 |
 |
|
Bearing Types
> Radial Bearings >
Preload Information Of Radial Bearings
Bearing moving the world. Browse through the
suppliers of tapered bearings. |
 |
 |
 Bearing Market |
 |
Buyers Guide |
|
Bearing Glossary |
|
Bearing Standards |
|
Bearings Manufacturers |
|
Bearings Trade Leads |
 |
|
|
|
Radial Bearings |
| Types of Radial Bearings | Preload Information | Buying Tips |
| Lubrication Information | Research Papers | Related Articles |
| How Radial Bearing Works | Load Glossary | Industry News |
| Radial Bearings Suppliers | Trade Leads | Trade Fairs & Shows |
Preload Information Of Radial Bearings |
Purpose When
a radial ball bearing is used in a motor, it has "Zero" radial
clearance when an axial load is applied. If there is any radial
clearance, vibration and noise of the balls will occur, and the
stiffness of the ball bearing will be very low. This force that is
applied in the axial direction is known as preload. An optimum preload
should be individually specified for each ball bearing size. If the
Preload is applied excessively, Bearing Fatigue Life will be short and
will increase raceway noise as well. Bearing starting and running torque
will also be high. If the applied Preload is insufficient, fretting
corrosion can occur. This happens as a result of vibration causing the
balls to resonate and abrade on the raceways. Therefore, obtaining the
correct Preload is very important.Optimum Preload Optimum Preload is normally recommended after calculating the optimum operating surface stress at the contact ellipse. The contact ellipse is the area of contact between the ball and raceway that occurs as a result of elastic deformation of both parts under load. Regarding the figure, the contact ellipse area (S) between the ball and raceway is formulated as S = pab (a: the major axis of the contact ellipse area, b: the minor axis of the contact ellipse area). Operating surface stress (P) is given by Q/S, where Q = Ball load or load on the raceway (Perpendicular to the area of contact), and S = Surface area of the contact ellipse. Generally, the unit is shown "MPa" (Kgf / mm2). The aim for the surface stress is below. The following is one of the guidelines for noise life. If the noise life requirement is over 10,000 hours, the Preload can be calculated based on an optimum surface contact stress that does not exceed 800 MPa {80 Kgf/mm2}. For general applications with a noise life requirement between 5,000 and 10,000 hours, the optimum Preload can be calculated using a contact ellipse stress that does not exceed 1000 MPa {100 Kgf/mm2}. For stiffness critical applications requiring an operating noise life of less than 5,000 hours, a surface stress of less than 1500 MPa {150 Kgf/mm2} should be used. A way of looking at the Preload from the Basic Dynamic Load Rating (Cr)
Preload And Stiffness There are two basic methods of Preloading: Solid Preload and Spring Preload. Solid Preload can be obtained by mechanically locking all of the rings in postion while under an axial load. The advantages of this type of design are that the components remain simple and the stiffness is high. The disadvantage is high variation in Preload under temperature variation, and that the Preload can reduce with wear. Spring Preload (or Constant Pressure Preload) can be applied using a coil spring or a spring wave washer, etc. An advantage of Spring Preload is that it maintains consistent Preload with temperature variation.The disadvantages are that the designs are more complex and normally have lower stiffnesses.
|
