Talking about the Application of Magnetic Bearings on the High Speed ​​Spindle of Machine Tools

The magnetic bearing can be used on the high-speed spindle to obtain 100,000 rpm. On the one hand, it can improve the surface processing effect, on the other hand, its service life is far greater than that of the conventional bearing. Although this technology is still in the prototype test stage, many advantages have been fully reflected. Its performance is not affected by thermal effects, no wear and tear, and can be automatically shut down in case of overload.

Conventional bearings provide radial or axial support to the main shaft, allowing relative movement between the inner and outer rings. The inner ring and the outer ring are connected by balls or rollers, and the supporting force is also transmitted between the three. Oil film bearings have no balls or rollers and are lubricated or dissipated with pressurized oil. Both of these bearings have been used for hundreds of years. Magnetic bearings support the rotating parts differently than the above two products.

A magnetic bearing is a non-contact bearing that suspends a rotating component between fixed components by electromagnetic force. This means no friction, no wear, and higher stability, and higher speeds can be achieved. The electromagnetic force is mainly related to the current and the size of the gas gap. The sensor collects the data of the gap size, and the control system adjusts the current output according to the input signal.

The magnetic bearing is mainly composed of three parts:

Bearings and sensors: Bearings provide support to the spindle and sensors are responsible for collecting position signals.

Control system: responsible for providing power and calculating the correct corrective force based on the feedback signal to drive the controller in different directions.

Software system: responsible for calculating and outputting feedback signals.

The main disadvantages of magnetic bearings are: they are bulky, require power, and complex structures and algorithms.

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Some methods for reducing the bearing temperature of horizontal hydro-generator sets

1 Power station overview

Guangdong Gezhou Cang Hydropower Plant is a run-of-river power station with a rain collection area of ​​39.6km2 and an installed capacity of 2800kW, one of which is 800kW and the other is 2000kW. The turbine models are: HLA218-WJ-60 and HL160-WJ-71; the generator models are: SFW800-6/1180 and SFW2000-6/1430. The two hydro-generator units are products of Chongqing Turbine Works. They are two-point structure. The thrust bearing is located on the side of the permanent magnet machine, which changes the traditional setting, that is, the thrust bearing is between the generator and the turbine. Both units were put into operation in September 1991. Until the seven months of January 1998, the bearings of the unit were in an ultra-high temperature operation, sometimes as high as 73 ° C, and forced to stop, which has caused burnt accidents many times. After numerous treatments by our technicians, engineers of the Bureau and neighboring brothers, it still has little effect. Later, after the participation of the engineer and author of the factory, Wang Shouzhong, the bearing circulation oil circuit and the cooling system were transformed, and the temperature was significantly reduced, which was a complete success.

2 existing defects

In the past maintenance process, we strictly deal with the levelness, concentricity, smoothness and sanding of the main shaft in accordance with the requirements of the factory and relevant regulations. The water quality and water pressure of the cooling water are also in line with the standard, but the temperature is not lowered. Finally, in December 1997, the engineer Wang Shouzhong came to the site to instruct and inspect, and found that there are some problems in the internal design of the main thrust bearing: 1. The cooler capacity is too small to take away a large amount of the bearing inside. The residual heat causes the temperature to rise. 2. The verticality of the main mirror plate of the thrust plate is not enough, and one of the units is mainly caused by the looseness of the thrust head. Some places are 0.5mm higher, and some places are depressed by 0.15mm, causing some places on the thrust tile surface to be overstressed, and some places are not stressed at all, so that the temperature of the force surface is frictional after a certain period of operation. The temperature gradually rises, eventually leading to a burnt tile accident. 3. The thrust bearing is not specially equipped with a cooling oil pump. The circulation of the cooling oil mainly relies on the high-speed rotation of the smooth and complete thrust ball to bring a part of the cold oil, which fails to produce the effect of temperature reduction. 4. The oil inlet holes of the upper and lower bearing bushes are too small, so that the circulation of the cold oil is greatly hindered, so it cannot reduce the temperature.

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