Journal Bearing

Front 1

What are the main objectives of the journal bearing experiment?

Back 1

• Measure hydrodynamic pressure variation in a journal bearing at different speeds

• Calculate load carrying capacity of the journal bearing and compare it with theory

• Measure the location of maximum film pressure

• Measure the friction loss in the bearing and compare it with theory

Front 2

What was the critical speed in this experiment and how did you determine the critical speed?

Back 2

• Critical speed was not achieved because machine could run at full power without reaching critical speed. RPM said to be critical speed was 2910.

Front 3

What did you mean by "axially averaged pressure"-explain how did you calculate these axially averaged values?

Back 3

• It was hypothesized that a higher journal bearing speed would cause higher centrifugal forces on the journal and higher oil pressures to react to the higher centrifugal forces

• As the speed changes so does the forces around the bearing (axially)

Front 4

Draw a cross sectional view of the journal and the bearing showing minimum and maximum film thickness.

Back 4

Front 5

What do you mean by radial clearance?

Back 5

• The radial clearance is the distance from the shaft and the bearing. The shaft should be forced towards the middle of the bearing without touching it due to hydrodynamic pressure.

Front 6

The maximum film pressure is a function of several parameters; discuss them in the light of your experience in this lab.

Back 6

It can be found from the pressure distribution curve resulting from the acquired experimental data. The line of centers is the centerline drawn through the shaft connecting the point of smallest radial clearance to the largest radial clearance. Max film pressure was also a function of eccentricity ratio.

Front 7

What is the purpose of the lubricant film?

Back 7

• The purpose of this film of lubricant is to keep the two surfaces separate at all times and thus prevent metal to metal or dry contact which otherwise will create bearing failure

Front 8

What lubricating oil did you use in this experiment and what was the density of this fluid?

Back 8

• Lubricant = SAE 15 W 50

• Lubricant’s density = 0.0282 lb/in3

Front 9

How did you calculate the tap pressure at certain location say at tap no.6? What was the significance of the pressure value at the tap no. 3?

Back 9

• The pressures were measured in distance of travel up individual tubes attached to a wall.

Front 10

What is Sommerfeld number?

Back 10

• A dimensionless number called the Sommerfeld Number or Characteristic Number defined by relates the bearing performance to the design parameters.

Front 11

Explain in terms of design parameters--- how did you calculate the load on the projected area of the bearing?

Back 11

• By using the equation P=w/(2rL) where W is the load carried by the bearing and L is the bearing length and r is the radius.

Front 12

What was the weight of each movable load that has been used in this experiment Journal Bearing?

Back 12

0.22 lbs

Front 13

What instrument was used to measure the angular velocity of the rotating shaft? How does it work?

Back 13

•The stroboscope is the instrument used for this application. It senses the velocity or rotation of the shaft using electronic sensors that relate the information back to a digital tachometer for readout.

Front 14

What does the term “eccentricity” mean? What are the consequences of the eccentric rotation of the shaft in the bearing?

Back 14

• Eccentricity is the act of deviating from a circular path or having constant variation of center of rotation. The eccentric rotation of the shaft in the bearing acts some-what like a rotary pump and generates a relatively high hydrodynamic pressure in the con-verging zone.

Front 15

What information does the polar plot of theoretical pressure give?

Back 15

•The polar plot gives the pressure distribution around the bearing.

Front 16

Name two applications for journal bearing. Explain what is the major difference between these types of bearing compared to other types?

Back 16

• Journal bearings are widely used in gasoline and diesel-fueled piston engines in motor vehicles, and allow parts to move together smoothly. Main bearings support a rapidly rotating crankshaft within an engine block, while connecting rod bearings help resolve the reciprocating linear motion of pistons to the rotating motion of the crankshaft by means of crankpin journals on the crankshaft.

Front 17

10. What was the dimensionless number used in this experiment? What were the effective parameters on it?

Back 17

•The Sommerfeld number was the dimensionless number in the experiment. Effective parameters that make up the Sommerfeld equation include journal radius, radial clearance, Oil viscosity at operating temperature, Journal speed, and Hydrodynamic pressure at position

Front 18

11. If the Journal radius is increased 3 times and the bearing length is decreased four times, with the same carried load, what is the change in the projected pressure?

Back 18

• The projected pressure will be ¾ what is originally was.

Front 19

Discuss the effect of Summerfeld number on the coefficient of friction and ho/c?

Back 19

Coefficient of friction is represented by “S” curves vs. Sommerfeld number, but are almost linear and get more curved as Sommerfeld number increases. So the effects of Sommerfeld number on friction coefficient are the reverse effect as that on ho/c.