Patent Application
20190176199
The invention is related to the field of long product mills, and in particular to long product mills utilizing tensionless or loop-less smart rolling.
Inter-stand tension is inherent in all long rolling mills. The physical manifestation of tension is the difference in speed from one rolling mill stand to the other, in theory the speed of each rolling mill stand is derived from the work being carried out, however due to differences in material spread, roll wear and stock control, the speed between two rolling mill stands in a long products mill is never 100% matched. This mismatch is called tension or compression as the material can be pushed and or pulled dependent on the error in speed between the two rolling mill stands.
In the early part of a rolling mill, tension control is managed using a minimum control tension system (MTC). The MTC calculates the speed and torque for each rolling mill stand allowing for speed adjustments.
In the later part of the rolling mill, loopers are utilized that are natural breaks in the mill rolling process. A loop is formed to give an area of float or a buffer in the continuous process between two rolling stands. This loop can be pushed or pulled as the mill speed changes. If the loop grows or shrinks out of a preset position the rolling mill stands can adjust their speeds accordingly in an attempt to maintain equilibrium.
The theory being that with the looper in the ideal or dead band position, an error in speed between the rolling mill stands is compensated for and the process remains stable. A looper, however, never removes all tension or compression in the mill as by nature the true material speed is never known and the force of the push or pull is inherent in the material. Loopers include mechanical and electrics/automation (EA) equipment that has an added cost and they add length to the overall rolling mill further adding to the overall cost of a rolling mill line.
According to one aspect of the invention, there is provided a rolling mill for producing rolling mill product. The rolling mill includes a rolling mill line that moves the rolling mill product. A plurality of rolling mill stands are coupled to the rolling mill line that receives the rolling mill product and rolls the rolling mill product. A plurality of speed measuring devices that are positioned in close proximity to each rolling mill stand, where each speed measuring device measures the speed of the rolling mill product as it passes the speed measuring devices. A control device receives information associated with the speed measuring devices and adjusts the speed of the rolling mill product for any speed differential that might exist between any of the rolling mill stands.
According to another aspect of the invention, there is provided a method for producing rolling mill product in a rolling mill. The method includes providing a rolling mill line that moves the rolling mill product. Also, the method includes providing a plurality of rolling mill stands that are coupled to the rolling line that receives the rolling mill product and rolls the rolling mill product. A plurality of speed measuring devices are positioned in close proximity to each rolling mill stand, where each speed measuring device measures the speed of the rolling mill product as it passes the speed measuring devices. Furthermore, the method includes adjusting the speed of the rolling mill product for any speed differential that might exist between any of the rolling mill stands using a control device that receives information associated with the speed measuring devices.
The invention describes a systematic approach that eliminates the need for a mechanical looper in a rolling mill and its associated control. The looper is replaced with a simple laser velocimetry system and/or camera arrangement where one laser is positioned in-between each individual rolling mill stand. This can include machines of multiple rolls but with one drive motor.
In the prior art, the tension and loop control systems work from a theoretical speed calculated from a theoretical working diameter. This diameter change is dependent on the process section being rolled. Furthermore, as the material is rolled in the rolling mill, its area is reduced and passes through each subsequent rolling mill stand at higher velocities. This complicates a looper design and control as enough buffer “storage” must be accounted for each looper to effectively support and control smaller product or sections sizes.
As an example, if a section in question is travelling at 15 m/s and the rolling stands in question have the ability to adjust at 2.5 m/s/s. Then the required loop storage for a speed differential of 3% would be 0.18 m of material, from the initial start position or pass line to reach equilibrium.
The invention eliminates the need for the complications and limitations referenced above, as the actual product speed between rolling mill stands is measured with non-contact velocimetry. In the early part of the rolling mill line, speed measurements can be utilized as the rolling mill stands are positioned close to one another as the metallurgical process in the mill does not require water-quenching and/or equalization.
Each camera C12o, C13o, C14o is used as a visual tool to assess the quality of the rolling mill product, such as the height of a stock section for accurate control. Each laser L12o, L13o, L14o measures the true product speed of the rolling mill line 4 and compares this with the calculated speed at this point and makes the necessary speed adjustments to the rolling mill stand in question and the subsequent rolling mill stands if needed to balance the rolling process. The rolling mill stands are connected to a control system that allows for the speed adjustment at each rolling mill stand. Both the laser and the camera can share a common mount or enclosure.
In most rolling mills, the individual rolling mill stands are controlled from a master speed reference. This speed reference takes into consideration the calculated reduction in area achieved in each rolling mill stand, the roll diameter of each rolling mill stand, and the associated gear ratio.
The error can manifest itself due to slightly incorrect roll profiles or diameters, poor section control in the mill, or slight differences in the theoretical and actual gearbox ratios in the rolling mill stands. In the slower part of the rolling mill, a MTC (minimum tension control) system is utilized that leverages an iterative self-learning system to match the rolling mill stand speeds. Further upstream in the rolling mill, this iterative approach is not possible as the speed error grows and the risk of a rolling mill cobble increases.
The means for controlling this error in speed in most rolling mills in the prior art is the looper. The looper is effectively a mechanical piece of equipment that is controlled by a loop. The looper allows for a mismatch in equipment speed by giving the rolling mill product a buffer space to either grow a loop or collapse a loop to a setpoint with limits for loop growth or decay dependent upon process changes. The looper effectively balances any error in the rolling mill speed reference. A new speed reference is then sent to a control device in the mill to control the rolling speeds so as to ensure the speed of each rolling mill stand is correct relative to the one before it and/or after it. As one can theorize, the speed reference is a calculated value and is subject to error.
The invention eliminates the need for the mechanical looper and its associated control. The looper is replaced with a simple laser velocimetry system described herein. One laser is positioned in-between each individual rolling mill stand. This can include machines of multiple rolls but with one drive motor.
The incoming speeds and outgoing speeds of the rolling mill product at each rolling mill stand is compared to its theoretically controlled rolling speed as well as comparing the incoming speed and outgoing speed form a previous rolling mill stand. If there is a difference in speed between the entry to the subsequent rolling mill stand compared to the exit of the previous rolling mill stand, there is a known error and the speed reference of the entry stand will be adjusted by a set amount to remove the speed differential accordingly.
Using the invention and tying the actual rolling mill product speed into the control device of a rolling mill, one could further improve the control of ancillary machines, such as head and tail crop shears, or achieve shorter crop lengths thus reducing metallic yield loss.
Moreover, the invention can allow the ring spacing at the laying head area of a rolling mill to be maintained perfectly from head to tail of a rolling mill product. Any change in product speed could be instantly adjusted using the lasers and cameras discussed herein. Moreover, the information provided by the cameras and lasers can be used to devise an intelligent mill system that requires less mechanical equipment. This can reduce the building length and any associated costs as well as the cost of maintaining less equipment, and the product quality is improved due to the overall increase in accurate seed control of the rolling mill.
Where metallurgical processes dictate larger inter-stand distance due to the necessity to quenching and equalization, then two non-contact gauges can be utilized, one at the exit of the first rolling mill stand and one at the entry to the subsequent rolling mill stand. This ensures any effects from quenching and resistance to forward motion is accounted by the control device.
Although the present invention has been shown and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention.
