- Email: [email protected]
Strip Interface
The Neutral Zone and Temperature at the Roll/Strip Interface J. Jeswiet
- Submitted by W. B. Rice (1); Mechanical Engineering, Queen's University, Kingston, Ontario/Canada Received on December 21,1989
ABSTRACT This paper presents the results of ongoing work in measuring two very important parameters in rolling: friction and temperature. These parameters have an effect on the rolling process and are also a direct result of the rolling deformation process. The experimental results show how the neutral zone increases in size with increasing reduction and that peak temperatures in the roll gap coincide with the neutral zone. They also verify the obscrvation by previous researchers that the ncutral zone forms an arc across the roll face. These observations are for dry rolling of aluminum in an experimental two-high mill. KEYWORDS: ROLLING, FRICTION. TEhIPER ATURE, NEUTR.4L ZOSE INTRODUCTION Three parameters which have an effect upon the rolling process are flow stress, friction a i d temperature. hiacPherson (1) in a description of the rolling model at Kaiser Aluminum, discussed the influence of these parameters upon the rolling process and defined them as basic parameters which need to be known for the verification of models. Rolling models provide information on the deformation process and can be used to give insights into that process. However. experimental data on temperature and friction in the roll gap are lacking and one is usually forced to estimate the conditions that exist at the roll/strip interface as indicated at a recent manufacturing research discussion session (2). It. is the aim of research at Queen's Mechanical Engineering to provide sensors which measure the two parameters: friction and temperature, at the roll/strip interface. The ongoing development of these sensors has been described in a series of papers (3, 4, 5. 6) and the latcst results are described herein.
Rolling direction
De?r
Desi n I
I'
(If)
Annals of the ClRP Vd. B/l/liW
1200.
El i 1000.
!5
Sensor derived rolling torque
800.
F7
FRICTION h1EASUREhIENTS
Using the present cantilever sensor design, one can obtain the friction force profiles shown in figure 3. All the profiles shown are for the same reduction, but are located at different distances from the billet centre-line. When the through friction, F , crosses the horizontal axis the force has reversed direction giving the neutral points nl. n2 and 723. Although the magnitude of the friction force is out by a factor of two, the position of the neutral point is correct. Measuring the distance from the exit to the neutral point for the profiles shown. and b.J can be found. Using these disthe distances bl. tances to plot the neutral points, the arcs shown in figure 4
A 1400.
Roll se arating force torn mill gauges
The work reported used a two-high mill with 230 mm (9 inch) diameter work rolls. The roll surface speed was i6mm/s and the strip/bar was not lubricated. The strips were 1100 Aluminum with an aspect ratio of 2.6 (nominal h = 6.35 mm). All the results shown are for cold rolling.
Neutral Point
Forces Measured
h
Figure 1. The evolution of the cantilever sensor illustrated in its different phases of development. The forces measured in desi n I11 are, F : Normal Force, Ff: lolling directon Friction Force, Ft: Friction Force in $e direction orthogonal to the rolhg duection.
EXPERILIENTAL CONDITIONS
The cantilever friction sensor (design III), which is undergoing further development, has gone through a series of evolutionary steps which can best be seen in the illustration in figure 1, and is described in detail in reference (3). The latest sensor design has problems in that the torque measured externally at the roll spindle and the torque measured by the sensors are out by a factor of two, as shown in figure 2. However, it has also been shown (3,4)that the roll separating force measured by this sensor is correct leading to the conclusion that the normal force profiles measured in the roll gap are also correct.
u
Desi n III
fromsesensor force &rived arating design 111
0
5
10 15 20 25 30
REDUCTION, PERCENT
i2
6oo. 400.
200.
0
5
10 15 20 25 30
REDUCTION, PERCENT
Figure 2. Results obtained with sensor design 111 shown in figure 1 Both rolling torque and roll separatin force results are shown for experimental condibons ,listed in reference 6. can be obtained. These arcs, which are determined by direct measurement, verify the observation by Capus and Cockroft (7), that the neutral point forms an arc across the roll face. They found this by measuring the change in shape of scratches before and after rolling. The sensor results can also be used to show, qualitatively how the resultant friction vector acts in the roll gap. This can be done by plotting a series of x and y vector components (defined in figure 3 along path 1) giving the resultant vector field shown in figure 5. If one now considers the same profiles shown in figure 3, it can be seen that each profile makes an abrupt change in direction before and after the neutral point nl. By drawing
275
Rollino Direction
Figure 5. An illustration of the variation of the Friction Resultant, R,.throughout the roll y p , for a 28% reduction. The neutral arc or this reduction is also shown for tpis reduction. Vectors x and J were obtamed from figure 3.
1billet edoes' Figure 3. Experimental data for a 28% reduction. The force rofiles shown are for F * the Normal Force, Ff. the Lction Force in the robing direction, Ft: Fric ion Force in the orthogonal (transverse) direction.
i
a line through the neutral point, along the linear section, two points of tangency can be observed at points v and w. The linear section of the curve is due to the response time of the recorder and is an area in the roll gap where large changes have occurred in direction of the friction force. This can be defined as the neutral zone. Measuring the points of tangency, hence the neutral zone, for different reductions, shows how the neutral zone increases with reduction for the rolling conditions stated. Figure 6 shows the friction profiles and figire 7 shows how the neutral zone increases with reduction.
,
billet edge
for 3% for 10% for 14% for 28%
3%
TEMPERATURE MEASUREMENTS The temperature increase in the roll gap is a direct result of the defoimation process and frictional heating. Friction is usually assumed to d e c t the temperature rise in two ways: 1) under conditions of sliding friction the work required to overcome frictional force is transformed into heat at the surface, 2) under conditions of sticking friction, changes in interface temperature are no greater than changes in bulk temperature as determined by the'relationsliip T = where T is the temperature increase, W is the work required to accomplish deformation, V is the volume of the deformation zone, fi is the density and c is the specific heat of the workpiece material. A variety of models exist for predicting the temperature variation in the roll gap (1, 8, 9, lo), but there appears to be a lack of experimental interface and bulk temperature data. The lack of such data was also mentioned in a recent manufacturing research conference (2). It is the goal of ongoing research (3) to develop sensors to measure these temperatures. Some of the latest interface temperature experimental results are included in figure 6. By checking with the calibration techniques, described in reference (3), these curves have been shown to be correct. The results agree with the models of Tseng (9) and Wilson (10) at high reductions and with the model of Lahoti, Shah and Altan (8) at low reductions.
%,
10%
1 4%
28%
Figure 4. The variation of the neutral point in the transverse direction to rolling. The ointa shown were obtained form figure 3. Only one-!alf the billet mdth is shown.
276
CONCLUSIONS
Rollina Direction 3.2
3.1
2.6
c
2.4
2.1
I
Len th of
-+p y p yp Nedral zone, mm's.
The development of sensors to the measure friction and temperature in the roll gap is continuing. R o m experiments with the latest sensors, the results obtained so far have shown the following: 0
the maximum interface temperature coincides with the neutral region.
0
the neutral zone increases in tlie rolling direction with increasing reduction. the neutral zone forms an arc across the width of the roll gap, a verification of previous research by Capus and Cockroft (7).
0
the neutral zone does not always coincide with the peak pressure in the gap.
0
the double hump shown for the Xormal Force at 14random and did always occur for the rolling conditions listed earlier.
0
the temperature profile is flat at low reductions and becomes curved with increasing reduction showing a peak at tlie neutral zone.
Temperature increase, deg C.
37
28
14
21
10
3
Reduction, %
erimental results of Britten, Parker and Jeswiet. The shown are for Tem erature, Normal Pressure, hrough Friction [Ff], and fransoerse Friction [Ft]. Conditions: 1100 Aluminum, dry rolling, 76 mm/s, h = 6.35 mm, b/h = 2.6, roll radius is 114 mm.
E"f
6. ro ilea
The last version of the friction sensor is being revised in an attempt to get agreement between the input torque measured at the spindle and that measured by the sensor. This will give accurate experimental friction data on conditions at the roll/strip interface. More work is also planned in the further development of the temperature sensor. ACKNOWLEDGEMENTS The author wishes to gratefully acknowledge support by ALCOA Foundation grant 18961/24 AND NSERC grant A4960.
FRICTION AND TEMPERATURE RESULTS The friction and temperature results are for the same rolling mill and the samc cxpcrimcntd rolling conditions, and can therefore be combined as shown in figure 6. This figure shows the latest experimental results made with the temperature and friction sensors described earlier. The friction sensor results show how tractioii forces vary in the roll gap. Two friction forces are shown, those paallel (through friction, FJ ) to the rolling direction and those perpendicular (transverse friction, Ft ) to the direction of rolling. The normal forces and interface temperat,ures are also shown. Also, from previous discussion, it can be seen how through friction forces, F, , show the existence of a definite neutral region which becomes larger with increasing reduction. It can also be seen that the point of maximum temperature coincides with the neutral zone. Also, the maximum transverse friction force coincides with maximum temperatures observed.
gi
g
1.0
I
20 25 30 35 40 REDUCTION, percent Figure 7. Graph ?holing the increasing size of +e neutral zone mth increasing reduchon. The points were obtained from figure 6. 0
5
1'0
1'5
REFERENCES' 1. MacPherson, D.J., 1974, "Campbell Memorial Lecture: Contributions to the Theory and Practice of Cold Rolling", ASM Metallurgical Transactions, vol. 5, p. 2497. 2. Discussion session at NAMRC-XVII, "Recent Developments and Trends in Forming Research and Technology", 1989 NAMRC-XVII conference. 3. Parker, N. and Jeswiet, J., 1987, "The Measurement of Billet Surface Temperatures in the Roll Gap", 1987 NAMRC XV conference, vol.XV, 312-315. 4. Britten, D. and Jeswiet, J., 1986, "A Sensor for Measuring Normal Forces with Through and Transverse Friction Forces in the Roll Gap", 1986 NAMRG XIV conference, VOl.XIV, 355-358. 5. Jeswiet, J. and Rice, W.B., 1982, "The Design of a Sensor for Measuring Normal Pressure and Friction Stress in the Roll Gap During Cold Rolling", 1982 NAh4RC conference, VOl.X, 130-134 6. Jeswiet, J. and Rice, W.B., 1975, "hleasurement of Strip Temperature in the Roll Gap During Cold Rolling", Annals of CIRP, vol. 24/1/1975, 153- 156. 7. Capus, J.M. and Cockroft, J., 1961, "Relative Slip and Deformation During Cold Rolling", J. Inst. of Metals, V O ~ . 90, 289-297. 8. Lahoti, G.D., Shah, S.N., Altan, T., 1977, "Computer Aided Analysis of Deformations and Temperatures in Strip Rolling", ASh4E paper no. 77 WA/Prod-34. 9. Tseng, A., 1982, "Numerical Methods in Industrial Forming Processes", Pineridge Press, p. 774 10. Wilson, W.R.D., 1982, Private Communications, Northwestern Univ. 11. Banerji, A. and Rice, W.B., 1972,"Experimental Determination of N o r d Pressure and Friction Stress in the Roll Gap During Cold Rolling", Annals of CIRP, vol. 2/1, 53. 277
- Submitted by W. B. Rice (1); Mechanical Engineering, Queen's University, Kingston, Ontario/Canada Received on December 21,1989
ABSTRACT This paper presents the results of ongoing work in measuring two very important parameters in rolling: friction and temperature. These parameters have an effect on the rolling process and are also a direct result of the rolling deformation process. The experimental results show how the neutral zone increases in size with increasing reduction and that peak temperatures in the roll gap coincide with the neutral zone. They also verify the obscrvation by previous researchers that the ncutral zone forms an arc across the roll face. These observations are for dry rolling of aluminum in an experimental two-high mill. KEYWORDS: ROLLING, FRICTION. TEhIPER ATURE, NEUTR.4L ZOSE INTRODUCTION Three parameters which have an effect upon the rolling process are flow stress, friction a i d temperature. hiacPherson (1) in a description of the rolling model at Kaiser Aluminum, discussed the influence of these parameters upon the rolling process and defined them as basic parameters which need to be known for the verification of models. Rolling models provide information on the deformation process and can be used to give insights into that process. However. experimental data on temperature and friction in the roll gap are lacking and one is usually forced to estimate the conditions that exist at the roll/strip interface as indicated at a recent manufacturing research discussion session (2). It. is the aim of research at Queen's Mechanical Engineering to provide sensors which measure the two parameters: friction and temperature, at the roll/strip interface. The ongoing development of these sensors has been described in a series of papers (3, 4, 5. 6) and the latcst results are described herein.
Rolling direction
De?r
Desi n I
I'
(If)
Annals of the ClRP Vd. B/l/liW
1200.
El i 1000.
!5
Sensor derived rolling torque
800.
F7
FRICTION h1EASUREhIENTS
Using the present cantilever sensor design, one can obtain the friction force profiles shown in figure 3. All the profiles shown are for the same reduction, but are located at different distances from the billet centre-line. When the through friction, F , crosses the horizontal axis the force has reversed direction giving the neutral points nl. n2 and 723. Although the magnitude of the friction force is out by a factor of two, the position of the neutral point is correct. Measuring the distance from the exit to the neutral point for the profiles shown. and b.J can be found. Using these disthe distances bl. tances to plot the neutral points, the arcs shown in figure 4
A 1400.
Roll se arating force torn mill gauges
The work reported used a two-high mill with 230 mm (9 inch) diameter work rolls. The roll surface speed was i6mm/s and the strip/bar was not lubricated. The strips were 1100 Aluminum with an aspect ratio of 2.6 (nominal h = 6.35 mm). All the results shown are for cold rolling.
Neutral Point
Forces Measured
h
Figure 1. The evolution of the cantilever sensor illustrated in its different phases of development. The forces measured in desi n I11 are, F : Normal Force, Ff: lolling directon Friction Force, Ft: Friction Force in $e direction orthogonal to the rolhg duection.
EXPERILIENTAL CONDITIONS
The cantilever friction sensor (design III), which is undergoing further development, has gone through a series of evolutionary steps which can best be seen in the illustration in figure 1, and is described in detail in reference (3). The latest sensor design has problems in that the torque measured externally at the roll spindle and the torque measured by the sensors are out by a factor of two, as shown in figure 2. However, it has also been shown (3,4)that the roll separating force measured by this sensor is correct leading to the conclusion that the normal force profiles measured in the roll gap are also correct.
u
Desi n III
fromsesensor force &rived arating design 111
0
5
10 15 20 25 30
REDUCTION, PERCENT
i2
6oo. 400.
200.
0
5
10 15 20 25 30
REDUCTION, PERCENT
Figure 2. Results obtained with sensor design 111 shown in figure 1 Both rolling torque and roll separatin force results are shown for experimental condibons ,listed in reference 6. can be obtained. These arcs, which are determined by direct measurement, verify the observation by Capus and Cockroft (7), that the neutral point forms an arc across the roll face. They found this by measuring the change in shape of scratches before and after rolling. The sensor results can also be used to show, qualitatively how the resultant friction vector acts in the roll gap. This can be done by plotting a series of x and y vector components (defined in figure 3 along path 1) giving the resultant vector field shown in figure 5. If one now considers the same profiles shown in figure 3, it can be seen that each profile makes an abrupt change in direction before and after the neutral point nl. By drawing
275
Rollino Direction
Figure 5. An illustration of the variation of the Friction Resultant, R,.throughout the roll y p , for a 28% reduction. The neutral arc or this reduction is also shown for tpis reduction. Vectors x and J were obtamed from figure 3.
1billet edoes' Figure 3. Experimental data for a 28% reduction. The force rofiles shown are for F * the Normal Force, Ff. the Lction Force in the robing direction, Ft: Fric ion Force in the orthogonal (transverse) direction.
i
a line through the neutral point, along the linear section, two points of tangency can be observed at points v and w. The linear section of the curve is due to the response time of the recorder and is an area in the roll gap where large changes have occurred in direction of the friction force. This can be defined as the neutral zone. Measuring the points of tangency, hence the neutral zone, for different reductions, shows how the neutral zone increases with reduction for the rolling conditions stated. Figure 6 shows the friction profiles and figire 7 shows how the neutral zone increases with reduction.
,
billet edge
for 3% for 10% for 14% for 28%
3%
TEMPERATURE MEASUREMENTS The temperature increase in the roll gap is a direct result of the defoimation process and frictional heating. Friction is usually assumed to d e c t the temperature rise in two ways: 1) under conditions of sliding friction the work required to overcome frictional force is transformed into heat at the surface, 2) under conditions of sticking friction, changes in interface temperature are no greater than changes in bulk temperature as determined by the'relationsliip T = where T is the temperature increase, W is the work required to accomplish deformation, V is the volume of the deformation zone, fi is the density and c is the specific heat of the workpiece material. A variety of models exist for predicting the temperature variation in the roll gap (1, 8, 9, lo), but there appears to be a lack of experimental interface and bulk temperature data. The lack of such data was also mentioned in a recent manufacturing research conference (2). It is the goal of ongoing research (3) to develop sensors to measure these temperatures. Some of the latest interface temperature experimental results are included in figure 6. By checking with the calibration techniques, described in reference (3), these curves have been shown to be correct. The results agree with the models of Tseng (9) and Wilson (10) at high reductions and with the model of Lahoti, Shah and Altan (8) at low reductions.
%,
10%
1 4%
28%
Figure 4. The variation of the neutral point in the transverse direction to rolling. The ointa shown were obtained form figure 3. Only one-!alf the billet mdth is shown.
276
CONCLUSIONS
Rollina Direction 3.2
3.1
2.6
c
2.4
2.1
I
Len th of
-+p y p yp Nedral zone, mm's.
The development of sensors to the measure friction and temperature in the roll gap is continuing. R o m experiments with the latest sensors, the results obtained so far have shown the following: 0
the maximum interface temperature coincides with the neutral region.
0
the neutral zone increases in tlie rolling direction with increasing reduction. the neutral zone forms an arc across the width of the roll gap, a verification of previous research by Capus and Cockroft (7).
0
the neutral zone does not always coincide with the peak pressure in the gap.
0
the double hump shown for the Xormal Force at 14random and did always occur for the rolling conditions listed earlier.
0
the temperature profile is flat at low reductions and becomes curved with increasing reduction showing a peak at tlie neutral zone.
Temperature increase, deg C.
37
28
14
21
10
3
Reduction, %
erimental results of Britten, Parker and Jeswiet. The shown are for Tem erature, Normal Pressure, hrough Friction [Ff], and fransoerse Friction [Ft]. Conditions: 1100 Aluminum, dry rolling, 76 mm/s, h = 6.35 mm, b/h = 2.6, roll radius is 114 mm.
E"f
6. ro ilea
The last version of the friction sensor is being revised in an attempt to get agreement between the input torque measured at the spindle and that measured by the sensor. This will give accurate experimental friction data on conditions at the roll/strip interface. More work is also planned in the further development of the temperature sensor. ACKNOWLEDGEMENTS The author wishes to gratefully acknowledge support by ALCOA Foundation grant 18961/24 AND NSERC grant A4960.
FRICTION AND TEMPERATURE RESULTS The friction and temperature results are for the same rolling mill and the samc cxpcrimcntd rolling conditions, and can therefore be combined as shown in figure 6. This figure shows the latest experimental results made with the temperature and friction sensors described earlier. The friction sensor results show how tractioii forces vary in the roll gap. Two friction forces are shown, those paallel (through friction, FJ ) to the rolling direction and those perpendicular (transverse friction, Ft ) to the direction of rolling. The normal forces and interface temperat,ures are also shown. Also, from previous discussion, it can be seen how through friction forces, F, , show the existence of a definite neutral region which becomes larger with increasing reduction. It can also be seen that the point of maximum temperature coincides with the neutral zone. Also, the maximum transverse friction force coincides with maximum temperatures observed.
gi
g
1.0
I
20 25 30 35 40 REDUCTION, percent Figure 7. Graph ?holing the increasing size of +e neutral zone mth increasing reduchon. The points were obtained from figure 6. 0
5
1'0
1'5
REFERENCES' 1. MacPherson, D.J., 1974, "Campbell Memorial Lecture: Contributions to the Theory and Practice of Cold Rolling", ASM Metallurgical Transactions, vol. 5, p. 2497. 2. Discussion session at NAMRC-XVII, "Recent Developments and Trends in Forming Research and Technology", 1989 NAMRC-XVII conference. 3. Parker, N. and Jeswiet, J., 1987, "The Measurement of Billet Surface Temperatures in the Roll Gap", 1987 NAMRC XV conference, vol.XV, 312-315. 4. Britten, D. and Jeswiet, J., 1986, "A Sensor for Measuring Normal Forces with Through and Transverse Friction Forces in the Roll Gap", 1986 NAMRG XIV conference, VOl.XIV, 355-358. 5. Jeswiet, J. and Rice, W.B., 1982, "The Design of a Sensor for Measuring Normal Pressure and Friction Stress in the Roll Gap During Cold Rolling", 1982 NAh4RC conference, VOl.X, 130-134 6. Jeswiet, J. and Rice, W.B., 1975, "hleasurement of Strip Temperature in the Roll Gap During Cold Rolling", Annals of CIRP, vol. 24/1/1975, 153- 156. 7. Capus, J.M. and Cockroft, J., 1961, "Relative Slip and Deformation During Cold Rolling", J. Inst. of Metals, V O ~ . 90, 289-297. 8. Lahoti, G.D., Shah, S.N., Altan, T., 1977, "Computer Aided Analysis of Deformations and Temperatures in Strip Rolling", ASh4E paper no. 77 WA/Prod-34. 9. Tseng, A., 1982, "Numerical Methods in Industrial Forming Processes", Pineridge Press, p. 774 10. Wilson, W.R.D., 1982, Private Communications, Northwestern Univ. 11. Banerji, A. and Rice, W.B., 1972,"Experimental Determination of N o r d Pressure and Friction Stress in the Roll Gap During Cold Rolling", Annals of CIRP, vol. 2/1, 53. 277