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    Crushing magnetic coupling

    Crushing magnetic  coupling (also known as magnetic coupling) transmission is a new technology that applies the basic theory of modern magnetism and uses the magnetic force generated by permanent magnet materials to achieve contactless transmission of force or torque. Compared with other transmission methods, the performance advantage of the crushing magnetic  coupling is obvious. It has the characteristics of smooth start and buffer impact load, especially in the actual operating conditions of high-power crushers such as heavy-load start-up and overload protection. It can protect the equipment, prolong the service life of the motor, and effectively promote the safety management of enterprises and the barrier-free operation of equipment. This article demonstrates the performance of the crushing magnetic coupling in an open-pit coal mine crushing station in China.

    Climatic environment

    The open-pit coal mine of an energy company is in Inner Mongolia. It has a continental subarctic climate, with long and cold winters, short and extremely hot summers, large temperature differences between day and night, large coal dust on site, and large sandstorms in spring. The seasonal freezing depth is 2.41 meters, and the permafrost thickness is 2-4 meters. The mine requires that the equipment can operate normally in the weather such as wind, snow, rain and sand, and in the environment of -50 ~ +40 C.

    The working environment

    This energy company can produce 35 million tons of high-quality lignite annually. The storage center is a comprehensive ground production system of 10 million tons that integrates functions of crushing, screening, coal storage, and rapid quantitative loading. It is mainly responsible for secondary crushing of coal produced by the company, rapid loading of railway coal, and providing different coal quality screening blocks and final coals for the company’s the production and living areas in winter heating, surrounding civil heating and power generation heating in northern China, and at the same time for local coal-to-liquid, coal chemical, upgraded briquette and other industrial and mining enterprises. Reserve and transport Coal with different particle size and coal quality requirements. It is mainly composed of two parts: the 10-million-ton surface production system of the first-stage open-pit mine and the 20-million-ton surface production system of the second-stage open-pit mine. The motor and reducer of the crushing station of the 10-million-ton production system use hydraulic coupling as soft-start equipment. Due to the long-term operation under full load conditions, the hydraulic coupling needs to be refueled and maintained during use, and the oil seal also needs to be Replace frequently to keep the coupling functioning properly. Once the hydraulic coupling fails, it must be shut down for maintenance, and its disassembly and assembly is very inconvenient. It takes about 5 hours to replace the entire hydraulic coupling, which will inevitably bring economic losses to the production department and many other adverse effects.curshing magnetic coupling

     Characteristics of crushed materials

    (1) Lose sand layer and soft clay layer: the shear strength value is 25, and the C value is 0.015mpa.
    (2) Fragmented rock mass: the rock mass in the coal-measure strongly weathered zone, with a compressive strength of 1.56mpa.
    (3) Layered block fractured rock section: it is all coal measure strata below the weathering zone, consisting of mudstone, sandstone and coal seam. Among them, mudstone accounts for 70%, the thickness is large, and the compressive strength is between 1.56 and 9.60mpa.
    (4) The feed material is lump coal, the compressive strength of coal seam is between 5.48~16.8mpa (F3~F5), the average is 10.18mpa; the average shear strength is 0.88mpa.
    (5) The bulk density of coal: 1.28~1.41t/m3.
    (6) Coal loosening coefficient: 0.7.
    (7) Rock body bulk density: average bulk density ≤2.14t/m3.
    (8) Rock loosening coefficient: 1.3.
    (9) Moisture content of coal and rock: the moisture content of raw coal in coal seam is between 3.59% and 19.87%, and the average water content of each rock formation is ≤23.4%.

    Problems existing with hydraulic coupling

    (1) No. 3 secondary crusher is a parallel double unit, the crushing capacity of each unit is 2000t/h (400kw/unit, the input particle size is below 300mm, and the discharge particle size is below 50mm). Designed and installed by a construction machinery company, the impact load of the double-motor-driven crusher is very large, and the couplings are imported hydraulic couplings. However, due to the influence of foreign iron objects (the stope in the open-pit mine, the iron objects left behind), the toothed rollers of the crusher often appear jammed, causing the coupling, reducer and even the toothed rollers to be damaged to varying degrees, or even deformed, and cannot be used. , causing the entire production system to be unable to run, bringing many hidden dangers to the safety production work, and also seriously restricting the production.
    (2) While considering its own strength, due to environmental factors, crusher equipment manufacturers often vigorously increase the output power of the crusher, so the hydraulic coupling as a connecting piece will instantly bear a very large impact force, because the structure Due to its characteristics, it is inevitable to suffer damage. For example, the pin coupling is frequently damaged. The normal operation of the hydraulic coupling requires hydraulic oil to complete the transmission of torque. The hydraulic oil often leaks due to overload or poor sealing, which pollutes the environment and also affects the normal torque transmission. Therefore, in order to ensure the normal operation of the hydraulic coupling, it is necessary to maintain and repair the working chamber and seal frequently, and to regularly refill or replace the hydraulic oil. These maintenance work will inevitably cause the equipment to start and stop many times, and increase the workload of the staff. More importantly, the output, efficiency and equipment utilization rate of the coal mine will also decrease, while the maintenance cost and other expenses are in the rise.

    coal mill motor with magnetic coupling

    Crushing magnetic coupling

    (1) The crushing magnetic coupling has a simple mechanical structure. Once installed and put into use, it is basically not disturbed and affected by the use environment, and its operation is stable and reliable. Because there is no electricity, there is no electromagnetic interference problem. Since the shaft connection between the motor and the load is non-contact with the Magnetic motor coupling, the vibration of the load is not transmitted to the motor. It is precisely because the shaft connection is non-contact, it brings two benefits:
    First, the requirements for alignment during installation are low;
    Second, in the long-term operation, the bearing and seal damage caused by the direct connection of the shaft will not occur, thus ensuring the service life of the equipment. The crushing magnetic motor coupling is designed with a theoretical life of 30 years, showing excellent long-term operating stability.
    (2) On December 9, 2013, the crusher was overloaded during the working process, the crushing magnetic  coupling acted instantaneously, the disk was effectively disengaged, and the motor was protected. After verification, a piece of iron component was stuck between the roller teeth, causing overload. It can be seen from this case that the instantaneous disconnection of the disk accurately and powerfully ensures the normal operation of the system. Then there were many actions to protect the crusher.
    (3) The structure of the crushing magnetic coupling: It is mainly composed of two parts, one part is a conductor of special material connected to the shaft end of the motor, and the other part is a permanent magnet connected to the load end. During operation, the relative motion of the two parts creates a magnetic field that creates eddy currents in the disc-shaped conductor. The magnetic field generated by the eddy currents interacts with the permanent magnets, so that the two parts, rotor and conductor, transmit torque through the air gap.
    (4) The performance characteristics of the crushing magnetic  coupling: Compared with the hydraulic coupling and other transmission equipment, the crushing magnetic coupling has a compact structure and does not need to install other auxiliary equipment. Because the torque is transmitted through the air gap, there is no contact between the two parts, so there are no wearing parts, and the vibration can be reduced by up to 80%, extending the life of the equipment parts and bearings; large eccentricity is allowed; no lubrication; can provide specified It allows the pulsating load, absorbs and buffers the impact load; can realize soft start, load start, overload protection, and no damage to the motor, load, easy installation, maintenance-free; the actual service life can reach 25 years above.

    Advantage of magnetic motor coupling

    1) 25% to 66% reduction in energy consumption.
    2) The maintenance workload for this product is small and the product requires little maintenance. The cost of maintenance is low.
    3) The installation alignment error can be as much as 5mm, which greatly simplifies the installation and debugging process.
    4) The function of overload protection enhances the reliability of the whole system and prevents the damage caused by an overload in the system.
    5) The starting ability of a motor can be improved by reducing the impact and vibration and coordinating load distribution for multi-machine drives.
    6) The speed-regulation type can realize the continuous adjustment of output speed, where the motor speed does not change.
    7) Long service life, the design life is 30 years, and the service life of the components in the system can be further extended.
    8) Remote and automatic control can be accomplished, and the process control precision is high.
    9) The structure is simple, suitable for harsh environments, with no pollutants and no harmonics. It is small in size and can be installed easily.
    10) When the active magnetic pole moves at the speed V, the components of the acting forces P1 and P2 generated by the active magnetic pole and the driven magnetic pole in the moving direction are superimposed, while the components perpendicular to the moving direction are opposite and basically cancel.

    Economic Analysis with the magnetic motor coupling

    (1) Initial investment: The initial investment of the Magnetic motor coupling is roughly the same as that of the inverter at present.
    (2) Maintenance cost: Since the magnetic motor coupling is basically maintenance-free, the maintenance cost is almost zero.
    (3) Economic losses caused by faults: Although the frequency converter is also an energy-saving device, the frequency converter cannot really let users see the benefits brought by energy saving, because its mean time between failures is too short, which occurs once a year on average. Because of the load shedding and increased fuel consumption caused by the failure, all the economic benefits brought by energy saving will be exhausted (it is very likely to be reversed).


    To sum up, whether considering single performance or overall performance, individual energy efficiency or overall system energy efficiency, Magnetic motor couplings are the best choice. The advantages of Magnetic motor couplings become even more pronounced when all costs over the life of the device are considered. Magnetic motor couplings are reliable and feasible to operate on crushers and belt conveyors.

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