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Millwright Yr2 > Lubrication > Flashcards

Lubrication Flashcards

Lubrication AB books Part A and B, and MM

1
Q

What is friction?

A

Resistance to movement between two touching surfaces

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2
Q

What are some negative effects of friction? (3)

A
  • Its resistance to movement increases energy consumption
  • causes wear
  • generates waste heat that can reduce life of components
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3
Q

What are some positive effects of friction? (4)

A
  • provides traction between rolling elements and raceways
  • promotes accurate tracking of raceways
  • provides a means of starting/stopping machines
  • provides a means of polishing
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4
Q

4 Types of friction

A
  • Sliding
  • Rolling
  • Fluid
  • Static(Starting)
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5
Q

What is sliding friction? Cause?

A

Resistance to movement produced when one surface slides across another. Produced by interlocking, tearing and momentary welding of the peaks of the asperities of the two surfaces

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6
Q

What are asperities?

A

High points on a metals surface, even when it appears flat or polished

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7
Q

What is rolling friction? Cause?

A

Resistance to movement of one surface rolling over another. Usually a result of of the resistance of a material being deformed

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8
Q

What is fluid friction? Cause?

A

Resistance to flow within the fluid. Result of a electromagnetic bond(attraction) between the molecules of a fluid. They resist movement of molecules sliding over each other

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9
Q

What is a fluid?

A

Anything that flows; liquid or gas

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10
Q

What is a lubricant?

A

A substance that reduces friction when applied as a surface coating to moving parts, reduces heat generate when surfaces move.

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11
Q

What is lubricity?

A

The property of reducing friction

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12
Q

What are the functions of a lubricant? (5)

A
  • reduce friction by separating moving surfaces with a lower friction film
  • to protect against corrosion of the surfaces
  • to carry away heat(fluids)
  • to carry away contaminants
  • to help seal
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13
Q

What is full film lubrication? 3 properties

A

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
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14
Q

What is Elasto-Hydrodynamic Film lubrication?

A

completely separates two surfaces the two surfaces (full film) but due to heavy load there is deformation on the loaded area. The deformation puts pressure on the lubricant and presses it very thin, and it acts as a spring

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15
Q

What is boundary film lubrication? When does it occur?

A

Does not completely separate the surfaces, so some of the asperities touch.

  • forms at low speeds
  • forms when viscosity of lubricant is too low to support the load
  • forms if not enough lubricant
  • results in wear, heat, friction etc compared to full film
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16
Q

Describe 4 stages of forming oil wedge

A

Stationary: oil sticks to the unloaded surface of shaft and bearing, loaded area is dry
Start rotation: shaft begins to climb up side of bearing on dry side until it rolls onto the oiled surface
Lube skid: when shaft rolls onto the oiled surface its skids back down and drags a layer of oil under the loaded area
Wedge: As shaft continues to turn it draws a wedge of oil under the loaded area and eventually lifts the shaft to form a full film

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17
Q

3 factors that affect thickness of of the hydrodynamic film

A

Speed- height of the film increases with speed
Viscosity- height of the film increases with viscosity
Load pressure- height decreases with load

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18
Q

What type of film has the most friction?

A

Boundary film lubrication

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19
Q

Does a boundary film provide a complete separation of surfaces?

A

No

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20
Q

Under what circumstances does a boundary film form?

A
  • Low speeds
  • Too little lubricant
  • Lubricant not high enough viscosity
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21
Q

Why is it important to bring shaft rotation up to speed as soon as possible?

A

To create fluid wedge and develop full film under the shaft

22
Q

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

A

smaller clearance means more surface area with full film coverage for the shaft to ride on

23
Q

What are the 2 conditions necessary for full film lubrication?

A
  • Must reach minimum speed

- Oil is at proper rated viscosity

24
Q

What is viscosity?

A

Resistance to flow/measurement of fluid friction. Higher viscosity, fluids flow slower.

25
Q

What things does viscosity effect in the performance of a lubricant? (5)

A
  • Film strength
  • Rate of flow
  • Internal friction (higher visc is greater)
  • Power consumption(higher visc, higher fluid fric)
  • sealing effect(higher visc, greater)
26
Q

Factors that effect viscosity? (3)

A
  • Temperature
  • Pressure
  • Speed
27
Q

How does temp, pressure and speed affect viscosity?

A

increased temp lowers viscosity, increased pressure increases viscosity, speed affects viscosity depending on the type and additives in the luibricant

28
Q

What are the measuring units for viscosity? What type of measurement and what is standard temperature?

A
  • Centistoke
  • SUS (Saybolt Universal Seconds)

Both are measures of kinematic viscosity, stand temp is 40C

29
Q

What is Absolute Viscosity? What is it measured in?

A

measures the force required to move a specific surface of a specific area across a film of fluid of a specified height at a specified rate of speed. Measured in centipoises

30
Q

What is viscosity index?

What is considered a good viscosity index?

A

A number that indicates the amount of change in viscosity over a temperature range.
VI 150 is considered good

31
Q

What is pour point?

A

The lowest temperature at which an oil is observed to flow

32
Q

How is pour point determined?

A

Pour point is 3 degrees above the temperature at which oil shows no movement from a container held horizontally for 5 seconds

33
Q

What is flash point? Why is it important? (2)

A

The lowest temperature at which the vapour above and oil ignites when a flame is passed over it

  • indicates fire or explosion hazard
  • Key WHMIS criterion for classifying as combustible
34
Q

What is oiliness?

A

A property that describes the adhesive strength of an oil to other materials

35
Q

What is SAE grading? What do the two numbers mean?

A

Society of Automotive Engineers viscosity grading system for engine oils, first number is for low temp, second number for high temp

36
Q

What does W indicate on oil grade?

A

low temperature engine oil grade.

37
Q

What are multigrade engine oils?

A

oils that have a viscosity index improver added to maintain viscosity at higher temperature.

38
Q

What is important to remember about SAE grade oils?

A

SAE grade engine oils dont correspond to viscosity ratings on industrial oils or to SAE ratings for axle/transmission oils

39
Q

What is the viscosity in centistokes of Telus 68 oil at 40C?

A

68 centistokes

40
Q

What is the practical importance of knowing the pour point of an oil?

A

-Lowest operating temperature of the oil
-Know whether the oil can be pumped at lowest operating temperature of the machinery
-

41
Q

Where do petroleum-based oils come from?

A
  • From base stock crude oil, paraffin or naptha

- Each base stock has its own properties and can be modified with additives

42
Q

List some characteristics of petroleum-based oils (7)

A
  • Do not wear out
  • they are re-refined to remove contaminants and new additives in added
  • Stable up to 55C
  • Operating temp can be extended with additives
  • Have good demulsibility (sep from water easy)
  • free from corrosives in their pure state
  • the least costly type of oil
43
Q

What are some Paraffin base-stock characteristics? (4)

A
  • highest wax content
  • least reactive base oil(most stable)
  • high viscosity index
  • less capacity to dissolve additives than naphtha base
44
Q

What are some Naphtha base stock characteristics? (5)

A
  • Used mainly as base oil in cold temp grease and refridge lubricants
  • more reactive base oil(less stable)
  • have low viscosity index, limited to indoor or mild outdoor temp
  • flow at lower temp than paraffin base
  • greater capacity to dissolve additives
45
Q

When is a good case to use synthetic oil?

A

When the synthetic use reduces operating costs enough to offset the higher purchase cost

46
Q

Characteristics of Synthetics? (8)

A
  • Some are stable up to 250C
  • Widest temp ranges of any oil
  • Some can be blended with petroleum oils
  • Some are toxic
  • Some are biodegradable
  • Some are fire-resistant
  • Some are water soluble
  • All are more expensive than petro-base oils
47
Q

What preto based limitations can synthetics overcome?

A
  • Presence of waxes that hinder flow at low temps
  • Oxidation at high temps
  • Thinning of oil at high temps
48
Q

Applications of synthetic oil? (6)

A
  • extremely hot conditions (gas turbines, paper machines, etc.)
  • Extreme temp ranges (Northern truck fleet)
  • dusty/dirty environments(pit mining)
  • radiation resistant hydraulic fluids in nuclear reactors
  • conduct heat readily(refrigerants)
  • aircraft hydraulics(fire resistance important)
49
Q

What are some types and characteristics of biodegradable oils?

A

Normally vegetable oils. break down easily with bacteria, much less stable

50
Q

What are oil additives?

A

Chemicals added to the base oil by the manufacturer to enhance performance

51
Q

What are oxidation inhibitors?

A

Also called antioxidants; additives that work to slow down oxidation

52
Q

When does oxidation occur? What can happen with oxidation?

A
  • when oil reacts with oxygen in the air and breaks down
  • increases with temperature
  • oxidation rate in petro-based oil doubles every 8 degrees C above 55C
  • increases in the presence of contaminants
  • produces sludge, acid and varnish
  • raises the viscosity of the oil

Millwright Yr2 (2 decks)

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