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► ROPE MATERIAL ► NYLON ► POLYESTER ► POLYPROPYLENE ► POLYETHYLENE ► ARAMID ► LIQUID POLYMER ► HMPE ► MATERIAL
PROPERTIES |
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 is the trade
name of Polyamide. There are two forms
of Nylon are used in synthetic fiber ropes; Nylon 6 and Nylon 6.6.
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 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 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 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 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.
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.
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.
Copyright@2006 Offshore Consulting Engineering All Rights Reserved Website developed by A.G.A. Hammoutene |
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