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TM 620 Bending elasticity in rotors



  • Investigation of bending vibrations in rotors1
  • Determining critical speeds1
  • Position of rotor mount and rotating mass can be adjusted
  • Optimal visibility and simultaneous protection thanks to transparent protective cover


Technical Description

At a certain speed the imbalance forces of a rotating mass can cause part of the machine or the entire machine to vibrate in resonance with bending vibrations. This speed is known as the critical speed. The rotor and shaft on a motor or a turbine, for example, form a system that can resonate. In rapidly rotating machinery this state presents a danger because it can lead to breakage and damage to the components of the system. 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 620 experimental unit teaches knowledge about how to determine the critical speeds. Illustrative experiments are used to explain resonance and supercritical or subcritical states of a vibrating system.

A three-phase motor drives a rotor shaft, onto which one or two masses may be fixed at various distances. The rotor shaft is mounted in two self-aligning ball bearings and connected to the motor 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. The position and distances to elements fixed onto the rotor shaft can be read on a scale mounted in parallel to the rotor shaft.

A transparent protective cover and safety bearing immediately next to  the masses attached to the rotor shaft ensure safe operation. 

The TM 620.20 accessory comes with measurement and evaluation software, including sensors, for data acquisition via a 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 bending vibrations and resonance of a rotating shaft 
- determination of critical speeds with different  arrangements of the bearing and masses on the rotor shaft
- investigation of the rotor shaft's self-centring effect


[1] investigation of bending vibrations and resonance of a rotating system
[2] two self-aligning ball bearings moveable to any point as the rotor shaft mount
[3] two masses that can be fixed at any point 
[4] safety bearing and transparent protective cover for safe operation
[5] two pre-selectable speed ranges, speed electronically regulated and infinitely adjustable
[6] digital speed indicator
[7] data acquisition system including GUNT software and sensors (TM 620.20) optionally available

Technical Data

Three-phase motor
- power 0,25kW
- max. speed 3000min-1 
Rotor shaft
- L=500mm
- D=6mm
- hardened steel
2x mass, disc-shaped
- m=965g
- D=80mm
- hardened steel
Shaft mount
- 2x self-aligning ball bearings
- 2x safety bearings

Measuring ranges 
- speed: 300...3000min-1
- scale for measuring distance: 0...500mm

Dimensions and Weight
LxWxH: 1150x375x405mm
Weight: approx. 49kg Required for Operation 230V, 50/60Hz, 1 phase or 120V, 60Hz, 1 phase

Scope of Delivery
1 experimental unit
1 set of instructional materials 

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