Analysis and Research on Working Environment and Use of Magnetic Coupling


Analysis and Research on Working Environment and Use of Magnetic Coupling

Fault Analysis and Treatment of Magnetic Drive Pump

In the application of magnetic drive pump, there are faults such as rapid wear of thrust bearing and large vibration of magnetic pump. Combined with the actual situation on site, some structures are modified and the vibration is analyzed. Fault analysis of magnetic drive pump.

In 1940, the British began to use magnetic drive pumps to solve the leakage problem of chemical pumps with dangerous media. In recent years, magnetic drive technology has developed rapidly and is gradually applied to petroleum, chemical industry, metallurgy, pharmacy, printing and dyeing, electroplating, food, environmental protection and other fields. The application and popularization of magnetic drive centrifugal pump (referred to as magnetic pump) are affected to some extent due to its many faults. For example, magnetic materials are easy to lose excitation, resulting in abnormal torque transmission, and the limitations of medium and pressure cannot meet the process requirements.

1、 Characteristics of magnetic pump

Magnetic pump is a new type of pump that uses permanent magnet magnetic drive to realize non-contact torque transmission. When the motor drives the external magnetic rotor (i.e., the external magnetic steel) assembly to rotate, the magnetic line of force passes through the isolation sleeve to drive the internal rotor (i.e., the internal magnetic steel) assembly and the impeller to rotate synchronously. As the medium is enclosed in the static isolation sleeve, the purpose of pumping the medium without leakage is achieved. The design ensures full sealing, no leakage and no pollution, which can solve the problem of shaft seal leakage of mechanical drive pump.

1. Advantages: The mechanical seal of the pump is canceled, and the inevitable problems of running, emitting, dropping and leaking of the mechanical seal of centrifugal pump are completely eliminated. It is a good choice to achieve zero leakage and no pollution, and can realize the intrinsic safety of the equipment. The flow passage parts of the pump are made of stainless steel and engineering plastics, which can achieve the purpose of corrosion resistance. The magnetic coupling is integrated with the pump body, which has the characteristics of compact structure and overload protection for the drive motor. Less wearing parts, convenient maintenance and long service life.

2. Disadvantages: The transmission efficiency is low. Compared with the centrifugal pump, the energy consumption is large under the same process conditions. The performance of permanent magnet materials such as NdFeB used in China is unstable, and the process selection has certain limitations. Generally, the rated temperature and pressure of the medium required by the process are related to the pump body material of the magnetic pump. When the pump body is made of metal materials or F46 lining, the rated temperature of the working medium is ≤ 80 ℃ and the rated pressure is ≤ 1.6MPa. When the pump body is made of non-metallic materials, the rated temperature of the working medium is ≤ 60 ℃ and the rated pressure is ≤ 0.6MPa. When the rated temperature of the working medium is ≥ 350 ℃, the magnetic pump is in danger of loss of excitation, and it is difficult to achieve long-term safe operation, so it needs to be designed separately. Suitable for conveying medium with density ≤ 1300kg/m and viscosity ≤ 30 × 10-6m/s liquid without ferromagnetism and fiber. For medium with high density and viscosity, due to relatively large transmission torque, there is no good application for the time being. The bearing is generally lubricated and cooled by the conveyed medium, so the magnetic pump is prohibited from no-load and reverse running. It is difficult to solve the problems caused by the failure of magnetic materials in actual operation.

2、 Fault analysis and treatment measures

1. Rapid wear of thrust bearing of magnetic pump

(1) Cause analysis

The benzene blowing raw material pump is a 50CQ-40 magnetic pump with a flow of 220L/min, a lift of 40m and a motor power of 4kW/set. After the pump runs for a period of time, the rear bearing is seriously worn, the rear thrust bearing is broken, and the impeller blade, the front cover of the pump body and the pump body components are worn. The wear direction of impeller and thrust bearing is the same, which shows that the impeller is channeling towards the inlet end, and the axial imbalance is obvious. Enlarge the original impeller balance hole without any effect after assembly. After re inspection, the wear depth of the front thrust bearing was about 2~3mm. After the thrust bearing material was changed to 1Cr13, the problem remained unsolved. According to the comprehensive analysis, when the pressure difference between the bearing inside the pump and the medium on both sides of the thrust disc is small, the flow rate of the medium lubrication is slow, or even cannot flow. In this way, the heat generated by mutual friction is not easy to take away, resulting in the aggravation of medium vaporization, dry grinding, and the failure of the thrust bearing. Therefore, the wear of thrust bearing is the main reason for rapid wear of thrust bearing of magnetic pump.

(2) Treatment measures

Increase the lubrication of support bearing and thrust bearing. 50CQ-40 magnetic pump adopts axial force automatic balancing device. However, if the front end bearing and thrust bearing are poorly lubricated, the self flushing cooling effect is poor. The benzene medium vaporizes and dry friction will inevitably lead to rapid wear of the bearing and thrust bearing. According to the calculation, the pressure difference between the front thrust bearing and the support bearing is less than 0.1MPa due to the friction loss and pressure distribution along the medium flow. Therefore, the key to solve the problem is to increase the lubrication. Increase the back blade clearance of the impeller by 1mm to reduce the axial imbalance force. Support the matching surface of the graphite bearing at the front and rear ends, add 4 straight grooves with a depth of about 3-4 mm, the width of which is equal to the width of the end groove, and deepen the end groove to improve the medium flow effect. Block the medium lubrication holes between the two supporting graphite bearings, force the cooling lubricant to pass through the inner wall of the bearing, avoid dry friction, and improve the lubrication effect through forced flow.

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