Patent Application
20140238093
The invention relates to a reversing mill and an operating method for a reversing mill comprising at least one reversing stand for rolling a metal stock, wherein the stock passes through the at least one reversing stand in a sequence of passes in alternating directions and is wound up after each pass by means of a reversing reel acting as a coiler.
In a reversing stand, the stock is reduced in thickness in a back and forth motion in a sequence of passes. In the case of known cold-rolling mills, an oil/water emulsion having an oil concentration of around 0.5 to 5% is normally used for roll gap lubrication, roll cooling and roll cleaning. If the oil concentration is increased, the lubricating effect generally increases, i.e. there is less roll gap friction, whereas the cooling effect is reduced.
In the case of tandem mills, approximately ⅓ the quantity of emulsion per stand is applied to the work rolls or to the metal strip on the entry side immediately upstream of the roll gap for roll gap lubrication. The remaining ⅔ are used on the exit side primarily for cooling the work rolls but also for roll cleaning, particularly for cleaning the back-up rolls.
In the case of a reversing stand, all the emulsion for each roll is generally applied on the entry side to the work rolls or to the strip immediately upstream of the roll gap.
Depending on the installed power of the main drives, the flow rate for a cold-rolling mill is e.g. 0.8 l per minute and kilowatt hour of input power. For a input power of 6000 kW per stand, for example, this means a coolant/lubricant (emulsion) flow rate of 4800 l per minute.
Despite this large quantity of lubricant, the required amount of lubricant in the roll gap may be inadequately adjusted. In particular, the problem arises that the amount of oil available in the roll gap for roll gap lubrication is primarily predetermined by the cooling requirements and not by the current lubrication requirements in the roll gap. It must be assumed that, in the case of emulsion lubrication in the roll gap, the oil concentration will be well below 100%, resulting in a reduced lubricating action. In practice, this means that the rolling oil consumption is much higher than the amount of lubricant actually required for lubricating the roll gap. Selectively controlling the current lubrication and friction conditions is only possible to a limited extent in this manner, e.g. only via the oil concentration in the emulsion or via additives.
In WO 2005/115651 A1 it is therefore proposed to inject a base oil without water as a carrier medium into the roll gap. As the lubricant is applied to the stock before it enters the roll gap, an appropriate quantity of lubricant for an even application is necessary.
The object of the invention is to specify a reversing mill and an operating method for a reversing mill, wherein the rolling oil consumption can be further reduced while maintaining good roll gap lubrication.
This object is achieved by a reversing mill having the features set forth in claim 1 and by an operating method for a reversing mill having the features set forth in claim 5.
According to a basic insight of the invention, instead of the lubricant being supplied to the roll gap on the entry side, the stock is lubricated in a preceding operation during coiling. As a result, the lubricant is compressed and homogenized by the successive layers so that the quantity of lubricant can be further reduced. The even surface application of the lubricant ensures that, despite the small quantity of lubricant, the roll gap can be sufficiently lubricated. Viewed in the axial direction of the work rolls, the same friction conditions obtain. The stock therefore undergoes uniform deformation and heating. This has an advantageous effect on the surface quality of the rolled stock, as it has fewer chatter marks. As the flow of coolant is decoupled from the supply of lubricant, the lubrication can be better matched to the parameters of the rolling process. There is the added advantage that the coolant, e.g. water, can be supplied at a low temperature compared to emulsion lubrication, so that the heat removal is better.
This makes conventional roll lubrication on mill stand entry obsolete. According to the invention, the lubricating action is achieved via the pre-lubricated incoming metal strip. In general, the precursor material for a reversing stand comes from a pickling plant (continuous or push-pull picking line) in which the metal strips are lubricated after pickling for the purpose of corrosion protection. These lubricated strips enter the reversing stand as the input material for the first pass. After the first pass the metal strip is wound on a reversing reel acting as a coiler and—if another pass is to follow—is lubricated prior to winding.
In order to a achieve a maximally uniform lubricating action while minimizing lubricant consumption, it may be advantageous if the rolling oil is applied evenly over the entire width of the stock in the form of an atomized oil mixture. During winding, the individual layers of the metal strip come into contact and have a homogenizing effect on the rolling oil applied. The rolling oil thoroughly penetrates the peak-to-valley roughnesses of the stock and produces a good lubricating action for the subsequent rolling process.
In a preferred embodiment it is provided that the rolling oil is applied in a comparatively small quantity of less than 200 ml per minute, preferably in a range of approximately 50 to 100 ml per minute.
As the stock is rolled in any case with low reductions in the final pass, it may be advantageous if no rolling oil is applied to the stock prior to the final and/or prior to the penultimate pass. This enables the consumption of lubricant to be reduced still further, as the lubrication requirements are less in the final pass. For the final pass, the oil remaining on the metal strip from previous passes is usually enough to still provide a sufficient lubricating effect for a small thickness reduction.
For further explanation of the invention, reference will be made in the following section of the description to the accompanying drawings from which additional advantageous embodiments, details and further developments of the invention will emerge on the basis of a non-limiting example:
The rolls of the mill stand 2 are cooled using a coolant completely separate from the lubricant. In this example the coolant is pure water which is sprayed onto the rolls of the reversing stand 2 by means of a device 8, e.g. a row of nozzles. When the strip 5 has passed through the roll gap, it is wound onto a reversing reel 4 on the right-hand side of
Lubrication of the stock takes place in an operation preceding the rolling pass, with rolling oil being applied to the metal strip prior to winding. This is performed by a rolling oil applicator 6 which sprays the rolling oil 9 onto both the upper side and underside of the strip 5. As a result, the rolling oil adheres very well to the rough surface of the stock. The rolling oil can be a base oil that is provided with additives.
Particularly for a cold-rolling process it is important that the film of lubricant is all applied as uniformly as possible over the entire width of the path. A rolling oil applicator suitable for this purpose can be of different designs, e.g. an arrangement of a plurality of nozzles in the form a spray, nozzle or injector bar. In the following, such devices are assumed to be known and are not the subject matter of the present invention.
As is clear from the above, in the example described a rolling oil applicator 6 of this kind is disposed upstream of each reversing reel 3, 4, as each of the reversing reels 3, 4 operates alternately as a coiler or uncoiler depending on the respective direction of travel 7 of the metal strip 5; for the sake of simplicity, only the rolling oil applicator 6 that is active, i.e. in operation, in the operating state shown is depicted in
Thickness reduction in the subsequent rolling passes takes place in the normal manner for reversing stands whereby the stock is successively reduced in thickness in a back and forth motion in the roll gap between the work rolls. These passes of the cold rolling process are not shown in the drawings.
The final pass is depicted in
An essential advantage of the invention is that the amount of oil required for a cold rolling stand can be significantly reduced. As the lubricating and cooling media are separated, the quantity of lubricant can be adjusted as a function of process variables such as strip speed, rolling force, roll roughness, etc. This possibility of differentiated lubrication adjustment is greatly advantageous.
As the oil concentration is 100% in the roll gap, rolling forces and rolling torques can be reduced, thereby providing an overall energy saving.
As lubrication is separated from cooling, a comparatively low temperature coolant can be used, which improves the cooling effect. As a result, further savings can be made in terms of the amount of water required for cooling. By way of comparison, when using emulsion the emulsion temperature must not be below about 48° C., as otherwise fungal and bacterial growth would be promoted.
Advantageously, a metastable or even unstable rolling oil having a low emulsifier content is used. The metastable or unstable rolling oil can be very easily separated from the water and only water needs to be conditioned in the circulating line. It is possible to re-use the oil that has been separated from the water.
Altogether, both the rolling oil consumption and the quantity of coolant can therefore be reduced. The equipment complexity for conditioning the media for lubrication and cooling is comparatively lower, resulting in lower capital investment and operating costs.
Although the invention has been illustrated and described in detail by the above exemplary embodiment, the invention is not limited by the example disclosed and other variations can be deduced therefrom by the average person skilled in the art without departing from the scope of protection of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11179241.2 | Aug 2011 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/064651 | 7/26/2012 | WO | 00 | 2/4/2014 |
