Machine Design
Gear Drive
Introduction:
The values for service factor are for enclosed well lubricated gears. In case of non-enclosed and grease lubricated gears, the values given in the above table should be divided by 0.65.
Design Procedure:
In order to design spur gears, the following procedure may be followed :
1. First of all, the design tangential tooth load is obtained from the power transmitted and the pitch line velocity by using the following relation :
P = Power transmitted in watts,
*v = Pitch line velocity in m / s , = πD N/60
D = Pitch circle diameter in metres,
*v = Pitch line velocity in m / s , = πD N/60
D = Pitch circle diameter in metres,
N = Speed in r.p.m., and
CS = Service factor.
CS = Service factor.
The following table shows the values of service factor for different types of loads :
2. Apply the Lewis equation as follows :
WT = σw.b.pc.y = σw.b.π m.y
= (σo.Cv) b.π m.y ... (Q σw = σo.Cv)
= (σo.Cv) b.π m.y ... (Q σw = σo.Cv)
Notes :
(i) The Lewis equation is applied only to the weaker of the two wheels (i.e. pinion or gear).
(ii) When both the pinion and the gear are made of the same material, then pinion is the weaker.
(iii) When the pinion and the gear are made of different materials, then the product of (σw × y) or (σo × y) is the deciding factor. The Lewis equation is used to that wheel for which (σw × y) or (σo × y) is less.
(ii) When both the pinion and the gear are made of the same material, then pinion is the weaker.
(iii) When the pinion and the gear are made of different materials, then the product of (σw × y) or (σo × y) is the deciding factor. The Lewis equation is used to that wheel for which (σw × y) or (σo × y) is less.
(iv) The product (σw × y) is called strength factor of the gear.
(v) The face width (b) may be taken as 3 pc to 4 pc (or 9.5 m to 12.5 m) for cut teeth and 2 pc to 3 pc (or 6.5 m to 9.5 m) for cast teeth.
(v) The face width (b) may be taken as 3 pc to 4 pc (or 9.5 m to 12.5 m) for cut teeth and 2 pc to 3 pc (or 6.5 m to 9.5 m) for cast teeth.
3. Calculate the dynamic load (WD) on the tooth by using Buckingham equation, i.e.
WD = WT WI
In calculating the dynamic load (WD), the value of tangential load (WT) may be calculated by
neglecting the service factor (CS) i.e.
WT = P / v, where P is in watts and v in m / s.
neglecting the service factor (CS) i.e.
WT = P / v, where P is in watts and v in m / s.
4. Find the static tooth load (i.e. beam strength or the endurance strength of the tooth) by using the relation, WS = σe.b.pc.y = σe.b.π m.y
For safety against breakage, WS should be greater than WD.
For safety against breakage, WS should be greater than WD.
5. Finally, find the wear tooth load by using the relation, Ww = DP.b.Q.K
The wear load (Ww) should not be less than the dynamic load (WD).
No comments:
Post a Comment