Page 118 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
96
Figure E4.1 Illustration for Example Problem 4.1.

Steps Computation Results Units

1. Select the type Select Type A parallel key Type A
of key
2. Decide the size Decide the size of key b × h from Table 4.1. b = 22 mm
of the key Since d = 80 mm, select b × h as 22 × 14; h = 14 mm
According to the width of the hub, select the length of L = 110 mm
the key from the same table as L = 110 mm. Therefore, l = 88 mm
the working length of the key is
l = L−b = 110–22 = 88 mm.
3. Select the The failure mode of key connection is the crushing of [ ] = 125 MPa
p
allowable stress the weakest material. For a steel gear and shaft under
stable loads, select the allowable bearing stress as
[ ] = 80 MPa.
p
4. Calculate the From Eq. (4.2) Select a key with mm
crushing strength = 4T × 10 3 = 4 × 1000 × 10 3 = 40.6 MPa b × h × L as
of the key p hld 14 × 88 × 80 22 × 14 × 110
Since < [ ], the selected key is acceptable.
p
p
5. Design If the transmitted torque is doubled, then
modification 4T 4 × 2000 × 10 3
= = = 81.2 > [ ]
p
p
hld 14 × 88 × 80
The following design modification are suggested:
1) Since the actual stress is close to the allowable stress,
select Type B parallel key can increase the working Select a type B key
length of the key that transmits torque.
with b × h × L as
The strength is 22 × 14 × 110 mm
4T 4 × 2000 × 10 3
= = = 64.9 < [ ]
p hld 14 × 110 × 80 p or
2) Select two Type A keys to carry the load. Select two Type A
The strength is keys with
4T 4 × 2000 × 10 3 dimensions mm
= = = 54.1 < [ ]
p hld 14 × 88 × 1.5 × 80 p 22 × 14 × 110

4.2 Splines

Splines are standardized products. They perform the same function as keys in transmit-
ting torque between a shaft and mating elements. Splines are used when multiple keys
are required or when a high torque needs to be transmitted.