Technical Field

The invention relates to the field of aluminium strip or foil rolling mills, and describes a new process which will improve the temperature control of the mil) rolls to improve strip flatness, and will enable a dedicated lubricant to be applied to the rolls to increase productivity and give other safety and product quality benefits.

Background

The process of rolling aluminium requires lubrication in order to gain a satisfactory surface finish of the strip at higher reductions. However, even with lubrication, the rolling process generates heat which must be removed. Traditionally this has been achieved in one of two ways:

A small number of mills use a water based emulsion as lubricant. This system has the advantage of using a liquid with a high cooling capacity, and the oil content and constitution can be optimized to give good lubricating properties. However, these emulsions may cause staining of the material unless they are removed completely from the strip. This can be achieved by installing sophisticated systems to remove the coolant, and by ensuring that the material exit temperature always significantly exceeds 100 deg C.

In practice the complete removal of the coolant is difficult to achieve so this method has had limited usage.

The vast majority of mills rolling aluminium foil or strip use kerosene as both coolant and lubricant. Kerosene was found to be the best compromise between cooling and lubrication properties, with few strip marking problems. However, kerosene is both a poor cooling medium due to its low specific heat capacity, and has poor lubricating properties compared to dedicated lubricants. In addition there are significant fire safety and EHS issues associated with its use and storage.

Due to the low Specific Heat Capacity of kerosene, it is necessary to use relatively large flow rates to achieve the desired cooling effect, delivered by complicated pump and spray systems. These large flow rates coupled with the high temperature of the material leaving the rolls results in the generation of large amounts of fumes, which must be extracted from the machine and the working area, and then cleaned from the air before exhausting the air to atmosphere.

In both the above solutions the coolant medium is applied externally to the rolls by means of row(s) of spray nozzles which apply the coolant directly to the exterior of the rolls.

In addition to the bulk cooling process described above, the coolant sprays have a further use in the control of the strip flatness.

The strip may become unflat during the rolling process due to differing reductions in thickness taking place at different points across the strip width. This difference in reduction is due to the difference in the shape of the working roll across its width, and a consequent difference in the gap between the rolls.

It has been found that by varying the cooling of the rolls across the width by means of localised control of the coolant sprays, this leads to a differing thermal expansion/contraction across the roll, which can compensate for the local variations in roll gap.

A number of patents (e.g. GB2012198, EP41863) illustrate the use of varying the cooling rate across the width of the roll(s), which, in conjunction with a strip flatness measuring device, can directly control the flatness of the rolled strip.

GB2156255 describes a process which employs separate lubrication and cooling (SLC). Banks of water jets are used to cool the rolls externally and effect strip flatness control, whilst low quantities of a more suitable lubricating oil are applied directly to the strip. Sealed boxes are used to prevent water contacting the material.

682080719 describes the use of electrical induction heaters to locally heat the work roll(s) in the area of the strip edges, in order to reduce the phenomenon of "Tight Edge". These inductors partially heat the exterior of the roll to prevent the under rolling of the strip and hence a tight edge, which is a major limit to rolling speed and a contributor to strip breaks.

US20070175255 discloses a method for cold rolling in which a number of nozzles are used to apply various combinations of lubricant emulsion or base oil, coolant and inert gas are applied to the wedge and arc areas of upper and lower work rolls, for the purpose of cleaning, cooling, lubrication. Flatness control is alluded to, but is it described as being achieved by using a combination of inert gas and conventional coolants applied to the exterior of the work rolls.

USD 20110308288A1 describes a rolling mill temperature control system using induction heaters and dedicated lubrication system, however the bulk cooling of the rolls is performed externally, by means of cryogenic gas.

Summary

According to an embodiment, an apparatus for rolling a metal foil or strip may comprise a pair of working rolls arranged to receive the strip in a nip region there between: said working rolls will contain one or more internal channels through which a cooling medium (liquid or gas) will be directed, and a means for heating one or more of a plurality of zones on the exterior of the working roll or rolls and a device for introducing a lubricating medium into the interface between the working rolls and the material.

According to a further embodiment, an apparatus may comprise a flatness measuring device arranged to provide a signal indicative of the flatness of the metal strip after it passes from the roll. According to a further embodiment, an apparatus may further comprise means for varying the application of heat to the one or more zones, responsive to said signal.

According to another embodiment, the flatness measuring device can be arranged to measure the profile of the roll.

According to another embodiment, an apparatus may comprise a lubricant supply system and means for directing the lubricant to the rolls or strip or both. Such lubricant supply may have the ability to be varied in volume by manual or automatic means. According to a further embodiment, this apparatus can manually or automatically select between one or more different lubricants.

According to another embodiment, a means of controlling the temperature of the works rolls during rolling, the work rolls will be internally cooled by coolant channels inside the rolls. These channels may be single or multiple, and may be radial or longitudinal or spiral within the roll. The cooling medium will be supplied at volumes and temperatures controlled automatically by a process control system, or manually controlled. According to a further embodiment, this internal cooling can be controlled at varying levels to enable faster warm up of cold rolls, and cooling of hot rolls prior to further processing on and off the machine for example, roll grinding.

According to a further embodiment, a method of controlling the shape of a metal or strip may comprise heating one or more of the plurality of zones on one or more rolls via one or more heating devices, thereby controlling the radial size of the roll across the rolls width. The heating elements may be controlled independently for top and bottom rolls. The heating elements may be placed on the exit or entry or both sides of the work rolls.

According to a further embodiment of the method, an apparatus may further comprise the steps of: arranging a strip flatness measuring device to provide a signal indicative of flatness of the metal strip after it passes from the rolls: receiving data from the flatness measuring device and varying the application of heat to one or more zones and one or more rolls, responsive to such data. According to a further embodiment, application of heat to one or more zones or rolls can be manually varied by a human operator.

According to a further embodiment, heating may be applied to zones of the roll or rolls outside the strip rolling width to accomplish heating of the rolls to achieve a change in the radial size of the roll or rolls to reduce any edge defects in the strip, such as tight edges. Description of the Drawing:

The invention will now be described, by a non-limiting example, with reference to FIG 1, which shows a side view of a rolling mill according to various embodiments.

Detailed Description

Embodiments offer a new improved cooling and flatness control technology to be conceived with the following features:

A pair of internally cooled working rolls. The rolls contain an internal labyrinth which may be straight or curved in shape. The coolant may be liquid or gas. The cooling rate may be adjusted automatically or manually to maintain the desired roll temperature. This adjustment may be performed by a flatness control system, or derived from process modelling calculations.

Additionally, one or more roll heating devices. These devices may be in the form of a fixed bank of heaters, or may be one or more moving heaters which traverse the length of the roll(s).

In addition, these heaters may be used to perform additional heating adjacent to the strip edge to improve the strip edge condition.

For both fixed and moving solutions, these heaters may be split either physically or logically into control zones. This heater or heaters may be applied to one or both rolls, and may be mounted on either side of the roll.

A flatness measuring system in conjunction with a flatness measuring device mounted on the exit side of the mill varies the amount of heating applied to the control zones in order to produce the desired strip shape. In its simplest form, the flatness control system is realised by a human operator who manually varies the amount of heating responsive to data provided by the flatness measuring device. In a more sophisticated embodiment, an electronic controller is provided and arranged to vary the heating responsive to such data.

Separate rolling lubricant is applied to the strip or to the rolls, or to both, by means of a lubrication spray bar or electrostatic deposition. The type and volume of lubricant applied may be adjusted automatically or by manual control.

This system offers numerous and large benefits over the prior art.

The complete removal of kerosene as a roll coolant significantly reduces the risk of and consequences of a fire on the mill, therefore removing the need to install expensive fire protection equipment. The complete removal of kerosene as a roll coolant significantly reduces the environment impact of the

cold rotting process, due to the reduction of hydrocarbon release into the atmosphere.

The full width heating control enables fast and effective response to reduce flatness errors, and can be used to prepare the roll temperature profiles in the cases of width changes or cold starts.

The ability to control the bulk temperature of the rolls by means of the internal cooling will result in faster warm up time of the work rolls after cold starts.

The application of a very small amount of rolling lubricant to the strip prior to rolling will lead to the following benefits over existing systems:

Optimisation of oil properties for lubrication only, allowing larger reductions to be taken for a given set of mill parameters, leading to higher production output.

Reduced incidence of coil staining due to excess lubricant left on the material after rolling, leading to a higher product yield.

Reduced incidence of coil staining due to contamination of the roll coolant by hydraulic oil leading to a higher product yield.

Reduced annealing times and no requirement to use inert gas annealing to avoid coil staining, leading to lower costs.

Additionally, the removal of kerosene and replacement with a liquid or gas coolant removes the requirement for the following pieces of equipment and their associated operating costs:

Kerosene storage tanks and circulations systems, including heaters and coolers.

Exhaust gas treatment equipment to remove kerosene fumes from the exhausted air.

Kerosene filtration plant, with associated benefits in the disposal of the filter media.

Mill civil works are signif icantly simplified as the need for cellars and oil catchment trays are removed.

FIG 1 shows a schematic diagram of a rolling mill stand 1 according to various embodiments with aluminium strip or foil 2 passing through the stand from left to right as arrowed. The mill work rolls 3 and back up rolls 4 are loaded and rotated in order to perform the reduction in thickness of the metal.

Before entering the work roll gap the strip 2 has a suitable lubricant applied by the lubrication system 5. The volume and type of lubricant applied may be varied manually or automatically, depending on

Page 6 parameters including but not limited to strip thickness, mill speed, work roll roughness. It may be possible to direct the lubrication flow to the strip, the work rolls or to both

The temperature and therefore the diameter of the works rolls is controlled in two ways.

Firstly a cooling medium is circulated through channels inside the work rolls 3 from a cooling system 6 to

control the average temperature of the rolls. This cooling medium may be liquid or gaseous. The flow rate and temperature of the cooling medium may be varied manually or automatically

Secondly, heaters 7 (shown in this case on the exit side of the rolls, but may be installed on either exit or entry or both) will control the localised heating of the work roll or rolls. These heaters may operate singly or in banks, and will apply varying heating effects across the width of the rolls(s). In the case of single heater operation, the heater or heaters will traverse the length of the roll or rolls, applying the varying heating described above.

These heaters may derive their adjustments from a flatness measuring system 8 and associated flatness control system 9, or may be manually controlled.