Blog 4


The team has completed a 3D CAD drawing of the test enclosure and the bearings that have been selected to support the shaft while it reaches its critical RPM speed. Figure 1 shows the shaft that is being used within the test enclosure. As stated previously, the shaft has been balanced through a balance machine and the natural frequency has been calculated to confirm that it is a rigid shaft. Figures 2 and 3 show the current progress made for the CAD drawings. 


Figure 1: 3D CAD of shaft 

Figure: 3D CAD of test enclosure 

Figure 4: 3D CAD of Ball Element Bearing

The team is currently working on designing an overspeed trip sensor. A Mechanical overspeed trip sensor is a device that is in contact when the plunger extrudes out of the overspeed trip system once it reaches its maximum RMPS. Once in contact, the sensor will shut down the system, and bring the shaft to a complete stop. This sensor will then rely on the operator or engineer to ensure that the system has exceeded its allowable operating speed. The team has started brainstorming possible ideas as shown in Figure 5. Figure 5 shows a 3D model of a trip lever. When the plunger extrudes out at comes into contact with the lever, the system will then shut off. This will rely to the operator that the shaft has reached its critical speed. 

   

Figure 5: 3D CAD model of trip lever 

Other possible ideas include using optical tape with a laser. The optical tape will be placed over the plunger hole on the overspeed trip system. A laser will be pointed directly at the tape. Once the plunger extrudes the tape will be broken and the laser will no longer be in contact with the optical tape. This will then shut down the system, indicating that the system has been tripped. Looking back at the problem statement, the goal was to design and construct a sufficient test configuration that makes use of oil-free bearings to support the rotation of the shaft, minimize vibration, and an effective means to tell when the overspeed trip has been released during testing in the enclosure. In the design, a test enclosure, ball element bearings, a shaft, and a trip indicator are incorporated by the team. The shaft is employed to replicate the RPMs of a gas turbine. To safeguard operators from potential hazards during operation, a dedicated test enclosure is included. The selection of ball element bearings was chosen for their unique operational characteristic of not requiring a fluid film, these bearings serve a dual purpose. They effectively minimize the potential mess typically associated with fluid-based bearings while also actively reducing vibrations experienced during operation. This design choice not only decreases maintenance demands but also ensures heightened stability and smoother operation of the system, ultimately enhancing its overall performance and reliability. The team has conducted a vibration analysis to calculate the natural frequency to show that it is greater than the operating speed. This shows that the shaft is rigid. Along with that, a bearing life calculation has been made by using the equation below. 

Key terms include the basic dynamic and static load ratings, rating life, and reliability. The L10 value represents the theoretical total number of revolutions that 90% of identical bearings will meet or exceed, or for a single bearing, it signifies the life associated with 90% reliability.

Additionally, the median life (L50) is typically no greater than five times the rating life, and adjustments for factors like life adjustment, material, and other operational parameters should be considered for accurate calculations. This information guides bearing selection to ensure optimal performance and longevity in diverse operating conditions. Additionally, the median life (L50) is typically no greater than five times the rating life, and adjustments for factors like life adjustment, material, and other operational parameters should be considered for accurate calculations. This information guides bearing selection to ensure optimal performance and longevity in diverse operating conditions. Looking forward to the spring of 2024, the team will have completed a list of potential buyers to purchase ball element bearings, a complete 3D CAD model of the design, and a working design of the overspeed trip sensor. The milestones set for this semester will help the team achieve the tasks that will help them finalize the design in the Spring of 2024. 

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