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TM 625 Elastic shafts



  • Investigation of the natural modes on 6 shafts with continuous mass distribution and of the Laval shaft1
  • Optimal visibility and simultaneous protection thanks to transparent protective cover


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


[1] experimental unit for determining critical speeds and investigation of the natural modes of a shaft
[2] 6 high-strength steel shafts
[3] up to 4 self-aligning ball bearings moveable to any point as the shaft mount
[4] a mass to construct a Laval rotor
[5] 3 safety bearings and transparent protective cover for safe operation
[6] 2 pre-selectable speed ranges, speed electronically regulated and infinitely adjustable
[7] digital speed indicator
[8] system for data acquisition including GUNT software and TM 620.20 sensors available as an option

Technical Data
6 rotor shafts
- D: 3mm, 6mm, 7mm
- L: 600mm, 900mm
- hardened steel
Mass, disc-shaped
- D: 80mm
- m: 965g
- hardened steel
- power: 0,25kW
- max. speed: 6000min-1 
- speed electronically controlled
Shaft mount
- 2x self-aligning ball bearings
- 2x safety bearings

Measuring ranges
- speed: 0...6000min-1
- scale for measuring distance: 0...1000mm

Dimensions and Weight
LxWxH: 1550x380x450mm
Weight: approx. 65kg Required for Operation 230V, 50/60Hz, 1 phase or 120V, 60Hz/CSA, 1 phase

Scope of Delivery
1 experimental unit 
6 shafts
1 set of tools
1 set of instructional material

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