The invention concerns a device for producing a metal strip by continuous casting with a casting machine in which a slab is cast, where at least one milling machine is installed downstream of the casting machine in the direction of conveyance of the slab, at least one surface of which and preferably two opposite surfaces of which can be milled down in the one or more milling machines, and where means for cooling a milling cutter are provided in or on the milling machine.
In the continuous casting of slabs in a continuous casting installation, surface defects can develop, for example, oscillation marks, casting flux defects, or longitudinal and transverse surface cracks. These occur in both conventional and thin-slab casting machines. Therefore, the conventional slabs are subjected to flame descaling in some cases, depending on the intended use of the finished strip. Many slabs are subjected to flame descaling as a general rule at the customer's request. In this connection, the requirements on surface quality have been continuously increasing in thin-slab installations.
Flame descaling, grinding, and milling are available methods of surface treatment.
Flame descaling has the disadvantage that the material that has been flashed off cannot be melted down again without processing due to the high oxygen content. In the case of grinding, slivers of metal become mixed with the grinding wheel dust, so that the abraded material must be disposed of. Both methods are difficult to adapt to the given conveyance speed.
Therefore, surface treatment by milling must be considered. The hot millings are collected during the milling operation. They can then be briquetted and melted down again without any problems and thus returned to the production process. Furthermore, the miller speed can be easily adjusted to the conveyance speed (casting speed, feeding speed into the finishing train). The device of the aforesaid type that constitutes the object of the invention thus involves the use of milling.
A device of the aforementioned type is disclosed by EP 0 881 017 A, which provides that the milling cutters are cooled by water to enable them to withstand the high temperatures of the strand that is to be milled. However, the cited document fails to provide more comprehensive directions or specific information regarding the design of the milling cutter cooling system.
Other solutions are described in US 2003/223831, U.S. Pat. No. 5,073,694 A, and U.S. Pat. No. 3,702,629 A.
Another device of a similar type with a milling machine arranged downstream of a continuous casting installation is already known from CH 584 085 and DE 199 50 886 A1.
Another similar device is also disclosed by DE 71 11 221 U1. This document discloses the processing of aluminum strip with utilization of the casting heat, in which the machine is connected with the casting installation.
In-line removal of material from the surface of a thin slab (flame descaling, milling) shortly before a rolling train on the upper side and underside or on only one side has also already been proposed. EP 1 093 866 A2 is cited in this connection.
DE 197 17 200 A1 discloses another embodiment of a surface milling machine. This document describes, among other things, the adjustability of the milling contour of the milling device, which is installed downstream of the continuous casting installation or upstream of a rolling train.
Another embodiment and arrangement of an in-line milling machine in a conventional hot strip mill for treating a near-net strip are proposed by EP 0 790 093 B1, EP 1 213 076 B1, and EP 1 213 077 B1.
In the surface treatment of thin slabs in a so-called CSP plant, about 0.1-3.5 mm should be removed from the surface on one or both sides of the hot slab in the processing line (“in line”), depending on the surface defects that are detected. A thin slab that is as thick as possible is advisable (H=60-120 mm) so as not to diminish the output too much.
The surface treatment and the equipment needed to carry it out are not limited to thin slabs but rather can also be used in line downstream of a conventional thick-slab casting installation as well as for slabs cast with a thickness greater than 120 mm up to 300 mm.
The in-line milling machine is not usually used for all products of a rolling program but rather only for those that have relatively high surface requirements. This is advantageous from the standpoint of output, reduces milling machine wear, and therefore is useful.
It has been found that the service life of the milling cutter or cutters with which the surface of the slab is milled in the milling machine, i.e., the length of time that the milling cutter or cutters can be used, is not always satisfactory. This is related to the relatively high material stress to which the material of the cutter edge is subjected during the machining of the hot slab.
Therefore, the objective of the present invention is to improve a device for producing a metal strip by continuous casting with the use of a casting machine in such a way that the aforementioned disadvantages are avoided. In other words, the goal is to create a device with which the milling tool or tools are protected, even when used for prolonged periods of time in the machining of hot slabs, so that longer service lives can be realized.
The solution to this problem by the invention is characterized by the fact that a collecting device for cooling medium is arranged near the milling cutter. The collecting device has a cover that covers the milling cutter on one side. Various embodiments are provided for this purpose:
The means for cooling the milling cutter can be realized as nozzles, with which a cooling medium can be applied to the area of the cutting surfaces of the milling cutter, preferably over the entire width. In this regard, the nozzles can be arranged in such a way that they apply the cooling medium to the milling cutter at a point some distance from the slab. This makes it possible to prevent excessive cooling of the slab. The cooling medium can be collected in a collecting device.
Alternatively or additionally, the milling cutter can have at least one internal cooling medium supply bore that leads to the region of the cutting surfaces. In this regard, the milling cutter can have a concentric supply bore, from which at least one additional supply bore leads to the region of the cutting surfaces.
In order to cool the slab as little as possible by cooling medium, since cooling of the slab is often a disadvantage, a collecting device for cooling medium can be arranged near the milling cutter. This device can have a collecting trough for cooling medium. As explained above, the collecting device has a cover that covers the milling cutter on one side. In this regard, the cover can have a semicircular design as viewed in the direction of the axis of rotation of the milling cutter. Furthermore, in one modification, it is provided that a collecting trough is located in the upstream and/or downstream end region of the cover with respect to the direction of conveyance.
Another alternative of the idea of the invention provides that the means for cooling the milling cutter are designed as a ventilator or a blower.
To be able to use liquid cooling medium but prevent the slab from cooling, another alternative or additional embodiment of the invention provides that the means for cooling the milling cutter are designed as bores, by which a cooling medium is conveyed through the inside of the milling cutter.
Means for conveying the liquid cooling medium are preferably present in a closed system. In this regard, it is especially preferred that the cooling medium be integrated in the circulation of the cooling system of the whole plant.
The cooling medium can be water, an oil-water emulsion, air, spray mist, or water vapor.
Means for adjusting the temperature distribution over the thickness of the slab and/or for cleaning the surface of the slab can be installed immediately upstream of the milling machine in the direction of conveyance. These means can be nozzles for applying a fluid to the slab.
One milling cutter each is usually installed for treating the upper side and the underside of the slab. Each milling cutter can cooperate with a support roll arranged on the other side of the slab. A rolling train is usually installed downstream of the milling machine in the direction of conveyance.
In accordance with a modification, both means for cooling the milling cutter from the outside and means for cooling the milling cutter from the inside are provided.
Preferably, it is provided that the means for cooling the milling cutter are designed for undercooling the surface of the slab shortly before the milling process.
The means for cooling the milling cutter can be designed in such a way that different amounts of coolant can be applied to the upper side and the underside of the slab.
One milling cutter each can be installed for machining the upper side and the underside of the slab.
A descaling sprayer can be installed between the milling machine and a downstream rolling stand. In this regard, in a preferred embodiment, the descaling sprayer is configured as a single row of sprayers.
The method for producing a metal strip by continuous casting with a device of the type explained above is characterized by the fact that the slab temperature is measured on the upper side and/or underside of the slab upstream and/or downstream of the milling machine, where the amount of coolant with which the slab is cooled is determined with a process model operated in a machine control unit as a function of the measured temperatures.
In this regard, in accordance with a refinement of the invention, the cooling of the slab can be carried out on the upper side and the underside of the slab.
An alternative embodiment of this method provides that the slab is cooled, and the amount of coolant for cooling the slab is determined with a process model operated in a machine control unit, where the process model determines the amount of coolant as a function of the volume of material milled from the slab.
The determination of the amount of coolant can be made by additionally considering the slab conveyance speed and/or the temperature of the surface of the slab and/or the type of material of the slab.
The proposed solution makes it possible to realize a significant reduction of the thermal load on the cutting tool. Hence, it is possible to realize significantly longer service lives than in conventional milling machines used for the specified application. Even when used for prolonged periods of time, the milling tool is protected from the high slab surface temperature in the hot rolling process, and this produces the specified advantage. Long service lives of this type were not previously attainable, because only the usual lubricating emulsion or lubricating oil was used during milling.
Specific embodiments of the invention are illustrated in the drawings.
a shows a side view and
b shows a front view of a transverse section of a cooled milling cutter in another embodiment of the invention.
a shows a side view of a milling cutter with a collecting device for cooling medium in an alternative embodiment to that of
b shows a variant of
a shows a side view and
b shows a front view of a transverse section of a cooled milling cutter in another embodiment of the invention.
Downstream of the furnace 21 and the transverse conveyor 22, the slab 3 enters a milling machine 4. In the present case, two milling cutters 6 are installed in the milling machine 4 some distance apart in the direction of conveyance F for milling the lower surface and the upper surface, respectively, of the slab 3. The corresponding opposite surfaces of the slab 3, i.e., the upper side and the underside of the slab, respectively, are supported by support rolls 18.
A descaling system 39 is located downstream of the milling machine 4 and in the present case comprises a single-row descaling sprayer above the slab and another below the slab. It is followed by a rolling train, which in the present case comprises the rolling stands 23 and 24.
A collecting tank 25, in which material that has been removed by milling is collected, is located under the milling machine 4.
As can be seen in
It can be seen that spray nozzles 7 can be arranged in such a way that the cutting surfaces 8 of the milling cutters 6 can be directly sprayed. However, as will be seen later, it can also be provided that cooling medium is delivered directly onto the slab 3, so that in this respect the milling cutters 6 are cooled indirectly. Both possibilities are illustrated in
As is indicated by position 26 in
In addition, the solution illustrated in
In the solution according to
In the solution according to
The cooling medium basically cools not only the milling cutter 6, as desired, but also the slab 3, which in some cases is not desired. To realize optimization in this respect, the embodiment of the invention shown in
In the embodiment illustrated in
a and 8b show a solution that is simpler but in many cases adequate. In this case, a simplified collecting device 11 is provided, which consists of a piece of sheet metal that is bent in such a way that a collecting trough 12 is formed. In the illustrated embodiment, it is provided that the means 5 for cooling are again realized as nozzles 7, which direct a jet of cooling medium over the whole width of the milling cutter 6. Depending on the arrangement and orientation of the nozzle 7 and of the jet of cooling medium, the collecting device 12 can be located downstream (
a and 10b show another alternative embodiment of the cooling of the milling cutter 6. This embodiment again takes into account the fact that it can be undesirable for the slab 3 to be cooled to an excessive degree by cooling medium. Therefore, this solution provides that a number of bores 15 run in the axial direction inside the milling cutter 6. Cooling medium is conveyed through these bores to cool the milling cutter 6. As in the embodiment illustrated in
The ideas of the invention in this respect can be summarized in the following way:
During prolonged use, the milling cutter 6 is subject to high thermal stress during the hot rolling process. Cooling is advantageous, so that the plain milling cutter, the bearings, etc., do not become too hot. Accordingly, in one embodiment of the invention, in order to protect the milling tool 6 from the high surface temperature of the slab during prolonged in-line processing, the surface of the strip is cooled shortly before the engagement of the milling cutters, which results in a reduction of the heat flux into the cutting edges of the milling cutters.
In addition, the plain milling cutter is shielded from the hot surface. In the case of IF steel or ULC steel, a target temperature at the surface that corresponds to the transformation temperature is aimed at for the short milling operation. It is expected that the material will temporarily experience thermal softening and that this will lead to lower deformation stress and thus lower cutting edge stress.
The rotating cutting surfaces 8 of the milling tool 6 are sprayed with lubricant (oil mist, oil-water mixture, etc.) in order to reduce the cutting force and thus increase the service life of the milling tool. However, in contrast to the prior art, the lubricant is not applied to the hot strip (as is customary in cold milling) but rather is sprayed onto the cutting edge, to which the oil adheres and later acts during the cutting process.
To avoid milling off of the hard layer of scale and thus to increase the service life of the cutting edges of the milling cutter, a (low-pressure) descaling of the surface (see reference number 17 in
The amounts of water delivered by the cooling and cleaning spray bars can be separately adjusted above and below in order to combat or prevent transverse camber of the slab.
Suction devices for cuttings, deflecting devices for cuttings, or areas for flushing out cuttings (collecting hoppers, deflecting plates, suction pipes, lateral sprayers, strippers on the strip, etc.) are provided upstream and downstream of a given milling cutter 6 to make it possible for the milling cutter 6 optionally to carry out downcut milling and upcut milling.
To allow the advantageous option of avoiding cooling of the slab 3 during the cooling of the milling cutter 6, the plain milling cutter 6 can be cooled internally. The cooling water is preferably supplied from one end through a rotating joint; the outlet at the opposite end is designed open, so that the water can drain freely at the end into a sintered channel.
In the case of external cooling of the milling cutter, the cooling water falls onto the slab, especially on the upper side of the slab. To avoid an undesired cooling effect on the slab, the water can be collected in a channel. In this case, cooling water is sprayed tangentially onto the cutting edges of the milling cutter and collected in the channel arranged on the downstream side, so that it can run off laterally next to the strip into the sintered channel.
In the case of relatively low thermal loads, air cooling is also possible for external cooling of the plain milling cutter 6. This type of cooling can also be combined with water cooling of the bearing of the plain milling cutter.
The amount of cooling medium for the milling cutter 6 is controlled as a function of the milling removal or the volume of milled cuttings.
Some especially advantageous design features should be additionally noted:
As
In addition, as shown in
Number | Date | Country | Kind |
---|---|---|---|
10 2006 024 586.5 | May 2006 | DE | national |
10 2007 022 929.3 | May 2007 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2007/004579 | 5/23/2007 | WO | 00 | 1/26/2009 |