“The china high sealing precision deep groove ball bearings in one of the large valves in the plant have relatively high temperatures and the bearings are always failing, is the grease not the right choice? Is there a high temperature grease recommended? Or are the bearings being used improperly?” .
High-temperature applications, engineers first think of lubrication options, rarely will consider whether bearing steel manufactured bearings to meet the high-temperature applications, because in the minds of many people, bearings are steel, steel is able to withstand very high temperatures, at least the melting point is more than 1,000 degrees Celsius.
In fact, bearings in high-temperature applications can not only consider lubrication, for some extreme high-temperature applications, the first thing should be considered is the impact of the bearing body material.
China high sealing precision deep groove ball bearings are made of bearing steel
Bearing steel is the steel used to make balls, rollers and bearing rings. Bearing steels have high and uniform hardness and wear resistance, as well as high elastic limits. The requirements for the uniformity of the chemical composition of bearing steel, the content and distribution of non-metallic inclusions, and the distribution of carbides are very stringent, making it one of the most demanding steel grades in all steel production.
International Organization for Standardization ISO will be some common bearing steel number into the international standard, the bearing steel is divided into: full hardened bearing steel, surface hardening bearing steel, stainless bearing steel, high temperature bearing steel and so on.
Bearing steel GCr15 is the world’s largest production of bearing steel, from the birth of more than 100 years to date, the main components are basically unchanged, with the progress of science and technology, product quality continues to improve, accounting for more than 80% of the world’s total production of bearing steel, bearing steel, if there is no special instructions, basically means GCr15.
Changes in mechanical properties
China high sealing precision deep groove ball bearings rolling body and inner and outer ring must have enough hardness and cope with fatigue and plastic deformation, enough strength to withstand the load of the equipment, enough stability to control the size of the change in a limited range.
In the high temperature working conditions, the same must achieve hardness, fatigue strength, dimensional stability are to meet the requirements of use, especially hardness.
- Methods and effects of bearing hardening
Hardening: Hardening is the complete hardening of the entire cross-section, which provides good fatigue and wear resistance and is therefore the standard hardening method used for most china high sealing precision deep groove ball bearings.
Induction hardening: Surface induction hardening is used to selectively harden the raceways of a component to minimize rolling contact fatigue, leaving the remainder of the collar unaffected by the process to maintain structural strength.
Surface Hardening: Surface hardening is the hardening of a surface. This method can be used for bearing rings that are subjected to high shock loads that cause structural deformation.
- Heat treatment is used to limit dimensional changes due to metallurgical effects at extreme temperatures
Effect of Tempering Temperature
As the tempering temperature increases, the hardness after tempering will decrease.GCr15 steel tempering temperature exceeds 200 ℃, will enter the first category of tempering brittle zone. Therefore, the tempering temperature of GCr15 steel is generally low-temperature tempering (160-180 ℃), and its working temperature is in the range of -40~130 degrees, which can meet the requirements of general machinery.
This is why most of the china high sealing precision deep groove ball bearings are not recommended to exceed 120 ℃ Use, not recommended to heat to 120 ℃ temperature above the installation of the reason. Above this temperature, there is a risk of annealing the bearing steel to reduce the hardness.
The high-temperature hardness of high-temperature bearing steel is also reduced when the working temperature exceeds the tempering temperature.
China high sealing precision deep groove ball bearings dimensional stability
Rolling bearings will be deformed over time during use, and the deformation will cause the inner ring to expand, which in turn will reduce the interference between the bearing and the shaft, thus causing creep or even running rings.
Why does the bearing deform over time? Bearing deformation is due to heat treatment, the steel residual austenite occurring time-lapse pyrolysis, with the phase transition (from austenite to martensite phase transition), the bearing gradually expand, the size of the larger.
Bearing Temperature and Thermal Stability
The higher the tempering temperature, the better the dimensional stability of the china high sealing precision deep groove ball bearings; the higher the operating temperature of the bearing, the stronger the tendency to participate in austenite pyrolysis, that is, the higher the temperature of the bearing, the more unfavorable to the dimensional stability of the bearing. Therefore, bearings for high temperature applications must undergo dimensional stabilization treatment, such as: supplementary tempering treatment process.
- In the case of uncertain bearing materials, rolling bearings should not be applied more than 120 ℃, (such as considering lubrication, sealing and other components, the use of temperature may be lower).
- In determining the need for high temperature applications, select high temperature bearings made of high temperature bearing steel, or even ceramic silicon nitride, silicon carbide bearings.
- More than the temperature limit value use, rolling bearing also does not immediately fail, but its reliability will be reduced, with the increase of time, the bearing may occur unpredictable failure.