1. ASSIGNMENT/ASSESSMENT ITEM COVER SHEET
Donald HEATHER
Student Name:
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2 0 0 8 8 0 9
Student Number: Email: donald.heather@det.nsw.edu.au
Course Code Course Title
E D U C 6 5 0 4 Engineering Education Studies 1
(Example) (Example)
A B C D 1 2 3 4 Intro to University
Campus of Study: Callaghan (eg Callaghan, Ourimbah, Port Macquarie)
23/4/2012
Assessment Item Title: CHALLENGE
Tutorial Group (If applicable): Word Count (If applicable): 1499
Lecturer/Tutor Name: Chris Hollis
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2. D. HEATHER - C2008809
COUPLINGS
Couplings are devices that are ulilised to connect two shafts together for the purpose of transmitting power.
The purpose of couplings is to join two rotating pieces of equipment together allowing for a small amount of
misalignment or end movement in each piece of equipment.
Substantial savings can be made by selecting, installing and maintaining couplings correctly which will result in
reduced maintenance costs and downtime.
Shaft couplings have several purposes when used with machinery with the most common reasons being:
To introduce mechanical flexibility
To allow for misalignment of shafts
To reduce shock transmission loads from one shaft to another
To introduce protection against overloading of machinery parts
To change the vibration characteristics of rotating units
Types of Couplings:
Rigid:
A rigid coupling can be used to connect two separate systems, such as a motor and a pump, or can be
utilised to repair a connection within a single system. A rigid coupling could also be used to reduce
shock and wear at a point where two shafts meet.
Rigid couplings are used when it is necessary to have precise alignment and the ability to hold the two
pieces of machinery securely in place. By aligning the two shafts and aligning them securely helps to
maximise performance and increase the expected life of the machine. Rigid coupling are available in
two types:
i) Sleeve style – they are a single tube of material with an inside diameter that is the same size of
the shaft. The sleeve slips over the shafts with screws that can be tightened to the top of each
shaft.
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3. D. HEATHER - C2008809
ii) Clamped rigid coupling – they are made with two parts that fit together around the shaft and form
a sleeve. They are secured by screws which pass all the way through the coupling and into the
second half to hold it rigidly in place. They are used to connect shafts that are fixed in place.
Constant-velocity couplings:
Constant velocity couplings allow a shaft to transmit power at varying angles and at a constant speed.
The constant velocity coupling was used in drive trains in cars with front wheel drive.
The Thompson Coupling consists of two cardan joints assembled within each other eliminating the use
of a shaft, along with a control yoke that geometrically constrains their alignment. The control yoke
has minimal inertia and generates virtually no vibration.
Shaft alignment and coupling setup need to be disconnected and connected easily. There should be
some allowance for misalignment between the two adjacent shaft rotation axes. Coupling
maintenance should be relatively easy by performing visual inspections, cleaning couplings regularly
and checking for signs of wear. Detection of potential coupling failure would be abnormal noise,
vibration and an indication of lubricant leakage.
Coupling
The coupling will fit over the shaft and be bolted together with M12 bolts. The reason is it needs to
withstand a lot of vibration. The coupling will be used to transverse power from an electric motor to
centrifugal pump to pump water for use in an agriculture farm. The precise alignment is necessary to
minimise vibration and maintenance.
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4. D. HEATHER - C2008809
Incorrectly aligned shafts.
The alteration to radius on the coupling body is to allow for more stress and strain to be absorbed.
The radius will assist the coupling by reinforcing a weak point. When a coupling is manufactured it
needs to be designed to maximise its ability to transverse power without failure. The radius is
designed to allow the component to have more strength at a point that would be weak.
There are several methods which could be used to manufacture the coupling.
Machining:
The coupling could be machined out of a billet. The process would need to be accurate and fine
tolerances would need to be maintained. The emergence of Computer Numerical Control is how it
would need to be produced for it to be a viable proposition cost wise. The machine would cut the
profile and drill and bore the hole in one process. The advent of technology would also allow the
machine to drill the four 12mm diameter holes while the coupling is in the machine. The chuck has
the ability to rotate at a given angle anywhere within the 360° rotation utilising a universal head to
drill holes. The keyway could be broached out to size.
Drop Forging:
The coupling could be drop forged to shape. If a material is worked by the application of localised
compressive forces, it is said to have been forged.
“Drop Forging is “it may be squeezed or hammered in between special dies so that the metal flows
and takes up the shape of the die cavity, Shlenkler 1986.
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5. D. HEATHER - C2008809
The machines utilise 2 dies that take up the shape of the coupling and have a capacity of up to 10 MN.
Drop forging is a mass production process using one die or a series of dies. Dimensional accuracy is
not high with drop forging however the couplings outside surfaces do not need machining. The bore
will be machined, holes drilled and keyway cut. When a components finished size is known the
forging could allow for balance by allowing the mass taken out by the keyway being applied exactly
opposite. This will result in the coupling when completed being balanced which will assist in less
vibration when turning at high speed.
Material:
The material I would use mild steel. Mild steel „contains 0.15 – 0.3%C. Wrought forms are used as
RSJ and other structural members, shafting, levers and various forgings”. Higgins 1977.
Mild steel is readily available and reasonably cheap compared to other materials. Mild steel is easily
formed, machined and does not harden much if cooled quickly, and is quite ductile. Copeland 2000
It should be noted that mild steel, like all steels (except stainless steels), readily corrode, and that the
product of corrosion (commonly known as rust) is porous, thus promoting further corrosion.
The radius is being applied to the coupling to add strength at the intersection of the two diameters.
When two diameters meet which have been machined the flow lines of the material in this case “fibre”
is cut. This reduces the strength of the coupling and is a weak point at which the material may fail due
to stresses. The coupling could develop cracks at this point running along the flow lines.
“High stress concentration is likely to cause failure along exposed fibres and so weaken the
component” Higgins 1977
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6. D. HEATHER - C2008809
The material being drop forged will have a radius at this point. The material has been upset from bar
stock with the result being flow lines following the contour of the coupling. This result is the radius at
the intersection of the two diameters being strengthened.
Billet or bar stock
Flow lines following outside profile.
Section displaying flow lines.
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7. D. HEATHER - C2008809
Conclusion:
By adding a radius at the point where diameters meet strengthens components so they will be able to
be utilised for longer periods. This results in less maintenance of the component, ability of the
component to withstand greater forces for longer periods and less down time replacing the component.
The time it would take to connect the coupling correctly and fixing both components securely in
position would offset costs utilising different couplings or methods to transmit power. The final
process could be trying to minimise corrosion by painting the coupling, and installing a cover to
protect the coupling from direct weather conditions. This could also be a safety measure so no
rotating parts of the machinery are exposed.
Bibliography
Copeland, P. L. (2000). Engineering Studies, The Definitive Guide. Australia; Anno Domini Pty Lty.
Higgins, R. A. (1977). Properties of Engineering Materials. Great Britain; The Chaucer Press.
Schlenker. B. R. (1986). Introduction to Material Science. [SI. ed]. Milton; The Jacaranda Press.
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