Torsional Vibration Analysis of Vertical Roller Mill Gearbox

Abstract

Due to increasing populations, human need is increasing exponentially day-by-day. To accommodate the need of people, the production should be done on large-scale like buildings, energy generation for that cement, coal and other raw materials are required in bulk, which yields the need of heavy machinery. To make cement or clinker from its raw material it is first crushed in roller mills. The best option with very high production output is Vertical Roller Mill (VRM). VRM gearbox is critical to design due to heavy load and high material quantity. So here the whole gear train is formulated according to gear-ratio required and then strength based gear design is also done. First of all, doing the strength based gear design for both, spiral bevel and planetary stage. After doing this procedure we can know that our design is safe or not. If design is not safe then we should require to change the previous dimensions. Gear is designed based on the AGMA standard. Material used for the gears is 18CrNiMo7-6. VRM gearbox consists of many rotating parts constitutes complex dynamic system. While designing gears of such machineries, it is very important to consider vibration characteristics into account. Rotating systems running at speeds close to the natural frequency of the system results in excessive deformation and large stresses can occur which leads to catastrophic failure of the system. This dissertation work focuses on performing vibration analysis of the system. As the physical system is complex, the lumped mass model considering various connections, power transmitting elements and inertia of rotating parts have been developed. To check the torsional vibrations, vibration analysis using Holzer method is also performed, which yields supportive results. Using the Holzer method we got the value of natural frequency is 628.2572 rad/sec or 99.9902 Hz. Now, analytical result will compared with simulated result after completion of Eigen value analysis in Hypermesh. And the result in Hypermesh is 102.3679 Hz, which is almost nearer. While input excitation frequency is 16.5 Hz, which is far away from natural frequency. Hence, inputs are safe for the gearbox.