Special wire ropes and crane ropes from Dolezych

Wire rope is a high-quality machine element produced according to the following principle: Several wires are helically wound around a core wire. If the production closes with this step, a spiral rope is made, which can be used as a guy rope or operating hoist.

For use as a machine element with bending stress, a single or multi-layer round strand rope is required. The described wire composite forms the strand, which in turn is helically wrapped around a core. The number, thickness and arrangement of wires and the selection of strands determine strand geometry and rope construction, rope Ø and rope flexibility. Different areas of application require special qualities: Requirements for strength, flexibility and resistance to wear must be combined.

It is important to select the wire rope according to the intended use – e.g. a wire rope with many thin wires is very flexible but sensitive to external wear; on the other hand, a wire rope with few thick wires offers more resistance to abrasion but is also less flexible and therefore requires e.g. pulleys with larger diameters. The wire diameters, their assignment to the rope and the permissible tolerances are mainly defined by DIN EN 12385.

However, the market demands more and more special ropes, the construction of which is done in computer design according to factory standards. The better cross-section geometry and highest manufacturing know-how of these special ropes compared to DIN ropes increases both breaking load and service life.

Brand new in the range: the new special wire ropes DoRope 8P and DoRope 8CP

The 8-strand special wire ropes with plastic liner are ideal for use on container crane systems, in large, portal or bridge cranes. Due to the lower purchase price, operating costs can be significantly reduced with DoRope 8P and DoRope 8CP.

The low-stress special wire ropes DoRope 8P and DoRope 8CP are usually made of steel wires with a nominal strength of 2160 N/mm2 .

Both wire ropes are 8-strand and have a plastic interlayer as a rope-protecting element, whereby the DoRope 8P is non-compacted and the DoRope 8CP is manufactured in a compacted version to increase the rope breaking strength.

The new special wire ropes are greased with special hoist rope impregnation and are bright as standard.

As usual, Dolezych also provides every end connection – and, of course, individually assembled for all conditions.

Our expert Thomas Kokott (0231 8285-20) will be happy to advise you!

DoRope 8P:

DoRope 8P2

DoRope 8CP:

DoRope 8cP2

Direction and type of lay of the round rope

The direction of lay can be seen from the helix of the outer strands. The difference: right-handed ropes “Z” and left-handed ropes “S”. In addition to the direction of impact, a distinction is also made according to the type of impact:

Crosscut

The wires in the strands have the opposite lay direction to the strands in the rope. They are more suitable than Langs lay ropes in most applications. External wire breaks occur earlier so that the ropes can be discarded in time – A plus in safety!

Direct impact

The wires in the strands are stranded in the same direction as the strands in the rope. This provides better support conditions in the rope groove. For multi-layer flushing, Langs lay ropes are superior because they are less damaged.

The illustrations show the stroke directions and stroke types with the aid of the letter shapes “Z” and “S”. The small “s” or “z” indicates the direction of lay of the wires in the strand, the large “S” or “Z” indicates the direction of lay of the strands in the rope. The combination of all four options is the stroke type.

If not specified in the order, Dolezych generally supplies the cross lay type right-handed “sZ”.

Heart inserts

A distinction is made between fiber core (FC = according to CEN standard Core Fiber) and steel core (IWRC = Independent Wire Rope Core).

The fiber core

The hemp core, which was common in the past, is hardly used any more because it is relatively soft, can only offer insufficient resistance to the external pressure, and hemp is also too expensive for the rope core. Fiber inserts today are mainly made of hard fibers (manila or sisal). They serve as an elastic support for outer strands. When properly sized, adequate support is achieved. Treatment with water-repellent and anti-rot oil makes them resistant and prevents rope corrosion from the inside. Polyester and polypropylene are also used as fiber materials. They have the advantage of being weather resistant. All fiber inserts act as grease reservoirs for the rope. When the rope is loaded, the diameter tapers; the pressure generated on the core allows the grease to escape, thus lubricating the rope. However, the rope geometry changes with increasing service life.

The steel insert

The purpose of the steel core is to provide better support for the strand vault, making the structure compact. The metallic cross-section is enlarged, resulting in increased breaking forces compared to the fiber core. In the case of thin rope diameters, for example, the steel core consists of only a single core wire. The rope interior is therefore subjected to point loads. With larger rope diameters, it leads to a possibly intentional stiffness of the rope. The steel strand core (SEL) is standard, especially for ropes in stainless grades (heart strand). However, to ensure optimum function, this strand should be manufactured larger in diameter than the outer strands. The steel rope insert (IWRC) is particularly suitable for the rope. Its design and diameter are especially adapted to the outer strands. Ropes with fiber core can be used up to approx. +100°C, while ropes with steel core can be used up to +400°C.

The plastic intermediate layer

Special ropes increasingly contain plastic interlayers.

Pros:

Great running smoothness
between soul and outer strands no contact
Reduced basket formation
Lubricant replacement
Corrosion protection of the steel core
greater rope stability during assembly

Compaction

The production begins conventionally. Subsequently, however, the strands and possibly also the finished rope or just the finished rope are plastically compressed with special tools. This reduces the rope diameter – the surfaces are smoothed. Advantages of strand compaction: The contact lines of the individual wires become “flatter”, i.e. the supports and contact areas increase. Compacted ropes have a higher breaking load (fill factor) than comparable non-compacted ropes. They have an increased resistance to abrasion, because the outer wires run more “flat”.

compacted rope conventional rope

Low twist – Low tension

A rope is low in tension (also called low in twist) if its strands and wires do not come out of the rope structure, or only slightly, after removal of the ligature. A rope with low tension does not tend to form kinks, it lies “dead”. Low-tension ropes are produced by special processing in the stranding process.

Freedom from rotation – Lack of rotation

A rope is rotation-free or rotation-reduced if it does not rotate or rotates only slightly about its longitudinal axis under the action of an unguided load acting on the longitudinal axis of the rope. A rope is rotation-resistant or rotation-reduced due to its geometry and the type of stranding (multi-layer round strand rope, flat strand rope, braided rope and other special constructions).

Non-rotational ropes, on the other hand, are more robust due to the larger strand diameters. They achieve higher bending cycles under the same conditions. When forcibly twisted, they are less prone to basketing.

Storage

Store ropes correctly

dry
dust free
at room temperature or cool
protected from mechanical damage (especially during storage and retrieval)
avoiding contact with the ground (soil moisture)

Mounting

if ropes are to be cut to length, tie off the ends beforehand (if possible with soft iron wire / stranded iron wire or with suitable adhesive tape)
Unwind as shown in the figures
Protect against sharp edges on structural parts when mounting (e. g. by edge protection)
For initial roping, use thin leader rope, which (as described below under 1) and 2) is connected to the rope to be hoisted.

Procedure for roping with rotation-free constructions:

Weld half a chain link to each end of the leader rope and new rope.
Connect the two half-links of the chain with a strand (dimensioned to withstand the tensile and weight load).
Twist the two ends together.

Simple, elegant variant:

Connect the ropes with 2 rope socks
Use an additional swivel between the 2 rope sockets, because this eliminates the transfer of twists from the old rope to be discarded to the new rope to be installed.

Procedure for roping with non-rotation-free constructions:

If the rope to be discarded is likely to have prior damage due to twisting, it is advisable to proceed with the welded-on chain half-links with strand as described above, because the twists of the old rope can be untwisted in the strand without being transferred to the new rope. On the other hand, the strand offers so much resistance to the new rope that the design-related torques cannot lead to untwisting. If a swivel were used, the resistance would be missing, the rope could untwist and become defective.

If twisting damage in the old rope is not likely, the ends can also be butt-welded together or connected by means of 2 rope pulling socks or a connecting sock (push rope ends together as closely as possible to prevent the sock from cracking due to possible twisting).

Caution: Langs lay ropes must not be pulled up with swivels or with assembly strand connections, but should be pulled in with rope socks. If there is no twisting of the old rope, they can be butt-welded together at the ends! The direction of impact must match! When pulling in a Langs lay rope, note that the rope socks can twist off on the rope like a nut on a bolt, despite the lacing tensions. Here, the rope sections held by the rope socks should be wrapped with a textile adhesive tape beforehand.

The installation instructions shown are based on the experience of many users. They are of a basic nature only; rope-specific deviations cannot be ruled out. For special rope types, even opposite installation recommendations may apply.

Drum up

Reeling should be carried out under pretension of 1-2 % of the minimum breaking load. Pre-tensioning is crucial in multi-layer spooling – otherwise, under load, upper layers can pull under lower rope layers and damage the rope. If the retracted layer is even jammed, the winding direction may be reversed: the load moving downwards, for example, may be abruptly lifted and vice versa. The necessary pretension is already achieved when the unwinding reel is braked by a board. Never brake the rope itself by pinching it – this can cause clanks to form and the rope to deform.

The rope is given a winding direction by the production winding. This “bending direction” should be strictly observed during assembly.

Pay attention to cleanliness during installation (sand, for example, can adhere to the lubricant and lead to premature rope damage).
Always unwind the rope (rope twists lead to changes in lay lengths and thus to the formation of pitches)

Running in

Between installation and start of work, the rope should be run in several times with partial loads so that the rope elements can “settle”. The common practice of running-in with overload directly after assembly is considered problematic by experts, it should be limited to the necessary overload test. If, in the case of multi-layer spooling, work is predominantly carried out in only one rope layer, the rope should be moved once a day along its entire length with the load attached.

Controls

Check correct rope fit in drum/ traction sheave grooves. Correct groove diameter according to DIN 15020 = 1.05 x d (= nominal rope diameter). Optimum groove diameter approx. 1.06 – 1.08 x d.

In the case of multi-rope guidance, ensure that each rope has an equal share of the force.
Inspect groove base for damage (dents will destroy the new rope).
Check deflection angle – max. 4° for non-rotating, max. 1.5° for rotation-free ropes.

Caution:

Not every rope can be used with maximum deflection angle. Let us advise you.

Larger deflection angles cause the rope to first run onto the flank and then slip into the groove while rotating. Consequences are violent twisting and the danger of jumping out of the disc.
Groove angle at least 45° (better 60°)
For multi-layer spooling, the direction of lay of the rope should be selected according to the layer in which the rope predominantly operates.

Follow

Consequences are twists of the rope. The direction of lay of the rope should be selected so that the drum twists the rope closed. This is exactly the case when the rope pitch is selected opposite to the drum pitch. A right-hand cut drum requires a left-hand cut rope, a left-hand cut drum requires a right-hand cut rope. The rope twist acts in exactly the same way in the belay, so that here, too, a left-hand rope must be selected for right-hand belay and a right-hand rope for left-hand belay. Here is a small overview:

Selection of the direction of lay opposite to the direction of travel of the single-layer drum:

-> right-hand drum = left-hand rope

-> left-hand drum = right-hand rope

Multi-layer drum by rope layer:

-> right-hand lay = left-hand lay rope

-> left-hand position = right-hand rope

Rope lay direction of multi-strand reeving:

-> right-hand reeving = left-hand rope

-> left-hand reeving = right-hand rope

What are the regulations for the use of crane and special wire ropes?

Depending on the intended use (application) of the rope, different standards or regulations within the BG rules must be referred to. There is no single standard that requires all ropes to undergo certain tests. The collection of DIN standards is impressive; for slings it is DIN EN 13414 with the standards e.g. for crimp clamps DIN EN 13411-3, for splices DIN EN 13411-2, for “Flemish eyes” DIN EN 13411-3. For rope drives e.g. ISO 4309 with VDI 2358 apply. The test results are entered with date in the crane or elevator logbook or in the sling index.

What to look out for?

Check end connections: Grouting must always be replaced in the event of wire breaks or corrosion at the rope exit point of a rope bulb or socket. Likewise, when maximum demurrage times are reached (time limits, e.g. for ropeways, are regulated by ordinances such as BO Seil and BO Schlepp).
Check screw connections (screw terminals) at intervals; tighten with the torque wrench.
Intensively stressed rope sections require special attention.
In the area of the rope end attachment (thimble, clamp, terminal) there is increased susceptibility due to stress changes and corrosion
In the area of compensating sheaves, there is a risk of wire breakage due to increased bending cycles.
On rope drums increased wear due to abrasion.
In the area of aggressive media or at temperatures above +50°C, lubricant losses can worsen the working conditions of the rope.

Rope sheaves, traction sheaves

Regularly check for ease of movement; sheaves that are difficult to move increase wear.
Measure groove base – optimum groove diameter = nominal rope diameter plus 6 – 8%.
Ensure sufficient wall thickness, record lateral recesses in the crane book and make a note of the component for timely replacement or reworking.
Replace or rework grooves with rope impressions in the groove base.

Lubrication of crane ropes and special wire ropes

Especially for running and standing ropes:

Regrease ropes if necessary (by hand or by automatic devices).
Lubricate ropes running over sheaves preferably with oil
If possible, oil at the bending point, as the lubricant can penetrate better into the inside of the rope at this point. Caution: Grease can destroy rubber-lined rollers; observe compatibility!
do not lubricate ropes running over sheaves with grease, as experience has shown that grease adheres to the surface longer.
Observe compatibility with original lubricant
Clean the ropes regularly; grease and dust become encrusted and hinder self-lubrication (clogged rope joints mean that grease can no longer penetrate from the inside to the outside). Suitable lubricants are:
Wire rope grease DoGrease F
Wire rope spray DoGrease
Wire rope oil DoGrease O

Discard criteria of crane ropes and special wire ropes

With regard to safety in hoist operation, the wire rope must be laid down in time. The following indicates when, based on the extent of damage, a wire rope must be discarded. Continued use may make the hoist dangerous to operate.

Type and number of wire breaks

Rope drives are designed so that the wire ropes are not fatigue resistant. Therefore, wire breaks occur during operation. A wire rope must be discarded at the latest when one of the numbers of visible wire breaks listed in the table is detected at any point.

Position of the wire breaks

When wire break nests occur, the wire rope must be discarded. If a strand breaks, the wire rope must be discarded immediately.

Time sequence of the occurrence of wire breaks

In important cases, it may be advisable to determine the number of wire breaks as a function of time. From this, the further increase in wire breaks and the presumed time of discard can be inferred. It should be noted that wire breaks only start after a certain operating time and then increase more and more rapidly.

Reduction of the rope diameter during the operating time

If, due to corkscrew formation and wave-like deformation, the rope diameter of wire ropes has become 15% or more smaller than the nominal dimension over longer distances, the wire rope must be discarded. The prerequisite for this is that the new wire rope complies with the tolerances according to DIN EN 12385 even if the wire rope is not of standardized construction.

Corrosion

Corrosion occurs in particular in seawater atmospheres, when operating in corrosive atmospheres and with wire ropes that are exposed to the open air for extended periods of time. Corrosion of the outer rope wires can be determined by visual inspection. Corrosion on wires that are not visible from the outside, on the other hand, can be difficult to detect. Corrosion can reduce both the static breaking load of the wire rope due to reduction of the metallic rope cross-section and the service strength due to rust scars. If the rope diameter is reduced by 10% or more compared to the nominal dimension, the wire rope shall be discarded even if no wire breaks are detected.

Abrasion

Abrasion on the rope wires occurs as “internal abrasion” due to the movements of the strands and wires against each other when the wire rope is bent, and as “external abrasion” due to movements between the wire rope and the rope groove (e.g. due to slipping of the wire rope in the groove when starting and braking) or due to grinding of the wire rope on the ground or the material conveyed. Abrasion is favored by inadequate or no lubrication and by exposure to dust. Abrasion can reduce both the static breaking load of the wire rope due to reduction of the metallic rope cross-section and the operational strength due to wear notches. If the rope diameter is reduced by 10% or more compared to the nominal dimension, the wire rope shall be discarded even if no wire breaks are detected.

smooth, tied (standard) welded, sharpened

Rope deformations

Deformations of the wire rope are visible changes in the rope structure. Depending on the appearance, the most important deformations are distinguished as: Corkscrew-like deformation, basket formation, loop formation of wires, loosening of individual wires or strands, knots, necking, flattening, curl-like deformation, chinks and kinks. Deformations generally also cause loosening of the rope structure, at least in the vicinity of the deformation point. In corkscrew-like deformation, the axis of the unloaded wire rope becomes a helix.

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