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About wire rope

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Outline of rope Cooperated by:Tokyo Rope Manufacturing

Index
1.Characteristics
2.Construction
3.Number of strands
4.Lay of the strands
5.Rope core
6.Type of lay
7.Performing
8.Breaking load (grade)
9.Kinds of coating
10.Greasing
11.Rope diameter
12.Length
13.Designation and symbol

1.Characteristics   INDEX  NEXT ITEM  TOP

Wire ropes have a complicated structure. It is important to know the characteristics of rope when select and use. The characteristics of the wire ropes differ from general iron and steel secondary products may be those below.
(1) High tensile strength
(2) Superior impact resistance
(3) Long items can be made (easy to transport)
(4) High flexibility (easy to handle)
On the other hand, There are short points such as (1) low coefficient of inelasticity (2) torque arising.
However, there is countermeasures , such as pretension for (1) and the use of non-rotating ropes for (2) .


2.Construction   INDEX  NEXT ITEM  TOP

The construction of rope differes depending on the number of strands, the number of the wires in the strands and wheter it is of a fiber core, or of rope core. As shown in Fig.1, the rope is made through stranding several to several tens of wires and closing the strands normally six strands around a core in a prescribed pitch.

ワイヤロープ 構成図Figure 1



3.Number of strands   INDEX  NEXT ITEM  TOP

From three to nine strands are used to make a rope. Apart from some special cases, practically all ropes are made of six strands as a balanced construction. However, when used for elevators where special flexibility is required, eight strands are used. Also, Two or more layers of strands are used when non-torque is required. For ropes of the same diameter, generally, the more the number of strands the smaller is the diameter of each strand. In such cases, the rope may gain flexibility but, on the other hand, the strength will drope and the rope will become inferior in corrosion resitance and deformation.

4.Lay of the strands(number of wires and position) INDEX  NEXT ITEM  TOP

One strand is normally made up of seven to several tens of wires with simillar or differing, diameters in single or multi-layers. In the method where the wires are positioned to form more than two layers, there is the cross lay where the wires of each layer are in the same lay angle, and the parallel lay where one process is used to lay the wires so that wires of each layer will be of the same pitch. For strands of the same diameter, the more the number of wires, smaller will be the diameter of each wire and the greater will be the flexibility of the strand. However, the rope will become inferior in its wear resistance and deformation resistance.


(1)Cross lay
The cross lay is also called as the point contact lay, as each wire is in contact with each other. The laying of the wires is carried out in such a way that the lay angle will be almost equal for each layer of wire of the same diameter. The length of the wires in each layer will also be the same and the wires of each layer will be in contact with each other.

(2)Parallel lay
Parallel lay is also called as the equal lay. It is also called one operation lay from the number of stranding processes and also as linear contact lay as each wire is in contact with each other. Moreover, at this company, the parallel lay rope has the product name of Super Rope. In the parallel lay, the wires of each layer are positioned in such a way that there will be no space between them and so that the upper layer wires will fit neatly into the groove of the lower wires of the strand. For this, wires of differing diameters are positioned at the same time so that each wire layer will have the same pitch and will be in contact with each other. Therefore, differing from the cross lay rope, although the lay angle of each wire layer and the length of the wires are not uniform, as each wire is in contact with each other, it is superior in its fatigue resistance. Moreover, the 6xFi(25),6xWS(36) and the 8xS(19) belong to this lay method.
・Basic types
As the basic parallel lay, there are the following three types.

(a)Seale type
The number of wires of each leyer is shown as 1+n+n and the number of wires of the inner and outer layers is the same. The wires of the outer layer fit completely into the grooves of the inner layer wires. The outer layer wires of this Seale type rope is thicker when compared to other parallel lays and so it is superior, particularly in its wear resistance and is mainly used for elevators.

(b)Warrington type
The number of wires of each layer is indicated as 1+n+(n+n) and there are two kinds of wires for the outer layers, one being large and the other small. The number of wires of the outer layer is double that of the inner layer and combination of the inner and outer layers fill the spaces between the wires. This Warrington type rope is seldom being used recently.

(c)Filler type(with filler wire)
The number of wires of each layer is indicated as 1+n+(n)+2n and the number of wires of the outer layers is double that of the inner layer. The inner wires and the same number of thin filler wires are used to fill the spaces in the inner and outer layers. This filler type rope has a good balance between the flexibility, fatigue resistance and wear resistance and has the widest range of use among parallel lay ropes.
・Combination types
Apart from the above three basic types, there are combinations of these types. Among these, the following two types are used the most.

(a)Semi-seale type
This is a combination between the cross lay and the parallel lay and around the center 7 wiers, 2 layers of simillar number wires are positioned in a Seale type. This semi-Seale type rope has a comparatively good fatigue resistance nature and has a wide range of uses.

(b)Warrington Seale type
This is a combination between the Warrington type and the Seale type and is extremely superior in its fatigue resistance. It also abounds in flexibility and is superior in its wear resistance and so has a wide range of uses.

(3)Flat type
The strands are combined in such a way that the outer circumference of the rope will be flat in shape. This rope has a smooth surface and specific pressure is small so it is superior in its abrasion resistance. In general, the triangular strand and the clam shaped strand are major type and flat strand type is partially seen.

(a)Triangular strand type
Up to now, an outer layer wire was positioned around the triangular wires but, recently, a single layer or two layers of wires are stranded around a triangular core made of round wires to form a round wire triangular core strands.

(b)clam shaped strand type
The cross sectional view of this type is in the shape of shell and this rope is usually in three strands, or four strands. Also, apart from the fatigue resistance, it also has a non-twisitng nature. The Mono-Rope of this company which is widely used belongs to this type.

(c)Flat strand type(oval strand type)
There is the type where two layers of strands in which the wires are stranded in an oval shape are positoned around a fiber core(Sinking Rope) and the type where the core is a multiple layer of wires around which 6 to 10 strands are positioned(Concentric Rope).


5.Rope core     INDEX  NEXT ITEM  TOP

The rope core can be classified into the fiber core and the steel core.

(1)Fiber core(abbreviated as FC)
The fiber core has two important functions, or @ to support the strand and at the same time to hold the shape of the rope, and A to hold the rope grease and to supply the necessary amount of grease to the inside of the rope, during use, for lubrication and to prevent corrosion. In the past, natural fiber was mainly used but, of late, synthetic fiber is starting to be used. Two kinds of natural fibers are used, one is the hard fiber, such as Manila and saisal, as well as jute and the other is the soft fiber, such as cotton threads, used in ropes with a comparatively small diameter. Also, for synthetic fiber, specially processed polypropylene is used so that the synthetic fiber will hold the grease well. The characteristics of fiber core compared to steel core are
(a)high flexibility
(b)superior shock resistance
(c)Holds rope grease well (in particular, in the case of natural fiber)
(d)The unit and mass of the rope is small. Moreover, synthetic fiber compared to natural fiber is superior in corrosion resistance.

(2)Steel core
For steel cores, there is the strand core (IWSC) and the rope core. Among the rope cores, there is the IWRC and the CFRC(center fit wire rope core).
(a) The IWSC (indepent wire strand core) has the strand as the core and those which have the same construction as the side strand are called as the common core.
(b)The IWRC (independent wire rope core) has a single independent rope as the core. Usually, a 7x7 construction is used but depending on the use a 6x7 or a 6x19 may be used.
(c)For the CFRC (center fit wire rope core), the outer layer strand of the core rope is fitted into the groove of the inside of the side strand of the rope. This core rope is positioned in one process with the outer layer rope. Moreover, for the core rope, the 7x7 and the 19+8x7 are used. The IWSC and the CFRC are used in only a few special cases. Among ropes with a steel core, the IWRC has a good flexibility and so is used the most. The characteristics of the steel core are as follows compared to the fiber core.
(a)The rope has a high strength.
(b)High resistance for lateral pressure and deformation.
(c)The elongation of the rope is small and the change of diameter is low.
(d)Superior heat resistance


6.Type of lay   INDEX  NEXT ITEM  TOP

(1)Direction of lay
As concerns the direction of laying the rope and the strand, there is the Z lay and the S lay. The rope shall be made of the Z lay and the strand products of the S lay, if there is no specific needs.

(2)Laying of rope
In laying of rope, there is the ordinary lay and the Lang's lay.
(a)Ordinary lay (or regular lay)
The lay of the rope and the lay of the strands are in opposite directions
(b)Lang's lay
The lay of the rope and the lay of the strands are in the same direction.
(c)Comparison of the characteristics which inevitably arises from the differences in laying of rope are as shown in Table 1.


Table 1・Comparison of the characteristics by laying of rope

Items Ordinary lay Lang's lay
Appearance The wires are approximately parallel to the axis of the rope. The wires form a certain angle with the rope axis.
Merits Kinks do not form easily and is easy to handle. The lays are tight and the form does not crumble. The wires appearing on the surface are long and superior in wear resistance. Flexibile and has good fatigue resistance nature.
Demerits Inferior in wear resistance nature and fatigue resistance nature compared to the Lang's lay. The rope has a large torque and forms kinks easily


7.Preforming   INDEX  NEXT ITEM  TOP

 Preforming is a method for lessening the springiness of the rope by giving each strand and wire a form in advance. Ropes made through this method are called preformed, or Tru-lay ropes. The strands and wires do not fall apart even when the rope is cut. The ropes being manufactured, at present, are practically all preformed ropes. Apart from the 6x61, the non-preformed ropes are only for special uses.

8.Breaking load(Grade)   INDEX  NEXT ITEM  TOP

 For the breaking load, there is the designated breaking load and the nominal breaking load. The designated breaking load is the standard value, or the lowest value of the breaking load, while the nominal breaking load is the lowest value at the time the test pieces break. The breaking load is determined by the nominal tension of the wires making up the rope and is classified as shown in Table 2.Apart from these, this company will make ropes that exceed the trengths shown, on request.

Table 2・Grade of wire rope
Standard Grade     Summary
JIS G3525 Grade E(1320N/mm2{135kgf/mm2}Class) Bright and galvanized
Grade G(1470N/mm2{150kgf/mm2}Class) Galvanized
Grade A(1620N/mm2{165kgf/mm2}Class) Bright and galvanized
Grade B(1770N/mm2{180kgf/mm2}Class) Bright and galvanized
----- Grade special(1910N/mm2{195kgf/mm2}Class) Bright

9.Kinds of coating   INDEX  NEXT ITEM  TOP

Ropes are usually of the bright type but when a corrosion resistant nature is required the ropes are coated. Among the kinds of coating, there is the zinc coating is used. Apart from the general hot dip galvanizing, this company is using a high corrosion resistant alloy-coating with zinc and aluminum, under the product name ZINCAL through a high speed coating method. Both are receiving high evaluation for their superior corrosion resistant nature. Apart from these , this company can make ropes with a special coating, on request.

10.Greasing   INDEX  NEXT ITEM  TOP

Rope grease is applied to the rope at the time of manufacture to prevent corrosion and also to provide lubrication. Great care is taken to apply the rope grease uniformly and so that it will penetrate to the core and strand, through an impregnation method. The kind of grease applied will greatly influence the life of the rope. Table 3 below show the number of bendings before a breaking arose, according to a fatigue test carried out by this company. Among rope greases, there are the non-crystalline grease such as the Petrolatum and Micro Wax and the red rope grease whose principal ingredient is a special kind of bitumen, such as asphalt. This company has manufactured a special rope grease that is superior in its rust prevention, lubrication, stability and safety.

Table 3・Cmparison of the fatigue characteristics of the rope, according to greased or non-greased

Grease condition Number of repeat bending
Up to the first breakage Up to 10% wire breakage per lay
Greased
non-greased
34,500
16,800
48,500
22,500
Greased
non-greased
2.05 2.15


11.Rope diameter   INDEX  NEXT ITEM  TOP

Among rope diameters, there is the nominal diameter and actual diameter (diameter actually measured) and, in principle, for JIS G 3525 (called to as JIS herein) the standard number (JIS Z 8601) is employed. On the other hand, as shown in Fig. 10, the actual diameter is the measurement of the circumscribed circumference and is expressed in mm. The tolerance on rope diameter shall be +0 +10% for the diameter less than 10mm and +7% 0% for that equal to or more than 10mm, according to JIS. This company is making ropes with a diameter of up to 200mm, depending on the construction of the rope.


Fig. 10・Measurement of rope diameter

ワイヤロープ 図り方

12.Length   INDEX  NEXT ITEM  TOP

The length of the rope is generally set at 200m, 500m and 1,000m but a longer length can be made on request. On the other hand, ropes that weight up to 120 tons are being made, depending on the construction of the rope.

13.Designation and Symbol   INDEX  TOP

the rope is reffered to in terms of construction, laying of rope, lay direction, whether bright or galvanized, the kind of rope grease, diameter, grade, breaking load, length and reels. Expressing these in words and numbers would make the designations too lengthy and complex and so this company is using the following symbols.

(1)Construction

Kind of core, Number of strands × Lay symbol of the strand, Number of wires per strand

Moreover, in the case there is a product symbol, the symbol is placed at the front (for example, this is T in the case of Tough-Rope).


Table 4・Symbol for the kind of core

Kind of core Symbol Remarks
Fiber core Usually not used Refer to designation examples 1 and 2
Strand core Usually not used In the case the construction of the core strand differs from that of the strand for the rope itself, a symbol is used for expressing this construction(see example 3). In the case the construction is the same, in place of showing IWSC, this is shown as "the number of strands of the rope itself +1" in the "number of strands" column (see example 4)
Rope core IWRC(Independent Wire Rope Core)
    or
CFRC(Center Fit Wire Rope Core)
In the case the core rope is other than 7x7 the composition is also shown (see example5) and in the case the core rope is 7x7 the construcion of the core rope may be omitted in the parentheses ( ) (see example 6)
Table 5・Lay symbol for strand
Lay method Cross lay Parallel lay
Symbol General Flat type Seale type Warrington type Filler type Warrinton Seale type Semi-Seale type
No symbol F S W Fi WS SeS
(Note) The total number of wires per strand is shown but of the flat type rope, apart from the Mono-Rope, the triangular strand rope is disassembled and expresses (see example 7)

Designation examples
@6x7、6x19、6x24、6x37
A8xS(19)、6xWS(36)
BAS(36)+8xS(19)
CIWSC6x37→37+6x37→7x37
DIWRC(6x19)8xWS(36)
EIWRC(7x7)6xFi(25)→IWRC6xFi(25)
F6xF[(3x2+3)12+12]


(2)Lay direction of rope, etc.
The direction of lay, whether galvanized or not and the kind of rope grease used are abbreviated in Table 6.

Lay Ordinary lay
Z lay S lay
Kind of rope grease Red Black Red Black
Bright or Galvanized  Bright O/O C/O O/S C/S
Galvanized G/O GC/O G/S GC/S


Lay Lang's lay
Z lay S lay
Kind of rope grease Red Black Red Black
Bright or Galvanized  Bright O/L C/L O/LS C/LS
Galvanized G/L GC/L G/LS GC/L


(Note)
1.Laying of rope: The Lang's lay is shown as L and the ordinary lay as O.
2.Direction of lay: In the case of the Z lay, no symbol are used while in the case of S lay, S is used.
3.Bright or galvanized: In the case of naked, no symbols are used, while in the case of galvanized the letter G is used.
4.Kinds of rope grease: Black rope grease is shown as C, while red rope grease is shown as O, However, in the case of galvanized ropes, the O is omitted. Moreover, in the case of the slip prevention grease, V is used and for fishing industry used the letter T or TN is used.

(3)Grades (breaking load)
 Grade E, grade G, grade A, grade B special grade or breaking load are expressed in "kN"
(4)Diameter
 The rope diameter is expressed in "mm".
(5)Length
 The rope (one drum)is expressed in "m".
(6)Rope designation examples

(a)6 strands of 19 wires, fiber core, naked, red rope grease, ordinary lay, Z lay, Grade A, rope diameter 20mm, length 500m, 2 reels, shown as: 6x19 O/O 20mm Grade A 500mx2
(b) 6 strands of 37 wires, fiber core, galvanized, red rope grease, ordinary lay, Z lay, Grade G, rope diameter 16mm, length 200m 5 reels 6x37 G/O 16mm Grade G 200mx5
(c)Filler type 6 strands of 29 wires, rope core, galvanized, black rope grease, Lang's lay, S lay, Grade B rope diameter 30mm, length 1,500m, 1 reel as: IWRC 6xFi(29) GC/LS 30mm Grade B 1,500m