The latest development of foreign permanent magnet transmission technology is reviewed. The application field is broadened and the technical performance is improved; some new technologies, new processes, and new structures appear; the application of advanced manufacturing technology and management makes the magnetic pump more efficient, reliable and durable.
In 1940, the British Charles and Geoffrey Hwward solved the leakage problem of chemical pumps with hazardous media for the first time. The solution was to drive the pumps with magnetic force. In the next 30 years, the permanent magnet transmission technology has made very slow progress due to magnetic materials. The advent of high-performance neodymium iron boron (NdFeB) permanent magnet materials in 1983 provided materials for key components for the rapid development of magnetic drive pumps. In recent years, permanent magnet transmission technology has been expanded from pumps to other sealing machinery. The technology has focused on improving the reliability of equipment, research on new materials resistant to media corrosion, fluid technology and the accuracy of manufacturing and assembly. Magnetic pumps represent the level of manufacturing technology in a country. In recent years, magnetic pumps in industrially developed countries have made breakthroughs in efficiency, life, manufacturing cycle, cost, and reliability.
Permanent magnet transmission technology is to transfer the power of the prime mover to the inner magnetic part on the working shaft through the outer magnetic part on the shaft. Sealing to achieve no sealing and zero leakage. Permanent magnet transmission technology is mainly used in pumps and compressors, mixers and valves in the chemical, petrochemical, pharmaceutical, and food industries. At present, traditional mechanical seals, which are widely used in China’s fluid machinery, have been gradually replaced by permanent magnet drives in these sectors abroad.
2 Broadened application areas and improved technical performance
2.1 Magnetic drive is the most effective and safest solution in the sealing field
Permanent magnet transmission, that is, permanent magnet coupling is the safest solution for machinery that needs to be sealed, harmful, toxic, polluting, dangerous, pure, and valuable products and production processes, and it has a wide range of applications. Most of the liquids in petrochemical, pharmaceutical, film, electroplating, nuclear power and other industries are corrosive, flammable, explosive, toxic, and valuable. Leakage will cause waste of working fluids and environmental pollution; vacuum and semiconductor industries must prevent outsiders Intrusion of gas: food and medicine should ensure that the medium is pure and hygienic. Permanent magnet transmission technology has found its place in these fields. British Howard Machinery Development Co., Ltd. (HMD) has been committed to the manufacture of sealless pumps since 1946, and has sold nearly 70,000 units in 37 countries around the world, with annual sales of 28 million pounds. A pharmaceutical factory in the United States has hundreds of centrifugal pumps equipped with mechanical seals to deal with various acids. These pumps often run dry due to design problems. They can only be used for 2 to 3 months before being destroyed by themselves. Instead, they are manufactured by Ansimag. The K1516 series magnetic drive pump was put into operation in 1993 (4.8 hours a day, 365 days a year) until 1998. In the container board plant in the Midwest of the United States, synthetic caustic soda is a huge problem for the sealing of rotary vane pumps. The engineers here call these pumps “maintaining the sky in the dark”. Ansimag’s ETFE lined sealless magnetic pump was installed and 11 units were in operation. There was no downtime in the month. A large chemical plant in the United States is facing serious difficulties in delivering methanol. Because methanol is flammable, it is close to boiling at 60°C, the flow rate is only 7m3/h, and the pressure difference is as high as 250m. The problem is solved by the Dickow magnetic drive multi-stage end-suction pump. Its flow rate is 15m3/h and the pressure difference is 400m. It ensures zero leakage of methanol, guarantees the safety of operators and the factory, and solves the problem of bubble transportation in methanol. problem.
2.2 Magnetic drive pumps are developing towards miniaturization and large-scale in terms of technical performance
In order to meet the needs of domestic and foreign markets, petrochemical companies are developing large-scale complete sets of equipment. China must have a number of refineries with an annual output of 10 million tons and ethylene plants with an annual output of one million tons. Mechanical equipment must meet heavy load, long cycle, low energy consumption, and meet environmental protection requirements. Our country has discovered in imitating foreign products that the material and process requirements for manufacturing magnetic pumps are very high. Even 11~13kW of small and medium power pumps, its reliability manufacturing cost cannot be accepted by users. For high-power pumps that are resistant to strong corrosion, high pressure, and high temperature, they are still blank. The current development limits of magnetic pumps should be described by HMD’s products: the flow rate is from 1m3/h to 681m3/h, the pressure difference is from 10m to 500m, the temperature range is from -100°C to 450°C, and the system pressure is from vacuum to 400bar. The motive power reaches 350kW. Micro pumps are specially developed for certain departments, such as the cooling of lasers, the supply of analytical instruments, the replenishment of chemical agents, biological engineering, cooling cycles, and even the nozzles of printers. The gear pump and the motor are integrated and closed connection, suitable for 24V, 36V DC power supply, and the speed is manually and automatically controlled. The minimum flow rate is 10ml/min, and the pressure difference is 7bar. The MD series miniature magnetic transmission gear pump used by Japan Iwaki Company for electroplating and cooling cycle has a flow range of 7.5~288L/min and a transmission power of 1/25~1/3.
2.3 Various types of pumps can be transformed into magnetic drive pumps.
Centrifugal pumps are the leading products of magnetic drive pumps. Although magnetic drive rotary displacement pumps have a history of 25 years, it has only been available in the design and manufacturing level and large torque capacity in the past seven or eight years. Broad foundation. The focus is on magnetic drive gear pumps and screw pumps, with a maximum transmission capacity of 400Nm and a power of 150kW at a speed of 3500r/min. Located at the Gas Power Plant in Utah, on the border of the United States, the lubrication pump of the turbo compressor is a constant-rail external gear pump. The oil pump was scrapped due to excessive wear every two months on average due to the high pressure difference, causing the compressor to shut down. After switching to a magnetic drive three-screw pump in 1992, it has been running continuously without any maintenance. The British Tuthill successfully used its magnetic drive gear pump to pump additives into the process water system of Scottish Company. The pump replaced the screw pump and complied with health and safety regulations.
2.4 Magnetic drive compressor
The inner bearing of the magnetic drive is located in the sealed space, and it is lubricated and cooled with a sealed medium. In view of the level of material manufacturing in China, magnetic transmission has not been applied in gas conveying machinery. The overpressure fan produced by Canada Nova Magnetics Co., Ltd. has a leakage rate of 1cm3/h as low as 170bar helium pressure, and the bearing life exceeds 10,000h. Another series of pressurized fans has a free discharge flow of 750m3/h, and the system pressure difference is 35MPa at a flow of 400m3/h, achieving zero leakage. In addition, the special performance of the magnetic drive is also applied to non-leakage agitators, valves and other equipment. Relevant information has not yet been obtained for the application in refrigerators. The author is making explorations to realize the application of magnetic transmission in refrigeration compressors. The leakage of refrigerants, especially Freon, will cause serious environmental problems.
3 New technology, new technology, new structure
magnetic transmission technology is not just a simple use of the same sex repulsion and opposite sex attraction of magnets, it is the integration of transmission technology, material technology, and manufacturing technology. The world’s first-class professional manufacturers, their products enjoy a reputation in the world, so that we can not imitate, the reason is that. Now these “veterans” are still improving efficiency and quality, reducing costs, and extending the average time between two inspections.
3.1 New materials and new processes
The selection of magnetic materials is basically unified in all countries. The working temperature of NdFeB material is lower than 150℃, and the working temperature of SmCo material is lower than 250℃. Ferrite can be used for micro pumps. The pump body materials are divided into two categories: metal and non-metal. Metal stainless steel does not mean that it is stainless for all liquids. It is mainly used for compatible process liquids, precious liquids, and ultra-pure liquids. Non-metals are specially developed for corrosive applications. It is divided into 2 situations. One is a pure plastic pump, which is molded of pure polypropylene or ethylene fluoride thermoplastic. For example, the British Vanton CGM pump has a flow rate of 136m3/h, a head of 84m (temperature 135°C), and a motor power of 32kW. The second is lining pumps, which is a popular method of lining plastics in corrosion-resistant pumps. Generally, the pump body can be made of malleable cast iron, seamlessly lined with FEP, PP, PFA, PVDF, ETFE. The key advantage of Magnetix’s new MTA series sealless pumps and other lined pumps is the application of its advanced PFA fluoropolymer lining. PFA has a unique and extensive resistance to chemical agents, which is better than ETFE, PVDF or other non-metallic materials. Well-known. Adopting patented technology: casting and pressing film technology, the PFA lining of the connection is thick and uniform, which is competitive with rotary die casting. It is more ideal for high-purity and high-temperature fluids. The minimum thickness of the ISO pump PTFE lining is 3mm, which is pressed into the pump casing with a tongue and groove, and the pump casing is made of borosilicate glass. The isolation cover is a key part of the seal, and its rupture can cause catastrophic damage to fluid leakage. The single-layer metal enclosure has a wide range of applications. Although the eddy current will generate heat and energy loss, if high-strength, high-resistance materials are used, the loss can be limited to the minimum, such as Hastelloy C-4 (2.4610). The metal laminated isolation cover invented by Taiani has obtained patents in 5 countries and has been applied in many designs. Its efficiency can reach 99% and its transmission power is 150. Single-layer ceramic ZrO2 (zirconia) isolation cover, resistant to caustic solutions, acid corrosion, high hardness and good sliding properties, and high mechanical strength and elasticity (E=2×105N/mm2), has been used for working pressure 250bar. However, the ceramic cover has a large wall thickness and cannot be plastically processed. The IMO pump obtained a US patent in early 1999. The new isolation cover is made of carbon fiber and epoxy resin, and the thickness is less than 2. 8mm, connected with stainless steel flange. It is suitable for operating pressure of 31bar, temperature of 232℃, transmission torque of 407Nm, and power of 149kW at 3600r/min. The double-layer isolation cover provides double insurance and space for testing. The double-layer cover of Japanese IWAKI MDE series pump is made of glass fiber reinforced plastic. AnSimag double-layer epoxy resin isolation cover magnetic drive pump transports alumina to the paper mill, and has not replaced any parts after 2 years of operation. Isolation cover welding is a weak point of the structure and a sensitive source of corrosion. The advanced manufacturing method is plastic forming, such as deep drawing, spinning, and extension spinning. The shaft and sliding bearing are made of SiC with high wear resistance. As usual, dry operation is a bad omen for sealless magnetic pumps. The meticulous fluid balance design, the rear sealing ring and the impeller hole work together to balance the axial thrust of the liquid and reduce the pressure of the impeller. The inlet adjustment valve prevents pre-swirl at low flow rate, reduces turbulence, and ensures low flow operation. Two sintered SiC bearings are optimally designed to support points. The spiral groove in the bushing helps flush and lubricate the shaft diameter, providing a guarantee of 30 minutes of dry running, allowing the operator time to adjust the system to resume normal operation and avoid catastrophic damage. The pure SiC bearing of the MNKA series pump from ITT Richter, Germany can run dry for 1h at 2900r/min.
3.2 The new technology
guarantees the economical and effective use of the volume of the magnet with the optimal physical size. The correlation between the magnetostatic decoupling torque and the temperature has been calculated by finite element analysis and extensive tests. The axial and radial bearings are lubricated by the pumped medium. The lubrication channel provides the necessary flow. The new self-adjusting bearing can withstand large axial thrust and radial force. Sliding bearings made of SiC or carbon graphite with superior corrosion resistance and wear resistance are shrink-fitted in a metal shell to ensure the stability of mechanical operation. Even if the shaft shoulder is damaged, the reliability and maintainability of the bearing are still maintained. Another technique is fluid balance, which limits the forces on the bearing to a minimum. The current life of the inner bearing can reach 10,000h. High temperature problem: KSB hot oil pump uses a ring cooler to surround the coupling chamber to keep the temperature near the magnet below the maximum allowable temperature of the material, even though the average temperature of the medium is 350°C. HMD’s eddy current coupling has a unique “torque ring” design, which expands the temperature range to 450°C without cooling. Patented technology-fan automatic cooling: the magnetic coupling can be automatically cooled in various speed ranges, no external cooling system is required, and only the annular air chamber transmission is used to automatically complete it. Complete reliability: a friction ring is installed on the magnetic coupling to protect the magnet; in order to prevent dry operation, the flow sensor can be installed on the user’s pipeline to determine whether the current is cut or low; the foreign unit is equipped with a digital power control monitor. Determine overload conditions, leak sensors,
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