Bearings
SM Roux
February 5, 2016
Bearings
Bearings permit smooth, low friction movement between two surfaces moving relative to one another.
This movement may be translational or rotational.
Bearings may employ a sliding (frictional) or rolling action
Chapter 4
For a torsion bar, k T = T/ = Fl/, and so = Fl/k T . For a cantilever, k l = F/ , = F/k l . For
the assembly, k = F/y, or, y = F/k = l +
Thus
F Fl 2 F
y
k
kT kl
Solving for k
kk
1
k 2
2l T
Ans.
l
1 kl l kT
kT kl
_
4-1
For a torsion bar, k T =
Chapter 8
Note to the Instructor for Probs. 8-41 to 8-44. These problems, as well as many others in this
chapter are best implemented using a spreadsheet.
8-1
(a) Thread depth= 2.5 mm Ans.
Width = 2.5 mm Ans.
d m = 25 - 1.25 - 1.25 = 22.5 mm
d r = 25 - 5
Chapter 6
Eq. (2-21):
Eq. (6-8):
Table 6-2:
Eq. (6-19):
Sut 3.4 H B 3.4(300) 1020 MPa
Se 0.5Sut 0.5(1020) 510 MPa
a 1.58, b 0.085
b
ka aSut 1.58(1020) 0.085 0.877
Eq. (6-20):
6-1
kb 1.24d 0.107 1.24(10) 0.107 0.969
Se ka kb Se (0.877)(0.969)(510) 433 MPa
Chapter 9
Figure for Probs.
9-1 to 9-4
9-1
Given, b = 50 mm, d = 50 mm, h = 5 mm, allow = 140 MPa.
F = 0.707 hl allow = 0.707(5)[2(50)](140)(103) = 49.5 kN Ans.
_
9-2
Given, b = 2 in, d = 2 in, h = 5/16 in, allow = 25 kpsi.
F = 0.707 hl allow = 0.707(5/16
SCREWS, FASTENERS AND NON
PERMANENT JOINTS 1
MOW 227 2013
Shigley Ch 8
Department of Mechanical and Aeronautical Engineering
STANDARDS AND DEFINITIONS-THREAD
/Pitch diameter
Department of Mechanical and Aeronautical Engineering
Lead = distance that a nut
SCREWS, FASTENERS AND NON
PERMANENT JOINTS
2
MOW 227 2013
Department of Mechanical and Aeronautical Engineering
Department of Mechanical and Aeronautical Engineering
Department of Mechanical and Aeronautical Engineering
Yielding take place in the first th
Stress Concentration
Mow 227
Shigley Ch 3-13
Stress Concentration
Stresses and strains are uniformly distributed
for parts of constant cross-section with
uniformly distributed loads.
However,
applied
forces
are
often
concentrated (not uniform) where cro
SCREWS, FASTENERS AND NON
PERMANENT JOINTS
3
MOW 227 2013
Department of Mechanical and Aeronautical Engineering
Department of Mechanical and Aeronautical Engineering
Bolted and Riveted joints in shear
Department of Mechanical and Aeronautical Engineering
Chapter 7
7-1
(a) DE-Gerber, Eq. (7-10):
A 4 K f M a 3 K fsTa 4 (2.2)(70) 3 (1.8)(45) 338.4 N m
2
2
2
2
B 4 K f M m 3 K fsTm 4 (2.2)(55) 3 (1.8)(35) 265.5 N m
2
2
2
6
8(2)(338.4) 2(265.5) 210 10
d
1 1
6
6
210 10 338.4 700 10
3
d = 25.85 (10 ) m = 25.8
Chapter 11
11-1
For the deep-groove 02-series ball bearing with R = 0.90, the design life x D , in multiples
of rating life, is
L
60D nD 60 25000 350
xD D
525 Ans.
LR
L10
106
The design radial load is
FD 1.2 2.5 3.0 kN
1/3
Eq. (11-6):
525
C10 3.0
1/1.4
Chapter 10
10-1
From Eqs. (10-4) and (10-5)
KW K B
4C 1 0.615 4C 2
4C 4
C
4C 3
Plot 100(K W K B )/ K W vs. C for 4 C 12 obtaining
We see the maximum and minimum occur at C = 4 and 12 respectively where
Maximum = 1.36 % Ans.,
and Minimum = 0.743 % Ans.
_
Copyright reserved
UNIVERSITEIT VAN PRETORIA
UNIVERSITY OF PRETORIA
Departement Meganiese en Lugvaartkundige Ingenieurswese
Department of Mechanical and Aeronautical Engineering
MASJIENONTWERP MOW217
MACHINE DESIGN MOW217
April 2011
Time: 3 hours/ure
Mark
Kopiereg voorbehou
Copyright reserved
UNIVERSITEIT VAN PRETORIA
UNIVERSITY OF PRETORIA
Departement Meganiese en Lugvaartkundige Ingenieurswese
Department of Mechanical and Aeronautical Engineering
Masjienontwerp MOW217
Machine Design MOW217
Semester toets
MOW 217: Belt and Chain Problems
Specify a belt and chain design for the following problems:
Machine Type
Rotational Speed [rpm]
Shaft Diameter [mm]
Centre Distance (Belts Only)
Power [kW]
Operating time [hrs/day]
Driver
Shunt-wound DC Motor
350
50
~800
1
Question 1
The gear forces in Figure 1 shown act in planes
parallel to the yz plane. The force on gear A is
1.2kN. Consider the bearings at O and B to be simple
supports.
a. Calculate the force FC
b. Calculate the reaction forces at O and B
[FC = 3 kN, FO
MOW 217: Ball Bearing Problems
Using the NTN bearing catalogue, calculate the answer which is in braces:
(All loading is purely dynamic unless stated otherwise.)
D
[mm]
70
Fr
[kN]
3.2
Fa
[kN]
0
N
[rpm]
100
Adjusted life
Code
Remarks
25 000 hrs
[6914]
25
2
SCREWS, FASTENERS AND NON
PERMANENT JOINTS
2
MOW 227 2013
Department of Mechanical and Aeronautical Engineering
Department of Mechanical and Aeronautical Engineering
Department of Mechanical and Aeronautical Engineering
Yielding take place in the first th
SCREWS, FASTENERS AND NON
PERMANENT JOINTS 1
MOW 227 2013
Shigley Ch 8
Department of Mechanical and Aeronautical Engineering
STANDARDS AND DEFINITIONS-THREAD
/Pitch diameter
Department of Mechanical and Aeronautical Engineering
Lead = distance that a nut
SCREWS, FASTENERS AND NON
PERMANENT JOINTS 1
MOW 227 2013
Shigley Ch 8
Department of Mechanical and Aeronautical Engineering
STANDARDS AND DEFINITIONS-THREAD
/Pitch diameter
Department of Mechanical and Aeronautical Engineering
Lead = distance that a nut
WELDING 2
MOW 227 2013
Department of Mechanical and Aeronautical Engineering
Bending
Primary Shear Stress
d
V
M
y
V
A
Nominal Throat shear Stress
x
Mc
I
d
M
2
0.707h I u
1.414M
bhd
Compare 1.414 with 1.197 from
distortion theory and 1.207 from MSS
cons
WELDING 1
MOW 227 2013
Shigley chapter 9
Department of Mechanical and Aeronautical Engineering
Welding
Department of Mechanical and Aeronautical Engineering
Types of Welded Joints
Department of Mechanical and Aeronautical Engineering
Welding Symbols
Butt
Deflection and Stiffness
Shigley ch4
Lecture 1
Springs
A device that deflects at the application of a
force, and then returns to its former state
when the force is removed
If the spring returns to its former state it
means that the material did not unde
Deflection and Stiffness
Shigley ch4
Lecture 2
Strain energy
(Shigley 4-7)
If a member is deformed a distance y, and if
the force deflection relationship is linear, the
strain energy, or potential energy from
deformation is equal to the product of the
av
Material Selection
MOW227
Material Selection
The design process consists of determining
geometric shape, selecting materials,
choosing a manufacturing process and
analyzing all the above in order to satisfy a
set of functions.
Choosing appropriate mater
Free-body diagrams
When analysing the behaviour or performance of a complex
structure such as a bridge, tractor or gearbox, the designer is
faced with a bewildering array of complicated parts and
geometries.
A powerful analytical technique when analysin
Lecture 4
STRESS/STRAIN
MOW 227
1
Stress:
Units of force per area
-> = F/A
Strain
Unit of elongation per unit length
= /L
2
Hookes law
S ut
Sy
F
A
L
3
Hookes law
Working in the elastic region,
the inclination of the linear
line would be:
S ut
Inclinati
Design Process
Purpose: Design components strong enough
How: Generate a mathematical model which
expresses the strength of a component in
terms of some strength parameter (stress)
Mathematical Model:
External Loading
Magnitude
Type
Geometry
Materi
Static Failure Theories
ch. 5
Shigley
ch. 10
Hibbeler
Static Failure Theories
Objective is to determine state of stress which
causes a component to fail.
Failure is defined as behaviour that renders a
structure unsuitable for its intended function.
Fai
Material Behaviour
Department of Mechanical and Aeronautical Engineering
University of Pretoria
1
INTRODUCTION
Types of structural failure
DEFORMATION
Time independant
Elastic
Plastic
Time dependant
Creep
FRACTURE
Static Loading
Brittle / Ductile
Env