Four-point Contact Ball Bearings

Detail Introduction :

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

When there is only pure axial load, the steel ball and the collar become two-point contact, can bear two-way axial load. Four-point contact ball bearings have a recessed shoulder on both inner ring halves, which will effectively improve oil flow when the bearings are used in combination with SKF cylindrical roller bearings, in addition, the use of these recesses is very convenient for disassembly.

Therefore, Four-point contact ball bearings have many features that other types of bearings do not have, and can be used to great advantage in practical applications.

Main features of four-point contact ball bearing.

1.Four-point contact ball bearings are separable type structure, single bearing can replace the front combination or back combination of angular contact ball bearings.
2.Can bear radial load, two-way axial load, can limit the axial displacement in two directions, but than the current specifications of the double-row angular contact ball bearings occupy less axial space.
3.Four-point contact ball bearing compared with other ball bearings, when the radial clearance is the same, the axial clearance is smaller, the limit speed is higher.
4.Four-point contact ball bearings are suitable for bearing pure axial load or axial load mainly axial, radial combined load. Due to the double half inner ring (or outer ring), the number of installed balls increases, with a larger carrying capacity.  
5. In normal working condition, this kind of bearing bear any direction of the axial load, can form a contact angle, steel ball and inner and outer raceway contact in a point, avoid contact area occurs big sliding friction. Therefore, the bearing is not suitable for radial force-based and load.

The force characteristics of Skf's four-point contact ball bearings are significantly different from other bearings, and the following will provide you with a detailed analysis.

The force characteristics of four-point contact ball bearings.

Four-point contact ball bearing is a kind of radial single row angular contact ball bearing, the design of the raceway is used to support the axial load in two directions.Four-point contact ball bearing can bear up to a few percent of the axial load of the radial load. Four-point contact ball bearing and double row bearing, compared with the occupied axial space will be significantly reduced.

The contact angle of four-point contact ball bearing is 35° or 45°, and the inner ring is a collocated inner ring, which can allow a larger number of balls to be loaded into the bearing, which can give the bearing a higher load carrying capacity. This kind of four-point contact ball bearing is separated design, that is, the outer ring with ball and cage assembly can be mounted separately with two inner ring half rings.

The inner ring (or outer ring) of Four-point contact ball bearing is made of two half-rings precisely, and its overall periphery (or inner ring) of the radius of curvature is very small, so that the steel ball and the inner and outer ring in four "points" are in contact, so that not only increases the radial load capacity, but also with compact size to withstand the load capacity. And at the same time can be compact size to bear a large two directional axial load, and has a good two directional axial limit capacity, this is because its axial clearance is relatively small, and its contact angle (generally taken as 35 °) and relatively large reasons.

Four-point contact ball bearing's allowable speed is also very high, and the operation is very smooth, its double half-ring and can be taken off 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.

Half of the inner ring of Four-point contact ball bearing is with deep bottom shoulder (fig), when this Four-point contact ball bearing is used with SKF cylindrical roller bearing, it will increase the oil flow. In addition, these deep recessed bottoms can be used to hold the puller in place when the four point contact ball bearing is disassembled.

Based on the above features, four-point contact ball bearings are widely used in various industries, especially in some high-speed operation occasions, four-point contact ball bearings can play a strong advantage.

The main applications of four-point contact ball bearings.

1.Four-point contact ball bearings can withstand moment loads, both single-row angular contact ball bearings and double-row angular contact ball bearings.
2. Four-point contact ball bearings only form two-point contact to ensure normal operation, so generally applicable to those pure axial load or load large synthetic load is two-point contact occasions.
3. Four-point contact ball bearing high limit speed, also suitable for those high-speed operation occasions.

Skf bearing is the world's leading bearing, in the industry has always been in the leading level, skf in adhere to the basis of high-quality production, unremitting scientific research and innovation, every year a large amount of money invested in research and development, for the bearing industry is constantly contributing to a strong innovative capacity, for the majority of customers to improve the quality of equipment has made outstanding contributions.

The following is a detailed description of Four-point contact ball bearings.

1.Four-point contact ball bearings Designs and variants

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

fig. 1

Bearings in the QJ 2 and QJ 3 series
Some sizes in the QJ 10 and QJ 12 series

SKF Explorer bearings

SKF Explorer rolling bearings accommodate higher load levels and provide extended service life. Optimized internal geometry reduces friction, wear and heat generation, allowing heavier loads to be accommodated. Advanced surface finish reduces friction and enhances lubricating conditions.

Benefits of using SKF Explorer bearings include:

1.significantly extended service life
2.increased uptime and productivity
3.extended lubricant life
4.reduced sensitivity to misalignment
5.reduced noise and vibration
6.enabling downsized applications
7.SKF Explorer bearings

Four-point contact ball bearings：
Four-point contact ball bearings can be supplied with two locating slots in the outer ring (designation suffix N2, fig. 2):

fig. 2

Preventing the bearing from turning
Positioned 180° apart

The dimensions and tolerances of the locating slots are in accordance with ISO 20515 and are listed in table 1.

table 1

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

2、Four-point contact ball bearings Design considerations

Used as a thrust bearing
Four-point contact ball bearings are often used as entirely thrust bearings, together with a radial bearing. When used in this way, the four-point contact ball bearing should be mounted with radial clearance in the housing (fig. 1).

in combination with a cylindrical roller bearing:
the radial internal clearance of the cylindrical roller bearing should be smaller than the theoretical radial internal clearance of the four-point contact ball bearing after both have been mounted
the theoretical radial clearance can be calculated from:
Cr = 0,7 Ca
where
Cr theoretical radial internal clearance
Ca axial internal clearance (table 1)

the outer ring of the four-point contact ball bearing must be able to accommodate thermal 

movements Therefore, it should not be clamped axially, but a small gap should be maintained between the outer ring and the cover flange. bearings with locating slots should be used (fig. 1) to prevent the outer ring from turning If clamping the outer ring cannot be avoided, the outer ring must be carefully centred during mounting.

Load ratio
For proper functionality, the balls should contact only one inner ring raceway and the opposite side of the outer ring raceway. This is the case when the load ratio is:

Fa/Fr ≥ 1,27 for bearings in the QJ 2, QJ 3 and QJ 10 series
Fa/Fr ≥ 1,78 for bearings in the QJ 12 series
A load ratio that is smaller than recommended can reduce bearing service life.

三、Four-point contact ball bearings Temperature limits
The permissible operating temperature for four-point contact ball bearings can be limited by:

1.The dimensional stability of the bearing rings and balls
2.The cage
3.The lubricant.

Where temperatures outside the permissible range are expected, contact SKF.

Bearing rings and balls
The bearings are heat stabilized up to at least 150 °C (300 °F).

Cages
Steel, brass or PEEK cages can be used at the same operating temperatures as the bearing rings and balls.

四：Four-point contact ball bearings Permissible speed
The limiting speed listed in the product table is a mechanical limit that should not be exceeded unless the bearing design and the application are adapted for higher speeds.

SKF recommends oil lubrication for bearings with a ring centred cage (designation suffix MA or PHAS). When these bearings are grease lubricated, the ndm value is limited to 250 000 mm/min.

A Complete Guide to Four-point Contact Ball Bearings.
Bearings are the basis for the development of modern industrial industry, skf is the industry's leading bearing manufacturer, skf bearings have gained remarkable achievements, Four-point contact ball bearings have very good applications.
The following will provide you with a detailed introduction to some common questions and answers about four-point contact ball bearings.

1. What are Four-point contact ball bearings?
Four-point contact ball bearings are radial single row angular contact ball bearings, a kind of separation bearings, but also a set of angular contact ball bearings that can bear two-way axial load.
When the bearing also bear radial load and axial load, rolling body (steel ball) and outer ring contact force point and rolling body (steel ball) and inner ring contact force point of the line, and bearing the radial vertical line is a certain angle, such bearings called angular contact ball bearings.
Can bear radial load and axial a directional load bearing called single row to the heart angular contact ball bearing (rolling body for steel ball). This kind of bearing rolling body (steel ball) only up and down two force points.
Four-point contact ball bearings can withstand radial load and two-way axial load, when the bearing with different directions of axial load, the role of the rolling body on the force point is also different. That is, when bearing a direction of axial load, there are two up and down force points, when bearing another direction of axial load, there are two force points different from the previous two force points. In the same rolling body with different forces, there are different points of force. In layman's terms, these stress points add up to four, so it is called four-point angular contact ball bearing.

2.What are the advantages of four-point contact ball bearings?
Four-point contact ball bearings are single row angular contact ball bearings, so they require much less space in the axial direction than double row designs. The bearings consist of a solid outer ring, a split inner ring and a ball and cage assembly with brass or polyamide cage. The two-piece inner ring can accommodate a large number of balls. The inner ring halves are matched to specific bearings and are not interchangeable with other bearings of the same size. The outer ring with ball and cage assembly can be mounted separately from the two inner ring halves, the main advantages of which are shown below.
1. Simple force distribution and clear force analysis .
2. More flexible than other compact bearings. 
3. Permanent fatigue resistance and long service life.
4. Maintenance and repair and technical level of relatively simple its characteristics is the ball is very large, inside and outside the collar thickness and height is very large, thick skin, arbitrarily able to bear several hundred tons of bearing. In order to strengthen the protection lubrication system, extend the service life of the bearing, can improve the version.
5.Four-point contact ball bearings have the advantage of flexible application of a variety of equipment, adaptability, through the double row of ball bearings and ball ball combination bearings of the improved version, can be capable of very pair of working conditions.
6.Four-point contact ball bearings are the bearings of choice for high-speed, high-precision, low-noise precision bearings.

3.What is the difference between angular contact bearings and Four-point contact ball bearings?
Angular contact ball bearings limit speed is higher, can simultaneously withstand radial load and axial load, can also withstand pure axial load, its axial load capacity by the contact angle decision, and with the contact angle increases and increases
The defect of single row angular contact ball bearing is that it can only bear axial load in one direction. In order to make up for the defect, can become subject to two-way axial load, you need at least two sets of single-row angular contact ball bearings, back-to-back or face-to-face combination together, or use double-row angular contact ball bearings, in order to achieve the effect of being able to withstand two-way axial load. But then there is another problem, that is, two bearings together or double-row bearings, it requires a larger design space, so the emergence of Four-point contact ball bearings, and save space, but also to solve the problem of two-way axial load.
Four-point angular contact ball bearings can withstand radial load and two-way axial load: when bearing an axial load in one direction, there are two upper and lower force points, when bearing an axial load in another direction, there are two force points different from the previous two force points. In layman's terms, these bearing points add up to four, can solve the two-way axial load problem.

4. What is the difference between angular contact ball bearing and deep groove ball bearing?
1.The construction field is not the same
Deep groove ball bearing outer section on both sides of the double shoulder, and angular contact ball bearings are widely single shoulder; deep groove ball bearing outer section refractive index and angular contact ball is not the same, the latter one usually more than the previous one; deep groove ball bearing external section parts and angular contact ball bearing external section parts are not the same, other parts, its actual value is angular contact ball bearing design scheme to be considered, and the contact angle of the degree. The actual value is considered in the design of angular contact ball bearings, and is related to the degree of contact angle.
2. Different use
The main use of the two is different, deep groove ball bearings are suitable for bearing radial force, smaller axial force, shaft radial synergy load and torque load, while angular contact ball bearings can bear a single radial load, a large axial load (with the contact angle is different), double matching (with the matching method is different and different) can bear double axial load and torque load. Deep groove ball bearings and angular contact ball bearings have different limiting speed ratios, under the same specification, the limiting speed ratio of angular contact ball bearings is higher than that of deep groove ball bearings.

5. What are the main applications of Four-point contact ball bearings?
Four-point contact ball bearings are a single row angular contact ball bearings with raceways designed to withstand axial loads in both directions. The contact angle can be 30 degrees, 35 degrees, 45 degrees, the inner ring can be divided into two pieces, can be loaded with a larger number of purposes of the ball, therefore has a larger bearing capacity. The bearings are separable, i.e. the two pieces of the inner ring and the outer ring with ball and cage assembly can be installed separately. The four-point contact ball turntable bearing is compact, light in weight, and the steel ball is in contact with the circular raceway at four points, which can simultaneously withstand axial force, radial force and overturning moment, and has strong dynamic load capacity.
Applicable working conditions: the load is generally below 100T, you can choose single-row four-point contact ball bearings, double-row ball contact ball bearings, ball-bead combination bearings. Can use the whole cage, segment cage to improve stability and service life, speed can be appropriately increased to 30rpm-120rpm. precision level is best to control.
At present, the common four-point contact ball bearings are excavator bearings, truck crane bearings, crane bearings, crawler crane bearings, turret bearings, CT machine bearings, blowing machine bearings, filling machine bearings, turntable bearings, klink crane bearings, etc.

6.The relationship between load direction and bearing selection
The choice of bearings is also related to the direction of load, pure radial load can be used deep groove ball bearings or cylindrical roller bearings, thrust ball bearings are only suitable to withstand a moderate amount of pure axial load, one-way thrust ball bearings can only withstand a direction of axial load, two-way thrust ball bearings and two-way thrust angular contact bearings can withstand two directions of axial load. When bearing radial and axial joint load, generally applicable angular contact ball bearings or tapered roller bearings, Four-point contact ball bearings and two-way thrust angular contact ball bearings can withstand two directions to the axial load for the advantage of the joint load.

The main feature of the joint load is the bearing axial load capacity depends on the contact angle α, the larger the angle the more suitable for axial load. Axial load coefficient Y (see bearing size table) with the contact angle increases and decreases. Deep groove ball bearing contact angle and axial load capacity and radial clearance. Angular contact ball bearings and tapered roller bearings can only withstand single direction axial load. If the direction of the load needs to change, the opposite direction of the bearing should be arranged to bear the axial load.

When the joint load in the axial load is larger, thrust bearing only used to bear the axial load and radial load has nothing to do with. When a suitable single row to the heart of the ball bearing or four-point contact ball bearing to bear the axial load, its outer ring and seat hole must have radial clearance.

7.Four-point contact ball bearings mounting method
Four-point contact ball bearing installation than deep groove ball bearing complex, more for the pair installation, and need to use preload. Well installed, the host work accuracy, bearing life greatly improved; otherwise, not only the accuracy can not meet the requirements, life will also be affected.
Four-point contact ball bearing installation form, there are back-to-back, face-to-face and tandem arrangement of three. Back-to-back (two bearings of the wide end face relative) installation, bearing contact angle line along the direction of the rotary axis diffusion, can increase its radial and axial support angle rigidity, resistance to deformation is the largest; face to face (two bearings of the narrow end face relative) installation, bearing contact angle line towards the direction of the rotary axis convergence, its ground bearing angle rigidity is smaller. As the inner ring of the bearing extends out of the outer ring, when the outer ring of the two bearings are pressed together, the original clearance of the outer ring is eliminated, which can increase the preload of the bearing; tandem arrangement (two bearings with wide end faces in one direction) when installed, the contact angle line of the bearing is the same and parallel, which can make the two bearings share the working load in the same direction. But when using this installation form, in order to ensure the axial stability of the installation, two pairs of tandem arrangement of bearings must be installed at both ends of the shaft opposite.

8.What is the preload of Four-point contact ball bearings
According to the application, it is necessary to add positive or negative working clearance in the bearing configuration, in most applications, the working clearance should be positive, that is, in operation, the bearing should have residual play. In many cases, such as machine tool spindle bearings, automobile axle rotation on its pinion bearings, small motor bearing configuration or for swinging motion bearing configuration, need negative working clearance, that is, preload, to improve the rigidity of the bearing configuration or improve the running accuracy.

Pre-load can be by grinding bearing in a collar end face, or with two different thickness of the spacer in a pair of bearings between the inner and outer ring, the bearing clamped together, so that the steel ball and raceway close contact and get.

The size of the preload has a great impact on the bearing life, according to the relevant information, when the bearing assembly has 0.012mm interference, the service life is reduced by 38%, with 0.016mm interference, the service life is reduced by 50%; when the bearing assembly has 0.004mm clearance, the service life is significantly reduced, with 0.008mm clearance, the service life is reduced by 70%. Therefore, it is very important to make a reasonable choice of the size of the preload. Generally, a small preload should be used for high speed, and a large preload should be used for low speed. At the same time, the preload should be slightly greater than or equal to the axial working load.
 

Bearings Model: