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ENGINEERING, PPT 2023 HSC 7 MC

Why is cast iron preferred to steel when used as a heavy machine base?

  1. It is less brittle.
  2. It is more malleable.
  3. It has a lower damping capacity.
  4. It has a higher damping capacity.
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\( D \)

Show Worked Solution

→ Cast iron has exceptional damping capacity, meaning it can absorb vibrations, providing stability during machine operation.

\(\Rightarrow D \)

ENGINEERING, PPT 2023 HSC 24b

A roller coaster component is fabricated using cold rolled steel. Two webs are welded onto a base plate as shown.   (2 marks)
 

The diagram shows a partially completed microstructure of the parent and weld metals.

Complete the microstructure by drawing and labelling the following grain types in the heat-affected zone for ONE of the webs:

    • chill crystals
    • equi-axed grains
    • columnar grains.

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Correct answers include one of the labelled grain types:

Show Worked Solution

Correct answers include one of the labelled grain types:
 

ENGINEERING, PPT 2016 HSC 24c

Truck tyres are made using vulcanised synthetic rubber combined with high tensile steel wire.

Explain why this combination of materials has been chosen.   (3 marks)

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Vulcanised synthetic rubber construction:

→ High coefficient of friction.

→ Resilience, formability and wear resistant.

→ Elastic and highly flexible.

→ High tensile steel bands ensure distortion properties of rubber are managed.

Show Worked Solution

Vulcanised synthetic rubber construction:

→ High coefficient of friction.

→ Resilience, formability and wear resistant.

→ Elastic and highly flexible.

→ High tensile steel bands ensure distortion properties of rubber are managed.

ENGINEERING, PPT 2018 HSC 8 MC

In which of the following do all of the processes require plastic deformation to achieve a final shape?

  1. Brazing, casting, rolling
  2. Brazing, soldering, welding
  3. Extruding, casting, forging
  4. Extruding, pressing, rolling
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`D`

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→ Brazing, casting, soldering and welding involve metal in liquid form and therefore do not require plastic deformation. (Cannot be `A`, `B` or `C`)

`=>D`

ENGINEERING, PPT 2017 HSC 25b

A small truck chassis rail has been made from rectangular hollow section (RHS) steel. The RHS has been cold formed from an alloy steel with a yield strength of 500 MPa. A manufacturer's sign on the chassis rail is shown below.
 

  1. Explain why the chassis rail should normally not be drilled or welded.   (3 marks)
  1. A large reinforcing plate that supports a new attachment is to be welded onto the chassis rail according to the manufacturer's specifications.   
  2. Use the diagram below to draw and label the macrostructure of the weld area, including the surrounding chassis rail and reinforcing plate.   (2 marks)
     

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i.   Welding

→ The chassis rail steel becomes molten when welded at temperatures exceeding the A1 temperature.

→ Columnar grains may form on some parts of the weld upon cooling.

→ Martensite may form on cooling, creating a brittle, hard microstructure with less strength than that of the steel chassis (500 MPa).

Drilling

→ Stress raisers are produced by drilling the flanges.

→ Fatigue failure is initiated by surface roughness that can occur around the drill hole.

Show Worked Solution

i.   Welding

→ The chassis rail steel becomes molten when welded at temperatures exceeding the A1 temperature.

→ Columnar grains may form on some parts of the weld upon cooling.

→ Martensite may form on cooling, creating a brittle, hard microstructure with less strength than that of the steel chassis (500 MPa).

Drilling

→ Stress raisers are produced by drilling the flanges.

→ Fatigue failure is initiated by surface roughness that can occur around the drill hole.
 


♦♦ Mean mark (i) 39%.

ii.


♦♦ Mean mark (ii) 27%.

ENGINEERING, PPT 2017 HSC 21b

Gears used in automotive engines can be manufactured using ferrous alloys.

  1. Sand casting and powder metallurgy are methods that can be used.
  2. Compare the properties of the gears manufactured by each method.   (4 marks)
  1. After manufacture the gears are case hardened.
  2. Describe how case hardening produces the required structure-property relationships for this application.   (3 marks)
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i.   Sandcasting

→ Weaker dimensional stability than powder metallurgy.

→ If not poured correctly, grains can be columnar.

→ Fatigue can be initiated through poor surface finish.
 

Powder metallurgy

→ Greater dimensional stability.

→ A variety of gears that cannot be made using conventional methods can be produced using powder metallurgy.

→ A custom component can be initially produced as close as possible to the final shape of the product (near net shape forming).

→ Alloys can be produced with pores (self-lubricating).
 

ii.  Case hardening

→ Gears are heated to red heat in a nitrogen and/or carbon environment.

→ Nitrogen and carbon disperse into the steel’s surface at these high temperatures, increasing the carbon content to a level where it is hardened by quenching.

→ Martensite is formed when the steel is quenched.

→ Hence, the inside remains soft and tough whilst the outer case becomes wear resistant and hard.

→ The outer casing may be tempered back for improved surface toughness or the gear can be used with the martensite casing.

Show Worked Solution

i.   Sandcasting

→ Weaker dimensional stability than powder metallurgy

→ If not poured correctly, grains can be columnar

→ Fatigue can be initiated through poor surface finish.
 

Powder metallurgy

→ Greater dimensional stability

→ A variety of gears that cannot be made using conventional methods can be produced using powder metallurgy

→ A custom component can be initially produced as close as possible to the final shape of the product (near net shape forming)

→ Alloys can be produced with pores (self-lubricating).

 


♦♦♦ Mean mark (i) 26%.

ii.  Case hardening

→ Gears are heated to red heat in a nitrogen and/or carbon environment.

→ Nitrogen and carbon disperse into the steel’s surface at these high temperatures, increasing the carbon content to a level where it is hardened by quenching.

→ Martensite is formed when the steel is quenched.

→ Hence, the inside remains soft and tough whilst the outer case becomes wear resistant and hard.

→ The outer casing may be tempered back for improved surface toughness or the gear can be used with the martensite casing.


♦♦♦ Mean mark (ii) 23%.

ENGINEERING, PPT 2019 HSC 17 MC

Which row of the table correctly identifies the rolling process used to manufacture each of the components listed at room temperature?

\begin{align*}
\begin{array}{c|c}
\rule{0pt}{2.5ex}\text{          }\rule[-1ex]{0pt}{0pt} \\
\rule{0pt}{2.5ex}\text{A.}\ \ \ \ \ \rule[-1ex]{0pt}{0pt} \\
\rule{0pt}{2.5ex}\text{B.}\ \ \ \ \ \rule[-1ex]{0pt}{0pt} \\
\rule{0pt}{2.5ex}\text{C.}\ \ \ \ \ \rule[-1ex]{0pt}{0pt} \\
\rule{0pt}{2.5ex}\text{D.}\ \ \ \ \ \rule[-1ex]{0pt}{0pt} \\
\end{array}
\begin{array}{|l|l|}
\hline
\rule{0pt}{2.5ex}\textit{Lead alloy battery plates}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\textit{Steel body panels}\rule[-1ex]{0pt}{0pt} \\
\hline
\rule{0pt}{2.5ex}\text{Cold rolling}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\text{Cold rolling}\rule[-1ex]{0pt}{0pt} \\
\hline
\rule{0pt}{2.5ex}\text{Cold rolling}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\text{Hot rolling}\rule[-1ex]{0pt}{0pt} \\
\hline
\rule{0pt}{2.5ex}\text{Hot rolling}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\text{Cold rolling}\rule[-1ex]{0pt}{0pt} \\
\hline
\rule{0pt}{2.5ex}\text{Hot rolling}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\text{Hot rolling}\rule[-1ex]{0pt}{0pt} \\
\hline
\end{array}
\end{align*}

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`C`

Show Worked Solution

→ Steel body panels are formed by cold rolling to make them hard and rigid.

→ Lead alloy battery plates are formed by hot rolling to make them less brittle and to create an equiaxed, uniform grain structure.

`=>C`


♦♦ Mean mark 37%.

ENGINEERING, CS 2019 HSC 16 MC

The image shows part of a large anchor recovered from waters off Western Australia. The anchor's approximate date of manufacture was 1790 .
 

This anchor is most likely made from

  1. cast iron.
  2. cast steel.
  3. wrought iron.
  4. laminated silicon steel.
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`C`

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By Elimination:

→ In 1790 mild steel and silicon steel did not exist (eliminate `B` and `D`).

→ Since it is less brittle, wrought iron would have been used as anchors are subjected to sudden impacts against rocks (eliminate `A`).

`=>C`


Mean mark 52%.

ENGINEERING, PPT 2022 HSC 23c

Steel `text{I}`-beams have been used when large, open spans need to be created inside buildings.

Explain how microstructural changes take place in steel when an `text{I}`-beam is formed using the process of hot rolling. You may use a drawing to support your answer.   (4 marks)

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→ During hot rolling the steel is heated to above its recrystallisation temperature.

→ Therefore, due to the pressure of the rollers, the grains change from their original state to become elongated.

→ However, as the steel exits the rollers it is still above recrystallisation temperature, resulting in the recrystallisation of the elongated grains to create finer, equiaxed grains.

Show Worked Solution

→ During hot rolling the steel is heated to above its recrystallisation temperature.

→ Therefore, due to the pressure of the rollers, the grains change from their original state to become elongated.

→ However, as the steel exits the rollers it is still above recrystallisation temperature, resulting in the recrystallisation of the elongated grains to create finer, equiaxed grains.


♦ Mean mark 48%.

ENGINEERING, PPT 2020 HSC 24b

The photograph shows two stainless steel yokes which attach a turnbuckle to a baseplate fixed to a concrete pad.
 

   

Provide a step-by-step description of an appropriate method to manufacture the yoke.  (3 marks)

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→ The metal for the yoke is stamped out of a piece of steel plate.

→ A press is then used to punch out the slot and the holes.

→ The plate is then formed around a mandrel or mould to develop the final shape.

→ The piece can then be further machined if required.

Show Worked Solution

→ The metal for the yoke is stamped out of a piece of steel plate.

→ A press is then used to punch out the slot and the holes.

→ The plate is then formed around a mandrel or mould to develop the final shape.

→ The piece can then be further machined if required.

Mean mark 59%.

ENGINEERING, PPT 2021 HSC 22b

A 0.2 kg metallic baseplate is to be cast.

What are the advantages of pressure die casting over sand casting?   (3 marks)

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Advantages of pressure die casting over sand casting

→ Pressure die casting results in a smoother finish than sand casting and provides better dimensional accuracy.

→ There is also less potential for flaws and voids when pressure die casting is used.

→ Permanent metal mould allows for more castings and produces a harder surface than sand casting.

Show Worked Solution

Advantages of pressure die casting over sand casting

→ Pressure die casting results in a smoother finish than sand casting and provides better dimensional accuracy.

→ There is also less potential for flaws and voids when pressure die casting is used.

→ Permanent metal mould allows for more castings and produces a harder surface than sand casting.