TECH TIPS: ROPE SELECTION

Transcription

1 TECH TIPS: ROPE SELECTION Brugg Wire Rope, LLC Appropriate Applications For Various Hoist Rope Constructions High-rise Travel Height ft m 9-Strand PWRC (Parallel Wire Rope Core) Mid-rise 8-Strand 9-Strand PWRC (Parallel Wire Rope Core) Low-rise 8-Strand Natural/Synthetic Fiber (NFC/SFC) PWRC (Parallel Wire Rope Core) Strand* 0 0 * NOTE: Review relevant professional codes Rope Speed ft/min m/s When looking for guidance concerning appropriate handling, installation, maintenance and replacement of hoist ropes, one may consult these international bodies for relevant standards: Europe Great Britain Japan : USA: EN, ISO or DIN BS JIS ASME Such groups however do not offer guidance as to which rope design is appropriate for use in a specific installation. For that one must review an installation s design, determine performance criteria, ascertain the level of maintenance to be provided and then consider overriding budgetary considerations. One must remember that rope life expectancy and field performance largely depend upon factors that are well outside of the manufacturer s area of influence, and such considerations are critical in any discussion on hoist rope selection. The guide provided is for reference only. While some may substitute ropes designated for Low-rise installations in Mid or High-rise uses despite our warnings of reduced rope life and less than nominal performance we cannot recommend this practice. Should you have questions concerning an installation and in specifying the rope that fits your needs, please speak to your rope manufacturer before ordering. A review of the rope components. A review of rope cores. Before one can discuss which of the many varieties of hoist rope available are appropriate for a particular usage, one must be familiar with the basic components of rope design. Core Inner Wire Wire Natural Fiber Core MIxed Core Strand Wire Rope Components Steel Core Brugg Lifting_Brugg Wire Rope 0712 How does one decide which rope to use with which installation? and guidlines as small diameter ropes are used in situations where low-rise occurs

2 For years elevator cores were primarily made of natural vegetable fiber, such as sisal or manila, and then coated with a lubrication mixture in order to prolong the life of the natural fiber itself (and to a minimize wear between the wires, strands and rope core). Called NFC, (Natural Fiber Core) this core proved sufficient for classic undemanding installations featuring both large sheaves and basic U-grooves. Over time however such natural vegetable cores have since become insufficient to handle the needs of modern elevator designs. This has led to the development synthetic cores (SFC) in order to overcome the inherent limitations posed by naturally imperfect cores. Despite this advancement, advances in installation designs have also led manufacturers to create exotic combinations of Steel Core ropes (featuring IWRC, or Independent Wire Rope Core; or PWRC, Parallel Wire Rope Core) and Mixed Core ropes (featuring a polyethylene central core member encased in a layer of steel strands). No matter its particular design, the essential function of a rope core is to provide a degree of elasticity and support for the surrounding strands. Indeed, the amount of breakage one can survey in the outer strands of a rope during its life is directly related to the amount of support provided by the core. However, let us be clear, the core is not intended to serve as a reservoir for lubrication for its entire life. Lubrication must be routinely replaced during service as system loads and stresses serve to compress and squeeze lubricant from ropes and make them become dry. Though easy to diagnose, insufficient rope lubrication is one of the prime reasons behind the reported rise in incidences of system breakdowns. What is the difference between Parallel (Equal Lay) ropes and Point Contact (Cross Lay) ropes? Simply put, a Parallel (also called Equal) Laid rope construction is where the rope core and the outer strands were laid simultaneously in one operation, whereas a Point Contact (also known as Cross Lay) rope is one whose core and outer strands were laid independently in separate work processes. In a parallel rope, the lay length is equal and the wires of any two superimposed layers are parallel. This results in linear contact (see figure 1) of the wires. This kind of construction results in strands where the wire of an outer layer is supported by two wires of an inner layer. Parallel lays strands with two wire layers may have Filler, Seale or Warrington (or a combination of these) constructions. Parallel designs create ropes that offer both a high breaking strength and favorable fatigue bending characteristics. However parallel ropes can be susceptible to untwisting, either during installation, or when used in situations where close multiple rope deflections figure 1 figure 2 Parallel Lay Strand Point Contact Lay Strand (reverse rope bends) at harsh angles are required (which can be found in 2:1 or double wrap roping arrangements). When handling parallel ropes one should always follow recommended manufacturer guidelines and exhibit care as aggressive handling will damage hoist ropes and consequently shorten rope life. Though not exhibiting as high as breaking force as Parallel designs, Point Contact ropes (see figure 2) are better able to tolerate the more casual rope handling techniques one usually finds at most installation sites. In addition, Point Contact ropes offer advantages in modern installations that feature multiple bends, smaller and faster drive sheaves, extremely close sheave placements, and fast acceleration and deceleration speeds. Such ropes are very useful in modern elevator systems that demand lower safety factors in dynamic rope loads. A negative aspect in using Point Contact as opposed to Parallel constructions is that they are somewhat less forgiving towards certain soft traction sheave designs. How does one determine elevator rope lay direction Rope lay can be a confusing term to understand. It requires one examine both the direction of lay of the individual wire of a rope and the direction of lay of the strands of the rope itself. Though one may be tempted to use the term twist instead of lay, this would be incorrect. Great care has been taken by the rope manufacturer to ensure that no unwanted twist (or torque) has been imparted into the rope itself. Each strand has been carefully laid into position with respect to the other members. One determines rope lay by observing the direction strands rotate around the rope. One uses a capital Z to denote right direction, or a capital S to designate a leftward direction lay of the strands themselves. The terms Regular Lay or Ordinary lay and Lang Lay refer to the direction wires rotate around the strands in relation to the direction of the strands within Right Regular/Ordinary Lay (sz) Right Lang Lay (zz) figure 3 figure 4 the rope. To denote wire direction a lower case z (for right) or s (left) is used. In rope descriptions, the direction of wire lay is always presented first, followed by the direction of the rope lay. Any rope where the direction of lay of the wires is opposite the direction of lay for the completed strands is called Regular Lay (see figure 3) or Ordinary Lay rope. This means a rope classified as sz is called Right Regular, while a rope defined as zs is Left Regular Lay. Any rope where the individual strand wires and assembled strands are laid in the same direction create a type of rope called Lang Lay (see figure 4). This means a rope classified as zz is called

3 Brugg Wire Rope, LLC Right Lang Lay, while a rope defined as ss is Left Lang Lay. The visual difference between Regular Lay and Lang Lay ropes are striking. Regular Lay ropes display wires that tend to run roughly parallel to the axis of the rope, while Lang Lay rope wires appear to spiral diagonally around the rope s axis. Today most part elevator ropes are Right Lay (Right Hand Lay) ropes. Once designers paired Right and Left Lay ropes together to counterbalance forces of twist imparted to the ropes by loads. However these forces are small relative to the forces absorbed by the guard rails. Today most standards require that all suspension ropes be as nearly identical in properties as possible. For the most part, the practice of mixing Left-hand with Right-hand ropes has been abandoned. In Drum Elevators, the drum pitch must be selected to match the direction of rope lay (i.e. Right-Lay rope for a Left-Hand drum.) What are the advantages to using a Regular Lay rope or a Lang Lay? Regular Lay ropes are hard-wearing and easy to mount on a system. They have only a small tendency to untwist when hanging freely in a shaft and they exhibit lower elastic elongation that Lang Lay ropes. For this reason they are more frequently selected for elevator installations. Regular Lay: 8x19W IWRC Lang lay: 8x19S NFC Although Lang Lay ropes show greater bending resistance in round grooves compared to Regular Lay. They are far more sensitive to forces of diagonal pull and will untwist if left hanging freely in the hoistway. This means an installer must take precautions with Lang Lay ropes otherwise wires can work loose, resulting in shortened rope life. In some cases sheave liners are required to be used to prevent sheave damage when one is using Lang Lay ropes. While Lang Lay ropes remain a viable hoist rope alternative for professionals, their acceptance varies widely throughout the world today. However Regular Lay ropes have no such prohibition and have become practically the norm. What are pre-formed ropes? A rope made from wire strands that have been twisted (formed) into the helical shape they will assume in a finished rope is called pre-formed. As a result the strands fit naturally in their final position without constraint. In preformed ropes, the inner tensions of wires inside the strands, and the strands within rope, are reduced. This results in a rope that will not spring open when a binder has been removed prior to cutting and installation. Preformed elevator ropes have become the industry standard today. What are pre-stretched ropes and are they necessary? When a manufacturer applies tension to a rope in an effort to remove the effects of constructional stretch in advance it is called pre-stretching. In essence, the procedure tries to induce the core compaction (and subsequent rope elongation) that normally occurs after a rope has been installed. Due to inherent system limitations in their rope closing processes some manufacturers find that prestretching is the only way they have to lower rope elongation. Some manufacturers offer the process in an effort to reduce the need, or frequency of rope shortenings over a rope s lifetime. Many agree that prestretching is only of limited effectiveness, except when dealing with 8-strand ropes featuring NFC (and even then impact upon permanent rope elongation is negligible). At present no single internationally approved process to induce prestretching exists. Some find the process to be counterproductive, as it reduces the rope diameter to that of being either nominal or even slightly less than nominal in diameter. This can adversely impact expected rope longevity. While a few professionals believe prestretching creates a rope that fits more snuggly into a worn groove (and thus lessens the opportunity for rope vibration), this can also serve to disguise a far greater problem in regards to system performance, such as in recognizing and addressing sheave wear and sheave groove deviations. for MRL or Low-rise lift installations? 6 x 19W IWRC or (Brugg TSR) Designed for modern Machine-Room-Less elevator designs, this rope s small diameter provides excellent fatigue properties, high breaking load capabilities and good elongation values. This rope may be used with sheaves as small as 6.3 in. (160 mm) diameter and is ideal in special applications where a high degree of flexibility is required, or when space maximization needs must be addressed. Though widely used in Europe, ASME standards have only recently approved its use for North American installations. For information on permissible rope diameters consult relevant ASME standards or contact your rope manufacturer. 6 x 19S NFC 6x19W IWRC 6x19S NFC Used for slow travelling freight elevators and low-duty passenger traction sheave and hydraulic elevators for Low-rise installations of up to 160 ft. (150 m). Widely used in Governor applications, serving exceptionally well if rope construction offers core of polyethylene instead of standard sisal (NFC). Rope offers relatively high breaking strength (in comparison to its rope diameter) and low elongation (both permanent and elastic). Due to its small number of strands this rope provides minimal support surface and offers less than optimal bending characteristics for traction elevators. Not recommended for U-grooves with large undercuts or V-grooves. 8 x 19 S NFC/SFC 8-Strand ropes are rounder than their 6-strand counterparts, creating more points of contact between rope and groove which results in more favorable contact pressure conditions. In addition, 8-strand ropes use thinner wires in their design than 6-strand ropes of the same construction and diameter. This creates a less rigid rope which provides better fatigue bending characteristics. Used throughout the world in many Low-rise installations, the quality of this product greatly depends upon the quality of the fibers used to Brugg Lifting_Brugg Wire Rope 0712

4 8x19S NFC/SFC bending characteristics. Such ropes offer little permanent or elastic elongation, low rope diameter reduction under load and the steel core helps create a rope with a high breaking load relative to its diameter. This means the rope is excellent for both Low and some Mid-rise installations. PWRC constructions are considered to be more forgiving for certain soft sheave constructions and more sensitive to aggressive handling during installation and reroping. As with all ropes, care should be taken to secure rope terminations in order to prevent the rope from untwisting during installation. 8x19 W IWRC (MCX 8) for Mid-rise lift applications? 9 x 19S PWRC or (Brugg DP9) produce its core. Most frequently used as a traction sheave rope, this rope can also be used effectively in governor applications for high performance installations when a polyethylene (SFC) core is used instead of a sisal core. The rope can be found in either Seale or Warrington constructions. Though still quite popular, modern high acceleration/heavy-use elevators have pushed the capabilities of this rope to its limit. Consequently manufacturers have had to design more advanced, more cost-effective, high performance rope selections to address 8 x 19 s limitations. 8 x 19 S PWRC 8x19W SFC 8x19S PWRC (Brugg SC8) 8-strand ropes using steel wire at their core offer great advantages over six strand ropes in roundness and are ideally suited for use with sheave grooves that feature wide undercuts. As with 8-strand NFC and SFC ropes, steel core selections offer good flexibility and optimum fatigue 9x19 S PWRC Designed to offer even rounder cross sections for Mid-rise installations, such double parallel designs offer very good bending fatigue characteristics, high flexibility, high breaking strength, low vibration and low elongation properties. The use of a polyethylene core (the combination of Polycore and steel wire inner strands surrounding makes a combination that some term Mixed Core ) provides great strength yet reduces overall rope weight. Polycore designs are known to be more forgiving towards certain sheave constructions. 9 x 19 PWRC ropes are designed to better meet the high demands of modern high-speed elevators while still being cost-efficient. Made to offer occupants a smooth ride, such ropes are able to be used in long rope lengths and in installations that offer multiple sheave deviations. As with any parallel design care must be taken during installation as such designs are more sensitive to aggressive handling. Less than careful handling can result in less than optimal rope performance and shortened rope life expectancy. 8 x 19W IWRC or (Brugg MCX8/SCX8) 8 x 19W-IWRC (with Mixed and Steel Cores) can handle wide sheave undercuts and medium to heavy-use Mid-rise installations, and require only 8x19 W IWRC (SCX 8) routine maintenance. Due to their non-parallel Point Contact design, both MCX8 and SCX 8 are better able to withstand routine handling during installation. They are also better able to handle the fatigue of increased bending cycles from multiple sheave and close sheave placements than typical 8 x 19 NFC/SFC ropes. for High-rise lift applications? Though some of the previous ropes mentioned for Mid-rise designs can, in some cases, work in High-rise installations, the prime objective in any rope selection is to seek a successful mix of overall economy and long-lasting optimum performance. One should never take the short term view and base their decision solely on initial price. For instance ropes bearing NFC cores, though offering a cheaper cost at first, seldom prove to be profitable choice after one considers the cost (and frequency) of reroping, the wear on sheaves and surrounding components, and the expense and anger (which can be considerable) that can ensue from building owners due to system breakdowns from poor rope selections. By no means can we fault only bad rope selection for the increase in system breakdowns. Today s MRL installations feature aggressive sheave groove undercuts and close deflector sheave placements

5 Brugg Wire Rope, LLC ments. And in their quest to reduce the size of elevator components and the amount of floor area they occupy, designers have created installations that must handle far greater cycles, require multiple bend roping arrangements, and utilize faster acceleration and deceleration speeds. In short, elevator design, even for Low and Mid-rise installations, has advanced to such a point that high performance ropes have almost become a necessity if one is to achieve a balance of rope life expectancy, performance and economy. This is why that, despite the fact that the ropes specified here are listed as Hi-rise selections, one should examine them closely as long-term and cost-effective choices that will service very well in highly challenging installation environments. 8 x 19W IWRC or (Brugg SCX8) 8x19W IWRC such a rope can be used in long to extremely long rope lengths. This rope is more forgiving for certain soft sheave constructions, however it must be handled carefully as, with all parallel rope designs, it is more sensitive to aggressive handling. 9 x 19S IWRC or (Brugg MCX9) 9 x19s PWRC 9x19 S IWRC sheaves, or installations where sheaves are placed closely together. A 9 x 19S-IWRC Steel Core rope offers very low diameter reductions over the rope s lifetime, high breaking force, round cross sections, great flexibility, and the lowest permanent and elastic elongation rates available. Easily handles stresses and pressures of modern traction drive elevator designs. As with all Point Contact (or Cross Lay) designs, such a rope is less forgiving towards certain soft sheave designs. However it is better able to withstand routine installation handling and demanding shaft environments. Ideal for installations designed to accept heavier rope weights. Characterized by rounder cross sections than 6-strand ropes, greater flexibility (good fatigue bending characteristics) and one of the lowest rates of permanent and elastic elongation. Such an IWRC rope offers low reduction of diameter over its lifetime, high breaking force and remains round. An excellent choice for wide undercut sheave grooves. However, due to its Point Contact design the grooves of the sheave should be inspected when reroping, as these ropes will not adapt to worn grooves as readily as PWRC steel core ropes to this condition. Provides maximum strength from pressures created by high profile elevator designs in installations where weight considerations are less of a concern. Such as rope is able to withstand routine handling during installation better than the PWRC alternative. 9 x 19S PWRC or (Brugg HRS) Nine-strand Double Parallel rope designs offer rounder cross sections than 8-strand ropes and better flexibility and strength for Hi-rise installations. Nine-strand designs offer extremely high breaking strength, low vibration and very low permanent and elastic elongation. Highly suitable for high performance traction sheave elevators with high comfort requirements, high rope speeds, multiple sheave bends, close deflector sheave placements, 9 x19s IWRC This Mixed Core Point Contact construction offers distinct advantages compared to the mixed core parallel designs reviewed previously. Such a 9-strand rope is better able to bear the bending cycles created by extremely close sheave placements and withstand overly strenuous, casual handling during installation. Such a rope has an extremely high breaking force, a very round cross section, extreme flexibility and very low permanent and elastic elongation qualities. Such a rope need not be confined merely to usage to Hi-Rise installations, due to the prevalence of highly aggressive tight roping designs being used in various Mid-rise installations. Such a rope is well able to handle the increase in the fatigue cycles, offer a smooth ride, and provide for increased rope life expectancy. 9 x 19S IWRC or (Brugg SCX9) Steel Core Point Contact design this is the premium choice for High-rise elevator designs, traction drive elevators featuring multiple deflection Brugg Lifting_Brugg Wire Rope 0712

6 6x19 S NFC/SFC 6x19 W NFC 6x19 S SC 8x19 S SFC 8x25 F SFC for Governor applications? As mentioned previously in our review of Low and Mid-rise facilities, many manufacturers offer varieties of 6 and 8-strand rope designs for Governor applications. Governor ropes are a critical component in the overspeed controller for an installation. The governor rope runs in the moulded groove of a governor wheel and is engaged when the safety device detects an emergency overspeed situation. When a safety device is triggered force is transmitted by friction between the rope and groove. Depending upon the system used, a Governor Wheel is either blocked or brake shoes are then closed and this halts the car. Traditionally 6-strand rope constructions featuring natural fiber cores (either Seale or Warrington) have proved sufficient for Governor applications. This has been challenged recently by the increased popularity and demand for 8-strand ropes that feature synthetic cores, which are far more environmentally stable than NFC ropes. 8-strand designs have proven beneficial for those requiring smooth performance in challenging Mid- and Hi-rise installations. One advantage to using synthetic core (usually polypropylene material) is that the rope is far less susceptible to core shrinkage, which leads to rope stretch (which can create problems with tighter operating governors). An additional benefit to using SFC is the greatly reduced opportunity for core lubricant throw-off. Such weeping of lubricant onto a rope s surface attracts dust, dirt and debris. This residue is then deposited over all the components that the Governor rope contacts. This can be expensive and time consuming for a maintenance professional to rectify. Though steel core governor ropes do exist, and prove useful in handling high breaking loads and offer very good elongation rates, one must be careful in trying to match nominal tensile strength to those installations that use brass brake shoes in order to avoid excessively fast wear of gripping components. Please note that certain ropes such as 8x25 F-SFC are also used in the Mining industry in galvanized variations. Such ropes are better suited to take advantage of installations that offer larger drive sheaves and must move at slower speeds than conventional hoist elevators. For additional details on the proper rope for this industry, or for further questions on ropes used for elevators, please consult your Brugg Lifting representative. for Door Closing applications? Door Relating Cable 6x19 S IWRC or (Brugg GAC) Door Operator for single-speed, center opening door Most door closing ropes consist of 6-strand Seale constructions that feature high tensile strength outer wires and a steel core interior. Predominantly they are RRL ropes.