High speed gears

Synchronous speeds are calculated by Eq. (29-10). Speeds above the limits given are obtained through step-up gears large high-speed centrifugal compressors are examples. Two-pole (3600 r/min at 60 Hz) synchronous motors can be built but are uneconomical in comparison with geared drives. 

The maintenanee staff at the plant ehanged the high-speed pinion bearings in the train s gear box, but only as part of preventive maintenanee and as a preeautionary measure. Otherwise, maehinery availability has been high. 

The main power source is a 2,200 kW rated motor, which drives two high-speed pinions through integral gears. The first stage of the compressor operates at 17,900 rpm, while the second and third stages operate at 21,800 rpm. The unit is controlled by a local control system, but operators can also monitor the operating parameters from the plant control room. 

High-speed gear eouplings are seleeted in whieh the piteh diameter is substantially smaller than that of the pinion. Axial forees produeed will be high, and the eombination should be examined very elosely as a potential trouble souree. 

The oil furnished to high-speed gears has a dual purpose tooth and bearing lubrication and cooling. Usually, only 10-30% of the oil is for lubrication, and 70-90% is for cooling. 

When selecting a high-speed gear unit, the possibility of using an AGMA No. 2 oil should be considered. In most cases, the sleeve bearings in the system can use this oil and, if not, a compromise 200 SSU at 100°F (38°C) oil should be considered. 

Phinney, J.M., Selection and Application of High-Speed Gear Drives, Proceedings of the 1st Turbomachinery Symposium, Texas A M University, October 1972, pp. 62-66. 

High speeds require relatively lightweight gear elements. All case-hardening procedures produce distortion—to keep this distortion to a minimum, nitriding is the preferred hardening method. This method is employed after all machinery operations are complete and no further corrections are to be made to the tooth geometry. 

For most of the rotary compressors in process service, the driver is an electric motor. Compressors in portable service, however, particularly the helical-lobe compressor, use internal combustion engines. Many of the rotary compressors require the high speed that can be obtained from a direct-connected motor. The dry type helical-lobe compressor is probably the main exception as the smaller units operate above motor speed and require a speed increasing gear which may be either internal or external (see Figure 4-1). The helical-lobe compressor is the most likely candidate for a driver other than the electric motor. Aside from the portables already mentioned, engines are used extensively as drivers for rotaries located in the field in gas-gathering service. Steam turbines, while not common, probably comprise most of process service alternate drive applications. 

Synchronous and induction motors cannot always be compared on an equal speed basis. In geared applications such as high-speed centrifugal compressor drives (above 3,600 rpm), the most economical induction moior speed is usually 1,800 rpm. The most economical synchronous motor speed for the same application might be 900 or 1,200 rpm, depend-... 

Speed changers, industrial high speed drives, and gears... 

---