Large Port Lifting Machinery Wheel Pressure Test Method
wheel pressure detection method
Large Port Lifting Machinery Wheel Pressure Test Method
At present, with the continuous development of port logistics and economic construction, the tonnage requirements for loading, unloading and transportation equipment in ports are also increasing, which makes the port lifting machinery is also developing in the direction of large-scale, and the wheel pressure of the crane is a key and important parameter for the design, manufacture and installation of large lifting machinery. The maximum wheel pressure of lifting machinery not only affects the design of the overall structure of the crane, but also is the main design basis of the track foundation, and is an important design parameter of the port lifting machinery.
At present, the traditional empirical formulas and data obtained according to classical mechanics can not meet the requirements of efficiency optimization and lightweight design of large port lifting machinery, and can not solve various problems caused by uneven large wheels in engineering practice. Engineering practice requires more accurate detection methods for the maximum wheel pressure value of lifting machinery, but now most of the crane wheel pressure distribution is statically indeterminate, and its distribution is related to the load conditions of the crane’s foundation stiffness, structure, track flatness and manufacturing accuracy, so the theoretical calculation is often very difficult. Therefore, the correct selection of an accurate and convenient method to test the maximum wheel pressure of large port lifting machinery will be helpful to engineering practice.
The traditional calculation method of wheel pressure will produce a large deviation to the design, installation and maintenance. In this paper, through the comparison of the detection methods of wheel pressure of large port lifting machinery: Barkhausen noise stress test method, track indirect electrical measurement method and direct measurement method, it provides a reference for customers in the detection and selection of wheel pressure of large port lifting machinery wheels, and can choose the appropriate wheel pressure detection method of port lifting machinery wheels according to the applicable project.
1. Factors affecting wheel pressure
The wheel pressure of port lifting machinery refers to the pressure of wheels on the track. At present, most port cranes (such as shore Bridges, rail container cranes, door cranes) use a four-point structure, which has good symmetry and process, and high stability. But the wheel pressure distribution of this structure is indeterminate, which is related to the stiffness of the structure and foundation, the manufacturing accuracy of the structure and the flatness of the track.
Secondly, the lifting impact coefficient, lifting dynamic load coefficient, sudden unloading impact coefficient, running impact coefficient (walking lifting machinery with load), lifting mechanism acceleration and deceleration dynamic load coefficient. It will impact the whole or part of the structure of the lifting machine, so that the assembly gap between the components is too large or the wear is serious, resulting in uneven wheel pressure.
2. Barkhausen noise stress test method
The “Barkhausen effect” is a physical property of a ferromagnetic material discovered by German scientist Professor Barkhausen in 1919. He found that a measurable noise signal could be induced in a ferromagnetic body.
Using portable non-destructive testing of ferromagnetic materials, the stress meter can easily collect the stress value of the wheel shaft of a large vehicle under static and dynamic conditions, according to which the stress value can be converted into a large wheel pressure value.
The Barkhausen noise stress measurement method has the advantages of high detection accuracy and fast detection speed, and can realize the transient, linear, portable and non-fixed point stress detection of ferromagnetic materials. However, the detection accuracy is affected by surface roughness and residual stress of materials, so the combination of BN method and engineering practice requires the establishment of comparative experimental graphs of each steel grade.
3. Indirect electrical measurement of track
The track indirect electrical measurement method is based on the crane wheel is the only part of the crane and the truck track to transfer force, the force in the direction of the hammer on the track comes from the wheel, the principle of wheel pressure measurement is based on the crane wheel over the truck track, the force acting on the direction of the hammer on the track will make the track strain characteristics, The resistance strain gauge (referred to as strain gauge) is pasted on the side of the track passed by the measured wheel. When the strain gauge deforms with the track when the wheel passes, the resistance value of the strain gauge will change accordingly. The dynamic signal test and analysis system will convert the resistance change into the strain value and record it. The wheel pressure of each wheel can be measured by pressing each wheel through a test point with a strain gauge
The method can be used to measure the static and dynamic wheel pressure of multi-wheel crane by obtaining the wheel pressure indirectly through the strain value of track. However, this method needs to measure the strain of the no-load uniform velocity passing through the measuring point, so as to obtain the calibration coefficient of wheel pressure and strain. However, the measured no-load strain is often inaccurate and difficult to identify because of vibration and unequal track. Moreover, this method converts strain into wheel pressure through a linear empirical formula. However, due to the inevitable plastic deformation during wheel-rail contact, the relationship between strain and wheel pressure is often not linear. With the increase of crane weight and load, the measurement accuracy of this method will become lower and lower. Therefore, a strain-wheel pressure model based on elastoplastic contact theory is needed to correct the wheel pressure.
4. Direct measurement method
The direct measurement method is to lift the wheel off the track with a jack, so that the weighing sensor is placed at the bottom of the wheel, and the wheel pressure parameter acquisition instrument is connected. In the state of no movement of the truck, the lifting machinery carries out no-load lifting, full load lifting, car running, unloading and other actions, and the acquisition instrument can collect the wheel pressure value under the working condition in real time.
This method is only applicable to the condition that the cart does not move, and the wheel pressure value may be changed by the change of the center of gravity when the lifting machine uses the jack to lift off the track surface, which requires multiple measurements to obtain the average value.