This section deals with mechanical application guidelines essential to achieving optimum performance, safety, reliability and long service life.
Correct cable selection is determined by evaluating the mechanical forces acting on the cable for each type of force-guided application.
The application chart has been established to assist in this procedure.
Once the optimum cable is selected, the application notes that apply to your application must be considered to obtain the best possible system results
These guidelines reflect decades of research, development, and practical field experience gained by our company in markets throughout the world.
When cable-anchoring methods such as Kellems® Grips are utilized, a recommended length of coverage over the cable is 20 x cable O.D. This will aid in spreading the dynamic stresses over a sufficient jacket surface area to inhibit cable damage.
This type of system is located below the cable run plane as indicated in the drawing. The system may be above ground or placed in a pit depending on the location of the cable run. At least 2 ½ cable turns should be wound around the fixed stress relief drum to ensure sufficient contact area for adequate stress relief. Click here for the table “Bending radii" that shows the appropriate minimum bending radii for entry and stress relief.
Two-way center point anchoring is the most difficult type of anchoring operation because of dynamic load peaks that occur as the machine passes over the anchoring point requiring the reel to change its direction of rotation.
When an underground center point attachment is installed, the vertical distance between the entry bell and the crane's payout guide should not be less than 15 x cable O.D. or 3 ft. (1m), whichever is larger.
Where cable anchors are used below ground level, the entry bell can often be clogged with debris leading to cable damage. This problem can be minimized by simply installing a rubber flap over the entry to the bell, thus minimizing maintenance and the chances of cable damage. Dynamic tensile stress on the cable can lead to premature failure, especially in high travel speed applications. Several options have been developed to minimize tension problems at the anchor:
| 1. Cable support 2. Entry bell 3. Stress bearing drum 4. Cable wound twice around stress bearing drum 5. Supply cable 6. Cable termination box 7. Clamp |
An end fed supply anchor is not usually subjected to the dynamic stresses associated with center fed anchors. However, even with this type of anchoring, a stress bearing drum system is recommended. The system is maintenance free, absorbs dynamic stresses, and permits easy removal and replacement of the cable. This type of anchor can be installed above ground level as shown, or below ground level, to provide additional protection against accidental damage.
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1. Radiussed roller guide 2. Stress bearing drum 3. Clamp 4. Cable termination/connection box 5. Supply cable A. Minimum distance of 40 X O.D. of cable |
The anchoring of spreader cable is best achieved with a stress relief drum as shown. The open-ended construction facilitates installation and replacement while affording better stress relief and jacket protection than cable grips. The increased weight of SPREADERFLEX cable and its long service life make this anchoring system an important part of a virtually maintenance free spreader cable system. At least 2 ½ cable turns should be wound around the drum. Click here for the table “Bending radii". This shows the minimum, bending radii for stress relief.
The anchoring of vertical cables is best achieved with a stress relief drum as shown. The open-ended construction facilitates installation and replacement while affording better stress relief and jacket protection than cable grips. At least 2 ½ cable turns should be wound around the drum. Click here for the table "Bending radii" This shows the minimum bending radii for stress relief.
Correct cable anchoring is important i establishing reliable operation of a cable handling system. Various methods may be used. They share same basic intent of spreading the tensile forces on the cable over a sufficiently large cable jacket area to avoid damage or failure at the anchoring point.
The table that follows provides details relating to minimum bending radii, which are extracted from German (VDE) standards. These application oriented recommendations are intended to optimize cable life. Reduced bending radii result in reduced cable life due to increased stress on the copper conductors and overall distortion of the cable's structural elements. Therefore, reduced radii should only be considered for applications in which other factors, such as reduced cable tension, lower operating speed and ambient temperature are more favorable to cable life, or where the mechanical limitations of the installation do not allow the optimum radius. If for any reason, the minimum bending radius can not be met, please contact Prysmian for further advice.
Testing of CORDAFLEX cables has shown that doubling the minimum bending radius for reeling applications, triples cable life at the maximum recommended tensile stress. Therefore, the largest possible bending radius should be incorporated to increase cable life. Click here to see the bend radius table.
A proper cable catenary is required to allow sufficient release of cable tension prior to the cable's placement on the ground, track, or cable tray. The cable catenary is the curvature of the cable, between the bottom of the roller guide or sheave assembly and the ground or cable tray. A minimum height of 15 x Cable O.D. or 3 feet (1 meter), (whichever is larger) between the bottom of the roller guide or sheave assembly and the ground or cable tray is recommended.
Even when cable and reel have been correctly selected and installed, major reeling system problems can occur when cable guides are not given proper consideration.
One option is, of course, to eliminate cable guides altogether where practical.
However, in many cases it is essential to employ cable guides to meet mounting, payout and operational requirements.
The correct design and placement of cable guides is essential to obtain reliable performance, and long cable service life. Reels should be positioned so the number of cable direction changes is minimized.
Radii used guide rollers are preferred over sheaves whenever practical. They should reflect generous bending radii and minimum deflections for optimum performance. Click here for recommended minimum bending radii.
It is important that cable guides are maintained in alignment with the payout plane of the cable. Excessive misalignment can cause a significant increase in torsion to be applied to the cable.
For operational safety and long cable life some form of cable protection is often necessary. The simplest and most economical method is to provide an open duct or slot into which the cable is deposited by the payout guide.
However, a problem may arise with debris clogging the channel leading to possible cable damage.
Increased protection can be provided by covering the slot. The hinged steel plate covering usually has high maintenance and noise levels. An alternate system is a continuous steel reinforced semi-flexible rubber covering which lies over a cast channel along the crane's route length. The belting protects the cables from cross traffic; spillages of oil, chemicals and debris, and can accommodate multiple crane cables along the travel length, e.g., PANZERBELT. The covering is raised and lowered by a belt lifting plough mounted on the crane at the payout point.
For retrofits where it is impractical to cast a channel into the existing surface covering, an above ground trough can be installed. This allows traffic to pass without damaging the cable and can be installed as shown.
All forms of cable slots must be well drained to prevent build-up of water, snow, ice or debris. If adequate drainage cannot be achieved, the cable should be elevated from the bottom of the slot.
An alternate cable protection method is to provide an above ground
elevated cable tray where the cable is protected. This system is
often employed for bulk handling plants where the cable tray can
be economically mounted alongside conveyor structures.
A problem that must be avoided is where the runway is installed
on an elevated bed of crushed rock. The cable can roll down the
bank creating high torsion. Excessive tension may be placed on
the cable when the reel pulls the cable back up the incline during
retrieval.
A large variety of cable reels are available which range from small spring loaded versions to large level wound reels. Motor driven reels are the most reliable method of payout and retrieval of power and control cables to mobile machines and equipment. Each have there own particular benefits and areas of application. There are three major designs; random wound, mono-spiral, and drum type level-wind, each having its' own advantages and disadvantages regarding cable life. To extend the cable's life the following recommendations are given:
The cable tender is recognized for its excellent performance in high speed, high acceleration multiple cable applications. This system effectively halves the amount of cable required for operation by providing dual routing of cables from the center point. This feature is particularly important when high accelerations and decelerations are involved. The mass reduction, when compared to an end fed festoon system, can play a significant role in operation and structural design.
Depending on design, the cable lengths must be carefully adjusted to enable the tow rope and the strongest power conductors to carry the majority of the tensile load. Proper adjustment assures extended life of the lighter control cables.
Cable tension or line-pull plays an extremely important role in determining the life of a flexible cable. Unless other supporting elements are used, the copper conductors are the principal strength member in flexible cable constructions.
Tensile stress testing of soft annealed copper wires indicates there is only slight permanent elongation or deformation up to a stress of about 2,900 p.s.i (20 N/mm²). However, from this point until the yield zone is reached at approximately 23,000 ~26,000 p.s.i. (160 -180 N/mm²), there is a marked increase in permanent deformation.
When flexible cables are subjected to tensions well above the 2,900 p.s.i. (20 N/mm²) value, they exhibit the "knuckling" of conductors common in difficult high-tension applications. This effect is created when relief from elongation causes the formation of loops in the conductor as the elastic Insulating and jacket materials regain their shape. However, when passing the cable repeatedly over guides, it is internal abrasion of the conductor strands rather than elongation of the conductor, that causes the limit of 2,900 p.s.i. (20 N/mm²) to have been established to ensure long and reliable conductor life.
It is clear that much higher values such as 7,250 p.s.i. (50 N/mm²) can be applied as pulling tensions during installation for fixed cables without damage to the cable.
However, even here, the relationship between bending radii and the maximum allowable tension is a critical one, as sharp bending radii associated with these high tensions can lead to jacket and overall cable damage.
In reeling applications, it has been demonstrated that the use of the minimum recommended bending radii while simultaneously maintaining the maximum allowable tension of 2,900 p.s.i. (20 N/mm²) can lead to a significant reduction in cable life when accompanied by high duty cycles.
Testing of the CORDAFLEX range of cables has shown that the cable's life can be tripled at the recommended bending radius if the tension is halved from 2,900 p.s.i. (20 N/mm²) to 1,450 p.s.i. (10 N/mm²).
Where the cable passes over sheaves or other guide equipment, flexural forces act at the initial point of contact. This stress is not only exerted on the conductors, but also on the entire cable assembly.
Supporting elements such as central messengers are often used for self-supporting applications. In reeling applications, these elements are limited in their contribution to tensile strength due to the transverse pressures set up when passing over guide equipment.
Actual values for all reeling cables are given individually in their respective section.
Split ground and/or ground check conductors cannot be added to
the total copper cross sectional area because these smaller conductors
are manufactured with a shorter length of lay ensuring damage will
not occur due to tension and bending forces.
| CORDAFLEX (K) | 2,900 p.s.i. | (20N/mm²) |
| CORDAFLEX (SM) | 2,900 p.s.i | (20N/mm²) |
| PROTOLON (SM-R) | 2,900 p.s.i | (20N/mm²) |
| PROTOLON Flat Cable | 2,175 p.s.i | (15N/mm²) |
| PROTOMONT Single Conductor | 2,175 p.s.i | (15N/mm²) |
Actual values for all reeling cables are given individually in their respective section.
Split ground and/or ground check conductors cannot be added to the total copper cross sectional area because these smaller conductors are manufactured with a shorter length of lay ensuring damage will not occur due to tension and bending forces.
When designing a cable guiding system, allow sufficient distance between any direction changes. The recommended distance should be at least 20 x cable O.D. (longer for high speed systems). Implementing this design will extend cable life by giving the cable's memory an opportunity to shed torsion before making another change in direction. “S” type directional changes and alternate plane changes should be avoided where possible. This unduly stresses the conductor assembly, especially at higher travel speeds. PROTOLON flat reeling cable must not be force guided out-of-plane.
This type of reel may be used on smaller installations, but is
especially suitable for extremely large cable diameters and lengths.
Economically, the guide mechanisms for this type of reel frequently
dictate increased costs, which may lead to the use of alternate
reel designs. Space considerations may also influence the selection
of this type of reel.
The number of layers of cable wound onto the reel can substantially affect the ampacity of the cable. One or two layers are preferred to minimize thermal derating.
It may be difficult to avoid numerous cable guide direction changes due to the reel's location. Minimizing the number of changes is essential to avoid excessive torsion.
The major advantage of using drum type level wind reels are their ability to handle a large amount of cable at a constant reeling tension over long travel distances.
A basic decision for festoon design is the selection of a flat or round cable. System design and the installations in particular requirements are normally used to choose the correct cable. Among the selection aspects are:
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1. Fixed trolley 2. Cable trolley 3. Saddle 4. Moving trolley 5. Tow rope 6. Power cables 7. Control cables 8. Cable clamps |
Regardless of flat or round cable selection, cable loop depths are important. With large, fast moving systems, the stronger power cables should have a shorter loop depth than the lighter control conductors.
This design allows the tensile force to be carried by the stronger cables as the system accelerates open. After the system is extended, the tow ropes should then accept the majority of the load. With increased speeds, greater emphasis must be placed on the shock loading and energy absorption of the cables support trolleys. When these trolleys stop, they will either be restrained by the tow ropes or collide into each other with a considerable amount of energy. Fitting elastic ropes to the tow wires can dampen the shock loading of acceleration forces. It may also be necessary to use foam or oil filled shock absorbers with the elastic tow ropes. Please click here for "Festoon Installation Notes” for additional information regarding clamping arrangements and their location.
Mono-spiral type reels control the cable in a single plane. They are usually preferred over other reels whenever cable diameters and run lengths permit their use.
When installations allow mono-spiral reels to be mounted directly over the cable runway, a single or two-way cable guide is usually necessary. This simple guide route results in extended cable life compared to other types of reels. Higher operating speeds are possible due to even and controlled layering. Conductor sizes for power cables are generally smaller than for random wound reels because of improved heat dissipation.
However, mono-spiral reels are restricted in their application by cable diameter and length. These factors are based on the balance between the reel's inner and outer diameters, which are critical for determining cable tension.
Constant torque reel drives for mono-spiral reels are limited by the amount and size of cable being reeled. These types of drives can cause excessive tensions on the cable during part of the travel distance. Varying reel rotation speed can also be critical to the cable and drive system, particularly in high-speed applications.
The multi-roller guide is the preferred method for guiding cables.
It consists of multiple rollers mounted into a housing designed for uni-directional or bi-directional cable payout. Because the individual rollers move independently of each other, torsion build-up is reduced significantly. The recommended minimum width profile is 1.12 x cable O.D. to allow for the cable's lateral movement and to reduce torsion.
The mass of the rollers should be minimized. Materials to reduce weight may include aluminum, Nylatron, etc. Rollers should have flat roller surfaces and flanges. Bearings should be as low friction as possible. Roller guides should be designed to continue the arc beyond the anticipated angle of deflection to ensure that minimum bending radii are maintained.
In some reeled cable layouts with cable payout take up in two directions, it may appear economical at first observation to use a unidirectional cable guide.
However, superior cable life is obtained when a symmetrical two-way guide is employed.
This is because net torsional and "massaging" effects imparted by the guides to the cable are balanced with the use of a symmetrical two-way cable.
Unidirectional or non-symmetrical guides for opposite directions of travel should be avoided to optimize cable life.
When a reeling system is end fed, the use of a unidirectional guide does not cause this problem as the same guide is in contact with the cable regardless of the direction of travel of the machine.
The products listed in this catalog are designed to meet the requirements of modern high-speed cable handling systems as long as the other important parameters of cable handling systems such as bending radii, cable tension and temperature remain within the permissible range.
When these parameters are applied and the correct cable selection
is made from the application guide, the following maximum speeds
may be implemented. Utilizing speed as an application engineering
guideline is a nominal method that is nevertheless fundamentally
correct. Higher operating speeds are almost invariably associated
with greater rates of acceleration and deceleration as well as
high duty cycles. These increased forces acting on the cable demand
that greater attention be paid to correct cable and hardware selection
when operating speeds beyond those listed are required. In those
cases, we recommend contact with your local sales office or distributor
to assist with cable and guide equipment selection.
It is highly recommended that cable-guiding systems include both under and over tension protection systems. Even a short exposure to over tension caused by mechanical failure or accidents can render a cable inoperable due to permanent conductor deformation or breakage. Conversely, under tension protection is desirable to ensure that cable cannot free spool from the reel and sustain damage. This protection is particularly important for high mounted cable reels. Most cable reel manufacturers offer these systems as options to avoid accidental damage and extend cable life. All over tension protection devices should be set to the “Maximum Continuous Safe Reeling Tension” as noted in each product category.
Cables being utilized for push button pendants on cranes are exposed
to static loads due to the weight of the vertical cable plus
the weight of the pendant. Furthermore, excessive tensile loads
may be applied to the conductors if the cable is used to pull
the crane along its track. The cable is also subjected to torsional
forces in a free swinging application. These factors contribute
to reduced cable life.
Proper strain relief of pendant station cables can be accomplished
by the use of either Kellems® grips or a steel messenger rope
attached from the pendant to the crane structure. The cable should
be looped at the crane end to offer additional relief from tensile
forces. Please click here for more information on "Anchoring
with a Kellems® grip". If a steel messenger rope is used,
the cable should be clamped to the messenger at three feet (1 meter)
intervals.
The power track can accommodate multiple cables from a stationary power source to mobile equipment on machinery while protecting them against tension, torsion, and accidental damage. When the system is center point fed, the amount of cable can be halved compared to a festoon system. This reduction in cable quantity reduces the mass of the system and the force required to accelerate and decelerate the system. The chain link design is a self supporting structure, giving good cable bending radii and virtually no tensile load on properly installed cables. Although both round and flat cables may be utilized in power tracks, round cables are generally preferred.
The simplest type of reel is the random wound cylinder or drum
type reel. Inexpensive and simple in design, it can be either
motor or spring driven. Where available space is limited, it
can accommodate the cable on a smaller diameter reel. It is often
used without guides, which offers the advantage of minimizing
cable torsion.
However, this type of reel has some disadvantages. Its field of
application is restricted to relatively small cable diameters and
short runs. An additional problem is the cable payout and retrieval
is random over the width of the reel. This lack of control can
create operational difficulties due to uncontrolled layering. This
results in buildup and slippage of coils on the reel, leading to
abrupt tensile forces, torsion and abrasion of the cable jacket.
Another factor is conductor sizes may need to be increased to compensate
for thermal rise caused by multiple cable layers on the reel.
Sheaves are commonly employed as guides in reeling or other forced
guided applications. Some difficulties exist compared to other
types of guide equipment. Due to its weight, a sheave increases
inertia, and, therefore, requires more reeling torque than radiused
roller guides. The resulting increase in cable tension may reduce
cable life. This condition may not be critical in less demanding
applications, but must be considered if there are several changes
in cable direction. Another detrimental effect of sheaves is
the cable jacket contact area on the circumference of the sheave.
This contact area with sheaves is greater than when using guide
rollers. The greater contact area causes higher torsion to be
applied to the cable. This is a particularly significant condition
when the incorrect sheave profile is used as shown.
Spreader baskets must be designed with the largest practical diameter because this is directly proportional to the number of twists that the cable makes for a given operating height. Optimum cable flex life can be achieved with the use of baskets 5 ft. (1.5 meters) in diameter, although basket diameters of less than 4 ft. can give an acceptable cable life span for cranes with lower hoist heights and speeds.
For applications in which high wind or hoist speeds (over 200 feet/minute or 60 meters/ minute) cause cable feed-in problems, increasing the basket height beyond 6 feet, 6 inches (2 meters) will help to improve coiling performance. Enclosing the bottom and sides of the spreader basket enhances coiling by preventing external influences, such as wind, from affecting the natural cable curvature.
Placing a centrally located coiling guide inside the basket is recommended to ensure that the cable coils correctly. However, experience with the latest generation container cranes has shown that high speeds and accelerations can lead to "backwrapping" of the cable when the guide cone and/or basket diameter is too restrictive. The use of a steep, small diameter cone or total elimination of the cone has helped to improve cable coiling under these circumstances.
Experience with high lift and high speed installations has shown that tub/basket designs, which provide the best vertical drop between the top guide and the bottom of the tub, offer the most reliable coiling performance. The enhanced weight-to-sail area of the SPREADERFLEX cable has eliminated the need for "funnel" type top guides on the basket. Relatively small diameter (e.g. 4 to 6 inches) top guides placed at maximum height keep the cable feed centered and provides the maximum possible vertical drop within the basket.
This has proven to be effective, even at the highest speeds and promotes consistent coiling when almost eliminating the chances of the cable falling from the basket. For applications where hoist speeds and heights are not critical (e.g. yard stacking cranes, timber cranes or older generation dockside container cranes), adequate performance may be attained without placing heavy emphasis on the above criteria.
