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Welcome to the Certex News Centre, the only place for information on Certex. Remember to keep returning to this page to keep up-to-date with Certex.Why an Internal Inspection is the Best Health Check for your RopeWe can only expect ropes to perform well if they are physically fit for the job.When a patient goes to a doctor, they can often reach a diagnosis by careful questioning and an analysis of the symptoms. With a wire rope, evidence of ‘illness’ is not so obvious. Ropes can’t communicate, they may look fine and there may be no outward symptoms. Yet, unbeknown to the operator, a rope could only be hours away from a catastrophic failure. It is, therefore, essential to examine the physical condition of a rope and this invariably means ‘opening them up’. Are internal inspections necessary?Simple constructions, such as six or eight strand ropes, hold most of their strength in the outer strands, with only 6-10% of the product strength being contained in the ‘invisible’ core. If this is the case, it may seem superfluous to carry out an internal inspection of this type of rope. Yet, nothing could be further from the truth and it is the good condition of this part of the rope that is paramount to its overall effectiveness. This is because the core provides support to the outer strands and ensures that the strand gaps are maintained, thereby reducing the effects of friction or abrasion. This is even more relevant when dealing with multi-strand ropes, such as Bridon’s high performance Endurance Dyform ® 34LR and the Endurance 50 DB, which have a much higher proportion of their strength (up to 50%) held within the invisible core. Many people also fall into the trap of assuming that if a rope looks all right on the outside then it will be fine inside too – a misconception often reinforced by over-reliance on industry guidelines. International Standards such as ISO 4309 lay down criteria (see tables 1 & 2) which detail the maximum allowable wire breaks visible on the outside of the rope and recognize the difference between a standard rope and a multi-strand variety. Given that these tables err on the side of caution, it might seem safe to assume that if you have a small number of external wire breaks then you can remove the rope before it reaches an unsafe condition. However, while it is important to take into account all visual clues when examining a rope, it is unwise to rely on this method alone. What are the consequences of not examining a rope properly? Modern cranes, particularly those using plastic sheaves, are designed to be much kinder to the wire rope than some of the older designs and thus wear and external wire breaks are minimized. However, this can lull operators into a false sense of security, because the inside of the rope is still subject to inter-strand contact and friction. This is why a cursory external examination can show a perfect rope on the outside but inside it is a different matter. Several times in my career, I have been presented with broken ropes that only a few days before had been given a clean bill of health. The first thing that happens when we receive such a rope is look at the condition inside and sure enough, although the rope is pristine on the outside, the inside shows a ‘Christmas tree effect’ of broken wires. Is Non-Destructive Testing a safe alternative?Non-Destructive Testing (NDT) is a proven method of examining long lengths of wire rope but its purpose is to aid visual inspection rather than act as a substitute. NDT incorporates the use of either electromagnetic or permanent magnetic equipment – using magnetic-flux and/or magnetic flux leakage principles – and is capable of detecting discontinuities and/or changes in the cross-sectional area of ferromagnetic wire ropes. This method can be used for short lengths of wire rope but is expensive and should only be carried out by a skilled operator. It also requires the rope to be taken out of situ so that every millimetre of rope can be passed through a test head. While NDT is a valuable aid for determining where there may be a degradation in the wire rope, it is still necessary to examine the area where a problem has been indicated. Carrying out an internal inspection So, this leads us back to internal inspections, which are a cheaper, more effective, and more practical method of inspection for shorter lengths of smaller diameter ropes. It is also a process that can be carried out by any competent person who has received the right training. The method described below is the one followed by engineers from wire rope and lifting gear companies such as Bridon Ropes and Certex (UK) Ltd. Areas of rope to examineThe diagram (below) shows the areas where the rope is likely to deteriorate first. The length of rope running over sheaves and the hook block are the heavily worked parts of the rope and the examination should concentrate on these. The state of the drum anchorage is also important and the area immediately adjacent to any termination is likely to experience degradation.
Examination tool kitOnly a few specialized tools are required to carry out the inspection, including:
What to check for?
How to examine ropes running over sheavesImportant – The rope MUST NOT be under any tension during this process. 1) Attach clamps approximately 100mm-200mm apart 2) Contra-rotate clamps to unlay outer strands 3) Ensure that the strands are not excessively moved thus avoiding any permanent deformation 4) Manipulate the strands with probe to facilitate examination Once the examination is complete: 1) Apply dressing 2) Apply additional reverse torque to re-bed strands on core How to examine ropes at terminationImportant – The rope MUST NOT be under any tension during this process. 1) Attach clamp, usually only ONE clamp is necessary 2) Rotate clamp to unlay outer strands 3) Manipulate strands with probe to facilitate examination 4) Ensure that the strands are not excessively moved thus avoiding any permanent deformation 5) Manipulate the strands with probe to facilitate examination Once the examination is complete: 1) Apply dressing 2) Apply additional reverse torque to re-bed strands on core Carrying out this simple process will enable any crane operator to gain the most from his ropes while avoiding any unnecessary accidents or damaging expensive equipment. Just as a doctor would recommend a regular health check, so a regular examination of your wire ropes will ensure a safe and long working life! Charles Gillespie is currently Sales and Marketing Manager of Certex (UK) Ltd and has 18 years experience of working in the wire rope and lifting industry. Previous roles have included heading up the crane rope sales of UK-based Bridon Ropes. CAPTIONS AND TABLESPicture 1 shows a multi-strand rope that has broken due to internal corrosion. The exterior exhibited a minimum amount of corrosion, with no broken wires and limited wear. The rope broke because the core had corroded to such a degree that it failed, causing the outer strands to impinge on each other leading to a catastrophic failure.
Picture 2 shows the inside of rope, which has heavily indented strands only visible by internal examination. The next stage would be broken wires leading to a catastrophic failure.
Picture 3 shows home-made clamps that are effective for examining ropes internally whilst not damaging them. The diameter of the grips must be closely matched to avoid damage to the rope.
Picture 4 Shows the method for examining ropes at the termination.
Table 1 Guidance for the number of visible broken wires necessitating discard( For 6 and 8 strand ropes working in metal sheaves)
Table 2 Guidance for the number of visible broken wires necessitating discard (For multi-strand ropes)
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