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Design 1 - Spur Gear
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A cast steel pinion running at 960 rpm transmit a maximum power of 20 kW to a cast iron gear running at 144 rpm. Design a spur gear drive having a standard 20° stub tooth of involute profile. Check the design for dynamic load & wear. Take static safe stress a 103MPa & 55MPa for cast steel pinion & cast iron gear respectively. Assume [σc]=1000mPa

Solution:

Steps Particular Details
Step 1 Given data Spur gear, Power(Pm)=20kW, N1 =960rpm, N2 =144rpm, α=20 design criteria- Lewis dynamic load, checking criteria- wear strength, pinion-cast steel [σb1]=103MPa, gear-cast iron [σb2]=55MPa
Step 2 Assumptions '1' or 'p'-driver (pinion) and 2 or 'g'-driven (gear), external meshing, closed structure, carefully cut gears, service factor=1.3(light shock), module-m, face width (b) = 10m

Further steps are explained as below


3) Gear pair dynamics

Design Power, ( P ), P = Pm x Service Factor, P = 20 x 1.3 = 26kW

Gear Ratio, ( i )

i=NpNG=N1N2=960144=6.67

Selection number of teeth on pinion and gear

Z1=Zp=14 to 17=14

Z2=Zg=i×Z1=6.67×14=93.3893

Lewis form factor PSG 8.50

Y=π[0.1750.95Z] for 20 Stub teeth  a) Yp=π[0.1750.95Zp]=π[0.1750.9514]=0.3365 b) Yg=π[0.1750.95Zg]=π[0.1750.9593]=0.5176


4) Strength factor calculation to find weaker element

(SF)P=(σb)P×Yp=103×0.3365=34.66

(SF)g=(σb)g×Yg=55×0.5176=28.47


5) Comparing both, gear is weaker hence designing the gear.

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