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speed limit

speed limit

2022-05-27

Both of these rated speeds are warning values rather than prohibitive values, but approaching either limit means that a more in-depth analysis of the operating conditions is required.


For bearings with contact seals, the reference speed is not listed in the data sheet. Usually, the limiting speed determines the maximum speed of these bearings.


Approximate thermal limiting speed based on ISO standard conditions

The reference speeds listed in the product table are based on the WXING friction model and are derived from the thermal balance under ISO 15312 standardized operating and cooling conditions. Its main purpose is to quickly assess the rotational speed capability of the bearing. You can also use it to estimate the thermal limit speed:


The ISO reference speed is only valid for open bearings under the following operating conditions:


Predefined reference heat dissipation values

light load

Radial load P = 0.05 C0 for radial bearings

Axial load P = 0.02 C0 thrust bearing

The nominal temperature rise is 50 °C (90 °F) higher than the standard ambient temperature of 20 °C (70 °F)

Oil lubrication with mineral oil without EP additives

ISO VG32 for radial bearings

ISO VG68 for thrust bearings

clean condition

Sufficient working clearance (select initial internal clearance)

Horizontal shaft, rotating inner ring and stationary outer ring

ISO standards do not provide reference conditions for sealed bearings.


The ISO standard for oil lubrication also applies to grease lubrication, as long as it is a mineral oil based lithium grease with a viscosity between 100 and 200 mm²/s. However, grease-lubricated bearings may reach a certain temperature peak at initial start-up and reach a steady-state operating temperature after a run-in period.


Adjusted reference speed

The ISO reference speed applies to a standardized set of operating conditions, including standardized heat dissipation. Therefore, WXING recommends that the actual load and lubricant viscosity of the application be taken into account when calculating the adjusted reference speed. You can use the WXING bearing selection to perform this calculation. However, this reference RPM adjustment does not include data related to your application's actual heat dissipation, so it is recommended to take a conservative approach to the results. To include the effects of heat dissipation, a detailed thermal analysis is required.


Mechanical speed limit

Limit speeds in product tables are the maximum speeds that should not be exceeded for standard bearing types, unless the bearing design and application can accommodate higher speeds.


The limiting speed (lubrication) can only be reached when the bearings are properly lubricated. When the speed is close to the limit speed of the bearing, oil lubrication is required.


The limit speed depends on:


The stability or strength of the cage structure

Lubrication of cage guide surfaces

Centrifugal and rotational forces acting on rolling elements

Other speed limiting factors such as seals and lubricants for sealed bearings

Note

Partially open ball bearings have very low friction and the reference speed may be higher than the limit speed. Do not use only mechanical RPM limits. At the same time, the adjusted reference speed is calculated. The lower of the two sets of speed limits.


Speed above reference speed or limit speed

Bearings can run above their reference speed, adjusted reference speed, or even limit speed. Until then, do a detailed thermal analysis and take any further action that may be required, such as using a special cage type or considering high-precision bearings. For handling of the effects of increased RPM, please refer to the following options:


Control the rise in bearing temperature with additional cooling.

Make up for any reduction in bearing play due to increased bearing temperature.

Modify the housing fit tolerance option to ensure that the increase in bearing temperature does not impair the axial displacement of the floating end bearing outer ring.

Modify the tolerance class of the bearing and the geometric accuracy of the shaft and housing to ensure that it is sufficient to avoid excessive vibration.

Consider using cage alternatives that can accommodate higher speeds, especially when approaching or exceeding the limit speed.

Make sure the lubricant and lubrication method used is compatible with the higher operating temperature and cage type.

See if the relubrication interval is still acceptable, especially for grease lubricated bearings. Oil lubrication may be required.


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