High-speed rolling by hybrid-lubrication system in tandem cold rolling mills

Accepted Manuscript Title: High-Speed Rolling by Hybrid-Lubrication System in Tandem Cold Rolling Mills Author: Yukio Kimura Noriki Fujita Yukihiro Matsubara Koji Kobayashi Yosuke Amanuma Osami Yoshioka Yasuhiro Sodani PII: DOI: Reference:

S0924-0136(14)00369-0 http://dx.doi.org/doi:10.1016/j.jmatprotec.2014.10.002 PROTEC 14140

To appear in:

Journal of Materials Processing Technology

Received date: Accepted date:

8-9-2014 2-10-2014

Please cite this article as: Kimura, Y., Fujita, N., Matsubara, Y., Kobayashi, K., Amanuma, Y., Yoshioka, O., Sodani, Y.,High-Speed Rolling by Hybrid-Lubrication System in Tandem Cold Rolling Mills, Journal of Materials Processing Technology (2014), http://dx.doi.org/10.1016/j.jmatprotec.2014.10.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

＜Title＞

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High-Speed Rolling by Hybrid-Lubrication System in Tandem Cold Rolling Mills

＜Full Name･Affiliation＞

JFE Steel Corporation, Steel Research Laboratory

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Noriki FUJITA

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Yukio KIMURA

JFE Steel Corporation, Steel Research Laboratory

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Yukihiro MATSUBARA

JFE Steel Corporation, Steel Research Laboratory

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Koji KOBAYASHI

JFE Steel Corporation, West Japan Works (Fukuyama)

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Yosuke AMANUMA

Osami YOSHIOKA

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JFE Steel Corporation, West Japan Works (Fukuyama)

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JFE Steel Corporation, Tin Mill Products Business Planning Dept. Yasuhiro SODANI

JFE Steel Corporation, Steel Research Laboratory

＜Address＞

1 Kawasaki-cho, Chuo-ku, Chiba 260-0835, Japan JFE Steel Corporation, Steel Research Laboratory, Rolling & Processing Research Dept. Tel

: +81-43-262-2918

Fax

: +81-43-262-4730

E-mail : [email protected]

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＜Synopsis＞ Lubrication is one of the most important factors for improving the productivity of tandem

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cold rolling mills, as it is possible to increase the rolling speed of thin gauge steel strips and prevent chatter when rolling materials with high deformation resistance. In this study, a

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new hybrid lubrication system is proposed and its effectiveness is clarified. The system is based on a lubricant recirculation system combined with a system for flexible lubrication

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control. The key to realizing the new lubricant system is control of plate-out oil film formation on the strip surface under high-speed rolling conditions. The plate-out oil film

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formation of emulsions is investigated, and the conditions for achieving a sufficient plate-out oil film are clarified. The time-dependent property, oil droplet size, and emulsion

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concentration are found to have significant effects on plate-out behavior. In addition, the conditions for practical application of hybrid lubrication systems are discussed from the

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viewpoint of realizing effective plate-out control. A new hybrid lubrication system was investigated, and it successfully enabled flexible controllability of lubrication conditions

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and achieved the high-speed stable rolling, while maintaining an oil consumption rate

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equal to that of recirculation systems.

＜Keywords＞

lubrication; emulsion; cold rolling; plate-out; hybrid-lubrication system; chatter

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＜Text＞ 1. Introduction

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High speed rolling technology for thin gauge steel strips is very important for improving the productivity of tandem cold rolling mills. As a matter of fact, production of steel strips

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is shifting to thinner gauges and higher strength materials with the aim of reducing the weight of steel products from the viewpoint of environmental preservation. In this

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situation, lubrication technology becomes more important for realizing stable and high-speed cold rolling. Oil-in-water (O/W) emulsions are generally used as lubricants in

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tandem cold rolling mills, as they provide good lubricity as well as cooling performance.

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In conventional cold rolling mills, the emulsions are supplied by either a recirculation system or a direct application system. In direct application systems, which are applied for

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thinner gauge materials such as tin-mill products, a high concentration emulsion is used for lubrication, and water is used for work roll cooling. An unstable emulsion is positively

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used for oil film formation. This type of system is thought to be more appropriate for high

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speed rolling. Kaneko et al. (2000) reported that the maximum rolling speed reached over 2,800 m/min with this type of lubrication system in the 1990s. At present, no other mills have exceeded that maximum rolling speed, which shows the advantage of direct application systems for high speed cold rolling. However, because the key to providing good lubricity in direct application systems is to use unstable emulsions, recycling of the emulsions is difficult, oil consumption is large, and the process generates a large volume of waste emulsions. In spite of attempts to recycle the waste lubricants, most emulsions need to be disposed of due to their unstable characteristics.

On the other hand, in recirculation systems, a low concentration steady emulsion is used for the functions of lubrication and cooling. Due to the stable characteristics of the

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emulsions, they maintain oil droplet dispersion in water even when used repeatedly. Recirculating use means that recirculation systems have a good oil consumption rate and generate less waste lubricants. However, since it is difficult to form an oil film on the strip

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surface with stable emulsions, lubricity is not comparable to than that of direct application systems, especially in high speed rolling. This is the main problem of recirculation

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lubrication system, and as a result, their application is mainly limited to sheet gauge

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products.

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In the 1980s, Muramoto et al. (1982) proposed a hybrid lubrication system which simply combined a recirculation system and a direct application system. In the reported hybrid

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lubrication system, basically, the recirculation system is the main emulsion supply method, and a high concentration emulsion is supplied from additional nozzle headers. However, in this system, emulsions are supplied to all stands in a tandem cold rolling mill. Therefore, a

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large amount of highly-concentrated emulsions are mixed in the recirculation system,

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causing large fluctuations in the emulsion concentration in the lubricants, and these

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fluctuations makes it difficult to realize stable high speed cold rolling. Moreover, improvement of rolling oil properties, as exemplified by the development of synthetic esters, has eliminated the superiority of the hybrid system as a lubrication system for high speed cold rolling.

In this paper, a new hybrid lubrication system is proposed in order to realize high speed cold rolling of thin gauge steel strips. The basic aims of the proposed system are high efficiency oil film formation, even when using stable emulsions, and good lubricity with a low emulsion supply rate. The lubrication property is comparable to that of direct application systems, and stable high speed rolling can be realized in spite of a low oil consumption rate equal to that of recirculation systems. The concept, basic features and

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2. Lubrication systems in tandem cold rolling mills 2.1 Recirculation system and direct application system

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production line tests of the new system are discussed in the following.

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Lubrication systems for tandem cold rolling mills are mainly classified as either

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recirculation systems or direct application systems, as shown in Fig. 1. The differences were described by Semoto and Okamoto (1992) with the historical background.

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Recirculation systems are mainly applied to sheet gauge products, while direct application systems are mainly used in high speed rolling mills for thin gauge steel strips. In both

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types of systems, oil-in-water (O/W) emulsions are generally used as the lubricant, which

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te

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in an idiomatic manner is referred to as a coolant.

(b) Direct application system

(a) Re-circulation systems

Fig.1 Concepts of lubricant systems used in tandem cold rolling mills, (a) Re-circulation systems, (b) Direct application system

In recirculation systems for cold rolling of steel strips, low concentration emulsions, typically with a concentration of 1-3%, are used. These emulsions are supplied to the roll

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bites for lubrication and to the work rolls and back-up rolls for cooling. One feature of this system is use of the same emulsions for both lubrication and cooling. The main advantage of this system is reduction of oil consumption. The waste lubricants treatment processes

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can also be simplified. Furthermore, the choices of base oil are more flexible than in direct applications systems, because synthetic esters specifically designed for each tandem cold

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rolling mill can be selected as base oils. Iwado et al. (1996) reported an example of the

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design of synthetic esters as cold rolling mill lubricants and explained that the selection of base oils and emulsifiers is flexible and design of lubricity is possible by using synthetic

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esters.

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In direct application systems, emulsions with a concentration of 5-15% are supplied to the strip surface for lubrication before the strip enters the roll gap. Cooling spray systems, which supply water to the roll surfaces, are provided separately. The direct application

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system has the advantage of a good lubrication property because oil film on the strip

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surface is easily formed, enabling formation of a large amount of oil film. Its disadvantages

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are high oil consumption and the need for an additional waste lubricants treatment process because the fundamentally unstable property of the emulsions prevents reuse in the circulation system. The choice of the base oil is also limited by economical reasons, as high oil consumption inevitably necessitates the use of less expensive oils like natural fats and oils, which are usually more prone to deterioration than synthetic esters.

In spite of the differences in these two types of lubrication systems, emulsions are supplied for roll bite lubrication in both systems. The interesting point of emulsion lubrication is that lubrication in the roll bite is achieved only by an oil film, even if a mixture of oil and water is supplied to the roll bite or the strip surface. Two representative theories are well known as explanations of the mechanism of oil film formation, one being the dynamic

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concentration theory and the other the plate-out theory.

The dynamic concentration theory has been widely reported since the 1980s. The basic

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idea is that an oil droplet in an emulsion may be trapped at the geometrically wedge-shaped region between the work roll and the strip with a certain probability, and

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the oil concentration increases to 100% while water is excluded before entering roll bite.

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Wilson et al. (1993) explained the inlet oil film thickness was much smaller than the oil droplet size of emulsion due to the dynamic concentration of emulsions. Kimura and Okada

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(1989) also proposed a dynamic concentration model and they investigated the influence of surfactant on oil film formation behavior. This theory is widely accepted as an emulsion

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lubrication mechanism. Recently, Reich and Urbanski (2004) investigated the dynamic concentration behaviors of emulsions in experimental high speed rolling, and Lo et al. (2010) adopted an analytical approach, in which a CFD (Computational Fluid Dynamics)

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analysis was applied to numerically simulate the dynamic concentration behavior.

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The plate-out theory is based on the idea that the oil phase transformation from an O/W emulsion spontaneously progresses on the strip surface. Because the surfaces of steel strips show lipophilic and hydrophobic properties, the oil droplets in an emulsion preferentially spread on the strip surface. The theory was mainly reported in the 1970s. Roberts (1966) proposed the basic concept, and it has large influence on lubrication properties in cold rolling. Mase et al. (1977) investigated the properties with some different experimental methods, showing the spraying conditions have large influence on plate-out oil film thickness. Recently, Kimura et al. (2009) reported that plate-out oil film formation has a clear time-dependent property, and this time-dependency may have a large effect on roll bite lubrication in high speed cold rolling. Analytical approaches based on the plate-out theory have also been proposed. For example, Azushima et al. (2011) proposed an oil film

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thickness estimation model using a new starvation model which considers the plate-out film on the roll and strip surfaces. Guillaument et al. (2011) analyzed plate-out oil film formation after emulsion supply on the strip surface using CFD, and Laugier et al. (2011)

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reported that the rolling force can be controlled to a suitable level under high speed cold

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rolling conditions by controlling the plate-out oil film at the entry section on the roll bite.

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The different lubrication mechanisms described above can be considered to correspond to the two representative lubrication systems. That is, in recirculation systems, dynamic

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concentration may be the dominant mechanism of oil film formation because stable, low concentration emulsions are used, and they are usually supplied directly to the

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geometrically wedge-shaped region formed by the work roll and the strip. On the other hand, in direct application systems, plate-out plays a more important role in oil film formation because unstable, high concentration emulsions easily form an oil film by

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plate-out and are usually supplied to the strip surface before the strip enters the roll bite.

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The properties of emulsions for tandem cold rolling mills are also different in recirculation systems and direct application systems, as shown in Fig. 2. Emulsions for direct application systems usually contain no emulsifiers in order to secure an unstable emulsion and increase the amount of plate-out oil film before the strip enters the roll bite. Since the emulsifier is not necessary to be used in online circulation systems, separation of the oil from the emulsion after supply to the strip surface is easily obtained. Furthermore, in practical operation, addition of cationic cohesion agents to the base oil is used in combination with an emulsifier-free emulsion composition in order to enhance the oil film forming ability, as reported by Kaneko et al. (2000). The instability of the emulsions and effective plate-out oil film formation are the reason why direct application systems are suitable to high speed rolling.

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Re-circulation system

Direct application system

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Water Oil

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Emulsifier

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Fig.2 Schematic diagram of comparison of two types of emulsions used as lubricants

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In recirculation systems, on the other hand, the emulsions used in tandem cold rolling mills should be stable enough to maintain their properties in repeated use. To satisfy this

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requirement, emulsions contain a sufficient amount of emulsifier, which is higher than the critical micelle concentration, and stable oil droplet dispersion can be maintained in the emulsion. Therefore, a large plate-out oil film cannot be expected, and the dynamic

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concentration mechanism plays the dominant role. In such systems, the oil droplet trap

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property which was discussed by Kimura and Okada (1989) is important. In the

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development of lubricants, the main focus is an effective trap ratio, which is obtained by selecting an appropriate emulsifier. Furthermore, the design of the base oils also helps to secure good lubricity because synthetic esters can be selected according to the specific requirements of each tandem cold rolling mill. However, even if such high performance oils can be designed and selected, stable emulsions tend to have lower oil film formation ability, and for this reason, the lubricity of recirculation systems is thought to be inferior to that of direct application systems.

2.2 Hybrid lubrication system The above-mentioned differences between recirculation systems and direct application systems may lead to the conclusion that emulsion stability and lubrication properties are

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inherently incompatible. In other words, if a higher lubrication property is required, less stable emulsions are desirable, but recirculating use of the emulsions will not be practical. On the other hand, if lower oil consumption is desired in order to reduce the capacity of the

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waste lubricant system, stable emulsions should be applied. However, in this case, the oil film forming ability will be insufficient, and lubricity may be inadequate to achieve high

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speed rolling or high productivity.

In this paper, a new hybrid lubrication system is proposed and developed in order to satisfy

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these contradictory requirements. The proposed system is a kind of recirculation system combined with a direct application system in downstream stands where higher rolling

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speed and severe rolling load conditions occur, as illustrated in Fig. 3. The system can satisfy both low oil consumption, which is an inherent feature of recirculation systems, and

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the good lubricity attributable to direct application systems.

Fig.3 Schematic diagram of developed hybrid lubrication system

The system is based on a conventional recirculation system, that is, one in which stable emulsions are circulated in a closed system. Therefore, the emulsions contain a sufficient amount of emulsifiers and the dynamic concentration mechanism is dominant as oil film

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formation in the roll bite. In this system, however, additional emulsion supply nozzles are combined with the recirculation system. These nozzles are provided at the downstream stands, where lubrication conditions are generally severe, and high concentration

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emulsions with large oil droplet are supplied to the strip surface. The plate-out oil film formed on the strip surface as a result of this additional emulsion supply enhances

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lubricity in the roll bite by the contribution of the dynamic concentration mechanism. The

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distinctive feature of this system is that the emulsions sprayed by the different supply system are collected in a single circulation tank and are then recirculated in the lubricant

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system as stable emulsions.

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The idea of the hybrid lubrication system is quite simple, but there are several issues that must be overcome to enable practical application as a lubrication system. Firstly, the emulsion supplied by the additional nozzles, which is called a hybrid lubrication spray here,

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must consist of the same base oils and same emulsifiers as those in the recirculation

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system because it is extremely important to avoid contamination by different lubricants in

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the single circulation system. The use of emulsions containing no emulsifiers or containing a sufficient amount of emulsifiers is also an essential difference between direct application systems and the new hybrid lubrication spray system proposed here.

Secondly, high efficiency plate-out oil film formation comparable to that in direct application systems is required because the oil concentration in the recirculation system will gradually increase, leading to unstable rolling conditions, if a large amount of high concentration emulsions is collected and mixed in the circulation tank. To overcome this difficulty, it is advantageous to use high concentration, large oil droplet emulsions because a sufficient lubrication effect can be achieved even with a small supply of the emulsion. Moreover, an oil consumption rate equal to that of recirculation systems can be achieved by

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reducing the supply amount of the high oil concentration emulsions.

The conventional concept of a hybrid lubrication system was reported by Muramoto et al.

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(1982). However, that system was proposed on the assumption that high concentration emulsions are supplied to improve the lubricity. Therefore, the plate-out oil film formation

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by the hybrid lubrication spray system was not sufficient to achieve a higher rolling speed.

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Moreover, stable high speed rolling could not be realized due to large fluctuations in the oil concentration in the recirculation system. Subsequent improvements in lubrication oils are

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thought to be one reason why the conventional hybrid lubrication system lost its advantage, but in any case, this type of system has not been widely used as a lubrication system for

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cold rolling mills.

On the other hand, the newly-proposed hybrid lubrication system shown in Fig. 3 achieved

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a high efficiency of plate-out oil film formation by supplying a high concentration of large

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droplet emulsions. This means that the amount of oil supply by the hybrid lubrication

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system could be reduced, and the problem of fluctuations in the oil concentration in the recirculation system was resolved. Moreover, the combination of a recirculation system and a hybrid lubrication spray system enables flexible lubrication control by combining different emulsion lubrication mechanisms. This idea is the crucial difference between the newly-proposed hybrid system and the conventional hybrid lubrication system described later.

3. Plate-out characteristics of emulsions 3.1 Plate-out behavior in high speed rolling A schematic diagram of the mechanism of oil film formation in the hybrid lubrication system is shown in Fig. 4. The emulsion is supplied at a position distant from the roll bite

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and is trapped in the roll bite while forming the plate-out oil film. As reported previously by Kimura et al. (2009), plate-out oil film formation depends on the elapsed time after spraying and is influenced greatly even the oil film formation time is extremely short, such

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as approximately 0.1 sec. Here, the plate-out characteristics of the emulsions generally used in high speed cold rolling mills with recirculation systems are investigated by the

Spray nozzle of O/W emulsion

Oil droplet Length from emulsion supply to roll bite

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Water

Work roll

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Plate-out oil film

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same method as that described in reference (Kimura et al., 2009).

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Fig.4 Schematic diagram of mechanism of oil film formation with O/W emulsions

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The emulsions used in the experiment were made by adding rolling oil to water of 55°C

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while controlling the oil concentration. The emulsion was mixed in a high-speed mixer to control the size of the oil droplets. The characteristics of emulsion A correspond to those of emulsions used in recirculation systems, and emulsion A was mixed strongly using a circulation pump in order to obtain a small oil droplet size like that normally used in a recirculation system. The emulsion supplied from the spray nozzle was collected in a beaker, and the oil droplet size distribution was measured by the electrical sensing zone method (Multisizer 3 Coulter Counter).

The compositions of the rolling oils used in the experiments are shown in Tables 1 and 2. Both of these oils have the same compositions as those in conventional recirculation systems and possess the stability necessary for recirculation. However, the oil shown in

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Table 1 contains a higher fraction of synthetic ester and its viscosity is relatively low, like that of oils which are usually used in cold rolling of thick gauge steel strips. On the other hand, the oil shown in Table 2 contains a high viscosity base oil, which was designed for

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O/W emulsions (A-C) used in experiments

Emulsifier (%) Kinematic viscosity at 50 ºC (mm2/s) Emulsion concentration (%) Average oil droplet size (mm)

O/W emulsions (D-E) used in experiments

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Table 2

A B C Refined vegetable oil; 45–50 Synthetic ester; 30–40 Nonionic surfactant; 1–2 19.0 2 5 10 5.3-7.1 11.8-15.0 12.0-18.4

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Emulsion Base oil (%)

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Table 1

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high speed cold rolling of ultra-thin gauge steel strips.

D E Refined vegetable oil; 70-75 Synthetic ester; 20-25 Nonionic surfactant; 1–2 29.0 5 10 11.0-15.3 12.0-16.0

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Emulsion Base oil (%)

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Emulsifier (%) Kinematic viscosity at 50 ºC (mm2/s) Emulsion concentration (%) Average oil droplet size (mm)

The test material was a bright SPCC steel with surface roughness of 0.02 m Ra. The dried test piece was heated by an electric furnace to 120-150°C, and the emulsions were then sprayed in the test apparatus (Kimura et al., 2009) by the same method. To measure the amount of plate-out oil film, the test piece was taken from the test apparatus while checking that there was no emulsion left on the test piece surface. The amount of oil film per unit of area was calculated from the weight difference before and after removing the oil. The mean value of five test pieces was used as the amount of plate-out oil film in order to reduce deviations in the measured data due to handling when removing the oil.

Figure 5 shows the influence of the oil film formation time on plate-out characteristics

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(Kimura et al., 2012b). In the figure, the horizontal axis is the elapsed time after spraying and corresponds to the time from emulsion spray to the roll bite in Fig. 4. The vertical axis is the amount of the plate-out oil film measured by the above-mentioned method. The

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results for emulsions A, B, and C, which were previously reported in (Kimura et al., 2009), show that the amount of plate-out oil film increased as the elapsed time after spraying

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increased. Moreover, when a high concentration, large droplet emulsion was supplied, the

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time dependency of the plate-out oil film increased greatly. Emulsions D and E also showed the same tendency but a larger dependence on elapsed time. Thus, assuming the emulsions

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have the same concentration and oil droplet size, the rolling oils used for ultra-thin gauge steel strips with the high viscosity base oil in Table 2 are appropriate for obtaining a larger

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plate-out oil film, when compared with emulsions used for thick gauge steel strip, like

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Amount of oil supply: 2000-3500mg/m2

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1500

Amount of plat-out oil

E

10%

1200

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[mg/m 2]

those shown in Table 1.

Concentration 5% B

900 600

C D A 2%

300

0

0.01 0.1 1 10 Time from emulsion spray to air blow [s]

Fig.5 Influence of oil film formation time on plate-out characteristics

3.2 Influence of oil supply amount on plate-out oil film

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To evaluate plate-out oil formation behavior, which occurs within a very short time, the influence of the oil amount per unit of strip surface area was investigated. Figure 6 shows the results, where the elapsed time of the plate-out oil film after emulsion supply was

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0.077 sec. With each of the emulsions, it is clear from this figure that the plate-out oil film increases as the amount of supplied oil increases. In particular, at the same oil supply

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amount, emulsions D and E show larger amounts of plate-out oil compared with emulsions

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A-C, which were already reported in reference (Kimura et al., 2009). In addition, the dependence on the change in the oil supply amount is also larger with emulsions D and E.

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This result suggests that emulsions D and E (with high viscosity base oil used for ultra-thin gauge strip) are advantageous for controlling lubricity in cold rolling because the

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1500

ts=0.077s

Concentration 10%

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1200

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Emulsion E

900 600

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2

Amount of plate-out oil [mg/m ]

plate-out oil film can be controlled easily by small changes in the emulsion supply amount.

C D

5% B

300

A

2%

0

0

1000

2000

3000

4000

5000

2

Amount of supplied oil [mg/m ]

Fig.6 Influence of oil supply amount on plate-out characteristics

3.3 Influence of large droplet emulsion on plate-out oil film To evaluate the influence of the emulsion concentration and oil droplet size on plate-out characteristics, the influence of the emulsion droplet size was investigated using emulsions

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D and E. In this case, the droplet size was controlled by mixing conditions. In addition, an emulsifier-free emulsion was also evaluated as a condition corresponding to that in direct application systems. Figure 7 shows the influence of the emulsion concentration and oil

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droplet size on plate-out characteristics. As in the previous section, the elapsed time of the plate-out oil film after emulsion supply was set at 0.077 sec. It can be seen that the amount

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of plate-out oil film increases as the oil concentration increases, and the amount of

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plate-out oil film increases as the oil droplet size increases at the same oil concentration. In this figure, the amount of plate-out oil increases twofold as a result of application of the

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emulsion with a high oil concentration compared with that with a low concentration, small droplet emulsion like that used in conventional recirculation systems. Furthermore, the

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amount of plate-out oil increases threefold by combined use of a high concentration, large droplet emulsion. Thus, it is possible to realize high efficiency plate-out oil film formation

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comparable to that of direct application systems by optimizing the emulsion conditions.

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2

Amount of plate-out oil [mg/m ]

2000

1500

1000

No emulsifier contained

D/A level

Influence of emulsifier

Oil droplet size 15m

Larger oil droplet

7-9m Higher concentration

500

R/C level

0 0

5 10 Oil concentration [%]

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Fig.7 Influence of emulsion concentration and oil droplet size on plate-out characteristics

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3.4 Influence of air atomizing on plate-out oil film To improve the plate-out characteristics in the proposed hybrid lubrication system, an air atomizing nozzle was evaluated. The air atomizing nozzle is a nozzle which supplies a

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mixture of emulsion and air and has the advantage of minimizing differences in the spray quantity distribution under low supply conditions. Figure 8 shows the influence of air

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atomizing on plate-out characteristics (Fujita and Kimura, 2013). When the air atomizing

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nozzle was used, an increased amount of plate-out oil film could be obtained in comparison with that at the minimum supply amount with a flat nozzle. This suggests the possibility

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that high efficiency plate-out oil film formation can be realized while minimizing the

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2000

1000

d

1500

Flat nozzle Air atomizing nozzle

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Amount of plate-out oil [mg/m 2]

amount of supplied oil per unit of strip surface area.

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500 0

0

10% Emulsion Pre-tank mixing

2000 4000 6000 2 Amount of supplied oil [mg/m ]

Fig.8 Influence of air atomizing on plate-out characteristics

4 Realization of high efficiency plate-out 4.1 Development of plate-out control The following presents the idea of a new lubrication control method, which is based on the basic experiments concerning the plate-out characteristics of emulsions supplied by the proposed hybrid lubrication system. In this system, a high concentration, large droplet

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emulsion comparable to that of recirculation systems is used. As shown in Fig. 7, high efficiency plate-out oil film formation comparable to that of direct application systems can be realized by combined use of a high concentration, large droplet emulsion. This idea is

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different from that of the conventional hybrid lubrication system (Muramoto et al., 1982), in which only a high concentration emulsion is supplied. Moreover, as shown in Fig. 8,

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plate-out oil formation can be improved by optimizing the emulsion supply conditions.

From the results shown in Fig. 5, in order to improve the lubrication characteristics in the

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high speed rolling stands, it is necessary to achieve plate-out film formation by securing a longer oil film formation time. Therefore, the spray nozzle header for the hybrid lubrication

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system should be installed at a position distant from the roll bite. Moreover, in the high speed rolling stands, plate-out characteristics are improved greatly by supplying a high concentration, large droplet emulsion. As the plate-out film formation time or the travel

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time from emulsion supply to the roll bite changes depending on the rolling speed,

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plate-out oil film control considering time dependence is necessary. As shown in Fig. 6, to

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enable the maximum control of the plate-out oil film amount, the influence of the supplied oil amount in the plate-out film must be large. From this perspective, a high concentration, large droplet emulsion is effective, and a rolling oil with a high viscosity base oil designed for cold rolling of ultra-thin gauge strips is desirable.

Table 3 shows the factors which influence the plate-out characteristics of O/W emulsions. Two rolling oils were investigated in this experiment, as shown previously in Tables 1 and 2. However, it is also necessary to evaluate the influence of other base oils and emulsifiers on plate-out oil film formation in order to clarify the influence of emulsions on plate-out behavior in greater detail. Furthermore, because it is thought that plate-out characteristics are influenced by the strip surface roughness and temperature, it is also

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necessary to evaluate the influence of these factors.

References Fig.5 Fig.6 Fig.7 Fig.7 Fig.8 (Table 1,2)

4.2 Emulsion droplet size control method

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Influence factors Rolling speed (Time dependence of plate-out) Amount of oil supply Emulsion concentration Oil drop size Type of spray nozzle Emulsion formulation (Base oil, emulsifier and other additives)

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Factors influencing plate-out characteristics of O/W emulsion

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Table 3

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In the proposed lubrication system, controlling the emulsion droplet size is important because the large oil droplet emulsion supplied from the hybrid lubrication system is the

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key method. In the hybrid lubrication system shown in Fig. 3, the emulsion droplet size

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can be controlled by the mixing power supplied to the hybrid lubrication tank. The rolling oil supplied to the hybrid lubrication tank was the same as that in recirculation type

Ac ce p

lubrication systems, but the average oil droplet size was larger than in the recirculation systems. Figure 9 shows the results of oil droplet size control in the hybrid lubrication tank. Although the conventional emulsion droplet size in recirculation systems is approximately 7 m, it is possible to control the emulsion droplets to a larger size by utilizing the mixing power in the hybrid lubrication tank. Although a part of the emulsion supplied from the hybrid lubrication system is mixed in the recirculation tank, it was confirmed that an emulsion droplet size comparable to that of recirculation systems could be maintained by mixing with the circulation pump in the recirculation system. Therefore, stability can be maintained in the recirculation system even if a high concentration, large droplet emulsion is mixed in the recirculation tank.

20

Page 20 of 50

30

Small droplet

10

cr

20 Floating oil

0 0.0

0.1

ip t

Control range

40

1.0

us

Average oil droplet size [m]

50

10.0

100.0

an

Mixing power in tank [kW/m3]

M

Fig.9 Concept of oil droplet size control by mixing power in mixing tank

te

5.1 Idea of lubrication control

d

5 Lubrication control technology by plate-out oil film

Figure 10 shows a schematic illustration of a hybrid lubrication system. A mixed

Ac ce p

lubrication condition is assumed to exist in the roll bite in cold rolling. The friction coefficient under mixed lubrication is given by Eq. (1).

   b  1    f

・・・(1)

where, μb is the friction coefficient in boundary lubrication, μl is the friction coefficient in hydrodynamic lubrication, and α is the contact ratio between the work roll surface and the strip surface. In Eq. (1), the friction coefficient in hydrodynamic lubrication is far smaller than the friction coefficient in boundary lubrication (Soda, 1966). Therefore, the friction coefficient under mixed lubrication is approximated by Eq. (2).

   b

・・・(2)

The contact ratio α is variable depending on the inlet oil film in the roll bite.

21

Page 21 of 50

Hybrid lubrication spray Emulsion supply from re-circulation system

ip t

Remained oil on roll surface Work roll Mixed lubrication regime

cr

Plate-out oil film formation

Strip

an

us

Inlet oil film Dynamic concentration of oil droplet Emulsion with low concentration & small oil droplet Emulsion with high concentration & large oil droplet Remained oil from previous stand

Fig. 10 Schematic illustration of hybrid lubrication system

M

The hybrid lubrication system is installed at a position distant from the roll bite, and a high efficiency emulsion with a high concentration and large droplets is supplied. The aim

te

Ac ce p

formation time.

d

of this arrangement is to accelerate plate-out film formation by securing a longer oil film

However, as shown in Table 4, in order to control the plate-out oil film in tandem cold rolling, it is necessary to consider not only the oil film formed by the hybrid lubrication system, but also the oil film carried over from the preceding stand and the oil film formed on the work roll. Moreover, when a recirculation coolant is supplied to the roll bite, it is also necessary to consider the outflow of the oil film on the strip surface and the oil trapped at the inlet of the roll bite (Wilson et al., 1993).

Table 4 Factors contributing to plate-out oil film formation

22

Page 22 of 50

an

us

cr

ip t

Plate-out by emulsion supply from hybrid lubrication system Rolling speed (Time dependence of plate-out) Amount of oil supply Emulsion concentration Oil droplet size Type of spray nozzle Emulsion formulation (Base oil, emulsifier and other additives) Temperature of strip surface Dynamic concentration mechanism at inlet of roll bite Trap behavior of oil droplet (Emulsifier, viscosity of base oil et al.) Other factors to be considered Remained oil from previous rolling stand Plate-out oil on work roll surface Influence of emulsion supply at inlet position roll bite (Wash out effect of plate-out oil film)

M

The plate-out oil film is influenced by the above-mentioned factors in tandem cold rolling, and only a partial oil film is trapped in the roll bite by the hydrodynamic behavior at the

d

inlet of the roll bite. The oil film thickness at the position where the strip starts to deform

te

is defined as the inlet oil film thickness (Azushima and Noro, 1998). This suggests that it is necessary to consider the influence of various factors for control of

Ac ce p

the lubrication characteristics in tandem cold rolling. Therefore, in order to control the lubrication characteristics flexibly in tandem cold rolling, it is thought that it is not sufficient simply to control the plate-out oil film formation.

5.2 Meaning of lubrication control in high speed rolling Chatter has been recognized as a major restriction that could adversely affect the achievement of high rolling speed of high strength thin steel strips. Chatter is abnormal vibration in a rolling mill; the most likely instability in tandem cold rolling mills is due to vertical oscillations of the rolls, and the typical frequency of chatter ranges from 150 to 250 Hz (Furukawa et al., 1976). Once chatter occurs, it is necessary to decrease the rolling speed in order to prevent chatter, but this reduces production efficiency. Although it is 23

Page 23 of 50

empirically recognized that chatter is influenced by the lubrication characteristics in cold rolling, the mechanism of chatter had not been fully clarified. Especially, the relationship between tribology phenomena in the roll bite and the vibration of the rolling mill is not

ip t

clearly understood.

cr

Kimura et al. (2003) proposed a simple self-excited vibration model, and examined the

us

response characteristics of rolling force and any conditions under which vibration occurs. Also, Kimura et al (2012a) modified the model and quantitative estimation method to

an

predict chatter was proposed. There, unstable vibration in cold rolling mills is understood based on the idea that the damping effects in roll the bite decrease as the rolling speed

M

increases, and the rolling force response is delayed by the roll gap changes resulting from tension fluctuations in continuous rolling. When the delay of rolling force response is influenced by the friction coefficient, the stability of vibration also changes. Especially, it

d

was found that rolling mill vibrations in the high speed region become less stable when the

te

friction coefficient at the final stand is outside the optimum range. In order to realize

Ac ce p

stable high speed rolling while preventing chatter, proper control of friction coefficient changes by control of rolling conditions is considered important. Therefore, friction coefficient control using the plate-out oil film was developed for the final stand.

6 Experiment in laboratory tests 6.1 New rolling simulator for evaluating plate-out oil film control A proposed simulator was designed to investigate the possibility of lubrication control by the plate-out oil film, as schematically represented in Fig. 11 (Fujita and Kimura, 2012a). This simulator is set up at the entry section of a two-high rolling mill corresponding to the work roll diameter and rolling speed in actual tandem cold rolling, and can control the amount of plate-out oil film on the test piece before rolling. The heater and the spray box

24

Page 24 of 50

are arranged in the rolling direction. The amount of plate-out oil film can be changed by controlling the emulsion spray conditions and the entry speed of the test piece in the spray

us

cr

ip t

box.

an

Fig. 11 Schematic view of plate-out simulator

M

The spray box contains an emulsion spray nozzle and an air-blowing nozzle. Emulsion is supplied in the rolling path, and the air-blowing nozzle is positioned after the emulsion

d

supply. The emulsion that has not been plated-out as a complete oil film is blown away by

te

the air jet. The plate-out oil film on the test piece is evaluated as the oil film formed during the elapsed time between the emulsion spray and the air spray. This makes it possible to

Ac ce p

evaluate the relationship between the plate-out oil film formed at various rolling speeds and rolling lubrication.

6.2 Influence of plate-out oil film on friction coefficient Figure 12 shows the experimental results obtained with the proposed simulator. It shows the relationship between the friction coefficient and inlet oil film thickness, which was changed by using different work roll roughnesses and test piece roughnesses. The test material was a bright SPCC steel with surface roughness of 0.02μmRa.

25

Page 25 of 50

0.10

us

0.08 0.06 0.04 0.02 0.00 0.06

0.09

0.12

M

0.03

an

Friction coefficient coefficient Friction

ip t

Surface roughness / µmRa WR Workpiece 0.02 0.02 0.20 0.02 0.20 1.00 0.20 0.02 0.20 1.00

cr

○ ◇ △ ◆ ▲

Amount of plate-out oil / mg・m-2 0, 170, 500 0, 270, 460 0, 90, 480 980, 1200, 1650 780, 1320, 1600

0.15

0.18

Inlet oil film thicknes s / μm

te

d

Fig. 12 Relationship between friction coefficient and inlet oil film thickness

The rolling oil consists of a refined vegetable oil, synthetic ester and nonionic surfactant as

Ac ce p

the emulsifier. The amount of plate-out oil film from 0 to 1700mg/m2 was adjusted by controlling the emulsion supply conditions and the entry speed of the test piece in spray box, as shown in Fig.11. The diameter of the work roll was φ500mm, which is the diameter in actual tandem cold rolling mills. Two work roll surface roughness conditions were used (0.2μmRa and 0.02μmRa). Experiments were performed at various rolling speeds up to 1200m/min. The temperature of the test piece was set at 100℃ to consider the dependence of lubrication characteristics on the strip temperature in tandem cold rolling mills.

The horizontal axis shows the inlet oil film thickness calculated from the plate-out oil film thickness and rolling conditions and that calculated using the model proposed by 26

Page 26 of 50

Azushima et al. (2011). When the pressure of the oil film reaches the yield stress of the test piece, the inlet oil film thickness in the roll bite is given by Reynolds equation, as shown in Eq. (3), and the oil viscosity equation in Eq. (4).

ip t

dP 6 (U1  U 2 ) h  h1  ( 3 ) dh tan  h

・・・(3)

cr

   0 exp(P   (Tm  T0 ))

・・・(4)

us

where, P is the rolling pressure, h is the oil film thickness, U1 and U2 are the speed of the test piece and the speed of work roll, respectively, θ is the gap angle between the test

an

piece and the work roll, η0 is the reference viscosity of the rolling oil at 40℃. α is the pressure coefficient, β is the temperature coefficient, Tm is the average temperature

P  0 at h  h2

・・・(5)

P   0 at h  h1

・・・(6)

te

d

boundary conditions are given by

M

between the test piece and work roll and T0 is the reference temperature (40℃). The

Ac ce p

where, σ0 is the yield stress of the test piece. The hydrodynamic oil film thickness h1 can be calculated by solving the differential equation in Eq. (3). The parameter in Table 5 was used for the analysis of the inlet oil film thickness. The vertical axis is the friction coefficient calculated by the Orowan model (1943) using the measured forward slip and rolling force. Measurement of forward slip was calculated by

(lS-lR)/lR, where lS is the distance between the marks left by scratches on the work roll and lR is the distance between the two marks on the work roll surface.

Table 5 Data used in the inlet oil film calculation Yield stress / MPa

320

27

Page 27 of 50

1.6 15∼25 100 15 20 1200 0.039 (40℃) 43 (40℃) 17 (70℃) 14.3 0.027

cr

Oil viscosity / Pa・s Oil kinematic viscosity / mm2・s-1

ip t

Gap angle θ / ° Rolling reduction / % Workpiece temperature / ℃ Workpiece speed / m・min.-1 Workroll temperature / ℃ Rolling speed / m・min.-1

us

Pressure coefficient α / GPa-1 Temperature coefficient β / ℃-1

In Fig.12, when the amount of plate-out oil exceeds a certain level, the work roll roughness

an

has little influence on the friction coefficient. However, when the amount of plate-out oil is

M

small, the friction coefficient is influenced by the work roll roughness.

From the above-mentioned results, basic guidelines for controlling the lubrication

d

characteristics in actual tandem cold rolling were proposed. Especially, it was found that it

te

is necessary to change the spray quantities from the hybrid lubrication system as the work roll roughness decreases by wear. The above-mentioned knowledge was reflected in the

Ac ce p

spray quantity settings in the hybrid lubrication system.

7 Evaluation in actual tandem cold rolling mill 7.1 Setting of hybrid lubrication system In order to verify whether it is possible to control lubrication characteristics by applying plate-out behavior, demonstration experiments were conducted in a five-stand tandem cold mill (Fujita et al., 2012b). The test header was set up at the entry section of the final stand, where rolling speed is high and the emulsion starvation region began to shift. To increase the phase transformation time from emulsion to plate-out oil film, the emulsion was supplied at a position distant from the roll bite.

28

Page 28 of 50

The test material was hard and thin strip with T5CA grade, the rolling thickness was controlled from 1.8mm to 0.18mm. A high concentration, large droplet emulsion was mixed

ip t

in existing pre-mix tank, and the oil droplets were controlled by the agitator.

In recirculation systems, a low concentration, small droplet emulsion is used. On the other

cr

hand, a hybrid lubrication system was set up at the entry section of the final stand in the

us

tandem cold mill, a high concentration, large droplet emulsion was supplied on the strip by an air atomizing nozzle, which enables uniform supply of the emulsion. The differences

an

from conventional recirculation systems were investigated. The composition of the rolling

M

oil and the supply conditions used in the experiments are shown in Table 6.

Table 6 Emulsion and spray conditions used in experiments

d

Recirculation emulsion

Ac ce p

te

Emulsion concentration / % Average oil droplet size / μm Emulsion temperature / degree Flowing quantity of spray / L・min.-1 Air quantity of spray / Nm3・h-1

3.1

Hybrid lubrication emulsion 6.5 12.4

8.6

16.3

18.9

64.7

48.0

47.0

−

0∼50

0∼50

−

5∼20

5∼20

Figure 13 shows the influence of the spray quantity in the hybrid lubrication system on the friction coefficient when the rolling speed is 1790m/min. The friction coefficient was calculated by the Bland & Ford model (1948) using the measured forward slip and rolling conditions, as shown in Table 7. The vertical axis shows the friction coefficient ratio standardized by the friction coefficient in recirculation systems. The horizontal axis shows the amount of supplied oil per unit of strip area.

29

Page 29 of 50

-1

Hybrid lubrication spray / L・min. 0 20 40 60 at 6.5% 0 10 20 30 40 50 at 12.4%

ip t

1.0

12.4% emulsion 6.5% emulsion

cr

0.9 0.8 0.7

us

Friction coefficient ratio

1.1

Rolling speed 1790m/min. 0.6 0

500

1000

1500

2000

-2

an

Amount of supplied oil / mg・m

Table 7

M

Fig. 13 Influence of hybrid lubrication spray on friction coefficient

Data used in friction coefficient calculation

Ac ce p

te

d

Width of strip / mm Deformation resistance / MPa Entry thickness / mm Exit thickness / mm Rolling reduction / % Back tension / MPa Front tension / MPa WR radius / mm

900 kf = 800(ε+0.005)0.28 0.260 0.180 30.0 14.0 9.50 288

In this figure, the friction coefficient in final stand decreased as the flowing quantity of hybrid lubrication spray increased. The friction coefficient decreases over 20% in the high speed region. And, when comparing the flowing quantity of hybrid lubrication spray, the control range of the friction coefficient in 12.4% emulsion is more widely than that of 6.5% emulsion.

Figure 14 shows the influence of rolling speed on the ratio of the oil pit area. The ratio of the oil pit area was calculated from the binarization image of the strip after rolling. In this

30

Page 30 of 50

figure, when the rolling speed in conventional cold rolling is over 1000m/min., the ratio of the oil pit area decreases gradually. The oil film thickness decreased because the spray

cr

Conventional Hybrid lubrication 6.5%, 50L/min. Hybrid lubrication 12.4%, 50L/min.

us

40 30

an

20 10 0 500

M

Oil pit area ratio (%)

ip t

time of the emulsion supplied on the strip became shorter with increasing strip speed.

1000 1500 Rolling speed (m/min.)

2000

te

d

Fig. 14 Influence of rolling speed on ratio of oil pit area

Ac ce p

In contrast to this behavior, when the hybrid lubrication system was applied, the ratio of the oil pit area remains high in the high speed rolling region. Especially, these results were remarkable in 12.4% emulsion. It is conjectured that the oil film thickness in the roll bite increased because the plate-out oil film formed at the inlet of the roll bite increased due to the supply of the high concentration, large droplet emulsion from the hybrid lubrication system. Moreover, when comparing Fig.13 and Fig.14, the plot of the ratio of the oil pit area and the friction coefficient shows the same correlation. In other words, the friction coefficient decreases as the ratio of the oil pit area increases when they are the same rolling speed.

The above results in connection with recirculation systems verified the possibility of

31

Page 31 of 50

changing lubrication characteristics by controlling the plate-out oil film in the high speed rolling region. These results correspond to the calculation results of the inlet oil film thickness using the elastohydrodynamic theory (Fujita et al., 2012c). This means that it is

cr

7.2 Control technology of friction coefficient

ip t

possible to estimate lubrication characteristics quantitatively.

us

The research described above demonstrated that control of the plate-out oil film is an effective technology for controlling the friction coefficient within the optimum range. As

an

part of this technology, spray quantity control for the hybrid lubrication system and feedback control for the friction coefficient were realized in order to achieve stable high

M

speed rolling by controlling the friction coefficient.

Figure 15 shows an example of the dynamic lubrication control method considered for the

te

2100

Hybrid lubrication spray / L・min-1

Friction coefficient at final stand

Ac ce p

Rolling speed / mpm

d

friction coefficient.

0

0.015 0.010

50

Time Risk of chatter

Target range

Risk of chatter Feedback control Feedback control

0

Fig. 15 Example of dynamic lubrication control in actual production mill

In preset control, preset spray flow quantities are supplied from the hybrid lubrication system as the rolling speed changes. In dynamic control, on the other hand, the spray flow 32

Page 32 of 50

quantities from the hybrid lubrication system are adjusted automatically when the friction coefficient is outside the optimum range. This is the first application of feedback control in

ip t

cold rolling to direct control of the friction coefficient.

In this technology, control of the spray flow quantities, which depends on rolling speed, is

cr

stopped when the strip being rolled is soft and thick, and the spray flow quantities from

us

the hybrid lubrication system are controlled when the strip is hard and thin. Moreover, to prevent the chatter in high speed rolling, the hybrid lubrication system is applied

an

positively when the work roll roughness is high after a roll exchange, and the spray flow quantities from the hybrid lubrication system are decreased when work roll roughness is

M

small due to wear. In other words, this technology can realize the appropriate lubrication characteristics for the production mix, and has the major feature of enabling flexible

te

the work rolls.

d

application corresponding to fluctuations in the production mix and the actual condition of

Ac ce p

7.3 Results of hybrid lubrication system Figure 16 shows the changes in rolling force before and after application of the developed technology. The hybrid lubrication system was applied to the fourth and fifth stands for hard and thin strip with T4CA grade. As emulsion conditions in the hybrid lubrication system, the concentration of the emulsion was controlled to 10%. The flow quantity of the emulsion supplied to the fourth and fifth stands were 10L/min. and 25L/min., respectively.

33

Page 33 of 50

2.0→0.200t×892w mm WR diameter : 530mm (#1-4std) 590mm (#5std)

ip t

9.0

cr

8.5 8.0

us

Rolling line load / kN ・ mm

-1

Conventional Hybrid Lubrication (#4, #5std)

7.5 7.0

an

#1std #2std #3std #4std #5std Rolling STD

M

Fig. 16 Changes in rolling force before and after application of developed technology

d

Generally, in the case of high speed rolling in tandem cold rolling, large work roll is used in

te

final stand because the rolling distance increases under smaller rotation speed. However, when work hardened strip is rolled by large work roll in final stand, the rolling load

Ac ce p

increases as the contact area increases because large work roll is flattened. When the hybrid lubrication system was applied to the fourth and fifth stands, the rolling force decreased. Especially, this effect was remarkable in the fifth stands which uses large work roll. It can be assumed that energy consumption also decreased as a result of this reduction of rolling force.

Figure 17 shows the relationship between the rolling speed and the friction coefficient before and after application of the hybrid lubrication system. In actual rolling from T1CA to T3CA grade, the friction coefficient was calculated by the Bland & Ford model using the rolling conditions and the deformation resistance. Data used in friction coefficient calculation is shown in Table 8. 34

Page 34 of 50

0.020

ip t

No chatter Chatter Hybrid lubrication

0.025

0.015

cr

0.010 0.005

Size:2.3×872→0.202mm

us

#5std friction coefficient

0.030

0.000 500

1000

1500

2000

an

Rolling speed / mpm

Fig. 17 Relationship between rolling speed and friction coefficient

M

before and after application of hybrid lubrication system

Average data used in friction coefficient calculation

d

Table 8

Ac ce p

te

Deformation resistance / MPa Rolling line load / kN・mm-1 Rolling reduction / % Back tension / MPa Front tension / MPa WR radius / mm

kf = 665(ε+0.015)0.26 6.8 30.0 12.8 10.9 294

In this figure, the occurrence of chatter corresponds to the X plots. Under conventional recirculation system, chatter occurred in the high speed rolling region because the inlet oil film in the roll bite decreased. On the other hand, after application of the new technology, the friction coefficient was maintained within a certain range because the inlet oil film in the roll bite was provided by the hybrid lubrication system, and chatter was successfully prevented.

35

Page 35 of 50

8 Effects of application This technology was completed for Fukuyama No. 2 TCM at JFE Steel Corporation's West Japan Works in 2010, and stable high speed rolling was achieved as planned. Fukuyama

ip t

No. 2 TCM is a five-stand mill using recirculation type lubrication systems. In the past, the specification of rolling speed (2100m/min) could not be achieved consistently because

cr

chatter occurred. However, by appling this technology, the achievement rate of the

us

maximun rolling speed was greatly improved. In addition, there was no deterioration of the oil consumption rate after application, and high speed rolling was realized while

an

maintaining a favorable oil consumption rate.

M

Moreover, a new lubrication control technology was developed, in which the friction coefficient is controlled as the target parameter, and flexible control of lubrication characteristics based on a recirculation lubrication system was realized. In conventional

d

recirculation systems, it was necessary to install multiple emulsion tanks and change the

te

oil concentration in the recirculation systems gradually when hard and soft materials were

Ac ce p

rolled in the same production cycle. In contrast, this new technology can adapt flexibly to changing conditions, and can realize flexible production in response to changes in the production mix from hard and thin strip to soft and thick strip.

9 Conclusions

In order to develop a new hybrid lubrication system for tandem cold rolling mills, the improvement of plate-out characteristics by emulsions containing an emulsifier was investigated. Although the idea of the conventional hybrid lubrication system was limited to use of a high concentration emulsion, high efficiency plate-out oil film formation comparable to that of direct application systems was realized by combined use of a high

36

Page 36 of 50

concentration, large droplet emulsion. Moreover, by improving the emulsion supply conditions, it is also possible to achieve a sufficient lubrication effect with a small emulsion supply. As a result of these improvements, the amount of high concentration emulsion

ip t

mixed in the recirculation tank can be reduced, and fluctuations in the concentration in the

cr

recirculation system can be minimized.

us

Moreover, the production line test was investigated, and stable rolling at the rolling speed of 2100m/min was realized in a five-stand cold rolling mill based on a recirculation

an

lubrication system. The achievement rate of the maximun rolling speed and productivity were improved with hard and thin strips for tinplate, and the problem of chatter when

M

rolling thin and hard steel strips was solved. Simultaneously with improving the rolling speed and productivity, a low oil consumption rate equal to that of recirculation systems

Ac ce p

te

ecological process.

d

was also maintained. Therefore, this technology is also effective as an economical and

37

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＜References＞ Azushima, A., Noro, K., 1998. Analysis and quantitative consideration of inlet oil film

ip t

thickness in cold sheet rolling with oil in water emulsions-An investigation of friction and lubrication in cold rolling VI-. J. Jpn. Soc. Technol. Plast. 39,

cr

1238-1242.

Azushima, A., Inagaki, S., Ohta, H., 2011. Plating out oil film thickness on roll and

us

workpiece during cold rolling with O/W emulsion. Tribol. Trans. 54, 275-281. Bland, D. R., Ford, H., 1948. The calculation of roll force and torque in cold strip rolling

an

with tensions. Proc. Inst. Mech. Eng. 159, 144-163.

Fujita, N., Kimura, Y., 2012a. Influence of plate-out oil film on lubrication characteristics

M

in cold rolling. ISIJ Int. 52, 850-857.

Fujita, N., Kimura, Y., Kobayashi, K., Amanuma, Y., Sodani, Y., 2012b. Verification test of

d

plate-out oil film control in actual tandem cold mill. Proc. 63rd Jpn. Joint Conf. Technol. Plast., 451-452.

te

Fujita, N., Kimura, Kobayashi, K., Amanuma, Y., Sodani, Y., 2012c. Estimation of

Ac ce p

lubrication characteristics in actual tandem cold mill. Proc. 63rd Jpn. Joint Conf. Technol. Plast., 453-454.

Fujita, N., Kimura, Y., 2013. Plate-out efficiency related to oil-in-water emulsions supply conditions on cold rolling strip. Proc. ImechE, Part J: J. Engineering Tribology 227, 413-422.

Furukawa, K., Yarita, I., Seino, Y., Takimoto, T., Nakazato, Y., Nakagawa, K., Fukunaga I., 1976. An analysis of "Chattering" in cold rolling for ultra thin gauge steel strip. Kawasaki Steel Technical Report 8, 60-79. Guillaument, R., Vincent, S., Caltagirone, J. P., Laugier, M., Gardin, P., 2011. Plate-out modeling for cold-rolling systems lubricated with oil-in-water emulsions. Proc. ImechE, Part J: J. Engineering Tribology 225, 905-914.

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Iwado, S., Morita, Y., Gakuhari, F., Tokunaga, M., 1996. Development of synthetic ester based rolling oil for tin gauge cold rolling. Tetsu-to-Hagane 82, 220-225. Kaneko, T., Saito, T., Kawashima, K., Takezawa, K., Chonan, T., Okamoto, K., 2000.

ip t

Technological developments of high speed (2800mpm) cold rolling. CAMP-ISIJ 13, 318-321.

cr

Kimura, Y., Okada, K., 1989. Lubricating properties of oil-in-water emulsions. Tribol.

us

Trans. 32-4, 524-532.

Kimura, Y., Sodani, Y., Nishiura, N., Ikeuchi, N., Mihara, Y., 2003. Analysis of Chatter in

an

Tandem Cold Rolling Mills. ISIJ Int. 43, 77-84.

Kimura, Y., Fujita, N., Mihara, Y., 2009. Plate-out behaviors of O/W emulsions for cold

M

rolling in a short time interval. Tetsu-to-Hagane 95, 340-346. Kimura, Y., Fujita, N., Nishiura, N., Tomotsune, S., Sodani, Y., 2012a. Friction control in hybrid lubrication system for high speed cold rolling. Proc. Jpn. Spring Conf.

d

Technol. of Plast., 2012, 157-158.

te

Kimura, Y., Fujita, N., Nishiura, N., Sodani, Y., 2012b. Plate-out properties for high speed

Ac ce p

cold rolling with oil-in-water emulsions. Proc. Jpn. Spring Conf. Technol. of Plast., 2012, 159-160.

Laugier, M., Tornicelli, M., Leligois, C. S., Bouquegneau, D. Launet, D., Alvarez, J. A., 2011. Flexible lubrication concept. The future of cold rolling lubrication. Proc. ImechE, Part J: J. Engineering Tribology 225, 949-958.

Lo, S. W., Yang, T. C., Cian, Y. A., Huang, K. C., 2010. A model for lubrication by oil-in-water emulsions. ASME J. Tribol. 132, 011801.

Mase, T., Kono, T., Yamamoto, H., 1977. Study on lubrication characteristics of cold rolling. Proc. 28th Jpn. Joint Conf. Technol. Plast, 114-116. Muramoto, H., Matsumoto, M., Teshiba, T., Yanagishima, F., Yamada, Y., 1982. Curtailment of the unit consumption of the rolling oil with hybrid system.

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Tetsu-to-Hagane 68, S370. Orowan, E., 1943. The calculation of roll pressure in hot and cold flat rolling. Proc. I. Mech. E. 150, 140-167.

ip t

Reich, R., Urbanski, J., 2004. Experimental support for the dynamic concentration theory of forming an oil reservoir at the inlet of the roll bite by measuring the onset speed

cr

of starvation as a function of oil concentration and droplet size. Tribol. Trans. 47,

us

489-499.

Roberts, W. L., 1966. Friction and Lubrication in Metal Processing. New York, ASME, 103.

an

Semoto, S., Okamoto, T., 1992. Present and recent trends of cold rolling oil for steel strips. J. Jpn. Soc. Technol. Plast. 33, 790-796.

M

Soda, N., 1966. Friction and wear in metal forming. J. Jpn. Soc. Technol. Plast. 7, 249-254. Wilson, W. R. D., Sakaguchi, Y., Schmid, S. R., 1993. A dynamic concentration model of

Ac ce p

te

d

emulsions. Wear 161, 207-212.

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＜Caption List＞ O/W emulsions (A-C) used in experiments

Table 2

O/W emulsions (D-E) used in experiments

Table 3

Factors influencing plate-out characteristics of O/W emulsion

Table 4

Factors contributing to plate-out oil film formation

Table 5

Data used in the inlet oil film calculation

Table 6

Emulsion and spray conditions used in experiments

Table 7

Data used in friction coefficient calculation

Table 8

Average data used in friction coefficient calculation

Figure 1

Concepts of lubricant systems used in tandem cold rolling mills, (a)

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Table 1

Re-circulation systems, (b) Direct application system Schematic diagram of comparison of two types of emulsions used as lubricants

Figure 3

Schematic diagram of developed hybrid lubrication system

Figure 4

Schematic diagram of mechanism of oil film formation with O/W emulsions

Figure 5

Influence of oil film formation time on plate-out characteristics

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Figure 2

Figure 6

Influence of oil supply amount on plate-out characteristics

Figure 7 Influence of emulsion concentration and oil droplet size on plate-out characteristics

Figure 8

Influence of air atomizing on plate-out characteristics

Figure 9

Concept of oil droplet size control by mixing power in mixing tank

Figure 10

Schematic illustration of hybrid lubrication system

Figure 11

Schematic view of plate-out simulator

Figure 12

Relationship between friction coefficient and inlet oil film thickness

Figure 13

Influence of hybrid lubrication spray on friction coefficient

Figure 14

Influence of rolling speed on ratio of oil pit area

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Figure 15

Example of dynamic lubrication control in actual production mill

Figure 16

Changes in rolling force before and after application of developed technology

Figure 17

Relationship between rolling speed and friction coefficient before and after

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application of hybrid lubrication system

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A B C Refined vegetable oil; 45–50 Synthetic ester; 30–40 Nonionic surfactant; 1–2 19.0 2 5 10 5.3-7.1 11.8-15.0 12.0-18.4

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Emulsifier (%) Kinematic viscosity at 50 ºC (mm2/s) Emulsion concentration (%) Average oil droplet size (mm)

ip t

Emulsion Base oil (%)

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Emulsifier (%) Kinematic viscosity at 50 ºC (mm2/s) Emulsion concentration (%) Average oil droplet size (mm)

D E Refined vegetable oil; 70-75 Synthetic ester; 20-25 Nonionic surfactant; 1–2 29.0 5 10 11.0-15.3 12.0-16.0

ip t

Emulsion Base oil (%)

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References Fig.5

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Fig.6 Fig.7 Fig.7 Fig.8 (Table 1,2)

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Influence factors Rolling speed (Time dependence of plate-out) Amount of oil supply Emulsion concentration Oil drop size Type of spray nozzle Emulsion formulation (Base oil, emulsifier and other additives)

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ip t cr

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Plate-out by emulsion supply from hybrid lubrication system Rolling speed (Time dependence of plate-out) Amount of oil supply Emulsion concentration Oil droplet size Type of spray nozzle Emulsion formulation (Base oil, emulsifier and other additives) Temperature of strip surface Dynamic concentration mechanism at inlet of roll bite Trap behavior of oil droplet (Emulsifier, viscosity of base oil et. al.) Other factors to be considered Remained oil from previous rolling stand Plate-out oil on work roll surface Influence of emulsion supply at inlet position roll bite (Wash out effect of plate-out oil film)

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0.039 (40℃) 43 (40℃) 17 (70℃) 14.3 0.027

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Pressure coefficient α / GPa-1 Temperature coefficient β / ℃-1

cr

Oil viscosity / Pa・s Oil kinematic viscosity / mm2・s-1

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320 1.6 15∼25 100 15 20 1200

us

Yield stress / MPa Gap angle θ / ° Rolling reduction / % Workpiece temperature / ℃ Workpiece speed / m・min.-1 Workroll temperature / ℃ Rolling speed / m・min.-1

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8.6

16.3

18.9

64.7

48.0

47.0

−

0∼50

0∼50

−

5∼20

5∼20

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cr

3.1

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Emulsion concentration / % Average oil droplet size / μm Emulsion temperature / ℃ Flowing quantity of spray / L・min.-1 Air quantity of spray / Nm3・h-1

Hybrid lubrication emulsion 6.5 12.4

ip t

Recirculation emulsion

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ip t cr

900 kf = 800(ε+0.005)0.28 0.260 0.180 30.0 14.0 9.50 288

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Width of strip / mm Deformation resistance / MPa Entry thickness / mm Exit thickness / mm Rolling reduction / % Back tension / MPa Front tension / MPa WR radius / mm

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ip t

kf = 665(ε+0.015)0.26 6.8 30.0 12.8 10.9 294

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Deformation resistance / MPa Rolling line load / kN・mm-1 Rolling reduction / % Back tension / MPa Front tension / MPa WR radius / mm

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