1. DESIGN OF SPUR GEARS By C.VIGNESH ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
THIAGARAJAR COLLEGE OF ENGINEERING
MADURAI

2. AGMA Standard of Gear Design
A designed gear should meet following design criteria conforming to AGMA standards. It should have
Enough mechanical strength to withstand force transmitted.
Enough surface resistance to overcome pitting failure.
Enough dynamic resistance to carry fluctuating loads.

3. DESIGN PROCEDURE FOR SPUR GEAR
The gear is designed on the basis of beam strength using lewis equation and checked for dynamic loading and wear using Buckingham equation. Step 1: Selection of materials: Select a suitable material for gear and pinion, if not given select materials from PSG Design Data book. Step 2: Calculation of number of teeth Gear(T2) and Pinion (T1) a) Assume Number of teeth on pinion(T1) if not given. b) Then Number of teeth on Gear(T2) = i× T1 i= Gear ratio Step 3: Calculation of Initial dynamic load (PSG Design Data book P.No-8.50) Transmitted load (Ft) = HP ×(75/Vm) HP = Power (kW) Vm= Pitch line velocity(m/min)

4. [σb] = Design bending stress in kgf/cm2
Initial dynamic load (Fd) = Ft × Cv
Cv = Velocity factor based on velocity of the gear.
Step 4:
Calculation of beam strength (Fs) (PSG Design Data book P.No-8.50)
Fs = [σb] × π × m × y × b
[σb] = Design bending stress in kgf/cm2
m = Module in cm
y = Form factor(PSG Design Data book P.No-8.18)
b = Face width in cm
Step 5:
Calculation of module(m)
Since the gear is designed based on strength so equating Fd and Fs
Then select the nearest higher standard module from (PSG Design Data book P.No-8.2)

5. Step 6: Calculation of b,d and v b = face width ; b = 10×m d = Pitch circle diameter ; d1 = T1 × m v = Pitch line velocity ; v1 = (π d1 N1) /60 Step 7: Recalculation of the beam strength (Fs) = [σb] × π × m × y × b Step 8: Calculation of accurate dynamic load (Fd) (PSG Design Data book P.No-8.51)

6. Step 9:
Check for beam strength
Compare Fd and Fs
Fd ≤ Fs , then the gear tooth has adequate beam strength and it will not fail by breakage. Thus the design is Satisfactory.
Fd ≥ Fs , Design is not satisfactory, Now increase the face width ,module.
Step 10:
Calculation of the maximum wear load (Fw) (PSG Design Data book P.No-8.51)
Fw = d1 × b × Q × Kw
Q = Ratio factor
Kw = Load stress factor
Step 11:
Check for wear strength
Fd ≤ Fw , then the gear tooth has adequate wear capacity and it will not wear out. Thus the design is Satisfactory.

7. Step 12: Calculation of basic dimensions of pinion and gear

8. THANK YOU