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NSWEngineering StudiesQuick questions
Lifting Devices
Quick questions on Wire rope and factors of safety: HSC Engineering Studies Lifting Devices
7short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is construction of steel wire rope?Show answer
A steel wire rope is built from three nested elements:
What is lay direction?Show answer
The strands are laid around the core; the wires are laid around their strand. Each can be right-hand or left-hand lay.
What is minimum breaking load and factor of safety?Show answer
The minimum breaking load (MBL) is the load at which the rope, in new condition, will fail by tensile fracture. It is given on the rope manufacturer's test certificate.
What is inspection and retirement?Show answer
Steel wire ropes wear progressively. Routine inspection looks for:
What is wire rope on a typical lifting device?Show answer
A tower crane on a Sydney CBD building site might have 19 mm or 22 mm diameter 6 x 36 IWRC rope on the main hoist drum. The rope passes through the boom-tip sheaves and the load block (typically 2-fall or 4-fall, providing additional mechanical advantage as discussed in the pulleys dot point) and terminates at a wedge socket or thimble.
What is forgetting dynamic effects?Show answer
SWL is a static value. Shock loads from a stalled lift or a snatched start can momentarily double the rope tension. The factor of safety is partly to cover this.
What is using rope past retirement?Show answer
Visual inspection criteria are strict because partial rope failure is not visually obvious. Lay length and broken wire counts must be measured. :::
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