ITS Technology Knowledge: New Type Ball Roller Bearing

New type ball roller bearing and comparison of bearing structure for double shaft gearbox and disadvantages of ball bearing.

 

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Abstract: a new type of ball roller bearing is introduced, which combines the advantages of ball bearing and roller bearing. Under the same load, the ball roller bearing occupies less space, has lighter weight and lower friction; In the same structure space, the ball roller bearing has higher bearing capacity, larger grease loading space and better sealing. The development and application prospect of ball roller bearing are also prospected.

 

Key words: rolling bearing; ball roller bearing; structure; design

 

1. New type ball roller bearing

The ball bearing invented more than 100 years ago is still the most produced one of all bearing types. At present, the world produces about 7 billion sets every year. Although roller bearing has high radial bearing capacity, the problem is that it occupies more space than ball bearing. An effective solution is to combine the advantages of ball bearing and roller bearing to form a new type of bearing))) ball roller bearing (kugel rollen lager), see Fig. 1.

 

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Fig. 1 new type ball roller bearing integrating advantages of roller bearing and ball bearing

 

In order to compare with ball bearing, tapered roller bearing and needle roller bearing, a / virtual 0 double shaft gearbox is purposefully designed (Fig. 2). The shaft 1 is fixed supported by a set of ball bearings, and a roller assembly is used as a floating support. The shaft 2 is supported by two sets of identical tapered roller bearings, which can withstand two-way axial force. Of course, other assembled supports can also be selected, but the axial clearance needs to be adjusted to ensure the best function.

 

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Fig. 2 dual shaft gearbox using conventional rolling bearings

 

2. Comparison of bearing structure for double shaft gearbox

It can be clearly seen from the supporting bearing structure that the roller of the tapered roller bearing is guided by the end face of the inner ring flange, and the flange bears the axial force. Therefore, the rolling of the roller will cause sliding friction at the flange. From the perspective of friction, tapered roller bearing is also a hybrid bearing. The bearing has high radial and axial bearing capacity: the load weight ratio of 32007 tapered roller bearing (Fig. 2) in the gearbox is 223kN / kg. The bearing with an outer diameter of 62mm cannot bear any larger radial load. However, the weakness of tapered roller bearing is its large structural width and large friction.

 

From the structure of the floating / fixed bearing of shaft 1, it can be seen that the roller assembly is used as a floating bearing, and the radial bearing capacity is small, which may be caused by integrating the inner ring raceway into the shaft and using a thin chip free machined (stamped) outer ring. The load weight ratio is very high, reaching 478kN / kg. However, the cylindrical roller assembly can only bear radial loads. The roller assembly is a variation of the needle roller family, so it is a technically mature and absolutely economical choice in pure radial support. The maximum outer diameter of 6207 ball bearing (Fig. 2) used as fixed bearing is 72mm, and the load weight ratio is the lowest, only 93kn / kg. However, the ball bearing can bear radial and axial loads.

 

3. Disadvantages of ball bearing

Eccentric assembly (Fig. 3) can make the bearing ring of deep groove free of weak links such as ball mounting notches. In addition, the deeper channel can improve the axial bearing capacity. During assembly, the ball filling amount will be limited by the sickle shaped space between the ferrules. Only 70% of the ball width is used. This means that 30% of the ball width occupies the axial structure space and increases the weight.

 

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Fig. 3 ball bearing: ball loading and width utilization

 

When the load is small, the contact area is point contact. The contact ellipse is small and the surface contact pressure is increased due to poor adhesion. Therefore, the surface contact pressure of the ball bearing is greater than that of the linear contact roller bearing.

 

It is found that the higher the load, the wider the wear band. The spin axis of the ball does not change under axial load. Of course, if a non-load region is formed in the bearing under the radial load, the change of the spin axis of the ball is irregular at each revolution.

 

4. Solution: ball roller bearing

This so-called ball roller bearing has been developed in order to overcome the above-mentioned disadvantages and make use of the advantages of the ball bearing and the roller bearing at the same time. By cutting off the non-loaded / meat 0 on the left and right sides of the ball, each accounting for 15% of the ball diameter (Fig. 4), the ball was subjected to / weight loss 0. The bearing ring can thus be narrowed by 20% of the ball diameter. The rolling elements are guided by a newly developed cage. This guide can correct the rolling elements when starting operation at zero load and zero speed. The bottom of the cage pocket shall be designed so that the bearing ball roller related to the pressure angle can be automatically adjusted.

 

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Fig. 4 ball roller bearing: ball loading and width utilization

 

5. Advantages of ball roller bearing

The ball loading capacity of ball roller bearing is larger than that of ball bearing. Since the ball roller is narrow (Fig. 4), the basic model 6207 bearing can be equipped with 11 ball rollers instead of 9 balls. In addition, the most wonderful thing is that the ball rollers can be eccentrically assembled and installed by rotating 90B. When the inner and outer rings are centered, the ball roller can rotate along its running direction. More rolling elements mean higher bearing capacity. Since the width of the ball roller is fully utilized, the bearing width is reduced, usually from 17mm to 13.5mm (20%). The bearing weight is also reduced by 20% due to the reduced width. Fig. 5 is an exploded view of the new ball roller bearing.

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Fig. 5 exploded view of new ball roller bearing

 

The point contact of the ball bearing can cause high surface pressure. The change of the logarithmic profile of the ball roller contact direction also helps to improve the load capacity. Although the contact area is also very narrow (small radius), the logarithmic profile of the surface of the ball roller can avoid the edge pressure of the axial edge area (large radius) of the ball roller. A lower surface contact pressure will produce a wider contact ellipse even at small and medium loads. Therefore, the ball roller can be designed in a logarithmic profile. Since the rotation axis is always perpendicular to the changing pressure (angle) line, if the axial / radial load ratio and pressure angle are unchanged, the tightness will not change. But the degree of adhesion varies with the load. The ball roller can rotate around its axis optimally with its special mass distribution. Since the ball roller bearing retains the deep groove of the ball bearing, it has high axial bearing capacity. This allows a smaller structural space to have a larger bearing capacity.

 

KXR type, such as KXR207 single row ball roller bearing, has the following advantages compared with ball bearings of the same size:

 

#When the outer diameter and the inner diameter are the same, the bearing capacity is larger and the bearing is narrower.

 

#Under the same width, the bearing capacity is higher, the grease filling space is larger, and the sealing is better.

 

#When the power is the same, the radial dimension of the bearing becomes smaller and the width becomes narrower.

 

6. Instead of tapered roller bearing

In tapered roller bearing, the application of single row fixed bearing is different from that of double row support bearing. KXRT (T) series configuration) double row ball roller bearing can replace tapered roller bearing and multi row ball bearing: in Fig. 6, two ball rollers replace one tapered roller. Under the same load, the friction of KXRT bearing is lower and narrower than that of tapered roller bearing. KXR4 four row ball roller bearing can replace double row tapered roller bearing, four row ball bearing or double row ball bearing with the same inner diameter and outer diameter. However, at this time, the diameter of the ball roller is relatively small, so the outer diameter of the bearing can be reduced.

 

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Fig. 6 ball roller bearing arranged in series

 

7. Gearbox with ball roller bearing

For the shaft configuration of the gearbox discussed in the example, it is more advantageous to use the ball roller bearing of the new KXR structure (Fig. 7). The fixed end bearing of shaft 1 is replaced by a single row KXR bearing with the same load but smaller and narrower. Two sets of support bearings of shaft 2 are replaced by double row KXRT bearings. Since the required bearing installation space is small, if other factors are not considered, the wheelbase and bearing span can be reduced. Moreover, the friction of KXRT bearing is less than that of tapered roller bearing due to the elimination of sliding friction at the flange. KXRT support bearing is more convenient and reliable for installation and lubrication.

 

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Fig. 7 dual shaft gearbox with KXR / KXRT bearing

 

8. Simulation and test under load

Because of the different moment of inertia, the ball roller enters the stable state faster than the complete ball. This indicates that it is caused by centrifugal force. In the severe test under torque load, the pressure angle of each ball roller per revolution changes from positive to negative (value). This shows that the variation of the ball roller with the pressure angle agrees with the theory. In addition, dynamic tests were carried out under axial and radial loads. The service life of ball roller bearing has reached the theoretical expectation.

 

9. Outlook

As a new rolling element, ball roller has produced a new rolling bearing series, which may be widely used in industry and automobile manufacturing. Especially in the gearbox, the ball roller bearing and the ball roller series bearing are more suitable. Under the same load, the ball roller bearing occupies less space, is lighter, and has lower friction, so the energy consumption is lower. In the same structure space, the ball roller bearing has higher bearing capacity, larger grease loading space and larger structure space for improving sealing.

 

More about ITS Self-aligning Ball Bearing

ITS self-aligning ball bearing top quality brand has guaranteed production and highly active management.

 

Self-aligning ball bearings have a spherical raceway in the outer ring with a center of curvature matched with the bearing center. This allows the inner ring, balls, and cage to rotate freely around the bearing center, maintaining alignment. Permissible dynamic misalignment is about 0.07 to 0.12 radian (4 to 7 degrees) under normal loads.

 

For trouble-free operation, ITS offers sealed self-aligning ball bearings in the 22 and 23 series. Sealed bearings have a contact seal on both sides that is made of oil and wear-resistant and reinforced with a sheet steel insert. Sealed self-aligning ball bearings are lubricated for the life of the bearing.

 

Self-aligning Ball Bearing 


2022-08-15

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