Wire Rope Slings PDF

LEEA – Foundation Certificate (Global) – Course Workbook Wire Rope Slings Wire rope slings are very popular for general lifting duties. Due to their rigidity, they can be easily passed under loads when slinging. However, they are more susceptible to damage than chain slings....

LEEA – Foundation Certificate (Global) – Course Workbook Wire Rope Slings Wire rope slings are very popular for general lifting duties. Due to their rigidity, they can be easily passed under loads when slinging. However, they are more susceptible to damage than chain slings. The construction of the rope from which the sling is made is within reason unimportant provided that the rope has adequate flexibility and an adequate minimum breaking load (from which the SWL of the sling is calculated). The rope should be ordinary lay and maybe six or eight strands having a fibre or a wire core. As with any lifting media, slings of all configurations can be assembled from wire rope and will be found in service. Those working in the offshore industry will be familiar with the ‘five leg’ slings attached to offshore containers. These are actually four-legged wire rope slings with a pendant sling attached to the master link. In general industry, the most common type of wire rope slingin service is the single leg. Thimbles: these are a protective insert that is fitted to the eye of a sling leg at the time of manufacture. Thimbles are fitted where it is desirable to protect the eye from the worst effectsof abrasion and point loading. Two common types of thimble are used in the construction of slings. The teardrop-shaped thimble, which is used where sling legs are to attach to other fittings, and the reeving thimble, is designed to permit the passage of one eye through the other so that the sling may be used in choke hitch. A similar protective inset, known as the stirrup or half thimble, is designed to protect the wire rope of a soft eye when the sling is used in choke hitch. Hand Spliced Eye: the hand spliced eye is an eye formed at the end of a sling by the traditional method of threading the individual strands of the rope back along the main body of the rope ina prescribed pattern. This type of eye is now less popular than the more modern ferrule secured eye, but it is still available and preferred by some users. 61 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Common Sling Assemblies: in addition to 2, 3 and 4 leg wire rope slings, the most commonly used wire rope sling assemblies are: Single leg with soft eye or thimble eye at each end. They can also be fitted with a link at one end and a hook at the other. 62 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Terminal Fittings Notes: 63 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Eye Terminations There are two ways that eyes can be made, ferrule secured (sometimes incorrectly referred to as a mechanical splice) and hand spliced. 1. Turn Back Loop The turn back loop is the cheaper option to manufacture and therefore is perhaps used more commonly for general purpose slings. With this method, an aluminium ferrule is used to secure the eye made in the end of the rope The eye is simply formed by passing the ferrule over the rope, bending the rope back on itselfto form the eye, pulling the ferrule back over the returning tail end of the rope and then pressing the ferrule. Under pressure the aluminium flows into the rope formation, making a homogeneous joint Ferrule Secured Eyes When square-cut ferrules are used, it is necessary for a small amount of the tail to protrude through the ferrule to ensure that the rope is fully engaged within the ferrule. The standard says that the length of this should be no more than one half of the rope diameter. However, if the rope has been cut by a heat process, a portion of the rope will have become annealed (softened) in the heat-affected area. The protruding tail in this case should be no more than an amount equal to one diameter of the rope and positioned so that none of the annealed section is within the ferrule Tapered Ferrules Tapered ferrules are also available from some manufacturers. In this case, the tail end remains within the ferrule and it is essential that the ferrule manufacturer’s instructions for fitting are followed. Often, the manufacturer of the ferrule will provide a small view hole in the ferrule to enable the tail end to be seen 64 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook 2. Flemish Eye A tapered steel ferrule is passed over the rope. The standing part of the rope is then taken, and three strands are unravelled and opened so that a ‘Y’ formation is made. Care must be taken to ensure that the strands still lay together as they had in the rope The leg of the ‘Y’ that includes the core is bent to form an eye so that the ends of the strands sit against the undisturbed part of the rope at the bottom of the ‘Y’. The remaining three strands are then re-laid into the rope in the opposite direction, taking up the position they originally had inthe rope so that the lay of the strands is not disturbed The ends of the strands are then evenly distributed around the intact standing part of the ropeto complete the eye. The ferrule is then slid back over the distributed wires without displacingthe strands and then pressed. The ferrule compresses and grips the rope Stirrups The minimum peripheral length of a soft eye should be four times the rope lay length. This is so as to ensure that the lay of the rope is not disturbed. It is extremely difficult to fit thimbles whenmaking Flemish eyes. If the sling is to be used in a choked situation then a protective attachment, known as a stirrup thimble, is commonly used to protect the rope from damage Hand Spliced Eyes A hand-spliced eye is an eye formed at the end of a sling by the traditional method of threading the individual strands of the rope back along the main body of the rope in a prescribed pattern Whilst this type of eye is now less popular than the more modern ferrule secured eye, it is still available and preferred by some users In the case of hand splices, these should be made with five tucks against the lay of the rope. The type of splice where the tucks are made with the lay of rope, should not be used as this tendsto undo if the rope rotates in use and is effectively banned from splicing wire ropes for lifting purposes Wire Rope Grips For many years it has been common practice to make temporary eyes in wire rope, particularly winch wires, by using clamp-type grips, commonly known as ‘bulldog’ grips. The use of such gripping devices which clamp the wire to form temporary eyes is not recommended for the manufacture of slings. The reason for this is that tests have showed that these grips do not give an acceptable or consistent level of safety. Sockets and Fork Ends Sometimes used fitted to the rope by a compression process or 65 by a white-metal or resin bonding process. The manufacturer’s/supplier’s advice should always be sought and Page followed where their use is intended. © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Single and 2-Part This is not a common way of producing sling legs but is used for WireRope Slings very large capacity slings, so the examiner needs to be aware of them. An endless sling is produced and then a thimble is bound at each end. The thimbles that are used must be two or three sizes larger than would normally be used for the rope diameter. The looped sling leg will take a greater load than a single part sling made from the same size rope and a thimble for the actual rope diameter would collapse under the increased load it has to take. In order to make the thimble fit the rope it is necessary to serve the rope with wire or spun yarn. A sling leg produced by this method is not capable of twice the WLL of a single part of the rope, as one might expect, but is in the order of 25% less than this. This is due to the increased stress due to the rope being bent around such a tight radius. Notes: 66 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Rating of Wire Rope Slings The working load limit of a wire rope sling depends upon the following factors: The size and tensile It will be noted that different but similar constructions of rope of strength of the rope equal tensile strength have the same minimum breaking loads. The core of the rope A rope with a steel core will have a marginally higher breaking load than a similar rope with a fibre core. It will at the same time be slightly less flexible and more resistant to crushing. The number of parts of wire For some applications, double part legs are preferable as they rope (single or double) per give more flexibility than the equivalent capacity single part leg. sling leg They are however more costly and therefore normally only used for large capacities in order to utilize smaller diameter wire rope whilst offering a greater bearing area to the load. The geometry of the sling For example, the number of legs and, in the case of multi-leg slings, the angles between the legs and the vertical and their arrangement in plan. The method of rating This may be either the uniform load method or the trigonometric method, dependent on the application. Whilst slings may be found in service rated by either method, the uniform load method is the preferred method for rating multipurpose slings. The maximum angle of inclination at which the sling may be rated is 60° (120° included angle) but it may only be rated for use at 45° (90° included angle). The SWL to be marked on the sling should be assessed by a Competent Person and will be the same as the WLL in normal conditions or less than the WLL under special conditions. The maximum load that can be lifted by a sling may also vary from the marked SWL depending upon the method of use. Notes: 67 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Chain Slings How is a Chain made? Chain is made by passing lengths of steel bar into a machine that uses a series of automated processes to shape, form and weld each link into the finished chain. Following welding of the links, the chain will undergo a process of heat treatment to achieve the desired material properties such as strength, ductility and toughness. Chain slings are versatile and provide a safe method of lifting loads, but it is important that they are used correctly to avoid damage and potentially serious incidents. Material Chain slings manufactured from wrought iron are obsolete and no longer available. Similarly, mild steel chain slings have been obsolete since the early 1980’s following the publication of newer standards which specifically exclude the use of this grade of chain for lifting applications. However, it is possible that examples of wrought iron and mild steel chain slings may occasionally be found in service, but their continued use is not recommended by LEEA. Most modern chain sings are constructed from grade 8, and although not yet covered by standards in certain regions, grade 10 chain is becoming increasingly popular. Medium tolerance chain intended for sling manufacture needs to be more ductile to withstand shock loading. However, in use it is not subject to wear and can therefore have a softer skin. As it does not mate with other moving parts, it does not need to have such a precise pitch. Calibration When chain is produced by machine the links are not all exactly the same exact shape; the sides have a slight curve. When the manufacturer ‘calibrates’ it by the application of a force, the links bed down on each other and the sides of the link straighten. As a result, the chain extends by a very small amount. With load chains for lifting appliances (e.g. hand chain hoist), it is vital that the links are of precise size and form so that they engage correctly in the pocketed load wheels of the machine. This is achieved by manufacturing the chain to a calculated undersize. The finished chain is then subjected to an increased force, which pulls it to the required even shape, size and pitch. 68 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Finish Various finishing treatments are then given to fine tolerance chain to increase its wear resistance (e.g. case hardening). The loss of some ductility due to the manufacturing and finishing processes is relatively unimportant for load chains. However, these features are undesirable in a sling chain where it is less likely to wear. Sling chain is more liable to be shock loaded, so good ductility is essential. Fine tolerance chain may be recognised in two ways. The calibrating process has the effect of removing all of the residual scale from the heat treatment process and many of the finish treatments include corrosion resistant finishes. As a result, it has a bright finish and of course there is also the grade mark. Assembly Older chain slings, and currently a few for special applications, were assembled by a blacksmith and had welded joining links. These are very rarely found in service nowadays. Modern chain slings are assembled from components that have mechanical fixings, such as spiral roll pins, to retain them. They are therefore assembled and repaired very easily using standardised ranges of fittings. A full range of fittings is available with the clevis form of chain connection, such as hooks, shackles and egg links This system of assembly minimises the number of components necessary to assemble a sling, as the terminal fittings locate directly onto the chain With clevis attachment, the end link of the chain is passed into the jaw of the clevis A load pin is passed through the clevis and chain, on which the chain seats Spiral roll pins or circlip type fixings are used to lock the load pin in position ▪ A full range of fittings is available with the clevis form of chain connection, such as hooks, shackles and egg links ▪ This system of assembly minimises the number of components necessary to assemble asling, as the terminal fittings locate directly onto the chain ▪ With clevis attachment, the end link of the chain is passed into the jaw of the clevis ▪ A load pin is passed through the clevis and chain, on which the chain seats ▪ Spiral roll pins or circlip type fixings are used to lock the load pin in position 69 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook ▪ For the connection of the chain to master links a simple shackle like ‘coupler’ is available in some systems: Rating of Chain Slings The factors to be considered fall into three main groups 1. How the sling is attached to the load 2. The geometry of the sling, i.e. the angle of the legs to the vertical and the arrangement of the legs in plan 3. The number of legs in use The amount of load that will be carried by an individual leg will depend on the angle between each of the legs and the vertical, the arrangement of the legs in plain view and the total load being lifted. The reduced ratings for slings when used in choke hitch take account of higher stresses at the point where the choking hook or link bears upon the chain. The maximum angle of inclination at which the sling may be rated is 60° (120° included angle) but it may only be rated for use at 45° (90° included angle). The SWL to be marked on the sling should be assessed by a Competent Person and will be the same as the WLL in normal conditions or less than the WLL under special conditions. The maximum load that can be lifted by a sling may also vary from the marked SWL depending upon the method of use. Notes: 70 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Textile Slings Textile slings are manufactured from man-made fibres such as: Polyamide (nylon) Polyester Polypropylene Additionally, fibre rope slings may also be produced from natural fibres such as: Manila Sisal Hemp Although these will very rarely be found in service nowadays. New, specialist man-made fibres, such as HMPE (High Modulus Polyethylene) are now being produced to manufacture specialised lifting slings. These feature high cut and abrasion resistance; Although the various fibres have many common features, they react differently to temperature, chemical contact and environment. We will consider these matters in the Lifting Accessories Diploma training course. Types of textile slings Textiles slings can be found in various forms: 71 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Flat woven webbing slings Are also commonly known as belt slings, are used for a variety of lifting purposes. They are a textile sling which is soft and easy to handle whilst offering rigidity across their width. They are ideal for handling loads which require some support when being lifted as the load is spread across the full width of the webbing, avoiding point contact as is the case with chains or ropes. They are therefore less likely to cause damage to the load’s surface than rope, wire rope or chain slings. However, they are less robust and more easily damaged than equivalent capacity wire rope and chain slings. Roundsling Roundslings comprise of a core enclosed in a protective cover. The core is the load-bearing part of the roundsling and is in the form of a hank of yarn made up from one or more strands of the parent fibre material wound together continuously and joined to form an endless sling. The protective cover is a woven tubular outer sleeve of the same parent material as the core, whichis designed to be non-load bearing as it is intended only for protection and containment of thecore. Man-made fibre roundslings are an endless textile sling that is soft and pliable to use, easy to handle and especially useful on delicate surfaces. They are less robust and more liable to damage than equivalent capacity wire rope and chain slings. Fire Rope Slings Fibre rope slings are the traditional form of textile sling whose origins are recorded in the earliest history of lifting equipment. Their use has declined in recent years in favour of the newer forms of textile slings, i.e., flat woven webbing slings and roundslings but they may still be found in general use throughout the industry. Fibre rope slings are produced from cut lengths of rope which are then hand spliced. 72 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Fibre rope slings are less pliable than other forms of textile sling and are bulky to handle. Unlike flat woven webbing slings and roundslings they present a hard, point contact to the load although this is less severe than with chain or wire rope. Single leg, multi-leg or endless fibre rope slings can be produced. They are made by hand splicing eyes at each end of a piece of rope or by splicing one cut end of a rope to the other end, forming an endless loop. With multi-leg slings, the eye one end of each sling leg is made through a master link. Where this is done, the use of thimbles is advised to protect the eyes. Eyes are produced by bending the rope to form a loop. The strands at the end of the rope are separated and then tucked back into the standing part of the rope against the lay to form the eye, in a similar way as with wire rope. This is done in such a way that they lock and do not slip when a load is applied. There are differences in the splicing requirements, depending on the type of rope used. This is due to differing coefficients of friction. Identification visually, the various fibres appear much the same. This makes identification extremely difficult. An international system of colour-coded labels, which carry the information necessary to be marked on a sling (see marking), has therefore been adopted in standards as follows: 73 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Shackles Shackles are probably the most common and universal lifting accessory. Their uses are extensive. They may be used to connect a load directly to a lifting appliance, to connect slings to the load and/or lifting appliance, as the suspension for lifting appliances or as the head fittingin certain types of pulley blocks. There are three main types of shackles used for lifting today: 1. Bow 2. Dee 3. Grab types Shackles are normally forged from various grades of steel. Higher quality alloy steels give a higher safe working load than those made in higher tensile steels, while higher tensile steel shackles have a higher safe working load than those made in mild steel. Some manufacturers continue to make shackles to old now withdrawn standards, whereas many have now adopted the current standards. The older, now withdrawn shackle standards fully specified all dimensions of the shackle. In contrast, the current standards tend to specify only some dimensions fully, the rest being specified as a maximum or minimum value. Shackles to the older standards are sized by the diameter of the material in the shackle body and not the diameter of the pin. Shackles to later standards are usually sized by their WLL. Dee Shackle All shackle standards specify dee shackles, with some specifying both a large dee and a small dee shackle. A large dee shackle is a shackle that has ample internal clearances in the body and jaw, and which is appropriate for general engineering purposes. A small dee shackle is a shackle that has moderate internal clearances in the body and jaw but, size for size has a SWL higher than that of the large dee. It is suitable for use with hook eyes, eyebolts, egg links, wire rope thimbles, etc. and for the head fittings of ships’ blocks. Bow Shackle Similarly, all shackle standards specify bow shackles, with some specifying both a large bow and a small bow shackle. A large bow shackle is a shackle which has ample internal clearances in the body and jaw, and which is appropriate for general engineering purposes. A small bow shackle is a shackle which has moderate internal clearances in the body and jaw but, size for size, has a SWL higher than that of the large bow. It is suitable for use with the eyes and bodies of hooks, eyebolts, egg links, wire rope thimbles, etc. and for the head fittings of ships’ blocks. Grab Shackle A grab shackle is a dee shackle having a screwed countersunk pin, designed for use with grabs where the shackle must pass through a circular aperture of minimum diameter. 74 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Application The selection of the shape of the shackle body will depend on the intended use. It is desirable to use a shackle with as small a jaw opening as is consistent with an adequate articulation of the connection. Dee shackles are, in general, used to join two pieces of lifting equipment. Bow shackles are, in general, used where more than one attachment is to be made to the body or to allow freedom of movement in the plane of the bow. Pins There are two types of shackle pin in common use, the screw pin, and the bolt, nut and cotter pin (commonly referred to as the safety pin or 4-piece shackle). Screwed pins with eye and collar are the most common type of pin and are suitable for a wide range of uses. However, if they are subject to movement and vibration (e.g. by a sling moving over the pin), they can loosen and unscrew. The bolt with hexagon head, hexagon nut and split cotter pin is used where a positive connection is required as it cannot unscrew unintentionally. They are also ideal where a permanent connection is required, (e.g. connecting the top slings to a spreader beam). Notes: 75 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024