Balancing of Rotating Masses
Balancing of rotating masses refers to the process of ensuring that the center of mass of a rotating system coincides with its axis of rotation. This is important to prevent vibration, reduce wear and tear, and improve the overall performance and longevity of the system. Balancing can be achieved through various methods such as adding counterweights or adjusting the distribution of mass.
3 Key excerpts on "Balancing of Rotating Masses"
eBook - ePub- Dick Jeffrey(Author)
- 2013(Publication Date)
- Routledge(Publisher)
...The only (radial) load imposed on the bearings should be due to the weight of the rotating element. In practice, it is impossible to achieve perfect balance and, even after sophisticated balancing techniques have been used, a rotating element will always possess some residual imbalance. The need for accurate balancing increases with the mass and size of the rotor and the speed of rotation. To ensure safe and reliable operation of any rotating machine it is desirable that the rotating elements be balanced within defined limits according to the size and nature of the machine. It is common practice these days to monitor machine vibrations as a means of determining standards of machine balance and the technique involved is discussed in Chapter 10. The mass distribution of a machine element can be changed by either adding or subtracting mass at any position on the rotor. Mass may be added by welding, bolting or otherwise attaching additional material to the rotor, usually in measured quantities. Mass may be removed either by drilling a hole in the rotor or by grinding or filing material from the surface. The key to successful balancing lies in the method used to determine the position at which mass is to be added or removed. In most cases it is preferable to remove material from the heavy side of a rotor, rather than add material to the light side because this overcomes the problem of having to provide a means of attaching the additional material. However, there may be circumstances where this is not possible because of strength or visual considerations. Static Balancing The simplest and easiest method of balancing is one that uses static conditions to determine the relative position of the centre of gravity and centre of rotation...
eBook - ePub- Clifford Matthews(Author)
- 2011(Publication Date)
- Wiley-Blackwell(Publisher)
...The objective is to maintain the operating vibration of the machine within manageable limits. Dynamic balancing normally involves two measurement/correction planes and involves the calculation of vector quantities. The component is mounted in a balancing rig which rotates it at or near its operating speed, and both senses and records out-of-balance forces and phase angle in two planes. Balance weights are then added (or removed) to bring the imbalance forces to an acceptable level. Figure 5.3 5.6.1 Balancing Standard: ISO 1940/1: 2003 The standard ISO 1940/1: 2003 (identical to BS 6861: Part 1: 1987): Balance quality requirements of rigid rotors is widely used. It sets acceptable imbalance limits for various types of rotating equipment. It specifies various (G) grades. A similar approach is used by the standard ISO 10816-1. Finer balance grades are used for precision assemblies such as instruments and gyroscopes. The principles are the same. 5.7 Vibration Vibration is a subset of the subject of dynamics. It has particular relevance to both structures and machinery in the way that they respond to applied disturbances. 5.7.1 General Model The most common model of vibration is a concentrated spring-mounted mass which is subject to a disturbing force and retarding force. Figure 5.4 The motion is represented graphically as shown by the projection of the rotating vector x. Relevant quantities are The ideal case represents simple harmonic motion with the waveform being sinusoidal. Hence the motion follows the general pattern: Vibration displacement (amplitude) = s Vibration velocity = v = d s /d t Vibration acceleration = a = d v /d t 5.8 Machine Vibration There are two types of vibration relevant to rotating machines Bearing housing vibration. This is assumed to be sinusoidal. It normally uses the velocity (V rms) parameter. Shaft vibration. This is generally not sinusoidal...
- Robert X. Perez, Robert X. Perez(Authors)
- 2022(Publication Date)
- Wiley-Scrivener(Publisher)
...This kind of random imbalance distribution is referred to as dynamic unbalance. Dynamic unbalance in a rigid rotor requires balance correction in 2 planes. (A rotor that operates at a rotational speed below 70% of its critical speed is considered to be a rigid rotor. The critical speed is the speed at which the natural frequency of the rotor is excited. Ninety percent or more of industrial rotors are rigid.) Flexible rotors often required balance corrections at more than two planes. Balancing Balancing is the process of adding or removing weight from the rotor to align the effective mass center with the axis of rotation. The ultimate goal of balancing is to add the proper correction weights, at the right locations, to offset the net imbalance on a troublesome rotor in order to minimize rotor shaking forces. Rotor unbalance generates forces that cause a rotor and support structure to vibrate at a frequency equal to running speed, commonly called the 1x frequency. Vibration associated with imbalance is the most common type of vibration found around industrial machines, which is why great time and effort is expended to balance rotors to accepted standards. In the case of a flexible rotor, we hope to ensure that vibration levels remain below an acceptable magnitude of rotor deflection at all speeds, up to the maximum service speed. Most rotors are balanced before machine assembly because of the limited access to the rotor in the field. Most balancing standards, such as ISO and API standards, classify rotor in accordance with their balancing requirements and establish methods of assessment of residual unbalance. When analyzed with a spectral analyzer, imbalance tends to show up as a predominant 1x peak in the vibration spectra. These high 1X amplitudes show up predominantly in the radial direction, i.e., normal to the axis of rotating. X-Y radial 1x components should be approximately equal...
