DESCRIPTION

Technical Description

The terms 'critical speeds' and 'resonance' are often used to talk about rotating systems. Resonance occurs when the natural frequency and the excitation frequency match. The natural frequency of an oscillatory system is that frequency at which the system can oscillate with the associated natural mode after a single excitation. Operation at critical speed can lead to breakage and damage to the components of the system in high-speed rotating machinery. To prevent this, the system is operated well above or below the critical speed and quickly driven through the critical speed range. Structural changes, e.g. changes to rigidity, can cause the critical speed to change, meaning the operational requirements have to be adapted.

The TM 625 experimental unit can be used to study the natural modes of various shafts. Illustrative experiments are used to explain resonance and supercritical or subcritical states of an oscillating system. Six shafts of different lengths and diameters are available. The shafts can be mounted on four self-aligning ball bearings and fitted with a mass to construct a Laval rotor. The axial positions are read on a scale mounted parallel to the shaft. A three-phase motor drives the shaft via a flexible coupling. The electronically regulated speed can be selected via two potentiometers and is continuously variable. It is displayed on a digital readout by a revolution counter.

A transparent protective cover and safety bearings ensure safe operation. 

The TM 620.20 accessory provides measurement and evaluation software, including sensors, for data acquisition via PC.

The well-structured instructional material sets out the fundamentals and provides a step-by-step guide through the experiments.

Learning Objectives / Experiments

- investigation of a Laval rotor
  * critical speed
  * self-alignment
- natural modes on a shaft with continuous mass distribution with 
  * different bearing intervals
  * different shaft diameters
  * different shaft lengths