Descaling rolled material

Abstract: When a strip (2) of e.g. hot steel is rolled by a rolling or roughing mill, scale develops on the surface of the strip (2) which must be removed. The strip (2) is passed over a bending roller (5) which bends the strip (2) and causes cracks in the scale. Then water is injected (11) on to the strip (2) to wash the roller (5) to lift off the scale. Inertia then causes the water and scale to leave the surface of the strip (2) and pass to a collection means (12) whose water collecting surface (14) is out of contact with the strip (2) and on the opposite side of the bending roller (5) from the water injection (11). In this way the time of contact of the water with the strip can be kept short and the strip is not damaged by contact with the collection means (12). A further bending roller (6), water injection means (15), and collection means (16) may be provided to remove scale from the other side of the strip (2).

Description: The present invention relates to the descaling of rolled material (for example, steel) which may be produced by e.g. a hot strip rolling mill. The present invention relates to both method and apparatus aspects of descaling. It is well known to use a hot strip rolling mill to produce rolled material. A conventional hot strip rolling mill is shown in Figure 7 of the accompanying drawings, in which the material passes first through roughing mills 50, which provide preliminary milling, and finishing mills 51 which complete the milling. On material entry side of the roughing mills 50, and also on the material entry side of the finishing mills 51, are descaling headers 52, the purpose of which is to remove scale from surface of the rolled material as will be described subsequently. As illustrated in Figure 7, there are a pair of the descaling headers 52 arranged at the entry side of the finishing mills 51, which together with rollers pinch 54 and 55 form a descaling device 53, which is shown in Figure 8. In the descaling device 53, a strip 56 of the hot rolled material passes between the pinch rollers 54,55, and between the descaling headers 52. Figure 8 also illustrates that the descaling headers 52 arranged adjacent table rollers 57, and water collecting devices each provided with a water collecting plate 58, arranged above the table rollers 57. Water pressurised to about 100 to 150 kg/cm2 is injected from the descaling headers 52 on to the strip 56 of rolled material, which loosens the scale on the strip 56. Water and scale on the upper surface of the strip 56 is then collected by the water collecting devices 58. However, as illustrated in Figure 7, there may be as many as six or seven finishings mills 51 in a hot strip mill, and therefore the thickness of the strip of hot rolled material at the entry side of the series of finishings mills 51 is relatively large, for example about 20 to 30 mm. Recently, however, "mini" hot strip mills have been developed in which the length of the rolling line is shortened so as to minimise the apparatus necessary. In such a mini hot strip mill, the thickness of the strip of rolled material at the entry side of the finishing mill is relatively small, e.g. about 8 to 15 mm, and the number of finishing mills is only three or four. The rolling speed is relatively low because there is a direct connection to a continuous casting machine. The descaling device shown in Figure 8 was developed for a standard hot strip mill, such as that shown in Figure 7, and it is thought that if it is applied to a mini hot strip mill, operating at low speed, there will be a large temperature drop in the rolled material due to the injection of a large amount of water at high pressure. Since this occurs before the finishing mills, the cooling may make rolling more difficult, or impossible, and the reduction in temperature will inevitably increase the production costs. It is necessary for the descaling device shown in Figure 8 to inject water at high pressure in order to remove scale as discussed above, but little thought is given to what happens to the water after that. In a conventional hot atrip rolling mill, the thickness of the rolled material means that the problem with temperature reduction is not acute, but in a mini hot strip mill, the fact that the water remains in contact with the rolled material, and because the water collecting efficiency and water leaks from the space between the rolled material and the water collecting plates, then excess cooling is likely to occur. There is the further problem that the water collecting plates 58 contact the rolled material, and flaws may thereby be generated, particularly in the case where the rolled material is thin such as when the material is being rolled by a mini hot strip mill. An alternative method of removing scale from a hot rolled material uses a wire brush, instead of a descaling header which injects water under pressure, and an example of such an arrangement is shown by JP-U-60-71416. The use of a wire brush roller to remove scale does not suffer from the disadvantage of causing a substantial reduction in the temperature of the rolled material but it is found that it is difficult to achieve efficient scale removal, due to abrasion and deformation of the wire brush forming the roller that removes the scale. It is therefore necessary frequently to exchange the wire brush in order to maintain efficiency, and this creates a disadvantage in cost. It is also known to inject water under pressure from the descaling headers onto a part of the rolled material in contact with a bending tool, such as rollers, so that the bending opens cracks in the scale so that the water can enter those cracks and so assist in the scale removal. Examples of such an arrangement is shown in JP-A-55-5156 and JP-A-61-269925 whereby the latter document discloses the combination of features according to the pre-characterising parts of the independent claims. In each of these documents, it is important to note that the water is injected at the point of bending. However, where the rolled material is bent and presurised water injected, effective descaling can be achieved at lower pressures than the standard method as discussed with reference to Figs. 7 and 8, but removal of injected pressurised water is not considered in either of these prior art documents so it remains on the roller material. As a result, in a mini hot strip mill, there can be a significant temperature drop in the rolled material. JP-A-63-183714 discloses an arrangement in which water is injected on a strip and is then collected by a collection means which has a water reception surface in contact with the strip. The water is injected onto a straight part of the strip. The present invention seeks to overcome, or at least ameliorate, the problems associated with the known descaling devices discussed above. According to a first aspect of the present invention a descaling device for a strip of material comprising: means for bending said strip with at least one bending roller at a predetermined point; and a water injection device for injecting water onto said strip; wherein: said water injection device is arranged to inject said water at a further predetermined point spaced from said predetermined point on one side of said predetermined point; and the device includes collection means for collecting said water, said collection means having a water reception surface located adjacent but spaced from said strip said water reception surface being on the opposite side of said predetermined point from said further predetermined point and being positioned to intercept a line extending beyond said predetermined point in a direction opposite to the path of travel of said strip followed after said predetermined point. According to a second aspect of the present invention a method of descaling a strip of material comprising: injecting water onto said strip of material; and bending said strip at a predetermined point with a bending roller; wherein: the water is injected onto the strip of material at a further predetermined point spaced from said predetermined point on one side of said predetermined point; and water which has been separated from said strip is collected by a collection means on the opposite side of said predetermined point from said further predetermined point, and having a collecting surface positioned to intercept a line extending beyond said predetermined point in a direction opposite to a path of travel of said strip followed after said predetermined point. In the present invention, the surface of the rolled material opposite to the bending tool (normally a bending roller) is put under tension and therefore small cracks are generated on the layer of scale on the surface of the rolled material. A part of that scale is exfoliated and lifted, and therefore pressurised water can remove the scale with only a small force being needed. As a result, the pressure and amount of water can be reduced, as compared with the known arrangements. Furthermore, since the water is injected at a point spaced from the point of bending, and is directed towards the point of bending water that is on the surface of the roller material will leave that surface at the point of bending due to inertia, and therefore can be efficiently collected by the water collecting device on the opposite side of the bend. As a result, the length of rolled material which is in contact with the water can be kept small. In prior art arrangements in which water is injected at the point of bending, some water inevitably remains on the rolled material after that bend. Since inertia causes the water to leave the surface of the rolled material, and unlike other prior art arrangements, the water collection surface is spaced from the rolled material which prevents contact damage to that surface. That water collection surface should also be close (e.g. 100 mm) to the point of bending. Since the pressure and the amount of water, and the length of time which that water is in contact with the rolled material is small, as compared with the known arrangements, there is no significant temperature drop in the rolled material. As a result, if it is used to form part of a descaling device on the entry side of finishing rollers in a mini hot strip mill, the efficiency of the rolling can be maintained. Preferably, means are provided for withdrawing the bending means (bending roller) and the water collection device from adjacent the strip of rolled material. This feature may be developed further, in arrangements of the present invention in which two descaling devices are provided, to remove scale from opposite surfaces of the strip of rolled material. In this case, the bending device (bending roller) of one descaling device and the water collection device the other descaling device may be interconnected so that they may simultaneously be withdrawn from the strip of rolled material. Embodiments of the invention will now be described in detail, by way of example, with reference to the accompanying drawings in which: Figure 1 shows a descaling device according to a first embodiment of the present invention; Figure 2 shows the descaling device of Figure 1 in a non-operative position; Figure 3 shows the positioning of a descaling device according to Figs. 1 and 2 in a rolling mill; Figure 4 shows a descaling device according to the present invention mounted in an alternative position in the rolling miller Figure 3; Figure 5 shows a second embodiment of a descaling device according to the present invention; Figure 6 shows a part of a further embodiment of the present invention, being a variation of that shown in Figure 5; Figure 7 shows a known rolling mill and, as has already been described; and Figure 8 shows a known descaling device, and again has already been described. Referring first to Figure 1, a descaling device 1 being a preferred embodiment of the present invention has an inlet pinch roller 3 and an outlet pinch roller 4 through which a strip 2 of hot rolled steel is passed. Between the inlet pinch roller and the outlet pinch roller 4 are an inlet bending roller 5 and an outlet bending roller 6 which act as bending devices for bending a strip 2 of rolled steel. The lower rollers of the inlet pinch roller 3 and the outlet pinch roller 4 are fixed, and the upper rollers are supported by cylinders 7 and 8, respectively, so that they can be raised or lowered. Similarly, bending rollers 5 and 6 are supported by cylinders 9 and 10 respectively, so that they can be raised and lowered. As shown in Figure 1, the inlet bending roller 5 can be raised slightly higher than the "nips" between the pinch rollers 3 and 4, so that the rolled steel strip 2 passing over it is bent, and tension is generated on the upper surface of the strip 2. Similarly, the outlet bending roller 6 is a little lower than the horizontal line between the "nips" between the pinch rollers 3 and 4 so that the rolled steel strip 2 is bent downwardly and tension is generated on the lower surface of the strip 2. An upper descaling header 11 for injecting pressurised water on to the surface of the strip 2 is placed on the exit side of the bending roller 5, and an upper water collecting device 12 having a water collecting surface 13 which extends to a leading 14 immediately adjacent, but spaced from, the strip 2 is positioned on the entry side of the roller 5. Similarly, a lower descaling header 15 and a lower water collecting unit 16 (with water collecting surface 17 having leasing edge 18) is provided on opposite sides of the bending roller 6, exactly as header 11 and collecting device 12, but on the opposite side of the strip. The headers 11,15 are arranged to inject water onto the strip 2 in a direction towards the corresponding bending roller 5,6. As illustrated in Figure 1, the water collecting devices 12 and 16 have a spiral cross-section from their leading edges 14, 18, terminating in curved parts 19, 20 which receive the water, and lead to an outlet. That outlet is not shown in the case of the water collecting unit 12, but is shown at 21 for the water collecting unit 16. A plurality of guides 22 and projections 23 are arranged adjacent the strip 2, those guides 22 and projection 23 which are positioned at the front and rear of the bending roller 6 being connected to a supporting body 24 of that bending roller 6, so that they can be raised and lowered with that bending roller 6 by cylinder 10. A cover (not shown) may be located above the inlet and outlet bending rollers 5 and 6 respectively. When the strip 2 of hot rolled steel is first sent to the descaling device 1, the pinch rollers 3 and 4 are opened as shown in Figure 2, and the bending rollers 5 and 6 are respectively lowered and raised to their withdrawn positions, so that the strip 2 may pass directly through the descaling device in the direction of arrow A. In the position shown in Figure 2, it can be seen that the guides 22 and projections 23 are also raised, so that they provide a guide for the strip 2. Then, the pinch rollers 3 and 4 are closed immediately after the tip of the strip 2 has passed the outlet pinch rollers 4, and then the bending rollers 5 and 6 are respectively raised and lowered by cylinders 9 and 10 to their working positions shown in Figure 1, in which the strip 2 is bent at those bending rollers 5 and 6. Pressurised water is then injected from the descaling headers 11 and 15, to mix with the scale, and the mixture of water and scale is collected by the water collecting devices 12 and 16. The cover prevents spray from scattering into the rest of the system. It should be noted that the pressurised water is injected immediately after the bending of the strip 2 of rolled steel, since then the tension created on the surface of the strip 2 opposite to the bending rollers 5 and 6 generates small cracks which are exfoliated and lifted by the water. Since that tension assists in this operation, the pressure of the water need not be large, and the amount of water injected can be less than in the known arrangement discussed with reference to Fig. 8. However, the pressure must be sufficient to ensure that water flows towards the bent part of the strip 2 (i.e. in the opposite direction to movement of the strip 2) so that its inertia causes it to separate from the strip 2 at the bend. Hence, the length of strip 2 over which the water is in contact can be kept short, and by placing the leading edge 14, 18 of the water reception surface of each collection device 12, 16 close to the point of bending (e.g. within 100 mm) substantially all the water can be collected. Therefore, in this preferred embodiment, the pressure and amount of water injected from the descaling headers 11 and 15 is small, and the time of contact of water with the strip 2 is short, and therefore any temperature drop in the strip 2 (assuming that strip 2 is hot rolled steel) can be kept small, even if the strip 2 is moving at low speed. Furthermore, as the pressure and amount of water is reduced, the cost can also be reduced. It can also be seen that as the leading edges 14, 18, of the water collection surfaces of the water collecting devices 12 and 16, are spaced from the strip 2, flaws in the rolled steel due to contact can be prevented. It can also be seen in Figure 1 that the inlet roller 5, the descaling header 11 and the water collecting device 12 form a unit, as does the outlet bending roller 6, the descaling header 15 and the water collecting units 16. If scale exfoliated by bending reaches the next bending roller, the scale is forced into contact with that roller and the scale may be forced back into the strip 2 due to contact pressure generated between the roller and strip. This reduces the descaling performance. Therefore, it is important that the inlet bending roller 5, and the associated header 11 and collection device 12 remove scale from the upper surface before it reaches the outlet bending roller 6, so that the above problem can be eliminated. Figure 3 shows the application of the descaling device of Figure 1 and 2 to a mini hot strip mill. A strip of hot steel is produced by a rapid casting machine 30 and passes to a roughing mill 31, so that it has a thickness of about to 40 mm. In this state it is passed between coilers 32, 33 on opposite sides of the roughing mill 31, and passed repeatedly between those coilers 32, 31, and hence the roughing mill 31 until it has been rolled to a suitable thickness. Then, the strip passes to a finishing mill 34 and then to a final coiler 35. In the arrangements shown in Figure 3, the descaling device 1 according to the present invention is arranged on the entry side of the finishing mill 34. The thickness of the strip of hot rolled steel at this point is relatively thin, e.g. about 8 to 15 mm, but even with a thicker material, effective scale removal with a small temperature drop can be achieved. Therefore, the strip of hot rolled steel reaches the finishing mills 34 at a sufficiently high temperature to achieve suitable milling. The arrangement illustrated in Figure 3 shows the descaling device 1 positioned on the entry side of the finishing mill 34. It is also possible to mount the descaling device 1 between the roughing mill 31 and one of the coilers 32 or 33, as is illustrated in Figure 4. In that Figure only the key features of the descaling device are illustrated; other features may be the same as the embodiment shown in Figure 1 and 2. In the descaling device 1 shown in Figure 4, the strip 2 passing from the coil 33 is bent around a first bending roller 35, and water is injected onto the strip 2 from a first descaling header 36. The water from that descaling header passes to a water collection device 37. Similarly, the strip 2 is bent in the opposite direction by a second bending roller 38, water is injected via a second descaling header 39, and that water is collected by a second collection device 40. The assembly formed by each collection device 35, 38, corresponding descaling header 36, 39, and the corresponding water collection device 37, may be structurally similar to that shown in Figs. 1 and 2. However, as illustrated in Figure 4, at least one bending device may be formed from a pinch roller, comprising the bending roller 35 and a further roller 41. Rollers 42 illustrated in Figure 4 are guide rollers as the strip 2 passes from the casting machine 30 to the roughing mill 31, prior to being wrapped around coilers 32 and 33. Another embodiment of the invention will now be described with reference to Figs. 5 and 6. The descaling device shown in Figs. 5 and 6 is generally similar to that shown in Figs. 1 and 2, except that the inlet bending roller 5a is fixed and only the outlet bending roller 6 can be raised and lowered. In this embodiment, the upper water collecting device 12a, which operates in conjunction with the bending roller 5a and descaling header 11, is connected to the outlet roller 6 through a frame 40. When the outlet roller 6 is lowered, not only does it bend the strip 2 round itself, but also causes the strip to bend around the inlet bending roller 5a, so that a similar effect to the embodiment of Figs. 1 and 2 can be achieved. Furthermore, since the outlet bending roller 6 and the water collection device 12a are interconnected by the frame 40, they can be raised and lowered by a common cylinder 41. In this embodiment, it is not necessary to raise or lower the inlet roller 5a, and therefore the mechanism is more simple than the embodiment of Figs. 1 and 2. The roller arrangement shown in Figure 5 may be modified as shown in Figure 6, with a fixed roller 42 between the outlet bending roller 6 and the outlet pinch roller 4. This simplifies the passage of the strip 2 of hot rolled steel, hence the bending at the pinch roller 4 is reduced. Again, as in the embodiment in Figs. 1 and 2, the bending rollers 5a and 6 are held in the position shown in Figure 5 when the strip 2 is being rolled, and the lowering of the outlet bending roller 6 may be determined according to the tension of the strip of hot rolled steel, so that further rollers, such as looper rollers, are not required. Of course, as illustrated, one descaling header and one water collecting device is associated with each bending roller, but further descaling headers may be provided if necessary to supply additional water. Furthermore, although illustrated with two units, (each having a bending roller, descaling header, and water collecting device) further units may be provided if necessary. The present invention has been devised particularly for use in a mini hot strip mill, but the descaling device of the present invention can be applied to a standard hot strip rolling mill, as even in a standard system, machine milling can be performed with a temperature drop less than is normal, so that a high quality can be obtained. The present invention can also be applied to a cold strip mill. According to the present invention, it becomes possible to achieve effective scale removal from a strip of rolled material with a small temperature drop, so that high quality milling can be achieved. If the rolled material is thin, and moving at low speed, it is still possible to ensure that any temperature drop in that material is small, and this is particularly important when the invention is applied to a mini hot strip mill. As a result, satisfactory finishing milling can be achieved using an economical arrangement. Furthermore, effective scale removal can be achieve without generating contact flaws in the rolled material. Further reductions in production cost can be achieved since the pressure and amount of injected water can be reduced, as compared with known arrangements.

Claims: A descaling device for a strip (2) of material comprising: means for bending said strip with at least one bending roller (5,6) at a predetermined point; and a water injection device (11,15) for injecting water onto said strip (2); characterised in that: said water injection device (11,15) is arranged to inject said water at a further predetermined point spaced from said predetermined point on one side of said predetermined point; and the device includes collection means (12,16) for collecting said water, said collection means having a water reception surface located adjacent but spaced from said strip (2) said water reception surface being on the opposite side of said predetermined point from said further predetermined point and being positioned to intercept a line extending beyond said predetermined point in a direction opposite to the path of travel of said strip followed after said predetermined point. A descaling device according to claim 1, wherein said water reception surface is spaced from said predetermined point by a distance not greater than 100 mm. A descaling device according to any one of the preceding claims, including means for adjusting said bending roller (5,6) vertically with respect to said strip (2). A descaling device according to any one of the preceding claims, wherein said bending means comprises a pair of rollers (5,6). A descaling device according to any one of the preceding claims, having means for withdrawing said bending roller from contact with said strip. A descaling system comprising a pair of descaling devices, each of said descaling devices being according to any one of the preceding claims. A descaling system according to claim 6, wherein said water injection device (11,15) and said collection means (12,16) of one of said pair of descaling devices is on one side of said strip (2) and said water injection device (11) and said collection means (16) of the other of said pair of descaling devices is on the opposite side of said strip (2). A descaling system according to claim 6 or claim 7, further including means for simultaneously withdrawing said collection means of one of said pair of descaling devices and said bending roller of the other of said pair of bending devices. A method of descaling a strip of material comprising: injecting water onto said strip of material; and bending said strip at a predetermined point with a bending roller (5,6); characterised in that: the water is injected onto the strip of material at a further predetermined point spaced from said predetermined point on one side of said predetermined point; and water which has been separated from said strip is collected by a collection means (12,16) on the opposite side of said predetermined point from said further predetermined point, and having a collecting surface positioned to intercept a line extending beyond said predetermined point in a direction opposite to a path of travel of said strip followed after said predetermined point. A method according to claim 9, wherein: said strip (2) is bent with a further bending roller (5,6) at a further predetermined point spaced from said predetermined point. A method according to claim 9 or claim 10, wherein said bending bends said strip (2) through an angle between 10° and 35°. A method according to any one of claims 9 to 11, wherein said water is injected onto said strip in a direction towards said predetermined point. A hot rolling mill for rolling a strip of heated material said rolling mill including a descaling device for descaling said strip, said descaling device being according to any one of claims 1 to 5. A hot rolling system for rolling a strip of heated material, said rolling system including: at least one roughing mill for rolling said strip; at least one finishing mill for rolling said strip; and a descaling device for descaling said strip, strip descaling device being located between said at least one roughing mill and said at least one finishing mill being according to any one of claims 1 to 5. A hot rolling system for rolling a strip of heated material, said rolling system including a pair of coilers for reversibly rolling said strip therebetween, and a descaling device for descaling said strip, said descaling device being located between said pair of coilers and being according to any one of claims 1 to 5. A process of rolling a strip (2) of heated material, said method including descaling said strip 92) by a method according to any one of claims 9 to 12. A process according to claim 16, wherein said strip is of steel.

Inventors: KIMURA TOMOAKI, SEKIYA TERUO, KIMURA, TOMOAKI, SEKIYA, TERUO
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1989
Main classification: B21B45
IPC codes: B21B45, B21B1