I. Introduction 

friction hoist plays a vital role in mine transportation, and whether the tension of the first rope is balanced directly affects the safe operation and service life of the hoist. Accurately checking the tension of the first rope and ensuring that it is in a reasonable range is one of the key links in the maintenance of the mine hoist. This article will elaborate the friction hoist first rope tension inspection method experience. 

Second, the importance of friction hoist first rope tension 

1. Improve safety 

unbalanced headline tension can cause the lifting vessel to tilt during operation. In the process of lifting, if the container is seriously tilted, it may collide with the wellbore equipment (such as tank channel, etc.), which will not only damage the wellbore equipment and lifting the container, but also cause more serious safety accidents. Excessive tension difference may make the tensile force of part of the wire rope exceed its ultimate strength, increasing the risk of wire rope fracture. Once the first rope breaks, the consequences will be unimaginable during the lifting process of high-speed operation.

2. Service life of equipment

the uneven tension will cause the friction lining to be overstressed locally. Friction liner is a key component of the hoist to generate friction, and excessive local force can easily lead to increased wear of the liner and shorten its service life. And the uneven wear of the liner will also affect the distribution of friction between it and the wire rope, and further affect the normal operation of the hoist. For the wire rope itself, uneven tension will cause uneven wear. Part of the wire rope may be due to excessive force and the fatigue fracture of the steel wire, scrapped in advance, increasing the maintenance cost of the equipment.

III. Inspection Methods

(I) Manual observation method

1. Static observation

vessel level inspection: When the lifting vessel is in a static state (such as at the wellhead or bottom hole loading position), the level of the lifting vessel is observed to preliminarily determine whether the tension of the head rope is balanced. A horizontal mark may be provided at the edge of the container or at a specific position to visually observe whether the container is tilted. If the container is obviously tilted, there is a big difference in the tension of the head rope. However, this method is relatively crude and can only be used as a preliminary inspection method.

Observation of rope spacing: when the container is stationary and the head rope is slack, observe the spacing between the head ropes. If the tension is not uniform, the degree of slack of the wire rope will be different, and the spacing will also be different. For example, a wire rope with low tension will be relatively more slack, and its spacing from adjacent wire ropes may be greater than other locations.

2. Dynamic observation

observation of container swing during Operation: Observe the swing of the lifting container during the operation of the lifting machine. If the headline tension is not balanced, the vessel will oscillate irregularly in the wellbore. Field staff can stand on an observation platform near the wellbore (to ensure safety) and observe the amplitude and frequency of the swing of the container as it passes through this position. Generally speaking, the side where the swing amplitude is large and frequent, the corresponding head rope tension may be small.

Listen to the sound to judge: When the hoist is running, the unbalanced tension may cause the friction sound between the wire rope and the sheave or other parts to be abnormal. Experienced maintenance personnel can judge by listening to the sound. For example, when a wire rope with too little tension comes into contact with the sheave, there may be intermittent slight beating, emitting a "click" sound different from normal operation.

(II) Measuring method of hydraulic tension meter 

1. Measurement principle

the hydraulic tensiometer is designed based on Pascal's law. It closes the hydraulic oil in an elastic element (such as a piston cylinder). When the tension of the wire rope acts on the force-bearing part of the tension meter, the hydraulic oil will produce corresponding pressure changes. By measuring the pressure of the hydraulic oil and according to the calibration coefficient of the tensiometer, the tension of the wire rope can be accurately calculated.

2. Measurement steps

install the tensiometer:

first, stop the lifting container at a suitable location (such as the wellhead or the bottom of the well) and ensure that the wire rope is in a slack state. Then install the hydraulic tensiometer on the headline. When installing, pay attention to the good contact between the tensiometer and the wire rope, and the connection is firm to prevent loosening or displacement during the measurement process.

Measurement records:

start the hoist, gradually tighten the wire rope, and observe the reading of the hydraulic tension meter. When the wire rope reaches the normal operating tension, record the reading of each tensiometer. Generally, multiple measurements should be made. Before each measurement, the tensiometer should be zeroed and measured under different operating conditions (such as no-load, half-load and full-load) to obtain comprehensive data.

Data analysis:

analyze the measured data and calculate the tension difference between the headstrings. Generally, the tension difference is required to be within the specified range. For example, for multi-rope friction hoists, the tension difference should not exceed 5% - 10% of the average tension (the specific value is determined according to the model of the hoist and relevant standards). 

(III) Vibrating wire sensor measurement method 

1. Measurement principle

the vibrating wire sensor measures the tension by using the relationship between the frequency of the vibrating wire and the tension it is subjected. When the tension of the wire rope acts on the sensor, the vibrating wire inside the sensor will be deformed, and its vibration frequency will also change. By measuring the frequency change of the vibrating wire, the tension of the wire rope can be calculated according to the pre-calibrated frequency-tension curve.

2. Measurement steps 

sensor Installation:

similar to the hydraulic tension meter, first stop the lifting container at a suitable position to relax the wire rope, and then install the vibrating wire sensor on the head rope. The installation of the sensor should be carried out in accordance with the manufacturer's instructions to ensure that the installation position is accurate and the signal transmission line is well connected.

Data acquisition and processing:

during the operation of the hoist, the signal of the vibrating wire sensor is collected by the supporting data acquisition system to obtain the frequency data of the vibrating wire. These data are transferred to the computer software, and the software automatically calculates the tension value of each rope according to the pre-stored calibration curve. The tension change can be monitored in real time, and the tension change curve can be automatically generated, which is convenient for maintenance personnel to analyze the dynamic change law of tension. 

(4) Electromagnetic induction tension detection method

1. Measurement principle:

electromagnetic induction tension detection is based on the principle of electromagnetic induction. When there is a current through the wire rope (a weak alternating current can be applied by an external excitation device), a magnetic field will be generated around the wire rope. When the tension of the wire rope changes, its magnetic permeability and other electromagnetic characteristics will also change. The change of the magnetic field is detected by the induction coil set around the wire rope, and the tension information of the wire rope can be obtained through signal processing and conversion. This method is non-contact and has little interference with the physical state of the wire rope.

2. Measurement steps: 

first of all, it is necessary to install an electromagnetic induction detection device, including an excitation coil and an induction coil. The excitation coil is correctly wound on the wire rope to ensure that the current can be effectively generated in the wire rope. The induction coil should be installed in a suitable position to accurately receive the signal generated by the change of the magnetic field around the wire rope. After turning on the detection system, calibrate the signal. Because different wire rope material, diameter and other factors will affect the electromagnetic characteristics, it is necessary to calibrate according to the specific wire rope parameters. During the operation of the hoist, the signal of the induction coil is collected in real time, and the tension curve of the wire rope is obtained by analyzing the signal processing software.

3. Applicable scenarios and advantages and disadvantages: 

This method is suitable for long-term dynamic monitoring of wire rope tension. The advantage is that it is non-contact and does not need to be installed on the wire rope like a hydraulic tensiometer or a vibrating wire sensor, which may hinder the normal operation of the wire rope (although this obstacle is small). And it can be continuously monitored without stopping the operation of the hoist. However, the equipment cost is relatively high, and there are certain requirements for the electromagnetic environment. In the mine environment with strong electromagnetic interference, the detection accuracy may be affected.

IV. Practical Experience

(I) Combination of regular inspection and dynamic monitoring 

1. Regular inspection plan 

according to the use of mine hoist frequency, load conditions and other factors, a reasonable first rope tension regular inspection plan. Generally speaking, for the main hoist, manual observation and inspection shall be carried out at least once a month, and accurate measurement by hydraulic tension meter or vibrating wire sensor shall be carried out once a quarter. For the auxiliary hoist, the inspection cycle can be appropriately extended, but it should not be less than a manual observation inspection every two months, and an accurate measurement every six months.

2. Dynamic monitoring system settings

install an online monitoring system to monitor the tension of the headline in real time using vibrating wire sensors or other advanced monitoring technologies. In this way, abnormal changes in tension can be found in time, for example, tension changes caused by unexpected situations such as uneven ore loading during the lifting process. Once an abnormality is found, the system can immediately issue an alarm to remind operators and maintenance personnel to take measures.

(2) Consider the impact of environmental factors on the inspection results. 

1. Temperature factor

temperature has a certain effect on the tension of the wire rope. When the temperature is low, the wire rope will shrink and the tension may increase; When the temperature is high, the wire rope will stretch and the tension may decrease. When performing a tension check, record the ambient temperature at the time, and consider the temperature factor when analyzing the data. For example, if the tension measured in winter is greater than in summer, it can be considered a normal phenomenon caused by temperature changes within a reasonable range.

2. Wellbore drenching factors 

water in the shaft may cause the surface of the wire rope to rust or the grease to be washed away, increasing the friction between the wire rope and the liner or other components. This affects the distribution of tension and may lead to inaccurate measurements. In the case of water drenching in the wellbore, it is necessary to strengthen the cleaning and lubrication of the wire rope, and when checking the tension, special attention should be paid to the wire rope in the drenching part, and if necessary, multiple measurements should be made to obtain accurate data. 

(III) Adjust the tension in time according to the inspection results

1. Tension adjustment method

if the tension of the head rope is found to be unbalanced through inspection, it can be adjusted in a variety of ways. A common method is to increase the tension of the less tensioned wire rope by adding a weight to the suspension device. When increasing the weight, it should be carried out step by step, and the tension should be measured again after each increase to prevent excessive adjustment. Another method is to balance the tension by adjusting the suspension length of the wire rope, which requires professional tools and technicians.

2. Verification after adjustment

after adjusting the tension of the first rope, the adjustment effect shall be verified. The previous inspection methods can be used, such as hydraulic tension meter measurement or vibrating wire sensor measurement, to re-check whether the tension of each head rope is within the specified range, and to observe the operation of the lifting container to ensure that the container runs smoothly without tilting or abnormal swinging. 

(4) Strengthen the inspection of wire ropes and related parts

1. Wire rope inspection

when checking the tension of the first rope, the surface condition of the wire rope should be checked. Observe whether the wire rope has broken wire, abrasion, rust, etc. Because these problems may affect the strength and elastic modulus of the wire rope, and then affect its tension. For example, a wire rope with more broken wires has a reduced carrying capacity, which may cause changes in tension distribution during operation. Regularly carry out non-destructive testing on the wire rope, such as magnetic particle inspection, ultrasonic inspection, etc., to find the internal defects of the wire rope in time to ensure that the quality of the wire rope meets the requirements.

2. Inspection of friction lining and sheave

check the wear of the friction lining. If the liner wears unevenly, it will affect the distribution of friction, which will have an indirect effect on the tension of the headline. For severely worn liners, replace them in time. Check the wear of the sheave groove. The worn wheel groove will change the winding state of the wire rope, resulting in a change in tension. The sky wheel should be maintained and repaired regularly to ensure its normal operation. 

V. Conclusion 

it is a complex and critical work to check the tension of the first rope of the friction hoist. Through the comprehensive application of a variety of inspection methods, and combined with rich practical experience, we can accurately judge whether the tension of the head rope is balanced, and find and solve the problem in time. In daily use and maintenance, we must attach great importance to the inspection and adjustment of the tension of the first rope to ensure the safe, stable and efficient operation of the hoist, and provide reliable transportation guarantee for the production of the mine. At the same time, with the continuous development of technology, new inspection technology and equipment are also emerging, mine hoist maintenance personnel to constantly learn and update knowledge, to better adapt to the needs of the work.

END

Article source: Mine hoist safety and management

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