Method for detecting an at least partly arched roller

Abstract

A method for detecting an at least partly arched roller in a continuous casting machine in which the machine includes a plurality of rollers forming upper and lower tracks and arranged substantially perpendicular to the longitudinal extent of the tracks, with the rollers being rotatably mounted in supporting members to transport elongated material produced in the machine. The method includes measuring the reaction forces resulting in the supporting members by counteracting the weight of the roller and the load from the material and any dynamic forces exerted by the material on the roller, with the measuring being made at least two times during a rotation of the roller and at at least one of the supporting members of the roller. The presence of an at least partly arched roller is established based on a considerable fluctuation of the reaction force value during a rotation of the roller.

Description

[0001] This application is based on and claims priority under 35 U.S.C. §119 with respect to Swedish Application No. 0101835-7 filed on May 23, 2001, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention generally relates to continuous casting machine. More particularly, the invention pertains to a method for detecting an at least partly arched roller in a continuous casting machine.

BACKGROUND OF THE INVENTION

[0003] A continuous casting machine produces steel material from molten steel. The steel material can be used for example as a starting material in rolling processes for producing sheet metal to be used in, for instance, vehicles.

[0004] In the continuous casting machine, molten steel flows from a ladle and down in a tundish from which it is transported further down into a mold. In the mold, which is water-cooled, the slab of continuous cast material begins to form a solid shell. Then, the slab is continuously transported in between two curved tracks, an upper track and a lower track, by a large number of rollers arranged in segments which continue to shape and cool the slab to the final thickness of the steel material. At the end of the tracks, the material is cut into suitable pieces. The cooling is achieved by spraying water onto the slab and the rollers.

[0005] The rollers of the continuous casting machine are mounted with their axes substantially perpendicular to the longitudinal extension or longitudinal extent of the curved tracks. To lead and support the slab of continuous cast material, the rollers are arranged in pairs, with each pair comprising an upper roller of the upper track and a lower roller of the lower track.

[0006] Further, the rollers are rotatably mounted in supporting members at each end of the rollers. Due to the length of the rollers, and thus the load on the rollers, the rollers are generally split into roller portions. These roller portions are either independently supported in supporting members or nonrotatably provided on a common shaft, with the shaft being supported in supporting members.

[0007] Preferably, to support the slab during the process, the rollers have a substantially axially straight profile. However, the rollers might not stay straight due to various factors.

[0008] For example, due to the high operational temperatures of the process, and the fact that the envelope or outer surface of the rollers is in rotational contact with the slab, the rollers can be deformed due to high local, thermal expansion.

[0009] This thermal expansion can become a serious problem if a slab stoppage occurs or if the speed of the process is slowed down for some reason, for example during a ladle or tundish changeover, as the normal cooling system cannot cool the rollers sufficiently at such an occasion. As a result, the temperature is considerably magnified in the portion of the roller in contact with the slab. This often leads to form deformations in the form of bulging and bending of the roller. That is, the roller adopts an at least partly arched shape. If the stoppage or the slow speed lasts for a considerable period of time, the roller can become permanently bent.

[0010] Secondly, it is also possible that the rollers can obtain an at least partly arched shape due to, for instance, the effect of abnormally high forces arising in the rollers during the process.

[0011] Unfortunately, a roller with such an arched shape can be disastrous to the process as the slab support will fluctuate during each rotation of the roller. When the slab comes in contact with the bulging portion of one or both of the two rollers in a pair, the slab will be temporarily bent, i.e., the middle portion of the slab will get squeezed between the upper roller and the lower roller of the track, at the same time as the side ends of the slab will experience less roller support or even loose contact with the roller. Moreover, when the bulging portion of the roller or rollers is directed away from the slab, the slab will more or less lack support from the roller. The amount of support is dependent on the solidification grade of the material in that if the material is almost entirely solidified it will be supported by the adjacent rollers and totally lack support from the arched shape roller. However, if the material still has a molten core, the middle portion of the slab will probably slacken towards the roller and gain some support from it.

[0012] As a result of the bending, cracks can arise in the material being cast, usually in the solidified portion of the slab. These cracks can be either internal cracks or surface cracks, both types of which can lead to decreased quality as a material having cracks will be almost impossible to roll.

[0013] Surface cracks can be treated by costly treatment after the casting process. One way of treating the surface cracks is to weld them and another way is to grind off the surface layer of the material. Both alternatives are expensive and because they cannot give a perfect result, the steel has to be classified in a lower quality class. Material with internal cracks cannot be treated, and will have to be discarded or classified in a lower quality class.

[0014] In substantially solidified material, a further problem can arise due to the squeezing and bending of the material. When the slab comes into contact with the bulge of the roller, the material is jammed, forcing any remains of the molten material away and when the bulge releases the slab, the molten material flows back. In this way, the point of solidification is displaced and molten material can be stuck in other locations than the original location. This can lead to irregularities in the slab surface and an uneven composition of the material in the center of the slab.

[0015] Furthermore, the forces exerted to the rollers and to the supporting members start fluctuating and each time the bulged portion of the roller comes in contact with the slab, the forces increase dramatically due to the addition of dynamic forces caused by the roll motion when the slab is squeezed. These forces can lead to roller and/or supporting member failures, especially if the slab is more or less entirely solidified. Such failures can lead to misalignments of the rollers, which in turn can lead to uneven stresses and cracks in the material being cast. Often, the rollers and/or supporting members have to be exchanged, which is expensive and requires a significant amount of time.

[0016] Therefore, a need exists for a way of detecting an at least partly arched roller in a continuous casting machine.

SUMMARY OF THE INVENTION

[0017] One aspect involves a method for detecting an at least partly arched roller in a continuous casting machine, wherein the continuous casting machine comprises a plurality of rollers forming upper and lower tracks and arranged substantially perpendicular to a longitudinal extent of the upper and lower tracks, with the rollers in the tracks being rotatably mounted in supporting members to transport elongated cast material produced in the machine. The method comprises measuring reaction forces in at least one of the supporting members of a roller which result from counteracting a weight of the roller and a load from the cast material and any dynamic forces exerted by the cast material on the roller, with the measurement of the reaction forces being made at least two times during a rotation of the roller. It is then established that the roller is an at least partly arched roller based upon considerable fluctuation of the reaction force during a rotation of the roller.

[0018] In accordance with another aspect, a method for detecting an at least partly arched roller in a continuous casting machine includes transporting elongated cast material between an upper track of rollers and a lower track of rollers in which the rollers of the upper track and the rollers of the lower track are arranged substantially perpendicular to a longitudinal extent of the upper and lower tracks, and with the rollers in the upper track and the rollers in the lower track being rotatably mounted in supporting members. The supporting members are subjected to reaction forces resulting from counteracting a weight of the roller and a load from the cast material and any dynamic forces exerted by the cast material on the roller. At least two times during a single rotation of at least one of the rollers the reaction forces are measured in at least one of the supporting members of the at least one roller. The method further includes determining a fluctuation in the measured reaction forces, and determining that the at least one roller is at least partly arched based upon the determined fluctuation in the measured reaction forces.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0019] The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawing figures in which like reference numerals designate like elements.

[0020] FIG. 1 is a schematic perspective view a set of rollers of a continuous casting machine.

[0021] FIG. 2 is a schematic front view of a roller in the lower track which possesses an arched shape illustrating the instant in which the bulging portion of the roller is directed away from the slab.

[0022] FIG. 3 is a view similar to FIG. 2 illustrating the instant when the bulging potion of the roller is pressing the slab in direction of the upper track so that the slab may become squeezed between the lower roller and the upper roller.

DETAILED DESCRIPTION OF THE INVENTION

[0023] FIG. 1 illustrates rows or pairs of rollers 10 of a typical section of a continuous casting machine having a top segment 12, an inside cooling chamber 14 and an outside cooling chamber 16. The pairs of the rollers 10 lead and support the slab 18 of a continuous length of continuous cast material. In the top segment 12, the slab 18 has a more or less liquid core. during feeding under continuous movement in the direction shown by the arrow, the slab 18 will solidify as it is cooled off by, for instance, water that is sprayed onto the slab 18 and the rollers 10.

[0024] Each of the rollers 10 is mounted with its axis substantially perpendicular to the longitudinal extensions of the two tracks constituted by an upper track 20 and a lower track 22. In the two tracks 20, 22, the rollers 10 are rotatably mounted in supporting members 24 at each end of each roller 10.

[0025] Generally, each of the rollers 10 is split or divided into roller portions 26. The roller portions 26 forming each roller are positioned axially adjacent or axially after each other. The roller portions 26 are either independently mounted in the supporting members 24 or are non-rotatably provided on a common shaft, with the shaft being mounted in supporting members 24. The supporting members 24 can, for instance, be rolling bearings, or sliding bearings with corresponding bearing housings.

[0026] An example of the present invention will be described with reference to FIGS. 2 and 3 in which a roller 30 has an at least partly arched shape due to heat transfer from the slab 18 during a stoppage of the machine. As mentioned above the cause of such a deformation can also be attributable to a considerable increase of forces in the rollers 10. However, the manner of detecting the at least partly arched roller 30 is similar irrespective of the cause.

[0027] The following example is explained in the context of only the lower track 22 of rollers 10 in a continuous casting machine. In addition, to simplify the example, the rollers 10 are not illustrated as being split into portions 26, although the invention is applicable to rollers split into roller portions.

[0028] In the continuous casting machine, the slab 18 of continuous cast material is transported along the upper and lower tracks 20, 22 of rollers 10 in the direction indicated by the arrow. The principle of the invention is that as long as the load distribution on a roller 10, and thus its supporting members 24, is equal to or within a predetermined load interval during one rotation of the roller 10, it is determined that no deformation such as the roller possessing an arched shape has occurred. If, however, such a deformation has occurred, the load on the roller 10, and thus on the supporting members 24, will fluctuate due to the fact that the slab 18 receives uneven support from the roller and dynamic forces arise which are caused by the roll motion when the material 18 gets squeezed. Thus, by measuring the reaction forces F in at least one of the supporting members 24 of a roller 10 at at least two times during a single rotation of the roller 10, it is possible to detect rollers 30 that are at least partly arched shape.

[0029] According to the method here, a measuring device 28 is provided in at least one supporting member 24 of each roller 10. This measuring device 28 is able to measure the reaction force F resulting in the supporting member 24 throughout the casting operation, by counteracting the weight of the roller 10 and the load from the slab 18 and any dynamic forces exerted by the slab 18 on the roller 10.

[0030] The example will now be more clearly described with reference to FIGS. 2 and 3, and the roller is fully denoted 30 as an at least arched roller. During the casting process, the measuring device 28 that is provided in at least one supporting member 24 of each roller 30 measures the reaction force F resulting in the supporting member 24 by counteracting the weight of the roller 30 and the load from the slab 18 together with any dynamic forces exerted by the slab 18 on the roller 30. This measurement is made at least two times during a rotation of the roller 30, but preferably the measurement is made more often to obtain a more reliable result. As long as the values of the force F in one supporting member 24 is equal to or within a predetermined load interval, it can be established that no deformation or substantially no deformation has occurred, and the slab 18 is correctly supported by the roller 30.

[0031] If the machine has to be stopped or if the transportation speed has to be slowed down for some time, the heat transfer from the slab 18 to the rollers 30 will implacably increase. As a result, the temperature is considerably magnified in the portion of the roller 30 that is in contact with the slab. This often leads to form deformations in the form of bulging and bending of the roller 30. That is, the roller adopts an at least partly arched shape. If the stoppage or the slow speed lasts for a considerable period of time, the roller 30 can become permanently bent.

[0032] In such a situation, the value of the reaction force F in the supporting members 24 will now start to fluctuate during rotation of the roller 30. In one instant of the rotation as illustrated in FIG. 2, the bulging portion of the roller 30 will be directed away from the slab 18. The slab 18 will then more or less lack support from the roller 30 and the reaction force F resulting in the supporting member 24 will have a value that is equal to the weight of the roller 30 or close to such weight. The amount of support is of course dependent on the solidification grade of the material 18. That is, if the material 18 is almost entirely solidified, it will be supported by the adjacent rollers 10 and totally lack support from the arched roller 30. However, if the material 18 still has a molten core, the middle portion of the slab 18 will probably slacken towards the roller 30 and gain some support from it.

[0033] After further rotation of the roller 30, the slab 18 comes into contact with the bulging portion of the roller 30 as shown in FIG. 3. Here, the slab 18 will be temporarily bent in that the middle portion of the slab 18 will get squeezed between the upper roller and the lower roller of the tracks 20, 22 while at the same time the side ends of the slab 18 will get less roller support or even loose contact with the roller 30 depending on the solidification grade of the material. The squeezing effect, which results in the addition of dynamic roll motion forces, will considerably increase the value of the reaction force F in the supporting member 24.

[0034] By comparing the reaction force values F in a supporting member 24 during a rotation of the roller 30, it will be evident that the value is considerably fluctuating, with the fluctuation being greater than a predetermined fluctuation value. If the measurement is made continuously during successive rotations of the roller 30, the fluctuation pattern will be even more visible. Thus, the presence of an at least partly arched roller 30 can be established through determination of a considerable fluctuation of the load value on the supporting members 24,

[0035] It can be appreciated that because an at least partly arched roller 30 causes quality problems to the material 18 being cast, it is advantageous to be able to detect or determine the presence of an at least partly arched roller 30 so that such roller can be exchanged as soon as possible.

[0036] In the description set forth above, an example of the invention has been described in which the detection of an at least partly arched roller 10 is relatively simple to perform. However, in complex systems with several roller portions 26 in each roller 10, the detection of at least partly arched rollers 30 is carried out by “recognition” of load/force patterns by using suitable mathematical methods. These mathematical methods will not be explained in detail here as they would be known to the ordinarily skilled artisan.

[0037] The principles, preferred embodiment and modes of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiment disclosed. Further, the embodiment described herein is to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.

Claims

1. Method for detecting an at least partly arched roller in a continuous casting machine, wherein the continuous casting machine comprises a plurality of rollers forming upper and lower tracks and arranged substantially perpendicular to a longitudinal extent of the upper and lower tracks, with the rollers in the tracks being rotatably mounted in supporting members to transport elongated cast material produced in the machine, the method comprising: measuring reaction forces in at least one of the supporting members of a roller which result from counteracting a weight of the roller and a load from the cast material and any dynamic forces exerted by the cast material on the roller, the measuring of the reaction forces being made at least two times during a rotation of the roller; and establishing that the roller is an at least partly arched roller based upon fluctuation of the reaction force during a rotation of the roller.

2. Method according to claim 1, wherein the supporting member is a rolling bearing.

3. Method according to claim 1, wherein the supporting member is a sliding bearing.

4. Method according to claim 1, wherein the at least one supporting member comprises a measuring device.

5. Method according to claim 1, wherein the roller is split into two roller portions.

6. Method for detecting an at least partly arched roller in a continuous casting machine, comprising: transporting elongated cast material between an upper track of rollers and a lower track of rollers in which the rollers of the upper track and the rollers of the lower track are arranged substantially perpendicular to a longitudinal extent of the upper and lower tracks, and with the rollers in the upper track and the rollers in the lower track being rotatably mounted in supporting members, the supporting members being subjected to reaction forces resulting from counteracting a weight of the roller and a load from the cast material and any dynamic forces exerted by the cast material on the roller; measuring at least two times during a single rotation of at least one of the rollers the reaction forces in at least one of the supporting members of the at least one roller; determining a fluctuation in the measured reaction forces; and determining that the at least one roller is at least partly arched based upon the determined fluctuation in the measured reaction forces.

7. Method according to claim 6, wherein the supporting member is a rolling bearing.

8. Method according to claim 6, wherein the supporting member is a sliding bearing.

9. Method according to claim 6, wherein the at least one supporting member comprises a measuring device.

10. Method according to claim 6, wherein the at least one roller is divided into two roller portions arranged axially adjacent one another.

11. Method according to claim 6, wherein the roller is split into two roller portions.