Right type of rope shall be selected for an installation to get best service from it and having selected right rope, it shall be correctly ordered to get desired rope. Information about factors to be considered for selecting a wire rope and detail to be specified in a purchase order is given in this article.
Selection of a wire rope
To get the best service from a wire rope on any specific installation, the following five principal factors should generally be considered.
Strength
The strength of a wire rope is a function of its size, grade, and construction. It must be sufficient to accommodate the maximum load that will be applied on it. The maximum load limit is determined by means of an appropriate design factor (also known as factor of safety). This design factor is the number by which the ultimate strength of a wire rope is divided to determine the working load limit.
For different strength, different grades of steel wires are used. Different grades of wires used to make wire ropes and their breaking strength are as under.
| Steel Grade (American) | Ultimate Tensile Strength | ||
|---|---|---|---|
| Tons / inch 2 (American) |
Kgf. / mm2 (Metric) |
N / mm2 (ISO) |
|
| Patent Steel | 80 / 90 | 125 | 1230 |
| Improved Patent Steel | 90 / 100 | 140 | 1420 |
| Plough Steel | 100 / 110 | 160 | 1570 |
| Improved Plough Steel | 110 / 120 | 180 | 1770 |
| Extra Improved Plough Steel | 120 / 130 | 200 | 1960 |
| Extra Extra Improved Plough Steel | 130 / 140 | 220 | 2160 |
Wire ropes are constructed with different arrangement of wires to make strands and strands to make wire ropes. As certain constructions are more suitable for certain applications, there are different specifications for different applications. Wire ropes are made as per IS, BS, DIN, API, ASTM and Lloyds specifications. IS specification numbers for various applications are as under.
| Wire Rope Application | Specification |
|---|---|
| General Engineering | IS 2266 |
| Lift and Elevators | IS 2365 |
| Mining | IS 1855 |
| Shipping | IS 2581 |
| Suspension Bridges | IS 9282 |
| Small Wire Ropes (Auto Cables) | IS 3459 |
Various international specifications are as under.
API (Oil well application): API Standard 9A
ASTM: ASTM A1023 / 1023M
USA Federal Specification: RR-W-410E
BS-EN-12385-1 to BS-EN-12385-10
These specifications give information on constructions, sizes, mass, lay, tensile grades and minimum breaking loads.
Minimum Breaking Loads and Mass (Weight) for round strand, cross lay and 6×19 (12/6/1) construction wire rope for general engineering purpose as per IS 2266 are as under.
| Nominal Diameter mm |
Approximate Mass | Minimum Breaking Load Corresponding to Tensile Designation of wires of | ||||||
|---|---|---|---|---|---|---|---|---|
| Fibre Core kg/100m |
Steel Core kg/100m |
1570 | 1770 | 1960 | ||||
| Fibre Core kN |
Steel Core kN |
Fibre Core kN |
Steel Core kN |
Fibre Core kN |
Steel Core kN |
|||
| 8 | 22.1 | 24.3 | 31 | 33 | 35 | 37.6 | 39 | 41.6 |
| 9 | 28.0 | 30.8 | 39 | 42 | 44 | 47.5 | 49 | 52.6 |
| 10 | 34.6 | 38.0 | 48 | 52 | 54 | 58.7 | 60 | 65.0 |
| 11 | 41.9 | 46.1 | 58 | 63 | 66 | 71.0 | 73 | 78.7 |
| 12 | 49.8 | 54.8 | 69 | 75 | 78 | 84.6 | 87 | 93.6 |
| 13 | 58.5 | 64.3 | 82 | 88 | 92 | 99 | 102 | 110 |
| 14 | 67.8 | 74.6 | 95 | 102 | 107 | 115 | 118 | 127 |
| 16 | 88.6 | 97.4 | 124 | 133 | 139 | 150 | 154 | 166 |
| 18 | 112 | 123.0 | 156 | 160 | 176 | 190 | 195 | 210 |
| 19 | 125 | 137.0 | 174 | 188 | 196 | 212 | 217 | 234 |
| 20 | 138 | 152.0 | 193 | 208 | 218 | 235 | 241 | 260 |
| 22 | 167 | 184.0 | 234 | 252 | 263 | 284 | 292 | 314 |
| 24 | 199 | 219.0 | 278 | 300 | 313 | 338 | 347 | 375 |
| 26 | 234 | 257.0 | 326 | 352 | 368 | 397 | 407 | 439 |
| 28 | 271 | – | 378 | – | 426 | – | 472 | – |
| 32 | 354 | – | 494 | – | 557 | – | 617 | – |
| 36 | 448 | – | 625 | – | 705 | – | 781 | – |
| 38 | 499 | – | 697 | – | 785 | – | 870 | – |
| 40 | 554 | – | 772 | – | 870 | – | 964 | – |
| 44 | 670 | – | 934 | – | 1053 | – | 1166 | – |
| 48 | 797 | – | 1112 | – | 1253 | – | 1388 | – |
| 52 | 936 | – | 1305 | – | 1471 | – | 1629 | – |
Information about many constructions is given in IS 2266. For other constructions, please refer the specification.
For more information on wire ropes, please refer following specifications.
IS 2363: Glossary of terms relating to wire ropes.
IS 6594: Technical supply conditions for steel wire ropes and strands.
IS 1835: Specification for round steel wire for ropes and
IS 3973: Code of practice for selection, installation and maintenance of wire ropes.
ISO 2532: Steel wire ropes – Vocabulary.
ISO 4345: Steel wire ropes — Fibre main cores – Specification and
ISO 4346: Steel wire ropes for general purposes — Lubricants — Basic requirements.
International specifications for wire rope materials are BS-EN-10264 and ISO 2232.
Abrasion Resistance
Abrasion is one of the most common destructive conditions affecting wire rope. It usually occurs on drums and sheaves or whenever rope rubs against itself or other material. Abrasive wear removes metal from the cross section of outer wires of a wire rope where it is exposed. Large diameter wires offer greater metallic area to withstand abrasive wear. Distribution of wearing surface also plays important role in abrasion. Due to larger wearing surface, Lang’s lay ropes are more abrasion resistant than regular lay ropes.
Fatigue Resistance
Bending of wire rope takes place around sheaves, drums, etc. Sharper or acute bend and close-coupled reverse bending speeds up fatigue. A wire rope must have the ability to withstand repeated bending without the failure of the wires from fatigue. A rope with more wires in a strand has greater resistance against fatigue as thinner wires are more flexible.
Crushing Strength
Crushing is the effect of external pressure on a rope, which damages it by distorting. When a rope is damaged by crushing, the wire, strands and core are prevented from moving and adjusting normally in operation. Rope with steel core (IWRC) and regular lay ropes are more crush resistant than fiber core and Lang’s lay ropes.
Corrosion
Normally corrosion takes place because of acid or alkali atmosphere which is due to sea, industrial fumes or abnormal conditions. Corrosion can be resisted by periodic cleaning and lubrication of wire rope or by galvanizing.
It may be noted that in certain cases above properties contradict each other. For example, increasing the diameter of the outer wires of a rope increases resistance to abrasion, but decreases resistance to bending fatigue. It is therefore, very important that the ultimate selection of rope must be a most acceptable compromise. Each of the desirable characteristics should be attained to the maximum degree possible without excessive sacrifice of the other required properties.
Detail for Enquiry / Order
Following information shall be given in an enquiry / purchase order to get the exact rope as per requirement.
Nominal Diameter
Try to maintain the same nomenclature as per the pertaining standards. If you require a rope as per IS, specify the rope diameter in mm. Alternatively, if you require an API rope, you shall specify the rope diameter in inches in conformance to the API standards. The actual diameter usually varies from the nominal diameter. As per IS 2266, actual diameter can be -1% to 4 % of the nominal diameter.
Rope Length
Specify the correct length and tolerance if any as per requirement.
Number of Lengths
Specify the number of ropes required.
Coating/ Finish
A rope can be either ungalvanized or galvanized. In rope nomenclature, an ungalvanized rope is also known as bright or black rope. Wires are also coated with plastic, nylon, etc. Specify required coating.
Tensile Grade of steel
This property signifies the strength / load bearing capacity of the wire rope. If you procure a rope as per IS specifications, the usual designations are 1770 N/mm2, 1960 N/mm2, or 2160 N/mm2. The other less frequently used tensile designations are 1420 and 1570 N/ mm2. Alternatively for imperial (inch) specification, give steel grade (IPS; EIP; EEIP, etc.) or tensile strength in Tons / sq. in.
Grade
Steel is melted in a furnace with either an acid bottom and lining or a basic bottom and lining. Specify required steel grade.
Construction
A rope is generally made up of number of strands twisted around a core. The strands are themselves formed from a number of wires twisted in a helical fashion. Give detail of rope construction like strand pattern with number of wires in a strand and number of strands in the rope.
Core Type
The core of a steel wire rope can be either fibre or steel. The fibre core can further sub divided into natural fibre or artificial fibre (Sisal). In case of steel core, the alternatives can be Independent Wire Rope Core (IWRC) or Wire Strand Core (WSC).
Lay
There are two different methods of laying up of wire ropes namely Ordinary (Regular) Lay and Lang’s Lay. And there are two directions for laying (hand of lay) namely Right Hand and Left Hand. Specify desired method and direction of laying.
If no indication of a lay is given, it will be assumed by the manufacturer that right hand ordinary lay rope is required.
Minimum Breaking Load
If possible, the same should also be furnished, as it aids in checking on the specifications of the offered rope
Preformed or Non-Preformed
A rope can be preformed or non-preformed. Usually, a general engineering rope is preformed. Specify the performing requirement.
Specification
Every rope is manufactured in conformance to specific quality conformation standards. The same may be either IS (Indian standards), DIN, BS, JIS, API or any other standard as specified by the customer.
Fittings / End terminations
Certain applications need to attach additional fittings such as thimbles, sockets (spelter/ swaged), rings, etc. Specify if any.
Lubrication
Usually manufacturers decide the type of lubrication based on the area of application of the rope. Give customized requirement any.
Packing
A steel wire rope can be packed either in wooden / steel Reels or coils. Specify type of packing required
Tests
Specify witnessing of tests if any, testing required from external testing agencies (e.g. from Lloyds), and type of test certificates from the manufacturer.
Area of Application
In addition to the above specification, it is advisable to give the area of application for the rope so that manufacturer can judge whether the specific rope that is being offered is suitable one for the application or not. It aids as an additional check for the rope selection.
In case of any possible doubt about details of specification, customers are advised to state the purpose of rope, and give complete information regarding the equipment on which it is to be installed. A sample length of the previous rope used will be immensely helpful to the manufacturer in advising correct rope for the job.
