How to get the best performance and lifespan of wire rope

Tuesday, 25 June 2019

Lifting equipment passes through many hands before it gets to you. Manufacturing, shipping, storage, distribution, possibly stored again and then used. During this time the equipment can be exposed to conditions such as moisture, extreme conditions or substances that may affect its integrity. Bearing this in mind it is important that lifting equipment is inspected by all parties as part of our duty of care; as opposed to relying on the belief that ‘someone else has checked it’. Taking responsibility for safety is essential in this industry. Due the nature of the work a small breach or oversight in safety can be fatal.

At Nobles, we put our wire rope suppliers through rigorous testing to ensure we only provide our customers with the best quality products. We test and certify the equipment before it gets to you and always store and transport the equipment to ensure its integrity. Whilst you can guarantee that the product we provide will meet your lifting requirements, here are a few helpful tips to ensure you get the best performance of your wire rope and improve the longevity of your investment.

Components of wire rope

A wire rope is made up of the basic components illustrated. The terms used to describe these component parts should be strictly adhered to, particularly when reporting on the conditions of ropes. Describing wires as strands and strands as wire can be grossly misleading. For example, a report that a rope has a broken strand in most applications calls for immediate discarding of the rope, and subsequent interruption of operation. In contrast, a report that a rope has a broken wire calls for a thorough inspection, prior to continued use allowing an informed decision on whether to continue using the wire rope.

Care and Maintenance

Breaking in

A wire rope may be looked upon as a machine composed of many moving parts. As such it should be broken in as soon as it is installed, by loading it very lightly for a few cycles and then gradually stepping up the load, to enable both wires and strands to ‘bed down’ into the working positions, with the load distributed as uniformly as possible.

With 6 and 8 stranded ropes, the torque can greatly diminish after breaking in by releasing the connection and allowing the torque to run out. This procedure may have to be repeated until the constructional stretch has been worked out of the rope and it has become neutral.

The use of ‘spinners’ or swivels should be avoided whenever possible. All ropes should be reeled onto winch drums as tightly and uniformly as possible during the initial installation.

Inspection

Wire rope is tough and durable, but nonetheless expendable when it reaches the end of its safe service life. Rope deterioration becomes noticeable through the presence of broken wires, surface wear, corrosion, wire or strand distortion due to mechanical abuse, or drastic reduction in diameter and lengthening of the lay. Also, deterioration can be detected by using non-destructive testing techniques. Wire ropes should be periodically inspected for signs of deterioration.

While statutory regulations govern the inspection and discarding of certain wire ropes, it is recommended that all lifting equipment be inspected by a qualified person prior to use. The determination of the point at which a wire rope should be discarded for reasons of safety requires judgment and experience in rope inspection in addition to knowledge of the performance of previous ropes used in the same application.

Sufficient records should be kept by the equipment owner providing a reliable history of the rope’s maintenance, incidents and other relevant information. Inspection of both operated and discarded ropes frequently indicates equipment faults that have a large bearing on the service life and safety of the rope. It is therefore essential to inspect the equipment on which the rope is used as well as the rope itself.

Always consult the relevant Australian Standard if in doubt as to how often you should inspect, test and service your equipment. Nobles can help you create a tailored inspection policy to ensure workplace safety and compliance. Lifting equipment inspections should be conducted by a trained professional who is an expert in their specialised field.

Deterioration

Typical examples of wire rope deterioration:

1. Mechanical damage due to rope movement over sharp edges whilst under load.

2. Localised wear due to abrasion on supporting structure.

3. Narrow path of wire breaks caused by working in a grossly oversized groove or over small support rollers.

4. Severe wear in Lang’s Lay, caused by abrasion at cross-over points on multi-layer coiling application.

5. Corrosion of severe degree caused by immersion of rope in water.

6. Typical wire fractures because of bend fatigue.

7. Wire fractures at the strand, or core interface, as distinct from ‘crown’ fractures caused by failure of core support.

8. Typical example of localised wear and deformation created at a previously kinked portion of rope.

9. Multi-strand rope ‘bird caged’ due to torsional unbalance. Typical of build-up seen at anchorage end of multi-fall crane application.

10. Protrusion of IWRC resulting from shock loading.

Rope Maintenance

End for ending and cropping

In certain applications, e.g., drag ropes, it is possible to “end for end” the rope. This will give longer rope life due to the wear points being re-located. If additional rope can be accommodated on the drum, then progressive cutting back (cropping) will bring “new” rope into the system and will re-locate wear points.

Treatment of broken wires

Broken wires affecting the life of adjacent wires should be removed. General purpose ropes, crane ropes and hoist ropes should be discarded whenever any of the types of degradation exceed the recommended limits in the table below. However, the rope life may be ended before these limits are reached.

The table below allows for internal wire breaks and is valid for all constructions of rope. In 6 and 8 strand ropes, wire breaks occur principally at the external surface. This does not apply to wire ropes having several layers of strands (typically multistrand constructions), where the majority of wire breaks occur internally and are therefore non-visible fractures.

Discard practices

Clear policies regarding discard should be formulated. Rope maintenance schedules should be drawn up to provide periodic inspections and removal cycles for each rope as well as inspections of individual components such as the sheaves. Regular maintenance ensures optimum rope life, minimises down time of plant and equipment and increases the efficiency of operations.

Non-Destructive Testing

This method of inspection involves using an electromagnetic instrument to non-destructively examine the rope. It incorporates a sensor head that can induce a magnetic field in a section of rope that is located within the instrument. Changes in the metallic field enable a chart to be produced showing changes in metallic cross-sectional area and any wire breaks or other anomalies. The life of costly wire ropes may be extended by using this sophisticated method of testing.

Transport, Storage & Handling

Transport

Ropes are supplied on reels or in coil form and should be lifted rather than dropped, tipped or rolled to avoid damage. When transporting, care must be taken not to damage the rope through contact with other goods and ropes should be uncovered as soon as they are received to check for possible transit damage.

Storage

Ropes on reel or in coils should be stored on blocks off the floor to prevent sweating and corrosion and under cover in dry conditions free from corrosive agents, such as mill dust, Sulphur or acid fumes.

Warm or hot conditions can cause the lubricant to drain to the lower side of the reel. If ropes are to be stored for any length of time in warm or hot conditions, the reels should be mounted on a horizontal shaft and turned over periodically to maintain uniform lubrication of the rope. Additional lubrication may be necessary.

Removed ropes awaiting further use, should be thoroughly cleaned, inspected, lubricated and stored under the same conditions as new ropes.

Handling

Incorrect handling of rope from reels and coils can result in springing of wires and strands and kinking of the rope. This type of damage can seldom be entirely corrected and can greatly reduce the effective life of the rope.

These drawings show the correct and incorrect methods of reeling a rope from the transport reel onto a drum or another reel. A suitable stand for the reel is also shown, the transport reel should be firmly mounted and braked to prevent overrunning and give tight rewinding.

     

The fleet angle has an important bearing on the winding of a rope from sheave to drum, particularly at high operation speeds. If winding is to take place smoothly, the fleet angles on both sides of the drum will have to be kept within acceptable limits.

Excessive fleet angles can result in considerable abrasive damage to both sheave flanges and rope and considerably reduce the life of the rope and the equipment.

Fleet angles normally range to a maximum of 1.5˚ for plain drums and to a maximum of 2.5˚ for grooved drums. Smaller angles are required for high speed haulage such as mine windings. Unless the head or guide sheave is centred with respect to the drum, there will be different values for the left and the right fleet angles.

Extending the life of wire rope

Two factors that affect the life of wire include the design and installation of equipment and the operating environment.

Design of equipment or installation

Sheave size, drum design and drum diameter can directly affect wire rope life. For example, doubling the sheave size can produce up to four times the rope life. The minimum ratios that should be adhered to are listed in the table below.

Operating Environment

When corrosive conditions exist regular rope inspections, particularly of the IWRC (independent wire rope core), is essential. The effects of corrosion can be partly offset by using galvanised wire rope. Excessively high operating temperatures can lead to deterioration of the wire rope core, and thereby cause rope fatigue.

Improving wire rope performance

Improved rope performance can be obtained by paying attention to the following areas:

- Sheaves should be grooved to the nominal rope diameter plus an allowance of 7% to allow for rope manufacturing tolerances and should be re-machined when worn to nominal diameter plus 3%. Sheaves must also be free from score marks, run freely and be true.

- Guides and rollers must be free from undersized grooving and broken flanges and should run free and true.

- Drum grooves should be checked for size and riser plates checked for effectiveness.

- Displaced or damaged cheek plates in rope blocks or safety guards should be repaired.

- Grabbing clutches and brakes should be repaired and adjusted to obviate impact loads on the rope.

- End fittings, such as wedges, sockets and drums anchorages, should be inspected for excessive wear.

Nobles Technical Services

Nobles have a team of 70+ highly trained service technicians who can inspect, service, test, repair and certify your lifting equipment to ensure it not only meets your operational safety standards but Australian Standards as well. We have NATA accredited tensile laboratories in various Nobles branches throughout Australia and can provide tensile destruction testing services as well as NATA accredited non-destructive testing on wire ropes in situ.

For more information on the services we offer head to the Services Overview section on our website or give our technical services team a call on 1300 711 559 or email techservices@nobles.com.au.

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