Lubrication and Journal Bearings

Flashcards covering key concepts from a lecture on lubrication and journal bearings.

What are the different types of lubrication?

Hydrodynamic, Hydrostatic, Elastohydrodynamic, Boundary, Solid film.

What is Hydrodynamic Lubrication?

A type of lubrication with a relatively thick film of lubricant that prevents surface contact, created by a moving surface pulling the lubricant into a wedge-shaped zone. It requires sufficient velocity to create pressure.

What is Hydrostatic Lubrication?

A type of lubrication where lubricant is introduced under pressure to separate surfaces with a relatively thick film, and it does not require motion, used when velocities are small or zero.

What is Elastohydrodynamic Lubrication (EHL)?

A type of lubrication where surface deformations play a key role in the development of a lubricant film. It can be either Hard EHL (rolling contact) or Soft EHL (contact over a substantial portion of the mating surfaces).

What is Boundary Lubrication?

A lubrication regime occurring when conditions do not provide a thick enough lubrication film for hydrodynamic lubrication, where the highest asperities of the surfaces may be separated by only a few molecules of lubricant. Viscosity is not as important as chemical composition.

What is Solid-film Lubrication?

A type of lubrication using solid materials like graphite or molybdenum disulfide to create a layer of solid material, often used at extreme temperatures.

What is absolute viscosity (dynamic viscosity)?

The measure of a fluid's resistance to flow under an applied force; shear stress in a fluid is proportional to the rate of change of velocity with respect to y.

What are Newtonian fluids?

Fluids for which the rate of shear is constant.

What are the units of absolute viscosity?

ips units: reyn = lbf·s/in2; SI units: Pa·s = N·s/m2; cgs units: Poise = dyn·s/cm2.

What is kinematic viscosity?

The ratio of dynamic viscosity to density; measured using a Saybolt Universal Viscosimeter.

What is the Saybolt Universal Viscosimeter used for?

A device used to measure viscosity by measuring the time in seconds for 60 mL of lubricant at a specified temperature to run through a tube.

What does Petroff's equation relate to?

It applies to lightly loaded journal bearings and relates variables such as viscosity, speed, load, and clearance to determine friction.

What is the Sommerfeld number?

A dimensionless parameter used in lubrication, also known as the bearing characteristic number.

What defines Stable Lubrication?

Characterized by conditions where changes are self-correcting and results in stable lubrication. Conditions to the left of this are unstable.

What are the design variables for journal bearings?

Viscosity (μ), Load (W) or nominal bearing pressure (P), Speed (N), and Bearing dimensions (r, c, β, and l).

What are the dependent variables or performance factors for journal bearings?

Coefficient of friction (f), Temperature rise (ΔT), Volume flow rate of oil (Q), and Minimum film thickness (h0).

According to Trumpler, what is the purpose of minimum film thickness?

To prevent accumulation of ground off surface particles.

What are Trumpler's design criteria?

Minimum film thickness, maximum temperature, maximum starting load, and minimum design factor on running load.

Who are Raimondi and Boyd?

Researchers who used an iteration technique to solve Reynolds’ equation and published charts and tables for bearing design.

What does Reynolds equation describe?

The pressure distribution in a fluid film, considering factors like viscosity, speed, and geometry.

What are pressure-fed bearings?

Bearings that increase lubricant flow with an external pump to reduce temperature rise.

What is the significance of Dynamic Loaded Journal Bearings

Some journal bearing systems are subjected to loads and speeds that vary with time

What is the Mobility Method?

The mobility method is used to solve for the journal orbit.

What is Boundary Lubrication?

Relative motion between two surfaces with only a partial lubricant film (not hydrodynamic) is called boundary lubrication or thin-film lubrication.

What is linear sliding wear?

wA KPAVt = w KPVt

What is bushing wear?

The acceptable reduction is material due to use.