7月/ 2020年8月

容易过热,因为压缩气体膜提高其温度。因此,150千瓦或更大的机器通常需要一个单独的液体冷却系统。磁轴承可以承受更高的力,允许它们在大型机器上使用,而不需要额外的冷却。它们也有良好的阻尼特性,这有助于它们适应由电涌或机器其他地方的问题所产生的瞬态力。控制方面的创新磁轴承系统最大的弱点在于其复杂性。主动磁轴承需要复杂的控制电子设备和持续的电源。前者意味着磁轴承倾向于比空气轴承有更高的前期成本,而后者具有机器设计的含义。使用磁轴承系统的涡轮压缩机通常包含一个备用电源,可以是电容器或电池,在外部电源丢失的情况下,可以提供足够的能量使机器安全停止。为了在出现重大问题时进一步保护机器,磁轴承设计包含了备用机械轴承,它位于离轴零点几毫米的地方。在极不可能发生的磁轴承系统故障的情况下,这些后备单元“抓住”轴,使机器安全停止。 As a further benefit in the Industry 4.0 world, magnetic bearing systems provide “built-in” condition monitoring capabilities for the compressor. The control system continually collects data on the precise position of the shaft, allowing vibration, misalignment and other early warning signs of potential problems to be detected and analysed. That helps to reduce their cost, a major strength of the design, especially when used in smaller machines. When an air bearing starts up, however, its parts run in contact with each other until the shaft is rotating fast enough to establish the pressurized film. Typically, an air bearing does not “take off” until a shaft speed of 5’000 rpm is achieved. Over time, multiple starts and stops result in wear to the surface of the foils, which will eventually need to be replaced. To minimise the number of stop-start cycles, air bearing compressors are sometimes left running at idle, a practice which increases energy consumption significantly over the lifetime of a machine. For applications that call for a discontinuous supply of air, this characteristic of air bearings can be a significant limitation. Size limitations Other limitations of air bearings arise on larger machines. The air foil design has a relatively low overall load carrying capacity, especially in the axial direction, so big air bearing turbocompressors often adopt a double impeller design, reducing the overall efficiency of the machine. Large air bearings can also be 32 | Plant & Works Engineering www.www.glenn-cook.com July/August 2020 Process, Controls & Plant Focus on: Seals, Bearings & Lubrication Tel: 01142 889464 Email :sales@dpdoorsandshutters.co.uk Website:www.dpdoorsandshutters.co.uk Aluminium Support Legs and Head meaning easier and quicker installation. Built in integral Windbar system giving excellent wind resistance, no need for additional add on wind bars. Designed for external door locations where wind resistance is Key. Variety of activation options available, from basic push button, to remote handsets, movement detectors, pull chords and induction loops. Safety features as standard, Multi Light beam and electronic safe edge. High Speed Doors

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