Shaft Design
Figure 1 shows a simple gear box with various machine elements and
components. Shaft No. 2 is rotating through gears by shaft No. 1 which is
rotating through two pulleys by an electric motor.
The transmission shaft No. 1 stands on two bearings and the rotational speed is transfer by the belt. The two shafts are made of hot–rolled alloy steel with yield strength σy= 500 MPa and σuts= 1200 MPa. The belt transmits (a) 14,7KW of power at (b) 1700 rpm.
The belt is prestressed with a ration of (c) 2,05 The two gears are spur gears with 20ο pressure angle. The bearing distance for the shaft 1 is (d) L1= 420 mm and for the shaft 2 is (e) L2= 260 mm. The output pulley has to be design for (f) Nb= 2 number of belts. For both shaft the safety factor is (g) SF= 3,3 – Data for each student: (a/a 64.)
Α. CALCULATIONS
1. Calculate the smallest safe shaft diameter for the shaft 1 and 2. Provide a free body diagram and all necessary bending moments and torque diagrams.
2. Calculate the dimensions of the keys and the keyways at shaft 1 and 2 for the two gears and the pulleys.
3. Determine the critical speed of rotating shaft 2.
B. DRAWINGS AND ASSEMBLY
1. Make the construction drawings of all different parts (2D)
2. Design the two shafts (shaft 1 and shaft 2 ) with all components and explain in details and explain in details how to make the assembly (assembly manual).
3. Design two different cross sections of the device with all components (2D).
4. Design the gear box with all components in 3D.
INTRODUCTION
The purpose of this assignment is to :
Determine the smallest safe diameter for the two shafts using the ASME design code for transmission shafts.
Calculate the dimensions of the keys and the keyways at shaft 1 and 2 for the two gears and the pulleys.
Calculate the critical speed of rotation for shaft 2.
Prepare the construction drawings of the device.
Design the full 3D part and two different cress sections.
Data :
Power transmitted by shafts = 14,7KW
Rotational speed of driving pulley = 1700rpm
Pre stress belt ratio = 2,05
Gear pressure angle = 20 deg
Safety Factor SF or ns = 2,7
Yield strength of shaft material = σy=500 MPa
Ultimate tensile strength of shaft material = σuts= 1200 MPa
Material of keys AISI 1020 cold drawn = σy = 350 MPa
A/A student data = 64
