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Mechanical Engineering Design Q and A T4
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Mechanical Engineering Design Q and A T4
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VAAL UNIVERSITY OFTECHNOLOGY
Cover sheet for Test
Faculty: Engineering
Department: Mechanical
Diploma: National Diploma: Engineering: Mechanical
Subject: Mechanical Engineering Design II
Date: 6 AUGUST 2021
Internal code: EMMED2A
Examiner: MD Mafoko
Moderator: AO Aniki
Hours: 90 min
Total Marks: 56 Full marks: 50
* Requirements: OPEN BOOK ASSESSMENT
* Instructions: Answer all the questions and write legibly.
Send one document only by email to VUT address.
Make your script portrait orientation only.
Do not congest all work on one page to save paper.
Give short sharp answers whose lengths correspond to
allocated marks.
Submit your answer scripts today and not later. Scripts
submitted on Saturday, 7 August 2021, will not be marked.
Signature of Examiner:…MD Mafoko……… Date: 6 AUGUST 2021
Signature of Moderator:…Abimbola Aniki….. Date:………………
, Q1. Name three types of bearing you may find in a motor vehicle.
Journal bearings, thrust bearings, ball bearings.
. 3 marks.
Q2. If mechanical efficiency is the ratio of output to input power, what is the effect of
friction on this efficiency?
Friction causes reduction in efficiency by causing heat, noise, vibrations and
other energy losses.
1 mark.
Q3. What property of bearing material enables it to conduct heat away from the
interface between bearing and journal?
Thermal conductivity.
1 mark
Q4. Only lead babbit is more suitable for use in applications where the operating
temperature is below 120O. True or false?
False. Lead and tin babbits are useable in applications with temperatures
below 120O.
1 mark
Q5. For wristpin bearings what is the recommended range of unit load to be used?
Unit load range 14 to 15 MPa.
1 mark.
Q6. Journal bearings support shafts in the ………………………… direction. While thrust
bearings support shafts in the ……………………………………………… direction.
Radial;
Axial.
2 marks.
Q7. How does the face width of a gear tooth affect the stress induced on the tooth?
As the gear tooth width increases, the area bearing load is increased thereby
decreases stress induced on the gear tooth.
1 mark.
Q8. The load supported by a bearing is born by a projected area of 36 mm diameter
and length of 36 mm. If the application is a wristpin bearing. What is the Pressure in
the lubricated space? What is the force (load )supported?
P=F/Area
For wristpin bearings the recommended pressure is 14 to 15 MPa. So at
midspan of this the
P=14,5 MPa.
The force that may be supported is
F=P x A
F= 14,5 MPa x (36 mm x 36 mm)
F= 18 792 N.
5 marks.
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