Final Assignment [30 marks] (ULO 1 & 2)
In this assignment, all design parameters should be decided by you. Make appropriate assumption for
information not provided here. If you prefer to read the instruction offline, a pdf version of this Final
Assignment is available here.
Problem statements
An intermediate shaft for a machine that transmits 6 kW to an output placed vertically above, through
a pair of helical gears (Figure 1 and Figure 2). The selection of the helical pinion is already decided,
and the pinion is supplied with a pilot bore (which is the initial hole diameter and subsequent
enlargement by reaming on the hole is expected). Thus, the finalized intermediate shaft diameter will
e applied to the finished bore of the pinion. The speed of the output shaft is approximately 250 rpm,
where a slightly higher output speed is acceptable. The source of power is an electric motor of 1500
pm, transmitting the power to the intermediate shaft using a chain drive. A smooth running from the
motor is expected, and the output shaft will run a heavy shock loaded conveyor (not shown in the
Figures). The intermediate shaft as shown in Figure 1, will be operated in the clockwise
direction. However, it is expected the shaft will also be operated in a reversed rotational direction,
continuously, at certain times. Since the operation in both clockwise and anticlockwise is
continuous, the torsional loading on the shaft is still considered uniform even though the rotational
direction will reverse. The driving sprocket is placed vertically below the shaft, and the centre
distance between the driving and driven sprockets has to be greater than 1.2 metres, but it should not
e larger than 1.4 metres. Also, if possible, the driving sprocket needs to be able to fit directly to a
motor spindle of 16 mm without the use of an adaptor or modification to the motor spindle
diameter. The maximum length of the intermediate shaft is 300 mm. The intermediate shaft has to
e supported by a pair of angular contact ball bearings. Assume there is negligible power loss.
Figure 1 The shaft assembly showing the intermediate shaft
600
Figure 2 Sample Design Layout
Design the chain drive, intermediate shaft, select appropriate bearings, and show the mathematical
modelling according to the sections below.
Components Catalogues
You are free to use the course learning materials to complete the design task. In addition, your selection
of the chain drive and bearings has to base on the catalogue information Item 1 to Item 3 below.
1. Renold Chain designer guide (page 101 to 106). Alternatively, see the Week 8 lecture slide
number 45 to 55, Belt and Chain Drive (link). The page 106 and 114 of the Renold Chain
designer guide also show force, velocity, torque and power calculation.
2. Chain and Sprocket catalogue (page 69 to 80). Please use the plain bore type sprocket. Note:
The Renold simplex chain has a strength ranging from 7,900 N to 223,000 N depending on the
pitch. The duplex chain has higher strength than the simplex chain. The strength values of the
chains are also tabulated from page 12 to page 31 depending on the type of chain.
3. Bearing catalogue information as in the Week 5 lecture slide (link), or Table 14.1 and Table
14.2 in the Formula List page 42 and 43.
Part (a) Chain Drive Design [8 marks] (ULO 1)
1. Determine the speed required for the driven sprocket.
2. Using the catalogue information provided, specify the type of chain, the length, the centre
distance, the sprockets, lu
ication method for the chain drive required. Please be noted that the
sprockets are also supplied with a pilot bore. Please state the catalogue page number of which
the chain and sprockets are selected.
Part (b) Design of the Intermediate Shaft [8 marks] (ULO 1)
1. Determine the tension of the chain that acts upon the intermediate shaft.
2. Determine the force components of the gear, and then determine the reaction forces at the
earings.
3. Construct the bending moment diagrams for the intermediate shaft for both rotational
directions.
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4. Determine the diameter of the shaft on the basis of fatigue strength, and a safety factor of 2.5.
The shaft is made of cold-drawn 1020 steel with an ultimate tensile strength of 530 MPa and
tensile yield strength of 450 MPa.
5. Present your final shaft design in a shaft layout sketch with the diameters, length and fillet
adius of each shaft section clearly labelled. You are allowed to use the layout in Figure 2 as it
is or modify the layout.
Note:
• The key seats at the shaft sections for the gear, sprocket and bearings are provided by the hubs
of the components and inner race of the bearing. Failure on precisely the location of the key
seats is unlikely. Thus, the stress concentration data for the key seats are not required for this
assignment. The calculation of Kf based on the shaft section where the diameter is reduced
should base on the course learning materials.
• Please make use of the charts on page 5-8 of the Formula List (link) to determine the Kf at the
shaft section where the diameter is reduced. During the initial calculation of the mean and
alternating stresses, in order to determine the Kt and q from the charts (page 5-8 of the Formula
List), assume D/d = 2,
d = 0.05, and notch radius, r = 1.5 mm.
• The dimension of the key seats is not required.
• The design and calculation of the output shaft is not required.
Part (c) Rolling Elements Bearing Design [8 marks] (ULO 1)
1. Determine the radial load acting on the Bearing A and D.
2. Also, using the catalogue information provided, specify all the bearings required, including
how the bearing will be a
anged on the shaft. Your answer should clearly specify which
earing will support the axial load and in what direction. All bearings should last for 9,000
hours of operation.
Part (d) Modelling and Derivation [6 marks] (ULO 2)
Derive an equation for the tangential and radial force of the helical gear by expressing them in terms of
sprocket diameter, chain tension, pressure angle and gear diameter.
Useful work examples
A few example calculations are provided on the canvas site of this unit. Particularly, pay attention to
Week 8 lecture slide number 45 to 55, Belt and Chain Drive (link), the analysis of bending moment and
torque diagram for a rotating shaft (Example 2.8), finding the equivalent mean and alternating stress
with consideration of fatigue stress concentration at the critical location (Example 17.2D). Note: a chain
equires no tension on the slack side, thus the force resulted from chain tension acting on the
intermediate shaft is equal to power divided by the pitch line velocity.
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www.renold.com
Transmission Chain
Product catalogue
Section 1 - European (BS) and
ANSI products and dimensions
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