Help with Bending Moment Diagrams & Shaft Design Questions

In summary, the conversation is discussing the design and calculations for a rotating shaft that can transmit 4kW of power at a speed of 450 revolutions per minute. The shaft is made of CS1030 material and can handle a maximum torque of 2.6 FLT. The effects of inertia are not significant and any resultant thrust can be taken at the left hand bearing. The conversation goes on to discuss the calculations for drawing bending moment diagrams, determining the bending moment at point A, and calculating the shaft diameter using the AS 1403 design code. Finally, it is mentioned to use self-aligning ball bearings with specific diameters and a design life of 32000 hours, and to calculate the torque transmitted by the shaft.
  • #1
reuben19
5
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Hi! Can someone please point me in the right direction with this? I'm having trouble and any form of help would be greatly appreciated :) It's a homework question!

A rotating shaft is able to transmit 4kW of power whilst rotating with a speed of 450 revolutions per minute. The maximum torque at the start period is equal to 2.6 FLT. Power can be applied in either direction and the helical gears are arranged to give opposing directions for the axial force generated by the tooth action. The shaft is manufactured from CS1030. Effects of inertia are not significant. Any resultant thrust can be taken at the left hand bearing. The number of revolutions of shaft per year > 900 The number of mechanism starts per year > 600

A) Draw bending moment diagrams for the horizontal and vertical planes for normal, full load, maximum speed (450 rev/min), running conditions. (Use the tension condition between gear and pinion).

B) From (A), determine the bending moment absolute at point A.

C) Assuming the machine starts under full load, use the AS 1403 shaft design code and check the shaft at point A. The calculations are to be done adopting 50 mm for the diameter at the step as specified. Material of manufacture is CS1030.

D) If the diameter (58mm) mentioned in (C) was not known, use AS1403 and determine a trial diameter.

E) Assuming the bearings are self-aligning ball, with a diameter of 55 at the left hand side and 50 at the right hand side, choose the most appropriate bearings. Design for 32000 hours life.

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  • #2
F) Calculate the torque transmitted by the shaft.For part A, you can use the equations for power, torque, and angular velocity to calculate the torque at the pinion gear and the gear, respectively. Then you can draw the bending moment diagrams for both the horizontal and vertical planes.For part B, you can use the equations for torque, angular velocity, and the distance between the center of the shaft and point A to calculate the bending moment at point A.For part C, you can use the AS 1403 shaft design code to calculate the shaft diameter at point A. The calculations should include a factor of safety, the torque transmitted by the shaft, the rotational speed, and the material of manufacture (CS1030).For part D, you can use the AS 1403 shaft design code to determine a trial diameter for the shaft. The calculations should include a factor of safety, the torque transmitted by the shaft, the rotational speed, and the material of manufacture (CS1030).For part E, you can use the bearing catalogs to find bearings that meet the requirements for self-aligning ball bearings, with diameters of 55 at the left hand side and 50 at the right hand side. Make sure to use bearings with a minimum rating of 32000 hours life.For part F, you can use the equations for power, torque, and angular velocity to calculate the torque transmitted by the shaft.
 

What are bending moment diagrams and why are they important in shaft design?

Bending moment diagrams are graphical representations of the bending moments (forces) acting on a shaft at various points along its length. They are important in shaft design because they help engineers determine the maximum stress and deflection that the shaft will experience, which is crucial for ensuring its structural integrity and preventing failure.

How do you calculate the bending moment at a specific point on a shaft?

The bending moment at a specific point on a shaft can be calculated by multiplying the force acting on the shaft by the distance from that point to the force. This is known as the moment arm. The bending moment can also be affected by the shape and orientation of the force, so it is important to consider these factors as well.

What is the difference between a positive and negative bending moment in a diagram?

A positive bending moment in a diagram indicates that the top of the shaft is in tension (being pulled apart), while the bottom is in compression (being pushed together). A negative bending moment indicates the opposite, with the top of the shaft in compression and the bottom in tension. It is important to identify these differences in order to properly design the shaft to withstand the forces acting on it.

How do you determine the maximum bending moment in a shaft?

To determine the maximum bending moment in a shaft, you must first calculate the bending moment at various points along the shaft and then plot these values on a bending moment diagram. The highest point on the diagram will correspond to the maximum bending moment. This information is crucial for selecting the appropriate material and dimensions for the shaft.

What other factors should be considered in shaft design besides bending moment?

In addition to bending moment, other factors that should be considered in shaft design include torsional stress, shear stress, and fatigue. These can all contribute to the failure of a shaft and must be carefully analyzed and accounted for in the design process. Additionally, the type of loading, operating conditions, and material properties should also be taken into consideration.

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