Ring and Ball Materials

CERAMIC

  • Hybrid and full ceramic bearings are made using silicon nitride or zirconium oxide material.
  • Hybrid bearings are constructed of steel inner/outer rings, ceramic balls and retainers made of steel or thermoplastic.
  • Full ceramic bearings are 100% ceramic. Balls, rings and retainers.
  • The density of ceramic is 40% that of steel, the resulting reduction in weight reduces centrifugal forces imparted on the rings, reducing skidding, allowing up to 30% higher running speeds with less lubrication.
  • Silicon nitride balls have a 50 % higher modulus of elasticity (resistance to deformation) than steel, which increases rigidity and improving accuracy.
  • Ceramic balls have a smoother finish than steel, vibration and spindle deflection is reduced allowing higher speeds.
  • Ceramic has a lower coefficient of friction and is nearly twice as hard as bearing steel resulting in less wear with less lubrication. Bearing life can be increased.

See Material Property Comparison Chart


Heat treated high carbon chromium bearing steel is the most common material used for rings and balls. Due to it low chromium content it exhibits poor corrosion resistance. The material does exhibit good mechanical properties up to 250F continuously. Above 250F bearing life is reduced as well as load capacity. Dimensional changes occur that require compensation in the overall bearing design and bearing fits. Applications are wide for this material. 52100 is magnetic.


440C STAINLESS STEEL

Heat treated 440C stainless steel offers fair to good corrosion resistance. It is the most common stainless steel used for rings and balls. With the addition of chromium and nickel corrosion resistance is greatly improved over 52100 steel. As oxygen reacts with the chromium a protective layer of chromium oxide is formed on the surface. This material can be passivated to improve corrosion resistance. Load capacity of 440C is about 20% less than that of 52100. With design considerations, this material can handle service temperature up to 350F with fair load capacity. Beyond 350F capacity and life is reduced.

Applications may include some vacuum and clean processes or where general preventative corrosion resistance is desired. This material is magnetic.


300 SERIES STAINLESS STEEL (316 & 304)

In a semi-precision grade bearing, 300 series stainless steel can be chosen for improved corrosion resistance over 440C. These materials are not heat treated so load capacity is significantly less than HT 52100 & 440C. It can be used for both rings and balls or SS rings with ceramic balls. 300 series stainless steel offers excellent corrosion resistance to water and excellent to good resistance when exposed to certain common acids. This material can be an excellent choice for food grade applications. Other applications may include marine and vacuum processes. 300 series stainless steel is also a common material used for ribbon and crown type retainers. 300 series stainless steels are generally considered non-magnetic. As 300 series bearings are not as common as 440C, size availability and minimum order requirements apply.


PLASTICS

Numerous types of plastics can be used to produce semi-precision bearings.
Environment compatibility determines the variety. Acetal (Delrin) is the most common for the rings with balls of either acetal or stainless steel. Other Materials such as PEEK, PPS, Vespel, Nylon and many others can be used for the rings.

Lightly loaded low RPM applications requiring corrosion resistance, non-magnetic/non-metallic and or lightweight bearings may benefit from a plastic ball bearing. Sizes start at 8mm inner diameter. Minimum order requirements may apply.

CERAMIC MATERIAL PROPERTIES

Mechanical SI/Metric Si3N4 ZrO2
Density gm/cc (lb/ft3) 3.29 6
Porosity % (%) 0 0
Color black ivory
Flexural Strength MPa (lb/in2x103) 830 900
Elastic Modulus GPa (lb/in2x106) 310 200
Shear Modulus GPa (lb/in2x106)
Bulk Modulus GPa (lb/in2x106)
Poisson’s Ratio 0.27
Compressive Strength MPa (lb/in2x103)
Hardness Kg/mm2 1580 1300
Fracture Toughness KIC MPa•m1/2 6.1 13
Maximum Use Temperature
(no load)
°C (°F) 1000 1500

 

THERMAL

Thermal SI/Metric Si3N4 ZrO2
Thermal Conductivity W/m•°K (BTU•in/ft2•hr•°F) 30 2
Coefficient of Thermal Expansion 10–6/°C (10–6/°F) 3.3 10.3
Specific Heat J/Kg•°K (Btu/lb•°F)

 

ELECTRICAL

Electrical SI/Metric Si3N4 ZrO2
Dielectric Strength ac-kv/mm (volts/mil)
Dielectric Constant
Dissipation Factor
Loss Tangent
Volume Resistivity ohm•cm >1010

CERAMIC VS. STEEL VS. STAINLESS STEEL

Item Ceramic, Si3N4 52100 Steel 440C
Density .114 lb/in³ 0.282lb/in³ 0.275lb/in³
Service Temp 1300 F 300 F 350 F
CTE 1.56µin/in-°F 6.94µin/in-°F 5.67µin/in-°F
Hardness ~ 76 RC 62 RC 58 RC
Magnetism No Yes YES
Conductivity Non-conductive Conductive Conductive
Corrosion Resistance Excellent Poor Fair

CORROSION RESISTANCE COMPARISON CHART

WATER

MATERIALS 316/304 Stainless Steel 440C Stainless Steel 52100 Chrome Steel
Stream A B NC
Domestic Water A B D
Sea Water A NC D

FOOD

MATERIALS 316/304 Stainless Steel 440C Stainless Steel 52100 Chrome Steel
Food Products A B NC
Fruit & Veg. Juices A B NC
Dairy Products A C NC

DILUTE ACIDS

MATERIALS 316/304 Stainless Steel 440C Stainless Steel 52100 Chrome Steel
HCL NC NC
H2SO4 B NC NC
HNO2 A A NC
Phosphoric B NC NC

ACIDS

MATERIALS 316/304 Stainless Steel 440C Stainless Steel 52100 Chrome Steel
H2SO4 A NC NC
HNO2 NC NC NC
Phosphoric A NC NC
MATERIALS 316/304 Stainless Steel 440C Stainless Steel 52100 Chrome Steel
Industrial Atmospheres B B C
Salt Air A C C
Ammonia A C B
Alkaline Salts B B C

A = excellent, B = good, C = fair, D = poor, NC = Not compatible

CHEMICAL COMPOSITION OF BEARING STEELS

Chrome Steel

Spec C% Si% Mn% P% S% Cr% Mo% Ni N Hard-ness
SAE52100 SUJ2 0.95-1.10 0.15-0.35 0.50max 0.025max 0.025max 1.30-1.60 60-64 HRC

Stainless Steel

Spec C% Si% Mn% P% S% Cr% Mo% Ni N Hard-ness
AISI440C SUS440C 0.95-1.20 1.00 max 1.00 max 0.04 max 0.03 max 16.0-18.0 0.75 max 58-62 HRC
AISI303 SUS303 0.15 max 1.0 max 2.00 max 0.2 max 0.15 min 18.0 – 20.0 0.6 max 9.0 0.1 max 83 HRB
AISI316 SUS316 0.08 max 0.75 max 2.00 max 0.045 max 0.03 max 16.0 -18.0 2.0 -3.0 10.0 -14.0 0.1 max 95 HRB
    AISI 304 AISI 440C SAE 52100
Specific Gravity 7.93 7.8 7.8
Tensile Strength N/mm2 520~600 1900~2000 1680
Elongation % 45~60
Elastic Modulus N/mm2 193000 203000 212000
Hardness HV
HRC
170
3.0
700
60.1
740
61.8
Magnetism Non Magnetic * 1 Magnetic Magnetic