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Affecting Factors to the service life of steel wire rope in friction hoist
- Time of issue:2022-05-06
Affecting Factors to the service life of steel wire rope in friction hoist
- Time of issue:2022-05-06
Friction hoist is more and more used in underground mining because of its strong lifting capacity, high lifting height, fast lifting speed, low motor power consumption, safe and reliable use and other advantages. The friction hoist drives the lifting container to run in the wellbore by relying on the friction between the lifting wire rope and the friction wheel pad. During operation, the steel wire rope bears the comprehensive action of tensile stress, torsional stress, bending stress, contact stress and various impact loads. At the same time, it is affected by water and moisture in the shaft, resulting in wire breakage, diameter shrinkage, corrosion and other damage to the steel wire rope. When the damage exceeds the standard, it needs to be scrapped or replaced. The service life of hoisting wire rope is affected by many factors. It is necessary to comprehensively consider the design of mine hoisting system and the maintenance during use, so as to improve the working conditions and stress conditions of wire rope and prolong the service life.
1 factors affecting the service life of hoisting wire rope
1.1 mine lifting height
Combined with the use of a large number of friction hoists at home and abroad, the service life of deep well hoisting wire rope is generally shorter than that of shallow well. The reasons are as follows: ① with the increase of well depth, the greater the torsional stress of hoisting wire rope, and the torsional fatigue increases the wire breaking probability of wire rope; ② With the increase of well depth, the terminal load change rate (stress amplitude) of lifting wire rope gradually increases, which accelerates the fatigue failure of wire rope. The lifting heights of the main shafts of zhangxiaolou coal mine and Dongguashan Copper Mine are 1039.6 m and 1094.0 m respectively, and the stress amplitudes reach 10.02% and 11.08% respectively, which is close to the limit value of 11.5% proposed in the literature , which is one of the reasons for the short service life of the lifting wire rope in the main shafts of these two mines, which is only about 6 months.
1.2 D / D ratio
D / D ratio is the diameter ratio of friction wheel to steel wire rope. Article 419 of the coal mine safety regulations stipulates that the ratio of the minimum diameter of the friction wheel and crown wheel of the floor friction lifting device and the friction wheel of the friction lifting device with an encirclement angle greater than 180 ° to the diameter of the lifting steel wire rope shall not be less than 90 when installed in the well and 80 when installed underground; The ratio of the minimum diameter of the guide wheel of the friction lifting device to the diameter of the steel wire rope shall not be less than 80. Similar provisions are also made in article 188.8.131.52 of the safety regulations for metal and nonmetal mines. In the same case, the larger the D / D ratio, the smaller the bending stress generated by the lifting steel wire rope, and the more favorable it is to the lifting steel wire rope; However, the larger the rope diameter ratio, the larger the hoist specification and the higher the equipment cost, so it needs comprehensive analysis and reasonable determination.
1.3 center height of friction wheel and guide wheel
When the lifting wire rope passes through the friction wheel and guide wheel (crown wheel), it shall constantly bear the action of forward and reverse bending stress. Especially for the friction hoist with guide wheel installed on the well tower, if the center height difference between the friction wheel and the guide wheel is small and the lifting speed is too large, the bending stress of the lifting steel wire rope is too late to release, which is easy to cause fatigue and wire breakage of the lifting steel wire rope. The central height difference between the friction wheel and the guide wheel in Dongguashan Copper Mine is 6 m, the lifting speed is 12 m / s, and the service life of the lifting wire rope is only about 6 months. The central height difference between the friction wheel and the guide wheel in zhangxiaolou coal mine is 5 m. when the lifting speed is 10 m / s, the service life of the lifting wire rope is half a year; When the lifting speed is 12 m / s, the service life of the steel wire rope is shortened to 3 months. Tangkou Coal Mine has a lifting height of 1050 m and a lifting speed of 12.36 M / s. It adopts the same triangular strand steel wire rope as zhangxiaolou coal mine and Dongguashan copper mine. However, because it adopts floor friction hoist, the distance between friction wheel and crown wheel is large, the forward and reverse bending stress borne by the lifting steel wire rope has been fully released, and the service life of the lifting steel wire rope is close to 2 years.
1.4 selection of hoisting wire rope
Whether the type selection of hoisting wire rope is reasonable has a direct impact on its service life. The selection of hoisting wire rope mainly includes the following contents.
(1) The surface condition of steel wire rope, such as whether it is coated with antifriction grease, galvanized, etc.
(2) The structural form of steel wire rope, such as the number of strands, the contact form between steel wires in rope strands, the diameter of outer steel wire, whether it is sealed rope or compacted strand rope, etc. For the mine with serious wear of hoisting wire rope, if the outer wire diameter of hoisting wire rope strand is small, it is easy to cause wire breakage due to wear and premature damage of wire rope; When point contact wire rope is selected, the wire rope will be broken due to the large contact stress between wires and strands in the rope strand.
(3) When the steel wire rope is twisted to the deep well, if the steel wire rope is twisted in the same direction, the steel wire in the rope strand will be fatigued and broken due to the violent rotation of the steel wire rope in the shaft.
(4) Strength grade of steel wire rope the higher the tensile strength grade of steel wire rope is, the worse the toughness of steel wire will be, and the ability to resist bending fatigue will be reduced accordingly, which will directly affect the service life of steel wire rope.
1.5 impact load and elastic vibration during operation
During the operation of the lifting steel wire rope, it shall bear the impact load and elastic vibration caused by startup acceleration, braking deceleration, loading and unloading, over winding, tank jamming, tank support, operation error and so on. When the hoist starts to accelerate, if the starting acceleration suddenly rises from zero to the maximum, the starting impact value (starting acceleration change rate) will be very large, resulting in a large dynamic tension in the lifting steel wire rope. Especially for the hoisting system with constant torque braking, under different working conditions such as heavy load hoisting, no-load operation and heavy load lowering, the variation range of braking deceleration is large, and the hoisting system will produce large impact load accordingly, aggravating the fatigue damage of hoisting wire rope.
1.6 manufacturing quality of steel wire rope
The quality grade of raw materials used in wire rope manufacturing, wire drawing, surface treatment, stranding, stranding and other manufacturing equipment and manufacturing process will affect the quality of wire rope. If the manufacturing quality of the lifting steel wire rope is poor, it will break the wire prematurely and directly affect its service life.
1.7 impact on installation, use and maintenance
During the installation or replacement of the lifting wire rope, the new rope collides with sharp objects or the old and new wire rope is clamped and fixed, which will damage the outer steel wire of the new rope strand to a certain extent and become a weak link after the wire rope is put into operation. In addition, the different diameter of the liner rope groove on the friction wheel, the different lifting speed of each rope, or the failure of the automatic tension balance suspension device of the lifting wire rope will cause the stress of a lifting wire rope to be too large and may be damaged in advance. If the cross-section shape of the rope groove of the friction wheel and guide wheel is inappropriate or there are attachments, the lifting steel wire rope will also be squeezed, resulting in additional contact stress, which will cause damage to the lifting steel wire rope.
2 measures for prolonging the service life of lifting steel wire rope
The hoisting wire rope is inevitably affected by various factors in the use process. However, through the reasonable design of the hoisting system and the selection of wire rope, strengthening the use and maintenance management, improving the operation conditions of the hoisting wire rope, seeking advantages and avoiding disadvantages, the service life of the wire rope can be extended to a certain extent.
2.1 reasonable design of lifting system
Scientific and reasonable design should be carried out for new mines, and the following aspects should be paid attention to.
(1) When conditions permit, adopt larger D / D ratio and smaller pad specific pressure to reduce the bending stress and contact stress of hoisting wire rope.
(2) When using the well tower hoist, the center height difference between the friction wheel and the guide wheel should be reasonably selected within the range of 0.5 ~ 1.0 times the lifting speed or 200 ~ 400 times the diameter of the lifting steel wire rope (between the larger value calculated according to the lower limit of the two methods and the smaller value calculated according to the upper limit of the two methods, reasonable value), so as to slow down the fatigue damage of the lifting steel wire rope caused by forward and reverse bending.
(3) On the premise of meeting the anti-skid calculation requirements, the lifting wire rope on the friction wheel adopts a small surrounding angle to reduce the bending fatigue degree of the lifting wire rope.
(4) Pay attention to the impact limit of the lifting system. Commonly used are rectangular acceleration / deceleration control and trapezoidal acceleration / deceleration control, as shown in Figures 1 and 2 respectively. Trapezoidal acceleration / deceleration control curve shall be adopted, and the change rate of acceleration / deceleration shall not be greater than 0.3 M / S3, so as to reduce the dynamic tension and elastic vibration of lifting steel wire rope during acceleration / deceleration. Constant deceleration braking should be adopted for the hoisting system of new mines, especially deep mines, which can effectively control the dynamic tension of hoisting wire rope in the process of emergency braking and avoid sliding of hoisting wire rope at the same
Figure 1 rectangular acceleration / deceleration control curve
Fig. 2 trapezoidal acceleration / deceleration control curve
(5) When conditions permit, the heavy tail rope hoisting system is preferred for the main shaft hoisting, which can reduce the starting torque, starting impact and braking impact.
(6) When the large auxiliary shaft goes up and down the large equipment, the mechanical or Electrical Tank locking system shall be adopted to reduce the elastic impact and vibration on the lifting steel wire rope caused by the large equipment entering and leaving the cage; When the deep well skip is loaded with large load, the deep well skip support system is configured in the loading station to reduce the elastic dynamic tension of the lifting steel wire rope during loading.
2.2 reasonable selection of steel wire rope
The hoisting wire rope shall be selected according to GB 8918-2006 steel wire rope for important purposes and GB / T 33955-2017 steel wire rope for mine hoisting. On the premise of meeting the requirements of safety factor, the tensile strength of lifting steel wire rope should not exceed 1870 MPa. The steel wire rope with excessive strength has poor toughness and fatigue resistance. For the mines with large water pouring in the shaft and strong acid-base corrosion, the galvanized steel wire rope with synthetic fiber core with good acid-base corrosion resistance shall be selected. For mines with a lifting height of more than 800 m, interactive twist steel wire rope with good rotation resistance or multi-layer non rotating steel wire rope should be selected. For example, the main shaft of Xieqiao coal mine uses alternating twist steel wire rope, which has a longer service life than that of Zhangji coal mine and Dingji Coal Mine. The comparison is listed in Table 1.
Table 1 Comparison of service life of three kinds of hoisting wire ropes
2.3 ensure the manufacturing quality of steel wire rope
The quality of lifting steel wire rope has a great impact on its service life. The wire drawing, twisting process, rope making steel wire batch number, heat treatment process, hemp core quality, pre tensioning process, friction increasing grease quality and dip coating quality of steel wire rope will all affect the quality of lifting steel wire rope. Try to use the steel wire rope manufactured by the manufacturer with mature technology, reliable quality and good reputation, and avoid the use of inferior rope; At the same time, do a good job in the mobilization acceptance and the test before hanging the rope, and eliminate the use of unqualified steel wire rope.
2.4 avoid damage during installation or replacement
When installing or replacing the lifting wire rope, protective measures shall be taken to avoid damage to the lifting wire rope. The traditional method of changing rope is to use the old rope with the new rope. The old rope and the new rope are fixed with a clip every 20 ~ 25m, which will damage the part of the new rope. In recent years, many mines such as Zhuji coal mine, Zhaoyuan Linglong gold mine and Beiminghe Iron Mine have used rope changing vehicles developed in China to replace the lifting wire rope, which avoids the damage to the new rope caused by traditional methods and is conducive to prolonging the service life of the wire rope. In addition, there are few rope changing operators, low labor intensity of workers and short rope changing time, which meets the requirements of "mechanized personnel replacement and automatic personnel reduction" of the State Administration of work safety, It is worthy of reference and promotion in domestic mines.
2.5 keep the tension of steel wire rope balanced
Strengthen the daily inspection and maintenance of the automatic tension balancing device of the lifting steel wire rope to ensure that it is intact and effective. First, avoid leakage of hydraulic cylinder of suspension device; Second, the rope should be adjusted and pressed frequently to ensure that the extension length of the piston rod of the hydraulic cylinder of the automatic steel wire rope tension balancing device is uniform and within the effective range, so as to make each rope bear the force evenly during operation and avoid excessive stress on a single rope.
2.6 strengthen the maintenance and management of rope groove lining
There shall be proper clearance between the rope groove of the friction pad and the steel wire rope. The radius of the rope groove shall be about 7.5% larger than the nominal radius of the steel wire rope, and the rope groove shall form an annular support for the steel wire rope with 33% circumference (contact angle 120 °) to reduce the extrusion of the steel wire rope. The relationship between lifting wire rope and rope groove is shown in Figure 3. Before the liner rope groove is worn to a certain extent or a new rope is replaced, the rope groove shall be turned in time to make the rope groove have good cross-section fit and good contact with the lifting steel wire rope, and the diameter deviation of each rope groove shall be controlled within 0.8 mm.
2.7 strengthen the use and maintenance management of lifting system
Strengthen the use, inspection and maintenance management of the hoisting system, including mechanical part, braking system, electric control system, steel wire rope, shaft tank way, tail rope isolation device, shaft switch, etc., so as to keep all parts of the hoisting system in good condition, avoid pipe loss and disrepair, avoid accidents such as over winding and sports car, avoid falling objects in the shaft, and avoid accidental damage and additional stress of the hoisting steel wire rope. In the cold winter in northern China, the viscosity of friction increasing grease on the lifting steel wire rope increases and adheres to the lifting steel wire rope. When passing through the friction wheel, it is easy to cause the lifting steel wire rope to fall off the groove, so it should be cleaned in time; At the same time, it is necessary to avoid shaft icing and prevent ice falling from damaging the steel wire rope.
2.8 accurately detect the damage of hoisting wire rope
Carry out nondestructive testing on the lifting wire rope in use, timely find its defects and hidden dangers, and appropriately prolong the service life of the lifting wire rope on the premise of ensuring safety, so as to avoid premature scrapping and cost waste of the wire rope. In recent years, the domestic aerial ropeway industry has been judging whether to scrap the steel wire rope according to the detection results of the Russian intros magnetic steel wire tester. Based on the strong magnetic principle, this instrument can directly display the damaged part of the steel wire rope, the loss of load area and the number of broken wires in real time, and the detection accuracy is relatively high. Domestic Huainan Guqiao Coal Mine, SDIC Xinji No. 1 mine, Lilou iron mine, Jinchuan Longshou nickel mine and other units have adopted the tester to detect the steel wire rope.
The hoisting wire rope of friction hoist bears the comprehensive effect of various stresses in the process of use. Various effective measures should be taken to reduce the stress of the hoisting wire rope in the process of use. In new mines, in particular, the defects of the design of the hoisting system should be avoided. Through the reasonable design of the lifting system, the correct selection of the lifting wire rope, good maintenance and accurate and reliable state detection, the service life of the lifting wire rope can be effectively prolonged, which has strong practical significance for reducing the production cost of the mine.
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