TIMKEN rolling bearings have a speed limit. In general, this speed limit set by the operating temperature or material of the bearing components of the lubricant. Reached the limits of operating temperature, the speed depends on the friction generated heat TIMKEN bearings run (including any external heat), as well as the heat from the bearings.
TIMKEN bearing type and size, internal design, load, lubrication method and cooling conditions, as well as maintain the frame design, accuracy and internal clearance, etc., will affect the speed the ability to determine. TIMKEN Bearing table generally lists the two speeds: the reference speed of the (hot) and the (motion) speed limit, the two speed values depending on the criteria taken into account.
TIMKEN bearing the reference speed
Listed in the table of TIMKEN bearing model (thermal) reference speed is a speed reference value used to determine TIMKEN bearings under conditions of a certain load and lubricant viscosity can be allowed to run speed. Listed in the reference speed value in line with ISO 15312:2003 standard (the standard does not include thrust ball bearings). This ISO standard is developed for oil lubrication, but equally effective grease lubrication.
A given TIMKEN bearing the reference speed represents the speed in certain operating conditions. Speed, bearing the heat generated and distributed from the bearing to the shaft, bearing and lubricant heat balance.
According to the ISO 15312:2003 standard to the reference conditions of this heat balance is: 50 degrees 20 degrees Celsius ambient temperature, bearing temperature is 70 degrees Celsius, TIMKEN bearing a fixed outer ring or bearing measurement point washers; TIMKEN radial bearings: a stable radial load, accounting for the basic static load rating C0; TIMKEN the thrust bearing: a stable axial load, accounting for 2% of the basic static load rating C0; with open bearings for routine clearance
For oil lubricated bearings: lubricant: mineral oil without EP additives, at 70 degrees Celsius when the kinematic viscosity
ν = 12mm2 / s (ISO VG 32) (for TIMKEN radial bearings)
ν = 24mm2 / s (ISO VG 68) for (for TIMKEN thrust roller bearings)
Method of lubrication: oil bath, lubricant reached the middle of the rolling element at the lowest position.
For grease lubricated bearings TIMKEN:
Lubricants: conventional lithium soap grease containing mineral base oil viscosity at 40 ° C from 100 to 200mm2 / s (such as ISO VG 150)
Oil content: about 30% of the free space inside the bearing.
May occur once the temperature peak at the start of the grease lubricated bearings. Therefore, TIMKEN bearings may need to run 10-20 hours before they reach normal operating temperature. Under certain conditions, equal to the reference speed for oil lubrication and grease lubrication. TIMKEN bearing outer ring rotation, it may be necessary to lower the rating.
For some TIMKEN bearings, the speed limit is not the contact surface by the rolling element / bearing raceway, bearing table only provides the speed limit value. These bearings include bearings with contact seals like.
Higher than the reference speed
TIMKEN bearings, if we can reduce the friction that could possibly run a speed higher than the reference speed. The way to reduce friction, lubrication system can accurately measure the lubricant usage, or cooling one of the following ways: using the circulating oil lubrication system, bearing cooling Rib, or the import of cooling airflow
Note that in the case of the above preventive measures, run any higher than the reference speed will cause overheating of the TIMKEN bearings. TIMKEN bearing temperature rise means that the lubricant viscosity is reduced, making the film formation more difficult, resulting in greater friction, so that the temperature is further increased. At the same time bearing running clearance due to an increase in inner temperature decreases, the ultimate consequences will be the bearings are stuck. Any speed increase than the reference speed, the difference is greater than the normal mean temperature of the inner and outer rings. Therefore, usually require the use internal clearance C3, TIMKEN bearings, clearance than the standard value, at the same time it is necessary to more closely observe the temperature distribution within the bearing.
TIMKEN bearing limiting speed
The speed limit is determined by TIMKEN standard. These criteria include shape stability and robustness, bearing cage and the cage guide surface lubricity, rolling the body to withstand the centrifugal and the maneuver force, and other factors of the speed limit. Laboratory testing and practical experience has shown that, TIMKEN the maximum operating speed bearings should be insurmountable; for technical considerations, the other because you want to run the temperature is kept at an acceptable level, the cost involved is very high.
The speed limit value, see TIMKEN bearings Model Form, under a variety of requirements for high-speed applications.
TIMKEN bearings may be listed in the table is higher than the speed run, but to do so must take into account the running accuracy, and to maintain the frame design, lubrication and cooling. There are other factors to consider, such as cage guide surface of lubrication and lubricant shear strength, determined by the base oil and thickener.
For some TIMKEN bearings, due to their speed limit is not determined by the heat of the rolling body / rail contact surface, so the bearing table only lists the speed limit. These bearings the TIMKEN full roller bearings, and TIMKEN bearings with contact seals.
Must remember that if you want to reach a satisfactory state at high speeds, TIMKEN bearings must withstand a minimum load. Reference TIMKEN bearing load on the introduction of the minimum load.
TIMKEN special circumstances
In some applications, there are more important than the speed limit factors to consider.
Low-speed
Very low speeds, the elastic hydrodynamic lubrication film can not be formed in the rolling element and raceway contact surface. In these applications, generally using lubricants containing EP additives.
Swing back and forth
Operating conditions, the direction of rotation TIMKEN bearing does not turn a full circle had been changed. Rotation speed is zero when the rotation Fang Xianggang reverse, so the lubricant fully hydrodynamic lubrication film can not be maintained. In this case, in order to obtain the boundary lubricant film can withstand the load, the use of lubricants containing an effective EP additives is very important. For this back and forth swing set a limit speed or rated speed is not possible, because of its speed limit is not subject to the heat balance, but the decision by the inertia force. In each direction reversal, there will be a danger, that is, the inertia force will glide a small distance to the rolling element and raceway dirt. Allowable acceleration and deceleration depends on the body weight of the rolling element and cage, lubricant type and dose, the running clearance and the bearing load. For example, the configuration of the connecting rod bearing, the rolling element is relatively small, the amount of light pre-load bearing.



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