According to the usage and gear structure of slewing bearings, they can be divided into three types: inner gear type, outer gear type, and gearless type. Each model of slewing bearing has these three types. Double row ball slewing bearings are divided into double-row internal gear slewing bearings, double-row external gear slewing bearings, and double-row gearless slewing bearings. Four point contact ball slewing bearings are also divided into four-point contact ball internal gear slewing bearings, four-point contact ball external gear slewing bearings, and four-point contact ball gearless slewing bearings.
Double-row ball turntables can simultaneously withstand radial forces, axial forces, and overturning moments due to the upper and lower rows of steel balls. They are widely used in large rotating devices such as excavators, cranes, and missile launchers.
To adapt to the different proportions of various torques, the contact angle ranges from very small to 90 degrees. When the diameter of the distribution circle of the steel balls is the same, the total load-bearing capacity of each row of steel balls is proportional to the diameter of the selected steel balls. Therefore, in the case of the same support section height and simultaneous axial and overturning moment bearings, double-row ball bearings can better utilize the section size. The double row ball slewing bearings produced by manufacturers of slewing bearings have first-class mechanical designers and quality engineers who track the production process from design to material selection and processing to ensure product quality.
Four point contact ball slewing bearings are a type of separable bearing. They can withstand bidirectional axial loads and are angle contact ball bearings with inner and outer ring raceways in the shape of a peach section. When there is no load or when a pure radial load is applied, the steel balls and bearing rings present as four-point contact, hence the name. When only a pure axial load is applied, the steel balls and bearing rings become two-point contact, thus able to withstand bidirectional axial loads. Four-point contact ball bearings can also withstand moment loads and have the functions of single-row and double-row angular contact ball bearings. The normal operation of four-point contact ball bearings requires them to form two-point contact. Therefore, they are generally suitable for cases where there are pure axial loads or when axial loads are large under composite loads and they form two-point contact. Four-point contact ball bearings have a high maximum limit speed and are also suitable for high-speed operation.
Four point contact ball bearings are radial single-row angular contact ball bearings, and the raceways are designed to support axial loads acting in two directions. Four point contact ball slewing bearings can withstand radial loads up to a fraction of the axial load. Compared with double-row bearings, four-point contact ball bearings occupy significantly less axial space.
The inner and outer rings of four-point contact ball bearings are made by precise splicing of two half-rings. The curvature radii of the outer or inner ring raceways are very small, so the steel balls and inner and outer rings contact at four "points". This increases the radial load capacity and enables compact dimensions to withstand large bidirectional axial loads. Moreover, it has excellent bidirectional axial limiting ability because its axial clearance is relatively small and its contact angle (usually 35 degrees) is relatively large. Four point contact ball slewing bearings are mostly used in engines because they can withstand large radial and axial loads at high speeds!