An Effective Way To Improve The Service Life Of Steel Wire Rope Of Four Column Automobile Hoist Mar 08, 2023
The steel wire rope is the key bearing part of the four-column automobile lifting machine. In the lifting operation of the lifting machine, the expansion and expansion of the cylinder rod installed under the main platform drives the traction platform to complete. The steel wire rope plays a bearing role in this system. Once the wire rope fails and there is no corresponding wire rope breaking protection device or the wire rope breaking protection device fails, the car will be overturned and the injury accident of personnel will occur. The following will be from the wire rope transmission traction structure description, failure form analysis, the main structural design requirements and customer in the use of the process of maintenance and inspection, talk about how to improve the service life of the four-column automobile lift wire rope, to prevent the use of wire rope failure in the process of adverse consequences.
A, four column car lift wire rope drive traction structure description
At present the domestic market use of four - column car lift, most of the wire rope traction. Wire rope traction of four column automobile lift, mainly by four columns, the main platform, auxiliary platform, two beams, pump station, control box and so on. Two steel ropes are fixed on the pull seat of the piston rod. The short end of each steel rope turns 90° by the pulley in front of the platform and is fixed to the top of the column after the vertical reversal of the beam pulley. After the long end of each steel rope turns 180° by the pulley in front of the platform, It is fixed to the top of the column after the horizontal reversal of the rear pulley of the platform and the vertical reversal of the beam pulley. Each end of the two beams is equipped with a vertical guide rope wheel, which connects the main and secondary platforms in the middle. When it is necessary to rise, press the rise button, after the pump station is connected to the power supply, the motor rotates, drives the gear pump to output high pressure oil to the system, enters the rod chamber of the cylinder, pushes the piston rod contraction, the piston rod contraction drives the pull seat fixed on the end of the piston rod to pull the wire rope, drives the platform and beam components to rise, when it is necessary to fall, first open the unlocking handle (such as electric unlocking, generally equipped with a delay to rise, Just press the down button), the insurance is unlocked, press the manual down valve, the oil return circuit is opened, the cylinder piston rod is extended, the hydraulic oil in the platform and the above lift under the action of the speed regulating valve flow back to the tank, the steel wire rope pulls the platform to complete the down operation.
2. Failure form analysis of wire rope
According to the standard GB/T5972-2016 for the maintenance, maintenance, inspection and scrap of steel wire rope of crane, the main failure forms of steel wire rope are: wire break, rope diameter becomes small, corrosion, deformity and damage. Among them, deformity and injury include: wavy, cage deformity, rope core or rope strand protrusion, steel wire protrusion, rope diameter local increase, local flat, kinks, bending, elasticity reduction, etc. This paper mainly analyzes the three kinds of failure forms of broken wire, smaller rope diameter and deformed in practical application.
1. Broken wire analysis
Broken wire is the most common form of wire rope failure. The low stress brittle fracture is mainly caused by the joint action of wire rope in working environment medium and working stress. Wire rope fracture failure, largely depends on its working environment, mainly divided into wear broken wire and corrosion broken wire two. Worn broken wire refers to the wear on the part of the wire rope in contact with the pulley during its operation, and the wear becomes more and more serious over time. Finally, broken wire is caused. The two sides of the fracture are inclined stubble and flat fracture, which occurs in the part of the wire rope with serious wear generally in the contact area with the pulley. Corrosion breaking generally occurs when the wire rope runs in a corrosive medium environment, so that the wire rope is corroded, the effective working area is constantly reduced to reduce the strength of the wire rope, but also cause irregular surface stress crack expansion, and then accelerate fatigue, and eventually lead to broken wire, the fracture shape is not orderly, pinpointed.
2. Diameter reduction analysis
External wear is the main reason for the decrease of the diameter of the wire rope, usually caused by the pressure between the wire rope and the pulley. For example, the Angle between the two sides of the wheel groove is small, and the wire rope tends to contact with the side of the wheel groove after being stressed, which may cause the wear on one side of the wire rope. Usually, the wear of the wire rope occurs in the section in contact with the pulley groove. Inadequate or incorrect lubrication and the presence of corrosive dust and sand can affect wear rates. At the same time, the following reasons will also lead to the decrease of wire rope diameter. (1) Internal wear and steel wire dents; (2) Internal wear caused by the friction between the connected strands and the steel wire, especially when the wire rope is bent; (3) deterioration of fiber core or fracture of steel core; (4) Fracture of the inner strand of the wire rope. The phenomenon of size reduction and surface state change due to wear, and the eventual loss of its function is called wear failure. There are two main modes of wire rope wear failure: mechanical wear and plastic wear. The main cause of mechanical wear is the wear caused by the contact between the outer steel wire and the groove surface in the process of use. This phenomenon is particularly obvious in the steel wire rope and pulley contact. The main performance is that the steel wire on the peripheral surface of the wire rope is smoothed, the rope diameter becomes thinner, the load area decreases, and the load capacity also decreases. In addition, insufficient lubrication of the wire rope and dust and sand between the strands of the wire rope will also accelerate the generation of mechanical wear. And plastic wear, mainly due to vibration, collision, internal extrusion caused by wire rope surface wear. Wear failure is a gradual and gradual process. It's not as sudden as a breaking accident. However, wear usually leads to the reduction of the load section area and the increase of fatigue sensitivity, resulting in fracture failure, especially in high humidity environment, wear will accelerate the corrosion process.
3. Deformity analysis
The visible shape distortion caused by the wire rope losing its normal shape is called "deformation". This deformation will lead to uneven distribution of stress inside the wire rope in the deformed area. The main reasons for the formation of this deformity are: (1) When the wire rope passes through the pulley at a large deflection Angle, it first contacts the edge of the pulley and then rolls into the bottom of the rope groove. This process loosens the strand, and the outer strand loosens more than the core of the wire rope, causing the length difference between them; (2) When the bottom diameter of the pulley groove is too small, the wire rope will be squeezed when it passes through the pulley. When the diameter of the wire rope is reduced, the length of the wire rope will increase. Because the compression and elongation of the outer strand of the wire rope are larger than the rope core, this process will also cause the length difference between them. In both cases, the pulleys change the position of the loose outer strand, "driving" this length difference to a location within the winding system, forming a cage deformity. In addition, the deformation also includes cord core or cord strand protrusion, steel wire protrusion, rope diameter increase, local flat and other characteristics. At present, it is found that the formation of wire drawing may be caused by the lack of clearance between the wire in the strand. The lack of clearance prevents these wires from moving with neighboring wires, resulting in overload or yield. If the diameter of the wire rope is too small, there will not be enough gap between the outer strands, resulting in cross bite damage between the strands. The fatigue life of wire rope will be greatly reduced due to lack of clearance. Cage distortion, which occurs mainly in wire ropes with steel cores. This deformation occurs when the outer guide rope strand becomes detached or longer than the inner rope strand, and the rope in a relaxed state is suddenly loaded. With the "bird cage" produced together with the rope strand extrusion and other failure phenomenon.
Three, the structure design should meet the bearing requirements of the wire rope
According to the above analysis, combined with the domestic and foreign standard requirements and the design and application summary of the automobile insurance industry, the design of steel wire rope related parts should meet the following requirements.
1. Selection of wire rope specifications
The correct selection of steel wire rope specifications can ensure that the steel wire rope meets the load requirement.
(1) According to EN 1493:2010 standard 5.6.2 transmission wire rope shall consist of at least 114 single steel wires, the normal tensile strength shall be at least 1570MPa but not more than 1960MPa, and the minimum terminal tensile strength shall be 80% of the rope. Considering the influence of the bending strength of the wire rope, it should be controlled within 1 770MPa as far as possible under the condition of meeting the safety factor.
(2) The bearing capacity of the wire rope is selected according to M5 of the working level of the mechanism, and its minimum actual safety factor is 5. Usually the design static stress safety factor N is not less than 7.
2. Design of wire rope pulley
(1) The ratio between the pulley diameter and the wire rope diameter should be greater than 18. If the bending radius of the wire rope is too small, it will increase the bending and breaking damage of the wire rope and shorten the service life of the wire rope.
(2) Radius of pulley rope groove bottom R= (0.53-0.6) D. Too small will result in malformed failure.
(3) Pulley materials commonly used Q235A, HT200, ZG230-450, QT400-18. QT400-18 and Q235A are the most beneficial to improve the service life of the wire rope, and the wear damage to the wire rope is the least, followed by the other two materials.
(4) The inner hole bushing of the pulley is commonly used for self-lubricating bearings and bronze bushing, and the service life of the bronze bushing is the longest under the same load.
(5) Align the front and rear pulley slots below the platform and the corresponding beam single slot wheel to minimize the deflection Angle to avoid the wear and failure of the wire rope caused by the side of the wire rope groove.
Iv. Maintenance, inspection and maintenance of wire rope and related parts
1. Usually, the tightness of the wire rope should be adjusted according to the levelness change of the platform to ensure the levelness of the platform, so as to facilitate the uniform bearing of the wire rope at the end of the four columns. During the adjustment, the platform can be leveled by adjusting the hexagon nut of the fixed screw at the end of the wire rope connected to the top plate of the column. The level of the platform is observed by using a level or water pipe. After the adjustment, the fixed nut at the top plate end is tightened. After completing the adjustment of the wire rope, adjust the safety plate in the four columns accordingly, so that the platform is in the same horizontal plane after the beam safety lock. The adjustment of the safety plate is realized by adjusting the fixed nut fixed on the roof.
2. In daily maintenance, the steel wire rope should be lubricated regularly, and the parts moving through the pulley should pay more attention to lubrication. In order to improve the lubrication effect, the steel wire rope should be cleaned before lubrication, and then grease should be added.
3. If the wire in one part of the wire rope is too protruding, when it passes through the pulley here, the wire will press on top of other parts, resulting in local deterioration. In order to avoid this local deterioration, the extension of the wire can be removed, the method is: clamp the extended end of the broken wire repeatedly bending, until broken. When removing steel wire during maintenance, it is appropriate to record its position. The operation of removing broken wire is also calculated as a broken wire and taken into account when evaluating the status of the wire rope according to the number of broken wires as a scrap benchmark.
4. At least one year after the use of the wire rope, the appearance of the working section of the wire rope passing through the pulley shall be inspected weekly, with the purpose of finding general deterioration or mechanical damage. This inspection shall also include the connection of the wire rope to the roof of the column. The correct position of the wire rope on each pulley slot should also be checked and confirmed to ensure that the wire rope does not deviate from the normal working position.
5. Check cycle: check once a month in early use; If it is out of service for more than 3 months, the surface quality of the wire rope should be checked before reuse; If the lifting process is abnormal due to the failure or improper operation of other parts of the lifting machine, the steel wire should be inspected for strong surface quality; The wire rope should be inspected once every two weeks after the product has been put into use for a year.
6. Scope of inspection: For each wire rope, inspection shall be carried out along the entire length, and special attention shall be paid to the following key areas and parts:
(1) The lower pull seat fixed joint of the main platform;
(2) the area under the main platform passing the pulley;
(3) the area in the column passing through the pulley;
(4) the top of the column is connected with the wire rope;
(5) Parts of the wire rope damaged due to improper installation or external reasons.
7. Inspection of wire rope: It should focus on inspecting the wire rope near the end fixing device, especially the part entering the end fixing device. Because this position is affected by vibration and other shocks and corrosion and other environmental states, it is easy to break the wire. Probes can be used to determine whether the wire is loose, and therefore whether there are broken wires within the end fixtures. The end fixtures should also be checked for excessive deformation and wear. In addition, the casing used to fix the rope sleeve and rope ring should also be visually inspected to see if the material is cracked and there are signs of possible slip between the wire rope and the casing; Whether there is a broken wire near the fixed buckle of the wire rope, and whether the direction of the wire rope is in the correct assembly state.
8. Scrap standard of wire rope: the wear and break condition of wire rope should be checked regularly in daily use, and timely replacement must be carried out when one of the following situations occurs:
(1) The improper use of the wire rope will cause local bending, kinking and flattening; Lanternlike deformity; The cord core or strand protrudes.
(2) The number of broken wires in the length of 60mm is greater than 5, or the number of broken wires in the length of 300mm is greater than 10;
(3) Deep pits appear on the surface of the steel wire, and the steel wire is quite loose;
(4) When the steel core is extruded, there is cage distortion in the adjacent position;
(5) the diameter of the wire rope decreases or increases by 5%;
(6) whole strand fracture occurs;
(7) The external corrosion of the wire rope, the feel of the steel wire surface is rough, the severe indentation of the steel wire surface is serious corrosion, and the internal corrosion is obvious;
(8) Under any conditions, as long as the following situations occur, the wire rope needs to be scrapped: One is that the gap between the ruler and the lower side of the spiral surface is greater than one third of the diameter of the wire rope. The other is that the gap between the ruler and the lower side of the spiral surface is greater than one tenth of the diameter of the wire rope.
(9) Use more than two years.
5. Failure protection of wire rope
In the four column lifting machine, there are wire rope breaking prevention devices. For manually unlocked four-column lift, when a column steel wire rope breaks, the regulating wheel of the connecting steel wire rope under the action of the spring pulls the mechanical safety hook and the safety plate in the column to engage the lock, then the operation should be stopped immediately. For the electrically unlocked lift, the regulating wheel drives the safety hook to self-lock at the same time. Also through the above action plate hit the limit switch mounted on the beam to cut off the main power supply. You can't go up or down.
Six, the main ways to improve the service life of four column lift wire rope
1. Select the appropriate wire rope according to the specified load, and meet the requirements of Section 3 (1) above;
2. Design suitable wire rope wheel according to the selected wire rope, and meet the requirements of Section 3 (2) above;
3. According to the requirements of Chapter 4, daily lubrication and maintenance of the steel wire rope of the four-column lifting machine in use, and check the wear condition of the steel wire rope regularly. Meet the replacement standard should be replaced in time.
4. Periodically check the fail-safe device of the wire rope, check the sensitivity and reliability of the reset spring, check the wear of the wire rope guide wheel, check the flexibility of the action of the safety block, check the engagement between the safety plate and the safety block, check the sensitivity and reliability of the limit switch.
