WCA January 2020

In the solidification and crystal- lisation process of hot continuous casting copper liquid, casting temperature, casting speed, casting angle and heat transfer coefficient are important parameters affecting the crystallisation quality of slab. The theoretical model of slab forming is established considering the influence of process parameters. Differential equation of heat conduction in crystal cavity [5] : Where c p and λ are specific heat capacity at constant pressure and thermal conductivity. There are momentum convection, interdendritic flow and flow with the mould in the solidification process of copper liquid. The differential equation of turbulent kinetic energy of copper liquid is established. ❍ ❍ Equation 1 ρ c p ∂ T ∂ t = ∂ ∂ t ( λ ∂ T ∂ x ) + ∂ ∂ y ( λ ∂ T ∂ y )+ Q

Copper billet

Tundish

Idler wheel

Pressing wh eel Copper strip heater

Casting wheel

Tension wheel

Tension adjusting mechanism

❍ ❍ Figure 1 : The structure diagram of a five-wheel casting machine system for SCR

Roughing

Finish rolling

Copper billet 3,800mm 2

Copper rod 50.27mm 2

❍ ❍ Figure 2 : Structural chart of hot continuous rolling mill

⎡ ⎣ ⎢ ⎢

⎤ ⎦ ⎥ ⎥

⎞ ⎠ ⎟⎟

⎛ ⎝ ⎜⎜

∂ ( ρ u i

k )

∂ k

∂ ( ρ k )

µ i σ k

µ i

∂ ∂ x

2 Theoretical modelling Continuous casting and hot rolling are the key processes of the SCR3000 production line. The theoretical models of continuous casting stage and hot rolling process are established respectively, and the production process of copper rod is analysed comprehensively. 2.1 Analysis of casting technology An SCR3000 five-wheel casting machine is composed of a casting wheel, steel belt, driving device of the casting wheel, follow-up wheel device, carbon coating device of casting mould, traction device of casting billet and conveying device of casting billet. The system structure is shown in Figure 1 . Copper liquid is injected into the trapezoidal crystallisation chamber, wrapped by a steel strip and casting wheel at a certain angle from the tundish casting pipe. Cooled by water of the casting machine, liquid copper solidifies and crystallises dynamically in the form of convection during the constant speed rotation of the crystallisation wheel to form high temperature copper billet. The crystallisation wheel is induced by a demoulding device and subsequent bridge guide wheel. After edge cutting, the crystallisation wheel enters the rolling mill system. Thus the continuous casting of ‘casting-cooling- demoulding’ can be realised. ❍ ❍ Table 1 : Analysis of relevant parameters of hot continuous rolling

+ G

− ρε + D +

k

∂ t +

=

µ i

+

k

∂ x

K

∂ x

i

i

i

p

❍ ❍ Equation 2

Where k and ɛ are turbulent kinetic energy and turbulent dissipation rate; µ i and f i are viscosity and turbulence parameters; C i , σ k , σ ε , c µ are K – ε model constant. 2.2 Deformation analysis of copper rod in hot continuous rolling The hot tandem rolling mill adopts ten Morgan two-high cantilever tandem rolling mills arranged alternately (Figure 2 ); each stand drives independently and the rolling speed is automatically controlled by the signal provided by the caster. The copper billet is bitten automatically after entering the rolling mill, and ϕ 8mm copper rod is formed after rolling through the roll system of each stand, controlled by ellipse-circular pass system ( Table 1 ). After ten passes of rolling, the temperature of the copper rod decreases greatly, and columnar crystal copper slab becomes equiaxed crystal copper rod. Continuous non-twist rolling greatly improves the production efficiency of copper rod. The copper rod hot rolling process is in the state of large deformation, high temperature and high strain rate, which belongs to a highly coupled thermal-mechanical non-linear problem. Considering the variation of the temperature field, stress-strain field and the law of interaction between temperature field and stress-strain field, the deformation process of copper

1H 2V

3H

4V

5H

6V

7H

8V

9H

10V

D k /mm 295.89 282.00 197.69 196.59 206.75 204.34 208.74 205.43 206.86 206.78 n /r·min -1 22.11 44.06 101.99 169.19 257.56 401.19 611.11 819.17 1,189.95 1,574.51 Z/% 34.21 47.20 39.39 40.00 37.50 35.00 35.90 24.00 31.58 22.66 δ 1.52 1.89 1.65 1.67 1.60 1.54 1.56 1.32 1.46 1.29

* Dk – Working diameter, n – Roll speed; Z – Section shrinkage; δ – Elongation coefficient

91

www.read-wca.com

Wire & Cable ASIA – January/February 2020