Views:1 Author:Site Editor Publish Time: 2021-10-12 Origin:Site
First of all, Let us indicate the situation of Hybrid ceramic ball bearing application. Ceramic material (Si3N4) has the advantages of low density, medium elastic modulus, small thermal expansion coefficient, high hardness, high temperature resistance, corrosion resistance, and non-magnetic. Hybrid ceramic ball bearings with silicon nitride ceramic balls as rolling elements can significantly improve the bearing The contact fatigue life greatly expands the application fields of rolling bearings, and has been widely used in various high-precision, high-speed machine tools, automobiles, racing cars, subways, motors, aero engines, petrochemical machinery, metallurgical machinery and other fields. At present, silicon nitride ceramic balls and Hybird ceramic ball bearings have begun to enter the stage of mass production, especially in the fields of high-speed precision spindle bearings for machine tools and high-temperature and corrosion-resistant bearings.
Why hybrid ceramic ball bearings are used at ultra-high-speed applications? First look at a set of experimental conclusions: the temperature rise of ceramic ball bearings in the low-speed area is not much different from that of all-steel bearings under the condition of no load, but in the high-speed area, the higher the speed High, the greater the temperature difference. When it reaches 48000r/min, the temperature rise of ceramic ball bearings is 7~8 degrees lower than that of all-steel bearings.
Hybrid Ceramic ball bearings have low temperature rise at high speeds: at high speeds, the centrifugal force and gyro torque of the Si3N4 ceramic ball are small, the contact pressure is small, and the sliding friction caused by the gyro torque is small, so there is less heat.
Bearing steel/bearing steel combination and Si3N4 ceramic/bearing steel combination have different resistance to adhesive wear at high speeds. The atomic affinity between bearing steel and bearing steel is stronger, while the affinity between ceramic and bearing steel is much weaker, so the former Glue wear is more likely to occur, which will also cause more heat.
Under the same radial load, the temperature rise of the all-steel bearing is higher than that of the Hybrid ceramic ball bearing when it is operated at the rated speed under the same radial load. However, the temperature rise of the two types of bearings has little change in a certain load range, but when the ceramic ball bearing is thermally balanced , The stable area of temperature rise is larger than that of all-steel bearings, that is to say, ceramic ball bearings can maintain a low temperature rise under the action of large loads at high speeds. Therefore, Hybrid ceramic bearings are under radial load. Time, with excellent high-speed performance.
The longitudinal elastic mold of Si3N ceramics is 50% higher than the longitudinal elastic mold of bearing steel. The use of Hybrid ceramic ball bearings can improve the rigidity of the main shaft. Centrifugal force and gyro torque reduce the pressure and sliding friction of the contact surface, and the temperature rise is lower. This not only improves the high-speed capability of the bearing, but also prolongs the service life of the bearing.
Full Ceramic Bearings are often the answer for extreme environments, such as high temperatures, corrosive chemicals, steam, and hard vacuum. These bearings have both the inner and outer rings in addition to the rolling elements manufactured from ceramic material. Like the balls in hybrid bearings, the rings in full ceramic bearings are typically manufactured from silicon nitride, Si3N4, or zirconia, ZrO2. Retainers in full ceramic bearings are typically made from high-performance plastics such as PEEK or PTFE. Full complement versions are also available.
|Characteristics||Unit||Chrome Steel||Stainless Steel||Nitrogen Enhanced Stainless Steel||Si3N4||ZrO2|
|Expansion Coefficient||x 10-6°C||10,9||10,1||10,1||2,9||10|
|Top Temperature Limit||°C||170||260||500||1000||600|
|Corrosion Resistance||limited||good||very good||very good||good|
|Magnetism||magnetic||magnetic||magnetic||not magnetic||not magnetic|
So we can see here Why hybrid ceramic ball bearings are suitable used at ultra-high-speed applications
1. Low density Due to the low density of ceramic rolling elements and small centrifugal load, it can work at higher speeds and generate less heat.
2. Medium modulus of elasticity The elastic modulus of ceramic balls is higher than that of steel rolling elements, and the dynamic stiffness of the bearing is improved, but too large elastic modulus will reduce the bearing capacity of the bearing due to stress concentration.
3. Small thermal expansion coefficient Small thermal expansion coefficient helps reduce the sensitivity to temperature changes, thereby preventing jamming. For hybrid ceramic ball bearings, the applicable operating speed range is wider.
4. The combination of high hardness and high toughness can obtain better surface roughness, and can prevent external hard particles and impact damage.
5. Good anti-rolling contact fatigue characteristics, this performance is very important to the requirements of bearing rolling elements.