Jeffcott rotor / Laval shaft / Lavalläufer - Experiments
The following special phenomena are investigated:
• Demonstration of the critical speed
• Self-alignment of the shaft at high speed
• Types of oscillation and modes
• Rotor-foundation coupling
A Jettcott rotor is the simplest rotor model. The most important characteristics are a massless shaft, a fixed rigid circular disc and rigid bearings. Commonly the Jettcott rotor is also called "Laval shaft".
The design model of a Jeffcott rotor should help pupils as well as students and engineers to get a first feeling of the shaft's behaviour at critical speed and what happens, if the shaft is driven faster than the critical speed.
Rotor dynamics are of great importance in the design, manufacture, assembly and in the use of shafts and rotating machines. Special phenomena occur, which people would not expect and which are difficult to understand and imagine.
Explanation of the test stand:
• The components of the model are mounted on a wood plate.
• The heart of the Jeffcott rotor is the steel shaft combined with the fixed rigid circular disc.
• Safety bearing: This kind of bearing is used as a safety equipment especially for the run of the shaft at critical speed. The oscillation of the disc is limited.
• Drive shaft: The drive of the Jeffcott rotor is carried out by a free wheel ratchet and a socket. The belt drive with a gear ratio of 8 is necessary to enable rotation speeds up to 2000rpm.
• Belt tension: A threaded rod and nuts are used to tension the belt.
• A profilometer for car tires is the basis for measuring the oscillation of the shaft and the disc.
• With a tachometer, usually used for bicycling, the revolution of the shaft can be measured. Therefore also a speed sensor has to be mounted.
• By mounting two additional bearings on a given position the critical speed of the shaft can be changed (not shown in the movie).
• The effect of the frame-foundation can be forecasted and simulated by adding an expanded material plate under the wood plate.
