What Is A Four-Point Contact Ball Bearing?

Four-Point Contact Ball Bearings

Four point contact ball bearings is a kind of separated bearing, can also be said to be a set of bearings can bear two-way axial load angular contact ball bearing. Its inner and outer ring raceway is peach type section, when there is no load or pure radial load, the steel ball and the ring presents four point contact, which is also the origin of the name.

Four-Point Contact Ball Bearings

When only pure axial load, the steel ball and the collar becomes two-point contact, can withstand two-way axial load. Four-point contact ball bearing can also withstand moment load, both single-row angular contact ball bearing and double-row angular contact ball bearing function. Four-point contact ball bearings can only form two-point contact to ensure normal operation. So it is generally suitable for those pure axial load or axial load with large synthetic load in two-point contact, four-point contact ball bearing limit speed is high, also suitable for those high-speed operation.

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Four-Point Contact Ball Bearings
Four point contact ball bearings Design.

A, four point contact ball bearing belongs to a radial single row angular contact ball bearing, the design of the raceway is used to support the axial load acting in two directions. Four-point contact ball bearings can withstand radial loads of up to a fraction of the axial load. Compared with double row bearings, four point contact ball bearings take up significantly less axial space.
Since the contact angle of four-point contact ball bearings is 35° or 45°, the inner ring is a laminated inner ring. The inner ring is a collapsed inner ring. This allows a larger number of balls to be packed into the bearing, which gives the bearing a higher load carrying capacity.These four point contact ball bearings are of split design, i.e. the outer ring with ball and cage assembly can be mounted separately from the two inner ring half rings.

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Bearings with a contact angle of 35° require high raceway shoulders, and these bearings with one-piece inner rings cannot be assembled with a reasonable number of balls. Four-point contact ball bearings with split inner ring designs can contain the maximum number of balls, limited only by the thickness of the cage rod.

Typically, there is a three-step assembly procedure.

The cage is inserted into the outer ring, the
the balls are pressed into the cage.
The inner ring halves are inserted from each side. The inner ring is not self-retaining. To prevent the bearing from falling out during transport and handling, the plastic insert is pushed into the hole.
Second, four-point contact ball bearing inner ring (or outer ring) is made of two half-ring precision mating, and its overall periphery (or inner ring) of the groove radius of curvature is very small, so that the steel ball and inner and outer ring in four “points” are in contact, so that both increased radial load capacity, but also a compact size to withstand a large two directional axial load, and has a very good two directional axial limit of capacity This is because its axial clearance is relatively small, while its contact angle (generally taken as 35 °) and relatively large reasons.
Third, the four-point contact ball bearing also allows a very high speed, and the operation is very smooth, its double half-ring and can be removed from the whole set of bearings to install, so four-point contact ball bearings are mostly used in the engine, because it can withstand a large radial load and axial load at higher speeds.
The two inner rings of the four-point contact ball bearing half have deep bottom shoulders. When these four point contact ball bearings are used with S cylindrical roller bearings, the oil flow is increased. In addition, these deep recessed bottoms can be used to hold the puller in place when the four point contact ball bearing is disassembled.

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Four point contact ball bearings Applications:

Four point contact ball bearings are worth considering if design space is limited and axial loads in both directions are high or speeds are high. This may occur in applications such as pumps, retarders, compressors, industrial or automotive transmissions, traction motors or steering columns. The following are some examples of equipment equipped with four-point contact ball bearings.

Screw compressors are used throughout the industry to compress a variety of gases at relatively high pressures. This can be air, corrosive gases, oxygen, refrigerants, etc. The compression process is achieved by the continuous rotation of two helical screws. The differential pressure between the two ends of the screws generates axial forces, which are usually supported by four-point contact ball bearings. The narrow clearance between the two screws and between the screws and the compressor housing requires a rigid bearing arrangement and small axial clearance.

Four-Point Contact Ball Bearings

Turbo reducers convert excessive kinetic energy of the truck into heat. This application requires bearings with high terminal speeds and the ability to accommodate rapid speed changes, which is typical for four-point contact ball bearings.

Multi-phase pumps help to extract oil fields more efficiently than conventional methods. The pump is located on the seabed, increasing the pressure of the upstream oil and gas mixture. The requirements for reliability are therefore very high. Typically four-point contact ball bearings can withstand axial loads.

Wind turbine gearboxes transfer the energy from a very slowly rotating main shaft (approx. 18 r/min) to a generator speed that is about 100 times higher. On the high-speed shaft, helical gears generate the heavy axial loads that need to be carried. A combination of cylindrical roller and four-point contact ball bearings is used.

For railroads, there are two main applications. Gearboxes and traction motors usually use a combination of cylindrical roller bearings and four-point contact ball bearings. The traction motor bearings need to be protected from damage caused by the passage of current. A common solution is to use insulated bearings. For four-point contact ball bearings with locating slots, the inner ring halves should be coated.

Under normal working conditions, this type of bearing can form a contact angle when bearing axial load in any direction, and the steel ball is in contact with the inner and outer raceways at one point to avoid large sliding friction in the contact area. Therefore, the bearing should not be subjected to radial forces and loads.

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