- Email: [email protected]
Proposal of a new method for the spread rolling of thin strips
Journal of Materials Processing Technology 87 (1999) 207 – 212
Proposal of a new method for the spread rolling of thin strips Hiroshi Utsunomiya *, Yoshihiro Saito, Shigemoto Matsueda Department of Materials Science and Engineering, Faculty of Engineering, Osaka Uni6ersity, 2 -1, Yamada-oka, Suita, Osaka 565, Japan Received 3 September 1997
Abstract It has been believed impossible to increase the width of thin and wide strips continuously by rolling. This paper proposes a new method for the spread rolling of thin and wide strips. The method consists of three-pass rolling operations. In the first pass, the thickness of several portions of the width is reduced between a grooved roll that has many protuberances and a flat roll, whilst the other portions bulge into the roll grooves. In the second pass, the bulged portions are flattened by flat rolls. In the final pass, the strip is again rolled by flat rolls, and widened flat strips are obtained. In order to evaluate the method, several rolling experiments have been conducted with a type of clay (plasticene) as a model material. The influence of the rolling conditions and of the grooved roll profile have been investigated experimentally. It has been found that 100-mm wide and 1-mm thick strips can be widened by up to 5 mm for a 90% reduction in thickness. The spreading effect is more obvious in the case of thinner strips. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Lateral spread; Strip rolling; Spread rolling; Caliber rolling; Deformation characteristics; Plasticene; Roll pass design
1. Introduction Since rolled products are supplied in various dimensions, the width must be controlled in manufacturing processes. A small number of stock widths is favorable for manufacturers because not only is the equipment cost low, but the productivity is high also. On the other hand, a small number of the stock widths requires the reducing or cutting of product edges in order to adjust the width, which causes low productivity and low yield efficiency. The width of continuously-cast slabs has been controlled not only by changing the mold width of the casters, but also by reducing the width by edgers or sizing presses. Since such a process requires great investment in equipment, width-controlling methods by means of rolling have been proposed [1 – 3]. Since the thin-slab caster began to be applied in industry recently, the demand for changing the width of thin slabs by rolling is growing. However, it has been believed that the lateral spread by rolling is negligible when the aspect ratio width/thickness of the material is * Corresponding author. [email protected]
Fax:
+ 81
6
8797936;
e-mail:
greater than 10. It is intended to develop a special rolling method to increase the width of thin strips. Such a method would have advantages not only in multiwidth production, but also in yield efficiency, productivity and texture control [5]. Intermittent pressing was proposed as a spreading method [4], although the process may have a problem in productivity. This paper proposes a new method for the spread rolling of thin strips, the method employing multi-pass caliber rolling. The spreading ability has been evaluated by model experiments.
2. Principle of the new spread-rolling method The proposed spread-rolling method is illustrated schematically in Fig. 1. The method consists of threepass rolling operations. In the first pass, several portions of the width are rolled between a flat roll and a grooved roll having many regular protuberances. Other portions that are not in contact with the rolls bulge into grooves, as shown in the figure. In the second pass, the bulged portions are flattened by flat rolls: this process can be thought of as roll forming. Note that the gap is greater than the thickness of thin portions. In the final
0924-0136/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII S0924-0136(98)00352-5
208
H. Utsunomiya et al. / Journal of Materials Processing Technology 87 (1999) 207–212
Fig. 2. Schematic diagram of the experimental rolling apparatus.
3. Model experiment Fig. 1. Diagrammatic representation of the new spread-rolling method.
third pass, the strip is flattened again by flat rolls. This method is based on the fact that when the width of the strip is rolled partially, the unrolled part constrains the elongation, and causes lateral spread. This method might be readily implemented in existing rolling-mill trains. In this study, the minimum roll gap for thin portions at the first pass, h1, was set to the product thickness, h3, whilst the roll gap at the second pass, h2, was set to the initial thickness, h0. The roll gap at the i-th pass, hi, can be summarized as follows: h1 = h0(1−rt)
(1)
h2 = h0
(2)
h3 = h0(1−rt)
(3)
where h0 is the initial (stock) thickness and rt is the total reduction in thickness.
In order to evaluate the proposed method, model experiments were carried out with a type of clay, white plasticene (Peter Pan Playthings), as the model material. The workpiece was prepared from bulk with a flat platen and a roller. The workpiece was rolled repeatedly through the gap between the platen and the roller. The final, gap, h0, was set to 1.0 or 2.0 mm, then the workpiece was held in a thermostat kept at 293 K (20°C) for 86.4 ks (24 h), the gap h0 being called the stock thickness hereafter. However, the actual workpiece thickness was no longer h0 due to the elastic recovery of the clay, as will be mentioned later. The workpiece was cut into 100 mm width by 300 mm length prior to the rolling experiments. A schematic illustration of the experimental rolling apparatus is shown in Fig. 2, whilst a photograph is shown in Fig. 3. The workpiece was rolled between a steel roll of 100 mm diameter and the flat platen, the latter being used instead of the bottom flat roll in the proposed method. The gap was set accurately by thickness gauges. Sufficient dead weights were applied at both necks of the roll in order to supply the rolling
Fig. 3. Photograph of the experimental rolling apparatus.
H. Utsunomiya et al. / Journal of Materials Processing Technology 87 (1999) 207–212
Fig. 4. Roll passes used at the first pass.
load. The workpiece was guided by the side guides on the entry table. Experiments were achieved by rolling the roll over the workpiece slowly by hand. Talcum powder was used as the lubricant. The total reduction in thickness, rt, was 10, 20 and 30%. In order to investigate the influence of the roll profile, three rolls having the different profiles shown in Fig. 4 were applied in the first pass. All of the rolls were
209
of 100 mm diameter and had trapezoidal protuberances of 5 mm height by 5 mm width. For all rolls, the side inclination angle was 45°, and the corner radius was 1 mm. The pitch of the protuberances was varied: 15 mm (roll A); 20 mm (roll B); and 25 mm (roll C). The flat roll of 100 mm diameter, was used for both the second and the third pass. Hereafter the rolling processes using rolls A, B and C in the first pass are denoted as rolling A, B and C, respectively. For comparison, a flat-rolling experiment was also carried out. In this case, the roll gap was set equal to the product thickness, h3, and the strip was rolled with the flat rolls in a one-pass operation.
4. Results The lateral spread (sideways spread) was measured by comparing the projected width after rolling with the stock width, and is plotted against the total reduction, rt, in Fig. 5. The history of the lateral spread is plotted in Fig. 6. The lateral spread obtained increases linearly
Fig. 5. Lateral spread of the strips as a function of total reduction: (a) stock thickness = 1.0 mm; (b) stock thickness = 2.0 mm.
Fig. 6. Variation of lateral spread as a function of total reduction: (a) stock thickness = 1.0 mm; (b) stock thickness =2.0 mm.
210
H. Utsunomiya et al. / Journal of Materials Processing Technology 87 (1999) 207–212
Fig. 7. Variation of elongation as a function of total reduction: (a) stock thickness = 1.0 mm; (b) stock thickness = 2.0 mm.
with the total reduction rt. For a 1.0-mm thick strip, the lateral spread is at least 3% for rolling with a reduction of 30%, whilst on the other hand, the lateral spread by flat rolling is 0.2%. The lateral spread achieved is thus far greater than that by flat rolling. It is noteworthy that the lateral spread decreases with the stock thickness, although the lateral spread increases with the stock thickness in the flat rolling. The lateral spread of rolling A is the lowest, 3%, amongst the three rolling processes. The difference of rolling B and C is not large. The incremental lateral spread at the first pass is the greatest amongst the three passes. The 1-mm thick stock also shows large lateral spread in the second pass. The elongation was measured as the nominal strain along the rolling direction, and is plotted in Fig. 7. The elongation is quite small in the first and the second pass, where the width is partially rolled, as expected. The strips elongate mainly in the final pass.
The successive changes of the cross sections during 30% rolling was observed, as presented in Fig. 8. In the first pass, thin portions are formed whilst thick portions bulge into the grooves. In the second pass, the thick portions are flattened. After the third pass, the thickness is almost uniform across the width. The degree of bulging in rolling A is greater than that in rolling B or C. The bulging is more obvious in the case of thin strips. It is found that the lateral spread corresponds well to the degree of bulging in the first pass: greater bulging results in greater lateral spread. Fig. 9 shows the variation of thickness in case of rolling to 30% reduction with roll B. The thickness before rolling is slightly greater than the nominal thickness, due to the elastic recovery of the plasticene [6]. The thickness of both the thick part and the thin part were measured around the center of the width and length. When the thin portions are formed in the first pass, the thickness of the thick portions increase. In the second pass, the thickness of the thick and the thin portions do not change substantially. In the final pass, the thickness of the thin portions slightly decreases by the rolling of the thick portions. Fig. 10 presents the plan view of products, whilst Fig. 11 shows these specimens after each pass. After the first pass, tongues were formed at both the leading and trailing ends of strips, but after the third pass, the tongues had almost disappeared. Flaring of the trailing end can be observed in the products, the flaring being obvious in the case of high reduction rolling with rolls B or C, the amount of such flaring corresponding well to the lateral spread.
5. Discussion Fig. 8. Variation of the cross sections of the strips (total reduction, 30%): (a) stock thickness = 1.0 mm; (b) stock thickness = 2.0 mm.
The above mentioned results show that the proposed method has feasibility for spreading the width of thin
H. Utsunomiya et al. / Journal of Materials Processing Technology 87 (1999) 207–212
211
Fig. 9. Variation of the thickness at the mid-width in rolling B (total reduction, 30%): (a) stock thickness=1.0 mm; (b) stock thickness=2.0 mm.
and wide strips continuously. The spreading ability depends on the grooved roll profile in the first pass. Many parameters are involved in the profile design, such as the pitch and width of protuberances, the radius curvature of corners, and the side inclination angle. Of course, it is difficult to optimize the roll profile to achieve the greatest lateral spread. Although only three different pitches of the protuberances have been investigated in this study, it was found that roll B or roll C is more effective than roll A, so that the optimized pitch may be between 20 mm (roll B) and 25 mm (roll C). The achieved lateral spread can be explained by the bulging of thick portions in the first pass. Since the flexural rigidity of the cross section of rolling A is greater than that of rolling B or C, the strip in rolling A does not bulge into the grooves apparently, and results in lower lateral spread. It is noteworthy that this process is more effective in the case of thinner strips, this behavior being opposite to that in conventional flat rolling, and can also be explained by flexural rigidity. Since the rigidity of the thinner strip is lower, bulging occurs significantly and results in greater lateral spread. The method causes the flaring at the trailing end of the strip, since it is a non-steady-state spreading deformation.
Fig. 10. Plan view of the strips produced (stock thickness =1.0 mm).
In subsequent papers, the proposed method will be applied to commercial materials and the detailed deformation characteristics as well as the textures of the products will be reported.
6. Conclusions A new rolling method to increase the width of thin strips has been proposed. The lateral spread with this method is far greater than that for flat rolling. 1.0-mm thick by 100-mm wide strips were spread by up to 5 mm by rolling to 30% reduction. The spreading effect is more obvious in the case of the thinner sheet. The method causes flaring at the trailing end of the products.
Acknowledgements Financial support from the Amada Foundation for Metal Work Technology is gratefully acknowledged.
Fig. 11. Variation of the plan view of the strips (stock thickness = 1.0 mm; total reduction, 30%).
212
H. Utsunomiya et al. / Journal of Materials Processing Technology 87 (1999) 207–212
References [1] S.-E. Lundberg, A. Holmberg, Steel Res. 61 (1980) 318. [2] T. Hope, J.C. Dobson, K.T. Lawson, in: B.A. Fazan (Ed.), Proceedings of the Fourth International Steel Rolling Conference, Deauville, France, 1987, p. A13.1. [3] M. Okado, T. Ariizumi, I. Nakauchi, H. Takei, Adv. Tech. Plast. 2 (1984) (1984) 1242.
[4] T. Takamachi, K. Yamada, S. Ogawa, M. Ataka, in: Proceedings of the 41st Japanese Joint Conference for Tech. of Plast., Nagano, Japan, Jpn. Soc. Technol. Plasticity, 1990, p. 117. [5] H. Utsunomiya, Y. Saito, T. Sakai, K. Morita, J. Jpn Inst. Met. 59 (1995) 191. [6] K. Chijiiwa, Y. Hatamuta, N. Hasegawa, Trans. ISIJ 21 (1981) 178.
Proposal of a new method for the spread rolling of thin strips Hiroshi Utsunomiya *, Yoshihiro Saito, Shigemoto Matsueda Department of Materials Science and Engineering, Faculty of Engineering, Osaka Uni6ersity, 2 -1, Yamada-oka, Suita, Osaka 565, Japan Received 3 September 1997
Abstract It has been believed impossible to increase the width of thin and wide strips continuously by rolling. This paper proposes a new method for the spread rolling of thin and wide strips. The method consists of three-pass rolling operations. In the first pass, the thickness of several portions of the width is reduced between a grooved roll that has many protuberances and a flat roll, whilst the other portions bulge into the roll grooves. In the second pass, the bulged portions are flattened by flat rolls. In the final pass, the strip is again rolled by flat rolls, and widened flat strips are obtained. In order to evaluate the method, several rolling experiments have been conducted with a type of clay (plasticene) as a model material. The influence of the rolling conditions and of the grooved roll profile have been investigated experimentally. It has been found that 100-mm wide and 1-mm thick strips can be widened by up to 5 mm for a 90% reduction in thickness. The spreading effect is more obvious in the case of thinner strips. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Lateral spread; Strip rolling; Spread rolling; Caliber rolling; Deformation characteristics; Plasticene; Roll pass design
1. Introduction Since rolled products are supplied in various dimensions, the width must be controlled in manufacturing processes. A small number of stock widths is favorable for manufacturers because not only is the equipment cost low, but the productivity is high also. On the other hand, a small number of the stock widths requires the reducing or cutting of product edges in order to adjust the width, which causes low productivity and low yield efficiency. The width of continuously-cast slabs has been controlled not only by changing the mold width of the casters, but also by reducing the width by edgers or sizing presses. Since such a process requires great investment in equipment, width-controlling methods by means of rolling have been proposed [1 – 3]. Since the thin-slab caster began to be applied in industry recently, the demand for changing the width of thin slabs by rolling is growing. However, it has been believed that the lateral spread by rolling is negligible when the aspect ratio width/thickness of the material is * Corresponding author. [email protected]
Fax:
+ 81
6
8797936;
e-mail:
greater than 10. It is intended to develop a special rolling method to increase the width of thin strips. Such a method would have advantages not only in multiwidth production, but also in yield efficiency, productivity and texture control [5]. Intermittent pressing was proposed as a spreading method [4], although the process may have a problem in productivity. This paper proposes a new method for the spread rolling of thin strips, the method employing multi-pass caliber rolling. The spreading ability has been evaluated by model experiments.
2. Principle of the new spread-rolling method The proposed spread-rolling method is illustrated schematically in Fig. 1. The method consists of threepass rolling operations. In the first pass, several portions of the width are rolled between a flat roll and a grooved roll having many regular protuberances. Other portions that are not in contact with the rolls bulge into grooves, as shown in the figure. In the second pass, the bulged portions are flattened by flat rolls: this process can be thought of as roll forming. Note that the gap is greater than the thickness of thin portions. In the final
0924-0136/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII S0924-0136(98)00352-5
208
H. Utsunomiya et al. / Journal of Materials Processing Technology 87 (1999) 207–212
Fig. 2. Schematic diagram of the experimental rolling apparatus.
3. Model experiment Fig. 1. Diagrammatic representation of the new spread-rolling method.
third pass, the strip is flattened again by flat rolls. This method is based on the fact that when the width of the strip is rolled partially, the unrolled part constrains the elongation, and causes lateral spread. This method might be readily implemented in existing rolling-mill trains. In this study, the minimum roll gap for thin portions at the first pass, h1, was set to the product thickness, h3, whilst the roll gap at the second pass, h2, was set to the initial thickness, h0. The roll gap at the i-th pass, hi, can be summarized as follows: h1 = h0(1−rt)
(1)
h2 = h0
(2)
h3 = h0(1−rt)
(3)
where h0 is the initial (stock) thickness and rt is the total reduction in thickness.
In order to evaluate the proposed method, model experiments were carried out with a type of clay, white plasticene (Peter Pan Playthings), as the model material. The workpiece was prepared from bulk with a flat platen and a roller. The workpiece was rolled repeatedly through the gap between the platen and the roller. The final, gap, h0, was set to 1.0 or 2.0 mm, then the workpiece was held in a thermostat kept at 293 K (20°C) for 86.4 ks (24 h), the gap h0 being called the stock thickness hereafter. However, the actual workpiece thickness was no longer h0 due to the elastic recovery of the clay, as will be mentioned later. The workpiece was cut into 100 mm width by 300 mm length prior to the rolling experiments. A schematic illustration of the experimental rolling apparatus is shown in Fig. 2, whilst a photograph is shown in Fig. 3. The workpiece was rolled between a steel roll of 100 mm diameter and the flat platen, the latter being used instead of the bottom flat roll in the proposed method. The gap was set accurately by thickness gauges. Sufficient dead weights were applied at both necks of the roll in order to supply the rolling
Fig. 3. Photograph of the experimental rolling apparatus.
H. Utsunomiya et al. / Journal of Materials Processing Technology 87 (1999) 207–212
Fig. 4. Roll passes used at the first pass.
load. The workpiece was guided by the side guides on the entry table. Experiments were achieved by rolling the roll over the workpiece slowly by hand. Talcum powder was used as the lubricant. The total reduction in thickness, rt, was 10, 20 and 30%. In order to investigate the influence of the roll profile, three rolls having the different profiles shown in Fig. 4 were applied in the first pass. All of the rolls were
209
of 100 mm diameter and had trapezoidal protuberances of 5 mm height by 5 mm width. For all rolls, the side inclination angle was 45°, and the corner radius was 1 mm. The pitch of the protuberances was varied: 15 mm (roll A); 20 mm (roll B); and 25 mm (roll C). The flat roll of 100 mm diameter, was used for both the second and the third pass. Hereafter the rolling processes using rolls A, B and C in the first pass are denoted as rolling A, B and C, respectively. For comparison, a flat-rolling experiment was also carried out. In this case, the roll gap was set equal to the product thickness, h3, and the strip was rolled with the flat rolls in a one-pass operation.
4. Results The lateral spread (sideways spread) was measured by comparing the projected width after rolling with the stock width, and is plotted against the total reduction, rt, in Fig. 5. The history of the lateral spread is plotted in Fig. 6. The lateral spread obtained increases linearly
Fig. 5. Lateral spread of the strips as a function of total reduction: (a) stock thickness = 1.0 mm; (b) stock thickness = 2.0 mm.
Fig. 6. Variation of lateral spread as a function of total reduction: (a) stock thickness = 1.0 mm; (b) stock thickness =2.0 mm.
210
H. Utsunomiya et al. / Journal of Materials Processing Technology 87 (1999) 207–212
Fig. 7. Variation of elongation as a function of total reduction: (a) stock thickness = 1.0 mm; (b) stock thickness = 2.0 mm.
with the total reduction rt. For a 1.0-mm thick strip, the lateral spread is at least 3% for rolling with a reduction of 30%, whilst on the other hand, the lateral spread by flat rolling is 0.2%. The lateral spread achieved is thus far greater than that by flat rolling. It is noteworthy that the lateral spread decreases with the stock thickness, although the lateral spread increases with the stock thickness in the flat rolling. The lateral spread of rolling A is the lowest, 3%, amongst the three rolling processes. The difference of rolling B and C is not large. The incremental lateral spread at the first pass is the greatest amongst the three passes. The 1-mm thick stock also shows large lateral spread in the second pass. The elongation was measured as the nominal strain along the rolling direction, and is plotted in Fig. 7. The elongation is quite small in the first and the second pass, where the width is partially rolled, as expected. The strips elongate mainly in the final pass.
The successive changes of the cross sections during 30% rolling was observed, as presented in Fig. 8. In the first pass, thin portions are formed whilst thick portions bulge into the grooves. In the second pass, the thick portions are flattened. After the third pass, the thickness is almost uniform across the width. The degree of bulging in rolling A is greater than that in rolling B or C. The bulging is more obvious in the case of thin strips. It is found that the lateral spread corresponds well to the degree of bulging in the first pass: greater bulging results in greater lateral spread. Fig. 9 shows the variation of thickness in case of rolling to 30% reduction with roll B. The thickness before rolling is slightly greater than the nominal thickness, due to the elastic recovery of the plasticene [6]. The thickness of both the thick part and the thin part were measured around the center of the width and length. When the thin portions are formed in the first pass, the thickness of the thick portions increase. In the second pass, the thickness of the thick and the thin portions do not change substantially. In the final pass, the thickness of the thin portions slightly decreases by the rolling of the thick portions. Fig. 10 presents the plan view of products, whilst Fig. 11 shows these specimens after each pass. After the first pass, tongues were formed at both the leading and trailing ends of strips, but after the third pass, the tongues had almost disappeared. Flaring of the trailing end can be observed in the products, the flaring being obvious in the case of high reduction rolling with rolls B or C, the amount of such flaring corresponding well to the lateral spread.
5. Discussion Fig. 8. Variation of the cross sections of the strips (total reduction, 30%): (a) stock thickness = 1.0 mm; (b) stock thickness = 2.0 mm.
The above mentioned results show that the proposed method has feasibility for spreading the width of thin
H. Utsunomiya et al. / Journal of Materials Processing Technology 87 (1999) 207–212
211
Fig. 9. Variation of the thickness at the mid-width in rolling B (total reduction, 30%): (a) stock thickness=1.0 mm; (b) stock thickness=2.0 mm.
and wide strips continuously. The spreading ability depends on the grooved roll profile in the first pass. Many parameters are involved in the profile design, such as the pitch and width of protuberances, the radius curvature of corners, and the side inclination angle. Of course, it is difficult to optimize the roll profile to achieve the greatest lateral spread. Although only three different pitches of the protuberances have been investigated in this study, it was found that roll B or roll C is more effective than roll A, so that the optimized pitch may be between 20 mm (roll B) and 25 mm (roll C). The achieved lateral spread can be explained by the bulging of thick portions in the first pass. Since the flexural rigidity of the cross section of rolling A is greater than that of rolling B or C, the strip in rolling A does not bulge into the grooves apparently, and results in lower lateral spread. It is noteworthy that this process is more effective in the case of thinner strips, this behavior being opposite to that in conventional flat rolling, and can also be explained by flexural rigidity. Since the rigidity of the thinner strip is lower, bulging occurs significantly and results in greater lateral spread. The method causes the flaring at the trailing end of the strip, since it is a non-steady-state spreading deformation.
Fig. 10. Plan view of the strips produced (stock thickness =1.0 mm).
In subsequent papers, the proposed method will be applied to commercial materials and the detailed deformation characteristics as well as the textures of the products will be reported.
6. Conclusions A new rolling method to increase the width of thin strips has been proposed. The lateral spread with this method is far greater than that for flat rolling. 1.0-mm thick by 100-mm wide strips were spread by up to 5 mm by rolling to 30% reduction. The spreading effect is more obvious in the case of the thinner sheet. The method causes flaring at the trailing end of the products.
Acknowledgements Financial support from the Amada Foundation for Metal Work Technology is gratefully acknowledged.
Fig. 11. Variation of the plan view of the strips (stock thickness = 1.0 mm; total reduction, 30%).
212
H. Utsunomiya et al. / Journal of Materials Processing Technology 87 (1999) 207–212
References [1] S.-E. Lundberg, A. Holmberg, Steel Res. 61 (1980) 318. [2] T. Hope, J.C. Dobson, K.T. Lawson, in: B.A. Fazan (Ed.), Proceedings of the Fourth International Steel Rolling Conference, Deauville, France, 1987, p. A13.1. [3] M. Okado, T. Ariizumi, I. Nakauchi, H. Takei, Adv. Tech. Plast. 2 (1984) (1984) 1242.
[4] T. Takamachi, K. Yamada, S. Ogawa, M. Ataka, in: Proceedings of the 41st Japanese Joint Conference for Tech. of Plast., Nagano, Japan, Jpn. Soc. Technol. Plasticity, 1990, p. 117. [5] H. Utsunomiya, Y. Saito, T. Sakai, K. Morita, J. Jpn Inst. Met. 59 (1995) 191. [6] K. Chijiiwa, Y. Hatamuta, N. Hasegawa, Trans. ISIJ 21 (1981) 178.