ROPE MATERIAL

 

    NYLON

 

    POLYESTER

 

    POLYPROPYLENE

 

    POLYETHYLENE

 

    ARAMID

 

    LIQUID CRYSTAL

        POLYMER

 

    HMPE

 

    MATERIAL

        PROPERTIES   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ROPE MATERIAL

 

 

Nowadays the ropes used for offshore mooring lines are manufactured from synthetic fibers. In the past rope for ship mooring was manufactured from natural fibers. The natural fibers are all replaced by synthetic fibers. The synthetic fibers have better properties than natural fibers. The synthetic fibers are continuous filaments of very long molecular chain polymers. The material of synthetic fibers determines mainly the rope properties like strength, stiffness, fatigue, density and creep. The material of synthetic fibers is more important than the rope construction. For offshore mooring synthetic fiber ropes the following materials are used:

 

  Nylon

  Polyester

  Polypropylene

  Polyethylene

  Aramid

  Liquid Crystal Polymer

  HMPE

 

 

 

NYLON

 

 

Nylon is the trade name of Polyamide. There are two forms of Nylon are used in synthetic fiber ropes; Nylon 6 and Nylon 6.6. The advantages of Nylon are that Nylon is the most strongest of the common synthetic fibers, highly resistant to mildew and it has the most elasticity and excellent resistance to aging. The disadvantages of Nylon are that wet strength is 15-20% less than its dry strength and UV radiation for long duration can damage the Nylon rope. For offshore mooring lines UV radiation is no problem. Under water there is a small UV radiation.

 

 

 

POLYESTER

 

 

Polyester is also known under the trade names Terylene, Dacron, Trevira, Diolen. Polyester has almost the same properties as Nylon. The advantages of Polyester over Nylon are that Polyester has better resistance to abrasion, Polyester has lower density, it has no wet strength loss and it has better fatigue performance. The disadvantages of Polyester are that Polyester has low stretch and higher energy absorption. Polyester is more preferred than Nylon, because its wet-strength, lower density, better fatigue performance for the same price. Polyester is the most common synthetic fiber used for offshore mooring lines.

 

 

 

POLYPROPYLENE

 

 

Polypropylene is also known as polypropene. The material copolymer is similar as Polypropylene. The advantages of Polypropylene are that it is the lightest of the common synthetic ropes (it floats) and it is cheap. The disadvantages of Polypropylene are that it has the low strength and it has moderate elongation. Polypropylene is commonly used in the fishing and marine industry.

 

 

 

POLYETHYLENE

 

 

Polyethylene or Polyethene is seldom used in large ropes. The advantage of Polyethylene is the low density. The disadvantage of Polyethylene is the low modulus and high elongation.

 

 

 

ARAMID

 

 

Aramid is also known under the trade names Kevlar and Twaron. Aramid is referred as high modulus fiber, because it has higher strength and it is stiffer than the common synthetic fibers. The advantages of Aramid are that Aramid has very good strength to weight ratio, good fatigue performance and Aramid has low creep. The disadvantages of Aramid are that the Aramid has poor resistance to abrasion and Aramid is susceptible to axial compression fatigue.

 

 

 

LIQUID CRYSTAL POLYMER

 

 

Liquid Crystal Polymer is also known under the trade name Vectran. Liquid Crystal Polymer is a high modulus fiber.

The advantages of Liquid Crystal Polymer are that Liquid Crystal Polymer has high strength to weight ratio and it has no creep. Liquid Crystal Polymer has better abrasion resistance than Aramid. The fatigue performance is better or the same as Aramid.

 

 

 

HMPE

 

 

High Modulus PolyEthylene is known as Gel-Spun Polyethylene. HMPE is improved polyethylene. HMPE is stiffer and stronger than polyethylene. HMPE has the trade names Dyneema and Spectra. HMPE is a high modulus fiber. The advantages of HMPE are that HMPE has very high strength, low density (it floats) and very good abrasion resistance. HMPE has very low elongation, good fatigue performance and good toughness. The disadvantage of HMPE is that HMPE has a high creep rate. The high creep rate makes creep rupture possible. Creep rupture is a very important concern.

 

 

 

MATERIAL PROPERTIES

 

 

The mechanical, physical material properties of the synthetic materials used for synthetic fiber ropes are listed in the tables below.

The materials used for large ropes are nylon, polyester, polypropylene, aramid, liquid crystal polymers LCP and HMPE.

The materials nylon, polyester and polypropylene are common synthetic fiber materials.

The price of common synthetic fiber materials are between 1 Euro/kg and 3 Euro/kg.

The price of carbon steel is around 0.5 Euro/kg and the price of stainless steel is between 2.5 Euro/kg and 4.5 Euro/kg.

The materials aramid, liquid crystal polymers LCP and HMPE are high modulus synthetic fiber materials.

The price of high modulus synthetic fiber materials is higher than common synthetic fiber materials.

The physical properties density, tenacity, modulus of elasticity, elongation, melting point are important

physical material properties to distinguish a material and to select a material for the rope.

A material can be determined by melt test, burn test, stain test and specific gravity test.

Other important considerations for selecting the material for a large rope are creep, wet abrasion resistance,

wet abrasion resistance, wet strength, chemical resistance, kinking, shock load absorption,  

water absorption, axial compressed fatigue, bending fatigue, UV radiation and heat resistance.

 

 

ROPE MATERIAL

NYLON

POLYESTER

POLYPROPYLENE

STEEL

SPECIFIC GRAVITY (kg/l)

1.14

1.38

0.91

7.86

TENSILE STRENGTH (N/mm2)

850

1050

500

2160

MODULUS OF

ELASTICITY (N/mm2)

5500

9000

4200

200000

ELONGATION TO BREAK (%)

18

12.5

12

1.1

MELTING POINT (°C)

219

256

170

1600

WATER ABSORPTION

( percent of dry weight )

9 %

1%

0 %

0 %

STRENGTH WET COMPARED TO STRENGTH DRY

80-85%

100%

100%

100%

ABRASION RESISTANCE

GOOD

VERY GOOD

VERY GOOD

VERY GOOD

UV RESISTANCE

GOOD

GOOD

GOOD

VERY GOOD

SHOCK LOAD

ABSORPTION ABILITY

GOOD

GOOD

GOOD

GOOD

CHEMICAL RESISTANCE

GOOD

GOOD

GOOD

VERY GOOD

CREEP

MEDIUM

LOW

MEDIUM

VERY LOW

KINKING

RESISTANT

RESISTANT

RESISTANT

VERY RESISTANT

AXIAL COMPRESSION FATIGUE

POOR

GOOD

VERY GOOD

VERY GOOD

 

 

ROPE MATERIAL

ARAMID

LCP

HMPE

STEEL

SPECIFIC GRAVITY (kg/l)

1.44

1.41

0.97

7.86

TENSILE STRENGTH (N/mm2)

3000

3000

3300

2160

MODULUS OF

ELASTICITY (N/mm2)

60000

80000

85000

200000

ELONGATION TO BREAK (%)

3.7

3.8

3.5

1.1

MELTING POINT (°C)

480

330

145

1600

ABRASION RESISTANCE

POOR

MEDIUM

GOOD

VERY GOOD

UV RESISTANCE

POOR

GOOD

VERY GOOD

VERY GOOD

CHEMICAL RESISTANCE

EXCELLENT

EXCELLENT

EXCELLENT

VERY GOOD

CREEP

LOW

LOW

HIGH

VERY LOW

KINKING

SUSCEPTIBLE

RESISTANT

SUSCEPTIBLE

VERY RESISTANT

AXIAL COMPRESSION FATIGUE

GOOD

GOOD

EXCELLENT

VERY GOOD

 

 

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