Patent Application
20070193322
In one embodiment, the invention relates to cold rolling, and a method of improving sheet flatness in cold rolled metal sheets utilizing induction heating.
Strip products composed of metal, such as aluminum, are typically rolled in four high or six high rolling mill stands. Prior methods for forming aluminum strip have been unable to roll the strip uniformly over its entire width, and have not been able to provide rolled products being free of undesirable flatness undulations in the middle area, the edge area or the quarter area of the strip. Unevenly distributed internal stresses resulting from the material being processed with prior methods typically result in edge cracking, wherein edge cracks need to be discarded resulting in sections of the rolled product being cut away and scrapped. Edge cracking in the middle of a coil, can require that the entire coil may need to be scrapped.
Generally speaking, in accordance with the invention, in one embodiment, a method of forming metal sheet is provided that employs induction heating to thermally expand portions of the diameter of a singular work roll in response to flatness measurements taken from the metal strip downstream from the work roller. The method includes:
In one embodiment, adjusting the temperature of the singular roller includes selectively heating the edge portions of the work roller to thermally expand the portions of the work roller corresponds to the longitudinal edge of the metal strip to have a greater diameter than the work roller's center portion to provide a work roller having a non-uniform diameter along its width. In one embodiment, inductive heating is employed to adjust the temperature, in which inductive heating is provided by induction heating coils that apply heat to the portions of the work rollers that correspond to the portion of the contact surface between the work roller and the longitudinal edge of the metal strip being rolled. The contact surface between the work roller and the metal strip is referred to as the working surface. In one embodiment, adjusting the temperature in the singular roller includes two induction heating coils positioned proximate to the singular work roller, wherein the heat applied by each induction heating coil is of a magnitude that adjusts the thermal expansion along a length of one of the work roller's axis such that the effect on the roll gap from the thermal crown on both rollers is fully compensated.
In one embodiment, tension measurements are provided by a flatness bar positioned downstream from the work rollers that are in contact with at least one surface of the rolled product after being rolled by the working rollers. The flatness bar may include a plurality of probes contacting the upper or lower surface of the metal sheet. In another embodiment, the tension measurements may be optically provided by methods including, but not limited to, optical scanning or laser measurements. In an even further embodiment, the tension measurements may be provided acoustically.
In another embodiment, a method for forming metal sheet includes:
In another aspect of the invention, a system for rolling metal sheet having a substantially uniform flatness is provided. In one embodiment, the system for rolling metal sheet includes:
In one embodiment, the induction heating apparatus is configured to eliminate high tension on the strip edges that may be caused by the temperature gradient in the work rolls at the edges of the metal strip. In one embodiment, the induction heating apparatus may further include bending jacks, work roll axial sliding mechanisms and a spray cooling system, wherein the bending jacks, axial sliding mechanism and spray cooling system may also be actuated by the mill control interface in response to flatness measurements.
The following detailed description, given by way of example and not intended to limit the invention solely thereto, will best be appreciated in conjunction with the accompanying drawings, wherein like reference numerals denote like elements and parts, in which:
a is a perspective view illustrating one embodiment of a system for controlling flatness in rolled sheet including two induction heaters corresponding to a singular work roller, in accordance with the invention.
b is a perspective view illustrating another embodiment of a system for controlling flatness in rolled sheet including four induction heaters in a stacked arrangement and corresponding to a singular work roller, in accordance with the invention.
c is a perspective view illustrating another embodiment of a system for controlling flatness in rolled sheet including four induction heaters in a side by side arrangement and corresponding to a singular work roller, in accordance with the invention.
d is a perspective view illustrating one embodiment of a cold rolling mill, in accordance with the present invention.
Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention are intended to be illustrative, and not restrictive. Further, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.
Cold rolling denotes metal sheet processing that have cooled to room temperature, but in the course of numerous cold rolling passes of aluminum sheet the material temperature may rise to approximately 330° F. Although, the following disclosure is generally directed to cold rolling, it has been contemplated that the following method and apparatus may also be applied to hot rolling, which is within the scope of the present invention. Hot rolling of aluminum sheet is generally characterized by processing temperatures ranging from approximately 550° F. to approximately 900° F. It is noted that the above temperatures are provided for illustrative purposes only, and are not intended to limit the invention thereto, as the processing temperatures may be modified by various processing conditions, such as rolling speed, number of cold rolling passes, and the degree of cooling between rolling passes.
Referring to
The mismatch or inconsistencies of the profile of the roll gap 4 and the cross width thickness distribution of the metal strip 1 that typically results in flatness defects may result from a force exerted on the work rollers 5 by the metal strip 1 being rolled, which may be referred to as bending deflections. The mismatch or inconsistencies between the profile of the roll gap 4, and the cross width thickness distribution of the metal strip 1 that typically results in flatness defects may also result from thermal expansion of the work roller 5 that is at least partially attributed to frictional heat of the rolling process, which creates a thermal camber of the work roller 15 surfaces. The temperature in each of the work rollers 15 typically peaks at the mid point M1 of the work roller's width W1, hence the thermal expansion in each of the work rollers 5 is typically greatest at the work roller's midpoint M1 and decreases towards the edges of the rolls, which may be referred to as a thermal crown.
During coiling the rolled product may be pulled under tension, wherein flatness defects may manifest as tight edges, which may have a propensity to crack. The formation of tight edges at the edge portion of the metal strip being at a higher tension than the center portion of the metal strip is typically the limiting factor in the coiling speed of prior methods. It is noted that although bending jacks, coolant sprays, crowns mechanically ground into the work rollers, and work roll side shifting mechanisms may have a positive effect on reducing flatness defects in the center portions of the rolled product, such mechanisms do not provide a substantial reduction in flatness defects formed at the edge portion of the metal strip, such as the formation of tight edges.
In one aspect of the present invention, a substantial increase in the reduction of tight edges has been realized using an induction heating apparatus 10a, 10, 10c, 10d configured to thermal expand the portions of a singular work roller of the pair of the work rollers that corresponds to the edge 13a, 13b of the metal strip 1. The term substantially uniform tension distribution across the width of the rolled product means that when external tension is removed from the rolled product, and the rolled product is placed on a planar surface, there is substantially no lift off of the rolled product from the planar surface on which the rolled product is place. Substantially no lift off means that that lower surface of the rolled product is entirely in contact with the planar surface on which the rolled product is placed. External tension is the tension that is placed upon the sheet during coiling following rolling. In one embodiment, in order for the rolled product to be flat the longitudinal fibers across the rolled products width may be of substantially the same length in the absence of external tension.
Referring to
In one embodiment, the plurality of rotors measure the cross width tension distribution across the width of the metal strip 1. The flatness bar may include a plurality of probes contacting the surface of the metal sheet. More particularly, the rolled product is coiled under tension, wherein prior to coiling the rolled product contacts the flatness bar under which a force is induced in the y-direction upon the probes of the flatness bar, as depicted in
In another embodiment, the flatness of the metal sheet 1 may be optically measured or may be characterized using lasers. In yet another embodiment, the flatness measuring device may also include a non-contact system that measures the tension distribution of the metal strip using acoustical measurements. The acoustical measurements may be provided by sinusoidally modulating a vacuum under the metal strip 1. It is noted that the above flatness measuring devices 15 are provided for illustrative purposes and that the present invention is not deemed limited thereto, since any flatness measuring device that is capable of measuring the flatness of the metal strip 1 being rolled, or determine the cross width tension distribution across the width of the metal strip 1 may be utilized and are within the scope of the invention.
Referring to
In one embodiment, the current through the electrically conductive coil may be on the order of about 80 amps to about 200 amps. In one embodiment, the power supply to the induction heaters has a fixed operating frequency, wherein the frequency of the electrical current signal sent to the heating coil is about 20 KHz. The current wave to the induction heater is sinusoidal with varying amplitude. Power to the induction heaters is adjusted by changing the amplitude of the sinusoidal current wave over a set number of cycles in a repeating pattern. The duration of the repeating pattern is about 8 cycles of the operating waveform. At full power, the current signal is a 20 KHz sinusoidal wave with constant amplitude. It is noted that the above currents and frequencies are provided for illustrative purposes and are not intended to limit the present invention, as other currents and frequencies have been contemplated and are within the scope of the present invention. Further, other modes of providing power have also been contemplated and are within the scope of the present invention.
In one embodiment, adjusting the temperature of the singular work roller includes induction heating coils 10 to induce heating in the portions of the work roller 5 adjacent to the work surface corresponding to the metal strip edges 13a, 13b. More specifically, the induction heating coils 10a, 10b, 10c, 10d are aligned with the portion of the work roller that contacts the longitudinal edge 13a, 13b of the metal strip being rolled to provide the rolled product, wherein the longitudinal edge 13a, 13b extends along the rolling direction. Referring to
In one embodiment, each induction coil 10 may correspond to the portion of the work roller 5 adjacent to the work roller's contact surface at which the metal strip 1 is being rolled, which may also be referred to as the working surface. In another embodiment, each induction coil 10 may be disposed laterally in a direction parallel to the roller's axis of rotation to reposition the coils to or near the edges of each strip. By providing induction coils 10 that may be laterally disposed the position of the induction coils may be positioned to account for metal strip's having different widths. In addition to providing that each induction coil may be disposed laterally, the induction coils may also include a mechanism to set the gap between the induction coil and the work surface of the work roll. In one embodiment, a hydraulic cylinder with a position control moves the induction coil forward until contact with roll is made and then backs off of the roll work approximately 3 mm. It is noted that other dimensions for the gap separating the induction coil from the work roll have also been contemplated and are within the scope of the present invention, so long as the degree of separation allows for effective coupling of the magnetic field from the coil to the roll so eddy currents are induced in the roll.
In one embodiment, the induction heaters 10a, 10b, 10c, 10d provide a sufficient heat to thermally expand the diameter of a singular work roller corresponding to the edge of the metal strip to be greater than the diameter of a center portion of the singular roller. The term “singular work roller” denotes one work roller of the pair of work rollers 5, wherein the singular work roller may be either the upper or lower work roller of the pair of work rollers. The term “edge diameter of the singular roller” means the diameter of the portion of the singular roller corresponding to the longitudinal edge 13a, 13b of the metal sheet. The term “center diameter of the singular work roller” denotes the diameter of the portions of the roller between each edge diameter of the singular roller.
In the embodiments of the present invention in which the induction heat coils are positioned relative to a singular work roller of the pair of work rollers, the energy applied by the induction heating coils to increase surface temperature is of a magnitude that may provide increased thermal expansion at the section of the work roller adjacent to the metal strip's edges 13a, 13b relative to the thermal expansion of the central section of the work roller.
In one embodiment, the degree of thermal expansion in the singular roller 50 is selected to compensate for the thermal expansion 51 in the opposing rolling that does not include induction heaters. More specifically, as depicted by reference line 50, the increased thermal expansion in the sections of the work roller 5 that are adjacent to the longitudinal edge 13a, 13b of metal strip in the work roller having induction heating coils offsets the decrease in thermal expansion in the sections of the work roller adjacent to the metal strip of the opposed work roller that does not induction heating coils, wherein the decrease in thermal expansion may be referred to as a roll off effect. The combination of the increased thermal expansion at the edge of the strip in the singular work roller and the normal roll-off at the edge diameter of the opposing work roller presents the equivalent of a uniform roll gap to the strip being deformed across its width and results in a strip having uniform flatness substantially free of tight edges upon exiting of the rolling mill stand. More specifically, the thermal expansion in the edge diameter of the singular work roller is selected to compensate for the opposing roller that has a greater diameter at the opposing roller's center in comparison to the opposing roller's edge diameter. In one embodiment, the change of dimension in the edge diameter of the singular work roller may be on the order of about 0.005 inch, in which greater and lesser degrees of expansion have been contemplated, since the degree of thermal expansion required to correct flatness defects may be effected by process conditions that include, but is not limited to, the rolling speed, rolled product material selection, the degree of heat provided by the induction heating apparatus, as well as the degree of coolant applied to the center portion of the work roller.
Referring to
Referring to
In one embodiment, the bending jacks are configured to provide a force opposed to roll flexing generated by the metal strip 1, and may be referred to as positive bending jacks 21. More particularly, the bending jacks 21 are configured to compensate for the force produced by the metal strip 1 against the surface of the work roller 5 that is in contact with the metal strip 1 during rolling, wherein the metal strip 1 produces forces on the top and bottom work rollers that causes them to flex and become bowed away from the strip.
In another embodiment, the rolling mill 100 may further include bending jacks 20 corresponding to each work roller 5, wherein the bending jack 20 may displace a portion of the work rollers 5 along the y-axis to substantially reduce the effect of the thermal crown on the metal strip 1 and along with the roll cooling sprays 25 facilitate the formation of a metal strip 1 having a substantially uniform flatness across the central portion of the strip, but leaving the outer edges of the strip under tension. These bending jacks 20 may be referred to as negative bending jacks, and flex the work roller in a direction opposed to the positive bending jacks 21.
The amount of bending jack force required and its direction is determined by the combination of the amount of flexing of the work roll 5 caused by strip force, the crown ground onto the work roll, and the amount of thermal expansion in the work roll 5.
In another embodiment, the work rollers 5 may also include a work roll side shifting mechanism (not shown) being configured to shift each roll 5 along a substantially horizontal axis, such as the x-axis as depicted in
In one embodiment, a pair of backup rollers 6 may be employed in conjunction with the work rollers 5 in a configuration typically referred to as a four high rolling mill stand. The backup rolls 6 are used to support the work rolls and minimize their bending in response to the force of the strip. In a further embodiment of the present invention, a pair of intermediate rollers 8 may be disposed between the backup rollers 6 and the work rollers 5 in a configuration typically referred to as a six high rolling mill stand. The intermediate rollers also may include intermediate side shifting mechanisms and intermediate roll bending jacks.
The rolling system 100 also includes a rolling mill control interface 30 connected between the flatness measuring device 15 and the rolling mill's actuators. The rolling mill control interface 30 receives a signal from the flatness measuring device 15 representing measurements of differentials in the sheet flatness of the metal strip 1 or the tension distribution across the width of the metal strip 1. The rolling mill control interface 30 then processes and analyzes the signal in comparison with a predetermined target flatness value or tension distribution. In one embodiment, the rolling mill control interface processes the measured signals and formulates control outputs to the mill actuators based on a set of mathematical algorithms. In one embodiment, the rolling mill interface 30 includes a computer. The rolling mill control interface 30 then sends actuating signals to at least the cooling spray system 25, bending jacks 20 or induction heating coils 10 to compensate for differentials measured in the sheet flatness or cross tension distribution of the metal strip resulting in a metal strip 1 having a substantially flat surface that is substantially free of tight edges and thermal crown effects.
Although the invention has been described generally above, the following examples are provided to further illustrate the present invention and demonstrate some advantages that arise therefrom. It is not intended that the invention be limited to the specific examples disclosed.
The tension distribution of the metal strip processed in accordance with the present invention 61, includes thermal control with induction heaters positioned corresponding to the portions of a singular work roller corresponding to the strip edge of the singular work roller and a roll cooling spray system corresponding to at least a portion of the center portion of the work roller. The tension distribution of the metal strip processed in accordance with the present invention further included bending jacks configured to flex the work rollers in a direction to oppose the normal flexing caused by the force produced on the work roller by the metal strip. Additionally, the tension distribution of the metal strip processed in accordance with the present invention further included a flatness measuring device and a rolling mill control interface, where tension measurements taken from the flatness measuring device were analyzed by the rolling mill control interface and in response to the tension measurement correction factors were actuated in the bending jacks, roll cooling system, and induction heaters. The comparative example 60 was a metal strip that had been processed with bending jacks and roll cooling to optimize the measured flatness, but did not include induction heaters positioned corresponding to a singular work roller and directed to thermally expand the edge diameter of the work roller to be greater than the work roller's center diameter.
In the comparative example 60, an increase in tension in excess of 1000 psi is measured in the edge portions of the rolled product, as indicated by the portions of the flatness measuring device corresponding to zone 1 and zone 20 of
The effects of thermal crown may be further reduced in combination with the substantial eliminating of the incidence of tight edges by utilizing induction heating coils 10 to induce heat to a singular work roller 5 corresponding to the longitudinal edges 13a, 13b of the metal strip 1, wherein the induced heat thermally expands the edge diameter of the work roller. In comparison to the comparative example 60, the tension distribution 60 corresponding to the metal strip processed using induction heating in accordance with the invention, provides a decrease in the tension measured at the longitudinal edge of the rolled product to approximately 500 psi or less, as indicated by the portions of the flatness measuring device corresponding to zones 1 and 20 of
By reducing the incidence of tight edges in one aspect of the present invention the coiling speed may be increased without resulting in edge cracking.
Referring to
While the present invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the spirit and scope of the present invention. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.
The present invention claims the benefit of U.S. provisional patent application 60/774,974 filed Feb. 17, 2006 the whole contents and disclosure of which is incorporated by reference as is fully set forth herein.
| Number | Date | Country | |
|---|---|---|---|
| 60774974 | Feb 2006 | US |
