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Four-point contact ball bearings

Increasing the reliability and productivity of your mining and mineral processing machinery can be a constant challenge. The NEWORLD four-point contact ball bearing solution for transmission, steering brake and clutch applications makes it easier to face that challenge.
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Product Description

Product Description

A four-point contact ball bearing can accommodate axial loads in both directions, in combination with radial loads up to a certain level, and provides a very tight axial shaft position tolerance. The bearing also saves space, because it can be seen as the combination of two single row angular contact ball bearings into one. Therefore, it is an excellent choice in applications such as industrial gearboxes, locomotive drives and compressors.


Four-point contact ball bearings.jpg

Bearing design

The NEWORLD standard assortment of four-point contact ball bearings (fig. 1) includes:

●   Bearings in the QJ 2 and QJ 3 series

●   Some sizes in the QJ 10 and QJ 12 series

●   Bearings with locating slots

     Four-point contact ball bearings can be supplied with two locating slots in the outer ring 

     (designation suffix N2, fig. 2):

●  preventing the bearing from turning

●  positioned 180° apart


Four-point contact ball bearings.jpg


Standard NEWORLD four-point contact ball bearings – also called QJ bearings (fig. 2) – consist of 

● a single piece outer ring

● a radially split inner ring

● a ball set and an outer ring guided cage


Theoretically, one ball has four different contact points to the rings (fig. 3). This happens if only radial load is applied. This load case may not occur in real applications. Most relevant are load cases with pure axial load (fig. 4a); in these cases only two contact points in diagonal position transfer load. If the axial load changes its direction, the two contact points move to the opposite position. This explains why this bearing type can accommodate axial loads in both directions.


There are also applications with combined loads, but dominating axial load (fig. 4b). If the same functionality should be reached with single row angular contact ball bearings, two identical bearings in a back-to-back or face-to-face arrangement need to be matched.

Fig. 5 shows a summary of the main characteristics of NEWORLD QJ series bearings.


Four-point contact ball bearings.png

Four-point contact ball bearings.jpgFour-point contact ball bearings.jpg



Bearing features

Features of four-point contact ball bearings


●  Improved brass cage

●  P6 running accuracy and P6 dimensional accuracy

●  High degree of stiffness

●  Manufactured from ultra-clean steel

●  Unique heat treatment

●  Unique raceway-shoulder transition

●  High performance PEEK cage

●  Unique inner ring design


User Benefits

●  Extended bearing service life

●  Accommodates heavier axial loads

●  Reduced lubricant consumption

●  Reduced noise and vibration levels

●  Reduced heat generated by the bearing


Performance Benefits

●  Radial and axial loads are supported in both directions

●  Can be used in transmissions located next to a bevel gear

●  More compact than competing designs, such as double row angular contact ball bearings

●  Inner and outer rings can be mounted individually Custom designs available


Cages

Cages


NEWORLD four-point contact ball bearings as standard are fitted either with a machined window-type brass cage (designation suffix MA) or an injection moulded window-type cage of polyetheretherketone (PEEK) (designation suffix PHAS). Both cages are outer ring guided. This gives a very good guidance, enabling to increase the speed limit. The very specific design of the symmetric cage enables to incorporate a maximum number of large balls.


NEWORLD four-point contact ball bearings are fitted with one of the cages shown in table 2


Cages for Four-point contact ball bearing.png


Load, basic rating life and speed ratings

The very compact design of a four-point contact ball bearing may lead to the concern that the load rating of a matched set of two single-row angular contact ball bearings might be comparatively higher. Fig. 6 shows a comparison of load ratings of QJ bearings in the 2 and 3 diameter series and corresponding matched sets of angular contact ball bearings in the 72 B and 73 B series respectively. 


It shows that there is almost no difference between the load carrying capacity of a four-point contact ball bearing compared with a corresponding matched set of angular contact ball bearings. All in all it appears that 50 % of axial space can be saved with a four-point contact ball bearing.


However, one should also consider basic rating life. The key factor is the equivalent dynamic load, calculated from the loads as:

P = 0,60×Fr + 1,07×Fa

for a four-point contact ball bearing (contact angle 35°)

P = 0,57×Fr + 0,93×Fa

for a matched set of angular contact ball bearings (contact angle 40°)


It is clear that the equivalent dynamic load for the four-point contact ball bearing will be higher, mainly due to the lower contact angle, but the resulting lower basic rating life is largely balanced by saving space in the design. 


Fig. 7 shows a comparison of limiting speeds between bearings in the QJ 2 and QJ 3 series versus matched sets of bearings in the 72 B and 73 B series. It clearly shows an approximate 70 % higher speed rating. This can be explained by the lower contact angle (35° versus 40°), high-quality cage material (solid brass or PEEK), an outer ring shoulder guided cage and special lubrication cage pockets.


Design of adjacent parts In many applications a four-point contact ball bearing is combined with a radial bearing such as a cylindrical roller bearing. Here, it is crucial that the four-point contact ball bearing only takes axial load.


Therefore, the outer ring of the four-point contact ball bearing should not be clamped axially, nor radially, but mounted with radial clearance (a gap of 1 to 2 mm) in the housing (fig. 8). Otherwise the outer ring cannot compensate for thermal movements, which will cause unwanted additional force in the bearing. 


To avoid rotation of the outer ring, most bearings are supplied with two locating slots in the outer ring. This allows connection of the outer ring and housing with a pin (fig. 8). If axial clamping of the outer ring cannot be avoided, the outer ring must be at least carefully centred during mounting. Be aware that the two inner ring halves always need to be clamped axially.


Four-point contact ball bearings.png

Four-point contact ball bearings.jpg



Application

Applications


If the design space is limited, heavy axial loads in both directions occur or speeds are high, four-point contact ball bearings are worth considering. Such conditions might occur in applications such as 


● Compressors

● Industrial transmissions

● Railway drive systems

● Automotive drive systems

● Pumps

● Retarders

● Compressors

● Industrial or automotive gearboxes

● Traction motors or steering columns


Here are some examples of equipment fitted with four-point contact ball bearings:


Screw compressors (fig. 9a) are used throughout the industry to compress various gases at relatively high pressure. This can be air, aggressive gases, oxygen, refrigerants and others. The compression process is realized by continuous rotation of two helical screws. The differential pressure between both screw ends causes axial forces that are often accommodated by four-point contact ball bearings. The narrow gap between the two screws, and between screws and the compressor housing, requests stiff bearing arrangements and small axial clearances.

Four-point contact ball bearings.jpg


Turbo retarders (fig. 9b) convert excessive kinetic energy of trucks into heat. This application requires bearings with high limiting speeds and the ability to accommodate rapid speed changes, a typical application for four-point contact ball bearings.

Four-point contact ball bearings.jpg


Multi-phase pumps (fig. 9c) help to exploit oil fields more effectively than what is possible with conventional methods. The pumps are located at the bottom of the sea, and increase the pressure of the Technology upstream oil gas mixture. Therefore the requirements on reliability are extremely high. Typically four-point contact ball bearings accommodate the axial loads.

Four-point contact ball bearings.jpg


Wind turbine gearboxes (fig. 9d) transfer energy of the very slow rotating main shaft (some 18 r/min) to a generator speed that is about

100 times higher. On the high speed shaft, helical gears cause heavy axial loads that need to be accommodated. A combination of cylindrical roller and four-point contact ball bearings is used.


Four-point contact ball bearings.jpg


For railway (fig. 9e) there are two main applications. Gearboxes and traction motors often incorporate a combination of cylindrical roller

and four-point contact ball bearings. Traction motor bearings need to be protected from damage occurring due to current passage. A

common solution is the use of insulated bearings (INSOCOAT).

For four-point contact ball bearings with locating slots, the inner ring halves are to be coated

Four-point contact ball bearings.jpg


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