Bearings

Definition of Terms

bearing, journal

A ___________ is a machine element which support another moving machine element (known as _________).

bearing

It permits a relative motion between the contact surfaces of the members, while carrying the load. A little consideration will show that due to the relative motion between the contact surfaces, a certain amount of power is wasted in overcoming frictional resistance and if the rubbing surfaces are in direct contact, there will be rapid wear.

lubricant

In order to reduce frictional resistance and wear and in some cases to carry away the heat generated, a layer of fluid (known as _________) may be provided.

mineral oil, vegetable oils, silicon oils, greases

The lubricant used to separate the journal and bearing is usually a _________ refined from petroleum, but ___________, __________, _________ etc., may be used

1. Depending upon the direction of load to be supported

a. Radial bearings

b. Thrust bearings

2. Depending upon the nature of contact

a. Sliding contact bearings

b. Rolling contact bearings

Classifications of Bearings

radial bearing

In __________, the load acts perpendicular to the direction of motion of the moving element.

thrust bearings

In __________, the load acts along the axis of rotation.

sliding contact bearings

In __________, the sliding takes place along the surfaces of contact between the moving element and the fixed element.

plain bearings

The sliding contact bearings are also known as __________.

rolling contact bearings

In ______________, the steel balls or rollers, are interposed between the moving and fixed elements. The balls offer rolling friction at two points for each ball or roller.

called slipper or guide bearings, cross-head

The sliding contact bearings in which the sliding action is guided in a straight line and carrying radial loads, may be _________________. Such type of bearings are usually found in ___________of steam engines.

journal or sleeve bearings

The sliding contact bearings in which the sliding action is along the circumference of a circle or an arc of a circle and carrying radial loads are known as _______________.

full journal bearing

When the angle of contact of the bearing with the journal is 360° then the bearing is called a _____________.

full journal bearing

This type of bearing is commonly used in industrial machinery to accommodate bearing loads in any radial direction.

partial journal bearing

When the angle of contact of the bearing with the journal is 120°, then the bearing is said to be ______________.

partial journal bearings

This type of bearing has less friction than full journal bearing, but it can be used only where the load is always in one direction. The most common application of the ____________ is found in rail road car axles.

clearance bearings

The full and partial journal bearings may be called as _______________ because the diameter of the journal is less than that of bearing.

fitted bearing

When a partial journal bearing has no clearance i.e. the diameters of the journal and bearing are equal, then the bearing is called a ______________.

1. Compressive strength

2. Fatigue strength

3. Comformability

4. Embeddability

5. Bondability

6. Corrosion resistance

7. Thermal conductivity

8. Thermal expansion

Properties of Sliding Contact Bearing Materials

high compressive strength

The maximum bearing pressure is considerably greater than the average pressure obtained by dividing the load to the projected area. Therefore the bearing material should have ________________ to withstand this maximum pressure so as to prevent extrusion or other permanent deformation of the bearing.

fatigue strength

The bearing material should have sufficient ______________ so that it can withstand repeated loads without developing surface fatigue cracks. It is of major importance in aircraft and automotive engines.

Comformability

It is the ability of the bearing material to accommodate shaft deflections and bearing inaccuracies by plastic deformation (or creep) without excessive wear and heating.

Embeddability

It is the ability of bearing material to accommodate (or embed) small particles of dust, grit etc., without scoring the material of the journal.

Bondability

Many high capacity bearings are made by bonding one or more thin layers of a bearing material to a high strength steel shell. Thus, the strength of the bond i.e. __________ is an important consideration in selecting bearing material.

Corrosion resistance

The bearing material should not corrode away under the action of lubricating oil. This property is of particular importance in internal combustion engines where the same oil is used to lubricate the cylinder walls and bearings. In the cylinder, the lubricating oil comes into contact with hot cylinder walls and may oxidise and collect carbon deposits from the walls.

Thermal conductivity

The bearing material should be of high ______________ so as to permit the rapid removal of the heat generated by friction.

Thermal expansion

The bearing material should be of low coefficient of _____________, so that when the bearing operates over a wide range of temperature, there is no undue change in the clearance.

Properties of Metallic Bearing Materials

lubricants

The ____________ are used in bearings to reduce friction between the rubbing surfaces and to carry away the heat generated by friction. It also protects the bearing against corrosion.

1. liquid lubricants

2. semi-liquid lubricant

3. solid lubricants

All lubricants are classified into the following three groups:

liquid lubricants

The _____________ usually used in bearings are mineral oils and synthetic oils. The mineral oils are most commonly used because of their cheapness and stability. The ___________ are usually preferred where they may be retained.

semi-liquid lubricant

A grease is a __________ having higher viscosity than oils. The greases are employed where slow speed and heavy pressure exist and where oil drip from the bearing is undesirable.

solid lubricants

The __________ are useful in reducing friction where oil films cannot be maintained because of pressures or temperatures. They should be softer than materials being lubricated. A graphite is the most common of the _________ either alone or mixed with oil or grease.

A. the lube oil is supplied under pressure

A hydrostatic bearing is one which:

A. the lube oil is supplied under pressure

B. lube oil is not pressurized

C. there is no lube oil

D. bearing is lightly loaded

A. the oil film pressure is generated only by the rotation of the journal

In hydrodynamic bearings:

A. the oil film pressure is generated only by the rotation of the journal

B. the oil film is maintained by supplying oil under pressure

C. external supply of lubricant is not needed

D. grease is used for lubrication

B. full bearing

Bearing surface that completely surrounds the journal is also called

A. offset bearing

B. full bearing

C. centrally loaded bearing

D. Babbitt bearing

D. full-bearing

A type of bearing that totally encloses the shaft.

A. offset bearing

B. central bearing

C. babbitt bearing

D. full-bearing

B. babbitt

A metal that assists lubrication or a lubricant itself:

A. zinc

B. babbitt

C. antimony

D. lead

D. a composition of antimony, lead, or tin alloy

A Babbitt is:

A. a eutectic of fron and iron phosphide

B. a gadget for measuring volume

C. a measure of magnetic induction produced in material

D. a composition of antimony, lead, or tin alloy

B. low carbon steel

One of the following materials is unsuitable as a bearing:

A. teflon

B. low carbon steel

C. cast iron

D. nylon

B. offset bearing

It is also called eccentrically loaded bearing.

A. full bearing

B. offset bearing

C. partial bearing

D. fitted bearings

B. 0.0010

As a rule of thumb in journal bearing design, the clearance ratio should be:

A. 0.0090

B. 0.0010

C. 0.0042

D. 0.0012

B. kinematic viscosity

The absolute viscosity of the fluid divided by its density expressed in the same terms of units is also called _________.

A. centistokes

B. kinematic viscosity

C. Reynold's number,

D. Relative viscosity

D. graphite

The most known lubricants being utilized in whatever category of load and speed are oil, air, grease and dry lubricants like _______.

A. bronze

B. lead

C. silicon

D. graphite

D. to lighten the load

All are functions of lubricating oils EXCEPT:

A. to prevent adhesion

B. to prevent corrosion

C. to act as coolant

D. to lighten the load

A. ZN/p

If p = bearing pressure on projected bearing areas, Z = absolute viscosity of lubricant, and N speed of journal, then the bearing modulus is:

A. ZN/p

B. Z/pN

C. Zp/N

D. p/ZN

D. Ball or roller bearing

Which of the following is an antifriction bearing?

A. Journal bearing

B. Partial bearing

C. Offset bearing

D. Ball or roller bearing

D. Needle bearing

Which of the following bearings may be operated without the use of a lubricant?

A. Journal bearing

B. Partial bearing

C. Offset bearing

D. Needle bearing

B. heavy load

A roller bearing is utilized on carrying capacity and is better than a ball bearing in this condition.

A. high temperature load

B. heavy load

C. low load

D. reversing load

C. Tapered roller bearing

To hold to minimum the axial direction of deflection/ movement, a separate thrust bearing or pre-loaded bearing capable of absorbing considerable load is required. The type of bearing to use is a ______________ bearing.

A. Double row angular contact

B. Wide type self-aligning

C. Tapered roller bearing

D. Deep groove bearing