外文翻译辊缝润滑工作辊冷却及反剥系统在热轧钢机上的协调应用.docx

1、外文翻译辊缝润滑工作辊冷却及反剥系统在热轧钢机上的协调应用附录A Coordinated Application of RollGap Lubrication, Work Roll Cooling and Antipeeling Systems in Hot Rolling MillsSurface quality requirements for hot rolled steel sheet have continued to become more stringent in recent years. This focus on sheet quality has developed in

2、 parallel with corresponding demands for increased productivity and reduced costs at the mill. Although not a panacea, roll gap lubrication systems have received increased attention in support of these objectives. Specifically, roll gap lubrication systems are used in combination with work roll cool

3、ing systems and antipeeling systems to: Reduce rolling loads and thereby reduce potential for chatter. Reduce rolling torques and associated energy requirements. Enable redistribution of loads among stands to address chatter issues. Increase reductions to decrease final strip thickness. Reduce poten

4、tial for rolled-in scale. Extend rolling campaign length.These systems must also be designed and operated in a manner that will: Assure good plating of the oil onto the work roll surface. Maintain stability of mill control systems. Minimize the environmental impact of vapor emissions and spent fluid

5、s. Prevent clogging of fluid supply lines.The effective implementation of these systems can provide enhance control over the thermal and tribological conditions in the roll bite to achieve objectives for product quality and mill productivity. These systems have undergone development for a number of

6、years and are now being implemented and refined throughout the world.Overview of Chatter and Peeling on Roll SurfacesThe early stands of steel hot finishing mills routinely operate at relatively high loads and relatively low speeds. These operating conditions represent a very aggressive environment

7、for mill work rolls. High loads, combined with other factors, can contribute to mill stand vibrations commonly known as chatter. These vibration produce cyclic loading conditions in the stand, which can produce visible marks on the roll surface. These marks are then transferred to the sheet, produci

8、ng an undesirable surface quality.The effective implementation of roll gap lubrication technology can make it possible to reduce and/or redistribute loads in the mill, thus decreasing or eliminating chatter. Furthermore, the strip surface temperatures that are the contact time between the strip and

9、the work roll, impacts the temperatures that are reached on the roll surface. Higher temperatures accelerate the formation of oxides on the roll surface. Thin layers of these oxides can then be “peeled off” the roll surface by the alternating shear stresses associated with slip in the roll bite. Whe

10、n this occurs, it results in a roll surface defect commonly called “peeling”.These peeling marks also negatively affect the strip surface quality , producing what is known as rolled-in scale. Solutions to the peeling problem involve establishing a balance between oxides growth and wear at a minimal

11、thickness in the roll bite.Antipeeling and work roll cooling technologies are utilized to achieve this balance. These technologies must be coordinated with the roll gap lubrication systems in order to assure optimal effectiveness of each technology.Overview of System Hardware and OperationThe work r

12、oll cooling headers are provided on both the entry and exit sides of the stand. The area of spray coverage in the roll is largest in the exit side. This provides the maximum cooling effect when the roll surface is at its highest temperature shortly after it rotates out of contact with the strip.Work

13、 roll cooling headers are also mounted on the entry side of the stand. These entry side headers are disabled when the roll gap lubrication headers are operated, so as not to wash off the oil before it can effectively plate onto the roll surface.The roll gap lubrication headers are also located on th

14、e entry side of the stand. They spray an oil/water dispersion onto the roll surface prior to its rotation through the stand entry wiper. As the water component of the dispersion is vaporized, the pressure that is exerted by the wiper enhances the plating of the oil onto the work roll surface.Configu

15、ring and operating the system in this manner ensures that the oil is plated onto the work roll surface so that it will enter the roll bite without being washed away. This oil provides the lubrication in the bite to reduce loading in the rolling process.Antipeeling headers are fitted on the entry sid

16、e of the stand. These headers apply coolant directly onto the strip to reduce its surface temperature before it enters the roll gap.Because of the close proximity to the roll bite, there is a very little time for conduction to redistribute the temperature within the body of the strip. Hence, only th

17、e strips surface temperature is significantly reduced before entering the roll bite, and temperature at the core of the strip remain essentially unchanged.The lower strip surface temperature also reduces the resulting roll surface temperature by reducing the driving force for conduction between them

18、. This decreases the rate of formation oxides on the roll surface, which reduces the tendency for peeling.Roll Gap LubricationThe roll gap lubrication headers are supplied with oil/water dispersion. Separate systems are provided for top and bottom headers in each equipped mill stand. The water /oil

19、dispersion is formed in a static mixer located just before the spray header. By creating the dispersion in close proximity to the header, the time for the oil to break out is minimized, and the length of piping subject to clogging by the dispersion is also reduced.The oil flow is provided by meterin

20、g pumps and is enable only during rolling. Metering pump speed is regulated to maintain a specified volume flowrate for the process. Adjustable throttling valves regulate the water flowrate. Water flow is maintained, even when the oil is shut off, to help clear piping deposits and thereby prevent cl

21、ogging.The headers spray width is adjusted to the width of the strip being rolled via air-operated shut off valves. This approach provides the dispersion only to the aea where it is required on the work roll barrel. By limiting the rolling operation, the volume of oil consumed, along with the associ

22、ated operating cost, is minimized.This approach also addresses environmental; considerations, in that the volume of vapor emissions and the volume of waste fluids that require special disposal are reduced. The result is that the headers and spray nozzles provide uniform application of the dispersion

23、 to the top and bottom work rolls in the area of contact with the strip.It should also be noted that water quality can significantly affect the performance of the oil/water dispersion. Therefore, the oil supplier must adapt the oil quality to the water quality.Impact of Roll Gap Lubrication and Oper

24、ating PhilosophiesProperly designed roll gap lubrication systems reduce friction in the roll bite and thereby reduce the resulting rolling load. Although some variations exist, there are predominantly three philosophies that are followed in the operation of roll gap lubrication systems.The first phi

25、losophy is “body only”. It is typical of operation for the first stand of the finishing mill, although some roll gap lubrication systems follow this practice on other stands as well. In this philosophy, the oil flow is not enabled until after the strip has threaded through the stand. This provides a

26、 higher friction condition during threading to reduce the potential for bite rejection.Note that when RGL is enabled, there is a significant reduction in rolling load. The oil flow is again disabled before tailout, so that any residual oil that remains on the roll surface can be consumed in the proc

27、ess. This restores the effective friction to a higher level prior to threading of the next strip. It also results in a corresponding increase in the rolling load.This approach supports threading operations, but the significant changes in loading that correspond to the activation and deactivation of

28、the roll gap lubrication system produce transients that must be addressed by the mill control systems. The impact of these transients will be discussed later.The second philosophy is “body and tail”. This approach has historically been followed on stands F2-F7. Here, the roll gap lubrication system

29、is enabled after threading, but it is not disabled until tailout is completed. Operating in this manner still produces a load transient at the beginning of the coil, but it eliminates the one at the end.Impact of Oil Volume Flowrate on Rolling Load The load reduction that is afforded by roll gap lub

30、rication depends on a number of factors, one of which is the volume flowrate of oil. Representative tests have been performed to analyze the effect of oil flowrate on rolling load at stands F2-F4. Note that roll gap lubrication is on only the upper work roll of stand F2.Also note that the loading re

31、duction on each of the stands appears to be approaching a limiting value asymptotically, as oil volume flowrate is increased. Hence, there is a limit to the benefit obtained with application oil application. Increasing oil application beyond this point would only increase operating cost and potentia

32、l environmental issues while providing little or no benefit.During these tests, only the upper header was operating on F2. Hence, the rolling force reduction may be different with both headers operating, but the trend of decreasing benefit with volume flowrate is still visible.Other loading and operating conditions, as well as other oil and water dispersion, may exhibit different volume flowrate requirements to approach this limiting point. Nevertheless, the general behavior of receiving diminishing returns for continued increases in oil volume flowrate is expected to hold for these other ap