Basic facts about steel ropes

Basic facts about steel ropes

A rope is made of several strands (usuallu 6 or 8) wound around a core. The core can be fibrous or made of steel. Each strand consists of several wires (6 – 61) wound around core, and in most cases it is made of steel wire, rarely the core is fibrous.

Basic elements of round steel rope are shown in picture no. 1 below.

From the picture, it is visible that certain number of wires was twisted according to the imposed geometric schedule, and certain number of strands twistwd around the core per the imposed geometric schedule in to a rope.

The most usual shapes of ropes

Ropes can be, conditionally, classified according shapes, as follows:

• spiral ropes
• normal ropes
• special ropes

Spiral ropes

This is the simple type of ropes made of one central wire and six or more surrounding wires of the same diameter twisted around the central wire in one or more layers.

The most often used shapes in car industry are: 1x3; 1x7; 1x12; 1x19; 1x25; 1x35;

Normal ropes

Distinctive characteristic of these ropes is that they are made of one dimension wires and the rope consists of 6 or 8 strands. The most often shapes are: 6x7; 6x19; 6x37; 6x12; 6x14; etc. These are used in mechanical and civil engineering, fishery, forestry etc.

Special ropes

These ropes consist of wires withseveral different dimensions, were pitch evevation is the same in all layers. The more wires of diffrent dimensions are used, the bigger metal cross – section of the rope is obtained and bigger complexion what finally gives the rope better resistance rupture to wear. The most represented shapes of special ropes are following.

a) Seal construction

Wires if samaller cros – section are used in the first layer and bigger cross – section in second, while pitch elevation is the same. Since the external layer is made of thicker wire these ropes have bigger resistance to friction, and for that reason they are usually used in conditions were external friction is prominent.

b) Warrington construction

Inner layer of strands is made of wires of the same diameter, while external consists of double number of thick and thin wires alternately placed. All wires in strands have pitch elevation.

c) Fuller construction

For better filling of these constructions in inner lazer and are used thinner, so called “Fuller” wires, hich are obtaining bigger metal cross – section and strength of rope. Pitch elevation in all layers is the same.

d) Non – rotating ropes “Herkules”

Main characteristic of these ropes is non – rotating, so they are used in situations one end of rope is free, i.e. for different cranes. Non – rotation is achieved by different direction of strands in alternate layers. The most usual shapes are: 17x7; 18x7; 34x7; 36x7.

Rope diameter measuring

Rope diameter is axil to the diameter of a rope crros – section cricle. Picture below shows corect and incorrect way of diameter measuring.

Correct		Incorrect

Following rules are to be respected in rope diameter measuring:

• rope diameter is to be measured by micro – meter caliper, in two points at least im distant and in the points in two perpendicular directions,
• The smallest and the biggest result of the measurement should not differ more than 4% from the nominal diameter of the rope,
• average value of four measurings is the real diameter of the rope,
• diameter should be measured on a straight, not curved part of rope in not loaded condition.

Pitch and direction of rope pleat

Steel ropes are made by cross or parallel twisting. In parallel (longitudinal) twisting direction of strands in rope and wires in strand is the same. Upon this, we distinguish longitudinal right Z/Z and longitudinal left S/S twisting. In cross twisted ropes direction of rope strands and wires in strands are different. Thus, there is cross right S/Z and cross left Z/S twisting.

Parallel twisted ropes ( Z/Z , S/S ) are more resistant to wear since they have bigger contact surface, but these ropes can be used only in conditions were both ends are fixed and rotating is prevented.

Cross twisted ropes ( S/Z , Z/S ) have smaller exposed to friction, so they are faster worn. On the other hand these ropes are easier to handle.

Core

Steel ropes are made with fibrous and steel core, which has basic task to provide regular order of strands in rope. Following materials are used for fibrous cores: jute, hemp, polypropilene. Fibrous cores are lubricated and their function is to obtain constant diameter of rope, flexibility and shelf life. Steel core is made of steel wires with same characteristic as wires used for strands of rope. Construction of steel core depends on type, diameter and purpose od steel rope and can be made in different manners, as follows:

• one wire as central one in twisted rope (strand),
• strand as steel core im small diameters ropes,
• steel core as several twisted strands usually of construction 7x7.

Ropes with steel core are applied were high rupture force as well as in high temperature conditions.

Unravellable ropes (Trulay)

All ropes manufactured in UNIS-USHA factory in Visegrad are unravellable (“trulay”). Since rope is made of six or more twisted strands it tends to unravel when cut. But, ropes made in our factory will not ravel due to application of the special procedure of preformation and the advantages are following:

• these ropes are released of internal tension
• they do not tend to make loops and are easier to handle
• they can be cut without previous binding
• they are easy to pleat, i.e fold
• without any problem they are coiled on and other devices for rope use.

Packing

Generally, ropes are packed on wooden transport drums in standard YUS N.CO.505 sizes. Upon special request of buyer, we deliver certain length of ropes in bundle from.

Characteristics of rope

Our factory UNIS-USHA Steel rope factory in Visegrad produces ropes as per YUS, DIN, BSS, AFNOR, ISO, API, GOST and other standards, which are used in industry, mining, shipbuilding, oil industry, etc. We issue faktory attestation certificates, and on special requests of buyer we obtain attestation of JR LLOYD or any other recognized institution for verification. General characteristics of rope are:

1. Rupture force – resistance to rupture

The first thing to know is what the load is expected for the rope to support. In order to get total load, loads, caused by sudden start and braking, by shock, high speed, friction, bearings, etc. should be added to the actual load. In normal circumstances the secrity factor 5-6 is added to this total load. For special purposes (transport of special loads or people) security factor 8-9 is added to total load. On the basis of thus calculated, requested rope load it is possible to choose the diameter, shape – construction and core which can guarantee minimal rupture force higher then calculated load. Minimal repture force is defined as strongest force which causes rupture of rope during testing.

2. Corrosion resistance

Corrosion of rope occurs when the rope is exposed to wather, different weather conditions or other aggresive evaporations. In order to reduce corrosion ropes can be:

• made of galvanized wires
• protected by lubricants

Protection with lubricants is applied during produktion as well as during explotation.

3. Compression resistance

Damage of rope caused by compression for following reasons:

1. pressure of rope itself on a pulley tackle
2. incorrect dimensions of tackle groove or cylinder

Compression effect can be reduced by proper selection of core, and it is completely eliminated by use of metal core rope.

4. Friction resistance

It is normal to expect friction when operating with rope due to the contact with hard surfaces of pulley tackle, cylinder or other hard basis. The same phenomenon is present inside the rope when it is loaded or bents in use. Removal of metal from external al well as from inner wires is friction effect. Rope with smaller number of strands ( with 6 in comparision to 8 strands ) with thicker wires in external layer will have higher resistance to friction, but it will be less flexibile. Also, parallel twistwd ropes (S/S and Z/Z) have higher resistance to fiction since contract of wires in rope is smaller.

5. Resistance to inflection

The rope can be used for purposes where it is moving over pulley tackles, , cylinders, rollers, and has to be coiled and uncoiled several times. This results in fatigue of material to inflection, which increases in proportion to rope working speed. Fatigue to inflection can be reduced by proper choice rope – pilley tackle relation, tension and shape of rope. Inflection relation rope/pulley tackle D/d where D= pulley tackle or roller diameter, and d= nominal diameter of the rope. The most usual relation, for very flexibile rope, is 19:1, and for 24:1. If construction of the equipment allows relation can be even more then 40:1. General recommendations for pulley choice are as follows.

Storage

A rope has to be stored indoor in good ventilated room isolated from humidity, dust and different evaporations. During storage period external rope layer should belubricated evry 3 months. Also, once in 3 mounts drum with rope should be turned for 180° in order to avoid leakage of lubricant from the layer. Floor of the storage should be comented to prevent insects to reach wooden drum.

Handling

For proper handling and appropriate loading and unloading crane or fork-left should be at disposal. For unwinding of rope, at least a primitive device should be available, as well as a simple breaking device, for control of constant tension of rope during uncoiling. A board or a beam which obtain friction on rope drum can be used to prevent twisting and appearance of loops while unwinding. If, when installing a rope it bents, pulley tackle of diameter 36 times bigger then rope diameter will be used. The greatest attention should be paid on cutting a rope. Make sure, before cutting, that the rope is tied in two places at least, so that ends are secured from ravel. If cutting was not performed properly, some strands can be pulled, so when loaded the load will not be evenly disposed what effects working span of the a rope. Cutting is performed by grinder.

Care and maintenance

• Till installation of rope it should be properly stored and checked whether it was damaged during transportation and if the damage had effects on working performances.
• During use of rope protect from corrosion regularly with appropriate lubricant.
• Make sure that only appropriate pulley tackles, rollers and anchors and used.
• Periodically check “Trulay” rope wires for braking. It is difficult to see because this rope is performatted and the broken wire does not appear especially when protected by thick layer of lubricant.
• Also periodically, check the damage degree, fatigue wear and balance of rope.