Increasing Hot Rolling Mass of Steel Sheet Products Viktor Artiukh1,a*, Vladlen Mazur2,b, Raghu Prakash3,c 1
St. Petersburg State Polytechnical University, Polytechnicheskaya, 29, Saint-Petersburg, 195251, Russia 2
LLC “Saint-Petersburg Electrotechnical Company”, Pushkin, Parkovaya, 56, Saint-Petersburg, 196603, Russia
3
Indian Institute of Technology Madras, C1-6-7, Second Loop Road, Madras Campus, Chennai, 600036, India a
[email protected],
[email protected],
[email protected]
Key words: Dynamic Loads, Accidental Failures, Workpiece, Rolling Mill Frame, Materials Science, Main Line, Contemporary Materials for Metallurgy.
Abstract. The article exposes contemporary materials and structures for metallurgy. Feasible increase of dynamic forces on the rolling machinery during rolling of billets with masses up to 20 t (Stand No.1 of CWM 1700 HR, «U.S. Steel Košice», Košice, Slovakia, and PJSC «Illich MMPP», Mariupol, Ukraine) is discussed. It is proved that weight of billet, velocities of metal delivery to working rolls and rolling significantly influence the dynamic loads during metal biting. The technical solutions are suggested which would allow the steady rolling process of billets with masses up to 20 t and prevent accidental failures of frame parts, chocks and main lines. 1. Introduction Presently in most metallurgical plants the efforts are focused, apart from the commercialization of rolling the new steel grade products, mostly on hot rolling of steel sheet products of increased weight by means of existing rolling mills. According to the practice, the new and required weight of rolled products (hot-rolled rolls, plate iron) should be increased over the indicated in specifications margins in 1.5… 2.5 times (or by 20… 30 tons, respectively). This consideration reflects increasing demand of the rolled products of enlarged dimensions, in particular, because of feasible reduction of welded joints in end items. Typically, construction of new rolling shop in a metallurgical plant is barely feasible in conditions of the world-wide economical crisis. Therefore the step-by-step modernization of the existing rolling shop machinery may be considered reasonable when the long-term shutdown of production is not necessary. 2. Materials and Methods Increasing of the rolled products weight problems are typically considered by the process experts, in particular, the problems of uniform heating of billets, transportation of billets by the means of furnace run-out table, positioning of billets on rolling tables between rolling stands and stability of rolling. It is assumed that when the existing equipment and the rolling regimes are used for production of rolled items of increased weight of the same grade steels the rolling forces and moments would not change since the billet cross section and temperature, the rate of the billet biting in rolls and rolling velocity are suggested unchanged. However, increasing the weight of the rolled mass causes increasing frequency of failures of the main drive lines and mill stand details, shortening of the interrepair time. That is why numerous accidental breakdowns of work rolls (WRs) and main drive lines (MDL) happen [1-5]. To substantiate the necessity of considering the growth of stray forces while rolling of heavy billets the present authors had shown increase of the dynamic forces on example of analysis of loads in the cage quarto No.1 of continuous wide-strip mill (CWM) 1700 for hot rolling (HR) («U.S. Steel
Košice», Košice, Slovakia) and PJSC «MMPP Illich» (Mariupol, Ukraine). Also, the technical measures are suggested to provide the hot rolling of plates from 20 t. slabs. Assessment of working capacity of the rolling mill machinery should be initiated with statistical analysis of its breakdowns and failure locations in the course of initial billets mass rolling and the data on production technology indicated in certificate of the machinery, original rolling schemes and accepted rules for production. The due analysis of published data [6-8] indicates the high rate of breakdowns and outage time of existing rolling mills. The following in solution of above mentioned problem is evaluation of static and dynamic forces and moments exerted on the working stand equipment under rolling of billets of different sizes and mass. It may be reasonable to apply the results of experimental estimation of dynamic moments, power consumption by the working roll drives, etc. Experiments were carried out on the roughing cage quarto No.1 PJSC «MMPP Illich» [9]. The following parameters were measured selected for the following analysis of rolling the slab with crossection 180х990 mm into the 8.4 t coil 2.0x1000 mm from the steel 08kp grade (GOST 105088): The dynamic torque on the AC motor shaft transferred to a particular work roll, Мdin, while rolling (Table 1, where the numerator figures show the torque on AC motor shaft); Static torque under steady-state rolling on the AC motor shaft transferred to particular WR, Мdin (Table 1); Metal delivery to WRs velocity, V0 = 2.1m/s, which depends on conditions of billet bottom surface and slip of billet over the surface of roller tables; Rolling velocity, Vr = 1.293m/s, at known diameter of WRs; The metal bite time, tb ≈ 0.123s. Apart from that, the factor of dynamics of the MDL depending on the total radial clearance in MDL, kd 2.05...2.74 2.4 , is given (for the above rolling issue). Table 1. Measured and operation rolling torques in principal components of the MDL of roughing stand No.l of the PJSC «MMPP Illich» Element Operation torque [kN∙m] Measured Мdin max [kN∙m] Measured, Мst max [kN∙m]
Motor coupling 245/586 0
Gear reducer
Basic coupling
Gear Stand
Spindle
2160
4400
2900
1900
228/5467 95/2272
The term «Operating torque» means torque which can be transferred to the stand details and elements during steady-state rolling. This torque may be regarded responsible for fatigue strength (actual durability) of the rolling stand details. The values of operating torque in Table 1 are taken from the equipment certificates (gear reducer and gear stand) and from design drawing, where they are established by the manufacturer. The data given in Table 1 analysis shows that the weakest component of the MDL is the gear reducer, and there is notable difference between operating torque values in details and elements of the line. Respectively, the strength analysis of the MDL details should be carried out by taking into account the torque value, Мdin max = 5467 kN∙m, measured at the rolling of the 8.4 t heavy billet which can not be exceeded to provide the stable rolling and to avoid the breakdown of the main line when the 20 t heavy billet would be processed.
The dynamic torque records show [8, 9] that maximum values of torque occur during metal biting by WRs. Therefore, it is necessary to analyze the dynamic loads in the metal biting area which are further transferred to WRs and equipment of the rolling mill. The main dynamic loads maximum values and oscillations of which may cause breakdowns of the MDL and housing details, rolling cage carriages are the dynamic rolling torque, Md [7, 10], and horizontal dynamic impacts of WR carriages against housings (carriages of the supporting rolls) during the rolling, Fhor. d [11, 12]. The relationship between Md and Fhor. d is known [13], which allows application of them both for analysis of causes of breakdowns of the rolling stand details. The horizontal impact of the upper roll carriage against the upper supporting roll was recorded while rolling the 8.4 t heavy steel 08kp grade slab (mentioned in above) shown in Fig. 1.
Fig. 1. Record of the horizontal impacts of the top WR carriage against the top BUR carriage in No.l stand of CWM 1700 HR Extremely high value of horizontal impact indicated in Fig. 1 is caused by inertia load, Qin, transferred from the billet to the WRs at the termination of rolling when the front face of the billet levels with the forthcoming plane of neutral section at the steady rolling process [14], Fig. 2. The horizontal inertia force, Qin, and force of interaction of top WR and BUR [13] are the cause of initial horizontal force, Fhor. (Table 2), which significantly increases due to acceleration of the WR assembly with carriages, beams, etc. within the clearance between WR carriages and housings (BUR chocks) [15]. The theoretical analysis of the horizontal impact of the top WR carriage against the top BUR carriage and respective impact of the latter against the mill housing has shown that it might be Fhor. d BUR = 3.518 MN based on assumption that about 1/3 of the time when metal would fill the deformation zone one of the work rolls were loaded by the double value of the rolling torque caused by opening of radial clearances in MDL. According to the [16, 17] data the graphs of the dynamic factors, kd , dependence on the time of filing the deformation zone, tb, for the mill stand No.1 of CWM 1700 HR are plotted corresponding to rolling of the billets differing by weight (Fig. 3 and 4). Results of evaluation of the principal parameters of rolling and of forces generated in roughing stand quarto No.1 of CWM 1700 HR for the rolling regime described in above are given in Table 2. The data of the Table 2 shows that, approximately, during the rolling of the 8.4 t heavy billet (the rolling case mentioned in above) at the metal bite moment (when the bite arch would form) the horizontal impact of the top WR carriage against the carriage of the top BUR (and of the top BUR top BUR against the mill housing, respectively) occurs the magnitude which is Fhor. d = 3.518…3.85 МN.
Fig. 2. Scheme of forces applied form the billet to the top WR when the billet stops: Nх – horizontal projection of the normal force; Тх – horizontal projection of the friction force; α0 – the bite angle during forming of the forward slip area; αN – angle of application of the Nх; Qin – horizontal inertia force applied to WRs; l – the initial bite arc length. Therefore, to maintain the steady rolling of the large weight billets the rolling regimes should be selected allowing for decrease of the horizontal impact values, Fhor. ≤ Fhor. d. To provide that it is necessary: 1. To reduce the velocity of the metal bite by the WRs matching it and the velocity of the metal delivery to RWs. The maximum influence on the magnitude of the horizontal impact renders the bite type (free, forced or dynamic), rolling velocity and the billet weight at given rolling parameters (spellerizing, temperature, WR radius, strength and plasticity of processed material). There are several means of reducing the rate of the biting process [17, 18]. 2. To eliminate the clearances. The clearances between RW carriages and housing liners (BUR liners) allow acceleration of WRs into the lateral clearance by initial inertia force. The larger is the clearance the higher energy would acquire WR with carriages, liners, etc. It might be reasonable to use the prospective technical means of reducing the clearances [19, 20]. 3. To provide damping of the contact surfaces of carriages, liners and housings by the means of the efficient shock absorbers [21].
Fig. 3. Dynamic magnification factor vs the time of metal bite at MDL of No.l stand of CWM 1700 HR. Rolling of the 8.4 t billet
Fig. 4. Dynamic magnification factor vs the time of metal bite at MDL of No.l stand of CWM 1700 HR. Rolling of the 20 t billet Table 2. Measured and operative torques of rolling in main details and elements of MDL of No.l stand of CWM 1700 HR Billet weight [t] 8.4
V0 [m/s]
Vr [m/s]
Qin [МN]
Fhor. [МN]
Fhor. d BUR [МN]
Fhor. d max [МN]
2.1
1.293
0.5
1.085
3.518
3.85 (Fig. 1)
20
2.1
1.293
1.2
1.778
7.871
20
0.75
0.75
0.15
0.492
3.697
3. Conclusions 1. The common opinion that dynamic loads in the rolling are affected only by the billets crossection area where plastic deformation occurs, rolling regime and temperature, but do not depend on the billet mass is erroneous. 2. To provide processing of billets of increased weight it is necessary to reengineer the rolling stands and to increase step-wise the weight of billets to avoid accidental breakdowns of the rolling machinery. Initially, it should be done using the overhauled equipment (e.g., resurface welding and machining of the contact surfaces of housings, carriages, axial clampers to the design dimensions, filling of the new liners, components of the main line, etc.). 3. There are available technical measures allowing prevention of rapid increase of the stray dynamic loadings. Acknowledgments This article is written under grant «Verification and development of models of inelastic deformation at the passive loading» of Russian Foundation for Basic Research. Conflict of interests The authors declare that there is no conflict of interest regarding the publication of this paper. References [1] V. Mazur, V. Artyukh, G. Artyukh, M. Takadzhi, Current Views on the Detailed Design of
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