EP1230045B1 - Cold rolling method - Google Patents

Abstract

The present invention relates to a method for cold-rolling metallic rolling stock (4), in which the rolling stock (4) passes through the roll nip (3) between oppositely driven rollers (2) at room temperature in order to undergo a plastic shape change. To avoid the problems caused by the use of liquid coolants and to achieve an improved surface quality of the rolling stock (4), the invention proposes that inert gas, which is at a lower temperature than the rolling-stock temperature in the roll nip, is blown into the region of the roll nip (3). The invention also relates to a cold-rolling stand for carrying out this method.

Description

The present invention relates to a method for Cold rolling of metallic rolling stock, in which the rolling stock at room temperature for plastic deformation by a Rolling gap between counter-driven rollers durchläft and in the area in the nip Inert gas is blown, which is a lower temperature has, as the rolling stock temperature in the nip. The invention further relates to a cold rolling stand for cold rolling metallic rolling stock by a method of the aforementioned Art.

Cold rolling is a long known process for shaping continuously passing strip, profile or sheet from steel or other metals. This is a cold deformation in which - in contrast to the hot forming - the rolling stock is not heated before the actual forming process, ie at the prevailing ambient temperature (room temperature) is subjected to the plastic deformation. This change in shape below the respective recrystallization temperature of the metals brings about advantageous changes in the properties of the deformed materials, for example an increase in strength and hardness. In addition, material surfaces with defined roughness values R _a can be realized thereby, and indeed both the highest surface qualities with a mean roughness value according to DIN 4768/1 R _a <0.3 μm - crack and pore-free (RP) or crack-free and pore-free brightly bright (RPG) - as well as roughened surfaces with R _a > 1.5μm. As a result, the surfaces can be optimally matched to the requirements for subsequent processing steps. In principle, all cold-workable metal materials can be processed in this way, ie steel, non-ferrous metals, aluminum and other alloys. For example, cold-rolled steel sheet is ideally suited for immediate further processing with the highest quality requirements, for example in the automotive industry.

To such high, defined surface qualities generate harmful influences that lead to a can cause undefined roughening of the surface, excluded as far as possible or by appropriate measures be mastered. Such an impairment gives during Walzgutdurchgang through the nip among others in that the material surface and the roll surfaces in the area of their contact surface outside the flow sheath in principle have different web speeds, which a mechanical frictional stress of the surfaces to Episode has. The resulting frictional heat leads together with the heat generated by internal friction due to the supplied deformation energy to a significant Material heating of the rolling stock in the nip. This thermal Stress of the material additionally favors one Impairment of the surface by changing the Material properties and by oxidation.

In the prior art one encounters the aforementioned mechanical and thermal stresses of the Strip surface through the use of at room temperature liquid coolants. Before entering the Rolling gap is the rolling stock while continuously with water, oil or wetting emulsions. As a result, the rolling stock is at the same time cooled and lubricated so that the required Surface qualities can be generated.

A major disadvantage of the aforementioned, liquid Cooling lubricants, however, is that they partially during rolling remain on the surface and there disadvantageous impact. This leads to water and water-containing emulsions Corrosion, i. with steel sheet or strip to rust formation. oil and oil-containing emulsions leave oil residues on the Surface, which before further processing by Welding, electroplating or the like in other, relatively expensive and common environmentally damaging operations as completely as possible must be removed again. Of course, this brings one very considerable work, time and expense.

DE-C-31 50 996 describes a method for cold rolling of metallic rolling of the type mentioned This method is a gas in the nip above and injected below the belt. The known method concerns the rolling or rolling of rolling stock Nachwalzgraden of not more than 2.5%, the flatness of Band to improve. It is described by the Use of the injected gas during rolling without Lubrication also belts with perfect smooth surface and without tarnish. It is in this Scripture talk about that by the injected gas additionally a cooling effect was exerted on the roll surface becomes. However, the injected gas is used in this process not cooled. The cooling effect is thus only insofar available, as z. B. blown at room temperature gas has a lower temperature than the surfaces of the rolls, which due to the deformation of the rolling stock Heat rolling process.

From the document JP-A-55-86602 is a method for Tailoring of cold rolled strip is known in which a local cooling of the rolling belt is provided to Avoid surface defects during the temper rolling process. For this purpose, a cooling medium by means of a nozzle blown the rolled strip, but this nozzle is in substantial distance to the work rolls.

In view of this, the present invention is the Task based, a cold rolling process and a Specify cold rolling mill for carrying out this method, which the aforementioned problems by the use avoids as far as possible conventional cooling lubricants. In particular, while a sufficient cooling and Lubrication be ensured in the nip, where possible no harmful residues remain on the rolling stock should.

The inventive method proposes to solve the aforementioned problems, in the area of the roll gap Inert gas or reactive gas deep-frozen blow and the Inert gas or reactive gas below its To supply liquefaction temperature in liquid form.

According to the method of the invention, the roll gap or the rolling stock passing through the nip with locally Inert gas circulates. As an inert gas is a non-oxidizing Gas, for example nitrogen, noble gases, Carbon dioxide or other gases and gas mixtures containing the Do not attack rolling stock, that means there is no Cause corrosion.

The method according to the invention is based on the surprising finding that effective heat removal from the roll gap, a corrosion-preventing effect and, what is particularly unexpected, a good reduction in friction in the roll gap are effected by a directionally cooled inert gas stream. This means that, according to the invention, gas cooling lubrication during cold rolling is realized for the first time.

Due to the injected in the region of the nip inert gas is there locally formed a protective atmosphere, which Corrosion, for example oxidation of the rolling stock surfaces and also the roll surfaces in the region of the roll gap reliably prevented. Unlike conventional, liquid coolant provides the inert gas through the complete displacement of the ambient air a particularly good Oxidation protection.

Due to the temperature gradient to the in the nip in the Deformation of locally heated rolling material causes this passing, relative to cooler inert gas an effective Cooling of the rolling stock directly in the area of the roll gap. As a result, the thermal load of the Surfaces. This gas cooling is probably because of that Especially effective because the cooling gas is relatively far in the Rolling gap between roller and rolling stock surface penetrates.

Surprisingly, it has also been found that by the inventively blown inert gas friction so far reduced between the roll and Walzgutoberfläche is that extra lubrication is no longer necessary is. An explanation for this unexpected, positive lubricating effect assumes that on the of the passing inert gas cooled Walzgutoberfläche and possibly also on the roll surface one microscopically thin layer of the inert gas is adsorbed. In the nip, that is the contact of Walzgut- and Roll surface, thereby apparently forms a kind Gas cushion, so that an improved lubricating effect occurs, as in the usual use of liquid Lubricants.

The inventive method thus shows a first Way, the previously considered mandatory, at Room temperature liquid cooling lubricants such as water, oil or emulsions by gaseous at room temperature Coolant gas to replace.

The particular advantages of the method according to the invention arise from the fact that all the disadvantages of liquid Cooling lubricants completely eliminated. Especially the inert cooling lubricant does not leave any harmful Residues on the rolling stock, so that before further processing no separate operations for degreasing, derusting or the like are more necessary. The rolling stock can rather directly further processed immediately after rolling be, for example, welded, electroplated, painted or deformed or the like. In addition, will by the inert gas Oxydationserscheinungen by far more effectively suppressed than with known ones Coolants would be possible.

Another very positive side effect has been that the service life of the work rolls, especially at the highest surface quality RPG (crack-free and non-porous brightly bright), is significantly increased. Of course, this is particularly advantageous since the rollers must be replaced and reworked accordingly less frequently. For surface qualities with higher, defined roughness values, the same applies accordingly, ie the given R _a values are reproducible for a longer time.

Preferably, the inert gas is limited to the limit Contact surface in the nip between rolling stock and roller directed blown. Through this targeted injection of the Inert gases in the areas where the rolling stock enters the nip enters or exits, the rolling stock is where the maximum thermal load occurs, especially good locally cooled. In addition, it is guaranteed that of the Rolled and rolled material entrained air oxygen is safely displaced and not in the nip is introduced. Furthermore, the lubricating effect of Gas lubrication according to the invention by the directed Insufflation to the edge of the interface also improved.

Preferably, the inert gas in Walzguteintritt and in Walzgutaustritt blown. This is a particularly good Cooling and safe shielding from harmful Guaranteed atmospheric oxygen. In individual cases, however, it can already sufficient, the inert gas in Walzguteinstritt or in Walzgutaustritt supply.

The inert gas is expediently at least on the Fed to the top of the rolling stock. It is exploited that the cold inert gas is heavier than the ambient air and thus alone under the influence of gravity the underside of the rolling stock and the lower roll also flows around.

The invention Method provides that the inert gas below its Is blown liquefaction temperature. The inert gas, For example, nitrogen, which under normal conditions (Room temperature, atmospheric pressure) is present in gaseous form, it is so far cooled down until it is the liquid state of aggregation occupies. As a liquefied gas, it is then according to the inventive method in the region of the roll gap injected or injected. In contrast to the known, liquid at room temperature cooling lubricants this LPG goes on warming to room temperature completely in the gaseous state of aggregation, leaves behind consequently, no harmful residues on the rolling stock, as if it is blown in gaseous form.

The significantly improved cooling effect when using Liquefied gas results from its extremely low temperature and from the fact that it is all its vaporization energy Transition into the gaseous state of aggregation as heat energy withdraws from the environment, resulting in relatively large amounts of heat be removed from the rolling stock within a short time. The Walzgut thus occurs at very low temperature in the Roll gap. The resulting heat of deformation is at Walzgutaustritt by liquefied natural gas cooling practically immediately dissipated. The thermal stress of the Surfaces, both the Walzgut- and the Rolled surfaces are thereby reduced to a minimum. In addition, due to the temperature differences is formed Gas cushion on the contact surface in the nip, so that the Roller friction and thus the mechanical stress of Surfaces is also significantly reduced. After all is due to the low surface temperatures Surface corrosion effectively reduced by oxidation, and Although even then, if the rolling stock or the Roll surface the directly flowed with inert gas Leave the area around the nip.

Initial experiments have shown that through the use of LPG, namely liquid nitrogen, otherwise same conditions a sudden quality improvement Ribbon surface finish of quality RP (crack and non-porous) to the quality RPG (tear and pore-free light shiny). At the same time, the service life of the Rolling a multiple. So far, after some time resulting matting of the roll surface, which in the Qualities RP and RPG can not be tolerated, whose Causes, however, are still unclear, is in the Process according to the invention also no longer occurred.

The process according to the invention is preferred during cold rolling of steel, in particular steel strip and sheet steel carried out, especially at high Surface finishes according to DIN EN 10139. The invention However, process is not based on the processing of steel limited, but can of course also at Cold rolling of other cold-workable metal materials be used, for example, non-ferrous metals, aluminum and other metals and alloys.

In summary, it should be noted that according to the invention for the first time a possibility is shown that so far usual, at room temperature liquid cooling lubricants by a gaseous cooling gas at room temperature completely replace. The special advantages arise from the fact that all, previously by the cooling lubricants self-caused problems disappear and at the same time one Significant improvement in surface quality Cold rolling is achieved practically without additional effort.

The inventive method can be relatively low design effort on a cold rolling stand for cold rolling of metallic rolling, which is at least two Rollers (work rolls) which can be driven in opposite directions are stored in a roll stand and between them the nip is through which the rolling stock Change in shape passes. According to the invention this has with cold inert gas acted upon nozzles on the Roll nip are directed.

Through these nozzles, with their gas outlet preferably in essentially aligned tangential to the roll surface are, the inert gas over the entire width of the rolling stock in the area of the roll gap inflatable, that is how described on the border of the interface between Rolling stock and roll surface.

Appropriately, the nozzles are at Walzguteintritt and on Walzgutaustritt mounted. At least they should be on the Be arranged top of the rolling stock. This arrangement is often sufficient, since the cold inert gas alone due Gravity will wash around the underside of the rolling stock. Optionally, however, on the underside of the rolling stock also be mounted nozzles.

Depending on the required cooling effect and Surface quality of the rolling stock, the nozzles with be acted upon cryogenic gas or liquefied gas.

Another advantageous alternative or development The present invention provides that instead of Inert gas, which is related to the material surfaces behaves passively, a reactive gas is used, which with the surface of the rolling stock to achieve defined Surface properties can undergo chemical reactions. By the use of this reactive gas are also the the problems underlying the invention by the use liquid cooling lubricants avoided. This can be done namely also a sufficient cooling and lubrication in Achieve rolling gap, and, as with the inert gas, no harmful residues remain on the rolling stock.

The previously explained, so far still scientifically not definitively clarified effects regarding the Gas cooling and lubrication of the rolling stock in accordance with the invention Roll gap can be due to the cool reactive gas supplied also be achieved. The atmospheric oxygen, which in the Rolling nip harmful effects on the Surface texture of the rolling stock and the rollers have can, is displaced by the reactive gas. In addition to this, already with inert gas achievable effects even more advanced through the use of reactive gas Achieve benefits. For example, it is conceivable that the initially cooled supplied reactive gas through the Heating in the roll gap targeted with the material surface of the Walzguts reacts. That way it would be, for example conceivable, reactive applied to the Walzgutoberfläche Apply protective layers, especially before the Walzgut comes in contact with the ambient air. this could especially with reactive metals, such as Bring special benefits to aluminum.

Reactive gases are all gases or gas mixtures in question, which under suitable conditions, for example in certain temperature ranges with the respective material of the rolling stock can react in a predeterminable manner. It is conceivable, for example, the use of carbon dioxide and other inorganic or organic gases or Gas mixtures.

Fig. 1

eine schematische Perspektivansicht eines erfindungsgemäßen Walzgerüsts;

Fig. 2

eine Seitenansicht des Walzgerüsts gemäß Fig. 1.

A cold rolling stand according to the present invention will be explained below with reference to the drawings. These show in detail:

Fig. 1

a schematic perspective view of a rolling mill according to the invention;

Fig. 2

a side view of the rolling stand according to FIG. 1.

Fig. 1 shows in a perspective view obliquely from above schematically a cold rolling mill according to the invention, wherein the better clarity the roll stand omitted are. This cold rolling mill, which as a whole with the Reference numeral 1 is provided, has two perpendicular superposed rollers 2, between which the nip 3 is located.

The rolling stock is represented by a metal band or Sheet 4, for example made of steel, formed in Arrow direction passes through the nip 3.

The reference numeral 5 denotes nozzles which are on the Bandeintritts- and the tape exit side of the roll stand. 2 are arranged and with their gas outlet obliquely from above in the area of the roll gap 3 are directed.

The arrangement of the individual parts arises again particularly clear from the side view in Fig. 2. Darin are additional nozzles 5 on the underside of the rolling stock. 4 indicated, which also directed to the nip 3 are.

To operate the cold rolling mill 1, the rollers 2 in driven manner known to rotate, whereby the rolling stock. 4 under shape change passes through the nip 3. The Nozzles 5 are subjected to inert gas according to the invention, and Although preferred with cold or cryogenic gas or Liquefied gas, for example nitrogen. This will be a effective local cooling of the rolling stock 4 in the region of Roll gap 3. Due to the local protective atmosphere in the area of the nip 3, oxidation is reliably suppressed. The Inert gas immediately ensures adequate lubrication between the roll and Walzgutoberflächen so that no additional coolants and lubricants are required.

Instead of chemically passive inert gas is also the Use of reactive gas conceivable. This is characterized by a certain chemical reactivity with the material of the Rolled out. In addition to the invention Gas cooling without the use of liquid Cooling lubricants can thus be targeted Surface effect realized during the rolling process be, for example, the training of Surface protective layers.

Claims (17)

1. A method for cold-rolling metallic rolling stock, in which the rolling stock passes through a roll nip between oppositely driven rollers at room temperature in order to undergo a plastic shape change, and in which inert gas, which is at a lower temperature than the rolling-stock temperature in the roll nip, is blown into the region of the roll nip, characterized in that the inert gas is blown in in cryogenic form and is supplied in liquid form at below its liquefaction temperature.
2. A method for cold-rolling metallic rolling stock, in which the rolling stock passes through a roll nip between oppositely driven rollers at room temperature in order to undergo a plastic shape change, and in which reactive gas, which is at a lower temperature than the rolling-stock temperature in the roll nip, is blown into the region of the roll nip, characterized in that the reactive gas is blown in in cryogenic form and is supplied in liquid form at below its liquefaction temperature.
3. The method as claimed in claim 1 or 2, characterized in that the inert gas or reactive gas is blown in such a way that it is directed onto the boundary of the contact surface in the roll nip between rolling stock and roller.
4. The method as claimed in claim 1 or 2, characterized in that the inert gas or reactive gas is blown in substantially tangentially with respect to the roll surface.
5. The method as claimed in claim 1 or 2, characterized in that the inert gas or reactive gas is blown in at the rolling-stock entry and/or at the rolling-stock exit.
6. The method as claimed in claim 1 or 2, characterized in that the inert gas or reactive gas is supplied at least on the top side of the rolling stock.
7. The method as claimed in claim 1, characterized in that nitrogen is used as inert gas.
8. The method as claimed in claim 1, characterized in that a noble gas is used as inert gas.
9. The method as claimed in claim 1 or 2, characterized in that a gas mixture is used as inert gas or reactive gas.
10. The method as claimed in claim 2, characterized in that CO₂ is used as reactive gas.
11. The method as claimed in claim 1 or 2, characterized in that the rolling stock is strip steel.
12. The method as claimed in claim 1 or 2, characterized in that the rolling stock is steel sheet.
13. The method as claimed in claim 1 or 2, characterized in that the rolling stock acquires a roughness average (Ra) of 0.03 to 1.5 µm (in accordance with DIN 4768/1).
14. A cold-rolling stand for cold-rolling metallic rolling stock using a method as claimed in any of claims 1 to 13, having at least two rolls which are mounted in a rolling frame in such a manner that they can be driven in opposite directions and between which the roll nip is located, through which the rolling stock passes, undergoing a change in shape, characterized in that nozzles (5) to which inert gas or reactive gas can be supplied and which are directed onto the roll nip (3) are arranged at the rolling-stock entry and/or at the rolling-stock exit, it being possible to supply the nozzles (5) with inert gas or reactive gas in liquid form at below its liquefaction temperature.
15. The rolling stand as claimed in claim 13 or 14, characterized in that the nozzles (5) are aligned with their gas outlet substantially tangential with respect to the roll surface.
16. The cold-rolling stand as claimed in claim 13 or 14, characterized in that the nozzles (5) are arranged on the top side of the rolling stock (4).
17. The cold-rolling stand as claimed in claim 13 or 14, characterized in that the nozzles (5) are arranged on the underside of the rolling stock (4).

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