Bearing basics SKF

2013-03-17 ©SKF Slide 1 WE 201 SKF Reliability Maintenance Institute

Materials Used for SKF Rolling Bearings

Bearing rings and rolling elements

Through-hardening steelsCarbon chromium steel containing approximately 1 % carbon and 1,5 % chromium

Case-hardening steelsChromium-nickel alloyed steel and manganese-chromium alloyed steel containing approximately 0,15 % carbon


Heat Treatments

AdvantagesBainitic hardening

Tough structure

Automatic dimensional stability

Compressive residual surface stresses

Case hardening

Hard surface and soft core resists through cracking

Highest compressive residual surface stresses

Martensite hardening

Less costly

Fixture can be used to reduce distortion

DisadvantagesBainitic hardening

Somewhat more costly than martensite

Lower hardness

Case hardening

Time consuming and costly process

Martensite hardening

Highest risk of propagation of surface cracks


Heat treat and hardness

Martensite-hardened material (through hardening)Bainite-hardened material

(through hardening)Tensile stresses 50 –

100 MPa Compressive stresses 50 –

100 MPa

Compressive stresses 200 –

400 MPa

60 HRC

60 HRC

59 HRC

35 HRC

59 HRC

58 HRC

: Tensile stresses

: Compressive stresses

Case-hardened material


Dimensional Stability

Change in diameter (μm/100 mm)

Holding time at 200 °C (392 °F)

Hours

Martensite

Bainite


Dimensional stability designation

Stabilization Class

Operating Temperature

Hardness HRC

SN

S0

S1

S2

S3

S4

up to 120° C (248° F) 59 to 63

up to 150° C (302° F)

up to 200° C (392° F)

up to 250° C (482° F)

up to 300° C (572° F)

up to 350° C (662° F)

58 to 62

57 to 61

56 to 60

54 to 58

50 to 54


The Principle SKF Rolling Bearing Range

Ball bearings

Roller bearings


Ball and Roller Bearing Ranges

Deep groove

Ball bearings Roller bearings+Angular contact

Self-aligning Cylindrical Taper Needle Spherical


Load Capabilities

Load carrying capacity is expressed as the basic dynamic load rating


Relative Speed Limitations

Oil lubrication speed rating

Grease lubrication speed rating

Bearing speed limit

r/min


Bearing components

Seal

Rolling Elements

Inner Ring Outer Ring

Cage

Seal


Bearing terminology...

Bore I.D.

Bore Surface

O.D. Surface

Outside Diameter

O.D.


Bearing terminology

Inner Ring Raceway

Side Faces

Outer Ring Raceway

Inner Ring Land(Shoulder)

Outer Ring Land(Shoulder)


Catalog dimensions

dDB


Bearing terminology for a spherical roller bearing

Outer RingCage

Inner Ring

Side FacesW33 Lubrication Groove and Hole

Rolling Element

Guide Ring

Inner Ring Raceway


Cage Variants

Polyamide cage

Window-type sheet steel cage

Window-type solid brass cage

Pressed cages


+ Lightweight

+ High strength

+ High vibration and acceleration resistance

– Sensitive to poor lubrication

+ No operating temperature limit

Machined cages: brass


+ Very high strength

+Suitable for very high speed in connection with circulating oil

– Relatively (very) expensive

+ Very high vibration and acceleration resistance

Molded cages: polyamide


+ Lightweight

+ High elasticity

+ Good sliding properties

+ Good marginal lubrication properties

– Operating temperature < +120 °C

Bearing basics SKF

Technology

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