ASSIGNMENT 3 ON CO3
(DESIGN OF MECHANICAL SPRING AND ROLLING CONTACT BEARING)
COURSE
:
MECHANICAL DESIGN
COURSE CODE
:
BMM3323
LECTURER
:
MD. MUSTAFIZUR RAHMAN
SUBMISSION DATE
:
17 JUNE 2023
SESSION/SEMESTER
:
SESSION 2022/2023 SEMESTER II
TOTAL MARKS
:
10
INSTRUCTIONS
TO CANDIDATE:
1. Answer the questions with HANDWRITING (Other than Handwriting is not acceptable).
2. SCAN the answer script in PDF form and upload it through Google Form.
3. WRITE Name, Student ID and Section clearly in your answer scripts.
4. Write your file name as STUDENT ID only (Example: MB20021. Any WRONG
information considers not submitted Assignment.
5. LATE SUBMISSION IS NOT ACCEPTABLE
EXAMINATION REQUIREMENTS:
-
None
DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SO
This assignment consists of SIX (6) printed pages, including the front page
CONFIDENTIAL
2223I/BMM3323
QUESTION 1 [20 Marks]
In the design of an automotive single-plate clutch, two pairs of friction surfaces are utilized:
one between the friction lining and the pressure plate and the other between the friction lining
and the flywheel. The axial thrust required on the friction surfaces is achieved by 12 identical
helical compression springs arranged in parallel. The total spring force exerted by all springs
is 2500 N, with each spring experiencing a deflection of approximately 65 mm. To begin the
design process, it is crucial to select an appropriate spring material that can withstand the
operating conditions and load requirements of the clutch. Consider factors such as strength,
durability, and resistance to fatigue. Additionally, evaluate the available spring wire diameters
provided: 1.8 mm, 2.0 mm, 2.1 mm, 2.3 mm, 2.4 mm, and 2.6 mm.
In the design evaluation process, start by determining the required spring rate based on the
given total spring force and deflection. Calculate the average spring rate by dividing the total
force (2500 N) by the deflection of each spring (65 mm). This value will provide a guideline
for selecting an appropriate wire diameter. Next, consider the assembly constraints specified.
The solid height of the spring cannot exceed 35 mm, and the free length should not exceed 125
mm. These limitations will help determine the maximum allowable number of active coils and
the corresponding wire length. Using the calculated average spring rate and the available wire
diameters, compute the necessary number of active coils to achieve the desired spring rate. It
may be necessary to perform multiple iterations to find the optimal combination of wire
diameter and number of coils that meet the design requirements while satisfying the assembly
constraints.
Evaluate each potential design configuration to ensure that the selected spring material can
withstand the expected forces, deflection, and cyclic loading. Consider factors such as stress
levels, fatigue life, and safety factors. Verify that the chosen spring material can provide the
necessary performance and durability for the automotive clutch application. Document the
design evaluation process, including the calculations, iterations, and reasoning behind each
decision made. This documentation will serve as a comprehensive record of the design process
and enable future analysis and modifications if necessary.
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CONFIDENTIAL
2223I/BMM3323
QUESTION 2 [20 Marks]
You are tasked with designing a helical compression spring that will be used in a valve
operating mechanism for the food industry machinery. The spring will experience fluctuating
loading conditions, ranging from 25 N to 120 N, and needs to have a stiffness of 2000 N/m.
However, there are several assembly constraints to consider. Firstly, the spring wire's free
length must not exceed 110 mm due to assembly considerations. Additionally, the solid height
of the spring cannot exceed 45 mm, and the free length should not exceed 125 mm.
To assist in your design, the manufacturer offers spring wire diameters of 1.6 mm, 1.8 mm, 2.0
mm, 2.3 mm, and 2.6 mm. You are required to use the Gerber-Zimmerli fatigue-failure criterion
with a fatigue design factor (nf) of 1.5, ensuring the spring can withstand the fluctuating loading
conditions over its lifespan. Your task is to select an appropriate spring material suitable for
food industry machinery applications and determine the design parameters for the helical
compression spring. These parameters may include the wire diameter, number of active coils,
mean coil diameter, and any other relevant specifications needed to meet the given
requirements.
3
CONFIDENTIAL
2223I/BMM3323
QUESTION 3 [20 Marks]
For the given application conditions specified in Table 1, the selection of a suitable single-row
cylindrical roller bearing from Table 11-3 is required. The available initial bearing bore
diameter is provided as 65 mm.
You will need to refer to Table 11-3, which likely contains information on various bearing
models, their dimensions, load capacities, and other relevant specifications. The goal is to
identify an "03-series" single-row cylindrical roller bearing that can meet the requirements of
the application.
Table 1
Radial load (kN)
Axial load (kN)
Design life
Ring rotating
12.5 kh, 450
12.5 plus the last 4.5 plus half of the
rev/min,
digit of your
last digit of your
outer
Application factor
Student ID
Student ID
is 1.10
Desired
reliability
97.5%
a) Evaluate the equivalent radial load subjected to the bearing.
(4 Marks)
b) Design the appropriate bearing with the appropriate bore size
(11 Marks)
c) Designation of finally selected bearing with International Organization of
standardization.
(2 Marks)
d) Determine the reliability of the final selected bearing. Justify whether the selected
bearing is suitable for application with 97.5% reliability.
(3 Marks)
4
CONFIDENTIAL
2223I/BMM3323
QUESTION 4 [20 Marks]
Consider that you recently graduated from Universiti Malaysia Pahang and joined as a design
engineer at a bearing manufacturing company in Malaysia–China Kuantan Industrial Park.
Your task is to design a suitable bearing attached to the end of the stepped shaft. The shaft then
is placed in the gearbox and rotated at a speed of (425 rev/min with the last 2 digits of your
ID). During the operation, the inner ring rotates, and the bearing carries a combined radial and
axial loading of (10.5 plus half of the last digit of student ID) kN and (2.5 plus half of the last
digit of student ID) kN, respectively. The bearing life cycle of 8 hours per day, 5 days per week,
for 8 years. hours with a reliability factor for the ensemble of bearings is equal to 98.5%
a) Evaluate the equivalent radial load subjected to the bearing and rating life in hours with
a load application factor 1.10.
(3 Marks)
b) Design the appropriate bearing when the inner ring is rotating (Single row 2-series
deep-groove bearings, angular-contact ball bearings, and cylindrical roller bearings are
all offered as bearing choices)
(12 Marks)
c) Your immediate senior manager instructed you to choose a single-row 02-series ball
bearing with the same bore diameter as a cylindrical roller bearing. Do you prefer to
select the ball bearing with a roller bearing? Justify your answer.
(3 Marks)
d) Designation of finally selected bearing with International Organization of
standardization.
(2 Marks)
e) Determine the reliability of the final selected bearing. Justify whether the selected
bearing is suitable for application with 98.5% reliability.
(3 Marks)
5
CONFIDENTIAL
2223I/BMM3323
QUESTION 5 [20 Marks]
As a design engineer at Bearing Manufacturing Company, you have been assigned to work on
a conveyor system design for a leading manufacturer's shipping and receiving system. The
specific component under consideration is a transmission shaft that will transfer 15 kW of
power at a speed determined by the formula (450 plus the last 2 digits of your student ID) rpm.
This power will be transmitted from a bevel gear G1 to a helical gear G2, with the shaft being
supported by two taper roller bearings, B1 and B2. The gear tooth forces acting on the helical
gear are concentrated at a pitch circle radius of 80 mm, while for the bevel gear, the forces can
be assumed to act at the large end of the tooth with a radius of 75 mm. The journal diameter at
bearings B1 and B2 is specified to be 40 mm. The design specifications require the bearings to
have a design life of 8 years, operating for 40 hours a week, at the mentioned speed (450 plus
the last 2 digits of your student ID). Additionally, an application load factor of 1.15 should be
considered, and a target reliability of 97.5% is desired for the bearing set. It is worth noting
that both bearings B1 and B2 are identical, with B2 specifically taking the thrust force due to
the bevel and helical gears. Your task is to select suitable taper roller bearings for this
application, taking into account the specified design life, operating conditions, load factor, and
reliability requirements. Consider factors such as bearing size, load-carrying capacity, speed
rating, and any other relevant considerations to ensure the chosen bearings can meet the
demands of the conveyor system in a reliable and efficient manner.
END OF QUESTION PAPER
6