wire rope fleet angle in stock

This one is about Fleet Angles on Wire Rope.  An important topic in any wire rope reeving system, this article looks at fleet angles both at the drum and at the sheave.

Fleet Angle is usually defined as the included angle between two lines, one which extends from a fixed sheave to the flange of a drum and the other which extends from the same fixed sheave to the drum in a line perpendicular to the axis of the drum.

When spooling wire rope onto a smooth/plain drum it is generally recommended that the fleet angle is limited to between 0.5 and 2 degrees.  If the fleet angle is too small, ie less than 0.5 degrees, the rope will tend to pile up at the drum flange and fail to return across the drum.  In this situation, the problem may be alleviated by increasing the fleet angle through the introduction of a sheave or spooling mechanism.

If the rope is allowed to pile up it will eventually roll away from the flange, creating a shock load in both the rope and the drum assembly, thus creating an undesirable and unsafe operating condition.

Excessively high fleet angles will return the rope across the drum prematurely, creating gaps between wraps of rope close to the flanges as well as increasing the pressure on the rope at the cross-over positions.

Where drum grooving is provided, large fleet angles will result in wear taking place to the drum grooving which may then result in the rope miss-spooling on the drum.  When spooling onto a grooved drum, it is recommended that the fleet angle is limited to between 0.5 and 4 degrees for 6&8 stranded single layer construction wire ropes and between 0.5 and 2 degrees for rotational resistant and parallel laid construction wire ropes.  Note, for high speed spooling of wire rope in excess of 8m per second it may be necessary to reduce the fleet angle to 0.5 to 1.5 degrees especially at high D/d ratios.

Level winding/spooling mechanisms can be positioned in front of a wire rope winch drum to guide the rope across the face of the drum to provide superior spooling utilising fleet angles between 0.25 and 1.5 degrees

When a fleet angle exists as the rope enters a sheave, it initially makes contact with the sheave flange.  As the rope continues to pass through and around the sheave it moves down the flange until it sits in the bottom of the groove.  In doing so, even when under tension, the rope will actually roll as well as slide.  As a result of the rolling action the rope is twisted where turn is induced into or out of the rope.  This either shortens or lengthens the lay length of the outer strands which can damage the rope and cause ‘birdcages’ or similar distortions within the rope. A s the fleet angel increases so does the amount of twist

The fleet angle within the reeving system should be limited to 4 degrees for 6 & 8 stranded single layer construction wire ropes and 2 degrees for rotational resistant and parallel laid construction wire ropes.  It is recognised that it is not always possible to comply with these general recommendations.  This may be the case in applications such as overhead hoists.  In which case the rope life can be affected.

Please do not hesitate to contact the team at Crane Ropes Australia or give us a call at LiftQuip on 7089 8335 if you would like more clarification or would like to work through some technical issues you may be having with your wire rope.

You may know the importance of fleet angles, but do you know the best ways to correct them? Cris Seidenather, managing director of Lebus International Engineers, explains how...

When spooling wire rope onto a drum, it is necessary for the rope to come onto the drum at a very slight angle, just enough to encourage each wrap to sit tidily next to the previous wrap, and for each layer to ride cleanly onto the layer beneath.

In fact, apart from the design of the drum itself, this angle – the fleet angle – is the most significant factor in the behaviour of a spooling system.

The fleet angle is defined as the largest angle of the rope between the first sheave and the drum flange, relative to the centre line of the drum. With all types of drum, the rope is subject to a fleet angle which directly influences its behaviour and impacts on its service life. If the fleet angle is too big, the wire will tend to pull away from the flange as the layer changes. It will want to spool towards the centre and so leave gaps. Gaps mean ragged spooling, which means (at best) excessive rope wear, or (at worst) snagging, catastrophic system failure and physical danger to all those around.

If the fleet angle is too small, the rope may not pull away from the flange soon enough. It will pile up on the flange for, perhaps, two or three wraps and then bang down with considerable force, damaging the rope and the equipment. Again, catastrophic failure and personal injury is a real threat.

Ideally, the fleet angle should be between 0.25 and 1.25 degrees. This is not an absolute rule of physics; it depends on the rope construction. Nor has it been calculated mathematically. Rather, it has been learned from years of experience. While some wire rope experts may cite slightly different numbers, this is the range that Lebus recommends, and we believe we have at least as much experience as anyone when it comes to multi-layer spooling since inventing the original Lebus counterbalanced spooling system in the 1950s.

The fleet angle can be varied by moving the first sheave closer to or further away from the drum. If the sheave is too close to the drum, the fleet angle will be calculated at greater than 1.25 degrees; if it is too far away, the fleet angle will be less than 0.25 degrees.

In general the distance between sheave and drum should be at least 20 times the width of the drum. Ideally a ratio of 23:1 works very well, we have found. Thus, the larger the drum, the further away the sheave needs to be to keep the fleet angle between 0.25 and 1.25 degrees.

It is not always possible, however, to achieve the optimum fleet angle. For example, there are massive winching systems at the top of mountain cable car systems, often housed in compact machinery sheds. There is often no space to rig a sheave the requisite distance from the drum, and so an alternative for how to reduce the fleet angle must implemented.

For just such cases two additional spooling devices are available. One is a fleet angle compensator, which is driven automatically by the rope tension. The other is a level winder that is mechanically driven. Both offer a solution to guide the cable along the drum between flanges, but each has its advantages and disadvantages.

The fleet angle compensator (FAC) is driven by the movement of the wire rope as it goes through the crossover sections of the drum. As the rope winds or unwinds, the FAC shaft slowly oscillates, allowing its sheave to slide back and forth across the shaft to maintain an optimum fleet angle and guide the rope smoothly onto the drum.

Certain operating conditions are necessary for the Lebus fleet angle compensator to function properly. The rope must go from the drum over the compensator sheave with a minimum contact angle of 60 degrees to a fixed point such as a fairlead or fixed sheave. To avoid excessive angles of the rope on the sheaves, the minimum distance between the fairlead (fixed sheave) and the compensator sheave must be at least six times the drum width. If spooling in multiple layers, the drum must have Lebus-style parallel grooving. For a single layer, helical (screw thread) grooving will also work. As always, there must be sufficient tension on the cable during the spooling operation. We recommend that minimum tension should be 1-2% of the wire rope’s breaking load.

There are three primary advantages of the Lebus fleet angle compensator. First, there is no mechanical connection between the drum and the compensator. Second, installation is easy and quick. And third, it is completely automatic and, after initial adjustments when the rope is first spooled onto the drum, only a minimum of maintenance is necessary.

A mechanical level winder comprises a main shaft (the lead screw) with helical screw grooving along which the rope feeder travels. The rope feeder housing includes two vertical roller bars and one horizontal roller or, alternatively, a wire rope sheave. The lateral movement of the housing is generated by a chain drive sprocket ratio between drum and lead screw, as shown in the image. The automatic level winder fitted is designed and engineered to be compatible with the grooving on the drum. Perfect, controlled spooling is guaranteed regardless the number of layers and slight changes in wire rope size.

The level winder unit – also sometimes called level wind pay-on gear – must be installed in front of the drum in line with the first fixed sheave when using the vertical rollers to guide the wire rope.

The level winder is engineered to be compatible with the parallel grooving on the drum. It is adjusted for the specific rope diameter, and the gear ratio is fixed (using a standard sprocket-chain connection) to match the ratio between coils of wire on the drum to the pitches on the lead screw. The result is perfect and controlled spooling, regardless of the number of layers or slight changes in wire rope size.

As before, certain operating conditions are required for the level winder to function properly. The rope must go from the drum through the vertical rollers or the level-wind sheave to a fixed point such as a fairlead or fixed sheave. To avoid excessive angles of the rope on the sheaves, the minimum distance to the fairlead or fixed sheave must be at least seven times the drum width. There must be a minimum tension of 1 to 2% of the wire rope’s breaking load when spooling more than one layer.

The advantages of level winders are that they keep the rope spooling properly even if there is slack in the line. As with the fleet angle compensator, once it is set up no more adjustment is necessary and very little maintenance is required. In case of damage to a mechanical level winder, parts are easy to replace and there is nothing electrical or hydraulic to worry about.

Oceanographic installations that spool rope up to 46 layers have demonstrated that level winders give synchronised and totally controlled spooling in the very harshest, most testing conditions.

The disadvantages of level winders is that they do require a little more space than fleet angle compensators and they are sensitive to high axial forces and shock loads.

If the fleet angle is just a bit too small, there is a really rather simple solution. A flat iron plate, which we call a kicker plate, is welded or bolted onto a specific point on the flange of the winch drum. This kicker costs no more than two dollars. Since the Lebus parallel grooving pattern on the drum controls the movement and spacing of the wire rope between the flanges, and from layer to layer, it is easy to identify the location on the drum circumference where the rope must return (kick back) from the flange to regain the proper position to assure proper spooling for each repeated layer.

This is where the kicker is placed. Once installed near the centre line of the groove crossover sections, the rope is given a kick after each complete wrap to take its proper position on the patterned drum.

A final option for adjusting the fleet angle, if it is not possible to move the fixed sheave, is simply to reduce the width between the flanges. The parallel grooving of the drum will continue to act effectively to provide smooth multi-layer spooling with a narrower drum, even if – as is likely – the number of layers on the drum needs to increase as a consequence of narrowing the width.

It’s a good piece of information to have in your back pocket when you are adjusting or inspecting your rigging, or if you have the opportunity to buy a new rigging system. If you notice an excessive fleet angle, it could be a clue that something is wrong with your mounting or machinery.

In a properly installed manual lineset, the cable comes out as parallel to the groove of the block as possible. It can form an angle of 1.5 degrees into or out of the block, but no more—if the angle is greater, the cable will rub against the sheave. This can cause the cable to fray and eventually break, which can bring scenery or stage weights down on someone’s head.

Chances are you’ve seen the term zero fleet angle in articles or advertising for motorized rigging equipment. A hoist with zero fleet angle has a non-moving set of blocks above the drum. As the drum turns, it actually moves, so the cable piles on and off of the drum with no change in the angle between the drum and the cable.

Zero fleet angle hoists can be installed in greater density than other drum or line shaft hoists—allowing for more sets on stage. These hoists are particularly useful in renovations of historic theatres, where there may be minimal loft space.

In this article, we outline important technical topics related to wire rope. This information has been sourced from and approved by Bridon American. Use the outline to skip to specific sections:

Any assembly of steel wires spun into a helical formation, either as a strand or wire rope (when subjected to a tensile load) can extend in three separate phases, depending on the magnitude of the applied load.

At the commencement of loading a new rope, extension is created by the bedding down of the assembled wires with a corresponding reduction in overall diameter. This reduction in diameter is accommodated by a lengthening of the helical lay. When sufficiently large bearing areas have been generated on adjacent wires to withstand the circumferential compressive loads, this mechanically created extension ceases and the extension in Phase 2 commences. The Initial Extension of any rope cannot be accurately determined by calculation and has no elastic properties.

The practical value of this characteristic depends upon many factors, the most important being the type and construction of rope, the range of loads and the number and frequency of the cycles of operation. It is not possible to quote exact values for the various constructions of rope in use, but the following approximate values may be employed to give reasonably accurate results.

Following Phase 1, the rope extends in a manner which complies approximately with Hookes Law (stress is proportional to strain) until the limit of proportionality or elastic limit is reached.

It is important to note that wire ropes do not possess a well defined Young’s Modulus of Elasticity, but an ‘apparent’ Modulus of Elasticity can be determined between two fixed loads.

By using the values given, it is possible to make a reasonable estimate of elastic extension, but if greater accuracy is required, it is advisable to carry out a modulus test on an actual sample of the rope. As rope users will find it difficult to calculate the actual metallic steel area, the values can be found in the Wire Rope Users Manual or obtained from Bridon Engineering.

The permanent, non-elastic extension of the steel caused by tensile loads exceeding the yield point of the material. If the load exceeds the Limit of Proportionality, the rate of extension will accelerate as the load is increased until a loading is reached at which continuous extension will commence, causing the wire rope to fracture without any further increase of load.

The coefficient of linear expansion (∝) of steel wire rope is (6.94 x 10-6 per °F) and therefore the change in length of 1 foot of rope produced by a temperature change of t (°F) would be:

Example: What will be the total elongation of a 200 ft. length of 1-1/8″ diameter Blue Strand 6 x 41 IWRC wire rope at a tension of 20,000 Ibs. and with an increase in temperature of 20°F?

In addition to bending stresses experienced by wire ropes operating over sheaves or pulleys, ropes are also subjected to radial pressure as they make contact with the sheave. This pressure sets up shearing stresses in the wires, distorts the rope’s structure and affects the rate of wear of the sheave grooves. When a rope passes over a sheave, the load on the sheave bearing results from the tension in the rope and the angle of rope contact. It is independent of the diameter of the sheave.

Assuming that the rope is supported in a well fitting groove, then the pressure between the rope and the groove is dependent upon the rope tension and diameter, but is independent of the arc of contact.

It must be realized that this method of estimation of pressure assumes that the area of contact of the rope in the groove is on the full rope diameter, whereas in fact only the crowns of the outer wires are actually in contact with the groove. It is estimated that the local pressures at these contact points may be as high as five times those calculated. If the pressure is high, the compressive strength of the material in the groove may be insufficient to prevent excessive wear and indentation, and this in turn will damage the outer wires of the rope and effect its working life.

As with bending stresses, stresses due to radial pressure increase as the diameter of the sheave decreases. Although high bending stresses generally call for the use of flexible rope constructions having relatively small diameter outer wires, these have less ability to withstand heavy pressures than do the larger wires in the less flexible constructions. If the calculated pressures are too high for the particular material chosen for the sheaves or drums or indentations are being experienced, consideration should be given to an increase in sheave or drum diameter. Such a modification would not only reduce the groove pressure, but would also improve the fatigue life of the rope.

The pressure of the rope against the sheave also causes distortion and flattening of the rope structure. This can be controlled by using sheaves with the correct groove profile, which, for general purposes, suggests a recommended groove diameter of nominal rope diameter +6%. The profile at the bottom of the groove should be circular over an angle of approximately 120° and the angle of flare between the sides of the sheave should be approximately 52°.

Bend fatigue testing of ropes usually consists of cycling a length of rope over a sheave while the rope is under a constant tension. As part of their ongoing development program, Bridon has tested literally thousands of ropes in this manner over the years on their own in-house design bend testing equipment.

Through this work, Bridon has been able to compare the effects of rope construction, tensile strength, lay direction, sheave size, groove profile and tensile loading on bend fatigue performance under ideal operating conditions. At the same time it has been possible to compare rope life to discard criteria (e.g. as laid down in ISO 4309) with that to complete failure of the rope, i.e. to the point where the rope has been unable to sustain the load any longer. As part of the exercise, it has also been possible to establish the residual breaking strength of the rope at discard level of deterioration.

What needs to be recognized, however, is that very few ropes operate under these controlled operating conditions, making it very difficult to use this base information when attempting to predict rope life under other conditions. Other influencing factors, such as dynamic loading, differential loads in the cycle, fleet angle, reeving arrangement, type of spooling on the drum, change in rope direction, sheave alignment, sheave size and groove profile, can have an equally dramatic effect on rope performance.

If designers or operators of equipment are seeking optimum rope performance or regard bending fatigue life as a key factor in the operation of equipment, such information can be provided by Bridon for guidance purposes.

Wire ropes are manufactured slightly larger than the nominal diameter. The maximum allowable oversize tolerances provided by industry standards are shown in the following table:

Under certain circumstances it may be necessary to use a swivel in a lifting system to prevent rotation of the load. This is typically done for employee safety considerations. It is possible however, that the use of a swivel will have an adverse affect on rope performance and may, in some cases, damage the wire rope.

The type of swivel that causes the most concern from the standpoint of the wire rope is the independent anti-friction swivel that attaches directly to the rope. The purpose of using a swivel in a lifting system is to prevent rotation of the load. This then allows the wire rope to rotate. Excessive rope rotation can damage a wire rope.

To assist in determining whether or not a swivel should be used in the lifting system, the following recommendations should be considered. It must also be recognized that the rotation characteristics of different types and constructions of wire rope vary considerably. The following types and constructions of wire rope are grouped according to their rotation characteristics.

These rope constructions will rotate excessively with one end free to rotate, and the rope will unlay and distort and be easily damaged with a loss of rope breaking force.Blue Strand 6 x 19 and 6 x 36 Class Lang Lay

Wire rope constructions having high rotation characteristics when used in single part reeving may require a swivel in the system to prevent rotation in certain operating conditions. However, this should be done only when employee safety is the issue.

These rope constructions, when used in a reeving system with one end free to rotate, will have a high level of rotation. This will cause the rope to unlay and, to some degree, distortion of the rope will occur.Blue Strand 6 x 19 and 6 x 36—Class Regular Lay

The ropes in this Group are designed with an inner rope that is laid in the opposite direction to the outer strands to provide a medium resistance to rotation. Ropes with medium rotation characteristics are used with a swivel in single part reeving applications. However, a swivel is not recommended for multiple part hoisting applications or in any application where the swivel is not necessary for safety reasons. If it is necessary to use a swivel, the rope must be operating at a design factor of 5 or greater, must not be shock loaded and must be inspected daily by a qualified person for distortion.

It should be noted that if a swivel is used on conjunction with Group 3a ropes, rope service life might be reduced due to increased internal wear between the outer strands and the inner rope.Group 3aEndurance 8RR Rotation Resistant

Wire ropes having low rotation characteristics used in either single or multiple part reeving may be used with a swivel. The reason for this is that the ropes will exhibit very little, if any, rotation when used at the proper design factor. Application parameters, such as a fleet angle, may induce turn into a wire rope that can be relieved by the use of a swivel. However, if the application does not induce any turn into the rope, or if a swivel is not beneficial to the performance of the rope, the swivel may not be necessary.Endurance 35 LS

Fleet angle is usually defined as the included angle between two lines: one which extends from a fixed sheave to the flange of a drum, and the other which extends from the same fixed sheave to the drum in a line perpendicular to the axis of the drum (see illustration).

If the drum incorporates helical grooving, the helix angle of the groove needs to be added or subtracted from the fleet angle as described above to determine the actual fleet angle experienced by the rope.

When spooling rope onto a drum, it is generally recommended that the fleet angle is limited to between 0.5° and 2.5°. If the fleet angle is too small, i.e. less than 0.5°, the rope will tend to pile up at the drum flange and fail to return across the drum. In this situation, the problem may be alleviated by introducing a ‘kicker’ device or by increasing the fleet angle through the introduction of a sheave or spooling mechanism.

If the rope is allowed to pile up, it will eventually roll away from the flange, creating a shock load in both the rope and the structure of the mechanism, an undesirable and unsafe operating condition.

Excessively high fleet angles will return the rope across the drum prematurely, creating gaps between wraps of rope close to the flanges, as well as increasing the pressure on the rope at the cross-over positions.

Even where helical grooving is provided, large fleet angles will inevitably result in localized areas of mechanical damage as the wires ‘pluck’ against each other. This is often referred to as ‘interference’, but the amount can be reduced by selecting a Langs lay rope if the reeving allows. The “interference” effect can also be reduced by employing a Dyform rope, which offers a much smoother exterior surface than conventional rope constructions.

Where a fleet angle exists as the rope enters a sheave, it initially makes contact with the sheave flange. As the rope continues to pass through the sheave it moves down the flange until it sits in the bottom of the groove. In doing so, even when under tension, the rope will actually roll, as well as slide. As a result of the rolling action, the rope is twisted, i.e. turn is induced into or out of the rope, either shortening or lengthening the lay length of the outer layer of strands. As the fleet angle increases, so does the amount of twist.

To reduce the amount of twist to an acceptable level, the fleet angle should be limited to 2.5° for grooved drums and 1.5° for plain drums and when using Rotation Resistant, ropes the fleet angle should be limited to 1.5°.

However, for some crane and hoist applications, it is recognized that for practical reasons. It is not always possible to comply with these general recommendations, in which case, the rope life could be affected.

The problem of torsional instability in crane hoist ropes would not exist if the ropes could be perfectly torque balanced under load. The torque generated in a wire rope under load is usually directly related to the applied load by a constant ‘torque factor’. For a given rope construction, the torque factor can be expressed as a proportion of the rope diameter and this has been done below.

Variation with rope construction is relatively small and hence the scope for dramatically changing the stability of a hoisting system is limited. Nevertheless, the choice of the correct rope can have a deciding influence, especially in systems which are operating close to the critical limit. It should be noted that the rope torque referred to here is purely that due to tensile loading. No account is taken of the possible residual torque due, for example, to rope manufacture or installation procedures.

Torsional Stability and the Cabling Graph are two methods which can be used to determine torsional stability or the tendency of the rope to cable. The torque factors quoted are approximate maximum values for the particular constructions. To calculate the torque value for a particular rope size, multiply by the nominal rope diameter.

The torsional characteristics of wire rope will have the effect of causing angular displacement of a sheave block when used in multi-fall reeving arrangements. The formula below gives a good approximation under such arrangements.

The preceding equations are all relative to a simple two part reeving. For more complex systems, a similar approach may be used if account is taken of the different spacings of the ropes.

The equations assume that rope is torque-free in the noload condition, therefore, induced torque during or immediately after installation will adversely influence the calculated effect.

The above data assumes a constant torque value which is a valid assumption for a new rope. Wear and usage can have a significant effect on the torque value, but practical work shows that under such circumstances, the torque value will diminish, thus improving the stability of the arrangement. Some arrangements may be of such complexity that the evaluation demands a computer study.

Assuming a pedestal crane working on two falls is roped with 20mm diameter DYFORM 34LR and the bottom block carries a sheave of 360mm diameter with the falls parallel:

If the rope is new (worst condition) and no account is taken of block weight and friction then angular displacement for a height of lift of 30 meters is given by:

Field research jointly conducted by the Wire Rope Technical Board and the Power Crane and Shovel Association has shown that cabling of the rope parts in a multiple part reeved hoisting arrangement is controlled by several factors. The following calculations and graphs can be used to determine when and if cabling will occur on multiple part reeved hoisting arrangements.

Various constructions of rope shown on the graph indicate the limited conditions for torsional stability with the angular displacement of the hoist block to a maximum of 90 degrees. When the operating conditions for a particular installation give a resultant above the appropriate band, then cabling of the falls will most likely occur. If the operating conditions give a resultant below any particular band, the cabling of the falls will most likely not occur. If the operating conditions for any particular installation fall within the band, cabling is unpredictable.

The achievement of even winding on a smooth faced drum is closely related to the magnitude of the D/d ratio, the speed of rotation, load on the rope, and the fleet angle. Of all these factors, the one that exerts perhaps the greatest influence on winding characteristics is the fleet angle.

The schematic drawing (Fig. 39) shows an installation where the wire rope runs from a fixed sheave, over a floating sheave, and then on to the surface of a smooth drum. The fleet angle (Fig. 39) may be defined as the included angle between two lines; one line drawn through the middle of the fixed sheave and the drum – and perpendicular to the axis of the drum and a second line drawn from the flange of the drum to the base of the groove in the sheave. (The drum flange represents the farthest position to which the rope can travel across the drum.) There are left and right fleet angles, measured to the left or right of the center line of the sheave, respectively.

It is necessary to restrict the fleet angle on installations where wire rope passes over the lead or fixed sheave and onto a drum. For optimum efficiency and service characteristics, the angle here should not exceed 1 1/2º for a smooth drum, or 2º for a grooved drum. Fleet angles larger than these suggested limits can cause such problems as bad winding on smooth drums, and the rope rubbing against the flanges of the sheave grooves. Larger angles also create situations where there is excessive crushing and abrasion of the rope on the drum. Conversely, small fleet angles – less than 1/2º – should also be avoided since too small an angle will cause the rope to pile up.

In order to avoid twisting of the wire rope by the drum, the drum rule should be obeyed. A right hand drum should be operated with a left hand lay rope, a left hand drum should be operated with a right hand lay rope.

In multi-layer drums, the direction of the drum changes with every layer. Here the direction of the lay of the steel wire rope should either be chosen to suit the direction of the reeving (a left hand reeving should have a right hand rope and a right hand reeving should have a left hand rope) or the lay direction of the steel wire rope should be chosen for the most used layer of the drum (see also page 52 & 53).

A block is a frame that encloses one or more sheaves and is provided with a hook or some other means that allows attachment to cargo or to a fixed anchor point. The purpose of a block is twofold. First, it is used to change direction of a wire rope line. Second, when used in pairs, blocks increase mechanical advantage by allowing the use of multiple parts of line. Blocks range in size from several pounds capacity to hundreds of ton

A block consists of a shell (or side plates), a center pin, and an end fitting. There are a variety of end fittings such as hooks, shackles, and clevices that facilitate attachment of the block to the cargo or to a fixed anchorage. Blocks are also equipped with a becket or mouse ear whereby the end of the rope line is affixed to the block. The sheaves of the block transmit the load from the wire rope to the center pin and then to the shell straps or side plates

2.Snatch Block :Snatch blocks refer to a group of intermittent service blocks that jerk or snatch their load over comparatively short distances. Snatch blocks are characterized by a side-opening plate that facilitates threading the wire rope through the block

3.Wire rope (construction or fixed) blocks.:Fixed blocks or construction blocks are typically used as upper blocks in multi-part reeving arrangements in derricks or material hoists. As such, they have large diameter multiple sheaves like crane blocks but the lack the additional cheek plate weights required for overhaul.

A hoist drum barrel is grooved to seat the first layer of the wire rope closely and uniformly. The correct way to wind wire rope on a drum will depend on the lay of the rope.

Each turn of the rope around the full circumference of the drum is called a wrap. Rope is wrapped around the drum, starting at one end flange and progressing to the other flange, which is called a layer. Drum flanges should extend beyond the fully loaded drum by a minimum of two rope’s diameter.

The wire rope end is attached to the drum by a socketing or clamping arrangement. A minimum of three wraps must remain on the drum at any time during the hoisting operation when required rope is spooled out.

It is important to install wire rope on a smooth drum correctly in regard to maintaining a correct relationship between direction of the lay of the rope (right or left) and direction of the rotation of the drum (overwind or underwind), winding from left to right or right to left. For proper installation of the wire rope on a drum, the following measures are required:

Drums should have sufficient rope capacity with proper rope size and reeving to perform all hoisting and lowering functions. In addition, all hoist drums should be provided with adequate means to ensure even spooling of the rope on the drum. Where the operator cannot see the drum or rope, drum rotation indicators should be provided for the operator’s sensing

Fleet angles may cause increased wear or strain on wire ropes. With coiling onto a smooth drum, the fleet angle should be 0.5 to 2.5 degrees. If the rope is damaged by adjacent windings, the service life may be improved by using compacted or lang lay ropes.

When spooling wire rope onto a drum, it is necessary for the rope to come onto the drum at a very slight angle, just enough to encourage each wrap to sit tidily next to the previous wrap, and for each layer to ride cleanly onto the layer beneath.

In fact, apart from the design of the drum itself, this angle – the fleet angle – is the most significant factor in the behaviour of a spooling system.

If the fleet angle is too big, the wire will tend to pull away from the flange as the layer changes. It will want to spool towards the centre and so leave gaps. Gaps mean ragged spooling, which means (at best) excessive rope wear, or (at worst) snagging, catastrophic system failure and physical danger to all those around.

If the fleet angle is too small, the rope may not pull away from the flange soon enough. It will pile up on the flange for, two or three wraps and then bang down with considerable force, damaging the rope and the equipment. Again, catastrophic failure and personal injury is a real threat.

The fleet angle should be between 0.25 and 1.25 degrees. This is not an absolute rule of physics; it depends on the rope construction. Nor has it been calculated mathematically. Rather, it has been learned from years of experience.

The fleet angle can be varied by moving the first sheave closer to or further away from the drum. If the sheave is too close to the drum, the fleet angle will be greater than 1.25 degrees; if it is too far away, the fleet angle will be less than 0.25 degrees.

In general the distance between sheave and drum should be at least 20 times the width of the drum. Ideally a ratio of 23:1 works very well, we have found. Thus, the larger the drum, the further away the sheave needs to be to keep the fleet angle between 0.25 and 1.25 degrees.

It is not always possible, however, to achieve the optimum fleet angle. For example, there are massive winching systems at the top of mountain cable car systems, often housed in compact machinery sheds. There is often no space to rig a sheave the requisite distance from the drum.

For just such cases two additional spooling devices are available. One is a fleet angle compensator, which is driven automatically by the rope tension. The other is a level winder that is mechanically driven. Both offer a solution to guide the cable along the drum between flanges, but each has its advantages and disadvantages.

The fleet angle compensator (FAC) is driven by the movement of the wire rope as it goes through the crossover sections of the drum. As the rope winds or unwinds, the FAC shaft slowly oscillates, allowing its sheave to slide back and forth across the shaft to maintain an optimum fleet angle and guide the rope smoothly onto the drum.

Certain operating conditions are necessary for the Lebus fleet angle compensator to function properly. The rope must go from the drum over the compensator sheave with a minimum contact angle of 60 degrees to a fixed point such as a fairlead or fixed sheave. To avoid excessive angles of the rope on the sheaves, the minimum distance between the fairlead (fixed sheave) and the compensator sheave must be at least six times the drum width. If spooling in multiple layers, the drum must have Lebus-style parallel grooving. For a single layer, helical (screw thread) grooving will also work. As always, there must be sufficient tension on the cable during the spooling operation. We recommend that minimum tension should be 1-2% of the wire rope’s breaking load.

There are three primary advantages of the Lebus fleet angle compensator. First, there is no mechanical connection between the drum and the compensator. Second, installation is easy and quick. And third, it is completely automatic and, after initial adjustments when the rope is first spooled onto the drum, only a minimum of maintenance is necessary.

A mechanical level winder comprises a main shaft (the lead screw) with helical screw grooving along which the rope feeder travels. The rope feeder housing includes two vertical roller bars and one horizontal roller or, alternatively, a wire rope sheave. The lateral movement of the housing is generated by a chain drive sprocket ratio between drum and lead screw, as shown in the image. The automatic level winder fitted is designed and engineered to be compatible with the grooving on the drum. Perfect, controlled spooling is guaranteed regardless the number of layers and slight changes in wire rope size.

The level winder unit – also sometimes called level wind pay-on gear – must be installed in front of the drum in line with the first fixed sheave when using the vertical rollers to guide the wire rope.

The level winder is engineered to be compatible with the parallel grooving on the drum. It is adjusted for the specific rope diameter, and the gear ratio is fixed (using a standard sprocket-chain connection) to match the ratio between coils of wire on the drum to the pitches on the lead screw. The result is perfect and controlled spooling, regardless of the number of layers or slight changes in wire rope size.

As before, certain operating conditions are required for the level winder to function properly. The rope must go from the drum through the vertical rollers or the level-wind sheave to a fixed point such as a fairlead or fixed sheave. To avoid excessive angles of the rope on the sheaves, the minimum distance to the fairlead or fixed sheave must be at least seven times the drum width. There must be a minimum tension of 1 to 2% of the wire rope’s breaking load when spooling more than one layer.

The advantages of level winders are that they keep the rope spooling properly even if there is slack in the line. As with the fleet angle compensator, once it is set up no more adjustment is necessary and very little maintenance is required. In case of damage to a mechanical level winder, parts are easy to replace and there is nothing electrical or hydraulic to worry about.

Oceanographic installations that spool rope up to 46 layers have demonstrated that level winders give synchronised and totally controlled spooling in the very harshest, most testing conditions.

The disadvantages of level winders is that they do require a little more space than fleet angle compensators and they are sensitive to high axial forces and shock loads.

Super high strength wire rope mainly used for engineered cable assemblies, counterweight ropes, winch lines, boom pendants, extension- and retraction cables, etc. Overhead crane applications for sizes above 3/4" (19 mm) may require some restrictions as to fleet angle and lay direction. Call before you select this rope.

Python® Ultra is our highest strength rope available. It is fully swage compacted resulting in an extreme smooth outer rope surface and the removal of nearly all of the constructional stretch. This is an important feature if you require a low stretch rope for cables assemblies. Ultra is an "all parallel" construction type meaning that there are no wire cross-overs within the rope body to ensure maximum fatigue life. Ultra provides a strength increase of up to 53% over regular 6-strand constructions. Refer to the conservatively calculated strength tables.

Python® Ultra requires corresponding drum grooving directions; e.g. use a right hand lay rope if the drum is left hand grooved. Large fleet angles may cause high strands or core protrusion because the rope will roll rather than glide into the sheave groove. Any introduction of torque into (any) wire rope will cause structural damages.

Note: The maximum CAPACITY, WORKING LOAD LIMIT (WLL), or LINE PULL of the rope usually is 1/5 of the below stated values. For specific information consult the standards applicable to your rope application.

Ultra high strength type mainly used as high fatigue resistant rope for engineered cable assemblies. Up to 55% strength increase over standard 6-strand constructions. Sensitive to introduced rotation so call before you select this type of rope for overhead crane applications.

The fleet angle Ø, as displayed in FIGURE 2, governs the position of the lead sheave with respect to the drum. When the rope is at one end of the drum, against the drum flange, this fleet angle may not exceed one and a half degrees (1.5˚) for plain drums to two degrees (2˚) for grooved drums left or right from the centre line passing through the centre of the sheave groove and the midpoint of the drum.

Fleet angles larger than these suggested parameters can cause bad rope winding on drums and the rope can rub against the flanges of the sheave groove.

The name LeBus has been around the oil field industry since it was just a blacksmith shop in 1900. LeBus started out by manufacturing speciality tools for the booming west Texas oil fields. Tool pushers and/or owners would see a specific need for a new tool and LeBus would forge the new tools on demand. Soon LeBus was into the manufacturing and selling of fishing tools, drill collars, tool joints and rotary bits. LeBus manufactured the "Eureka Pipe Wrench" and the "Slip Socket Overshot". The common element in each case was the hoisting machinery, specifically the drum and wire rope, which was the main "workhorse" of the drilling rig. LeBus noticed that the wire rope would not lay in a consistent pattern on the drum. This caused undue wear and scrubbing of the wire rope. Something better was on the horizon.

A common problem associated with wire rope is snagging on the winch drum, when an outer layer becomes trapped between wraps of underlying rope. Another common problem is damage to the lower layers caused by crushing from outer layers. With multiple layers of rope on a drum, the pressure on lower layers is immense.

In offshore applications, huge lengths of rope are often housed on drums. The anchor winches on Saipem"s Semac 1 pipe laying barge, for example, each hold 2,800 m of 76 mm diameter wire rope in 14 layers. It is bad enough having wire rope problems on a crane on a construction site, with the resulting replacement cost and lost time. Working offshore, though, the costs of rope or winching problems are huge.

The secret to avoiding problems, whatever the application, is to get the right drum. This means having it specially designed to specifically match the structure and length of the wire rope to be used.

Grooving on the face of the drum is commonly used to ensure that the rope spools smoothly and tidily. Where there is just a single layer of rope on the drum, a single helical groove, like the thread of a screw, will ensure the rope travels smoothly across the drum during spooling operations.

In multi-layer applications, however, a helical groove will result in additional layers of rope lying at an angle to lower layers, crosswise, and so risk crushing lower layers. This is where Lebus grooving comes into its own. It is a special grooving pattern developed in the 1950s by Frank LeBus, an American who supplied equipment to oilfields. In 1937 he had patented the use of a groove bar to guide the spooling of rope on hoist drums and later refined this to become what he called the LeBus Counterbalanced Spooling System. Though some companies have sought to imitate the Lebus system, the original is only produced by Lebus companies in the USA, Germany and the UK.

The Lebus grooving pattern has the grooves parallel to each other, and parallel to the flanges of the drum, with a crossover point on every groove on each side of the drum, (Figure 1). With this pattern, when the first layer has filled the drum, the second layer then travels back across the drum with each wrap of rope sitting precisely along the groove of two wraps of the first layer, (Figure 2).

With Lebus grooving it is possible to calculate the exact forces that the rope imposes on the drum because the spooling is totally controlled. This is not possible with any other spooling system.

Cross winding is reduced to approximately 20% of the circumference of the drum, and 80% remains parallel to the flanges in the inner layer rope groove.

This parallel grooving evenly distributes the load between the individual layers and has been shown to increase substantially – by more than 500% – tests have shown, the life of the wire rope.

Every Lebus system must be custom engineered. It is designed and produced specifically to meet the application for which it is used. The groove pattern is engineered to suit the rope"s length, diameter and construction type.

In any multi-layer spooling application it is important that when the rope is first installed on the drum, it is done so under tension to avoid any slack on inner layers that can be crushed or nicked against the groove walls by outer layers.

In general, the tighter the line, the better the spooling, but the rope should be tensioned with at least 2% of the breaking load or 10% of the working load. However, provision must also be made for the safety coefficient and the design of the cable. All subsequent spooling should also take place with the line under tension.

The fleet angle is the angle between the rope coming off the drum and the point at which it meets the first fixed sheave. Optimum fleet angle depends on the load, wire rope construction and line speed but our unrivalled experience has taught us that, as a good rule of thumb, it should generally never be any more than 1.5 degrees and no less than 0.5 degrees. Using these fleet angle guidelines means that for every 10 m that the drum is distanced from the sheave, the rope"s distance from the midpoint of the drum should never be more than 260 mm (520 mm between the flanges).

With helical grooved drums, the fleet angle can be up to 3 degrees, since the grooving is already at an angle to the flange, but only if the rope is wrapped in a single layer. If there is a second layer, such a large fleet angle will result in the rope cutting across too much and leaving gaps, which damages the rope.

When spooling a wire rope around a drum in multiple layers, the rope needs to be flexible enough to wrap tightly onto the drum, yet also sturdy, strong and rigid enough so that it does not suffer any deformation. Lebus has worked closely with all the major international wire rope manufacturers in developing optimum specifications for multi-layer applications.

Using a winch to lift or position a load gives your project flexibility because you can have this material handling muscle positioned in various ways. You can place the winch above the load and use it vertically as a hoist, or have it on the same level of the load to pull horizontally, or use pulleys with it so you can position the winch where you want it and move the load in the direction(s) that you need it to go. But when you are determining where to position your industrial winch, it is important that you consider the critical distance needed to maintain the necessary fleet angle to keep things safer and in proper working order.

What is fleet angle? Fleet angle is the angle between the wire rope and an imaginary line extending perpendicular to the drum. This angle varies with the width of the drum and the distance between the lead sheave and the drum. The proper fleet angle helps the wire rope to wind evenly onto the drum, and helps to reduce wear to the wire rope, drum, and lead sheave. Too large a fleet angle will cause the wire rope to wind loosely, overlap and possibly jump the flange and cause severe damage to the equipment. That"s why it"s important to properly distance the winch from the lead sheave (also sometimes called fixed sheave) when you are determining where to position your winch. A maximum fleet angle of 1-1/2° for smooth drums, and 2° for grooved drums, helps the wire rope wind uniformly. A narrower drum can also help stay within the recommended fleet angle if the critical fleet angle distance can’t be improved. Diagrams below are examples of common rigging layouts that show where critical fleet angle distances are to be measured so you can stay within the proper maximum fleet angle.

So next time you want to take advantage of the benefits of using an industrial winch to move or position a load, make sure you are practicing proper distancing...fleet angle distancing.