The correct selection, use, and maintenance of elevator traction wire ropes are not only related to the safety and normal operation of elevators, but also crucial for extending their service life.

1. Selection of Elevator Wire Rope

A steel wire rope is composed of strands, strands of steel wire, and a core. Elevator wire rope is made by twisting a single strand around the core in a spiral shape. Usually, high-quality carbon steel with grades 50-65 or 60Si2Mn steel wire is used. For safety reasons, elevator steel wire ropes are made of special or No.1 steel wire, with a diameter limit between 0.3-1.3mm. The commonly used elevator traction steel wire ropes include Xilu type (X-type) and Walingtun type (W-type). At present, domestically produced elevators commonly use Xilu style 8 or 6 steel wire strand steel wire ropes, with 8X (19) being more commonly used.

1.1 Examples of Wire Rope Marking Recognition

Taking a passenger elevator with a rated load capacity of 1000kg as an example, the traction steel wire rope adopts a right cross of 8X (19) -16-140, where 8 is the number of rope strands, X is the Xilu style, (19) is the number of steel wires in each rope strand, 16 is the nominal diameter (mm) of the steel wire rope, 140 is the tensile strength (kgf/mm2) of the steel wire rope, and the right cross is the twisting of the steel wire in the direction of the right cross between the rope strand and the rope strand. Domestic traction steel wire ropes are all right angled.

1.2 Rope Core

The elevator steel wire ropes are all made of fiber rope cores soaked in oil, which support and fix the position of the rope strands to improve the contact between the ropes, reduce impact loads, and serve as an oil storage tank for long-term lubrication of the steel wire ropes, ensuring good lubrication of the steel wires.

1.3 Structure and characteristics of Xilu style (X-type) steel wire rope

The cross section of the steel wire rope of the Xilu style elevator is 1+9+9 per strand, consisting of 19 steel wires including the core, first layer, and second layer: 1 central steel wire, ф 1.2mm, 9 inner steel wires, ф 0.6mm, and 9 outer steel wires, ф 1.05mm. The outer wire diameter is larger than the inner wire diameter, so it is also known as outer thick steel wire rope. Its characteristics include the same number of inner and outer steel wires per strand, but with different diameters. The outer layer is embedded in the inner groove, and the twisting pitch of the multi-layer steel wires is equal. The structure is tight and firm, and it is not easy to unwind. The outer layer of thick steel wire increases wear resistance, while the inner layer of thin steel wire improves flexibility, which is conducive to mutual sliding during bending, thus improving the flexibility and service life of the steel wire rope Parallel wire contact between layers of steel wires results in good fatigue resistance of the steel wire rope, good wear resistance between the internal wires, increased contact area, and reduced contact stress.

2. Safety factor of traction steel wire rope

From a safety perspective, elevators are required to have a certain number of steel wire ropes and a safety factor. GB7588 has specific regulations for K-static: elevators using three or more traction steel wire ropes have K-static=12; Elevators using two traction steel wire ropes, with K static=16, typically require at least 4 steel wire ropes for passenger, cargo, and medical elevators, with a safety factor of 12; There should be no less than 2 utility ladders with a safety factor of 10.

There are two types of loads on the steel wire rope during operation, static and dynamic, but the main factor affecting the service life of the steel wire rope is still static load. For the sake of calculation simplification, only practical calculations are made for static load.

2.1 Selection of Steel Wire Rope Diameter

In order to improve the strength and prolong the service life of elevator steel wire ropes, the diameter of the elevator steel wire rope is usually selected according to the formula D/d ≥ 40, where d is the diameter of the steel wire rope not less than 8mm; D is the diameter of the traction wheel;

2.2 Calculation of Safety Factor

In the formula, K represents the safety factor of the elevator wire rope; 

SP - breaking force of elevator steel wire rope;

M - the magnification determined by the elevator wire rope winding method, where m=1 for 1:1 winding and m=2 for 2:1 winding;

Q - rated load capacity of the elevator;

∑W—Wj+Wg+Wp

In the formula, Wi represents the self weight of the elevator car; Wg is the weight of the steel wire rope between the car and the traction wheel when the car is at the lowest level; Wp is half of the tension load of the balance rope (when there is a balance compensation device).

3. Use and maintenance of steel wire rope

3.1 Inspection of Steel Wire Rope

The condition of the elevator wire rope is directly related to the safety of the equipment and passengers, and must be given sufficient attention. Careful observation and inspection should be carried out during work. The inspection content includes: (1) checking the number, location, and twist length of broken wires; (2) Regularly measure the diameter and wear of the steel wire rope with a vernier caliper, in addition to visual inspection, to assess the thinning of the rope diameter; (3) Check the tension of the elevator wire rope, and the difference in tension between each rope should not exceed 5%; (4) Lubrication, cleaning, and corrosion of steel wire ropes; (5) The condition of the rope head and its combination, and whether there are any other abnormal conditions along the entire length, such as abnormal elongation changes of the rope.

3.2 Wear and deformation of steel wire rope

According to usage experience, the phenomenon of sudden breakage of elevator wire ropes under normal working conditions is rare, and their damage is generally formed gradually due to wear, bending fatigue, corrosion, or external trauma during long-term operation. Special attention should be paid to the inspection of wear and corrosion. Wear includes the wear on the surface of the steel wire rope, between strands, and between wires.

Mechanical wear mainly includes three types: uniform external wear, deformation wear, and internal wear, as shown in Figure 2 (please click). A is pure mechanical wear. Generally speaking, elevator wire ropes wear out slowly during use due to their higher hardness than the rope groove. However, due to tension, groove type, and steel wire rope slipping, eccentric wear, and rolling in the groove, wear occurs with the rope groove, which is normally uniform. B is deformation wear, which refers to the local wear of elevator steel wire rope in a certain section. Due to the chronic displacement of elevator steel wire rope and pulley or the severe vibration and impact of elevator steel wire rope on pulley, the elevator steel wire rope is locally squeezed and deformed; Although the cross-sectional area of the elevator steel wire has not decreased, the steel wire material at the local compression point has been damaged and is prone to breakage. C is internal wear. Due to the frequent bending of elevator steel wire ropes, there is relative displacement between the steel wires in the strands, and the contact pressure between strands increases, causing local indentation on the steel wires between adjacent strands. Over time, they will break due to stress concentration. As mentioned above, the wear and thinning of elevator steel wire ropes will result in a smaller cross-sectional area of the elevator steel wires inside the ropes, reducing their tensile strength. In severe cases, the elevator steel wire ropes should be scrapped and replaced. According to experience, when there is an internal breakage in the elevator wire rope, a "click" sound can be heard during operation.

3.3 The situation of steel wire rope lying in the rope groove

Check whether the working surface of the rope groove is smooth and whether the depth of the elevator steel wire rope lying in the rope groove is consistent. The method is to press the ruler tightly against the outer circumference of the traction wheel along the axial direction, and then measure the distance from the top of the steel wire rope in the groove to the ruler. When the difference reaches 1.5mm, the vehicle should be reloaded or the wheel rim should be replaced.

Check if the elevator wire rope has fallen to the bottom and slipped in the groove. When the gap between the wire rope and the groove bottom decreases to 1mm, the groove needs to be re turned. The thickness of the rim of the rope groove below the incision should not be less than ф 12.5mm when the diameter of the steel wire rope is ф 13mm; When the diameter of the steel wire rope is ф 16mm, it should not be less than ф 15.5mm.

3.4 Corrosion of Elevator Wire Rope

Elevator wire ropes may rust during use, leading to a decrease in mechanical properties, thinning of wire diameter, and loosening between strands, resulting in brittle fracture. This type of fracture is an "avalanche" fracture, which is more dangerous than ordinary wire breakage or wear. During maintenance, special attention should be paid to the corrosion of steel wire ropes, and careful observation should be carried out. If severe corrosion is found to have formed pits or loose outer steel wires on the rope strands, regardless of whether the wire is broken or the rope diameter has become thinner, it should be replaced; If "red oil" is found on the steel wire rope, it indicates that the rope core is free of oil and rusted internally. Attention should be paid, and if necessary, the rope head can be chopped off to check the internal corrosion of the steel wire rope. The method to prevent rusting of steel wire ropes is to apply oil protection on the ropes.

3.5 Analysis of broken wires

(1) Overloaded wire breakage. The fracture of elevator steel wire rope caused by overload or impact load shows cup-shaped plastic shrinkage. Due to the high safety factor of elevator steel wire rope, this type of wire breakage is rare; (2) Fatigue breaks out. The outer layer of steel wire that appears on the largest side of the bending program in the stock is a broken wire caused by metal fatigue, with a flat fracture shape. (3) Wear and tear, broken wires. Friction and slippage between the steel wire rope and the traction wheel cause wire breakage, which occurs when the steel wire is severely worn and occurs on the outer layer of the steel wire. The two sides of the fracture are inclined and the fracture is flat; (4) Corrosion and broken wires. Serious rusting has occurred. The fracture surface is uneven and presents a pointed shape; (5) Cut the broken wire. Caused by being forcibly pulled apart or subjected to significant external force such as impact or compression. The fracture surface is in a shear state; (6) Twist and break the wire. This type of wire breakage rarely occurs during normal use, and only occurs when the steel wire rope becomes loose and twisted. The fracture shape is flat and smooth.

3.6 Scrap and replacement of steel wire rope

Pay attention to the following points when using the above table:

(1) Although the surface of the steel wire has not been damaged, if the number of broken wires reaches the corresponding number in the table, it should be scrapped;

(2) When the surface wear or corrosion of the steel wire accounts for 30% of the diameter, even if the number of broken wires is 0, it should be scrapped;

(3) If the surface wear percentage has been reached, but the corresponding number of broken wires has not been reached, it will not be scrapped;

(4) When the elevator steel wire rope breaks, it should be scrapped;

(5) When the elevator steel wire rope is twisted in the same direction, the allowable number of elevator steel wire fractures is half of the values in the table;

(6) Estimation of twist length: Generally, a twist length of 6.5 times the rope diameter is used, for example, the twist length of 8X (19) Xilu style steel wire rope with 8 strands of Φ 16mm is about 6.5 × 16mm=100mm;

(7) The diameter of the elevator wire rope should be scrapped if it decreases by 10%.

(8) The surface of the elevator wire rope is severely corroded, blackened, spotted, pockmarked, and the outer wire is loose, and must be replaced immediately;

(9) When replacing elevator wire ropes, all elevator wire ropes in the same group should be replaced together;

(10) During use, if the lubricating oil inside is squeezed out like sweating, it indicates that the elevator wire rope has reached an overloaded state. If this phenomenon occurs, it should be checked immediately, and if necessary, a new rope should be replaced;

(11) Keep the elevator wire rope clean. If there is dirt such as sand on the surface, use kerosene to wipe it clean (gasoline is strictly prohibited);

(12) For steel wire ropes with unequal diameters, the number of broken wires refers to the number of fine wires, where one thick wire is equivalent to 1.7 thin wires.

3.7 Lubrication of Steel Wire Rope

Generally speaking, in places where the diameter of the traction wheel is large and the temperature is dry, the steel wire rope still has sufficient lubricating oil after 3-5 years of use, and there is no need to add new oil. But no matter how long it is used, lubricating oil must be added whenever rust or dryness is found on the elevator wire rope.

3.7.1 Lubrication method

On the surface of the steel wire, use a bristle brush to evenly apply a special ET dilution type elevator steel wire rope grease in the opposite direction of the steel wire rope's running direction, or use No. 20 engine oil. The advantage of this method is that it is simple, does not require heating, and is easy to apply. However, it should be noted that not too much oil should be poured, and there should be slight penetration lubrication on the rope surface. Do not apply calcium based grease. B Heating coating. First, use a wire brush to remove dirt and residue from the rope, and clean it with kerosene (gasoline cleaning is strictly prohibited). Heat the lubricating oil (a mixture of graphite and Vaseline) to above 80 ℃ and apply it. The lubrication of the steel wire rope should be moderate, and too much oil should not be applied to the surface. Otherwise, the drag force will decrease, and in severe cases, the load torque will not be balanced, resulting in the elevator running out of control and causing accidents such as top and bottom collision; The elevator wire rope slips in the groove, like a saw, causing severe wear on the groove and the wire rope itself.

3.7.2 Characteristics required for lubrication and smoothness

Free from acid, alkali, moisture, and moisture absorption; Not easy to dry in the atmosphere, does not harden (crack) at low temperatures, and does not lose at high temperatures; Having appropriate viscosity to prevent oil spillage during elevator wire rope operation; Has the characteristic of being able to penetrate into the elevator steel wire rope, between the strands, and the rope core.