Page 300 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
278
Steps Computation Results Units
2. Determine According to Section 10.3.1.1, the allowable shear stress [ ]
minimum for medium-carbon steels is within the range of 20∼40 MPa.
diameter of the Select a value of 35 MPa.
shaft From Eq. (10.2), the minimum acceptable diameter of the
shaft is estimated as
√ 6 P
3 9.55 × 10 √ 6
d ≥ n = 3 9.55×10 × 9.5 = 47.62mm
0.2[ ] 0.2×35 120
3. Preliminary structural design
(1) Decide the Two possible layouts of elements on the shaft are proposed,
layout of as shown in Figure 10.11. After comparison, select
elements on Figure 10.11a.
the shaft
(2) Shaft Axial positioning:
elements The half coupling is positioned by the end cap on the left and
positioning the shoulder on the right. The left bearing seats against the
shoulder and is located in place by the left bearing cover;
while the right bearing by the spacer and the right bearing
cover. The gear seats against the shoulder ring on the left and
have the spacer to located it in place on the right.
Circumferential positioning:
Both the gear and half coupling are circumferentially located

on the shaft by parallel keys.
(3) Determine Shaft segment I: d = 48 mm
I
the diameter and The initially estimated minimum diameter of shaft is the L = 82 mm
length of each location where a coupling is to be installed. The length and I
segment of the diameter of this segment should be compatible with the
shaft selected coupling.
An important parameter for selecting a coupling is torque.
The torque transmitted by the shaft is
P 3 9.5
6
5
T = 9.55 × 10 6 = 9.55 × 10 × = 7.56 × 10 N ⋅ mm
n 3 120
Considering the variation of load during operation, select
application factor K = 1.3 from Table 2.1, then the
A
calculated torque T ca is
5
5
T ca = K T =1.3×7.56 × 10 =9.83 × 10 N • mm
A
Select elastomeric pin coupling LX3 from GB/T 5014-2003
[11], whose nominal torque is 1 250 000 N mm. The aperture
of the half coupling d = 48 mm, the total length of the half
I
coupling is 112 mm and the mating length of hub bore is
84 mm.
Therefore, select d = 48 mm, L = 82 mm.
I
I
(continued)