June 20, 2010
June 20, 2010
June 23, 2010
15.855.1 - 15.855.10
Mass Unbalance in an MET Course Abstract
Mass unbalance, the condition where the centers of mass and rotation differ, is one of the most common sources of vibration in rotating machinery. Mechanical Engineering Technology (MET) students are likely to encounter vibration throughout their careers and need to understand its generation, transmission, and testing. Conveying vibration concepts effectively to students who typically have only limited exposure to differential equations presents a challenge for engineering technology faculty. Mass unbalance and related corrective procedures offer a practical venue for communicating fundamental vibration concepts, design concerns, experimental techniques, data analysis, and dynamic balancing methods to engineering technology students. The purpose of this paper is to document the versatility of mass unbalance and balancing as an instructional aid in an upper division elective course in machinery health monitoring. Examples of student assignments incorporating mass unbalance are presented. Results of ongoing assessment of related course learning objectives are provided.
Working from theory for a simple single degree of freedom vibrating system undergoing forced vibration, the force due to a rotating mass unbalance is the product of the eccentric mass, m, and its rotational acceleration component, eωf2, where e is the offset distance from the center of rotation to the eccentric mass and ωf is the rotor’s rotational speed in units of radians per second. The resulting applied force is modeled as F(t) = (meωf2)sin(ωft).1 Experimental data verifies the vibration energy caused by mass unbalance is essentially all included in a single sine wave at the frequency corresponding to operating speed.
Figure 1. Typical unbalance condition
Awareness of the existence of mass unbalance dates back at least several centuries.2 As machinery operating speeds have increased, understanding the force that mass unbalance causes
Denton, N., & Williams, M., & Kmec, J. (2010, June), Mass Unbalance In An Met Course Paper presented at 2010 Annual Conference & Exposition, Louisville, Kentucky. 10.18260/1-2--16131
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