Bearings and Seals Flashcards
(16 cards)
Journal bearings are typically more expensive than rolling element bearings
False
Journal bearings are generally less expensive than rolling element bearings, making them a good choice when cost is a primary consideration.
Rolling element bearings minimize friction primarily through sliding action between the rolling elements and the raceways
False
Rolling element bearings minimize friction by rolling action, not sliding.
The PV (Nominal Pressure x Sliding Speed) factor is a key parameter in the design of unlubricated plain sliding bearings
True
For plain sliding bearings, the nominal pressure P and sliding speed V are calculated, and their product PV is used to select a bushing material and is relevant for wear calculation.
The PV (P is the nominal pressure and V is the sliding speed) factor is a key parameter in the design of hydrodynamic bearings
False
Hydrodynamic bearing design focuses on maintaining a fluid film, and different parameters like the Hersey number (viscosity * speed / pressure) are more central to the lubrication regime.
Boundary, mixed, and hydrodynamic lubrication regimes can all be represented on the Stribeck curve
True
The Stribeck curve is presented as illustrating the relationship between friction and a parameter related to viscosity, speed, and pressure, clearly showing the regions corresponding to boundary, mixed (or EHD), and hydrodynamic lubrication.
Cylindrical roller bearings are designed to handle significant axial loads in addition to radial loads
False
While some bearings can carry axial load, roller bearings generally cannot carry axial load. Cylindrical roller bearings are a type of roller bearing.
Needle roller bearings can be used in situations where there is a limited space in the radial direction
True
A labyrinth seal is commonly used in high speed turbine machines
True
Any leakage flow is not allowed in the selection of a labyrinth seal
False
Labyrinth seals are designed to limit leakage, not necessarily eliminate it entirely in all applications.
Plain rubbing bearings are well-suited for applications involving low speeds and high loads
True
Plane bearings are described as well-suited for applications where the shaft rotates at low speeds and bears heavy loads, as the fluid film (if present) can support more load at lower speeds, or for dry rubbing where load capacity limits are key.
Rolling element bearings typically have a very long service life even if they are not properly lubricated
False
Rolling bearings typically have a very long service life if they are properly lubricated and maintained. Lack of proper lubrication is a major cause of failure.
Static load carrying capacity (C0) is the constant radial load which can be withstood for 1 million cycles without fatigue damage
False
That describes the basic dynamic load rating (C). C0 is the static load which causes a specified permanent deformation of the raceway and rolling element.
For a combined axial and radial load on a rolling element bearing, the equivalent dynamic load (P) is calculated as the simple sum of the radial force (FR) and the axial force (FA)
False
The equivalent dynamic load (P) for a combination of radial and axial load is calculated using the formula P = XFR + YFA, where X and Y are factors from the manufacturer’s data.
Wear is guaranteed to occur in plain rubbing bearings
True
It is explicitly stated that “Wear is guaranteed” for plain rubbing bearings.
Hydrodynamic bearings require continuous lubrication to function properly
True
Hydrodynamic bearings “Must be continuously lubricated”
Designing a journal bearing is a straightforward process that can be completed in a few simple steps without iteration
False
The step-by-step process for Journal bearing design is lengthy (16 steps after Childs), requiring several iterations
