Patent Application
20120235331
(1) Field of the Invention
This invention relates to methods and apparatus for applying liquid coolant to, and subsequently removing the coolant from, metal strip advancing in a continuous line. Preferably, although not exclusively, the invention is directed to the cooling of metal strip in single-stand and multi-stand cold rolling mills. Still more particularly, the invention is concerned with methods and apparatus for liquid cooling of metal strip, such as aluminum strip.
(2) Description of the Related Art
In the processing of metal sheet such as aluminum strip (the term “aluminum” being used herein to refer to aluminum-based alloys as well as pure aluminum metal), such metal sheet is often cooled by application of a coolant liquid (e.g. water) followed shortly thereafter by the removal of the coolant liquid before further processing or coiling takes place. For example, coated metal sheet may be cooled following the application and heat-curing of a layer of coating lacquer, or hot-rolled aluminum strip may be cooled before it is coiled at the end of a hot roll line or in a separate coil-to-coil operation. In such cases, the coolant liquid is often applied to just one side of the metal sheet and steps may be taken to avoid contact of the coolant liquid with the other side of the sheet if such contact would cause damage (e.g. to a coating layer) or undesirable marking or staining.
A further important situation where such cooling is carried out is during the reduction in thickness of metal (especially aluminum) strip by cold working in one or a tandem succession of roll stands each typically including upper and lower work rolls (between which the strip passes) and upper and lower backup rolls respectively above and below (and in contact with) the upper and lower work rolls. The strip to be reduced in thickness is paid out from a coil at the upstream end of the cold rolling line, and after passage through the roll stand or stands, is rewound into a coil at the downstream end of the line, the cold-rolling operation being essentially continuous. Unavoidably, the cold working of the strip as it passes through the nip of each roll stand is accompanied by some elevation of strip temperature. In a single-stand mill, this temperature rise is usually not troublesome provided the strip enters the mill near room temperature. In a multi-stand tandem mill, however, the increases in strip temperature at the several roll stands are cumulative, with the result that the intermediate and/or exit temperature of the strip from the mill may exceed acceptable limits, even with entry at room temperature. For example, computer model analysis of a three-stand mill indicates that the strip exit temperature can approach a value as high as 300° C., depending primarily on the particular alloy being rolled, the extent of the reductions to which the strip is subjected in the mill, and the rolling conditions. On the other hand, considerations related to process reliability, such as the avoidance of strip breaks, and metallurgical and mechanical considerations related to product performance, require that the exit or coiling temperature of cold-rolled aluminum strip be kept usually between 100° and 180° C., depending on the product, with a typical limiting value being around 150° C. Moreover, in the case of some products, it would be highly advantageous to control the coiling temperature of cold-rolled strip within some predetermined range for maximum efficiency and benefit in subsequent process steps.
At the same time, as the cold-rolled strip is cooled, it is important that the cooling operation not adversely affect other aspects of product quality. For example, while water is a preferred liquid coolant from the standpoint of cost and effectiveness, the presence of water may impair the performance of rolling lubricant at the roll stands and, if the strip is aluminum or other water-stainable metal, residual water in the rewound coil may cause unacceptable surface staining.
U.S. Pat. No. 5,701,775 which issued to Sivilotti et al. on Dec. 30, 1997 addresses these issues and provides a process and apparatus of cooling horizontally-advancing metal strips by applying upward jets of liquid coolant only to the lower surface of the strip and then removing the coolant from the lower surface by directing liquid knives against the lower surface of the strip. Recognizing that any given cold-rolling mill is usually employed at different times to roll metal strips of various different widths, arrays of laterally-movable overlapping metal shutters were provided along and slightly below each side of the strip path for deflecting upward jets of coolant positioned beyond the lateral edges of a particular strip undergoing a rolling operation. The shutters thereby prevent the cooling jets from splashing onto the upper surface of the strip and causing problems as indicated above.
While this patented solution is quite effective, experience showed that some coolant could still bypass the shutters and contact the upper surface of the strip. To prevent this, it has become usual to provide vertical brushes mounted on the upper side of the movable shutters closest to the strip. As the strip advances, the brushes push up against the underside of the strip at the edges and are slightly, and sometimes severely, splayed out under compression, thereby closing any gap between the shutters and the edges of the strip to prevent penetration of liquid. This solution also has its problems, however, in that it is not always possible to position the brushes exactly at the edges of the strip, especially if the width of the strip varies somewhat at different longitudinal positions. This can allow liquid coolant to extend onto the upper surface of the strip and/or can cause uneven cooling at the edge of the strip, thereby resulting in edge distortion (e.g. a wrinkling or buckling of the strip at the edges). There is therefore a need for further improvements of the method and apparatus.
An exemplary embodiment of the invention provides a method of cooling a metal strip. The method involves continuously advancing a metal strip, having lateral edges, generally horizontally in a direction of strip advance, delivering a coolant liquid onto a lower surface of metal strip from below across the entire width of the strip, preventing the coolant liquid from contacting the upper surface of the metal strip, and optionally subsequently removing said coolant liquid from said lower surface of the strip. The coolant liquid is prevented from contacting the upper surface of the metal strip by forming a gas-directing channel immediately above the upper surface of the metal strip adjacent to at least one of the lateral edges thereof and forcing a gas through the channel in a direction generally away from a center of the strip towards the at least one lateral edge to deflect coolant liquid away from the upper surface of the strip. In this way, coolant liquid emerging from below the strip at the lateral edge or edges thereof is directed away from the upper surface of the strip regardless of any slight variations that may occur in the width of the strip (causing slight undulations in the otherwise linear lateral strip edges) as the strip advances. A gas-directing channel is one that constrains or confines gas to move in a generally horizontal plane towards a lateral edge of the strip and helps to prevent dispersion (especially upward dispersion) of the gas so that the gas streams along the upper surface of the strip and directly across the lateral edge of the strip. Gas-directing channels are preferably formed above both lateral edges of the advancing strip to ensure that coolant liquid is preventing from contacting the upper surface from both sides, but in some circumstances it may be preferred to provide a gas-directing only on one side of the strip.
The gas-directing channel is preferably formed by positioning at least one stationary cover plate above and upwardly spaced from the upper surface of the strip adjacent to the at least one lateral edge, the gas-directing channel being defined between the upper surface and the cover plate. The cover plate is preferably positioned to extend laterally of the strip at least up to the at least one lateral edge of the strip, and more preferably beyond the lateral edge, most preferably covering all positions where there is upward delivery of coolant liquid beyond the lateral edge of the strip.
The coolant liquid is preferably delivered upwardly from at least one manifold extending transversely below the strip and extending laterally beyond the at least one lateral edge thereof (to ensure that all of the lower surface of the strip is cooled regardless of any variations on width of the strip as it passes the manifold(s)).
At least some of the coolant liquid delivered from ends of the manifold(s) extending outwardly beyond the lateral edge(s) of the strip may be deflected downwardly by at least one stationary shutter provided alongside the strip. This is preferably a flat plate normally positioned at about the same vertical height as the strip itself that sits above the upward jet of coolant liquid and deflects it back downwardly. However, the shutter cannot normally be positioned too close to the strip because there must be a gap wide enough to allow for variations in the width of the strip, and coolant liquid may pass upwardly through the gap. However, the any such liquid is deflected away from the strip by the gas passing through the gas-directing passage. Of course, such shutters may be dispensed with if the flow of gas in the channel is sufficient by itself to deflect all coolant liquid beyond the lateral strip edge(s).
The gas is preferably forced through the gas-directing channel by delivery of the gas under pressure from at least one elongated air knife positioned at an end of the channel positioned inwardly of the strip. Most preferably, the air knife is angled to deliver the gas under pressure into the channel at an angle within a range of 30 to 45° relative to the horizontal upper surface of the strip. The gas may be forced through the channel at an initial pressure in a range, for example, of 50 to 150 pounds per square inch (345 to 1034 kilo Pascals), and at a flow rate in a range, for example, of 40 to 50 cubic feet per minute (18.9 to 23.6 liters per second). Normally, the gas is directed through the channel at right angles to the edge of the lateral edge. However, the gas-directing channel may be elongated in the direction of strip advance so that it has upstream and downstream sides. The gas may then be directed generally at right angles to the lateral edge of the strip in a center of the channel between the upstream and downstream sides, but at slight upstream and downstream angles to the lateral edge of the strip at adjacent to the upstream and downstream sides, respectively, of the channel.
Another exemplary embodiment provides apparatus for cooling an elongated metal strip having lateral edges, as the strip is advanced generally horizontally in a direction of strip advance. The apparatus comprises coolant delivery equipment for directing a coolant liquid upwardly onto a lower surface of the advancing strip across an entire width of the strip between said lateral edges thereof, means for preventing said coolant liquid from contacting an upper surface of the metal strip, and optionally a removal device for subsequently removing the coolant liquid from said lower surface of the strip. The means for preventing the coolant liquid from contacting the upper surface of the metal strip includes at least one cover plate positioned above and spaced upwardly from the upper surface of the metal strip adjacent to at least one lateral edge thereof to create at least one gas-directing channel above the strip, and a gas delivery device positioned at an inward end of said at least one gas-directing channel to deliver gas through the channel generally towards said lateral edges.
In the apparatus, the at least one cover plate preferably extends laterally of the strip at least up to, and preferably beyond, the at least one lateral edge of the strip.
The upward delivery of coolant liquid is preferably provided by one or more (ideally two or more) coolant liquid manifolds each provided with at least one opening positioned to deliver the coolant liquid in an upward direction. The one or more manifolds are normally oriented transversely of the strip and are arranged side-by-side in the direction of strip advance. Preferably, the cover plate or cover plates extend above all of the coolant liquid manifolds in the direction of strip advance so that all upward jets of coolant liquid are affected by the flow of gas in the gas-directing channel. However, in some cases, there is insufficient room to extend the cover plates above all of the manifolds, and in such cases, the direction of the gas within the channel is orientated partially upstream or downstream to deliver gas across the lateral edge(s) at all positions where there is an upward flow of coolant liquid to ensure that all of the liquid is deflected away from the upper surface of the strip. Moreover, if there are relatively large gaps between adjacent manifolds below the strip, the gas flowing in the channel may be orientated to mainly pass across the edge(s) of the strip directly above the manifolds, with little or no gas directed to pass above the gaps between the manifolds.
The apparatus may preferably include one or more stationary shutters adjacent to the lateral edge(s) of the strip positioned to deflect downwardly some of said liquid coolant delivered beyond the lateral edge (or edges) of the strip. Such shutters are generally positioned at approximately the same vertical height as the strip and at a distance from the adjacent lateral edge to form a gap to accommodate variations of width of the strip as the strip advances past the shutter(s). The cover plate is generally at a higher vertical level than the shutter(s), and may extend partially or fully above the shutter(s), and even beyond the far side of the shutter(s).
The device used to deliver gas into the channel(s) is preferably an elongated air knife, preferably oriented to deliver the gas toward the lateral edge of the strip but at an angle in a range of 30 to 45° relative to said upper surface of the strip. The air knife may have a single elongated slot through which said gas passes, or multiple gas outlets provided with direction-adjustable nozzles. Moreover, the air knife may have a central region, an upstream region and a downstream region, wherein the central region is oriented to direct the gas generally at right angles to the lateral edge of the strip, the upstream region is oriented to direct the gas towards the lateral edge at an upstream angle, and the downstream region is oriented to direct the gas towards the lateral edge at a downstream angle.
When the gas is to be directed to each lateral edge of the strip, preferably two cover plates are provide, each one above the strip at each longitudinal side. The inboard edges of the cover plates may be separated by a distance suitable to allow one or more air knives to be positioned to introduce flows of gas into the channels defined by each cover plate. Alternatively, a single cover plate may be employed for both sides of the strip, with air knives being positioned between the strip and the cover plate, or passing through slots provided in the cover plate so that gas can be introduced into the channels on each side of the strip.
The cover plate(s) may be suspended from a support frame or the like positioned above the advancing metal strip and may include pivoted supports that allow the cover plate(s) to be raised and lowered relative to the support frame. The support frame may take the form of a box-like structure extending completely across the advancing strip, cover plate(s), manifolds, shutter(s), etc., itself supported by lateral walls.
The or each cover plate is preferably spaced upwardly from the strip by a distance in a range of 0.5 to 1.5 inches (1.3 to 3.8 cm), more preferably by 1 inch (2.5 cm)±10%. This allows the gas to be confined adjacent to the upper surface of the strip while allowing sufficient gas flow and volume. However, other spacings and dimensions may be suitable in particular circumstances.
A further embodiment of the invention provides apparatus for cold rolling a metal strip having lateral edges, having at least one roll stand for reducing a thickness of said metal strip, and an apparatus for cooling said metal strip immediately downstream of said at least one roll stand. The apparatus for cooling the metal strip comprises an apparatus as defined above.
In the illustrated embodiment, the cover plates 25 preferably extend over the strip 12 for the entire length of a cooling station 34 in the direction of strip advance, i.e. completely over the longitudinal extent of all of the coolant manifolds 14, as best seen from the plan view of
The cover plates 25 should preferably be positioned at a height above the strip 12 that gives the channels 24 a depth effective to confine, channel and direct the moving air streams 29 emerging from the air knives 28 across the upper surface 22 to and across the lateral edges 17 while allowing adequate speed and volume of air flow, preferably in a laminar fashion. By creating such channels, the cover plates enhance the water-deflecting ability of the air at the lateral edges 17 of the strip by directing the air flow to these edges and preventing dissipation or the formation of eddy currents in the air. If the height over the cover plates above the strip is too great, the cover plates will have no directive or channeling effect on the streams of air and these may disperse or rise too much to produce the desired deflection of cooling water at the strip edges. On the other hand, if the height is too small, the channels 24 will be shallow and may reduce the volume and/or velocity of the air flow. In general, a height of between 0.5 inch (1.3 cm) to 1.5 (3.8 cm) inches above the upper surface 22 of the metal strip is preferred in most cases, with a most preferred height of about 1 inch (2.5 cm)±10%. As can be seen from
The pressure of the air used for the air knives 28 should be sufficient to produce desirable deflection of water at the edges 17 of the metal strip. Generally, pressures from 50 to 150 psi (345 kPa to 1034 kPa) are effective, preferably generating flow rates of 40 to 50 CFM (18.9 to 23.6 liters/second), but other suitable pressures and flow rates may be used to achieve the desired effect and can be determined empirically in each case, as needed.
The cover plates 25 should preferably overlap the metal strip 12 for some distance inwardly from the edges 17 of the strip. For example, for a strip having a width of 60 inches (152 cm) the overlap may be in the range of 3 to 4 inches (7.6 cm to 10.2 cm), but the preferred overlap will generally increase as the strip width increases. At their outer sides, the cover plates 25 should preferably extend at least to the lateral edges 17, more preferably over gaps 33, and most preferably completely over the shutter 32 and beyond, but ideally short of side plates 19. At their inner sides the cover plates 25 can extend close to the middle of the strip but this would lead to the air knives being at a maximum distance from the strip edges 17, resulting in a less effective flow of air 29. It is also possible to have a single cover plate 25 extending across the entire width of the strip to and beyond both lateral edges 17, in which case the air knives 28 may be positioned in the gap between the cover plate 25 and the strip 12.
The air knives 28 are preferably positioned no more than about 1 inch (2.5 cm) inwardly of the cover plates 25 in the direction towards the center of the metal strip 12, and the nozzles 27 of the air knives are preferably oriented toward the lateral edges 17 at an angle between the horizontal and vertical, preferably to provide an impingement angle of the air with the strip of between 30 to 45°. The air knives 28 may also be made an integral part of the cover plates 25.
The manner in which the cover plates 25 are suspended from the support frame 35 is shown more clearly in
While it is desirable to extend the air knives completely across a series of manifolds 14 to ensure that the air stream 29 directly contacts each of the water jets 30 emerging through the gap 33, it will be appreciated from
Where possible, it may also be desirable to provide air knives that are longer than their respective cover plates so that the air knives project beyond the cover plates at the entrance and exit locations thereof. This also helps to ensure that the moving air streams beneath the cover plates do not have stagnant zones at the entrance and exit ends.
All of the above embodiments employ shutters 32 to minimize the amount of coolant water that jets above the level of the metal strip 12. While such shutters 32 are desirable in most cases, they may be entirely omitted when the streams of air 29 are strong enough to ensure that all of the water jets from the ends of the manifolds are deflected away from the upper surface of the strip. Furthermore, while the cover plate 25 has been shown as extending beyond the outer (outboard) edge of the shutter, in some cases it does not need to extend so far and indeed, need not extend even to the edge 17 of the strip 12 provided that the stream 29 of air emerging from the channel 24 is of sufficient force to suitably deflect the emerging jets of water and that the distance from the strip edge does not lead to undue dissipation of the air stream. If no shutter is provided, it is preferable that the cover plate extend at least to the outer (outboard) end of the jets of water emerging from the manifolds to provide some control of the extent of the water spray within the apparatus. Still further, while the above embodiments have provided cover plates 25 along both sides of the strip 12, embodiments having just a single cover plate arranged at one side of the strip may be desirable in some cases. Each side of a strip has its own functionality, although it is normally desirable to cool both edges in the same way. Still further, it may in some cases be desirable to provide a single cover plate extending completely over the metal strip from adjacent one lateral edge to the other. Air knives may be mounted beneath such a strip, or extend through it, to produce the desired air streams toward the strip edges. A single air knife having outlets directed in opposite directions may be effective in such cases.
While the embodiments of the invention described above are intended for use within a single-stage or multi-stage cold rolling mill, such embodiments may alternatively be used wherever a moving strip article is to be subjected to liquid cooling on one side while avoiding contact of the opposite side with the coolant liquid. As mentioned in the introduction of this specification, this may include (but is not limited to) the cooling of coated metal sheet following the application and heat-curing of a layer of coating lacquer, the cooling of hot-rolled aluminum strip before it is coiled at the end of a hot rolling line, the cooling of metal sheet during a stand-alone coil-to-coil operation or thermally conditioning the strip by pre-cooling prior to further rolling or surface pretreatment operations.
Other embodiments and variations of the invention will be apparent to persons skilled in the art after reviewing the above description. All such embodiments and variations form part of this invention to the extent that they are included within the following claims.
This application claims the priority right of prior copending provisional patent application Ser. No. 61/465,393 filed on Mar. 18, 2011 by applicants named herein. The entire disclosure of application Ser. No. 61/465,393 is specifically incorporated herein by this reference.
| Number | Date | Country | |
|---|---|---|---|
| 61465393 | Mar 2011 | US |
