6.2.15. WIRE ROPE When power source and load are located at extreme distances from one another, or loads are very large, the use of wire rope is suggested. Design and use decisions pertaining to wire ropes rest with the user, but manufacturers generally will help users toward appropriate choices. The following material, based on the Committee of Wire Rope Producers, "Wire Rope User's Manual," current edition, may be used as an initial guide in selecting a rope.

Wire rope is composed of (1) wires to form a strand, (2) strands wound helically around a core, and (3) a core. Classification of wire ropes is made by giving the number of strands, number of minor strands in a major strand (if any), and nominal number of wires per strand. For example 6 × 7 rope means 6 strands with a nominal 7 wires per strand (in this case no minor strands, hence no middle number). A nominal value simply represents a range. A nominal value of 7 can mean anywhere from 3 to 14, of which no more than 9 are outside wires. A full rope description will also include length, size (diameter), whether wire is preformed or not prior to winding, direction of lay (right or left, indicating the direction in which strands are laid around the core), grade of rope (which reflects wire strength), and core. The most widely used classifications are: 6 × 7, 6 × 19, 6 × 37, 6 × 61, 6 × 91, 6 × 127, 8 × 19, 18 × 7, 19 × 7. Some special constructions are: 3 × 7 (guardrail rope); 3 × 19 (slusher); 6 × 12 (running rope); 6 × 24 and 6 × 30 (hawsers); 6 × 42 and 6 × 6 × 7 (tiller rope); 6 × 3 × 19 (spring lay); 5 × 19 and 6 × 19 (marlin clad); 6 × 25B, 6 × 27H, and 6 × 30G (flattened strand). The diameter of a rope is the circle which just contains the rope. The right-regular lay (in which the wire is twisted in one direction to form the strands and the strands are twisted in the opposite direction to form the rope) is most common. Regular-lay ropes do not kink or untwist and handle easily. Lang-lay ropes (in which wires and strands are twisted in the same direction) are more resistant to abrasive wear and fatigue failure.

Cross sections of some commonly used wire rope are shown in Fig. 6.2.123. Figure 6.2.124 shows rotation-resistant ropes, and Fig. 6.2.125 shows some special-purpose constructions.

Figure 6.2.123 Cross sections of some commonly used wire rope construction. (Reproduced from "Wire Rope User's Manual, " AISI, by permission.) binary://mheaeworks/d03c7ddb475211da/158e7be668be00fdf011bdadd2ef3b2300f542e92687c6e02a998fc06e5a48d6/06x02_123.png Open in new tab Share Figure 6.2.124 Cross section of some rotation-resistant wire ropes. (Reproduced from "Wire Rope User's Manual, " AISI, by permission.) binary://mheaeworks/e19ef67be879c4d0/9ab225782b323010f79e566c12a458512274145d6877d8209774da72c34eda94/06x02_124.png Open in new tab Share Figure 6.2.125 Some special constructions. (Reproduced from "Wire Rope User's Manual, " AISI, by permission.) binary://mheaeworks/8627b14662f8a537/bb284940d47ada0df68e2027b63f42e8b5f813ef1a6eb57a1dc9e1bdcb726b5b/06x02_125.png Open in new tab Share The core provides support for the strands under normal bending and loading. Core materials include fibers (hard vegetable or synthetic) or steel (either a strand or an independent wire rope). Most common core designations are: fiber core (FC), independent wire-rope core (IWRC), and wire-strand core (WSC). Lubricated fiber cores can provide lubrication to the wire, but add no real strength and cannot be used in high temperature environments. Wire-strand or wire-rope cores add from 7 to 10 percent to strength, but under nonstationary usage tend to wear from interface friction with the outside strands. Great flexibility can be achieved when wire rope is used as strands. Such construction is very pliable and friction resistant. Some manufacturers will provide plastic coatings (nylon, Teflon, vinyl, etc.) upon request. Such coatings help provide resistance to abrasion, corrosion, and loss of lubricant. Crushing refers to rope damage caused by excessive pressures against drum or sheave, improper groove size, and multiple layers on drum or sheave. Consult wire rope manufacturers in doubtful situations.

Wire-rope materials and their strengths are reflected as grades. These are: traction steel (TS), mild plow steel (MPS), plow steel (PS), improved plow steel (IPS), and extra improved plow (EIP). The plow steel strength curve forms the basis for calculating the strength of all steel rope wires. American manufacturers use color coding on their ropes to identify particular grades.

The grades most commonly available and tabulated are IPS and EIP. Two specialized categories, where selection requires extraordinary attention, are elevator and rotation-resistant ropes.

Elevator rope can be obtained in four principal grades: iron, traction steel, high-strength steel, and extra-high-strength steel.

Bronze rope has limited use; iron rope is used mostly for older existing equipment.

6.2.15.1. Selection of Wire Rope Appraisal of the following is the key to choosing the rope best suited to the job: resistance to breaking, resistance to bending fatigue, resistance to vibrational fatigue, resistance to abrasion, resistance to crushing, and reserve strength. Along with these must be an appropriate choice of safety factor, which in turn requires careful consideration of all loads, acceleration-deceleration, shocks, rope speed, rope attachments, sheave arrangements as well as their number and size, corrosive and/or abrasive environment, length of rope, etc. An approximate selection formula can be written as:

DSL

(NS) K b K sf where DSL (demanded static load) = known or dead load plus additional loads caused by sudden starts or stops, shocks, bearing friction, etc., tons; NS (nominal strength) = published test strengths, tons (see Table 6.2.65); Kb = a factor to account for the reduction in nominal strength due to bending when a rope passes over a curved surface such as a stationary sheave or pin (see Fig. 6.2.126); Ksf = safety factor. (For average operation use Ksf = 5. If there is danger to human life or other critical situations, use 8 ≤ Ksf ≤ 12. For instance, for elevators moving at 50 ft/min, Ksf = 8, while for those moving at 1,500 ft/min, Ksf = 12.)

Table 6.2.65 Selected Values of Nominal Strengths of Wire Rope Classification

Nominal diameter

Fiber core

IWRC

Approximate mass

Nominal strength IPS

Approximate mass

Nominal strength

IPS

EIP

in

mm

lb/ft

kg/m

tons

t

lb/ft

kg/m

tons

t

tons

t

Source: "Wire Rope User's Manual," AISI, adapted by permission.

6 × 7 Bright (uncoated)

¼

6.4

0.09

0.14

2.64

2.4

0.10

0.15

2.84

2.58

3 / 8

9.5

0.21

0.31

5.86

5.32

0.23

0.34

6.30

5.72

½

13

0.38

0.57

10.3

9.35

0.42

0.63

11.1

10.1

⅝

16

0.59

0.88

15.9

14.4

0.65

0.97

17.1

15.5

⅞

22

1.15

1.71

30.7

27.9

1.27

1.89

33.0

29.9

1⅛

29

1.90

2.83

49.8

45.2

2.09

3.11

53.5

48.5

1 3 / 8

35

2.82

4.23

73.1

66.3

3.12

4.64

78.6

71.3

6 × 19 Bright (uncoated)

¼

6.4

0.11

0.16

2.74

2.49

0.12

0.17

2.94

2.67

3.40

3.08

3 / 8

9.5

0.24

0.35

6.10

5.53

0.26

0.39

6.56

5.95

7.55

6.85

½

13

0.42

0.63

10.7

9.71

0.46

0.68

11.5

10.4

13.3

12.1

⅝

16

0.66

0.98

16.7

15.1

0.72

1.07

17.7

16.2

20.6

18.7

⅞

22

1.29

1.92

32.2

29.2

1.42

2.11

34.6

31.4

39.8

36.1

1⅛

29

2.13

3.17

52.6

47.7

2.34

3.48

56.5

51.3

65.0

59.0

1 3 / 8

35

3.18

4.73

77.7

70.5

3.5

5.21

83.5

75.7

96.0

87.1

1⅝

42

4.44

6.61

107

97.1

4.88

7.26

115

104

132

120

1⅞

48

5.91

8.8

141

128

6.5

9.67

152

138

174

158

2⅛

54

7.59

11.3

179

162

8.35

12.4

192

174

221

200

2 3 / 8

60

9.48

14.1

222

201

10.4

15.5

239

217

274

249

2⅝

67

11.6

17.3

268

243

12.8

19.0

288

261

331

300

6 × 37 Bright (uncoated)

¼

6.4

0.11

0.16

2.74

2.49

0.12

0.17

2.94

2.67

3.4

3.08

3 / 8

9.5

0.24

0.35

6.10

5.53

0.26

0.39

6.56

5.95

7.55

6.85

½

13

0.42

0.63

10.7

9.71

0.46

0.68

11.5

10.4

13.3

12.1

⅝

16

0.66

0.98

16.7

15.1

0.72

1.07

17.9

16.2

20.6

18.7

⅞

22

1.29

1.92

32.2

29.2

1.42

2.11

34.6

31.4

39.5

36.1

1⅛

29

2.13

3.17

52.6

47.7

2.34

3.48

56.5

51.3

65.0

59.0

1 3 / 8

35

3.18

4.73

77.7

70.5

3.50

5.21

83.5

75.7

96.0

87.1

1⅝

42

4.44

6.61

107

97.1

4.88

7.26

115

104

132

120

1⅞

48

5.91

8.8

141

128

6.5

9.67

152

138

174

158

2⅛

54

7.59

11.3

179

162

8.35

12.4

192

174

221

200

2 3 / 8

60

9.48

14.1

222

201

10.4

15.5

239

217

274

249

2⅞

67

11.6

17.3

268

243

12.8

19.0

288

261

331

300

3⅛

74

13.9

20.7

317

287

15.3

22.8

341

309

392

356

80

16.4

24.4

371

336

18.0

26.8

399

362

458

415

Open in new tab Share Figure 6.2.126 Values of Kbend vs. D/d ratios (D = sheave diameter, d = rope diameter), based on standard test data for 6 × 9 and 6 × 17 class ropes. (Compiled from "Wire Rope User's Manual," AISI, by permission.) Interactive Graph Values of Kbend vs. D/d ratios (D = sheave diameter, d = rope diameter), based on standard test data for 6 × 9 and 6 × 17 class ropes. (Compiled from "Wire Rope User's Manual," AISI, by permission.) Click on the graph to launch interactivity or enter values below. D/d ratio Kb Open in new tab Share Having made a tentative selection of a rope based on the demanded static load, one considers next the wear life of the rope. A loaded rope bent over a sheave stretches elastically and so rubs against the sheave, causing wear of both members. Drum or sheave size is of paramount importance at this point.

6.2.15.2. Sizing of Drums or Sheaves Diameters of drums or sheaves in wire rope applications are controlled by two main considerations: (1) the radial pressure between rope and groove and (2) degree of curvature imposed on the rope by the drum or sheave size.

Radial pressures can be calculated from p = 2T/(Dd), where p = unit radial pressure, lb/in2; T = rope load, lb; D = tread diameter of drum or sheave, in; d = nominal diameter of rope, in. Table 6.2.66 lists suggested allowable radial bearing pressures of ropes on various sheave materials.

Table 6.2.66 Suggested Allowable Radial Bearing Pressures of Ropes on Various Sheave Materials Material

Regular lay rope, lb/in2

Lang lay rope, lb/in2

Flattened strand lang lay, lb/in2

Remarks

6 × 7

6 × 19

6 × 37

8 × 19

6 × 7

6 × 19

6 × 37

Source: "Wire Rope User's Manual," AISI, reproduced by permission.

Wood

150

250

300

350

165

275

330

400

On end grain of beech, hickory, gum.

Cast iron

300

480

585

680

350

550

660

800

Based on minimum Brinell hardness of 125.

Carbon-steel casting

550

900

1,075

1,260

600

1,000

1,180

1,450

30-40 carbon. Based on minimum Brinell hardness of 160.

Chilled cast iron

650

1,100

1,325

1,550

715

1,210

1,450

1,780

Not advised unless surface is uniform in hardness.

Manganese steel

1,470

2,400

3,000

3,500

1,650

2,750

3,300

4,000

Grooves must be ground and sheaves balanced for high-speed service.

Open in new tab Share All wire ropes operating over drums or sheaves are subjected to cyclical stresses, causing shortened rope life because of fatigue. Fatigue resistance or relative service life is a function of the ratio D/d. Adverse effects also arise out of relative motion between strands during passage around the drum or sheave. Additional adverse effects can be traced to poor match between rope and groove size, and to lack of rope lubrication. Table 6.2.67 lists suggested and minimum sheave and drum ratios for various rope construction. Table 6.2.68 lists relative bending life factors; Figure 6.2.127 shows a plot of relative rope service life versus D/d. Table 6.2.69 lists minimum drum (sheave) groove dimensions. Periodic groove inspection is recommended, and worn or corrugated grooves should be re-machined or the drum replaced, depending on severity of damage.

Table 6.2.67 Sheave and Drum Ratios Construction* †

Suggested

Minimum

• WS—Warrington Seale; FWS—Filler Wire Seale; SFW—Seale Filler Wire; SWS—Seale Warrington Seale; S—Seale; FW—Filler Wire.

† D = tread diameter of sheave; d = nominal diameter of rope. To find any tread diameter from this table, the diameter for the rope construction to be used is multiplied by its nominal diameter d. For example, the minimum sheave tread diameter for a ½-in 6 × 21 FW rope would be ½ in (nominal diameter) × 30 (minimum ratio), or 15 in.

Note: These values are for reasonable service. Other values are permitted by various standards such as ANSI, API, PCSA, HMI, CMAA, etc. Similar values affect rope life.

Source: "Wire Rope User's Manual," AISI, reproduced by permission.

6 × 7

72

42

19 × 7 or 18 × 7 Rotation-resistant

51

34

6 × 19 S

51

34

6 × 25 B flattened strand

45

30

6 × 27 H flattened strand

45

30

6 × 30 G flattened strand

45

30

6 × 21 FW

45

30

6 × 26 WS

45

30

6 × 25 FW

39

26

6 × 31 WS

39

26

6 × 37 SFW

39

26

6 × 36 WS

35

23

6 × 43 FWS

35

23

6 × 41 WS

32

21

6 × 41 SFW

32

21

6 × 49 SWS

32

21

6 × 46 SFW

28

18

6 × 46 WS

28

18

8 × 19 S

41

27

8 × 25 FW

32

21

6 × 42 Tiller

21

14

Open in new tab Download data Share Table 6.2.68 Relative Bending Life Factors Rope construction

Factor

Rope construction

Factor

Source: "Wire Rope User's Manual," AISI, reproduced by permission.

6 × 7

0.61

6 × 36 WS

1.16

19 × 7 or 18 × 7

0.67

6 × 43 FWS

1.16

Rotation-resistant

0.81

6 × 41 WS

1.30

6 × 19 S

0.90

6 × 41 SFW

1.30

6 × 25 B flattened strand

0.90

6 × 49 SWS

1.30

6 × 27 H flattened strand

0.90

6 × 43 FW (2 op)

1.41

6 × 30 G flattened strand

0.89

6 × 46 SFW

1.41

6 × 21 FW

0.89

6 × 46 WS

1.41

6 × 26 WS

1.00

8 × 19 S

1.00

6 × 25 FW

1.00

8 × 25 FW

1.25

6 × 31 WS

1.00

6 × 42 Tiller

2.00

6 × 37 SFW

Open in new tab Download data Share Figure 6.2.127 Service life curves for various D/d ratios. Note that this curve takes into account only bending and tensile stresses. (Reproduced from "Wire Rope User's Manual, " AISI, by permission.) Interactive Graph Service life curves for various D/d ratios. Note that this curve takes into account only bending and tensile stresses. (Reproduced from "Wire Rope User's Manual, " AISI, by permission.) Click on the graph to launch interactivity or enter values below. D/d ratio Relative rope service life Open in new tab Share Table 6.2.69 Minimum Sheave- and Drum-Groove Dimensions* Nominal rope diameter

Groove radius

New

Worn

in

nm

in

mm

in

mm

• Values given are applicable to grooves in sheaves and drums; they are not generally suitable for pitch design since this may involve other factors. Further, the dimensions do not apply to traction-

type elevators; in this circumstance, drum- and sheave-groove tolerances should conform to the elevator manufacturer's specifications. Modern drum design embraces extensive considerations beyond the scope of this publication. It should also be noted that dram grooves are now produced with a number of oversize dimensions and pitches applicable to certain service requirements.

Source: "Wire Rope User's Manual," AISI, reproduced by permission.

¼

6.4

0.135

3.43

.129

3.28

5 / 16

8.0

0.167

4.24

.160

4.06

3 / 8

9.5

0.201

5.11

.190

4.83

7 / 16

11

0.234

5.94

.220

5.59

½

13

0.271

6.88

.256

6.50

9 / 16

14.5

0.303

7.70

.288

7.32

5 / 8

16

0.334

8.48

.320

8.13

3 / 4

19

0.401

10.19

.380

9.65

7 / 8

22

0.468

11.89

.440

11.18

1

26

0.543

13.79

.513

13.03

1⅛

29

0.605

15.37

.577

14.66

1¼

32

0.669

16.99

.639

16.23

1 3 / 8

35

0.736

18.69

.699

17.75

1½

38

0.803

20.40

.759

19.28

1⅝

42

0.876

22.25

.833

21.16

1¾

45

0.939

23.85

.897

22.78

1⅞

48

1.003

25.48

.959

24.36

2

52

1.085

27.56

1.025

26.04

2⅛

54

1.137

28.88

1.079

27.41

2¼

58

1.210

30.73

1.153

29.29

2 3 / 8

60

1.271

32.28

1.199

30.45

2½

64

1.338

33.99

1.279

32.49

2⅝

67

1.404

35.66

1.339

34.01

2¾

71

1.481

37.62

1.409

35.79

2⅞

74

1.544

39.22

1.473

37.41

3

77

1.607

40.82

1.538

39.07

3⅛

80

1.664

42.27

1.598

40.59

3¼

83

1.731

43.97

1.658

42.11

3 3 / 8

87

1.807

45.90

1.730

43.94

3½

90

1.869

47.47

1.794

45.57

3¾

96

1.997

50.72

1.918

48.72

4

103

2.139

54.33

2.050

52.07

4¼

109

2.264

57.51

2.178

55.32

4½

115

2.396

60.86

2.298

58.37

4¾

122

2.534

64.36

2.434

61.82

5

128

2.663

67.64

2.557

64.95

5¼

135

2.804

71.22

2.691

68.35

5½

141

2.929

74.40

2.817

71.55

5¾

148

3.074

78.08

2.947

74.85

6

154

3.198

81.23

3.075

78.11

Open in new tab Share Seizing and Cutting Wire Rope Before a wire rope is cut, seizings (bindings) must be applied on either side of the cut to prevent rope distortion and flattening or loosened strands. Normally, for preformed ropes, one seizing on each side of the cut is sufficient, but for ropes that are not preformed a minimum of two seizings on each side is recommended, and these should be spaced six rope diameters apart (see Fig. 6.2.128). Seizings should be made of soft or annealed wire or strand, and the width of the seizing should never be less than the diameter of the rope being seized. Table 6.2.70 lists suggested seizing wire diameters.

Figure 6.2.128 Seizings. (Reproduced from "Wire Rope User's Manual, " AISI, by permission.) binary://mheaeworks/b5689cae67236644/dabbb5c8ab916a67588e9e15144fa3607cde3a92171221b8c915b2690ccc4448/06x02_128.png Open in new tab Share Table 6.2.70 Seizing* Rope diameter

Suggested seizing wire diameter†

in

mm

in

mm

• Length of the seizing should not be less than the rope diameter.

† The diameter of seizing wire for elevator ropes is usually somewhat smaller than that shown in this table. Consult the wire rope manufacturer for specific size recommendations. Soft annealed seizing strand may also be used.

Source: "Wire Rope User's Manual," AISI, reproduced by permission.

⅛- 5 / 16

3.5-8.0

0.032

0.813

3 /

8

9 / 16

9.4-14.5

0.048

1.21

⅝- 15 / 16

16.0-24.0

0.063

1.60

1-1 5 / 16

26.0-33.0

0.080

2.03

1 3 / 8 -1 11 / 16

35.0-43.0

0.104

2.64

1¾ and larger

45.0 and larger

0.124

3.15

Open in new tab Share Wire Rope Fittings or Terminations End terminations allow forces to be transferred from rope to machine, or load to rope, etc. Figure 6.2.129 illustrates the most commonly used end fittings or terminations. Not all terminations will develop full strength. In fact, if all of the rope elements are not held securely, the individual strands will sustain unequal loads causing unequal wear among them, thus shortening the effective rope service life. Socketing allows an end fitting which reduces the chances of unequal strand loading.

Figure 6.2.129 End fittings, or terminations, showing the six most commonly used. (Reproduced from "Wire Rope User's Manual, " AISI, by permission.) binary://mheaeworks/93cbb5f808260c54/0b81d52ad105f0752c71c8e820d154a2b2caedd00b267e91c7d74013bc0b3bbc/06x02_129.png Open in new tab Share Wire rope manufacturers have developed a recommended procedure for socketing. A tight wire serving band is placed where the socket base will be, and the wires are unlaid, straightened, and "broomed" out. Fiber core is cut close to the serving band and removed, wires are cleaned with a solvent such as SC-methyl chloroform, and brushed to remove dirt and grease. If additional cleaning is done with muriatic acid this must be followed by a neutralizing rinse (if possible, ultrasonic cleaning is preferred). The wires are dipped in flux, the socket is positioned, zinc (spelter) is poured and allowed to set, the serving band is removed, and the rope lubricated.

A somewhat similar procedure is used in thermoset resin socketing.

Socketed terminations generally are able to develop 100 percent of nominal strength.