2023 May the Fourth Week KYOCM Technical Knowledge: Analysis of Trouble Causes for Bearings of Diving Pump with Draining Sands

Abstract: The bearing trouble of diving pump with draining sands is importance reason for lowering the life span of diving pump. The parts of elaborateds the reason of the bearings wrong with the BQS series of diving pump with draining sands. For example ,the desing of bearing room, the electric motor spread hot, work environment, usage and so on. It gives a good way to solve the actual problem.

Key words: draining sands diving pumpbearingsmatchseal completely wreath


0 Preface

The BQS series vertical explosion-proof sand discharge submersible pump is a new type of submersible pump that integrates the motor and water pump. It is suitable for pumping wastewater containing solid particles in environments with methane explosion hazards. It is used for drainage in coal mine vertical and inclined shaft construction, main drainage at the bottom of the mine waterless silo, mining face drainage, automatic drainage at the bottom of the main shaft coal silo, old pond drainage, automatic drainage of water inrush in unmanned areas, and drainage at the clean water silo Cleaning up mud and sand drainage, disaster relief and emergency drainage, etc. have been widely applied. However, due to various reasons such as improper selection, harsh operating environment, and untimely maintenance, the service life of submersible pumps for sand removal always cannot reach the designed life, among which bearing failure is an important factor in reducing pump life.


The traveling end of vertical explosion-proof sand flushing submersible motor adopts Deep Groove Ball Bearing, which mainly bears the radial force generated by the imbalance of rotor or impeller. The shaft extension end (pump end) is generally equipped with angular contact ball bearings, which mainly bear the axial force generated by rotor gravity and impeller rotation. There are several main reasons for bearing failures.


1. Whether the design of the bearing chamber is reasonable will affect the service life of the bearings

The structural characteristics of the sand removal submersible pump are vertical installation and an internal motor structure. The motor is cooled by the conduction of the flowing water layer between the outer water guide sleeve of the motor shell and the motor shell, which carries away the heat inside the motor. Most motors are of a dry structure, and the heat generated by the bearings at both ends of the motor rotor during motor operation can be transmitted in two ways:  by the contact between the bearing outer ring and the bearing seat hole facing outward;  The internal circulation wind formed by the blades of the motor rotor during the rotation process hits the inner wall of the casing, allowing heat to be transmitted to the cooling water outside the casing through the casing steel plate to carry away the heat. When designing, the following points should be fully considered:


(1) The thickness of the outer wall in contact between the bearing outer ring and the bearing chamber should be uniform, and direct contact with the outer cooling water is the best option, so that the cooling water can directly act on the bearing shell. Some designs rely on rib plates to connect the bearing chamber and the outer ring of the bearing seat, which greatly affects the cooling of the bearing. Therefore, this structure should be avoided as much as possible.


(2) The internal space size of the bearing chamber should not be too small. The contact area between the internal circulation air and the shell should be increased to achieve good heat dissipation effect. When designing, the minimum distance between the winding end and the bearing seat should be greater than 150 mm.


(3) The motor rotor blades cannot be driven too short, as it will affect the internal circulation air volume and fail to achieve cooling effect. Generally, the height of the blades is designed to be 50-70 mm. The above three methods can effectively improve the heat dissipation effect of the inner cavity of the motor, making the bearing work in working environments below 90 ° C. If the design is not reasonable and the temperature inside the motor cavity is too high, it will cause lubricating oil vaporization, bearing failure, and the service life of the bearing will be shortened.


2. The installation position of the bearings is too close to the end of the motor winding, which is also an important reason for bearing damage

In the structural design of submersible pump motors, in order to reduce the volume and weight of the pump, the influence of small structural dimensions on the motor bearings is often ignored. Some designs design the bearings in the inner cavity of the winding end. When the motor is running, the bearings rotate in the winding coil, generating axial current, causing heat and damage to the bearings. Therefore, in the design, the bearings should be kept away from the motor winding end to reduce the generation of axial current, The general spacing should be designed at least 150 mm.


3. If the external design of the motor casing is not reasonable, the cooling water will generate eddy currents that affect heat dissipation, causing the internal bearings to heat up

The design of the motor casing should ensure smooth changes in the external water flow cross-section, avoid dead corners and areas that generate eddy currents, especially on the outer wall of the bearing chamber, where eddy current points cannot exist. Otherwise, it will affect the heat dissipation of the bearing. It is best to install heat dissipation fins outside the casing.


4. Poor fit between bearing and bearing seat hole or shaft

Excessive bearing seat holes can cause uneven bearing force on the shaft, generate heat from friction between the outer ring of the bearing and the bearing seat hole, increase the bearing temperature, vaporize the lubricating oil, and cause bearing failure. Excessive interference between the shaft and the inner ring of the bearing will reduce the clearance of the bearing and reduce its lifespan. In addition, the inner and outer rings of the bearing are fixed on the shaft or bearing seat to avoid relative radial, axial, and rotational movements between the ring and the mating surface of the shaft or bearing seat when under load. Otherwise, relative motion can cause wear, friction corrosion, or friction cracks on the mating surface, leading to damage to the bearings, shafts, and bearing seats, resulting in wear powder mixing into the interior of the bearings and causing problems such as poor operation, abnormal heating, or vibration.


5. Bending of rotor shaft

Improper heat treatment can cause bending of the rotor shaft; Improper operation of the rotor shaft during storage or handling can also lead to bending; When assembling bearings, the pump shaft is prone to bending due to excessive pressure. After the pump shaft is bent and deformed, the bearings are damaged due to uneven force during pump operation. The pump shaft is generally a slender shaft, and the stiffness verification of the shaft is also crucial. The selection of motor speed and shaft diameter requires stiffness verification to avoid vibration damage.


6. The axial displacement of the bearing is too small

When the electric pump is running, the rotor shaft heats up and expands. If the axial movement of the floating end bearing is restricted, it will be damaged due to the increase in bearing temperature. The submersible pump is a dry type motor that operates in a harsh environment. The motor often operates in an overloaded environment, and the temperature at the bearing end is higher than that of other ordinary machinery. When designing, the clearance should be increased to ensure that the movement of the bearing end of the shaft is not restricted under overload conditions.


7. Vibration caused by imbalance of rotor shaft or impeller

During manufacturing, the rotor shaft and impeller must be statically and dynamically balanced, otherwise the bearings will be damaged in a very short period of time.


8. Small gap between sealing rings

The interstage impeller seal of the pump is sealed by the gap between the impeller sealing ring and the pump body sealing ring. The gap of the sealing ring is determined by the size of the wheel hub diameter. If the gap is too small, the two sealing rings will rub and the shaft temperature will increase, causing damage to the bearing due to excessive temperature.


9. Poor working environment

The operating point of the submersible pump should be within ± 10% of the design operating point. If the operating point is high, it will cause an increase in working current, motor overload, high temperature rise, poor motor cooling, bearing temperature rise, lubricating oil vaporization, and bearing failure.


10. Improper use

In order to maintain the proper performance and long-term use of bearings under good conditions, it is necessary to inspect and maintain the bearings. Inspection and maintenance are important for preventing faults. During operation, it is important to focus on checking the rolling sound, vibration, temperature, and lubricant of the bearings.


In short, the BQS vertical explosion-proof sand removal submersible pump can cause bearing failures in every aspect of design, assembly, lubrication, use, and maintenance. Therefore, both manufacturers and users need to do a good job in bearing maintenance and upkeep. Only when the bearing failure rate is reduced, can the pump's lifespan be improved.


More about KYOCM Tapered roller bearing:

KYOCM tapered roller bearing adopts outer ring and inner ring components. The outer ring is composed of an outer ring, and the cone assembly is composed of an inner ring, a roller and a cage. This bearing structure can withstand combined loads and provide low friction during operation. Rigid bearing applications can be achieved by adjusting a single row tapered roller bearing to a second tapered roller bearing and applying preload. KYOCM tapered roller bearings include single row tapered roller bearing, double row tapered roller bearing and four row tapered roller bearing.