Ball and Roller Bearings

External bearing sealing devices12. External bearing sealing devicesExternal seals have two main functions: to preventlubricating oil from leaking out, and, to prevent dust, water,and other contaminants from entering the bearing. Whenselecting a seal, the following factors need to be taken intoconsideration: the type of lubricant (oil or grease), sealperipheral speed, shaft fitting errors, space limitations,seal friction and resultant heat increase, and cost.Sealing devices for rolling bearings fall into two mainclassifications: non-contact seals and contact seals.¡Non-contact seals: Non-contact seals utilize a smallclearance between the shaft and the housing cover.Therefore friction is negligible, making them suitable forhigh speed applications.In order to improve sealing capability, clearancespaces are often filled with lubricant.formed synthetic rubber lip on a steel plate is pressedagainst the shaft. Contact seals are generally farsuperior to non-contact seals in sealing efficiency,although their friction torque and temperature risecoefficients are higher. Furthermore, because the lipportion of a contact seal slides while in contact with theshaft, the allowable seal peripheral speed variesdepending on seal type.Lubrication is required in the place where the seal lipmakes contact with the shaft. Ordinary bearing lubricantcan also be used for this purpose.The following chart lists the special characteristics ofseals and other points to be considered when choosingan appropriate seal.¡Contact seals: A contact seal is a seal whereby aType Seal construction Name Seal characteristics and selection considerationsNon-contact sealsClearance sealOil groove seal(oil grooves onhousing side)Oil groove seal(oil grooves onshaft and housingside)Axial labyrinthsealRadiallabyrinth sealAligninglabyrinth sealThis is an extremely simple sealdesign with a small radialclearance.Several concentric oil grooves areprovided on the housing innerdiameter to greatly improve thesealing effect. When the groovesare filled with lubricant, theintrusion of contaminants from theoutside is prevented.Oil grooves are provided on boththe shaft outer diameter andhousing inner diameter for a sealwith even greater sealingefficiency.This seal has a labyrinthpassageway on the axial side ofthe housing.A labyrinth passageway is affixedto the radial side of the housing.For use with split housings. Thisoffers better sealing efficiency thanaxial labyrinth seals.The seal's labyrinth passageway isslanted and has sufficientclearance to prevent contactbetween the housing projectionsand the shaft even as the shaftrealigns.Cautionary points regarding selectionIn order to improve sealingefficiency, clearances between theshaft and housing should beminimized. However, care shouldbe taken to confirm shaft/bearingrigidity and other factors to avoiddirect shaft-housing contact duringoperation.Oil groove clearance (reference)Shaft diameter mmClearance mmUp to 500.20.450or above0.51.0Oil groove width, depth (reference)width : 25 mmdepth : 45 mmThree or more oil grooves shouldbe provided.Sealing efficiency can be furtherimproved by filling the oil grooveportion with grease of which theconsistency grade is 150 to 200.Grease is generally used as thelubricant for labyrinth seals, and,except in low speed applications,is commonly used together withother sealing devices.Cautionary points regarding selectionIn order to improve sealingefficiency, labyrinth passagewayclearances should be minimized.However, care should be taken toconfirm shaft/bearing rigidity, fit,internal clearances and otherfactors to avoid direct contactbetween labyrinth projectionsduring operation.Labyrinth clearance (reference)Shaft Clearance mmdiametermm Radial direction Axial direction 500.20.41.02.050200 0.51.03.05.0Sealing efficiency can be furtherimproved by filling the labyrinthpassageway with grease of whichthe consistency grade is 150 to 200.Labyrinth seals are suitable forhigh speed applications.A-80