Lubrication - Part A (160201fA) Flashcards
What is friction?
Friction is the resistance to movement of one surface across another.
Name three kinds of friction:
- Sliding
- Rolling
- Fluid
What type of friction exist within a lubricant?
Fluid friction
What are three negative effects of friction?
- Increases power consumption
- Causes wear
- Generates waste heat
What are four positive effects of friction?
- Provides traction between the raceways and the rolling elements of anti-friction bearings which ensures rolling instead of skidding
- Promotes accurate tracking in bearing raceways
- Provides a means of starting, stopping and accelerating most machines
- Provides a means of polishing
How does a lubrication reduce friction?
It produces a film of liquid between components which lubricates and reduces the friction. The metal surfaces are separated and sliding friction (highest) is replaced with fluid friction (lowest)
Name four functions of a lubricant
- To reduce friction
- To protect against corrosion
- To carry away heat if the lubricant is a fluid
- To carry away contaminants if the lubricant is fluid
What type of lubricant film forms under a loaded rolling element?
Elasto-hydrodynamic lubrication
Does elasto-hydrodynamic lubrication provides complete separation of the rolling elements and the raceway
Yes
Does a boundary film provide a complete separation of surfaces?
No
What type of film has the most friction?
Boundary film
Under what conditions does a boundary film form?
- At low speeds
- When the viscosity is too low to support the load
- When there is insufficient lubrication
Why is it important to bring the shaft rotation up to speed as soon as possible?
To establish full film lubrication which prevents wear
Why does a reduction in clearance increase the load capacity of a journal bearing?
It increases the arc of the load supporting film
What are the two conditions necessary to ensure full film lubrication?
- The shaft must rotate above the recommended minimum speed
- The viscosity must be high enough to support the load
What is viscosity?
Resistance to flow
How does an increase in viscosity affect the load-carrying capacity of a lubricant film?
It increases the load-carrying capacity
What is the most important property to consider when selecting oil?
Viscosity
What five things does viscosity affect in the performance of a lubricant?
- Load capacity
- Flow rate
- Fluid friction
- Heat generation
- Sealing effect
How does an increase in temperature affect viscosity?
It decreases viscosity
Does an increase in speed affect the viscosity in many of the commonly used oils?
No
How does an increase in speed affect the oil containing polymer additives?
An increase in speed decreases viscosity
What is the viscosity in centistokes of Telus 68 oil at 40°C?
68 centistokes
What units of viscosity are used by the AGMA?
SUS units
What does the viscosity index of an oil indicate?
It indicates how much the viscosity changes between 40°C and 100°C
What viscosity index is considered good in today’s society?
150
What is meant by the pour point of an oil?
It is the lowest temperature at which oil is observed to flow
What is the practical importance of knowing the pour point of an oil?
It determines the lowest temperature at which an oil can be used for low temperature start-up
What is the practical importance of knowing the flash point of an oil?
It indicates the explosion or fire hazard of a lubricant
Were SAE standards developed for automotive or industrial oils?
For automotive oils
What do the SAE grade numbers indicate?
Viscosity at 30°C and 100°C
How is the low temperature viscosity SAE grade indicated?
With the letter W
Would SAE grade 20 be suitable for winter start-up?
No
What is the purpose of multigrade oils?
To accommodate start-up at low temperatures and adequate film strength at running temperature
Is re-refined oil slightly substandard, or is it top quality?
Top quality
What is the most widely used crude oil base stock in North America?
Paraffin base stock
What does a pour point depressant do?
It hinders the formation of wax crystals at low temperatures in order to make the oil flow more easily
How does a viscosity index improver work?
It thickens the oil at high temperatures, but has little effect at low temperatures.
What does a demulsifier do?
It separates the water from the oil
Where are naphtha-based oils mainly used?
In cold temperature grease in refrigeration systems
What additive can be substituted for detergents?
Ashless dispersants
Why are high-detergent oils not suitable for high-temperature applications?
They leave an ash deposit
Why are EP additives unsuitable for some worm wheel reducers?
The EP additives would corrode the bronze worm wheel in some worm wheel speed reducers.
Why are anti-wear additives unstable for extreme temperatures conditions?
The high temperatures produced in extreme pressure conditions would destroy the
anti-wear additives
What is the temperature limit for anti-wear additives?
100°C
How can foam be suppressed?
Spray silicon into the oil from an aerosol can
What two things increase the tendency to foam?
- Contaminants
- Most additives
What are three results of rusting?
- Surface pitting
- Abrasion
- Oxidation acceleration
What are four results of oxidation in mineral oil?
- Produces acid
- Produces sludge
- Produces varnish
- Thickens the oil
Why were synthetic oils developed?
To solve lubrication problems that cannot be overcome by petroleum-based oils
Which wears out, the base oil or the additives?
The additives
Why have biodegradable oils proved to be impractical?
They are unstable and unable to meet the normal operating requirements of industry.
What are three common problems that synthetic oils can overcome?
- Oxidation at high temperatures.
- Waxes that hinder flow at low temperatures.
- Thinning of oil at high temperatures.
