machine elements problems
2505ENG Assignment
2
(7 marks in total)
(Due: 2
5
/0
9
/2014)
Problem 1.
(2 marks)
A
ball bearing
is listed in a
catalog
in which the
basic dynamic load rating
is
33,800 N for a rated life
of 1 million revolutions.
(1)
What would be the expected L10 life of the
bearing
in revolutions
if it were
subjected to
1
8
,000 N
?
(2)
D
etermine the life in hours if the speed of
rotation is 2000 rpm
.
Comment on the value
obtained and its suitability for a machine.
Problem 2.
(
2
marks)
A steel shaft has a diameter of 25 mm. The shaft rotates at a speed of 600
RPM
and transmits
30
kW through a gear. The tensile and yield strength of the material of shaft are 650 MPa and
353 MPa
respectively. Taking a factor of safety 3, select a suitable
key
(square key
, choose from Table 7
–
6 of
Shigley
’
s book, p 391)
for the gear. Assume that
the key and shaft are made of the same material.
Problem 2.
(3 marks)
A commercial enclosed gear drive consists of a 20
°
spur pinion having 16 teeth driving a 48
–
tooth
gear. The pinion speed is 300 rev/min, the face width
50 mm
, and the
module 4 mm
. The
gears are
grade 1 steel, through
–
hardened at 200 Brinell, made to No. 6 quality standards,
uncrowned, and
are to be accurately and rigidly mounted. Assume a pinion life of 10
8
cycles and
a reliability of 0.90.
Determine the
bending and contact stresses and the corresponding
factors of safety if
4 kW
is to be
transmitted.
(Using the simplified AGMA method).
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