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 |
