Bevel-helical gearboxes B3 ize or larger see page Flender GmbH Flender B3-CH-13-A

Flender/Flender Gear Units/Bevel-helical gearboxes B3

ourier transform (FFT) analysis of the casing vibrationcan also identify the difference between, for example, meshfrequency, natural frequency, or cavitation frequency generated by mechanical oil pump. Accelerometer information in low frequency range can confirm shaft displacement measurement andimprove unit protection reliability for alarm and trip. rapiddetection of the main vibration components in the FFT spectrumcan be very useful to focus an investigation on the root causes of aproblem. Temperature Measurements For sleeve bearing temperature measurements, flexible resistance temperature detector (RTD) probes are often specified. This type of probe has good precision, but is more fragile than athermocouple. The sensitive end of the RTD probe is brittle andcan be broken by vibrations. This can cause unit shutdown andinvolve maintenance action for its replacement. To avoidequipment shutdowns due to broken probe, install two separatedsimplex probes at each temperature measurement point, on theradial bearing or thrust pads, with voting logic on the monitoring system. In many cases today, the gearbox is inside closed package without crane for ease of disassembly. Special mechanicaldesigns allow bearing thermal probe replacement without casingdisassembly (Figure . From general point of view, smallincreases in capital cost, similar to this example, couldconsiderably reduce the maintenance costs and productiondowntime during the operating life of turbo units (accessibility to machines, cranes, etc.). OPERATING DIAGNOSTICS ON GEARBOXES The cases below illustrate problems encountered by gear specialist while diagnosing vibration levels on site. Overall Vibration Measurements on Gearbox Casing Are Not Sufficient for Diagnosis As explained above, gearbox shaft vibration can be detected on the casing. But external forces that are transmitted through thefoundation and gearbox skid can also excite the casing. For thesereasons, the casing overall vibration measurem