I. Common types of Rotating Machines
Most machines incorporate rotating components.
Rotary machines refer to machines whose main function is fulfilled through rotational motion, particularly those machines in which the main components rotate at high speeds.
The types of rotating machines are diverse and include steam turbines, gas turbines, centrifugal compressors, generators, pumps, hydraulic turbines, fans and electric motors.
The main components of these machines consist of rotors, bearing systems, stators and unit housings, as well as couplings.
The rotational speed of these machines can vary from a few tens to several hundred thousand rotations per minute. Some examples of typical rotating machines are described below.
1. Steam turbine
A steam turbine is a rotating machine that converts steam energy into mechanical work, also known as a steam rotor.
It is mainly used as a prime mover for power generation, but can also directly drive various pumps, fans, compressors and ship propellers.
Furthermore, the exhaust or intermediate extraction of a steam turbine can be used to meet heating needs in both industrial and domestic environments.
2. Centrifugal Compressor
A centrifugal compressor works by transferring energy to a gas through a rotor, thereby increasing its pressure.
It may consist of a single or multiple stages. This type of compressor falls into the category of rotary blade compressors, also known as turbochargers.
Inside the centrifugal compressor, the high-speed rotation of the rotor exerts a centrifugal force on the gas, and expansion in the diffuser channel further increases the gas pressure.
3. Electric generator
An electrical generator is a mechanical device that converts various forms of energy into electrical energy.
Originated during the Second Industrial Revolution, it was first developed by German engineer Siemens in 1866.
Powered by hydraulic turbines, steam turbines, diesel engines or other mechanical devices, generators transform energy generated by water flow, air flow, fuel combustion or nuclear fission into mechanical energy.
This mechanical energy is then converted into electrical energy by the generator. Generators have a wide range of applications in industrial and agricultural production, defense, technology and everyday life.
4. Water pump
A water pump is a mechanical device designed to transport or pressurize liquids.
Transfers mechanical energy from the main engine or other external energy sources to the liquid, increasing its energy.
It is mainly used to transport various liquids, including water, oil, acid-base solutions, emulsions, suspensions and liquid metals.
The pump can also handle mixtures of liquids and gases, as well as liquids containing suspended solids.
5. Fans
A ventilator is a mechanical device that relies on the input of mechanical energy to increase gas pressure and expel it.
It is a kind of fluid driven machinery, with exhaust pressure less than 1.5×10 5 Pa. Fans are widely used for ventilation, dust extraction and cooling in factories, mines, tunnels, cooling towers, vehicles, ships and buildings.
They are also used for ventilation and air extraction in industrial boilers and furnaces, for cooling and ventilation in air conditioners and household appliances, for drying and sorting grains, as well as for airflow in wind tunnels and inflation and propulsion of hovercrafts. .
6. Electric Motor
The electric motor is a device that converts electrical energy into mechanical energy. It was designed based on the phenomenon of an electrified coil rotating under the force of a magnetic field.
Depending on the energy source used, motors are categorized into direct current motors and alternating current motors.
Most motors in power systems are alternating current motors, which can be synchronous or asynchronous. The electric motor mainly consists of a stator and a rotor.
The direction of the force exerted on the electrified wire in the magnetic field is related to the direction of the current and the magnetic field lines.
The working principle of an electric motor is the force exerted by the magnetic field on the current, causing the motor to rotate.
II. Vibration classification of rotational machines
The main function of rotating machinery is performed by its rotating components, with the rotor being the most crucial.
The main indicator of malfunction in rotating machinery is abnormal vibration and noise. Vibration signals, reflected in amplitude, frequency and time domain, illuminate machine fault information.
Therefore, understanding the vibration mechanisms of rotational machines under malfunction conditions is essential for monitoring operational status and improving the accuracy of fault diagnosis.
Vibrations in rotational machines can be categorized into three types based on the nature of mechanical vibration.
1. Forced Vibration
Forced vibration, also known as synchronous vibration, is a type of vibration caused by continuous and periodic external excitation forces.
Forced vibration constantly acquires energy from the external environment to compensate for the energy consumed by damping, maintaining a consistent amplitude of vibration within the system.
This vibration, in turn, does not impact the disturbing force. The main causes of forced vibration include rotor mass imbalance, misaligned couplings, static friction in the rotor, loose mechanical parts, and damage to rotor components or bearings.
The characteristic frequency of the forced vibration is always equal to the frequency of the disturbing force.
For example, the forced vibration caused by rotor mass imbalance has a vibration frequency that is always equal to the rotational speed frequency.
2. Self-excited vibration
Self-excited vibration refers to vibration caused by alternating forces generated by the internal movement of the machine during operation. As soon as the vibration stops, the alternating force naturally disappears.
The frequency of self-excited vibration is the natural (or critical) frequency of the machine, regardless of the external excitation frequency.
Oil swirl and oil film oscillation are common types of self-excited vibration in rotating machines, mainly caused by the internal resistance of the rotor and friction between static and dynamic components.
Compared to forced vibration, self-excited vibration occurs more suddenly, with more severe vibration intensities, causing serious damage to the machine in a short period.
3. Non-constant forced vibration
Non-steady forced vibration is a type of forced vibration caused by external disturbances.
Characteristically, it shares the same frequency as the disturbance; the vibration itself reciprocally influences the magnitude and phase of the disturbance. Both the amplitude and phase of the vibration vary.
For example, if uneven thermal deformation occurs in a certain part of the rotor shaft, this is equivalent to the addition of an unbalanced mass to the rotor, causing changes in the amplitude and phase of the vibration.
On the other hand, these changes in amplitude and phase affect the magnitude and location of irregular thermal deformation, causing the forced vibration to vary continuously.
