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Procedia Engineering
Procedia Engineering 15 (2011) 4579 – 4584 Procedia Engineering Ce(2011) is6–067 www.elsevier.com/locate/procedia
Advanced in Control Engineering and Information Science
Study on the Temperature Changing Rules of U75V Rail in the Cooling Process Gao Mingxina, Song Huab*, Jia Haob, Jiang Juanjuanb, Tong Shanhub, Yuan Siyuc and Wang Zhongqiangc a
b
Heavy Equipment Manufacturing Factory of China First Heavy Industries School of Mechanical Engineering and automation, Liaoning University of Science and Technology, Anshan, Liaoning 114051, China c Anshan Iron & Steel Co; Ltd., Anshan, Liaoning 114021, China
Abstract Caused by the differences in volume and heat dissipation area of rail head and bottom, latent heat of phase transition releasing and other reasons, the complicated temperature changes occurs in rail head and bottom between during the cooling process, especially in solid state phase transition. In the paper, the ANSYS heat-stress couple module is adopted to carry on numerical simulation on the cooling process of 60kg/m U75V heavy rail. Though the postprocessing result analyzed by using the post-processor module, we got the temperature changing rules for heavy rail cooling process. This paper is of great reference value for the bending deformation study in the hundred-meter heavy rail cooling processing.
© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of [CEIS 2011] Open access under CC BY-NC-ND license.
Keywords: Heavy rail cooling; Phase transition; Temperature field
1 Introduction High speed running of railway train requires high straightness of heavy rail, and the distribution and temperature change of heavy rail in cooling process has effect on the straightness and residual stress of produced rail to a certain degree [1]. Heavy rail is special-shaped section steel, there are differences in heat radiation areas and cooling rates of each part section, which leads to an uneven temperature distribution of heavy rail, and produces thermal stress. The phase of high temperature rolled rail is main Austenitic, and on the cooling bed the change occurs from solid phase transition of Austenite to Pearlite. Latent heat releases in phase transition process which has an impact on temperature field, and leads to that the rail temperature changing become more complicated. Reference [2,3,4] study on the finite element simulation of temperature field to obtain the temperature distribution in the cooling process, however, Reference [2] doesn’t consider latent heat releasing from solid phase transition, Reference [3] considers the latent heat, but it doesn’t analyze the rules of temperature field change in the solid phase transition during cooling process, Reference [4] simulation calculation does not match the actual production that rail bottom temperature is higher than rail head. Some references only set up the 2-dimensional model [5]. In the paper, *
* Corresponding author: +8613188003145 E-mail address:
[email protected]
1877-7058 © 2011 Published by Elsevier Ltd. Open access under CC BY-NC-ND license. doi:10.1016/j.proeng.2011.08.860
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the ANSYS heat-stress couple module is adopted to carry on numerical simulation on the cooling process of 60kg/m U75V heavy rail. Though the post-processing result analyzed by using the post-processor module, we get the temperature changing rules for heavy rail cooling process, and further emphasize the temperature changing rules during latent heat releases in phase transition process. The heavy rail temperature changing rules are of great reference value for the bending deformation study in the hundredmeter heavy rail cooling processing. 2 The finite element simulation of temperature field in cooling processing 2.1 Differential equation establishment U75V heavy rail natural cooling process on cooling bed is in a certain initial conditions and boundary conditions of non-steady-state heat conduction problem. The heat conduction differential equation of heavy rail [6]： ∂T ∂T ⎛ ∂T ⎞ ∂T ⎛ ∂T ⎞ ∂T ⎛ ∂T ⎞ (1) ⎜ λ ⎟ + ⎜ λ ⎟ + ⎜ λ ⎟ + q = ρc ∂x ⎝ ∂x ⎠ ∂y ⎜⎝ ∂y ⎠⎟ ∂z ⎝ ∂z ⎠
v
∂t
If heat conduction coefficientλ in x、y、z direction has the same value, it turns: ∂2T ∂2T ∂2T qv 1 ∂T + + + = ∂x2 ∂y2 ∂z 2 λ a ∂t
(2)
In the formula： a = λ / ρc ——temperature diffusivity； ρ ——density； c ——specific heat； λ ——heat conduction coefficient.
2.2 Materials thermal physical parameters of heavy rail Flashline TM-5000 of Thermal Properties of Analyze produced by United States Anter Company is applied to measure specific heat c and coefficient of thermal conductivity λ of U75V heavy rail. Latent heat of phase transition is processed by heat enthalpy method [3], and the thermo-physical parameters are shown in Fig. 1.
Fig. 1 The thermal physical parameters of U75V heavy rail
Fig. 2 Meshing of heavy rail
2.3 Model establishment and meshing To reduce the calculation time, the section of 2000mm long 60kg/m U75V heavy rail model is simplified. The hexahedron solid5 unit which has the function of limited coupling between temperature and structure field is adopted in meshing, 60kg/m rail model is classified by a total of 44,000 units (dividing 250 equal parts along the length direction), 57,479 node, it is shown in Fig. 2.
Gao et al. / Procedia Engineering 15is6–067 (2011) 4579 – 4584 SongMingxin Hua/ Procedia Engineering Ce (2011)
2.4 Initial and boundary conditions The natural cooling process of heavy rail bed on the cooling bed is air cooling, heat transfer boundary conditions are mainly for the convection and radiation.So as to get the total heat-transfer coefficient [6] in the natural cooling process on the cooling bed, we calculate the value by the experience formula in this paper, as follows: 0.25 (3) H = 2.6(Tw − Tc ) + 4.84 ×10−8 Tw2 + Tc2 (Tw + Tc )
(
)
In the formula :Tw——workpiece temperature; Tc——environment temperature. In worksite measurements, the temperature when the heavy rail just finishing rolling is 920-930℃, and when through transport roller reaching cooling bed is about 900℃; so take 900℃ as initial cooling temperature of heavy rail on the cooling bed, environment temperature is 30℃. Preparation of cooling time is 9,000 seconds. 3 Analysis of simulation result Figure 3 shows the temperature field distribution contours of rail section at different moments.
(a) t=930s
(b) t=1110s
(c) t=4170s
(d) t=4530s
Fig. 3 The temperature field distribution contours of rail section at different moments
Figure 4 shows the whole and middle section temperature distribution after 9,000 second cooling on the cooling bed. As known in Fig. 4, Temperature is uniform distribution except the both ends of the rail, in the section temperature distribution, the rail head reaches the highest temperature, rail waist and rail bottom reduced in turn, and the temperature in the middle of rail head and bottom is higher than the two sides. The
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center of rail head temperature is highest which is 85.164℃, and lowest temperature is 56.967℃, which appears in the rail bottom side.
Fig. 4 Temperature distribution of heavy rail after cooling
Figure 5 shows temperature changes with time curve at the rail head mid-point, rail waist mid-point, rail bottom mid-point and bottom side point of the middle section. Table1 shows temperature values of rail head mid-point, rail waist mid-point, rail bottom mid-point of rail middle section during 930-4,530 seconds. Figure 6 shows the temperature difference curves between rail head and rail bottom during cooling. Rail cooling process can be divided into two part which are the phase pre-transition area and the transition area post-transition area.
Fig. 5 Heavy rail key points temperature changing with time curve
70
Temperature difference（ ℃）
60 50 40 30 20 10
0 390 750 1110 1470 1830 2190 2550 2910 3270 3630 3990 4350 4710 5070 5430 5790 6150 6510 6870 7230 7590 7950 8310 8670 9000
0
Time（s）
Fig. 6 Temperature difference between rail head and rail bottom
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Gao Mingxin et al. / Procedia Engineering 15 is6–067 (2011) 4579 – 4584 Song Hua/ Procedia Engineering Ce (2011) Table 1 Heavy rail key points temperature values in the phase transition Time (S)
The mid-point of rail head(℃)
The mid-point of rail waist(℃)
The mid-point of rail bottom (℃)
Temperature difference between rail head and rail bottom(℃)
930
855.626
848.31
849.894
5.732
1110
847.772
840.535
843.987
3.785
3810
665.729
636.301
638.824
26.905
3900
657.789
628.191
630.44
27.349
3990
649.791
620.046
622.013
27.778
4080
641.738
611.866
613.367
28.371
4170
633.634
603.642
603.149
30.485
4260
625.477
587.972
579.278
46.199
4350
617.179
570.588
559.354
57.825
4530
589.903
540.598
527.282
62.621
From Figure 5 and Figure 6 tells that at the 900-850℃ intervals, heavy rail cools faster, due to bigger radiation area, rail bottom cools faster than rail head and temperature difference increases, which is called pre-phase transition area. When the rail cooled in 930 second, rail bottom temperature first drops below 850℃, solid phase transition occurs in rail bottom, it goes to phase transition area. Due to the impact of phase transition latent heat, rail bottom cooling rate slowed, but rail head is still in the austenite cooling process, gets the faster cooling rate than rail bottom which decreases the temperature difference. As cooling continued, the solid phase transition occurs in rail waist and rail head, which increases the temperature difference. When the rail cooled in 4,170 second, rail bottom first completes solid phase transition, cooling speed becomes faster. while the external of rail head is still in the solid phase transition period, and the cooling rate is slower, the temperature difference between rail bottom and rail head increases to 30.5℃. Later than the 4,170 second, the middle of rail head enters solid phase transition period, cooling speed is still slow, although rail bottom cooling is faster, rail head and rail bottom temperature difference increases rapidly. When the rail cooled in 4,530 second, the center of rail head temperature drops to 589.9℃, solid phase transition of rail head ends. and the temperature difference between rail head and rail bottom reached the maximum at this time, 62.6℃. At this point, the rail solid phase transition completes. Then, the cooling rate increases again, rail head and rail bottom temperature difference will gradually decrease until the end of the cooling, rail temperature is more and more close to environment temperature, and becomes stabilized, which is called post phase transition period. The complicated temperature field change during rail cooling process is the main reason, which causes the complicated bending deformation. 4 Conclusions y The distribution rule of temperature field after cooling is that the center of rail head temperature is highest, which reached to 85.164℃, the rail bottom side temperature is the lowest, which reached to 56.967℃. The temperature difference between the maximum and minimum value is 28.197℃. y When the rail cooled in 930 second, heavy rail comes into the solid phase transition period, when in 1110 second, rail fully enters to the solid phase transition period, when in 4,170 second, rail bottom first complete the solid phase transition period, when in 4,530 second, heavy rail fully complete the solid phase transition, enters to the Pearlite cooling process. y In cooling process, temperature difference between rail head and rail bottom experiences the complicated change process that is called the increase-decrease-increase-decrease change, and the maximum temperature difference is 62.6℃, which appears when heavy rail totally completes the solid phase transition. The complicated temperature field change is main reason that results in complicated bending deformation during rail cooling process.
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Acknowledgement Supported by National Science Foundation of China (ID5107488) References [1] Filippov.K.S. Improvement in Quality of Rail Means of Degass. STAL, 1999(12): 35-42 [2] Zhou Jianhua, Lin Gang, Wu Di, Zhao Xianming. Finite Element Simulation and Analysis of Temperature Field of 60kg/m Heavy Rail During Cooling. Journal of iron and steel research.2007, Vol.19, No.11,29-32 [3] Li Ge, Cui Haiyan, Chen Lin. Finite Element Analysis on Temperature Field of 100-metre U75V Steel During Cooling Process before straightening, Special steel, 2009,Vol.30,No.1,1-3 [4] J Basu,S L Srimani,D S Gupta.Rail behaviour during cooling after hot rolling. The Journal of Strain Analysis for Engineering Design.2004,Vol.39,No.1:p.15-24 [5] Lenard J G.A Study of Temperature Distribution in Rails during Intermittent Cooling. Journal of Materials pressing Technology,1991,25(3);303 [6] Liu Gaodian. The Numerical Simulation of Temperature Field.ChongQing: ChongQing University Press,1990 [7] Li Ge, Jia Baohua, Jiang Xu. Finite Element Analysis on Bending Deformation of 100-metre U75V Steel During Cooling Process before straightening. Special steel, 2010,6,31(3):14-16 [8] Jonas W. Ringsberg, Torbjorn Lindback. Rolling contact fatigue analysis of rails including numerical simulations of the rail manufacturing process and repeated wheel-rail contact loads. International Journal of Fatigue.2003,p:547-558
Appendix A. Corresponding author Song Hua (1968- ), male, Han nationality, Shanxi people, Professor, PhD, mainly engaged in teaching and researching work in metallurgical machinery field. Address: Science and Technology Department, Qianshan 185th Liaoning University of science and technology, Anshan, Liaoning, China. Postcode: 114051. Tel: 0412-5928168. E-mail:
[email protected].
