DEVICE AND METHOD FOR COOLING ROLLS USED FOR ROLLING IN A HIGHLY TURBULENT ENVIRONMENT

Description

The present invention relates to a device and a method for cooling work rolls. This device permits to easily obtain satisfying cooling condition for any work roll diameter.

BACKGROUND

During the hot rolling of a metallic product, a coolant is sprayed on the work rolls to limit the thermal dilation inducing flatness defects and to prevent excessive roll degradation and strip defect. Due to thermomechanical deformation, a thermomechanical fatigue reducing the lifespan of the work rolls and lowering the surface quality of the rolled strip is engendered.

SUMMARY OF THE INVENTION

Patent EP 2 114 584 B1, as illustrated in FIG. 1, discloses a rolling stand 1 for metallic products comprising a pair of work rolls (2, 2′), a pair of back-up rolls (3, 3′), and a pair of water pillow cooling device (4, 4′) comprising a plurality of nozzles able to spray cooling jets (5) under pressure on at least one of said work roll. The cooling device has a concave and cylindrical shape facing the work roll which comprises said nozzles. The nozzles are located at a short distance, between 5 and 200 mm, from the work rolls.

When in use, such a system permits to create a liquid cushion, between the nozzles and the work roll, having a highly turbulent state and thus improving the cooling of the work roll.

In order to correctly evacuate the water and renew the coolant in contact with the work roll, the gap between the work roll and the nozzles should be greater in direction of the back-up roll, i.e. away from the product being rolled.

The work rolls tend to deteriorate while in use. For example, their rugosity can be increased, their curvature and diameter can deviate from the aimed one. All those changes lead to marks and defects on the surface of the metallic rolled product and flatness defects. This is why the work rolls are periodically dismantled and grinded to get the desired properties and shape.

Unfortunately, the grinding leads to a reduction of the work roll diameters and thus influence the geometry gap, reducing the cooling performance and the pass line.

The cooling device in EP 2 114 584, despite improving the cooling capability compared to a sprayed coolant, is unable to keep an optimal water cushion in a turbulent state, e.g. an optimal gap. The gap is the space between the work roll (2, 2′) and the cooling device (4, 4′). When the work roll is new, as illustrated in FIG. 2A, there is a gap from 5 to 200 mm. However, after grinding leading to a reduced work roll diameter, the gap is greater than 200 mm especially on the upper portion of the cooling device, as illustrated in FIG. 2B.

Consequently, the same cooling head is used on rolling stands having different work roll diameters, the gap condition is not optimal. As a reminder, the gap between the cooling box and the work roll should not exceed 200 mm and should increase in the direction of the backup roll.

There is a need to find a way to enhance the flexibility of a cooling head, especially with regards to the variation of the work roll diameters, permitting to have a water cushion in a turbulent state for various work roll diameter.

It is an object of the present invention to solve the aforementioned problems.

The present in invention provides a rolling stand for metallic products comprising:

• • a pair of work rolls;
  • a pair of back-up rolls;
  • at least one water pillow cooling device able to spray a plurality of cooling jets under pressure on at least one of said work roll; and
  • a removable plate,
    • wherein the removable plate is placed between the water pillow cooling device and the work roll,
    • wherein the removable plate is concave and with a curvature such that a gap between the removable plate and the work roll is constant or increases when moving in direction of the back-up roll and such that the gap is from 5 to 200 mm, and
    • wherein the removable plate is holed such that the cooling jets can pass through the removable plate.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention will become apparent from the following detailed description of the present invention.

To illustrate the present invention, various embodiment of non-limiting example will be described, particularly with reference to the following figures:

FIG. 1 exhibits an embodiment of a rolling stand using a cooling device as known in the prior art.

FIG. 2 exhibits the gap variations present in the embodiments of FIG. 1 due to a variation of the work roll diameter.

FIG. 3 illustrates an embodiment of the present invention.

DETAILED DESCRIPTION

In the following specification, the expressions «downstream» and «upstream» are to be understood relative to the path of the metal strip.

As illustrated in FIG. 3, the present invention relates to a rolling stand 11 for metallic products comprising:

• • a pair of work rolls (12, 12′),
  • a pair of back-up rolls (13, 13′),
  • at least one water pillow cooling device (14, 14′) able to project a plurality of cooling jets under pressure on at least one of said work roll,
  • a removable plate (15, 15′)
    • placed between said water pillow cooling device (14, 14′) and said work roll (12, 12′),
    • being concave and with a curvature C such that a gap G between said removable plate and said work roll is constant or increases when moving in direction of the back-up roll and such that said gap is from 5 to 200 mm and
    • being holed with holes H shown solely schematically such that said cooling jets can pass through said removable plate.

A water pillow cooling device consists in a box connected through a feeding pipe to a coolant container and to a pump. This box is watertight in itself except on its front face, positioned at a short distance from a work roll and in which nozzles or slits have been positioned or machined. The box is concave and cylindrical at the level of its front, forming a curved surface. Said coolant can, for example, be water or an emulsion of water and oil stabilised or not with surfactants.

Preferably, said cooling device comprises side plates. Those sides plates ease the formation of a turbulent coolant cushion by reducing the flow of coolant exits by the sides. Similar side plates are disclosed in EP 2 114 584.

The cooling device can comprise scraper nozzles as described in WO2008149195. A mechanical scraper is a device which is in contact with the roll and mechanically blocks the flow of the cooling fluid. This scraper is closing the passage for the cooling fluid coming from the roll cooling device, avoiding the fluid to come into contact with the metallic product, which could be detrimental for said product.

The purpose of the removable plate is to allow the formation of a coolant cushion, between the removable plate and the work roll, in a turbulent state. Depending on the work roll diameter, a removable plate satisfying the gap width and the gap increase in direction of the back-up roll can be used.

For example, after a grinding operation where the work roll diameter has been reduced, the removable plate can be replaced by a removable plate having a smaller curvature. However, the curvature of the removable plate should be greater than the curvature of the work roll so as to have a gap being constant or increasing when moving in direction of the back-up roll, i.e. when moving away from the product being rolled, and also allowing to have a gap between said removable plate and said upper work roll from 5 to 200 mm.

The removable plate is preferably attached to the water pillow cooling device. Preferably, the removable plate is attached to the cooling head via any means such as screws or nuts and bolts. Even more preferably, the removable plate is attached to the front face of the cooling head.

The removable plate is not an element of the water pillow cooling device. The removable plate is not part of said watertight box and is different from the front surface of said box.

In a cooling system of the prior art, as disclosed in EP 2 114 584, the water pillow cooling device is optimal only for a narrow range of work rolls diameter. On the contrary, the object of the present invention permits to form a coolant cushion having an optimal turbulent state for a wide range of work rolls diameters by using an appropriate removable plate.

Preferably, said at least one water pillow cooling device (14, 14′) comprises a plurality of cooling nozzles N (shown solely schematically) able to spray a cooling jet J. Preferably, the cooling nozzles have an orientation perpendicular to the work roll surface for nozzles far from the roll bite and tangentially for nozzles closer to the roll bite.

Preferably, the cooling nozzles can have various section shapes and/or sizes. Preferably, they are disposed in parallel rows, each row being laterally shifted from the adjacent rows, so as to create a quincunx disposition. The nozzles can also be replaced by transversal slits extending along all or part of the cooling device, parallel to the ground, generating flat jets.

Preferably, the exits of said nozzles are arranged along a curved surface, which curvature is greater than the radius of said work roll.

Preferably, the curvature C of said removable plate (15, 15′) is smaller than the curvature of said curved surface CS.

Preferably, said removable plate comprises a metal layer ML and a protective layer PL preventing corrosion (both shown solely schematically). Even more preferably, said metal layer is made of stainless steel or of aluminium. Even more preferably, said protective layer preventing corrosion comprises silicon and/or polypropylene and/or polytetrafluoroethylene. Preferably, said metal layer is a stainless-steel layer and said protective layer is a silicon layer. The protective layer preventing corrosion faces the work roll while the metal layer faces the cooling device.

Preferably, said water pillow cooling device is able to spray from 100 to 700 m³·h⁻¹ of coolant per square meter of work roll surface and at a pressure from 0.5 to 6 bar. Those features ease the formation of a turbulent coolant cushion along the upper roll width and thus improve the cooling of the upper work roll. Even more preferably, said water pillow cooling device is able to spray from 300 to 700 m³·h⁻¹ of coolant per square meter of work roll surface and at a pressure from 2 to 6 bar.

The invention also relates to a cooling method for cooling a work roll in an installation as previously described comprising the step of spraying a coolant by means of said cooling device towards said work roll producing a coolant pillow in a highly turbulent state in the gap between said work roll surface and said removable plate.

Preferably, said coolant is essentially water.

Preferably, said coolant is sprayed at a rate from 100 to 600 m³·h⁻¹ per square meter of work roll surface and at pressure from 0.5 to 6 bar. Even more preferably, said coolant is sprayed at a rate from 300 to 600 m³·h⁻¹ per square meter of work roll surface and at pressure from 2 to 6 bar.