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    CWC Technical Information

    CWC Technical Information

    There are two types of fibers used in the construction of ropes and twines, natural and synthetic. The most common natural fibers used are: Manila, Sisal, Jute and Cotton. Synthetic fibers such as: Polypropylene, Polyethylene, Nylon and Polyester have become the most popular fibers in today’s market.

    MANILA rope was once the preferred choice in ropes before synthetic fibers were developed. Manila ropes still maintain some advantages over synthetic fibers. Manila rope has good resistance to the UV (Ultraviolet) rays.

    SISAL fibers come from the Agave and Sisalana plants grown in tropical countries. Sisal has many of the characteristics of manila, but offers only 80% of its strength. It is more economical than manila and makes a good choice as a general purpose rope. Sisal is commonly used as a tying twine.

    JUTE is mainly used as a tying twine. It knots very well. Due to its short fibers, Jute does not have much strength.

    COTTON is a natural fiber, typically white in color. It is a soft fiber, which makes it nice to handle. Cotton also knots very well.

    POLYPROPYLENE & POLYETHYLENE make a flexible and lightweight rope. They are rot proof and resist degradation from exposure to: oil, water, gasoline and many chemicals. Polypropylene and Polyethylene are the only rope fibers that float. Available in twisted or braided constructions, they are a perfect economical choice as a general purpose rope.

    POLYESTER is very strong and provides excellent abrasion resistance. Polyester stretches less than nylon and does not have the elasticity or shock absorbing qualities of nylon. Polyester has good resistance to UV rays and resists rot and degradation from exposure to: oil, gasoline and many chemicals. Polyester is very popular as a marine or industrial rope where stretch is not desired.

    NYLON is known for its elasticity and shock absorbing qualities. Nylon has good abrasion resistance and is rot proof. Nylon fiber resists degradation from exposure to: oil, gasoline and many chemicals. Nylon has good resistance to UV rays. Nylon will last 4-5 times longer than natural fibers.

     

     

    Rope Selection Guide

    FIBER TYPE

    NYLON

    POLYESTER

    POLYPROPYLENE

    POLYETHYLENE

    MANILA

    COTTON

    STRENGTH

    1*

    2*

    3*

    4*

    5*

    6*

    WET STRENGTH VS. DRY STRENGTH

    85%

    100%

    100%

    100%

    115%

    115%

    SHOCK LOAD ABILITY

    1*

    3*

    2*

    4*

    5*

    6*

    FLOATS OR SINKS IN WATER

    SINKS

    SINKS

    FLOATS

    FLOATS

    SINKS

    SINKS

    ELONGATION AT BREAK

    20-34%

    15%-20%

    15%-20%

    10%-15%

    10%-15%

    5%-10%

    WATER ABSORPTION

    6%

    ZERO

    ZERO

    ZERO

    100%

    100%

    MELTING POINT

    480° F

    500° F

    330° F

    275° F

    DOES NOT MELT

    CHARS AT 350° F

    DOES NOT MELT

    CHARS AT 350° F

    ABRASION RESISTANCE

    2*

    1*

    4*

    5*

    3*

    3*

    DEGRADATION: RESISTANCE TO SUNLIGHT

    GOOD

    EXCELLENT

    POOR

    FAIR

    GOOD

    GOOD

    DEGRADATION: RESISTANCE TO ROT

    EXCELLENT

    EXCELLENT

    EXCELLENT

    EXCELLENT

    POOR

    POOR

    DEGRADATION: RESISTANCE TO ACIDS

    POOR

    GOOD

    GOOD

    GOOD

    POOR

    POOR

    DEGRADATION: RESISTANCE TO ALKALIS

    GOOD

    POOR

    GOOD

    GOOD

    POOR

    POOR

    DEGRADATION: RESISTANCE TO OIL AND GAS

    GOOD

    GOOD

    GOOD

    GOOD

    POOR

    POOR

    ELECTRICAL CONDUCTIVITY RESISTANCE**

    POOR

    GOOD

    GOOD

    GOOD

    POOR

    POOR

    FLEXING ENDURANCE

    1*

    2*

    3*

    6*

    4*

    5*

    SPECIFIC GRAVITY

    1.14

    1.38

    .90

    .95

    1.38

    1.54

    STORAGE REQUIREMENTS

    WET OR DRY

    WET OR DRY

    WET OR DRY

    WET OR DRY

    DRY ONLY

    DRY ONLY

     

    Specifications

    DIAMETER AND SIZE NUMERICAL VALUES

    Size is determined by linear density. Diameter is given as a minimal value and may vary slightly. If a specific diameter value is specified, linear density and minimum breaking strength values may be different from those given in tables.


    WORK LOAD LIMITS

    Minimum breaking strength is based on data from a number of manufacturers and represents a value of 2 standard deviations below the mean, as established by regression analysis. The Work Load Limits of a rope shall be determined by dividing the minimum breaking strength by the design factor. Design factors range from 5 to 12. Because of the wide range of rope use, rope conditions, exposure to the several factors affecting rope behavior, and the degree of risk to life and property involved, it is not realistic to make standard recommendations as to design factors or Work Load Limits. Work Load Limits are based upon rope in good condition with appropriate splices used in non-critical applications and under normal service conditions. Normal service is generally considered to be: use under static or very modest dynamic load conditions. Design factors at the low end of the suggested range should only be selected with expert knowledge of conditions and professional estimate of risk, based on the critical conditions of use listed below.

     

    SPECIAL SAFETY NOTE

    A dangerous situation occurs if personnel are in line with a rope under excessive tension. Should the rope fail, it may recoil with considerable force and injury or death may result. Persons must be warned against standing in line with the rope.

     

    DYNAMIC LOADING

    Whenever a load is picked up, stopped, moved or swung, there is an increased force due to dynamic loading. The more rapidly or suddenly such actions occur, the greater the increased force will be. In extreme cases, the force put on the rope may be two, three or even more times the normal load involved. Dynamic Loading occurs when picking up a tow on a slack line or using a rope to stop a falling object. Therefore, in applications such as: towing lines, life lines, safety lines, climbing ropes, etc., design factors must reflect the added risks involved. Users should be aware that dynamic effects are greater on a low elongation rope such as manila than on a high-elongation rope such as nylon and greater on a shorter rope than on a longer one. The range of design factors contains provision for very modest dynamic loads. This means that the load must be handled slowly and smoothly to minimize dynamic effects.

    Critical Conditions of Use: Larger Design Factors Shall Be Used When:

    1) Loads are not accurately known.
    (Always know load weight).
    2 Operators are not trained.
    (Do not use unless you are trained).
    3) Operation and use procedures are not well defined and/or controlled.
    4) Inspection is infrequent.
    (Inspect before use).
    5) Abrasion, cutting and dirt are present.
    (Use adequate protection).
    6) Shock loads or extreme dynamic loadings are likely.
    7) High temperatures are present. (Avoid heat damage).

     

    8) Chemicals are present. (Avoid harmful chemicals).
    9) Ropes are kept in service indefinitely.
    10) Rope tension is maintained continuously for long periods.
    11) Rope subjected to sharp bends if used over pulleys or surfaces with too small a radius.
    12) If knots are used, strength is reduced by up to 50%.

     

    Death, injury or loss of valuable property may result from failure to properly use and inspect ropes.

    Special Applications

    Design factor ranges are not necessarily intended to apply in those applications where a thorough engineering analysis of all conditions of use has been made by qualified professionals. In such cases: breaking strength, elongation, energy absorption, behavior under long-term or cyclic loading and other pertinent properties and operating procedures may be evaluated to allow the selection of a design factor best suited for the specific requirements.

     

    Rope Guidelines

    NOTE: Because of the wide range of rope use, rope condition, exposure to the several factors affecting rope behavior and the degree of risk to life and property involved, it is impossible to cover all rope applications. In all cases where risk is involved, or there is a question about the condition of use, consult the manufacturer. Consult the manufacturer for specific applications relative to rescue rope information.

    CHOOSING A ROPE

    Always consult the manufacturer before using rope when personal safety or possible damage to property is involved. Make sure the rope is adequate for the job. Do not use too small a rope or the wrong type. Specifications are readily available, which gives the strength for various sizes and constructions of natural fiber and synthetic ropes.

    REMOVING ROPE FROM COILS & REELS

    Remove rope properly from coils or reels to prevent kinking. If the rope is in a coil, it should always be uncoiled from the inside. If on a reel, the rope should be removed by pulling it off the top while the reel is free to rotate. This can be accomplished by passing a pipe through the center of the reel and jacking both ends up in a horizontal position until the reel is free from the surface. To proceed in any other manner may cause kinks or hockles (strand distortion).

    HANDLING ROPE

    Never stand in line with rope under tension. If a rope or attachment fails, it can recoil with deadly force causing serious injury or death. Synthetic rope has higher recoil/snapback tendencies than natural fiber rope.
    Reverse rope ends regularly, particularly when used in tackle. This permits even wearing and ensures longer, useful life. When using tackle or slings, apply a steady, even pull to get full strength from the rope. For maximum safety and economy, always use slings employing an angle of about 45° or less.

    OVERLOADING

    Do not overload rope. Sudden strains and shock loading can cause failure.
    Avoid sudden strains and shock loads as they can exceed rope breaking strength. Shock loading can cause failure of a rope normally strong enough to handle the load. Work Load Limits are not applicable when the rope is subject to significant dynamic loading. Whenever a load is picked up, stopped, moved or swung, there is an increased force due to dynamic loading. The more rapidly or suddenly such actions occur, the greater this increase will be.

    In extreme cases, the force put on the rope may be two, three or even more times the normal load involved. Examples could be picking up a tow on a slack line or using a rope to stop a falling object. Work Load Limits as given do not apply in applications such as: towing lines, life lines, safety lines or climbing ropes. Users should be aware that dynamic effects are greater on a low elongation rope like manila than on a high elongation rope like nylon and greater on a shorter rope than on a longer one. Excessive dynamic loading of a high elongation rope is equally dangerous, because of stored energy which will cause the rope to recoil dangerously if it breaks. When a Work Load Limit has been used to select a rope, the load must be handled slowly and smoothly to minimize dynamic effect and avoid exceeding the provision for them.

    WINCHING LINES

    Proper procedures will prevent kinks and hockles in three strand twisted rope. Repeated hauling of a line over a winch in a counterclockwise direction will extend the lay of twisted rope and simultaneously change the twist of each strand. As this action continues, strand hockles or back turning may develop. Once these hockles appear they cannot be removed and the rope is permanently damaged at the point of hockling. If the line is continuously hauled over a winch in a clockwise direction, the rope lay is shortened and the rope becomes stiff and will readily kink.

    CHECKING ROPE FOR WEAR

    Avoid using rope that shows signs of aging and wear. If in doubt, destroy the used rope.
    No type of visual inspection can accurately determine actual residual strength. When fibers show wear in any given area, the rope should be re-spliced or replaced. Check the line regularly for frayed strands and broken yarns. Pulled strands should be rethreaded into the rope if possible. A pulled strand can snag on a foreign object during rope operation. Both outer and inner rope fibers contribute to the strength of the rope. When either is worn, the rope is weakened.

    Open the strands of rope (either three strand or braided) slightly and look for powdered fiber, which is one sign of internal wear. A heavily used rope will often become compacted or hard which indicates reduced strength. The rope should be discarded if this condition exists.

    SPLICING

    Join Rope Ends by Splicing.
    Knots can decrease rope strength by as much as 60%. Use the manufacturers’ recommended splices for maximum efficiency. Other terminations can be used, but their strength loss with a particular type of rope construction should be determined and not assumed.

    CHEMICALS

    Avoid Damaging Chemical Exposure.
    Rope is subject to damage by chemicals. Consult the manufacturer for specific chemical exposure such as solvents, acids and alkalis. This is particularly true for natural fiber rope. Consult the manufacturer for recommendations when a rope will be used where chemical exposure (either fumes or actual contact) can occur.

    HEAT

    Avoid Overheating.
    Heat can seriously affect the strength of rope. When using rope where temperatures exceed 140°F (or if it is too hot to hold), consult the manufacturer for recommendations as to the size and type of rope for the proposed, continuous, heat exposure condition. When using ropes on a capstan or winch, care should be exercised to avoid surging while the capstan or winch head is rotating. The friction from this slippage causes localized overheating which can melt or fuse synthetic fibers or burn natural fibers, resulting in severe loss of tensile strength.
    Synthetic fiber ropes will show a reduction in strength when used at elevated temperatures. Because of this property, caution should be taken when using synthetic rope at elevated temperatures; rope will fail under loads well below the published breaking strength. In addition, even though synthetic rope is being used at 75°F, if it has been stored at elevated temperatures over a long period of time it can fail under loads below published break strength. If the user has any doubts concerning the strength of the rope contact the manufacturer.

    Caution
    Heat can seriously affect the strength of synthetic ropes. The temperature at which 50% strength loss can occur in new and unused rope is: Polypropylene at 150°F, Nylon or Polyester at 350°F.

    ABRASION

    Avoid all abrasive conditions.
    All rope will be severely damaged if subject to rough or damaging surfaces and/or edges. Chocks, bitts, winches, drums and other surfaces must be kept in good condition and free of burrs and rust. Pulleys must be free to rotate and should be of proper size to avoid excessive wear. Restraining clamps and similar devices will damage and weaken the rope and should be used with extreme caution.

    STORAGE AND CARE OF ROPE

    All rope should be stored clean, dry, out of direct sunlight and away from extreme heat.
    Rope should be stored in a cool, dry and well ventilated location. It should be kept off the floor and on racks to provide ventilation underneath. Never store rope on a concrete or dirt floor and under no circumstances should rope and acid or alkalis be kept in the same location. Natural fiber rope mildews and decays if stored wet. Do not store rope in direct sunlight. Some synthetic rope (particularly polypropylene and polyethylene) may be severely weakened by prolonged exposure to ultraviolet (UV) rays unless specifically stabilized and/or pigmented to increase UV resistance. UV degradation is indicated by discoloration and the presence of splinters and slivers on the surface of the rope.

    All synthetic rope under load will recoil if a fitting such as a chain, hook, cleat, bolt, pin or ball-hitch, etc., should fail. The snapback action can propel the fitting and the rope causing serious injury to persons or property anywhere in the vicinity. This danger can exist from failure of the fitting within the rope’s Work Load Limit. Before using, check all fittings, bolts, shackles, connectors, pins, mountings, splices, etc.


    The Cordage Institute publishes standards for strengths, weights and testing procedures. Contact us for a copy of the publications list.