General Vibration Standard - Evaluation Standard According to Bearing Vibration Amplitude
Introduction
The vibration of bearings is an important factor when considering the operational status of a mechanical system. In order to properly evaluate the performance of a bearing, the vibration emitted by it must be taken into account. This article will provide an overview of the general vibration standard used to evaluate and grade bearing vibration amplitude.
Basics of Vibration
Vibration is any kind of physical motion or deformation. Generally, when we discuss vibration, we think of the oscillating motion of an object; that is, the oscillation of an object around a central point. In the case of bearings, the vibration is the oscillatory movement of the bearing’s components as a result of tribological forces.
All vibration has amplitude, periodicity, and frequency. The amplitude describes the maximum displacement of an object from its rest position during an oscillation. The period is the duration of one cycle of oscillation and is measured in seconds. Frequency falls into two types- the number of cycles per second and the number of cycles per minute.
Common Measurement Units Used To Evaluate Bearing Vibration
Vibration amplitudes are usually measured in terms of peak-to-peak displacement, acceleration, and velocity. To measure displacement, peak-to-peak displacements are generally used. Peak-to-peak displacement is defined as the difference between the maximum and minimum positions of a given cycle of oscillation. Acceleration is the rate of change in velocity and is usually given in units of g (acceleration due to gravity). Lastly, velocity is the rate of change in velocity of an object and is in units of inches per second.
Vibration Levels in Bearings
Bearing vibration amplitudes vary substantially depending on the type of bearing, the load, and the operating conditions. Generally, the vibration emitted by a healthy bearing should be minimal compared with the maximum vibration it is capable of emitting. As such, when evaluating the performance of a bearing, the overall vibration level is compared to the maximum vibration level for that particular bearing. There are a variety of levels used to define different categories of vibration levels:
Low-level Vibration: Less than 1g (grms)
Medium-level Vibration: 0.5-2g (grms)
High-level Vibration: Greater than 1.5g (grms)
Evaluation Standard According to Bearing Vibration Amplitude
In order to evaluate the performance of a bearing, the overall vibration level must be compared to the maximum vibration level for that particular bearing. There are two common methods of evaluation that are used to grade bearing vibration according to its amplitude.
Firstly, vibration evaluation standards are often given in terms of “acceptance criteria”. This means that certain vibration amplitudes are used to determine whether the bearing is operating below an acceptable level or not. Acceptance criteria can vary, depending on the type of bearing and the application.
In other cases, vibration evaluation standards are given in terms of “thresholds”. This means that vibration amplitudes are used to define different vibration severity levels, ranging from minor to severe. Generally, these thresholds are used to indicate how close the bearing is to being damaged.
Conclusion
In conclusion, the general vibration standard used to evaluate and grade bearing vibration amplitudes depends on the type of bearing, load, and operating conditions. The most common methods of evaluation are in terms of acceptance criteria and threshold values. It is important to remember that even the most stringent evaluation standards may not always be sufficient to guarantee well-performing bearings, as factors such as lubrication, contamination, structural integrity, and bearing mismatch are not taken into account. Nevertheless, understanding the general vibration standard is essential for preventative maintenance and to keep a bearing in optimal condition.
