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CAE analysis of the rocker arm of domestic high-power shearer

Abstract: through the finite element analysis of the rocker arm of mg750/1800-wd shearer under development, the stress and strain laws of the rocker arm of the shearer in different positions and working conditions are obtained, the dangerous section, limit working condition, limit load and limit stress of the rocker arm are found out, and the optimization scheme of the bearing capacity of the rocker arm is put forward. At the same time, the natural frequency, vibration modes and dynamic performance of the rocker arm shell are also explored

key words: shearer; Finite element analysis; Dynamic analysis

the current design of shearer rocker arm shell in China basically adopts the traditional design method: Based on experience and previous design examples, designers design the required products on paper, and design the shearer rocker arm with greater power according to the appropriate enlargement of the rocker arm size of the low-power shearer. If there are problems or do not meet the predetermined design requirements, the design must be modified, There are many problems in real design. With the increasing installed power of the shearer, relying solely on experience, designing high-power machines based on small machines and increasing the safety factor often make the size of the designed products larger and larger, and the distribution of stress, deformation and internal force of the structure is difficult to be reasonably guaranteed. However, through the finite element analysis of the shearer rocker arm, we can get the stress and strain laws of the shearer rocker arm shell at different positions and under different working conditions, find out its dangerous section, ultimate working condition, ultimate load and ultimate stress, and put forward the optimization scheme of the rocker arm bearing capacity. At the same time, it can also carry out exploratory analysis and Research on the natural frequency, vibration modes of each step and dynamic performance of the rocker arm shell. The application of this technology can predict the product quality in the product design stage, so that the product can be optimized before being put into production to improve the product quality, so as to shorten the product development cycle, reduce the development cost and improve the market competitiveness

1 programming of drum load calculation

due to the special mechanical properties of coal and rock, the cutting tool is subjected to large dynamic load in the cutting process, which is random. It is very difficult to accurately calculate the force on the cutting tool by analytical method. The random load of the drum contains deterministic components, which allows us to estimate it with empirical formulas. The former Soviet Union once formulated the industry standard (oct12.47) for calculating the force on cutting tools, At present, it is relatively perfect and has been widely used. Combined with the "parameter optimization, loading efficiency and drum load calculation of shearer spiral drum" compiled by Shanghai branch in 1990, the drum load data model is established

the load at a certain instant of the drum refers to the superposition of the pick load participating in cutting at the same time at that instant. Taking the double drum as an example, the total number of picks of the drum is NP, and the position of pick a (front drum, rear drum is a ') on the drum is the initial cutting position, as shown in Figure 1. The circumferential angle of any pick Ni (i=1, NP) of the drum relative to pick a (a 'of the rear drum) is rjo (RAD). The load of the drum (MP, FX, FY, Fz) is determined by the force synthesis of the teeth in the cutting area EE (or e ′ e ′)

in the formula: FXI, FYI, FZI - the correct solution to the sudden power failure of the ith pick in X, y and Z is as follows: the component force in the direction

zi, Yi, Xi - tangential cutting resistance, radial resistance, lateral resistance of the ith pick

ri - angle from the initial position of the ith pick, rad,

ri=rj+rjo

rj - angle of pick a (or a ') during drum cutting, rad, RJ= ω；

ω— Angular speed of drum rotation, rad/s

rjo - the angle of pick I relative to pick a (a ') in the circumferential direction of the drum, rad

according to the mathematical model of three-dimensional force load of drum established above, a database system for calculating three-dimensional force load of drum is established by using object-oriented technology and database technology

2 analysis model

(1) geometric model

rocker arm 3D solid analysis model is completed in SolidEdge 3D modeling software. It is completely established according to the design size of the rocker arm, including the rocker arm shell, planetary head and drum. The fillet of important parts is reserved, and the insignificant chamfer and small hole are omitted. Considering the difficulty of loading the drum load in the dynamic analysis, the three-dimensional force participating in the cutting pick is equivalent to the center in the program, which will not have a great impact on the force analysis of the rocker arm shell

rocker arm material: zg25simn2mo; Elastic modulus: e=2.1 × 1011Ｎ/ｍ2； Poisson's ratio: υ= 0.3； Density: ρ= 78000ｋｇ/ｍ3。

(2) finite element division

the finite element analysis software MSC is used in this analysis Patran and msc Nastran. Tetrahedral elements with 10 nodes are used for lattice division. Using msc The free lattice divider provided by Patran can divide the lattice of the solid model freely and generate reliable and high-quality volume units, as shown in Figure 2. In order to ensure the rationality and calculation accuracy of the analysis model, it is necessary to reasonably control and transition the lattice density and lattice size of the support ears during lattice division. By reshaping the four sided physique, the quality of the overall lattice division is improved. Number of model units after division: 47957

(3) boundary conditions

the application of boundary conditions includes two parts: the application of concentrated force and additional torque in the center of the square tenon and the application of constraints at the three ears. It is difficult to impose constraints at the three ears. The constraint points are different when the rocker arm is in different positions, which should be analyzed according to the specific working conditions. This paper mainly focuses on the finite element analysis of the shearer rocker arm under the following two typical working conditions: ① the upper rocker arm (front drum) in normal use; ② Lower rocker arm (rear roller) in normal use

3 finite element static analysis

this paper mainly analyzes the situation when the rocker arm is under the maximum force under the above two working conditions, that is, when the upper rocker arm is lifted up to 54.7 ° of the highest point, and when the center line of the lower rocker arm forms the maximum included angle with the horizontal line of the fuselage of 23.44 °, the stress situation after the three-dimensional force direction square tenon center of the drum is equivalent under the two working conditions is calculated, as shown in Table 1

in the table: FXJ, fyj, FZJ - vertical reaction force, horizontal force and axial reaction force of the drum, kn

mpj - load torque of drum

mx, my, MZ - the additional torque when the three-dimensional force of the pick is equivalent to the center of the square tenon

the stress distribution of the upper and lower rocker arms is obtained by finite element analysis. Upper rocker arm σ Max=101.358mpa, far less than the allowable stress[ σ]= 221mpa, the maximum equivalent stress is at the lower support ear. In addition, the stress at the planetary head of the rocker arm is also relatively large, σ= About 98mpa is also the weak point of the rocker arm of mg750/1800-wd shearer. Lower rocker arm σ Max=88.94mpa, less than the allowable stress[ σ]= 221mpa, but smaller than the maximum stress of the upper rocker arm of 101.358mpa, with a difference of 12.418mpa. The maximum equivalent stress is at the planetary head, and the maximum equivalent stress at the lower support ear is only 31.95mpa, so the rocker arm will not fail and can work safely

4 dynamic analysis

structural dynamic analysis is different from static analysis. It is often used to determine the impact of time-varying loads on the whole structure or components, and at the same time, the effects of damping and inertia effects should be considered. The natural mode analysis of the structure shall be carried out to calculate the vibration modes of each order of the structure. It can evaluate the dynamic characteristics of the structure. For example, to install a rotating drum on the rocker arm, in order to avoid excessive vibration, we must consider whether the rotating frequency of the drum is close to a natural frequency of the rocker arm

(1) analysis model and boundary conditions

Dynamic Analysis of rocker arm shell must consider the elastic support cylinder that has a great impact on the dynamic performance of rocker arm. The cylinder is simplified as a grounding spring to simulate the cylinder. The beam element between the lower support ear and the oil cylinder (spring) is connected to simulate the connection of the solid connecting rod. One end of the spring is fixed, and the other end only retains the freedom of movement in the X direction. It is a beam element connected with the node at the lower support ear. In the software implementation, the constraint element is used to connect the solid element and the beam element to ensure the correct transfer of force and displacement between the two types of elements (beam element and solid element). Other boundary conditions are basically the same as those in statics, in which the force load is a dynamic load that changes with time

(2) frequency characteristics of drum load

due to the diversity of load frequencies of the drum in the coal cutting process, the natural modal frequency of the rocker arm shell obtained from the modal analysis should be far away from the drum load frequency, otherwise it will cause resonance and accelerate the destruction of the rocker arm. According to the drum pick arrangement, the drum load frequency can be calculated: 0.39, 1.56, 0.78, 3.12, 6.24, 9.36, 10.1 Abnormal hammer return 14, 10.53, 12.48hz

East light company always adheres to the implementation of the five development concepts(3) natural modal frequency of rocker arm shell

Lanczos method is used to solve the modal of rocker arm shell. The natural modal frequency and vibration mode of the rocker arm shell are obtained. Table 2 shows the results of the first five stages of analysis

the vibration of the rocker arm under the excitation of the drum load is the comprehensive reflection of the modal vibration of each order. It can be seen that the maximum frequency of the drum load is 12.48hz, while the minimum natural mode frequency of the rocker arm shell is 24.7517hz, which will not cause the resonance of the rocker arm

(4) dynamic analysis of rocker arm shell

according to the calculation and analysis of drum load, the three-dimensional force of front drum load changes periodically in normal use. Figure 3 and Figure 4 are the three-dimensional force changes when the drum rotates for one cycle

in the transient dynamic analysis, the integration method adopts the one-step Houbolt method of the direct integration method, and the appropriate integration step is selected according to the natural modal frequency of the rocker arm shell Δ T=0.00 three working meetings were held for 2S, and the integration time was 2.564s for the drum to rotate for one cycle. Using msc Nastran carries out linear dynamic transient analysis on the system model under the action of roller load. After calculation, the displacement curve of the first 33 steps of the square tenon center of the loading point is shown in Figure 5

the stress change curve of the maximum equivalent stress node at the planetary head, triaxial shaft hole, etc. is shown in Figure 6

compared with the results of static analysis, it can be seen that under the influence of the oil cylinder as an elastic support, the stress distribution law of the rocker arm is basically unchanged, but there is a certain decrease in the value

5 conclusion

(1) for the rocker arm with given size, structure and material parameters, the calculated maximum stress is 101.358mpa, which is far less than the allowable stress of the material. The maximum frequency of the drum load is 12.48hz, and the lowest natural mode frequency of the rocker arm shell is 24.7517hz, which will not cause the resonance of the rocker arm and can work safely

(2) as an elastic support, the rocker arm stress decreases in value, but does not change the distribution law of stress and strain

(3) the whole analysis process is universal. For the same series of rocker arms with similar working conditions, it can be calculated directly

apply advanced software platforms, such as SolidEdge, msc ＮＡＳＴＲＡＮ，ＭＳＣ. Patran et al. Applied the finite element method to the design of coal mining machinery, and preliminarily solved the key technologies of applying the finite element method to the design of coal mining machinery. Practice has proved that finite element technology will play a more and more important role in the design field of new coal mining machinery in China

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