The design methods and principle of bearings set used in vibrator.

Abstract: This article introduced the design methods and principle of bearings set used in vibrator. The vibrator designed according to the above principles was proved to be excellent in the production.

Key Words: vibrating equipment; vibrator; bearings set; seal; lubrication

Inertial vibration equipment is usually driven by vibration exciter. The performance of vibration exciter has a great impact on the overall performance of vibration equipment. Figure 1 shows a typical structure diagram of an exciter. It can be seen from the figure that the exciter is composed of eccentric block, bearing device, base, etc., and its key component is the bearing device. The design of the exciter bearing device will be discussed in detail below.

1. eccentric block  2. Labyrinth seal cover  3. Felt ring  4. Bearing

5. shaft  6. Bearing cover  7. Base  8. Ferrule

Fig. 1 structure diagram of vibration exciter

1 Design of bearing device

The bearing device includes the selection and calculation of bearings, the matching of bearings, the design of sealing lubrication, etc.

1.1 Selection and calculation of bearings

During the operation of the exciter, the bearing works under the vibration load, and the load is generally large, so the self-aligning roller bearing is generally selected. In addition, when the vibrating equipment is working, the equipment itself will produce very large noise, which does not have high requirements for the working noise and accuracy of the bearing. Therefore, the bearing with ordinary accuracy grade, i.e. grade g accuracy, is generally selected. Due to the large impact force on the bearing during the operation of the vibration equipment, the tight fit of the bearing and the low accuracy requirements, the bearing with large clearance, such as the bearing with the third group of auxiliary clearance, shall be generally selected.

The bearing specification is generally selected according to the rated dynamic load. Since the exciter basically has no axial force during operation, the excitation force can only be calculated according to the radial force. The basic rated dynamic load is calculated according to the following formula:

C - calculated value of basic rated dynamic load;

P - radial load, i.e. the exciting force on a single bearing;

F_h - life coefficient. The recommended service life of the bearing used in the exciter is generally 10,000 - 25,000t, F_h = 2.64 - 3.23. The specific value can be determined according to the working nature of the vibration equipment (continuous, intermittent) and the reliability of the vibration exciter.

F_n- speed coefficient, the speed of the exciter is generally 730 - 1,200rpm, F_n = 0.395 - 0.341; 

f _m - moment load factor, generally f_m = 1.5;

f_d- impact load coefficient. Since the inertial vibration equipment has certain impact force, f_d = 1.2 - 1.8;

f_t - temperature coefficient, because the temperature rise of the bearing during the operation of the exciter is generally lower than 120^。C, f_t= 1;

Cr - Radial Basic rated load listed in the bearing dimension and performance table.

After calculating C, according to the above formula, find out the bearing specifications listed in the bearing parameter performance table according to C < Cr.

1.2 Bearing matching and axial positioning

During the operation of the exciter, the load on the outer ring of the bearing is a rotating load, that is, the outer ring rotates relative to the load direction. At the same time, the load has a certain impact. In order to prevent the impact of the bearing chamber from expanding during the operation of the bearing, which will cause the rotation of the outer ring of the bearing and cause the bearing to be heated and damaged, the outer ring of the bearing is generally used with a large amount of interference, such as P7. The inner ring of the bearing is stationary relative to the load direction. At the same time, the shaft is not required to slide freely on the shaft during the working process. Therefore, its fitting is generally h6.

Since the outer ring of the bearing is a fit with a large amount of interference, the hot assembly process is generally used for the assembly of the bearing. In order to facilitate the assembly, a ring can be installed between the two outer rings of the bearing, as shown in Figure 1. The bearing cover shall be installed after the bearing chamber is cooled, and the buckle on it shall press the outer ring of the bearing after installation. As the shaft is in the bearing chamber, its temperature rise is higher than that of the bearing chamber. In order to prevent the shaft from extending after temperature rise and affecting the normal operation of the bearing, the length between the two shaft shoulders on the shaft is shorter than the length of the outer ring of the bearing about 2 mm.

1.3 Sealing and lubrication of bearings

The sealing and lubrication of the bearing have a great impact on the performance of the vibration exciter. Most of the bearing damage during the working process is caused by poor lubrication or dry running of the bearing after the loss of lubricating oil (grease). Therefore, the sealing and lubrication of the bearing must be paid great attention to.

Since the speed of the exciter used for inertial vibration equipment is low, generally not more than 1,500 rpm, most of which are between 730 rpm and 1,200 rpm, grease lubrication can generally meet the requirements of the bearing for the limit speed. For example, the box type vibration exciter lubricated with grease has been successfully applied to the super large heavy vibrating screen of 3,000*9,000 mm, and the use effect is good. For some vibration exciters with high speed and large load, thin oil lubrication can be used. When grease lubrication is selected, No. 2 or No. 3 lithium grease or No. 2 lithium grease is generally selected. This kind of grease has good mechanical stability, water resistance, rust resistance, extreme pressure and wear resistance, and the applicable temperature range is 20^。C - 120^。C.

For grease lubrication, mild steel paper gasket or rubber gasket is generally used for sealing between the bearing cover and the bearing chamber, felt ring seal, lip seal or clearance (labyrinth) seal is generally used between the excitation shaft and the bearing cover. The clearance seal is an ideal sealing method because there is no direct contact between the rotating shaft and the bearing cover, and the sealing part does not produce additional friction resistance moment and additional heat. However, its structure is complex, processing is difficult, and its overall dimension is also large. Felt ring or lip seal ring is simple and compact in structure, easy to manufacture, and also has certain sealing performance, so it can also be applied to the sealing of exciter bearing. However, some additional heat will be generated during use. In order to further improve the reliability of the seal, the combined sealing method of labyrinth seal and felt ring seal is adopted in practice, as shown in Figure 2. Adding an appropriate amount of grease into the labyrinth gap can not only effectively prevent the invasion of external dust, but also ensure the self lubrication of the felt ring. The use effect is good. At the same time, since the sealing of the grease is mainly guaranteed by the felt ring, the gap between the dynamic and static surfaces of the gap seal can be appropriately increased, Thus, the machining accuracy of the labyrinth is reduced.

Fig. 2 combined sealing mode

2 Use effect

The box type exciter designed according to the above principles has been used on nearly 100 inertial vibration equipment in China, with good effect. The bearing life is more than two years. At the same time, the excitation force is easy to adjust, and the installation and disassembly are convenient and reliable.

3 Conclusion

1) The box type vibration exciter generally adopts the large stroke self-aligning roller bearing with ordinary precision (Class G).

2) The outer ring of the bearing shall be matched with grade P7, and the inner ring shall be matched with grade h6. Lithium grease is generally used for lubrication, and labyrinth, felt ring, lip ring seal or combined seal is used for sealing.

More about GQZ Spherical roller bearing:

GQZ cylindrical roller bearing can meet the challenge of heavy radial load and high-speed application. Adapted to axial displacement (except for bearings with flanges on both inner and outer rings), they provide high stiffness, low friction and long service life.

Cylindrical roller bearings are also available in sealed or split designs. In sealed bearings, the rollers are protected from contaminants, water and dust while providing lubricant retention and contaminant removal. This provides lower friction and longer service life. Split bearings are mainly used for inaccessible bearing arrangements, such as crankshafts, which simplify maintenance and replacement.