Magnetic pump structure characteristics and use and maintenance

CQ type magnetic drive pump, referred to as magnetic pump, is a kind of centrifugal pump that realizes non-contact torque transmission through magnetic actuator (magnetic coupling) and replaces the dynamic seal with static seal, so that the magnetic pump can reach completely without leakage.

1, the magnetic pump structure characteristics

The magnetic pump consists of a pump, a magnetic coupling and a drive motor. The left end of the pump shaft is equipped with an impeller, the right end is equipped with an inner magnetic rotor, and the pump shaft is supported by a slide bearing. The bracket connects the pump and the motor and guarantees the position accuracy of the magnetic rotor inside and outside. When the motor drives the outer magnetic rotor to rotate, the magnetic field passes through the air gap and the spacer (separation) sleeve to drive the inner magnetic rotor to synchronously rotate, thereby driving the impeller to rotate.

1.1. Pumps Pumps are generally made of corrosion-resistant, high-strength engineering plastics, corundum ceramics, stainless steel, etc. as the production materials, have good corrosion resistance, and can be used to protect the medium being transported from contamination. For example, the contact liquid of the CQB series magnetic pump is manufactured from a chemical-resistant fluoroplastic alloy. The fluoroplastic alloy consists of a thermoplastic blend of ultrahigh molecular weight polyfluorinated ethylene propylene and one or more other plastics. For example, a plastic alloy composed of ultra-high molecular weight polyfluorinated ethylene propylene and polytetrafluoroethylene, the former accounting for 0.1% to 99.9% by weight, and the latter accounting for 99.9% to 0.1% by weight, using dry powder co-grinding or dry powder wetting Co-milling method for manufacturing. It can be processed into various products by hot pressing or cold-pressing sintering, which overcomes the shortcomings of cold flow and easy deformation of PTFE and can prolong its service life.
The bearings of the magnetic pump are immersed in the conveying medium and are lubricated and cooled with the conveying medium. More commonly used domestic bearings are mostly graphite and reinforced plastics. Graphite, especially impregnated graphite, has good self-lubricity, heat-resistant corrosion, low friction coefficient, and a wide range of applications. However, graphite is brittle and has low strength and is sensitive to shaft bending and local overload. Special attention should be paid to it. The three-layer composite bearing with steel as the matrix, porous bronze as the intermediate layer and plastic as the surface layer has high compressive strength, small friction coefficient, dimensional stability, and sound-absorbing and damping, and has been applied in recent years.

1.2. Magnetic Couplings Magnetic Couplings are key components that enable non-contact torque transmission to be completely leak-free. There are generally two types of discs and cylinders. Because the disk-shaped coupling is composed of two facing ring-shaped magnets and a spacer in the ring-shaped coupling, there is an axial force between the two ring-shaped magnets. Especially when the power is large, the axial force is large, and it is very difficult to overcome it. Generally less used. The cylindrical coupling consists of three parts: an outer magnetic rotor, an inner magnetic rotor and a spacer sleeve. The outer magnetic rotor is connected with the motor and is in the atmosphere. The inner magnetic rotor is integrated with the pump shaft and the whole rotor is Contained in the pump casing and spacer and submerged in the transmission medium, the spacer is located between the inner rotor and the outer rotor and fixed on the pump casing, so that the magnetic pump casing and the isolation casing form a communicating and completely sealed chamber. The magnetic steel is closely arranged along the circumferential direction on the outer cylindrical surface of the inner magnetic rotor and the inner cylindrical surface of the outer magnetic rotor to form a "combined push-pull magnetic circuit."
At present, there are many magnetic materials available for magnetic pumps. Commonly used are AlNiCo, ferrites, and rare-earth permanent magnets, SmCo5 (abbreviation 1:5), Sm(Co, Cu, Fe, Zr) 7.4 (abbreviation 2:17), Nd-Fe-B, etc. Among them, rare earth permanent magnet materials are preferred, and the powerful one is Nd-Fe-B, which has a large magnetic energy product of 28 x 104T·A/m or more and an intrinsic coercive force of over 1120 kA/m. However, the working temperature can not exceed 120 °C under high temperature conditions can choose to drill permanent magnet material, Sm (Co, Cu, Fe, Zr) 7.4 magnetic energy product is about 192 x 103T · A / m, and its operating temperature up to 300 °C .
The cylindrical coupling should pay great attention to the position between the inner and outer magnetic rotors during design, processing and assembly, otherwise it will generate radial force. This radial force not only affects the torque transmission, but also has a direct impact on the life of the bearing. In severe cases, the magnetic coupling can not work. The key to solving this radial force is to ensure that the inner and outer magnetic rotors have the necessary concentricity. In addition, when assembling and disassembling the magnetic pump, special tooling and tools should be provided to protect personnel and parts from being damaged.
When the magnetic pump is in operation, the spacer is in an alternating magnetic field, which induces eddy currents. This vortex, on the one hand, consumes shaft power and reduces transmission efficiency. On the other hand, it is converted into heat, transferred to the medium and increases the temperature of the circulating medium. Therefore, the design of the spacer must pay attention to the choice of materials and geometric dimensions, especially for the transport of easily vaporized liquids. After the parameters and requirements of the pump are given, the main factor of the power loss p of the spacer can be approximated as P∝d2/p·σ, where d is the diameter of the spacer and p is the resistivity of the material. Allow stress for the material. It can be seen that the main way to reduce the eddy current loss is to use materials with high resistivity and high strength, and to minimize the diameter of the spacer.
The materials used to make the glands are generally divided into two broad categories: metallic and non-metallic materials. The metal material has high mechanical strength, and the wall thickness can be controlled to be thin to reduce the gap between the magnetic rotor inside and outside, increase the transmission efficiency, and at the same time reduce the eddy current loss generated inside the spacer. Domestic generally use 1Cr18Ni9Ti and Chin alloys. Non-metallic materials have good corrosion resistance, do not generate eddy current losses, can improve transmission efficiency, but are often limited by the pressure and temperature of the transmission medium and limit the scope of application, commonly used in China is PTFE.

1.3. Motors The motors used in the magnetic pumps are generally used motors. Special requirements are selected according to the regulations.

2. Use and maintenance of magnetic pump

2.1. Precautions for Use of Magnetic Pumps (1) After installation, rotate the coupling by hand to check for rubbing.
(2) In order to prevent debris from entering the magnetic pump, a filter is provided at the inlet of the magnetic pump, and the filter area is larger than the pipe cross-sectional area by 3 to 4 times.
(3) No air running.
(4) The high-headed magnetic pump should be equipped with a check valve on the outlet pipe to prevent the sudden stoppage of water hammer damage.
(5) Open the pump program: Open the inlet valve before driving, fill the pump with the liquid to be delivered, close the outlet valve, move the electric hoist to check the magnetic pump's steering direction; after the magnetic pump starts, the outlet valve should be slow. Open, wait for the pump to reach normal operation, and then adjust the outlet valve to the desired opening. Test run for 5~10min. If there is no abnormality, it can be put into operation.
Parking procedure: Close the outlet valve; cut off the power supply; close the inlet; when it is not used for a long time, clean the flow path in the pump and cut off the power.

2.2, maintenance notes (1) magnetic pump shaft fracture. The material used for the pump shaft of the CQB type magnetic pump is 99% alumina ceramic. The main reason for the breakage of the pump shaft is that the shaft is broken due to the dry running of the pump due to the empty operation of the pump. When the pump is disassembled, it can be seen that the bearing is worn. The main way to prevent the pump from breaking is to avoid empty operation of the pump.
(2) The magnetic pump bearing is damaged. The material used for CQB magnetic pump bearings is high-density carbon, which can cause bearing damage if water is pumped off or there are impurities in the pump. If the coaxiality between the inner and outer magnetic rotors of the cylindrical coupling is not guaranteed, it will directly affect the bearing life.
(3) The magnetic pump does not produce liquid. The magnetic pump can't get out of the liquid, which is the reason why the pump is prone to failure. The reason is also more. First, check the suction pipe of the pump for leaks, check whether the air in the suction pipe is discharged, whether the amount of liquid poured in the magnetic pump is enough, whether the suction pipe is clogged with debris, and whether the pump should be reversed. (Especially after replacing the motor or after the power line has been repaired), it should also be noted whether the suction height of the pump is too high. If the above checks still cannot be resolved, the pump can be disassembled and inspected to see if the pump shaft is broken. Also, check whether the pump ring and the static ring are intact and whether the whole rotor can move in a small amount. If the axial movement is difficult, it can be checked whether the carbon bearing is too tightly coupled with the pump shaft.
It is worth noting that the magnetic pump can not find any problems after several times of repairs. It should be noted whether the magnetic coupling is working properly. Bearings, inner magnet rotors and spacers all generate heat during operation, which will increase the operating temperature. On the one hand, the transmitted power will be reduced. On the other hand, the magnetic pump that transports the easily vaporized liquid will cause great trouble. The power transmitted by magnet steel with temperature is a continuously decreasing curve. Generally, below the working temperature limit of magnetic steel, the decline of its transmission capacity is reversible, but above the limit temperature, it is irreversible, ie, the cooling of magnetic steel. After that, the lost transmission ability can no longer be restored. Under special circumstances, when the magnetic coupling is slipped (out of step), the eddy heat in the spacer will increase sharply and the temperature will rise sharply. If it is not dealt with in time, it will cause the demagnetization of the magnet and make the magnetic coupling failure. Therefore, the magnetic pump should be designed with a reliable cooling system. For the medium that is not easily vaporized, the cooling circulation system generally draws the flow from the impeller outlet or the pump outlet and returns to the population through the bearing and the magnetic transmission part. For the easily vaporized medium, the heat exchanger should be added or the liquid flow should be led outside the pump. The storage tank, to avoid the heat back to the suction population, should be considered for the medium with solid impurities or ferromagnetic impurities. For high temperature medium, cooling should be considered to ensure that the magnetic coupling does not exceed the working temperature limit.
When considering whether the speed is enough, first check whether the speed of the motor itself is normal or not, and use a tachometer to measure. If the speed of the motor is normal, consider whether the slippage of the magnetic coupling may occur.
(4) Insufficient head. Caused by this failure are: there is air in the conveying medium, the impeller is damaged, the rotation speed is not enough, the proportion of the transported liquid is too large, and the flow rate is too large.
(5) Insufficient flow. The main reasons for the lack of flow include: impaired impeller, insufficient rotational speed, excessive head lift, and blockage of debris in the pipe.