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ENGINEERING, CS 2018 HSC 24a

The diagram shows a scaffold supporting planks. The planks can be made from laminated timber, aluminium alloy or galvanised steel.
 

Outline an in-service advantage of each of these materials when used as a scaffold plank.   (3 marks)

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Answers could include one advantage from each material type below:

Laminated timber plank

  • Easily cut on-site to accommodate a non-standard opening.
  • Non-conductive.

Aluminium scaffold plank

  • Low density
  • Light weight makes aluminium planks easy to manoeuver on-site.

Galvanised steel planks

  • Can absorb energy through impact without shattering or fracturing (high impact resistance).
  • Appropriate for applications where the scaffold is likely to be exposed to falling loads eg concrete block laying, bricklaying, concreting and demolition work.
Show Worked Solution

Answers could include one advantage from each material type below:

Laminated timber plank

  • Easily cut on-site to accommodate a non-standard opening.
  • Non-conductive.

Aluminium scaffold plank

  • Low density
  • Light weight makes aluminium planks easy to manoeuver on-site.

Galvanised steel planks

  • Can absorb energy through impact without shattering or fracturing (high impact resistance).
  • Appropriate for applications where the scaffold is likely to be exposed to falling loads eg concrete block laying, bricklaying, concreting and demolition work.

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%.