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Essential information

 

General guidelines for steel wire ropes selection

Rope life in certain working conditions depends not only on the quality of wires used in its production or on the production technology but also on appropriate choice of wire rope construction. Moreover, it depends on the proper use in compliance with the rules of working with steel wire ropes. Before selecting construction and tensile strength of the ropes for the given device, one ought to realize that there is an optimal rope type for particular equipment, which shows not only longer working life on this device, but also assures greater work safety. During its working life the wire rope is exposed not only to fatigue, but also to many other factors – related to the mechanisms on which it works and also weather-related.

 

Description of steel wire ropes

 

Single laid ropes (twisted lines)

Single laid ropes are in fact strands made of round wires. They consist of central (core) wire, on which one, two, three or four layers of wire of the same diameter are wound. These ropes have linear contact of wires, which results from keeping the same angle of twisting wires in each layer. Each layer of wires is twisted by use of other lead. It means each layer must be produced in a separate operation.

Model constructions of single laid ropes:




1x7  (PN)

T 1x19  (PN)

T 1x37  (PN)

1x7  (PN-EN)

1x19M  (PN-EN)

1x37M  (PN-EN)

These ropes are characterized by minimal elongation and high rigidity. Therefore, they are used when the ropes are to be strongly stretched, for example in mast guys, as stretching rope or ropes for shaft signaling.

 

Round double laid ropes

In round double laid ropes the layers of strands (twisted lines) are wound onto a rope’s core (fibrous - organic or synthetic, or steel). If just one layer of strands is wound, it is single-layer rope, and it is non-rotating rope or rope with parallel arrangement of strands, if more layers are wound. In such ropes, each wire is twisted two times – first, during twisting strands and then, during twisting rope. Depending on the number of strands, we distinguish single- and multilayer ropes. And depending on the shape of cross-section, we distinguish:

round-strand ropes

triangular-strand ropes

oval-strand ropes

ropes with various shape of strands (flat, band or compact shape)

 

Single-layer round-strand ropes

These are most popular ropes. They consist of six or eight round strands twisted helical around the core. Strands may consist of one, two, three or four layers of wires. The strands may have:

point contact of wires; M,

linear contact of wires; S, W, F; WS (joint linear contact),

point-linear contact of wires (combined contact – ST acc. PN),

linear-point contact of wires; NS, NW (combined contact),

area contact of wires; K (compact).

 

Single-layer round-strand ropes – strands with point contact of wires

These ropes are characterized by high elasticity, low resistance to side thrust and short fatigue life.

Model constructions:




T 6x7+Ao  (PN)

T 6x19+Ao  (PN)

T 6x37+Ao  (PN)

6x7-NFC  (PN-EN)

6x19M-NFC  (PN-EN)

6x37M-NFC  (PN-EN)

These ropes are used in crane equipment (hoisting winches, windlasses), when the ropes work on wheels or pulleys and must be elastic enough. In mining industry, these ropes are used as guide ropes and fender ropes. They are used also in horizontal and slope transport systems. Type of particular construction depends on diameter of wheels or pulleys. During selecting rope type, one should bear in mind following rules:


where:

D – diameter of pulley

δ – diameter of wire

where:

D – diameter of pulley

d – diameter of rope


Single-layer round-strand ropes – strands with linear contact of wires

Strands with linear contact of wires are produced with keeping the same length of lead. It means such a strand is produced on one machine (pipe-type or basket-type stranding machine) in one operation. Twisting angles and lengths of wires are different in particular layers. These layers may contain rope strands with either wires of the same diameter (strands of Seale construction), or wires of two different diameters (strands of Warrington construction). Apart from that, there is also a construction of strands containing both wires of the same diameter and wires of different diameters (strands of Warrington-Seale construction).

These ropes are characterized by good elasticity, high resistance to side thrust and long fatigue life.

Model constructions:

S 6x19+Ao  (PN)

F 6x19+Ao  (PN)

WS 6x36+Ao  (PN)

6x19S-NFC  (PN-EN)

6x19F-NFC  (PN-EN)

6x36WS-NFC  (PN-EN)

In strands with linear contact of wires, the wires of neighboring layers are parallel and stress between wires is distributed evenly at their whole length. Fatigue life of these ropes is much longer than stranded rope with point contact of wires.

These ropes are used in crane equipment (lifts, windlasses, overhead cranes, and jib cranes), construction equipment (excavators, hoisting winches), ski lifts and cable railways.

 

Single-layer round-strand ropes – strands with point-linear or linear-point contact of wires

Model constructions:

ST 6x31+Ao  (PN)

WK 6x35+Ao  (PN)

 

6x35NW-FC  (PN-EN)

These ropes are used similarly as stranded ropes with linear contact of wires if main reason of their wear is fatigue.

Single-layer round-strand ropes may be produced with wire core (At-WC) in the form of rope strand WSC or in the form of independent wire rope IWRC (the most often of construction 7x7). Metal cores are used (made of steel wires) if side thrust of strands to the core is greater than 150 Mpa, which can occur in following situations: rope carries heavy load, is bent at low relation D/d or many layers of the ropes are wound onto pulley. Steel core enables lowering twisting moment, increasing modulus of elasticity and using the rope in higher temperatures.

If cross-section area involves core, then Rm of core wires is equal to Rm of other wires in the rope. If cross-section area does not involve core, then Rm of core wires is at least 200 Mpa lower than Rm of wires in the rope. Then the cross-section area (carrying area) of steel core is not taken into account while determining minimum breaking load (specified by the manufacturer). Wires of the core are treated as those that do not carry load.

These ropes are used in equipment where they are exposed to bending, strong side thrust or where conditions of work makes it impossible to use fibrous organic and inorganic cores (NSC and SFC).

Model constructions:

T 6x19+At  (PN)

S 6x19+At  (PN)

WS 6x36+At  (PN)

6x19M-IWRC  (PN-EN)

6x19S-IWRC  (PN-EN)

6x36WS-IWRC  (PN-EN)

In the case of low discrepancy between D/d and heavy loads, ropes with steel core displayed longer fatigue life than ropes with organic core.

 

Single-layer triangular-strand ropes

These are ropes consisting of six strands of triangular cross-sections. One, two or three layers of wires are wound onto the central strand 3F+3x2 made of 3 pairs of round wires and 3 filler wires.

The thinnest wires are used for central strand. In each next strand, the wires are thicker and thicker. Therefore, the rope is flexible and outer layers of strands are resistant to friction and mechanical damages.

Model cross-sections of triangular-strand ropes:

T 6x30+Ao  (PN)

T 6x34+Ao  (PN)

T 6x54+Ao  (PN)

6xV25B-NFC  (PN-EN)

6xV29B-NFC  (PN-EN)

6xV49B-NFC  (PN-EN)

These ropes are used in mining hoisting equipment as carrying ropes.

Main advantage of these ropes is their cross-section area, which is around 25% bigger than in round-strand ropes of the same diameter.

Thanks to their structure, triangular-strand ropes are resistant to side thrust. Forces between bottom of gorge of a pulley and the rope are distributed between more wires than in the case of round-strand ropes. Thanks to that, outer wires suffer wear at a uniform rate, which prolongs rope’s life.

Large contact area between rope and lining of a pulley enables obtaining good frictional contact between rope and Koepe pulley.

Disadvantage of triangular-strand ropes is point contact of wires in strands and Lang lay. Consequently, fatigue life of these ropes is shorter in comparison to ropes with linear contact of wires e.g. Seale or Warrington-Seale ropes. High twisting moment is also disadvantageous, in particular in deep shafts.

 

Multilayer round-strand ropes – non-rotating or with parallel strands

These ropes consist of two or three layers of strands. Parameters of wire’s lay in the strands and strands’ lay in the rope are adjusted so that the rope does not have a tendency to revolve on its axis when loaded (limited twisting moment).

Ropes of such properties are called non-rotating ropes.

In a two-layer rope the direction of lay in outer strands is opposite to the direction of lay in inner strands. It lowers significantly twisting moment of the rope and its tendency to rotate when loaded.

In ropes with three layers of strands, the tendency to rotate is even lower because the direction of lay in the inner and medium layer is the same and the outer layer, which consists of many strands, is twisted in the opposite direction.

Such ropes are used mainly in the equipment where rotation of load on its axis can be dangerous for the staff, for example in hoisting equipment and cranes. 

Examples of cross-sections of round-strand non-rotating ropes:

T 6x19+12x7+Ao  (PN) 34x7+Ao  (PN) 35x7  (PN)
18x7-NFC  (PN-EN) 34(M)x7-NFC  (PN-EN) 35(W)x7  (PN-EN)

A rope consisting of at least two layers of strands with linear contact or area contact (compact) of wires that are helically twisted around the core in one operation (the same lead in strands) is defined as rope with parallel arrangements of strands.

Model description: 8x19S-PWRC; 8xK36WS-PWRC

Multilayer round-strand ropes

Round-strand ropes constitute a type of non-rotating ropes, where cross-section of strands is similar to ellipse.

Their tendency to rotating or forming loops is lower than in the case of lang-lay ropes and regular-lay ropes. They are mainly used as carrying ropes in mining hoisting equipment and for the purpose of sinking shafts.

Model constructions of oval-strand ropes:

4x10+6x10+Ao  (PN) 4x7+5(7+13)+7(9+15)+Ao  (PN) 6(1+5)+5(7+13)+7(9+15)+Ao  (PN)
10xQ10FC-NFC  (PN-EN) 16(M)xQ24FC-NFC  (PN-EN) 12xQ24FC-IWRC  (PN-EN)

 

Round cable-laid ropes

A cable-laid rope is manufactured by winding double-layer round-strand ropes on the core. In this case, the wires are first twisted into strands, then twisted into rope and they are twisted for the third time when the rope is manufactured. The core in cable-laid ropes is usually constituted by an independent rope.

These ropes, due to their construction, can be easily deformed and, therefore, can be used under high tensile force only by a short period.

These ropes are used mainly in shipyard industry as towing and mooring lines. They are also used for production of suspensions.

Model constructions of cable-laid ropes:

T 6x6x7+7Ao  (PN) T 6x6x19+7Ao  (PN)  
6x[6x7-NFC]-[NFC]  (PN-EN) 6x[6x19M-NFC]-[NFC]  (PN-EN) 6x[6x36WS-IWRC]-[6x36WS-IWRC]

 

Flat ropes (sewed)

Such ropes consist usually of 6,8 or 10 independent lines (each line consists of four strands) with either left or right direction of lay, which are located one opposite to another and keep in place by wires, strands or rivets.

Flat rope sewed singly

 

Flat rope sewed double

 

FLAT HOISTING ROPE

(sewed singly by bundles of strands)

e.g.

104x19-8x4x7  (PN)

PS 8x[4x7]  (PN-EN)


FLAT BALANCE ROPE

(sewed double by bundles of wires)

60x14-6x4x5+24Ao  (PN)

PD 6x[4x5NFC]  (PN-EN)

 

 

FLAT BALANCE ROPE

(sewed double by bundles of wires)

67x15-6x4x6+24Ao  (PN)

PD 6x[4x6NFC]  (PN-EN)

 

 

FLAT BALANCE ROPE

(sewed double by bundles of strands or bundles of wires)

e.g.

101x25-6x4x7  (PN)

PD 6x[4x7]  (PN-EN)

 

FLAT BALANCE ROPE

(sewed double by bundles of strands)

e.g.

139x27-8x4x7  (PN)

PD 8x[4x7]  (PN-EN)

 

 

FLAT BALANCE ROPE

(sewed double by bundles of strands)

e.g.

174x34-8x4x9+32Ao  (PN)

PD 8x[4x9NFC]  (PN-EN)

 

 

FLAT BALANCE ROPE

(sewed double by bundles of strands)

e.g.

196x34-8x4x10+32Ao  (PN)

PD 8x[4x10NFC]  (PN-EN)

 

 

FLAT BALANCE ROPE

(sewed double by bundles of strands)

e.g.

213x36-8x4x14  (PN)

PD 8x[4x14M]  (PN-EN)

 

In practice, flat sewed ropes are rarely used when compare to other steel wire ropes.

As non-rotating ropes they are used in bobbin drives of shaft hoists for sinking, as rescue hoists and as balance ropes in mining shaft hoists with friction drives.

Flat ropes are characterized by specific properties which make them different to other constructions:

Their most important advantages:

-    lack of twisting moment,

-    high variability of mass density – it facilitates selection of rope to mining hoisting equipment,

-    low diameter of reverse loop,

-    easy and strong fitting at hanging hoisting vessels.

Main reason of these ropes’ wear is corrosion. The only control method is visual evaluation.

Flat sewed ropes are characterized by high cost of production (manual sewing partially mechanized).

 

Ropes made from strands with area contact of wires (compacted)

These are ropes, where strands are squeezed (compacted) before they are arranged.

 

Ropes of surface contact of wires (compacted)

These are ropes that undergo process of squeezing (compaction) after the process of arrangement, which diminishes their diameters.