Blackboard X FXC – A
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Question 1
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Determine the required key geometry (width (W), height (H), and length (L)). The key is for a V-belt sheave transmitting 125 Nm of torque to a 44 mm diameter shaft. The sheave is made from ASTM Class 20 Cast Iron with a material strength of 138 MPa and has a hub length of 5 cm. For the key material, use SAE 1018 steel first, and if the design is not satisfied, then use SAE 1040 steel for a harder material. For SAE 1018: Sy = 370 MPa and for SAE 1040: Sy = 490 MPa. Use design/safety factor, N = 3. You can make use of the table below. SI metric sizes
Key di
Over (mm) to-including (mm) Width, Nmm Height, mm
6
8 10 12 17 22 30 38 44 50 58 65 75 85 95 110 130
2 8 3 10 4 12 5 17 6 22 8 30 10 38 12 44 14 50 16 58 18 65 20 75 22 85 25 95 28 110 32
From the table, the width of the key is 10 mm and the height of the key is 12 mm. From calculation, the minimum length of the key should be 44 mm.
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