Discussion on Application of Horizontal Centrifuge in Production of Alumina Sintering Process

Graduate School of Central South University, Changsha 410083, China; 2. Shandong Aluminum Industry Co., Ltd., Zibo 255052, China)
[Abstract] This paper introduces the structure and working principle of LW350×1550NY centrifuge and the test results and discussion of the application in the production of alumina by sintering.
[Key words] centrifuge; alumina; rapid separation [CLC number] TH311 [Document code] B [Article ID] 1003-8884 (2005) 04-0006-04
In order to ensure the slag transfer, the whole cone radius of the slag section should be within a certain angle range, while the double cone angle snail centrifuge has a cone angle change point near the liquid surface under the liquid surface (as shown in the figure). 1)) The sediment output liquid pool is stably moved on a gentle slope, and the large cone angle is used under the liquid pool because the centrifugal force in the liquid pool is small, so the return force is naturally small, and the sediment backflow phenomenon is also small [1] ]. Due to the large cone angle of the * cone section, the axial distance of the * cone section becomes shorter, and the second cone section becomes longer when the total length of the centrifuge is constant. Therefore, the depth of the double cone angle decanter centrifuge can be appropriately increased without shortening the drying distance of the drum. At the same time, the increase of the depth of the liquid pool increases the settlement area of ​​the drum. According to the production capacity, it is proportional to the settling speed and the settlement area, and the gravity settling speed is constant. Therefore, the production capacity of the double cone angle horizontal snail centrifuge is also increased.

Since the double cone angle structure can ensure the smooth transportation of the sediment and has higher production capacity than the traditional structure of the single cone angle, the structural improvement of the domestic large horizontal screw centrifuge is carried out. However, the centrifuge drum is a high-speed rotary component, which has a relatively high strength requirement and the deformation cannot be too large [2]. Therefore, the improved double cone angle drum must be checked for strength and stiffness to prevent accidents.
In the national centrifuge strength standards, only the film stress of the drum body part is given [3], but the detailed stress of the whole drum body is not given. Therefore, the finite element method is recommended in the centrifuge drum strength standard in China. Calculate the stress of the drum [4]. In this paper, ANSYS finite element software is used to calculate and analyze the stress and deformation of the double cone angle drum of Φ1200mm horizontal screw centrifuge.
1 Establishment of finite element model 1 1 Finite element geometric model Since the drum is structurally axisymmetric, the loads (centrifugal force, material reaction force) and constraints are also axisymmetric, so the basis of the calculation accuracy is not reduced. On, the axisymmetric model of the drum is simplified to a 2D model. The analysis uses a 4-node axisymmetric unit plane42. The specific finite element model is shown in Figure 2. The inner diameter of the drum is 12 m, the wall thickness is 0 22 m, the large cone angle is 15°, the small cone angle is 8°, and the total number of units is 1044. The total is 1285.

1 2 Drum load and restraint 1) The load drum is mainly subjected to the following two loads during work [2]
1 Centrifugal force caused by its own mass The drum under high-speed rotation, the centrifugal force generated by the mass of the drum metal itself is applied to the finite element model of the drum in the form of angular velocity ω in the analysis.

2 Centrifugal pressure of the material The force is the pressure of the material moving along the radial direction against the drum wall under the action of centrifugal force, and the direction is perpendicular to the inner surface of the drum. The centrifugal pressure generated by the fluid material in the cylinder at high speed is
Where ρc is the density of the material in the cylinder, 1085 kg/m3; r is the radius anywhere in the fluid material layer, m; r0 is the free surface radius of the fluid when the cylinder is rotated, 0 525 m. It can be seen from the formula (1) that the centrifugal pressure generated by the material layer changes with the change of the radius, and the value is equal on the same radius, and the value is large on the cylinder wall, that is,
Similarly, the material pressure at the radius of the cone barrel wall and at any radius of the drum end cap is also calculated using equation (1), which is perpendicular to the inner surface of the action.
Strictly speaking, the drum should also have its own weight, but because the drum has a high separation factor, that is, the centrifugal force of the drum is much larger than its own gravity, so the influence of its own weight on the strength and stiffness of the drum is neglected.
2) Constraints The constraints of the drum are determined according to the specific structure. Since the finite element model of the drum is an axisymmetric model, a symmetrical constraint is imposed on the center line of the end cap of the drum, that is, the UX and UZ are constrained; and UY is constrained outside the center line zui of the drum end cap.
2 Finite Element Calculation and Analysis The static analysis of the double cone angle drum is mainly to investigate the strength and stiffness problems, that is, whether it has sufficient strength and small radial and axial deformation under a certain working load. The radial and axial deformations of the double cone drum during operation are shown in Figures 3 and 4.
As can be seen from Fig. 3 and Fig. 4, the large radial displacement of the double cone angle drum is 0 118 mm, and the large axial displacement of the Zui is -0 141 mm. Obviously, the large axial displacement of the drum and the large radial displacement of the Zui are small, meeting the rigidity requirements.
This analysis uses the stress intensity SINT to describe the stress state of the drum and compare it with the design stress intensity Sm of the material. The drum material is 0Cr19Ni9, and its design stress intensity is Sm=137MPa. For the average stress intensity along the wall thickness direction, the design stress intensity is doubled for the thickness of the wall thickness, ie Sm; for the large stress intensity along the wall thickness direction, due to the inclusion of less harmful bending stress Part, so take the design value of 15 times the design stress intensity, that is, 15Sm [5].


It can be seen from Fig. 5 that the stress level on the double cone angle drum is low, and the large value of Zui is only 72 9 MPa, while the large stress intensity of the drum is 109 MPa, which appears on the outer side of the center line zui of the drum big end cover. A little bit. This is different from the single cone angle drum. The large stress of the single cone angle drum appears on the cylinder, and its value is only 39 MPa (see Figure 6 for the single cone angle drum stress intensity distribution cloud map). It can be seen that the force state of the single cone angle drum is better than that of the double cone angle drum. However, since the large stress intensity of the double cone angle drum is also less than the allowable stress of the material of 15 Sm, the double cone angle drum strength is safe. The zui danger point of the double cone angle drum is not on the cylinder and outside the center line of the big end cover. This is because the large cone angle is large. When the material reaction force acts on the * cone section, the center line of the big end of the drum There will be a large bending moment, so that the stress is large at this point, so the design of the material and thickness should be fully considered.


In order to further study the stress distribution of the two special sections along the wall thickness direction of the drum, that is, the stress distribution of the SINTzui large value section and the drum column cone transition section, the following path operation is performed.
Path 1: the transition section of the cone, node491→node591;
Path 2: Zui value cross section, node1 → node70, the path operation position is shown in Figure 7.

Figure 8 and Figure 9 show the variation of MEMBRANE, MEM+BEND, TOTAL stress intensity along path one and path two, and m represents displacement.


It can be seen from FIGS. 8 and 9 that the membrane stress of path one is 35 78 MPa, and the membrane stress of path two is 59 85 MPa, which is smaller than the allowable stress Sm of the material. The calculation also found that the drum has only a large stress intensity (SMX) on the straight cylinder under the action of centrifugal force, and the value is 30 1 MPa. However, the value at this point is only 11 9 MPa under the action of material reaction, indicating that the drum cylinder stress is mainly caused by centrifugal force.
3 Conclusions This paper establishes a reasonable two-dimensional finite element model of the double cone angle drum, and checks the strength and stiffness under normal working conditions to verify that the improved structure is safe. It is also found that the dangerous position of the double cone angle drum is the outer side of the center line of the large end cap, where there is a high bending stress, so the design of the material and thickness should be fully considered.

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