Module - Lubrication - Part A Flashcards Preview

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Flashcards in Module - Lubrication - Part A Deck (28):

The 3 types of friction are?

1. Sliding
2. Rolling
3. Fluid


What is Friction?

Friction is the resistance to movement of two surfaces in contact with each other.


What are 3 negative effects of friction?

1. Increased power consumption
2. Causes wear.
3. Generates heat.


What are 4 positive effects of friction?

1. Provides a means of polishing.
2. Provides a means of starting, stopping, most machines.
3. Accurate tracking in bearing raceways.
4. Provides traction. Ensures rolling instead of skidding in anti-friction bearings.


What are 5 functions of a lubricant?

1. To reduce friction.
2. Protect against corrosion.
3. Carry away heat.
4. Carry away contaminants.
5. Help seal.


What are the three types of Lubricant Films?

1. Full film lubricaiton
2. Elasto-Hydrodynamic film lubrication
3. Boundary film lubrication


Define: Full Film Lubrication.

Full film lubrication is thick enough to completely separate the surfaces with a continuous film.
+ offers the least friction resistance
+ eliminates wear on the moving surfaces
+ generates the least amount of heat


Define: Elasto-Hydrodynamic Film Lubrication

An elasto-hydrodynamic film completely separates two surfaces and is therefore a type of full film lubrication. However, in this case the two surfaces are loaded to the extent that deformation takes place in the loaded area.
+ fluid film in extremely thin
+ fluid film offers low friction resistance
+ type of film forms at high speeds as well as high pressures.
+ example: Hydroplaning


Define: Boundary Film Lubrication

A boundary film does not completely separate the surfaces, so some of the tips of the asperities touch.
+ forms at low speeds
+ forms when the viscosity of the lubricant is too low to support the load
+ forms if there is not enough lubricant


Why does a reduction in clearance increase the load capacity of a journal bearing?

A reduction in clearance will increase the arc of the load supporting film.
+ Smallest total clearance gives largest support area.


Define: Viscosity

Viscosity is a measurement of fluid friction (resistance to flow). Fluids that flow easily, like water, have low viscosity. Fluids that flow very slowly, such as tar, have high viscosity.


Define: Viscosity Index

Viscosity index (VI) is a number that identifies the amount of change in the viscosity of a lubricant over a temperature range. This means that an oil that shows very little change in viscosity as it is heated from 40C to 100C would have a high viscosity index.


Define: Pour Point

Pour point is the lowest temperature at which an oil is observed to flow.


Define: Flash Point

Flash point is the lowest temperature at which the vapour above an oil will ignite when a flame is passed over it.


What 5 things does viscosity affect in the performance of a lubricant?

1. load capacity
2. flow rate
3. fluid friction
4. heat generation
5. sealing effect


A lubricant's main job is to
a) reduce power consumption.
b) reduce resistance.
c) reduce heat.
d) reduce rolling friction.

b) reduce resistance.


Which of the following offers the least resistance?
a) fluid friction
b) rolling friction
c) sliding friction
d) asperity welding

a) fluid friction


Viscosity is a measurement of
a) the fluid pour point.
b) the capacity of fluid film.
c) the fluid's flash point.
d) the fluid's resistance to flow.

d) the fluid's resistance to flow.


If a fluid flows easily we say it has a __________ viscosity.
a) low
b) high

a) low


As the temperature of an oil increases, viscosity
a) increases.
b) decreases.

b) decreases.


Which of the following is the accepted worldwide measure of viscosity?
a) SUS
c) CST
d) ISO

c) CST


The amount of change in the viscosity over a temperature change is referred to as
a) pour point.
b) flash point.
c) penetration number.
d) viscosity index.

d) viscosity index.


An oil with very little change in viscosity as it is heated from 40 degrees C to 100 degrees C is referred to as having a __________ viscosity index.
a) low
b) high
c) graded
d) neutral

b) high


The lowest temperature at which an oil will flow is knows as
a) flash point.
b) full film lubricant point.
c) oil wedge theory point.
d) pour point.

d) pour point.


In the oil designation, the W stands for
a) water soluble.
b) winter (cold weather starting ability).
c) wax ingredients.
d) wedge theory of lubrication.

b) winter (cold weather starting ability).


Chemicals added to the oils to give properties for various special uses are
a) additives.
b) emulsifers.
c) solubles.
d) biodegradeable.

a) additives.


Where there are heavy loads with metal to metal contact possibilities, protection against the asperities welding their surfaces is prevented by adding chemicals with which designation?
a) W
b) AS
c) SUS
d) EP

d) EP


Detergent oils __________ recommended for high temperature applications.
a) are
b) are not

b) are not