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Effects of lubricants on the rolling performances of cold rolled copper strips
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Available online at www.sciencedirect.com Procedia Engineering00 Engineering00 (2017) (2017) 000–000 000–000 Procedia
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Procedia Engineering 207 (2017) 2227–2232
International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom
Effects of lubricants on the rolling performances of cold rolled copper strips Xudong Yan, Jianlin Sun*, Sang Xiong School of of Materials Materials Science Science and and Engineering, Engineering, University University of of Science Science and and Technology Technology Beijing, Beijing, 30 30 Xueyuan Xueyuan Road, Road, Beijing, Beijing, 100083, 100083, P.R. P.R. China China School
Abstract Abstract Two parameters parameters in in rolling rolling process, process, the the forward forward slip slip value value (S (Shh)) and and the the minimum minimum rolling rolling gauge gauge (h (hmin were tested tested using using aa 4-high 4-high min)) were Two rolling mill in order to investigate the rolling performances of cold rolled copper strips under different lubricating conditions viz, rolling mill in order to investigate the rolling performances of cold rolled copper strips under different lubricating conditions viz, lubrication with with (i) (i) base base oil, oil, (ii) (ii) base base oil oil with with 0.5wt.% 0.5wt.% oiliness, oiliness, (iii) (iii) base base oil oil with with 0.5wt.% 0.5wt.% dialkyldithiophosphateester(DDE) dialkyldithiophosphateester(DDE) and and lubrication (iv) base base oil oil with with 0.25wt.% 0.25wt.% DDE DDE and and 0.25wt.% 0.25wt.% molybdenum molybdenum dialkyldithiophosphate dialkyldithiophosphate (MoDDP). (MoDDP). The The surface surface roughness roughness of of rolled rolled (iv) copper strips strips was was measured measured by by aa laser laser scanning scanning confocal confocal microscope. microscope. The The surface surface morphologies morphologies of of copper copper strips strips were were observed observed copper by aa scanning scanning electron electron microscopy microscopy (SEM) (SEM) and and the the compositions compositions of of the the surface surface residues residues were were analyzed analyzed with with an an energy energy dispersive dispersive by with different different lubricants lubricants ranged ranged from from spectrometer (EDS). (EDS). Results Results showed showed friction friction coefficients, coefficients, which which were were calculated calculated by by SShh with spectrometer 0.067-0.302. The The surface surface topography topography of of copper copper strips strips showed showed smooth smooth and and the the plowing plowing wear wear was was finer. finer. Meanwhile, Meanwhile, when when the the 0.067-0.302. lubricant was was base base oil oil with with 0.25wt.% 0.25wt.% DDE DDE and and 0.25wt.% 0.25wt.% MoDDP, MoDDP, the the hhmin of copper copper reached reached 19μm, 19μm, aa value value satisfied satisfied the the copper copper min of lubricant foil conduction. conduction. However, However, with with the the addition addition of of EP EP additives, additives, the the topographies topographies showed showed some some grind grind pits pits at at local local region. region. Indicating Indicating foil that EP EP additives additives containing containing P, P, S, S, Mo Mo moieties moieties possess possess aa better better thickness-reducing thickness-reducing performance, performance, but but cause cause corrosion corrosion at at the the same same that time. time. © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. © © 2017 The Authors. Published by Elsevier Ltd. the scientific committee of the International Conference on the Technology Peer-review under responsibility of Peer-review under under responsibility responsibility of of the scientific committee Peer-review of the International Conference on the Technology of Plasticity. of Plasticity.. Keywords:Cold rolled rolled copper copper strips; strips; Forward Forward slip slip value; value; Minimum Minimum rolling rolling gauge; gauge; Mixed Mixed film film friction friction Keywords:Cold
Corresponding author. author. Tel.: Tel.: +86-010-62333768 +86-010-62333768 ** Corresponding E-mail address: address: [email protected] [email protected] E-mail 1877-7058 © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. 1877-7058 Peer-review under under responsibility responsibility of of the scientific committee of the International Conference on the Technology of Peer-review Plasticity..
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity. 10.1016/j.proeng.2017.10.986
Xudong Yan et al. / Procedia Engineering 207 (2017) 2227–2232 Xudong Yan et al. / Procedia Engineering00 (2017) 000–000
2228 2
1. Introduction Rolled copper foil is widely used in manufacture of print circuits due to its excellent electrical conductivity, thermal conductivity, reliability and chemical resistance [1, 2]. During the cold rolling process, since the rollers and the work piece are in close contact, friction and wear will inevitably occur and increase the energy loss [3, 4]. Technological lubrication is one of the key factors to improve the technology for rolling of copper foil. Suitable lubricants possess excellent extreme-pressure properties, cooling performances and anti-wear properties so that the fiction coefficient, rolling pressure, and power consumption are significantly reduced. Researchers have shown more interest in lubricants, with which the thin and cheap rolled copper foils were fabricating. Huang [5] applied physical and chemical experiments on copper foil with a developed oil, the results showed that the developed oil has a good performance of oil film bearing capacity and oxidation resistance. Wen [6] has found the coefficient of friction (COF) was reduced with the addition of nano-TiO2 particles into the 1.0% (mass %, oil concentration) O/W lubricant. Huh [7] has analyzed the microstructures of copper with and without lubricants after cold rolling and founded the copper samples without lubricants showed a very inhomogeneous asdeformed microstructure consisting of rhombus-like parallelograms surrounded by shear bands while a better microstructure was obtained when lubricant was used. Although numerous studies about the tribological properties of lubricant or its impacts on copper structure have been done, the performances of lubricants on cold rolling, the friction conditions, as well the surface qualities of cold rolled copper are yet to be determined. In this paper, in order to investigate the rolling performances of cold rolled copper strips under different lubricating conditions viz, lubrication with (i) base oil, (ii) base oil with 0.5wt.% oiliness, (iii) base oil with 0.5wt.% dialkyldithiophosphateester (DDE) and (iv) base oil with 0.25wt.% DDE and 0.25wt.% molybdenum dialkyldithiophosphate (MoDDP), two parameters in rolling process, the forward slip value (Sh) and the minimum rolling gauge (hmin) were tested using a 4-high rolling mill. The influences of the roughness and oil film thickness on friction conditions were also addressed. Further, the surface topographies of rolled copper foil were obtained. Nomenclature Sh hmin L Ln μ △h R h hoilfilm Ra λ
the forward slip the minimal rolling gauge the length of two consecutive points the length after rolling the mean friction coefficient reduction in height of the rolled strip the radius of roller the rolling gauge the oil film thickness the surface roughness the ratio of hoilfilm and Ra
2. Experimental materials and methods Acetone, petroleum ether were used for cleaning rolled piece before each test. The specific physiochemical properties of Mineral base oil, D130 are given in Table 1 (in ASTM). 1-Dodecanol and Butyl stearate were utilized as oiliness additives with the proportion of 2:3. Dialkyldithiophosphate ester (DDE) and molybdenum dialkyldithiophosphate (MoDDP) were the compositions of EP additives. For the tests, lubricants were prepared by adding only oiliness additives, only DDE or mixture DDE and MoDDP as composite EP additives to the bass oil. The lubricants were consisted of 0.5wt.% additives and 99.5wt.% base oil.
Xudong / Procedia Engineering 207 (2017) 2227–2232 Xudong YanYan et al.et/al. Procedia Engineering 00 (2017) 000–000
22293
Table. 1. Physiochemical properties of D130 Main characteristics
Parameter
Density(25℃), g/ml Dynamic viscosity(25℃), mm2/s
0.824 6.12
Flash point(open), ℃
279-313
140
Boiling range, ℃
The experimental materials were C11000 (with a purity of 99.9%) copper strips that prepared with 0.5mm in thickness, 50mm in width before cold rolling. A 4-high rolling mill of Φ95/200mm×200mm with a velocity of 60r/min and a rolling power of 35kW was used to evaluate the rolling performances under different lubricating conditions. The reduction ratios of each pass are restricted by 20% and the rolled strips were collected, measured and compared after each pass. After the roller was in the work roll edge contact, the copper strips were rolled for another 4 passes to get the minimal rolling gauges. Another parameter of rolling, Sh was obtained after the number 4 pass of each rolling experiments. The principle diagram of the forward slip experiments was shown in Fig.3. The mean friction coefficient of work pieces under different lubricating conditions could also be deduced according to the equations as below.
Fig. 1. The principle diagram of the forward slip experiments
Sh
Ln L 100% L
h R μ S h 2(1-2 h ) h
(1)
(2)
The rolled pieces used in the experiments were analyzed with respect to surface properties and wear characteristics using various analytical tools. The surface roughness of the rolled pieces was measured with a German model LEXT OLS4000 laser confocal microscope. The surface topographies of copper foils were observed by a scanning electron microscopy (SEM) and the compositions of the surface residues were analyzed with an energy dispersive spectrometer (EDS). 3. Results and discussion 3.1. Rolling performances The rolling forces and the rolling gauges were measured after each passes. The result was shown in Fig.2 (a) and Fig.2 (b).
Xudong Yan et al. / Procedia Engineering 207 (2017) 2227–2232 Xudong Yan et al. / Procedia Engineering00 (2017) 000–000
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Fig. 2. Evolutions of (a) rolling forces and (b) rolling gauges via rolling pass under different lubrications. (25 ℃, 35 KW, 60 rpm)
It can be seen from Fig.2 (a), due to the effect of work hardening mechanism, the rolling forces rose at the first 5 rolling passes while dropped after the roller was in the work roll edge contact. When lubricants were introduced, the rolling forces obviously reduced at each pass. It is obvious that a lowest rolling force was obtained when the lubricant was D130 + 0.25wt.% DDE + 0.25wt.% MoDDP. Besides rolling forces, the minimum rolling gauges (Fig.2 (b)) showed that base oil containing EP additives had better rolling performances. The minimum rolling gauges reduced and satisfied the copper foil production. Especially for the lubricants was D130 + 0.25wt.% DDE + 0.25wt.% MoDDP, it obtained the lowest minimum rolling gauge with a value of 0.19μm. These results indicate that composite EP additives generate a synergistic effect on rolling efficiency improvement. 3.2. Friction conditions The relative parameters of the forward slip experiments were listed in Table. 2. When using lubricants, the friction conditions of copper strips changed from dry lubrication to boundary lubrication [8]. Especially with the EP additives containing only DDE or mixture DDE and MoDDP, the mean friction coefficient reached a properly low value of 0.089 and 0.067, respectively. It can be concluded that a stable tribo-film formed with the addition of EP additives and changed the friction conditions. Table. 2. Parameters of the forward slip experiments Lubricating conditions No lubrication Base oil(D130) D130+oiliness D130+0.5 wt% DDE D130+0.25 wt% DDE +0.25 wt% MoDDP
△h(mm) 0.095 0.092 0.090 0.088 0.088
Sh(mm)
μ
hoilfilm(10-3mm)
Ra(10-3mm)
λ
0.050 0.068 0.100 0.114 0.127
0.88 0.302 0.187 0.089 0.067
0.013 0.031 0.287 0.265
0.635 0.325 0.375 0.253 0.275
＜0.1 ＜0.1 ≈1 ≈1
According to Th. Mang’s theory [9], λ reflects the ratio of film thickness and surface roughness can be used to further demonstrate the friction conditions with different lubrication. An oil drop method was applied to investigate the oil film thickness in lubricant rolling. The tests involved dropping a known quality of oil on the rolled piece surface before rolling, measuring the coverage area with a mark-ups paper after rolling. The drop volume divided by the surface area of the mark gives the final thickness of oil film thickness hoilfilm. Combining with the value of surface roughness (Ra), the value of λ can be obtained. Obviously, when the copper were lubricated with base oil or D130 + 0.5 wt.% oiliness, the value of λ were less than 1, showed the boundary lubrication of these two conditions. Conversely, for the conditions of lubricants with
Xudong Yan et al. / Procedia Engineering 207 (2017) 2227–2232 Xudong Yan et al. / Procedia Engineering 00 (2017) 000–000
2231 5
EP additives, the value of λ were approximate to 1, demonstrating a mixed-film lubrication, which reduced the friction and changed the surface qualities at the same time. 3.3. Surface topographies The 3D topographies of rolled copper surface showed various with different lubrication. When only base oil was used (Fig.3(a)), there was noticeable adhesion with deep rolled trace on the copper surface. Simultaneously cracks and peeling existed and formed a relatively coarse topography. Oiliness added (Fig.3(b)) improved the surface glossiness and the topography was clean. Furrows and plowing were the main forms of wear on copper surface. Importantly, when only DDE was introduced (Fig.3(c)), the plowing was finer and the surface roughness significantly reduced. Meanwhile some grind pits were generated around the rolled traces. When the strips were lubricated with D130+ 0.25 wt.% DDE+ 0.25 wt.% MoDDP (Fig.3(d)). The pits and surface roughness increased, which could attribute to the corrosion caused by those composite EP additives.
Fig.3. The 3D topographies of rolled copper surface under different lubricating conditions: (a) base oil, (b) D130+0.5wt.% oiliness (c) D130+0.5wt.% DDE and (d) D130+ 0.25 wt.% DDE+ 0.25 wt.% MoDDP
To further investigate the composition of the residues on copper surface, the topography of copper lubricated with D130+ 0.25 wt.% DDE+ 0.25 wt.% MoDDP was enlarged to 1000 times with SEM and an EDS analysis had been done. As it can be seen in Fig.4, 1# and 2# represented the area of rolled traces and grind pits, respectively. Cleary there were grind pits existed around the fine plowing. 1# showed 92.17% Cu and an extremely low amount of C (7.83 %) on the rolled trace, while only 83.08% of Cu was presented on 2#, along with 7.83%, 4.78%, 2.45%, 1.86% of O, Mo, S, P elements, respectively. These results attribute to Mo, P, S moieties generate oxidation corrosion pits. Indicating that EP additives process the ability to finer rolled traces, but could also lead to corrode the surface at local region.
Xudong Yan et al. / Procedia Engineering00 (2017) 000–000 Xudong Yan et al. / Procedia Engineering 207 (2017) 2227–2232
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Fig.4. SEM images and EDS analysis of copper surface lubricated with D130+ 0.25 wt.% DDE+ 0.25 wt.% MoDDP
4. Conclusions With the addition of oiliness additives and EP additives into base oil, the rolling forces obviously reduced. A 19 μm copper foil was obtained when the copper was lubricated with D130+ 0.25 wt.% DDE+ 0.25 wt.% MODDP. Lubricants changed the rolling friction conditions from dry lubrication to boundary lubrication. Especially for the condition that lubricated with base oil with EP additives, the value of oil film thickness was approximate to the surface roughness, indicating a stable tribo-film formed on copper surface. EP additives made rolled traces finer, and oxidation corrosion pits generated on the surface, which caused by Mo, P, S moieties in additives. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Grant No. 51474025). References [1] T. Hatano, Y. Kurosawa, J. Miyake. Effect of material processing on fatigue of FPC rolled copper foil. Journal of Electronic Materials, 2000, 29(5):611-616. [2] X. Q. Yin, L. J. Peng, S. Kayani, et al. Mechanical properties and microstructure of rolled and electrodeposited thin copper foil. Rare Metals, 2016DOI: 10.1007/s12598-016-0806-4. [3] J. L. Sun, X. D. Wu, Y. L. Kang, et al. Experimental research and general evaluation of additives in rolling oil during aluminium cold rolling. Lubrication Engineering, 2004, 28(2): 5-8 (in Chinese). [4] X. Zhang, Y. Z. Wang, W. J. Yao, et al. Development and lubricating properties of rolling oil for stainless steel cold rolling. China Petroleum Processing and Petrochemical Technology, 2011, 13(2): 57-64. [5] F. Huang, F. Deng, K. C. Li, et al. Development of special lubricant for the copper belt cold rolling. Industrial Lubrication and Tribology, 2016, 68(5):586-590. [6] W. Z. Xia, J. W. Zhao, H. Wu, et al. Study on Tribological Property of Nano-TiO2 Additive Oil-in-Water Lubricant during Hot Rolling. Materials Science Forum.2016, 876: 381-386. [7] M. Y. Huh, Y. S. Cho, O. Engler. Effect of lubrication on the evolution of microstructure and texture during rolling and recrystallization of copper. Materials Science & Engineering A, 1998, 247(1–2):152-164. [8] S.J. Wen, P. Huang. Principle of Tribology 4th ed. Tsinghua University Press, Beijing, 2012.pp. 4-5. [9] Th. Mang, W. Dresel. Lubricants and lubrication 2nd ed. WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2007.pp. 13-15.
ScienceDirect
Available online at www.sciencedirect.com Procedia Engineering00 Engineering00 (2017) (2017) 000–000 000–000 Procedia
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Engineering 207 (2017) 2227–2232
International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom
Effects of lubricants on the rolling performances of cold rolled copper strips Xudong Yan, Jianlin Sun*, Sang Xiong School of of Materials Materials Science Science and and Engineering, Engineering, University University of of Science Science and and Technology Technology Beijing, Beijing, 30 30 Xueyuan Xueyuan Road, Road, Beijing, Beijing, 100083, 100083, P.R. P.R. China China School
Abstract Abstract Two parameters parameters in in rolling rolling process, process, the the forward forward slip slip value value (S (Shh)) and and the the minimum minimum rolling rolling gauge gauge (h (hmin were tested tested using using aa 4-high 4-high min)) were Two rolling mill in order to investigate the rolling performances of cold rolled copper strips under different lubricating conditions viz, rolling mill in order to investigate the rolling performances of cold rolled copper strips under different lubricating conditions viz, lubrication with with (i) (i) base base oil, oil, (ii) (ii) base base oil oil with with 0.5wt.% 0.5wt.% oiliness, oiliness, (iii) (iii) base base oil oil with with 0.5wt.% 0.5wt.% dialkyldithiophosphateester(DDE) dialkyldithiophosphateester(DDE) and and lubrication (iv) base base oil oil with with 0.25wt.% 0.25wt.% DDE DDE and and 0.25wt.% 0.25wt.% molybdenum molybdenum dialkyldithiophosphate dialkyldithiophosphate (MoDDP). (MoDDP). The The surface surface roughness roughness of of rolled rolled (iv) copper strips strips was was measured measured by by aa laser laser scanning scanning confocal confocal microscope. microscope. The The surface surface morphologies morphologies of of copper copper strips strips were were observed observed copper by aa scanning scanning electron electron microscopy microscopy (SEM) (SEM) and and the the compositions compositions of of the the surface surface residues residues were were analyzed analyzed with with an an energy energy dispersive dispersive by with different different lubricants lubricants ranged ranged from from spectrometer (EDS). (EDS). Results Results showed showed friction friction coefficients, coefficients, which which were were calculated calculated by by SShh with spectrometer 0.067-0.302. The The surface surface topography topography of of copper copper strips strips showed showed smooth smooth and and the the plowing plowing wear wear was was finer. finer. Meanwhile, Meanwhile, when when the the 0.067-0.302. lubricant was was base base oil oil with with 0.25wt.% 0.25wt.% DDE DDE and and 0.25wt.% 0.25wt.% MoDDP, MoDDP, the the hhmin of copper copper reached reached 19μm, 19μm, aa value value satisfied satisfied the the copper copper min of lubricant foil conduction. conduction. However, However, with with the the addition addition of of EP EP additives, additives, the the topographies topographies showed showed some some grind grind pits pits at at local local region. region. Indicating Indicating foil that EP EP additives additives containing containing P, P, S, S, Mo Mo moieties moieties possess possess aa better better thickness-reducing thickness-reducing performance, performance, but but cause cause corrosion corrosion at at the the same same that time. time. © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. © © 2017 The Authors. Published by Elsevier Ltd. the scientific committee of the International Conference on the Technology Peer-review under responsibility of Peer-review under under responsibility responsibility of of the scientific committee Peer-review of the International Conference on the Technology of Plasticity. of Plasticity.. Keywords:Cold rolled rolled copper copper strips; strips; Forward Forward slip slip value; value; Minimum Minimum rolling rolling gauge; gauge; Mixed Mixed film film friction friction Keywords:Cold
Corresponding author. author. Tel.: Tel.: +86-010-62333768 +86-010-62333768 ** Corresponding E-mail address: address: [email protected] [email protected] E-mail 1877-7058 © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. 1877-7058 Peer-review under under responsibility responsibility of of the scientific committee of the International Conference on the Technology of Peer-review Plasticity..
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity. 10.1016/j.proeng.2017.10.986
Xudong Yan et al. / Procedia Engineering 207 (2017) 2227–2232 Xudong Yan et al. / Procedia Engineering00 (2017) 000–000
2228 2
1. Introduction Rolled copper foil is widely used in manufacture of print circuits due to its excellent electrical conductivity, thermal conductivity, reliability and chemical resistance [1, 2]. During the cold rolling process, since the rollers and the work piece are in close contact, friction and wear will inevitably occur and increase the energy loss [3, 4]. Technological lubrication is one of the key factors to improve the technology for rolling of copper foil. Suitable lubricants possess excellent extreme-pressure properties, cooling performances and anti-wear properties so that the fiction coefficient, rolling pressure, and power consumption are significantly reduced. Researchers have shown more interest in lubricants, with which the thin and cheap rolled copper foils were fabricating. Huang [5] applied physical and chemical experiments on copper foil with a developed oil, the results showed that the developed oil has a good performance of oil film bearing capacity and oxidation resistance. Wen [6] has found the coefficient of friction (COF) was reduced with the addition of nano-TiO2 particles into the 1.0% (mass %, oil concentration) O/W lubricant. Huh [7] has analyzed the microstructures of copper with and without lubricants after cold rolling and founded the copper samples without lubricants showed a very inhomogeneous asdeformed microstructure consisting of rhombus-like parallelograms surrounded by shear bands while a better microstructure was obtained when lubricant was used. Although numerous studies about the tribological properties of lubricant or its impacts on copper structure have been done, the performances of lubricants on cold rolling, the friction conditions, as well the surface qualities of cold rolled copper are yet to be determined. In this paper, in order to investigate the rolling performances of cold rolled copper strips under different lubricating conditions viz, lubrication with (i) base oil, (ii) base oil with 0.5wt.% oiliness, (iii) base oil with 0.5wt.% dialkyldithiophosphateester (DDE) and (iv) base oil with 0.25wt.% DDE and 0.25wt.% molybdenum dialkyldithiophosphate (MoDDP), two parameters in rolling process, the forward slip value (Sh) and the minimum rolling gauge (hmin) were tested using a 4-high rolling mill. The influences of the roughness and oil film thickness on friction conditions were also addressed. Further, the surface topographies of rolled copper foil were obtained. Nomenclature Sh hmin L Ln μ △h R h hoilfilm Ra λ
the forward slip the minimal rolling gauge the length of two consecutive points the length after rolling the mean friction coefficient reduction in height of the rolled strip the radius of roller the rolling gauge the oil film thickness the surface roughness the ratio of hoilfilm and Ra
2. Experimental materials and methods Acetone, petroleum ether were used for cleaning rolled piece before each test. The specific physiochemical properties of Mineral base oil, D130 are given in Table 1 (in ASTM). 1-Dodecanol and Butyl stearate were utilized as oiliness additives with the proportion of 2:3. Dialkyldithiophosphate ester (DDE) and molybdenum dialkyldithiophosphate (MoDDP) were the compositions of EP additives. For the tests, lubricants were prepared by adding only oiliness additives, only DDE or mixture DDE and MoDDP as composite EP additives to the bass oil. The lubricants were consisted of 0.5wt.% additives and 99.5wt.% base oil.
Xudong / Procedia Engineering 207 (2017) 2227–2232 Xudong YanYan et al.et/al. Procedia Engineering 00 (2017) 000–000
22293
Table. 1. Physiochemical properties of D130 Main characteristics
Parameter
Density(25℃), g/ml Dynamic viscosity(25℃), mm2/s
0.824 6.12
Flash point(open), ℃
279-313
140
Boiling range, ℃
The experimental materials were C11000 (with a purity of 99.9%) copper strips that prepared with 0.5mm in thickness, 50mm in width before cold rolling. A 4-high rolling mill of Φ95/200mm×200mm with a velocity of 60r/min and a rolling power of 35kW was used to evaluate the rolling performances under different lubricating conditions. The reduction ratios of each pass are restricted by 20% and the rolled strips were collected, measured and compared after each pass. After the roller was in the work roll edge contact, the copper strips were rolled for another 4 passes to get the minimal rolling gauges. Another parameter of rolling, Sh was obtained after the number 4 pass of each rolling experiments. The principle diagram of the forward slip experiments was shown in Fig.3. The mean friction coefficient of work pieces under different lubricating conditions could also be deduced according to the equations as below.
Fig. 1. The principle diagram of the forward slip experiments
Sh
Ln L 100% L
h R μ S h 2(1-2 h ) h
(1)
(2)
The rolled pieces used in the experiments were analyzed with respect to surface properties and wear characteristics using various analytical tools. The surface roughness of the rolled pieces was measured with a German model LEXT OLS4000 laser confocal microscope. The surface topographies of copper foils were observed by a scanning electron microscopy (SEM) and the compositions of the surface residues were analyzed with an energy dispersive spectrometer (EDS). 3. Results and discussion 3.1. Rolling performances The rolling forces and the rolling gauges were measured after each passes. The result was shown in Fig.2 (a) and Fig.2 (b).
Xudong Yan et al. / Procedia Engineering 207 (2017) 2227–2232 Xudong Yan et al. / Procedia Engineering00 (2017) 000–000
2230 4
Fig. 2. Evolutions of (a) rolling forces and (b) rolling gauges via rolling pass under different lubrications. (25 ℃, 35 KW, 60 rpm)
It can be seen from Fig.2 (a), due to the effect of work hardening mechanism, the rolling forces rose at the first 5 rolling passes while dropped after the roller was in the work roll edge contact. When lubricants were introduced, the rolling forces obviously reduced at each pass. It is obvious that a lowest rolling force was obtained when the lubricant was D130 + 0.25wt.% DDE + 0.25wt.% MoDDP. Besides rolling forces, the minimum rolling gauges (Fig.2 (b)) showed that base oil containing EP additives had better rolling performances. The minimum rolling gauges reduced and satisfied the copper foil production. Especially for the lubricants was D130 + 0.25wt.% DDE + 0.25wt.% MoDDP, it obtained the lowest minimum rolling gauge with a value of 0.19μm. These results indicate that composite EP additives generate a synergistic effect on rolling efficiency improvement. 3.2. Friction conditions The relative parameters of the forward slip experiments were listed in Table. 2. When using lubricants, the friction conditions of copper strips changed from dry lubrication to boundary lubrication [8]. Especially with the EP additives containing only DDE or mixture DDE and MoDDP, the mean friction coefficient reached a properly low value of 0.089 and 0.067, respectively. It can be concluded that a stable tribo-film formed with the addition of EP additives and changed the friction conditions. Table. 2. Parameters of the forward slip experiments Lubricating conditions No lubrication Base oil(D130) D130+oiliness D130+0.5 wt% DDE D130+0.25 wt% DDE +0.25 wt% MoDDP
△h(mm) 0.095 0.092 0.090 0.088 0.088
Sh(mm)
μ
hoilfilm(10-3mm)
Ra(10-3mm)
λ
0.050 0.068 0.100 0.114 0.127
0.88 0.302 0.187 0.089 0.067
0.013 0.031 0.287 0.265
0.635 0.325 0.375 0.253 0.275
＜0.1 ＜0.1 ≈1 ≈1
According to Th. Mang’s theory [9], λ reflects the ratio of film thickness and surface roughness can be used to further demonstrate the friction conditions with different lubrication. An oil drop method was applied to investigate the oil film thickness in lubricant rolling. The tests involved dropping a known quality of oil on the rolled piece surface before rolling, measuring the coverage area with a mark-ups paper after rolling. The drop volume divided by the surface area of the mark gives the final thickness of oil film thickness hoilfilm. Combining with the value of surface roughness (Ra), the value of λ can be obtained. Obviously, when the copper were lubricated with base oil or D130 + 0.5 wt.% oiliness, the value of λ were less than 1, showed the boundary lubrication of these two conditions. Conversely, for the conditions of lubricants with
Xudong Yan et al. / Procedia Engineering 207 (2017) 2227–2232 Xudong Yan et al. / Procedia Engineering 00 (2017) 000–000
2231 5
EP additives, the value of λ were approximate to 1, demonstrating a mixed-film lubrication, which reduced the friction and changed the surface qualities at the same time. 3.3. Surface topographies The 3D topographies of rolled copper surface showed various with different lubrication. When only base oil was used (Fig.3(a)), there was noticeable adhesion with deep rolled trace on the copper surface. Simultaneously cracks and peeling existed and formed a relatively coarse topography. Oiliness added (Fig.3(b)) improved the surface glossiness and the topography was clean. Furrows and plowing were the main forms of wear on copper surface. Importantly, when only DDE was introduced (Fig.3(c)), the plowing was finer and the surface roughness significantly reduced. Meanwhile some grind pits were generated around the rolled traces. When the strips were lubricated with D130+ 0.25 wt.% DDE+ 0.25 wt.% MoDDP (Fig.3(d)). The pits and surface roughness increased, which could attribute to the corrosion caused by those composite EP additives.
Fig.3. The 3D topographies of rolled copper surface under different lubricating conditions: (a) base oil, (b) D130+0.5wt.% oiliness (c) D130+0.5wt.% DDE and (d) D130+ 0.25 wt.% DDE+ 0.25 wt.% MoDDP
To further investigate the composition of the residues on copper surface, the topography of copper lubricated with D130+ 0.25 wt.% DDE+ 0.25 wt.% MoDDP was enlarged to 1000 times with SEM and an EDS analysis had been done. As it can be seen in Fig.4, 1# and 2# represented the area of rolled traces and grind pits, respectively. Cleary there were grind pits existed around the fine plowing. 1# showed 92.17% Cu and an extremely low amount of C (7.83 %) on the rolled trace, while only 83.08% of Cu was presented on 2#, along with 7.83%, 4.78%, 2.45%, 1.86% of O, Mo, S, P elements, respectively. These results attribute to Mo, P, S moieties generate oxidation corrosion pits. Indicating that EP additives process the ability to finer rolled traces, but could also lead to corrode the surface at local region.
Xudong Yan et al. / Procedia Engineering00 (2017) 000–000 Xudong Yan et al. / Procedia Engineering 207 (2017) 2227–2232
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Fig.4. SEM images and EDS analysis of copper surface lubricated with D130+ 0.25 wt.% DDE+ 0.25 wt.% MoDDP
4. Conclusions With the addition of oiliness additives and EP additives into base oil, the rolling forces obviously reduced. A 19 μm copper foil was obtained when the copper was lubricated with D130+ 0.25 wt.% DDE+ 0.25 wt.% MODDP. Lubricants changed the rolling friction conditions from dry lubrication to boundary lubrication. Especially for the condition that lubricated with base oil with EP additives, the value of oil film thickness was approximate to the surface roughness, indicating a stable tribo-film formed on copper surface. EP additives made rolled traces finer, and oxidation corrosion pits generated on the surface, which caused by Mo, P, S moieties in additives. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Grant No. 51474025). References [1] T. Hatano, Y. Kurosawa, J. Miyake. Effect of material processing on fatigue of FPC rolled copper foil. Journal of Electronic Materials, 2000, 29(5):611-616. [2] X. Q. Yin, L. J. Peng, S. Kayani, et al. Mechanical properties and microstructure of rolled and electrodeposited thin copper foil. Rare Metals, 2016DOI: 10.1007/s12598-016-0806-4. [3] J. L. Sun, X. D. Wu, Y. L. Kang, et al. Experimental research and general evaluation of additives in rolling oil during aluminium cold rolling. Lubrication Engineering, 2004, 28(2): 5-8 (in Chinese). [4] X. Zhang, Y. Z. Wang, W. J. Yao, et al. Development and lubricating properties of rolling oil for stainless steel cold rolling. China Petroleum Processing and Petrochemical Technology, 2011, 13(2): 57-64. [5] F. Huang, F. Deng, K. C. Li, et al. Development of special lubricant for the copper belt cold rolling. Industrial Lubrication and Tribology, 2016, 68(5):586-590. [6] W. Z. Xia, J. W. Zhao, H. Wu, et al. Study on Tribological Property of Nano-TiO2 Additive Oil-in-Water Lubricant during Hot Rolling. Materials Science Forum.2016, 876: 381-386. [7] M. Y. Huh, Y. S. Cho, O. Engler. Effect of lubrication on the evolution of microstructure and texture during rolling and recrystallization of copper. Materials Science & Engineering A, 1998, 247(1–2):152-164. [8] S.J. Wen, P. Huang. Principle of Tribology 4th ed. Tsinghua University Press, Beijing, 2012.pp. 4-5. [9] Th. Mang, W. Dresel. Lubricants and lubrication 2nd ed. WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2007.pp. 13-15.