Plating Out Oil Film Thickness on Roll and Workpiece During Cold Rolling with O/W Emulsion

Transcription

1 Tribology Transactions, 54: 75-81, 011 Copyright C Society of Tribologists and Lubrication Engineers ISSN: print / X online DOI: / Plating Out Oil Film Thickness on Roll and Workpiece During Cold Rolling with O/W Emulsion AKIRA AZUSHIMA 1, SATOSHI INAGAKI, and HIROKI OHTA 1 1 Yokohama National University Department of Manufacturing Engineering Yokohama, Japan Daido Chemical Industry Co., Ltd. Department of Research & Development Yamatokouriyama, Japan The plating-out film thickness during rolling in cold rolling with emulsion is quantitatively estimated for the improvement of productivity and the precise control of surface qualities after rolling. The estimating method of the plating-out film thickness was investigated using the numerical method of the inlet oil film thickness under the starvation condition of emulsion. The estimation model was proposed using a new starvation model considering the plating-out film on the roll and strip surface proposed by Azushima, et al. Sheets and coil sheets of aluminum A1050H and mineral oil with a viscosity of 0.35 Pa s were used. It is reasonable that the value of trapping ratio in the sheet rolling could be used as the value of the trapping ratio in the coil rolling. From the experimental results, the effect of the emulsion concentration and the emulsifier on the plating-out film thickness was examined using the numerical method. The plating-out film thickness increased with increasing emulsion concentration and the plating-out film thickness was relatively dependent on the affinity of the emulsion particle for the steel surface of the emulsifier. KEY WORDS Cold Rolling; Oil-in-Water Emulsion; Plating Out Oil Film Thickness INTRODUCTION Oil droplets-in-water (O/W) emulsions are widely used in cold sheet rollings of steel, stainless steel, and aluminum due to their good lubricity and good cooling performance. When the emulsion was used in cold sheet rolling in the early days, it was understood that the plated-out oil film was effective for the lubricity at the interface between roll and workpiece (Roberts (1); Schey ()). Schey () reported that unstable emulsions were believed to become effective through plating out of the oil phase on the Manuscript received December 5, 009 Manuscript accepted November 16, 010 Review led by Dong Zhu strip and roll surface, thus essentially providing the lubricity of the dispersed phase. In Japanese steel making companies, it was also understood that emulsions with a good plating-out performance were effective for the lubricity, so that the plating-out performance of the emulsions for cold sheet rolling was examined by Mase, et al. (3), Nakajima, et al. (4), and Shirota and Sakai (5). On the other hand, in cold sheet rolling with O/W emulsions, the mechanism of film formation by emulsions at the entrance region of the roll gap is still not understood. Sakaguchi and Wilson (6) reported the starvation model at the inlet of roll bites with emulsion rolling, and Kimura and Okada (7) applied the starvation model to the film formation at the entrance. Schmid and Wilson (8) applied the dynamic concentration model proposed by Wilson, et al. (9) to aluminum rolling with O/W emulsions. Azushima and Noro (10) proposed the numerical method of the inlet oil film thickness in cold sheet rolling using the starvation model proposed by Sakaguchi and Wilson (6), Schmid and Wilson (8), Zhu, et al. (11), Yang, et al. (1), and Reich, et al. (13). Zhu, et al. (11) reported that in the low-speed region, the oil pool was formed in the inlet zone, so that the film thickness with emulsion is usually quite close to that of the neat oil. In the intermediate-speed region, the oil pool disappears so that the oil film starts to decrease. In this region, starvation occurs. In the high-speed region, the oil film thickness starts increasing again, and both the oil and the water phases are mixed and entrained into the contact zone. Moreover in the paper by Yang, et al. (1), they investigated the transition from the low-speed region to the intermediate-speed region and observed the disappearance of the oil pool. Recently, Azushima and Inagaki (14) reported that the difference of the inlet oil film thicknesses in the cases of sheet rolling and coil rolling was measured and a numerical method for determining the inlet oil film thickness in cold sheet rolling with O/W emulsion was newly proposed using the new starvation model considering the oil film thickness plating out on the surfaces of roll and strip. Moreover, Inagaki and Azushima (15) reported that the trapping ratio was estimated from calculation of the inlet oil film thickness using the numerical method proposed by Azushima and Inagaki (14) in the case of sheet rolling without 75

2 76 A. AZUSHIMA ET AL. point x 1 at which the pressure becomes the yield stress of the workpiece as shown in Fig. 1c. On the other hand, Azushima, et al. (16) proposed that when the surface roughnesses of the roll and the sheet are smooth and the reduction in thickness is constant, the surface brightness is given by Gs = a ln(h 1 ) + b [] where a and b are constants. Moreover, Azushima, et al. (17) confirmed that in cold sheet rolling with emulsion, the inlet oil film thickness could be estimated from the measured surface brightness of cold-rolled sheets using Eq. []. The plating out film thickness h can be calculated from the estimated inlet oil film thickness h 1 in cold sheet rolling with emulsion using the new starvation model if the oil film thickness h expressed is estimated as in the next equation with reference to Wilson, et al. s (9) paper, Fig. 1 Starvation model: (a) schematic representation of inlet zone; (b) concentration zone; and (c) pressure zone. the plating-out film on the roll and strip surfaces. However, it is desired that the emulsion behavior at the entrance between roll bites and, in particular, the plating-out film thickness during rolling in cold rolling with emulsion is quantitatively estimated for improvement of productivity and the precise control of surface qualities after rolling. In this article, the estimating method of the plating-out film thickness is investigated using the numerical method of the inlet oil film thickness under the starvation condition of emulsion and the effect of the emulsion concentration and the emulsifier on the plating-out film thickness is examined using the numerical method. ESTIMATION OF PLATING-OUT FILM THICKNESS DURING ROLLING Estimation Model An estimation model for estimating the plating-out film thickness on the roll and strip surfaces is proposed using a new starvation model considering the plating-out film on the roll and strip surface proposed by Azushima and Inagaki (14) asshowninfig. 1. The new starvation model shown in Fig. 1a, consists of the conventional starvation model and the plating-out model. In this new starvation model, at a distance of (h + d) between the surfaces of the roll and workpiece at a point x 3, the oil droplet adheres to the surfaces and the emulsion concentration increases to 100% at a point x as show in Fig. 1b. The oil film thickness at x is given by h = h + h [1] where h is the oil film thickness formed by the trapping of the emulsion particle and h is the plating-out film thickness on the roll and strip surface. The pressure within the oil is generated. The pressure increases with decreasing oil film thickness. The inlet oil film thickness h 1 is defined as the oil film thickness at a h = c/100 γ/100 d [3] where c is the emulsion concentration, γ is the trapping ratio, and d is the emulsion diameter. In this calculation, the trapping ratio must be given quantitatively. Determination of Trapping Ratio First, the trapping ratio in the starvation model without the plating-out film on the roll and strip surfaces is calculated in the rolling experiments using a short sheet workpiece. In this rolling experiment, the inlet oil film thickness is determined from Eq. [] using the value of the surface brightness of the sheet workpiece after rolling. Then, from the value of the inlet oil film thickness, the trapping ratio is calculated using the starvation model and Eq. [3]. On the other hand, the trapping ratio in the starvation model with the plating-out film on the roll and strip surface is calculated in the rolling experiments using a long coil workpiece. In this rolling experiment, the inlet oil film thickness is determined from Eq. [] using the value of the surface brightness of the coil workpiece after rolling. Then, the oil film thicknesses adhered on the roll and coil surfaces before rolling are measured using a fluorescence method (Azushima, et al. (18)). From the value of the inlet oil film thickness and the value of the oil film thicknesses adhered on the roll and coil workpiece surfaces before rolling, the trapping ratio in the starvation model with the plating-out film on the roll and strip surface is calculated using the starvation model and Eq. [3]. Experimental Procedures The rolling tests were carried out using a laboratory mill setup for two-high mill operation. The maximum rolling load was 15 tonf. The roll diameter was 76 mm and the peripheral speed ranged from 0. to 450 m/min. The roll material used was SUJ-. The surface roughness was controlled at a constant of 0.0 µm Ra using No emery (5 µm grit) paper. The workpiece material used was aluminum A1050H. The dimensions of the sheet workpiece were 0.4 mm thick, 30 mm wide, and 300 mm long. The dimensions of the coil workpiece were 0.4 mm thick and 30 mm wide. The surface roughness was 0.04 µm Ra. Mineral oil with a

3 Cold Rolling with O/W Emulsion 77 Fig. 4 Relationship between light intensity and oil film thickness. Fig. Distribution of particle diameter of O/W emulsions with concentrations of 10 and 0%. viscosity of 0.35 Pa?s was used as a base oil of the emulsion. Two different concentrations of O/W emulsions of 10 and 0% were prepared. The concentration of emulsifying agent was 10% and the emulsifying agent used was a nonionic agent. The average particle diameter of the emulsion was measured using a Coulter counter. The Coulter counter is a device that can accurately measure the number and volume of particles using the electrical sensing zone technique. The distribution of particle diameter of O/W emulsions with concentrations of 10 and 0% is shown in Fig. and the average particle diameters were 10 and 1 µm. The emulsion temperature was controlled at 0 C. The emulsion was circulated during rolling and the emulsion amount of 3.5 L/min was supplied at the entrance of the roll bite using flat nozzles. Figure 3 shows the schematic representation of the fluorescent method (Smart and Ford (19); Tanimoto and Rabinowicz (0)) which was used in the coil rolling. In coil rolling, the 1% fluorescent dye was added in the base oil for the fluorescence method. Thiophene compound is used as fluorescent dye. The fluorescent dye emits a visible light when an incident ultraviolet (UV) from the microscope is absorbed. The visible light can be observed with a CCD camera attached to the fluorescence microscope. The intensity distribution of the visible light can be measured using an image processor. Beccause the intensity of the fluorescence light is proportion to the illuminated oil volume, the oil film thickness can be determined by measuring the light intensity. A calibration curve is obtained from the relationship between the light intensity and the oil film thickness before rolling examinations as shown in Fig. 4. The mean oil film thicknesses on the roll and coil workpiece surface can be measured using the fluorescence method in order to estimate the trapping ratio. Before rolling experiments, the surfaces of the roll and workpiece were degreased with benzene. Tests were carried out at a rolling speed of 0.5 m/s and a constant reduction in thickness of 15%. After rolling, the surface brightness Gs (0 ) was measured at five points on the rolled sheet surface using a brightness meter. RESULTS AND DISCUSSION Figure 5 shows the relationship between surface brightness Gs (0 ) and inlet oil film thickness in this rolling. From these Fig. 3 Fluorescence method. Fig. 5 Relationship between surface brightness and inlet oil film thickness calculated from rolling conditions with neat oil.

4 78 A. AZUSHIMA ET AL. experimental results, the inlet oil film thickness is given by the following equation: Gs = ln (h 1 ) [4] The values of the surface brightness Gs (0 ) of the rolled workpiece in the sheet rolling experiments with emulsion concentrations of 10 and 0% are 775 and 679. The inlet oil film thicknesses in the sheet rolling are obtained from Eq. [4]. The values of the inlet oil film thickness in the sheet rolling are and µm. From the values of the inlet oil film thickness, the oil film thicknesses h at a point of x are calculated using the new starvation model and the values are 0.19 and µm. Then, the trapping ratios are estimated using the values of the oil film thicknesses h and Eq. [3] and the values are 19. and 1.6%. On the other hand, the values of the surface brightness Gs (0 ) of the rolled workpiece in the coil rolling experiments with the emulsion concentrations of 10 and 0% are 458 and 403. The inlet oil film thicknesses in the coil rolling are obtained from Eq. [4]. The values of the inlet oil film thickness in the coil rolling are 0.50 µm and 0.95 µm. From the values of the inlet oil film thickness, the oil film thicknesses h at a point of x are calculated using the new starvation model and the values are and.058 µm. Moreover, the oil film thicknesses adhered on the roll and workpiece surfaces are measured by the fluorescence method. The values are 0.98 and 1.78 µm. Then, the trapping ratios are estimated using the values of the oil film thicknesses h and Eq. [3] and the values are.1 and 11.7%. Values of the surface brightness, inlet oil film thicknesses, and estimated trapping ratio in the sheet rolling and the coil rolling are summarized in Table 1. From the comparison between the trapping ratios in the sheet rolling and the coil rolling the trapping ratio in the coil rolling is in good agreement with that in the sheet rolling at concentrations of 10 and 0%. Consequently, it is reasonable that the value of trapping ratio in the sheet rolling can be used as the value of the trapping ratio in the coil rolling. EFFECT OF EMULSION CONCENTRATION AND EMULSIFIER ON PLATING-OUT FILM THICKNESS Experimental Procedures In this experiment, the same material and oil were used. In the experiment on the effect of the emulsion concentration on the plating-out film thickness, three different concentrations of O/W emulsions of 5, 10, and 0% were prepared. The concentration of emulsifying agent was 10% and the emulsifying agent used was a nonionic agent (polyoxyethylene alkyl ether). The average di- TABLE 1 SURFACE BRIGHTNESS,INLET OIL FILM THICKNESS,OIL FILM THICKNESS H, AND TRAPPING RATIO FOR SHEET ROLLING AND COIL ROLLING Trapping Gs h 1 (µm) h (µm) ratio (%) Concentration 10% 0% 10% 0% 10% 0% 10% 0% Sheet rolling Coil rolling Fig. 6 Distribution of particle diameter of O/W emulsions with three different nonionic agents (I, II, and III). ameters of the O/W emulsions with 5, 10, and 0% contained the agent were 6, 10, and 1 µm. In the experiment on the effect of the emulsifier on the plating-out film thickness, three different emulsifiers were prepared. The concentration of emulsifying agent was 10% and the emulsifying agents used were three different nonionic agents. The emulsion concentration was 10%. The distribution of particle diameter of O/W emulsions with three different nonionic agents (I, II, and III) is shown in Fig. 6 and the average particle diameters are 10, 8, and 11 µm. The emulsion temperature was controlled at 0 C. The properties of the emulsion and emulsifying agent are summarized in Table. The emulsion was circulated during rolling and the emulsion amount of 3.5 L/min was supplied at the entrance of the roll bite using flat nozzles. Tests were carried out at a rolling speed of 0.5 m/s and a constant reduction in thickness of 15%. RESULTS AND DISCUSSION From the experimental results between the surface brightness and the inlet oil film thickness as mentioned above, the inlet oil film thickness is given by Eq. [4]. Figure 7 shows the relationship between the surface brightness Gs (0 ) of the rolled workpiece and the emulsion concentration in the sheet rolling without the TABLE EMULSIFYING AGENT USED AND PARTICLE DIAMETER Mineral oil (90)+Emulsifier I (10) Mineral oil (90)+Emulsifier II (10) Mineral oil (90)+Emulsifier III (10) Particle diameter Emulsifier (µ m) HLB (I) Polyoxyethylene alkyl ether (II) Polyoxyethylene mono ester (II) Sorbitan mono ester

5 Cold Rolling with O/W Emulsion 79 Fig. 7 Relationship between surface brightness of rolled workpiece and emulsion concentration in sheet rolling without plating-out film and in coil rolling with plating-out film. plating-out film and in the coil rolling with the plating-out film. The inlet oil film thicknesses in the sheet rolling and in coil rolling are obtained from Eq. [4] and the values of the surface brightness. Figure 8 shows the relationship between the inlet oil film thickness and the emulsion concentration without the plating-out film thickness and with the plating-out film. From the values of the inlet oil film, the oil film thicknesses h at a point of x are calculated sing the new starvation model. The experimental results in the sheet rolling and the coil rolling are summarized in Table 3. On the other hand, Fig. 9 shows the surface brightness Gs (0 ) of the rolled workpiece in the sheet rolling without the plating-out film and in the coil rolling with the plating-out film for emulsions with different emulsifiers. The inlet oil film thicknesses in the sheet rolling and the coil rolling are obtained from Eq. [4] and the values of the surface brightness. Figure 10 shows the inlet oil film thickness without the plating-out film and with the plating-out film. The value of the inlet oil film thickness and plating-out film cannot be calculated due to a surface brightness over 1,000. From the values of the inlet oil film thickness, the oil film thicknesses h at a point of x are calculated using the new starvation model. The experimental results in the sheet rolling and the coil rolling are shown in Table 4. Because it was confirmed that the trapping ratio in coil rolling is nearly equal to the trapping ratio obtained in sheet rolling without the plating-out film on the roll and workpiece surfaces, the Fig. 8 Relationship between inlet oil film thickness and emulsion concentration without plating-out film thickness and with plating-out film. Fig. 9 Surface brightness of rolled workpiece in sheet rolling without plating-out film and in coil rolling with plating-out film for emulsion with different emulsifiers. plating-out film thickness h in coil rolling is given by the following equation. h = h h [5] Figure 11 shows the relationship between the plating-out film thickness on the roll and workpiece surfaces in the coil rolling TABLE 3 SURFACE BRIGHTNESS, INLET OIL FILM THICKNESS, AND OIL FILM THICKNESS H FOR SHEET ROLLING AND COIL ROLLING Gs h 1 (µ m) h (µ m) Sheet Coil Sheet Coil Sheet Coil Mineral oil (90)+Emulsifier I (10) Mineral oil (90)+Emulsifier II (10) Mineral oil (90)+Emulsifier III (10) Fig. 10 Inlet oil film thickness without plating-out film and with platingout film.

6 80 A. AZUSHIMA ET AL. TABLE 4 SURFACE BRIGHTNESS, INLET OIL FILM THICKNESS, AND OIL FILM THICKNESS H FOR SHEET ROLLING AND COIL ROLLING WITH 5, 10, AND 0% EMULSION GS h 1 (µ m) h (µ m) Concentration (%) Sheet Coil Sheet Coil Sheet Coil and the emulsion concentration. The plating-out film thickness increases with increasing emulsion concentration. The value increases from 0. µm at an emulsion concentration of 5% to 1.8 µm at 0%. The values are in reasonable agreement with those obtained by Fujita and Kimura (1), who examined the platingout film thickness on the strip surface in the interval between mill stands. Figure 1 shows the plating-out film thickness in the coil rolling for emulsions with different emulsifiers. From the experimental results, it was estimated that if an emulsion with a superior plating-out property is used, the plating-out film thickness becomes about ten times that in the conventional emulsion. It is possible to develop a new rolling oil in which this inlet oil film thickness becomes thicker by understanding the trapping ratio and the plating-out film thickness. CONCLUSION The estimating method of the plating-out film thickness was investigated using the numerical method of the inlet oil film thickness under the starvation condition of emulsion, and the effect of the emulsion concentration and the emulsifier on the plating-out film thickness was examined using the numerical method. The results obtained were as follows: 1. An estimation method of the plating-out film thickness during cold rolling was proposed.. The plating-out film thickness increased with increasing emulsion concentration. Fig. 11 Relationship between plating-out film thickness on roll and workpiece surfaces and emulsion concentration. Fig. 1 Plating-out film thickness for emulsion with different emulsifiers. 3. The plating-out film thickness was relatively dependent on the property of the emulsifier. REFERENCES (1) Roberts, L. W. (1978), Cold Rolling of Steel, Marcel Dekker, pp () Schey, A. J. (1983), Tribology in Metalworking, American Society for Metals, pp (3) Mase, T., Kohno, T., and Yamamoto, H. (1978), Tetus-to-Hagane, 64-11,p s704. (4) Nakajima, K., Shibata, Y., and Uehori, Y. (1979), Introducing Characteristics of Rolling Oil in Cold Rolling, Proceedings of the Japan Spring Conference on Technology of Plasticity, 17 May 1979, pp (5) Shirota, M., and Sakai, K. (198), Plate-Out and Lubricity of Cold Rolling Fluids for Steel Strip, Journal of Japan Society of Lubricants, 8, pp (6) Sakaguchi, Y., and Wilson, W. R. D. (1984), EHD Analysis of the Emulsion at the Inlet of Roll Bites, Proceedings of the 35th Japanese Conference on Technology of Plasticity, 19 October 1984, Tokyo, pp (7) Kimura, Y., and Okada, K. (1985), Elastohydrodynamic Lubrication with Oil in Water Emulsion, Proceedings of the JSTL, International Tribology Conference, 8 July 1985, pp (8) Schmid, S. R. and Wilson, W. R. D. (1995), Lubrication of Aluminum Rolling by Oil-in-Water Emulsions, Tribology Transactions, 38, pp (9) Wilson, W. R. D., Sakaguchi, Y., and Schmid, S. R. (1994), A Mixed Flow Model Flow Lubrications with Emulsion, Tribology Transactions, 37(3), pp (10) Azushima, A., and Noro, K. (1998), Analysis and Quantitative Consideration of Inlet Oil Film Thickness in Cold Sheet Rolling with Oil in Water Emulsions, Journal - Japan Society for Technology of Plasticity, 39, pp (11) Zhu, D., Biresaw, G. S., Clark, J., and Kasun, T. J. (1994), Elastohydrodynamic Lubrication with O/W Emulsions, Journal of Tribology, 116, pp (1) Yang, H., Schmid, S. R., Kasan, T. J., and Reich, R. A. (004), Elastohydrodynamic Film Thickness and Tractions for Oil-in-Water Emulsions, Tribology Transactions, 47, pp (13) Reich, R., Panseri, N., and Bohaychich, J. (001), The Effects of Lubricant Starvation in Cold Rolling of Aluminum Metal When Using on Oilin-Water Emulsion, Lubrication Engineering, 57, pp (14) Azushima, A., and Inagaki, S. (009), Measurement and Analysis of Inlet Oil Film Thickness in Cold Sheet Rolling with O/W Emulsion, Tribology Transactions, 5, pp (15) Inagaki, S., and Azushima, A. (009), Influence of Lubrication Condition on Trapping Ratio in Cold Sheet Rolling with O/W Emulsion, Journal - Japan Society for Technology of Plasticity, 50, pp (16) Azushima, A., Noro, K., Iyanagi, Y., and Degawa, K. (1990), Proposal of Control System of Surface Brightness of Rolled Sheet in Cold Rolling, Tetus-to-Hagane, 76, pp (17) Azushima, A., Noro, K., and Iyanagi, Y. (1989), Surface Qualities after Rolling and Oil Film Introduced during Rolling in Emulsion Lubrication, Journal of the Japanese Society of Tribologists, 34, pp

7 Cold Rolling with O/W Emulsion 81 (18) Azushima, A., Natsui, M., Inagaki, S., and Sugai, T. (000), Explanation of Lubrication Behavior by Means of Oil Film Measurement on Rolled Sheet Surface Measurement, Tetsu-to-Hagane, 86, pp (19) Smart, A. E. and Ford R. A. J. (1974), Measurement of Thin Liquid Film by a Fluorescence Method, Wear, 9, pp (0) Tanimoto, K., and Rabinowicz, E. (199), A Fluorescence Technique for Measuring Lubricant Thickness of Hard Magnetic Disks, Tribology Transactions, 35(3), pp (1) Fujita, N., and Kimura, Y. (009), Influence of Plate-Out Oil Film on Lubrication Characteristics in Cold Rolling, Report of the ISIJ Meeting, -, pp