Do you know what is Preload?

Normally, bearings are used with a slight internal clearance under operating conditions.

However, in some applications, bearings are given an initial load; this means that the bearings' internal clearance is negative before operation. This is called "preload" and is commonly applied to angular ball bearings and tapered roller bearings

Purpose of preload

The following results are obtained by constant elastic compressive force applied to the contact points of rolling elements and raceway by providing preload.

(1) Bearing's rigidity increases, internal clearance tends not to be produced even when heavy load is applied.

(2) The particular frequency of the bearing increases and is becomes suitable for high-speed rotation.

(3) Shaft runout is suppressed; rotation and position precision are enhanced.

(4) Vibration and noise are controlled.

(5) Sliding of rolling elements by turning, spinning, or pivoting, is controlled and smearing is reduced.

(6) Fretting produced by external vibration is prevented.

Applying excessive preload could result in reduction of life, abnormal heating, or increase in turning torque. You should therefore consider the objectives before determining the amount of preload Preloading methods and amounts

The most common method of applying preload on a bearing is change the relative position of the inner and outer rings of the bearing in the axial direction while applying an axial load between bearings on opposing sides. There are two types of preload: fixed position preload and constant pressure preload.

The basic pattern, purpose and characteristics of bearing preloads are shown in Table 8.12. of NTN Corporation publication CAT. NO. 2202 .

The fixed position preload is effective for positioning the two bearings and also for increasing the rigidity. Due to the use of a spring for the constant pressure preload, the preloading amount can be kept constantly, even when the distance between the two bearings fluctuates under the influence of operating heat and load.