The invention relates to a method of and an apparatus for cooling rolls, in particular the working rolls, of a roll stand.
In the rolling of metals, the rolls that are involved in the rolling process, i.e. the working rolls, heat up. In order to protect them from damage and in order to extend their life span as much as possible, the rolls are cooled. In most rolling plants, today's cooling systems spray a cooling liquid onto the roll surface using nozzles (preferably flat spray nozzles). Such a cooling method is called “spray cooling”. The pressure used is between 6 bar and 12 bar depending on the rolling plant, and in some cases 20 bar. In addition to the task of cooling the working rolls as intensively as possible in order to limit the thermal load and geometric expansion thereof, the cooling of the working rolls must include keeping the rolls free of dirt, oxide particles and scale particles. The cooling effect increases as the amount of coolant and the coolant pressure increase. The disadvantage of the system is that a high level of energy is required and maintenance of the pumps is more expensive at higher pressure.
Another possibility for cooling the working rolls is low-pressure cooling. A cooling apparatus known from WO 2008/104037 [US 2008/0089112] has highly turbulent cooling at low pressure with the roll being cooled by nozzles and bore holes in a concave cooling bar. Through the arrangement of the cooling bar and with the help of end plates attached to the ends of the cooling bar, an even water cushion is formed that has a turbulent, random-directed flow. However, the cooling apparatus only operates in a satisfactory and reproducible manner when the roll diameter even when worn generally matches the curvature of the cooling apparatus. Since the currently common wear range of a roll is about 10% of the maximum roll diameter, multiple cooling apparatuses are required for different roll diameters; this requires an elaborate system of roll logistics. The fact that it is not possible to adjust the curvature of the cooling apparatus to accommodate different roll diameters for each stand and after each change of working rolls is a disadvantage, thus resulting in a different spacing between the nozzles and bore holes to the roll surface and thereby a different cooling effect is during the rolling process from roll change to roll change.
A low-pressure cooling system in the form of convection cooling is described in DE 36 16 070 [U.S. Pat. No. 4,741,193], where the cooling fluid flows past the roll surface in a directed fashion and with an external pressure in a defined, relatively narrow gap between the working roll surface and a cooling shell. The pressure level is lower and depends on the gap width and the flow rate. Higher cooling effects are accomplished by higher flow rates in this case. As a result of the lower pressure level, the system has no cleaning effect on the roll surface. A disadvantage of this device is that each roll requires its own cooling block since it is mounted on the roll chocks. Therefore, a large number of these cooling blocks are required for a conventional hot-rolling mill. The need to adjust the gap width to different working roll diameters and to move the cooling blocks to follow the respective working roll positions has also proven to be a disadvantage and very expensive since adjusting the gap has to be done manually and outside the roll stand.
Beginning with the prior art as discussed, the object of the invention is to provide a method of and an apparatus for optimally cooling the rolls of a roll stand, for protecting them against thermomechanical fatigue and against wear, energy considerations such as the minimization of the required amount of cooling fluid flow and cooling fluid pressure as well as incident design and manufacturing costs being taken into account.
This object is attained by a method with the features of claim 1 and an apparatus with the features of claim 24 in that the rolls are simultaneously subjected to a low-pressure cooling and to a high-pressure cooling system that sprays a coolant fluid directly under high pressure against the roll.
Basically, all rolls of a roll stand can be cooled using the cooling apparatus according to the invention; however, the invention is particularly useful for working rolls.
It is beneficial to feed about 20% of the total amount of cooling fluid to the high-pressure system and about 80% of the total amount of cooling fluid to the low-pressure system, which produces most of the cooling effect. The cooling fluid can be withdrawn from a container at a height of 7-12 m, for example, or can be produced directly by low-pressure pumps. The required pressure range for the cooling fluid for low-pressure roll cooling depends on the thermal load of the rolls and is between 0.5 to less than 5 bar, for example. As design embodiments, spray cooling, coolant curtains, gap cooling and convection cooling, high-turbulence cooling or a combination of the various low-pressure systems can be used.
For high-pressure roll cooling, which simultaneously performs the function of roll surface cleaning and removal of scale, a one or two-row spray nozzle bar can be used, as in conventional systems. The low fluid amount of about 20% of the total cooling fluid amount is sufficient for this task, with a required cooling fluid pressure range of between 5-50 bar, preferably 12 bar. The pressure range used for the cooling fluid for high-pressure roll cooling depends on the roll parameters of thickness reduction, specific surface pressure in the roll gap, roll speed, belt temperatures, roll material and rolled material.
For environmental considerations and from a “green plant technology” perspective, it is advantageous for the total energy used by the pumps to be lowered while at the same time fulfilling all system functions. If one compares the pump energy expended by conventional roll-cooling systems using high pressure with the proposed combined low/high-pressure cooling system, the following differences arise:
Using the example of a 2 m hot strip mill with a total roll coolant medium flow of 5000 m3/h, the pump energy requirement (not including the pump efficiency; pump power=volumetric flow*pressure increase [note: 36 is a conversion factor]) is:
Conventional Roll Cooling:
Pressure level of 12 bar, for example
Pump power=5000 m3/h*12 bar/36
Pump power=1667 KW
Combined Low/High-Pressure Cooling:
Pressure level of 12 bar, for example
High-pressure coolant amount of 1000 m3/h and
Pressure level of 2 bar, for example
Low-pressure coolant amount of 4000 m3/h
Pump power=1000 m3/h*12 bar/36+4000 m3/h*2 bar/36
Pump power=333 KW+222 KW=555 KW.
Using the combined low/high-pressure cooling system, a significantly lower amount of energy is needed. For the example above, a reduction in pumping power of about 1.1 MW thus results.
In case of increased dirt or scale particles and in the event of a rough roll surface, for example, or if there is a thermal crack pattern, the pressure level can be increased accordingly. The roll surface can be observed with a camera in order to determine the change in pressure level that results. Furthermore, the pressure level can be individually adjusted in stages (for example by switching additional pumps on or off), or continuously to effect the thickness of the oxide layer on the roll.
The combined low/high-pressure cooling system can be provided for the front stand of a hot strip mill, for example. Then, a strictly low-pressure cooling system can be used at the back stand.
The high-pressure cooling bar can act over nearly the entire barrel length or can be designed to move in the direction of its width or with only local cooling. If only simple low-pressure shell cooling is used individually, a combination with the cooling system according to the Japanese patent application JP 07290120 is conceivable and provided. In this case, two spray nozzle bar sections are moved axially or in the width direction using a motor, and the working roll is cooled differently locally. Instead of using an electric or hydraulic motor with a threaded rod or two motors for the separate adjustment on the left and right sides, respectively, it is preferred to alternatively design a hydraulically moved single- or multipart hinged pivot with spray bars attached thereto or rotatable nozzle units for directing the coolant streams to the desired regions of the working roll (within or next to the strip region) so that the strip profile and the flatness can be positively influenced.
Similar to the embodiment with the spray bar sections that can be moved in the width direction, short shell segment sections with a width of, for example, 150 mm can be axially adjusted in the width direction for a segment of the low-pressure shell cooling system and only acting locally (such as symmetrically at two locations on the working roll).
The purpose of the low-pressure working roll-cooling system according to the invention is to provide optimal and efficient cooling, the cooling effect (heat transfer from the roll to the cooling fluid) being maintained at a high level despite a low cooling fluid pressure. This results in a lower roll temperature or can be used to reduce the amount of cooling fluid. An efficient low-pressure roll-cooling system is preferably convection cooling in which the cooling fluid is led past the roll surface in a relatively narrow gap between the working roll and a curved cooling shell.
According to the invention, the cooling apparatus substantially comprises moving cooling shell segments that are pivoted on one another. Preferably, three cooling shell segments are used, but in general only two are used. In special cases, however, only one cooling shell segment can be used. The individual cooling shell segments preferably comprise lateral or end joints or joint halves. At least one pivot is provided on the center cooling shell segment, the pivot holding at least one, preferably two cylinders (hydraulic or pneumatic cylinders). The second support point for the cylinders is at the other members of adjacent cooling shell segments. The cylinders can be provided in the center of the cooling bar or on both sides at the edges thereof. Instead of adjusting the shell using cylinders, an adjustment using hydraulic motors or electric motors is conceivable, for example. The console or cooling bar support is located on the center cooling shell segment, with fastening holes. It is possible to move the center cooling shell segment. and thus all components connected thereto, using the cooling bar support, a horizontal, vertical and rotating motion being possible. The position adjustment is accomplished using a multipart linkage mechanism that is actuated pneumatically, hydraulically or electromechanically. It is also possible to advantageously position the center cooling bar support in the horizontal direction using a longitudinal or elongated guide and pneumatic or hydraulic cylinders.
The cylinders comprise path measurement systems and pressure transducers. The position of the cylinder and thus the gap adjustment and spacing determination between the cooling shell segment and the roll, as well as the monitoring of the adjusted positions, can be determined and carried out in the following different ways, wherein a combination of the methods listed is also possible:
To adjust the positions of the cooling shell segments, the cooling bar support positioning and the cooling shell segments are pressed against the roll with a defined pressure using the associated cylinders and linkage mechanisms. In this position, the path transducer is set to zero. Starting from this position, and with information about the geometric relationships, a defined gap between the cooling shell segment and the roll can then be adjusted. The cooling system calibration process can be carried out during the stand calibration procedure.
Since the geometric relationships (roll diameter, roll positions in the vertical direction, cylinder positions, spacings between joints and points of rotation, position of the multipart linkage mechanism, etc.) are known, the shell position and center gap width can be calculated with good approximation. Each relative change in roll position (when a strip thickness is changed, for example), can be converted during the roll process this way.
Using proximity sensors, the gap can be measured directly and the cylinders and linkage mechanisms can be correspondingly adjusted using a control system.
In contrast to a cooling apparatus according to the prior art, the cooling apparatus according to the invention adjusts to the roll diameter and roll positions using the joints provided since the positioning systems of the cooling bars are associated with the thickness control system and follow the vertical motion of the working rolls, for example when a thickness change is made. When the stand is opened up (for example upon Emergency-Open), the cooling shells are automatically tilted back somewhat.
In one design embodiment, the cooling apparatus forms a space with the aid of a seal, and very little cooling fluid escapes this space to the environment. The seal is formed by pressing the top and bottom of the shell against the working roll, which can be biased with a predefined pressure, and/or is accomplished by applying a dynamic pressure at the edge of the cooling shells. This arrangement makes it possible to design a nearly sealed cooling circuit.
The cooling bars and the cooling shells and conventional high-pressure and/or low-pressure spray bars can be attached to the cooling apparatus. By positioning the shells just in front of the roll, a gap is formed through which the coolant flows. The gap widths between the cooling shell and the working roll are adjusted to between 2 and 40 mm, for example to 5 mm, during operation and reproducibly independent of the roll diameter. The gap between the working roll and the cooling shell—as seen tangentially—can be uniform or the shell can be designed to narrow as it approaches the outlet.
When convection cooling according to the invention is used, two different cooling variations are possible; zoned convection cooling and continuous convection cooling.
Zoned convection cooling is subdivided into zones. For example, the cooling fluid flows from a conical rectangular slit into the individual regions of the cooling shell toward the roll and is redirected toward both sides (upward or downward) or even primarily to one side only, the cooling shell forcing flow along the roll. By redirection of the flow and flow with a higher relative velocity along the roll, the cooling fluid absorbs heat from the roll efficiently. The heated cooling fluid then flows back in a backward direction and thus makes room for new cold cooling fluid. In the process, the cooling bars are designed such that the cooling fluid flowing backward (away from the roll) can discharge easily at a gradient. The returning coolant is also redirected to the side using redirecting baffles in order to reduce the pooling effect over the doctor blade. The individual cooling regions are separated from one another by a mutual shielding effect so that the cooling fluids of the adjacent cooling bars do not disrupt one another much.
In continuous convection cooling, the cooling fluid is fed through a larger continuous angular range of the roll. A minimal, adjustable gap width and a high flow velocity are required in order to generate good heat transfer. The gap width and the amount of cooling fluid must therefore be matched to one another. Continuous convection cooling can be operated with is countercurrent or concurrent flow. Due to the long path between the upstream and outlet sides, end sealing of the cooling shells is required. An alternative to the countercurrent or concurrent principle is an operating mode in which the cooling fluid is fed from the upper and the lower cooling bar pipeline. The discharge is then done toward the ends. This way, first of all the cooling fluid flowing toward the roll tangentially absorbs the heat and is then redirected to the end. The warm cooling fluid thus heats the roll regions adjacent the regions in which the strip runs and this leads to the desired positive affect of thermal crowns there. This system is especially effective when zone cooling is carried out in which the regions next to the strip are not directly cooled.
In zone cooling, only certain regions along the length of the roll in the coolant feed channel of the cooling bar are released for flow, or else narrow cooling shells with different gap widths are arranged in succession at a spacing from one another. Depending on the different gap widths, different specific cooling fluid flows result for the narrow cooling shells, and thus a different cooling of the working roll results for each cooling shell. To separate the different cooling fluid flows, a blocking cooling fluid or a gap seal is placed between the narrow cooling shells depending on the design.
A computational model (process model or Level 1 model) is used for optimum control of the cooling apparatus; the model performs the following tasks:
Further advantageous embodiments of the invention are objects of the dependent claims.
Further details of the invention are illustrated by way of embodiments illustrated in schematic drawing figures.
a-f shows embodiments of nozzles and shells,
a-c illustrates adjustment of a gap width,
a and b show a locally acting axial adjustable roll-cooling system,
A spray cooling system according to the prior art is shown in
A continuous convection cooling system according to the invention with a continuous cooling shell 11 is shown in
The pivoted connection between the individual cooling segments of a cooling shell advantageously produces an optimum fit of the cooling shell on the actual diameter of the roll and thus an energy-efficient cooling of the roll. The pivot axis of the joint lies preferably parallel to the longitudinal axis of the roll.
The cooling fluid 7 flows through a feed pipe 25 and an inlet opening 29 to the gap 30 in countercurrent flow to the direction of rotation of the rolls 5; the fluid then exits through the outlet opening 24 and the discharge pipe 26. If in a special case the discharge pipe 26 of the outlet opening 24 is closed or if there is none, the coolant can be discharged perpendicular to the roll. Partial end seals are only used in that case. The angular dimensions of the cooling shell segments 13 that form the gap 30 should be of approximately the same so that when the diameter of the working roll 1 changes, the cooling shell segments 13 can optimally follow the change in curvature of the outer roll surface 6. The ends of the individual cooling shell segments 13 form hinges or hinge halves that form a corresponding number of pivots 22 when connected together, and also have pivots 21 that are connected together by cylinders 20, for example hydraulic or pneumatic cylinders. The cooling bar support 16 is connected to the center shell segment 13, and is carried on a pivot 23 by a multipart linkage mechanism that is not shown to move the cooling shell segments 13 and all components connected thereto (horizontal, vertical and rotationally) in the cooling bar support adjustment directions 45 indicated. A scraper 17 below the cooling shell 11 ensures that as little cooling fluid 7 as possible makes its way onto the rolled material 4.
The entire cooling shell 11 can be positioned using sensors 37 for measuring distances, pressure sensors 36 in the cylinder connecting lines, and path sensors 39 at or on the cylinders 20. The roll temperature is continuously monitored by temperature sensors 38 (in the center of the rolls or along the width) so that the size of the gap 30 can be controlled accordingly to maintain the desired cooling effect.
The cooling apparatuses described below are of similar designs, which is why details with regard to the design that are identical are not further described; only the reference numbers as listed above are included as needed.
In the cooling apparatus 10 of
A cooling apparatus 10 comprising a sectioned low-pressure convection cooling arrangement is shown in
Instead of using cylinders to position the individual shells as in the previous illustrated embodiments in
If the working-roll diameters for the rolls being cooled are small or within the same range per stand, a rigid cooling system is provided as a special case, in other words a system with stationary cooling shells (no cylinder between the shells and no springs 8). Then, an advantageous feature would be rigid spacer rods instead of moving cylinders 20. Then, the gaps between the roll and the cooling shell vary somewhat, but the system is still effective with convection cooling in sections, and the system is simpler to manufacture. The only requirement is to position the cooling bar support in front of the roll depending on the working roll diameter and the working roll position, so that the gaps are optimally placed, i.e. the outlet openings are relatively close in front of the roll. The design can then be the same for multiple stands, and the adjustment to the various stand diameter ranges of a roll mill can be done in a simple fashion by the length-adjustable rods.
In addition to the previously described combined low/high-pressure cooling, low-pressure convection cooling with integrated roll-gap lubrication 19 and roll gap cooling 18 on the upstream side is provided in the cooling apparatus 10 of
The region in which the roll-gap lubrication 19 is provided is kept largely dry due to the working-roll cooling flow direction and/or by provision of the cooling shells 50 with an elastic plastic surface, or provision of the cooling shells 51 with elastic plastic or laminated fabric plates. This causes a slight pressure to be applied by the plates to the roll by the cooling bar support mechanism. The plates themselves are continuous across the width and have an elastic effect due to their physical design (not shown). The roll surface upstream (in the direction of rotation) of the application of the roll gap lubricant can optionally get a blast of compressed air (not shown) in order to blow the roll surface dry in a defined fashion.
Instead of using three cooling bars with rectangular nozzles, according to the cooling apparatus 10 of
In a special variation, which is not shown, the cooling shells are adapted so that the coolant outlet opening comprises a rectangular slit 24 if desired combined with holes 52 in the plate in order to increase turbulence in the flow gap.
Further details on nozzle and shell design can be found in
In particular:
a shows a symmetrical arrangement of the lower part of the cooling bar 54 on the cooling shell 11, 12 with exchangeable nozzle 27,
b shows cooling fluid exiting from the nozzle 27 at an angle α oblique relative to the roll,
c shows a nozzle 27 with alternative cross sectional form and possible embodiments of the ribs or grooves 9,
d shows cooling shells 11, 12 shortened or extended asymmetrically relative to the nozzle 27.
The conical outlet opening extending in the flow direction can be provided with baffles if necessary in order to aim the coolant inward, outward or straight so that a closed and even cooling fluid stream ultimately exits along the length of the cooling bar. A conical shape of the cooling fluid feed channel at the cooling bar broad sides is also possible in order to reduce the cooling fluid amount flowing beneath the shell laterally toward the side (edges of the bar).
It is also possible to design the cooling shell in sections across the length of the cooling bar, with the gap width adjusted in the cooling fluid feed channel, thereby affecting coolant distribution and cooling effect along the length of the roll. In order to make a simplified parabolic change in the gap width of the outlet opening over the width, spring plates 53 can be provided inside the conical feed channel 55 as in the embodiment of
Details of an embodiment involving gap adjustment in the feed channel 55 are shown in
In the illustrated embodiment of
A different zone cooling principle is shown in
Possible materials for the cooling shells 13,14 advantageously include a material that can sit against the roll without damaging it and that is elastic. For example, this can be a non-sand based cast iron, slidable plastic, self-lubricating metals, aluminum or laminated fabric.
Shown in
A locally acting, axially moveable working roll spray cooling system, which can be designed as a high-pressure or low-pressure cooling system, is shown in
The low-pressure cooling system can also be used by itself, i.e. not in combination with the high-pressure cooling system.
Number | Date | Country | Kind |
---|---|---|---|
10 2009 011 110.7 | Mar 2009 | DE | national |
10 2009 011 111.5 | Mar 2009 | DE | national |
10 2009 014 125.1 | Mar 2009 | DE | national |
10 2009 036 696.2 | Aug 2009 | DE | national |
10 2009 053 074.6 | Nov 2009 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP2010/001274 | 3/2/2010 | WO | 00 | 10/26/2011 |