What is the definition of "hydrodynamic lubrication"?
A type of lubrication in which a lubricant film completely separates two surfaces in contact. Hydrodynamic lubrication is achieved when a bearing rotates quickly enough for lubrication to flow around the bearing and cover its entire surface. Hydrodynamic lubrication is also called full-fluid lubrication.

Learn more about hydrodynamic lubrication in the class Bearing Applications 210 below.


Mechanical Systems Training


Class Information
Mechanical Systems Training Tooling U-SME classes are offered at the beginner, intermediate, and advanced levels. The typical class consists of 12 to 25 lessons and will take approximately one hour to complete.
Class Name:Bearing Applications 210
Description:This class describes different types of bearings, the operating conditions in which they are used, and important considerations for proper installation and maintenance of the major types of bearings available. Includes an Interactive Lab.
Prerequisites: 560100  560130 
Difficulty:Intermediate
Number of Lessons:20
Language:English, Spanish
 
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Class Outline
  • Objectives
  • What Are Bearings?
  • Factors Affecting Bearing Selection
  • Plain Bearings
  • Hydrostatic and Hydrodynamic Lubrication in Plain Bearings
  • Boundary and Mixed-Film Lubrication in Plain Bearings
  • Journal Bearings
  • Thrust Bearings
  • Anti-Friction Bearings
  • Ball Bearings
  • Angular and Thrust Ball Bearings
  • Roller Bearings
  • Types of Roller Bearings
  • Tapered Roller Bearings
  • Magnetic Bearings
  • Pros and Cons of Magnetic Bearings
  • Bearing Assembly
  • Causes and Symptoms of Bearing Fatigue
  • Improper Lubrication of Bearings
  • Summary
  
Class Objectives
  • Define bearings.
  • List factors affecting bearing choice.
  • Describe plain bearings.
  • Identify lubrication types for plain bearings offering the greatest friction-reducing properties.
  • Identify lubrication types for plain bearings offering compromised friction-reducing properties.
  • Describe journal bearings.
  • Describe plain thrust bearings.
  • Describe anti-friction bearings.
  • Identify the parts of a ball bearing.
  • Identify types of anti-friction bearings designed to resist thrust load.
  • Describe roller bearings.
  • Distinguish between cylindrical, needle and spherical roller bearings.
  • Describe the unique features of tapered roller bearings.
  • Describe magnetic bearings.
  • Distinguish between magnetic bearings and anti-friction bearings.
  • Describe important considerations for installing bearings.
  • Identify the common symptoms of bearing fatigue.
  • Identify common symptoms of improper lubrication.

Class Vocabulary

Vocabulary TermDefinition
abrasive Any hard foreign material that wears down the surface of components. When abrasives enter a bearing, they can break the lubrication film and cause damage.
active magnetic bearings A type of magnetic bearing requiring an external controlling system. Active magnetic bearings can operate at higher temperatures and support a higher load than passive magnetic bearings.
angular ball bearings A type of ball bearing in which the contact angle of the balls to the raceway is angled to allow them to accept greater thrust load than possible with non-angular ball bearings. Angular ball bearings are used in many machines, including gearboxes.
anti-friction bearing A type of bearing using rolling motion to support a load and reduce friction. Anti-friction bearings produce less friction than plain bearings.
arcing Overheating that occurs when electricity flows from one surface to another. In bearings, arcing can occur when insufficient lubrication leads to extensive contact between moving surfaces.
asperity A microscopic peak on a surface. Even surfaces that appear smooth contain many asperities. When objects are in motion, contact between their asperities causes friction.
axis An imaginary straight line that passes through the center of an object. A cylindrical component typically rotates around its axis.
axle A rotating shaft for a wheel or gear.
babbitt A metal alloy often used to line plain bearings. Babbitts are commonly made of large amounts of tin with a smaller amount of antimony, copper, and lead.
ball bearing A type of anti-friction bearing designed with metal balls that provide rolling motion and reduce friction between moving parts. Ball bearings are capable of operating at high speeds but cannot carry as great of a load as roller-element bearings.
bearing A friction-reducing device that allows one moving part to glide past another moving part. Bearings operate using a sliding or rolling mechanism.
bore The diameter of an anti-friction bearing's shaft. The bore is also called the interior diameter (ID).
boundary lubrication A type of lubrication in which the bearing and shaft rub together in partial contact and there is only a thin film of lubricant separating them.
brinneling A sign of damage in anti-friction bearings resulting from excessive load. Brinneling appears as indentions in the raceway.
bushing A type of plain bearing with a wall thickness between 1/16 and 1/2 inch designed to carry limited radial motion. Bushings are often used in oil pumps, electric motors, and alternators.
cage A part found in some anti-friction bearings that separates and prevents rolling elements, such as balls, from sliding against each other.
Conrad ball bearing A type of ball bearing that can accept both radial and thrust loads. It is also called a non-fill slot bearing because a cage keeps the bearings from moving. The Conrad ball bearing carries a smaller radial load than a fill-slot bearing.
contact angle The angle at which rolling elements of an anti-friction bearing contact the bearing rings.
crankshaft A rotating shaft with offset sections that transfers rotational motion into reciprocating linear motion. Crankshafts are used to power the pistons in an engine and to move the ram of a press.
cylindrical roller bearing The most common and basic type of roller bearing designed with cylinders of slightly greater length than width. Cylindrical bearings commonly operate in high speed, high radial load environments where thrust loads are low.
double-row bearing A type of roller-element bearing consisting of a double-row of rolling elements. Bearings with a double row accept a greater amount of load than single-row designs. In some cases, a double-row design makes it possible for load to be carried in two directions.
double-row spherical roller bearing A type of spherical roller bearing that can carry 30% more radial load than single-row spherical roller bearings.
downtime Unproductive blocks of time during which operations cease to function, normally due to mechanical problems or a lack of materials.
electrical fluting An extreme form of electrical pitting. Fluting appears as closely spaced lines running parallel to the bearing shaft.
electrical pitting A sign of damage in improperly lubricated bearings used in electrical equipment. Although it is not always visible to the naked eye, pitting appears as either frosted or darkened spots.
electromagnetic Pertaining to a type of magnetism produced by an electrical current.
ferromagnetic material A type of material that is highly attracted to magnets and can become permanently magnetized. Examples of ferromagnetic materials are iron and nickel.
fill-slot bearing A type of ball bearing that can accept relatively high radial loads, but very little thrust. It contains notches in the inner and outer rings that permit filling the bearing to capacity with balls once it has been installed and aligned.
flanged end A projecting rim or edge designed to increase stiffness and support greater thrust load.
flat-race thrust bearing A type of thrust ball bearing designed to accept some misalignment, but with a limited ability to accept load and operate at high speeds.
fluid film bearing A plain bearing operating using hydrodynamic lubrication. Fluid film bearings are also called hydrodynamic bearings.
four-row bearings A type of roller-element bearing consisting of four rows of bearings. Bearings with multiple rows of rolling elements accept a greater amount of load than single-row designs.
friction The resistance between the contact surfaces of two objects. Friction generates heat and increases the wear between components.
grooved-race thrust ball bearing A type of thrust ball bearing designed with a grooved raceway. The grooved-race thrust bearing can operate at higher speeds and carry a higher load than flat-race thrust bearings.
hydrodynamic bearing A plain bearing operating using hydrodynamic lubrication. Hydrodynamic bearings are also called fluid film bearings.
hydrodynamic lubrication A type of lubrication in which a lubricant film completely separates two surfaces in contact. Hydrodynamic lubrication is achieved when a bearing rotates quickly enough for lubrication to flow around the bearing and cover its entire surface. Hydrodynamic lubrication is also called full-fluid lubrication.
hydrostatic lubrication A type of lubrication in which moving surfaces are separated externally by a highly pressurized fluid such as air, oil, or water. Hydrostatic lubrication is expensive and its use is limited.
ID The diameter of an anti-friction bearing's shaft. The ID is also called the bore.
inner ring The inside portion of an anti-friction bearing that contains the rolling elements.
journal The shaft of a journal bearing. The journal is softer than the outer casing of the bearing.
journal bearing A type of plain bearing designed to reduce friction by supporting radial loads. Journal bearings are often used when the load is light and motion is relatively continuous, such as in crankshafts. Journal bearings are also called radial or sleeve bearings.
Kingsbury thrust bearing A type of plain thrust bearing capable of high thrust capacity able to operate even when there is some significant misalignment.
length-to-diameter ratio A numerical expression of the relationship between the length and diameter of an object. For example, the length of the rolling elements in a needle roller bearing is four times greater than the diameter of the bearing.
load The overall force that is applied to a material or structure. Bearings must support components and withstand various machine loads during operation.
lubricant A substance used to reduce friction between two surfaces in relative motion. Oil and grease are common industrial lubricants.
magnetic bearing A bearing that uses magnetic forces to support the rotating shaft and carry a load.
magnetic flux path The direction and flow of the magnetic forces of attraction created by a magnet.
mixed-film lubrication A type of lubrication in which bearings support their load partially with a boundary lubrication and partially with a hydrodynamic lubrication.
needle roller bearing A type of cylindrical bearing with long, thin rollers at least four times greater in length than their diameter. Needle roller bearings have the highest radial load capacity in relation to their height.
non-fill slot ball bearing A type of ball bearing that can accept both radial and thrust loads, because its cage keeps the bearings from moving. However, it carries a smaller radial load than a fill-slot bearing. It is also called a Conrad ball bearing.
OD The largest diameter of an anti-friction bearing indicating its overall size.
oil inlet An opening on a bearing where lubricant is supplied.
outer ring The outside portion of an anti-friction bearing that contains the rolling elements.
passive magnetic bearings A type of magnetic bearing that does not require an external controlling system. Passive magnetic bearings are not capable of operating under as high of temperatures or sustain as high of a load as active magnetic bearings.
perpendicular Forming a 90° right angle. The corner of a piece of paper is forms perpendicular lines.
plain bearing A type of bearing using a sliding motion to reduce friction. Types of plain bearings include journal bearings, plain thrust bearings, and bushings.
plain thrust bearing A type of thrust bearing consisting of two parts: a wedged lower section which reduces friction and accommodates lubrication, and a rotating upper section. Plain thrust bearings are often used along with journal bearings, such as in crankshafts.
raceway The grooves within an anti-friction bearing that run along the middle of the inside and outside bearing rings. The raceway provides a path for the balls or rolling elements.
radial load Force that is applied perpendicular to the axis of a bearing's shaft. Radial loads are also called rotary loads.
roller A cylindrically shaped rolling element that decreases friction when used in a rolling element anti-friction bearing.
roller bearing A type of anti-friction bearing designed with rollers that provide rolling motion and reduce friction between moving parts. Roller bearings demand slower speeds than ball bearings, but they can support greater loads.
rolling-element bearing A type of bearing using rolling motion to support a load and reduce friction.Rolling-element bearings produce less friction than plain bearings. They are also called anti-friction bearings.
rotor A rotating component used together with a stationary part, the stator, in magnetic bearings.
scoring Damage done to plain bearings due to direct contact between moving parts. Scoring appears as long scratches in the direction of motion.
shaft A rod on which wheels, gears, and bearings rotate, or a rod that rotates within the bearing. Bearings operate by limiting the friction applied to shafts.
single-row bearing A type of roller-element bearing consisting of a single row of rolling elements. Bearings with a single row accept less load than double and multi-row designs. In some bearing styles, a single row of rolling elements can support load in one direction only.
sleeve bearing A type of plain bearing designed to reduce friction by supporting radial loads. Journal bearings are often used when the load is light and motion is relatively continuous, such as in crankshafts. Sleeve bearings are also called journal bearings.
spalling A sign of damage in anti-friction bearings resulting from normal use or excessive load. Spalling appears as fractures in the raceway.
spherical roller bearing A type of roller bearing featuring a spherical barrel shape that allows the component to carry some thrust load in addition to high radial load.
start-up friction The initial friction caused when a machine begins operation. Start-up friction is greater than the friction that takes place once components are in motion.
stator A stationary component used together with a rotating part, the rotor, in magnetic bearings.
tapered roller bearing A type of roller bearing featuring tapered inner and outer ring raceways and rollers. The tapered roller bearing can withstand high radial and thrust loads.
Teflon A solid lubricant used to coat surfaces and reduce friction.
thin-film lubrication A type of lubrication in which the lubricant film becomes too thin to separate a bearing and shaft completely. This can happen when the shaft does not rotate quickly enough to allow for hydrodynamic lubrication.
thrust ball bearing A type of ball bearing designed specifically to handle thrust load.
thrust bearing A type of bearing designed to reduce friction by carrying thrust or axial loads. Thrust bearings can be either plain or anti-friction bearings. The type of component supported determines the type of thrust bearing used.
thrust load Force that is applied parallel to the bearing's axis. Thrust loads are also called axial or linear loads.
viscosity The resistance to flow of a fluid or semi-fluid substance. Viscosity is one of the most important factors to consider when selecting a lubricant.
washer A thin disc with a hole in the middle used to support load when using bearings or fasteners. Washers are used to support thrust ball bearings.