPED FREE VIBRATION OF EQUIVALENT SPRING MASS SYSTEM.

DESCRIPTION: THE EQUIPMENT IS DESIGNED TO STUDY FREE DAMPED AND UNDAMPED VIBRATION. IT CONSISTS OF M.S. RECTANGULAR BEAM SUPPORTED AT ONE END BY A TRUNION PIVOTED IN BALL BEARING .THE BEARING HOUSING IS FIXED TO THE SIDE MEMBER OF FRAME. THE OTHER END OF BEAM IS SUPPORTED BY THE LOWER END OF HELICAL SPRING. UPPER END OF THE SPRING IS ATTACHED TO SCREW, WHICH ENGAGES WITH SCREWED HAND WHEEL. THE SCREW CAN BE ADJUSTED VERTICALLY IN ANY CONVENIENT POSITION AND CAN BE CLAMPED WITH THE HELP OF LOCK NUT.

THE EXCITER UNIT CAN BE MOUNTED AT ANY POSITION ALONG THE BEAM .ADDITIONAL KNOWN WEIGHTS MAY BE ADDED TO THE WEIGHT PLATFORM UNDER SIDE EXCITER.

EXPERIMENTAL PROCEDURE:

1. SUPPORT ONE END OF BEAM IN THE SLOT OF TRUNION AND CLAMP IT BY MEANS OF SCREW.
2. ATTACHED THE OTHER END OF THE BEAM TO LOWER END OF SPRING
3. ADJUST THE SCREW TO WHICH THE SPRING IS ATTACHED WITH THE HELP OF HAND WHEEL SUCH THAT BEAM IS HORIZONTAL IN POSITION.
4. WEIGHT THE EXCITER ASSEMBLY ALONG WITH DISCS, BEARING AND WEIGHTS PLATFORM.
5. CLAMP TAE ASSEMBLY AT ANY CONVENIENT POSITION.
6. MEASURE THE DISTANCE L 1 OF THE ASSEMBLY FROM PIVOT.
7. MEASURE THE TIME FOR ANY 10 OSCILLATIONS AND PERIODIC TIME AND NATURAL FREQUENCY OF VIBRATION.
8. REPEAT THE EXPERIMENT BY VARYING L 1 AND ALSO PUTTING DIFFERENT WEIGHTS ON PLATFORM.

FORMULAE:

1. TIME PERIOD,

T_THEO=2*∏√ (M_E/K)

2. EQUIVALENT MASS AT THE SPRING

ME=M [L₁²/L²]

M= (W+W)/G

3. ACTUAL TIME PERIOD,

T_ACT=T/N SEC.

WT. (KG)	L1 IN CM.	NO. OF OSC. (N)	TIME FOR N OSC.	TACT =T/N SEC.	FREQ. IN HZ FACT	TTHEO (SEC.)	FTHEO

6. NOMENCLATURE:

G= ACCELERATION DUE TO GRAVITY

K=STIFFNESS OF SPRING

L1=DISTANCE OF W FROM PIVOT

L=DISTANCE OF SPRING FROM PIVOT

T=TIME TAKEN FOR N OSSC.

W=WT. OF EXCITER ASSEMBLY ALONG WITH WT. PLATFORM=18.7KG.

W=WT. ATTACHED ON EXCITER ASSEMBLY

EXPERIMENT NO. - 8

AIM: TO STUDY THE PRESSURE PROFILE OF LUBRICATING CONDITIONS OF LOAD AND SPEED.

EQUIPMENTS: JOURNAL BEARING APPARATUS.

INTRODUCTION: THIS APPARATUS HELPS TO DEMONSTRATE AND STUDY THE EFFECT OF IMPORTANT VARIABLES SUCH AS SPEED, VISCOSITY AND LOAD, ON THE PRESSURE DISTRIBUTION IN A JOURNAL BEARING.

THE PORTION OF A SHAFT, WHICH REVOLVES IN A BEARING AND IS SUBJECTED TO LOAD AT RIGHT ANGLE TO THE AXIS OF SHAFT, KNOWN AS JOURNAL. THE WHOLE UNIT CONSISTING OF JOURNAL AND ITS SUPPORTING PART IS A BEARING. THE WHOLE ARRANGEMENT IS KNOWN AS JOURNAL BEARING.

A. THEORY:

JOURNAL BEARING APPARATUS IS DESIGNED ON THE BASIS OF HYDRODYNAMIC BEARING ACTION USED IN PRACTICE. IN A SIMPLE BEARING THE BEARING SURFACE IS BORED OUT TO A SLIGHTLY LARGER DIAMETER THAN THAT OF JOURNAL. THUS, WHEN THE JOURNAL IS AT REST, IT MAKES CONTACT WITH THE BEARING SURFACE ALONG A LINE, THE POSITION OF WHICH IS DETERMINED BY THE LINE OF ACTION OF THE EXTERNAL LOAD. IF THE LOAD IS VERTICAL AS IN FIG.3.THE LINE OF CONTACT IS PARALLEL TO THE AXIS OF THE JOURNAL AND THE BEARING WILL BE FILLED WITH LUBRICANT. WHEN ROTATION BEGINS THE FIRST TENDENCY IS FOR THE LINE OF CONTACT TO MOVE UP THE BEARING SURFACE IN THE OPPOSITE DIRECTION TO THAT OF ROTATION AS SHOWN IN FIG. 2.WHEN THE JOURNAL SLIDES OVER THE BEARING, THE TRUE REACTION OF THE BEARING ON THE JOURNAL IS INCLINED TO THE NORMAL TO THE SURFACE AT THE ANGLE Ѳ AND THIS REACTION MUST BE IN LINE WITH THE LOAD. THE LAYER OF LUBRICANT IMMEDIATELY ADJACENT TO THE JOURNAL TENDS TO BE CARRIED ROUND WITH IT, BUT IS SCRAP OFF BY THE BEARING, SO THAT A CONDITION OF BOUNDARY LUBRICATION EXISTS BETWEEN THE HIGH SPOTS ON THE JOURNAL AND BEARING SURFACES WHICH ARE ACTUALLY IN CONTACT.

AS THE SPEED OF ROTATION OF THE JOURNAL INCREASES, THE VISCOUS FORCE WHICH TENDS TO DRAG THE OIL BETWEEN THE SURFACES ALSO INCREASES, AND MORE AND MORE OF THE LOAD IS TAKEN BY THE FILM IN THE CONVERGENT SPACE BETWEEN THE JOURNAL AND BEARING. THIS GRADUALLY SHIFTS LINE OF CONTACT ROUND THE BEARING IN THE DIRECTION OF MOTION OF THE JOURNAL. DUE TO THIS TWO SURFACES ARE COMPLETELY SEPARATED AND THE LOAD IS TRANSMITTED FROM THE JOURNAL OF THE BEARING BY THE OIL. THE FILM WILL ONLY BREAK THROUGH IF IT IS POSSIBLE FOR THE RESULTANT OIL PRESSURE TO BE EQUAL TO THE LOAD, AND TO HAVE SAME LINE OF ACTION. THE PRESSURE OF THE OIL IN THE DIVERGENT PART OF THE FILM MAY FALL BELOW THAT OF THE ATMOSPHERE, I WITCH CASE AIR WILL LEAK IN FROM THE ENDS OF THE BEARING. ASSUMING THAT THE NECESSARY CONDITIONS ARE FULFILLED AD THAT THE COMPLETE FILM IS FORMED, THE POINT OF NEAREST APPROACH OF JOURNAL TO THE BEARING WILL BY THIS TIME HAVE MOVED TO THE POSITION SHOWN FIG. 1.

DESCRIPTION:

THE APPARATUS CONSISTS OF A M.S. BEARING MOUNTED FREELY ON A STEEL JOURNAL SHAFT. THIS JOURNAL SHAFT IS COUPLED TO A D.C. MOTOR. SPEED REGULATOR IS PROVIDED WITH THE SETUP TO CONTROL THE SPEED OF JOURNAL SHAFT. THE JOURNAL BEARING HAS COMPOUND PRESSURE GAUGE MEASURE PRESSURE AT DIFFERENT POINTS. THE WEIGHT IS HANGED ON THE CENTRE OF THE BEARING. ON OIL INLET MOUNTED ON JOURNAL TO SUPPLY LUBRICATING OIL. ONE VALVE IS ALSO PROVIDED TO RELEASE THE TRAP AIR.

AN OIL RESERVOIR ACCOMPANIES THE SETUP TO STORE THE SUFFICIENT OIL FOE EXPERIMRNT.THIS RESERVOIR IS SUPPLIES OIL TO THE BEARING.

PROCEDURE:

1. FILL 2 LTS LUBRICATING OIL IN FEED TANK

2. RELEASE THE OIL FROM THE SUPPLY TUBE AND JOURNAL WITH HELP OF BALL VALVE.

3. CHECK THAT SOME OIL LEAKAGE IS THERE FOR COOLING.

4. SET THE SPEED WITH HELP OF DIMMER STAT AND LET THE JOURNAL RUN FOR ABOUT 5 MIN TO ACHIEVE THE STEADY STATE.

5. ADD THE REQUIRED LOADS AND KEEP IT HORIZONTAL POSITION.

6. NOTE THE RPM OF THE JOURNAL SHAFT.

7. NOTE PRESSURE READINGS AT DIFFERENT PERIPHERAL POSITIONS (AFTER 100 OR 150). ROTATION OF THE JOURNAL, WITH THE HELP COMPOUND PRESSURE GAUGE.

8. AFTER EACH READING, RELEASE PRESSURE AND TAKE THE NEXT READING.

9. REPEAT THE EXPERIMENT FOR THE VARIOUS SPEEDS AND LOADS.

10. AFTER THE TEST IS OVER SET DIMMER TO ZERO POSITION AND SWITCH OFF MAIN SUPPLY.

OBSERVATION & CALCULATION:

OBSERVATION:

W₂ = ----------KG.

N = -------RPM

OBSERVATION TABLE:

S.NO.	Ѳ	P, KG/CM2

PLOT A GRAPH B/W Ѳ VS. P

PRECAUTIONS:

1. NEVER RUN THE APPARATUS IF POWER SUPPLY IS LESS THAN 180VOLTS AND ABOVE230VOLTS.

2. INCREASE THE SPEED GRADUALLY.

3. DO NOT RUN THE JOURNAL & BEARING WITH OUT LUBRICANT OIL.

4. USE CLEAN LUBRICANT OIL.

5. ALWAYS KEEP THE APPARATUS FREE FROM DUST.