2007-05-24 16:01:23 · 4 answers · asked by Mukesh Dak 3 in Science & Mathematics ➔ Engineering
A machine can have any number of critical speeds. Critical speeds are termed due to criticality in operation of the equipment at that particular rpm or speed. At these RPM the amplitude of vibration is theoretically infinte or very large amplitude of vibrations are observed.
Some machines do not have specific speed or RPM as critical rpm but a range or ranges of RPM.
The basic idea to find the critical RPM or speed is that it should not match with the operating speed of the machine in any circumstances. meaning during no-load to overload speeds as well.
The machines are suitably designed to allow that the machines do not acquire any high critical speeds. For low critical speeds, the increase of speed or RPM should be very fast and accurate enough so that the machine passes the low critical speed or range very fast without being damaged by vibration.
2007-05-25 19:58:04 · answer #1 · answered by poppins 4 · 0⤊ 0⤋
Theoretically, rotating equipment can have infinite critical speeds. Each critical speed is characterized by the number of nodes in the wave shape. You can have radial and torsional critical speeds.
The only ones that you have to worry about are the ones that are within the operating range of the machine.
2007-05-24 18:21:26 · answer #2 · answered by hpfgirl 2 · 1⤊ 0⤋
Any rotating shaft will have lateral (or flexural) and torsional natural frequencies.
If the shaft is subjected to a force at any of these frequencies, the amplitude of vibration will be particularly large.
The dynamic forces in a rotating machine will generally occur at multiples of rotational frequency and at certain speeds one of the forcing frequencies will coincide with a natural frequency.
These speeds are known as critical speeds. The most significant critical speed is usually the speed at which the rotational frequency coincides with the first flexural natural frequency of the shaft.
However, there can be other flexural frequencies at which the forcing frequencies will match a lower or higher natural frequency than the most significant frequency.
2007-05-24 18:18:27 · answer #3 · answered by gatorbait 7 · 1⤊ 0⤋
Only one, if it is "critical" to producing the most PPH
2007-05-24 16:18:53 · answer #4 · answered by Anonymous · 0⤊ 1⤋