Modeling and finite element analysis of rod and wire steel r(2)

3. Modeling 3.1. FE model Dongbei Special Steel Group has imported a block with a 30-stand continuous rod and wire production line with temperature control facilities. The mill as-signment of the front 12 passes is represented sche-matically in Fig. 1. The GCr15 square billets of 150 mmu150 mm are passed through the 12 passes and rolled into a rod-wire with a radius of 16 mm. The

rolling line length is extremely large compared with the billet thickness. Therefore, the whole rolling proc-ess is described using two FE models based on the

commercial software MSC.Marc. In the two models,

414 J. Univ. Sci. Technol. Beijing, Vol.15, No.4, Aug 2008

the billet is defined as a deformation body and the P T1 T2 T3 1.05 0.0005T (11) rolls are defined as rigid bodies. Owing to the symme-try of billet and rolls, a quarter of the billet and rolls was included in the geometric model. Fig. 2 shows the first model, which includes the descaling stage and rough rolling stands. The x, y, and z axes in the model represent the directions of rolling, thickness, and width, respectively. The total element number of the billet is 1035 and the total node number is 1392. The length of the billet is 400 mm and the distance be-tween the two stands is 2600 mm. The quasi static analysis is adopted in the simulation of the first model. A rigid body whose speed is controlled by MSC.Marc’s subroutine is employed to stick to the end of the billet, so it can push the billet to the entry of the next stand with a slight force and an actual exit speed during the inter-pass time. The method has also been employed in the static analysis of the second model, which is similar to the first model, but also has differences, such as the shape and dimension of rolls and billet, the distances between stands, and rolling speed. The second model includes the cooling process on the conveyer and the first section of intermediate stands. Fig. 3 shows the second model in which the length of the billet is 300 mm and the distance be-tween the two stands is 2500 mm. The total element number is 2730,

and the total node number is 3621.

Fig. 1.

Mill layout of rolling mills.

Fig. 2. FE model of the rough rolling process.

3.2. Simulation condition

The friction is a complex physical phenomena on account of the variations in surface conditions, relative sliding, temperature, geometry, and so on. Marc al-lows users to define the friction model by means of using its UFRIC subroutine. The friction coefficient is obtained as

whereT is the temperature of the contact surface, T1 and T3 are the modifying factors determined by different rolls and steels, respectively.T2 0.4 0.6e[ 0.2 v 2.0 ], it is determined by the roll-

ing speed.

Fig. 3. FE model of the mid-rolling process.

The heat generated by friction is fairly assigned to the rolls and billet. The deformation of the billet will generate heat, and 90% of the power of deformation is transformed into heat. On the symmetrical surface of the billet, it is supposed that the heat flux is 0. And the main parameters adopted in the two models are shown in Table 1.

Table 1. Thermal conditions used in the analysis

Initial temperature of material / qC 1045

Temperature of roll / qC 100

Heat transfer coefficient from roll to material /

(kW m 2 K 1)

9.5

Emission and convection coefficient from

material to surroundings / (kW m 2 K 1)

0.07

Atmospheric temperature / qC 20

4. Data transfer technique

Because of the limitation of the current computer speed, the whole rolling process was described with two three-dimensional models. To keep the continuity of simulation, the temperature results of the first mod-el should be inherited as the initial conditions of the second model. Therefore, a procedure for data transfer with the aid of MSC.Marc and its subroutines to ac-complish the process is developed in this article. The data transfer technique consists of three parts. The first is to extract the output data of the first model including nodal temperature, nodal coordinates, Guas-sian point coordinates, element number, and nodal displacements. The second is to judge the relationship between each node in the second model and the ele-ments in the first model andto solve the nodal tem-

S.L. Liao et al., Modeling and finite element analysis of rod and wire steel rolling process 415

peratures of the second model by means of data map-ping. The third is to feed the temperature results into the new model as an initial condition of calculation with Marc’s subroutine USINC. Fig. 4 shows a sche-matic diagram of data mapping. As shown in Fig. 4(a), there is a final mesh with a large deformation after six rolling passes. Fig. 4(b) shows an entirely new mesh, which has the same shape and dimension in cross-section as the one in Fig. 4(a). With assumptions of accuracy, it is necessary to employ a new mesh, which is shortened so as to reduce the computational time. When the final mesh in Fig. 4(a) is replaced by the new mesh in Fig. 4(b), the temperature values of all nodes in the new mesh need to be determined ac-cording to the temperature results of the final mesh. The new mesh can be regarded as a part of the final mesh in Fig. 4(a), and then there exists a connection that each node in the new mesh will locate inside some elements of the final mesh in Fig. 4(a). In the proposed models, the billet is modeled as an elas-tic-plastic object using an eight-node isoparametric hexahedron element that uses eight-point Gaussian integration. If all the eight nodes of an element are determined, the element is then known. That is to say, each node of the mesh in Fig. 4(b) can be expressed by eight nodes of its related elements on the mesh in Fig. 4(a). Therefore, the temperature field values of each node in the new mesh can be determined by the …… 此处隐藏：6109字，全部文档内容请下载后查看。喜欢就下载吧 ……