Notes on Ropes
Working Loads
Safe Work Loads of Fibre Ropes
3-Strand Ropes Safety factor = 5
(new rope)
|
| Rope Diameter (cm/inches) |
Manila |
Nylon |
Poly-propylene |
Polyester |
Poly-ethylene |
| |
Kg.
|
Kg.
|
Kg.
|
Kg.
|
Kg.
|
| 0.64 (1/4") |
54
|
136
|
113
|
136
|
114
|
| 0.79 (5/16") |
90
|
227
|
182
|
227
|
159
|
| 0.95 (3/8") |
122
|
317
|
227
|
318
|
227
|
| 1.27 (1/2") |
239
|
567
|
377
|
545
|
363
|
| 1.59 (5/8") |
400
|
908
|
590
|
863
|
477
|
| 1.91 (3/4") |
490
|
1271
|
772
|
1090
|
681
|
| 2.22 (7/8") |
699
|
1725
|
999
|
1544
|
953
|
| 2.54 (1") |
817
|
2179
|
1317
|
1907
|
1135
|
Types of Fibre Ropes
Fibre ropes are made from either natural or synthetic fibres.
| |
Pros
|
Cons
|
| Natural Fibres |
- Resistant to heat
- Do not burn fast
- Hold simple knots
|
- Susceptible to rot and mildew
- Shrink and stiffen when wet
|
| Manila |
|
- Weakens when exposed to sunlight
|
| Sisal |
|
|
| |
Pros
|
Cons
|
| Synthetic Fibres |
- Stronger x3 than Natural fibres
- Impervious to rot and mildew
- Lighter
- Do not stiffen when wet
|
|
| Nylon |
- Strongest of all fibres
- Highly elastic and will elongate 10% to 40%
- High abrasion resistance
|
- Lose 10% of their strength when wet
- Very slippery when wet
- Attacked by acids and paints
- Dangerous when it snaps under load
- Susceptible to heat and sunlight
|
| Polypropylene |
- Light
- Floats on water
- Will not conduct electricity when dry
|
- Weaker than polyester and nylon
- Weakens progressively when temperatures rise (+65°C)
- Low melting point
|
| Polyethylene |
- Resistant to acids and alkalis
|
- Weakest of synthetic fibres
- Softens with rising temperatures
|
| Polyester |
- Lower stretch properties than nylon
- No strength loss when wet
- High resistance to sunlight and weather
- Resistant to acids and alkali
|
- Weaker than nylon under shock load
|
Safe use and storage
|
- All ropes should be kept dry and away from chemicals
- Never overload a rope
- A frozen rope should be carefully allowed to thaw and dry before use
- A rope should never be dragged over the ground or sharp objects
- Avoid abrupt bends if possible as they weaken rope considerably. Pad all sharp corners
- Synthetic ropes can be slippery when wet or new. Use additional care when handling or tying knots
- Store ropes in a cool dry place with good ventilation. Hang loose coils over a peg
- Dry and clean wet rope before storing. Allow them to dry naturally, as too much heat will make the fibres brittle.
- Keep all ropes away from any source of heat.
- Inspect ropes regularly for extreme wear and cuts
- Untwist strands carefully and check for bright clean internal conditions
- Pull out a couple of fibres from the end of a rope and try to break them. If they break easily then the rope should not be used when safety is required.
|
Knots, Bends, and Hitches
All knots bends and hitches reduce the strength of rope
Knots and bends by 50%
Hitches reduce by 25%
Splices by 20%
Monofilament ropes such as polyethylene and polypropylene require special knots to prevent slipping
Cutting Ropes:
Wrap tape around rope at the cutting point and then cut through the tape.
Information taken from a pamphlet issued by the Canada Safety Council and from information shipped with Lehigh rope.