Li Ziguang Fu Caiming Mao Wengui Abstract: Visual Nastran finite element simulation software is used to simulate the stress and strain of the drum under various loading conditions, and the wall thickness parameters of the drum are adjusted to study the strength and radial deformation of the drum. Impact. The simulation results show that the maximum stress of the drum is located on the inner wall of the cylindrical cylinder near the bottom of the big end drum; the maximum stress and maximum radial displacement caused by the centrifugal hydraulic pressure of the material increase with the decrease of the wall thickness of the drum; The maximum stress and maximum radial displacement generated by the drum's own mass centrifugal force in the wall are independent of the drum wall thickness. [4] Yan Wei. The influencing factors and parameter relationship of the wall thickness of the centrifuge drum l_J]. Filtration and separation, 2002, 12 (1): 18-2O. (Editor He Chenggen)
1. Changsha University of Science and Technology, Changsha, 410076 2. Hunan Institute of Engineering, Xiangtan, 411101
Key words: drum; stress and strain simulation; drum wall thickness; structure optimization
CLC number: TH452; TR752.24 Article ID: 1O04—132X(2006)23-2454--04
introduction
The horizontal screw discharge sedimentation centrifuge (referred to as the horizontal screw centrifuge) uses the principle of centrifugal sedimentation to carry out solid-liquid separation of the suspension.] It has rapid development due to its advantages of large single-machine processing capacity, convenient operation and low maintenance cost. It is widely used in chemical, metallurgical, light industry and other departments, but its working performance is not ideal, the sediment has high moisture content, and the separation effect is not good. The drum component is the main component of the decanter centrifuge. The structural parameters of the drum largely determine the characteristics and separation effect of the centrifuge. The design of the centrifuge is moving towards increasing the capacity of the single machine, increasing the speed and increasing the diameter, which makes the stress and strain problem of the drum structure more important. Therefore, under the premise of solving the stress and strain problem, it is of great engineering practical significance to analyze and optimize the structural parameters of the drum set to improve the separation effect, reduce the quality and reduce the cost of the centrifuge. The structure of the drum set is complex, and the force is related to the material. It is difficult to model and solve by the traditional analytical method. The virtual prototype technology and the finite element simulation method can optimize the parameters and provide valuable value for the centrifuge design. Theoretical reference.
Finite element simulation of the drum
1.1 Drum virtual prototype model
The drum mainly includes a drum body and a size end cover (including a liquid level adjusting device). The characteristics of the drum geometry, constraints and loads are more complex. The drum is composed of a cone and a cylinder and is an axisymmetric structure. Modeling and stress-strain simulation analysis of the drum using solid modeling technology has the following advantages: the modification of the model and parameters is very convenient; the time required to determine the reasonable structural parameters can be greatly shortened; the cost is low; The process is completed on the computer, which is beneficial to the development of superior performance products through optimization and other means. In this paper, the 3D modeling system Pro/E software Is] with highly integrated design function is used to establish the solid model of the LW520 horizontal screw centrifuge drum (Fig. 1), and the quality matching, gap check and interference check are performed at the same time. The solid model can provide accurate quality parameters, namely part quality, centroid position and moment of inertia, and prepare for the analysis of the latter model; the solid model is guided by Visual Nastran software in STEP format for stress-strain simulation. The structural parameters of the drum are the drum inner diameter D-520ram, the cone section drum length H 777mm, and the drum liquid surface inner diameter D. =420mm, the length of the drum is H:==1064mm, the wall thickness of the drum is t18mm, and the cone angle of the cone is n-8. The rotation speed of the drum is 2800r/min, the total length of the drum is L-1800mm, and the height of the liquid pool is h-33~55mm. The drum material is 1OCr22Ni5Mo3N. The solid phase density of the material is 1470kg/ma, liquid phase density. 0—1085kg/m. The processing capacity of the drum is from 13 to 20 m. /h.
1.2 Finite element simulation of the drum
1.2.1 Type, size and application of the load During the operation of the centrifuge, the drum is mainly subjected to the following two loads:
Similarly, the material pressure at the radius of the tapered section and at any radius of the drum end cap is still calculated using equation (2), and the direction is perpendicular to the inner surface of the action, and is applied to the finite element model as a line load.
1.2.2 The stress strain of the drum is like a nose
The stress and strain simulation of the drum is carried out to solve the stress and displacement distribution of the whole structure of the drum under the conditions of centrifugal force (working condition) and material centrifugal pressure (household condition), and the two types are linearly superimposed. Stress and displacement under working conditions to investigate whether the drum has sufficient strength and small radial deformation when fully loaded (+P.) and compared with the allowable stress of the material. The drum material is 10Cr22Ni5Mo3N. The stress is 205 to 225 MPa, which is a small value, and the allowable stress is 205 MPa. The deformation of the drum needs to be controlled within a certain limit. Before El, there is no uniform standard in China's centrifuge industry. From the engineering point of view, it is required that the drum can not be obviously deformed during the operation, and the drum and the fixed casing may not be rubbed due to deformation and other factors. The distance between the drum shell of the LW520 decanter centrifuge and the inner surface of the cabinet is 5mm.
In Visual Nastran, 1OCr22Ni5Mo3N material was added to the virtual prototype model and the tetrahedral solid element mesh was divided. The average mesh length was 30 ram, with a total of 61 697 nodes and 3278 cells. In the analysis, a rolling hinge constraint is applied at the contact of the size end journal of the drum with the ball bearing. The simulation analysis of the above three working conditions is carried out separately. The centrifugal force (F working condition), the centrifugal pressure (work condition) stress and displacement simulation cloud diagram of the material are shown in Fig. 2 and Fig. 3. The stress cloud diagram shows that the maximum stress is 164. .2 MPa, on the inner wall of the cylindrical cylinder near the big end drum, and the stress level on the entire cylindrical body is higher than the stress of the cone cylinder, the top cover and the drum bottom. Since the maximum stress is less than the allowable stress of the material of 205 MPa, it indicates that the drum of this analysis is safe during normal operation. It can be seen from the radial displacement cloud diagram that the cylindrical simplified body expands outward when the drum is in normal working condition, and the maximum radial displacement also occurs in the simplified body (O.1812ram). The deformation of the drum is not obvious and meets the stiffness requirements. It can be seen that the drum structure has the possibility of further optimization.
2 Structure optimization of the drum
Since the current design of the drum wall thickness has met the strength requirements and has a large safety margin, from the perspective of cost saving, we use the finite element method to optimize the drum, under the premise of ensuring strength and deformation, The wall thickness of the drum is gradually reduced, and the influence of the wall thickness parameter on the stress and radial deformation is investigated.
2.1 Influence of the wall thickness of the drum on the drum stress
Through the simulation analysis, the curve of the maximum value of the drum stress with the wall thickness of the drum is obtained, as shown in Fig. 4. It can be seen from Fig. 4 that the maximum stress of the full load condition increases with the decrease of the wall thickness of the drum, and the increase is small at the beginning, even when the wall thickness of the drum is 10 ram, the maximum value of the stress Still less than the allowable stress of the material is 205 MPa, which meets the strength requirement; the increase speed is obviously larger after the thickness is less than 10 ram, and the curve becomes steeper after the thickness is less than 6 ram, but the maximum stress exceeds the material when the wall thickness of the drum is 6 mm. Allowable stress does not meet strength requirements. It can be seen from Fig. 4 that the maximum value of the stress generated by the centrifugal pressure of the material is almost parallel with the curve under the full load condition, and the maximum stress generated by the centrifugal force changes with the wall thickness. Little change. This shows that the centrifugal force of the drum itself is independent of the thickness of the drum in the wall. The drum wall is mainly subjected to the centrifugal pressure of the material, so increasing the thickness of the drum wall does not reduce the stress caused by the centrifugal force of its own mass.
2.2 Influence of the wall thickness of the drum on the radial displacement of the drum
Fig. 5 is a graph showing the maximum value of the radial displacement d as a function of the wall thickness of the drum. It can be seen from Fig. 5 that the maximum value of the radial displacement increases with the decrease of the wall thickness of the drum under the three operating conditions, and The growth trend is similar to the stress curve. When the wall thickness of the drum is reduced to a certain extent (4 ram), the radial displacement increases faster, so the stiffness (deformation) condition must be considered when selecting a smaller drum wall thickness.
In order to ensure the accurate processing, reasonable installation and safe operation of the centrifuge drum, the wall thickness of the drum should not only meet the requirements of strength and deformation, but also not less than a certain value, that is, t≥tmin.
3 Conclusion
(1) The maximum stress of the drum is located on the inner wall of the cylindrical cylinder near the bottom of the big end, and the stress on the entire cylinder is higher than that of the cone, the top and the bottom of the cone; the maximum radial displacement is also Occurs on the barrel.
(2) Under full load condition, the maximum value of the force increases with the decrease of the wall thickness of the drum, and the increase is small at the beginning. When the thickness is less than 10 ram, the increase speed is obviously larger, and the thickness is less than 6 ram. The curve becomes steeper, but when the wall thickness of the drum is 6 mm, the maximum stress exceeds the basic allowable stress of the material by 205 MPa, which does not meet the strength requirements.
(3) Simulation studies show that the stress generated by the centrifugal mass of the drum itself is independent of the thickness of the drum. The drum wall is mainly subjected to the centrifugal pressure of the material, so increasing the thickness of the drum wall does not reduce the centrifugal force caused by its own mass. Stress.
(4) The wall thickness of the drum will also significantly affect the radial displacement of the drum, and the radial displacement will directly affect the dynamic performance of the centrifuge, so it should be highly valued in the design.
references:
[1] Sun Qicai, Jin Dingwu. Centrifuge principle structure and design calculation [M]. 3 edition. Beijing: Mechanical Industry Press, 1987.
[2] Dong Junhua, Liu Zhongming, Fan Deshun. Finite element analysis of double cone angle drum structure of decanter centrifuge [J]. Journal of Beijing University of Chemical Technology, 2004 (4): 99-102.
[3] I. In Y J, Farahati R. cAD Based Virtual AssemblyPrototyping - an A Case Study [J]. The International Journal of Advanced Manufacturing Technology, 2003 (5), 111 l25.
Finite element simulation of horizontal screw discharge sedimentation centrifuge drum