GB2073080A

GB2073080A - Hot rolling of metal strip

Info

Publication number: GB2073080A
Application number: GB8100920A
Authority: GB
Original assignee: Davy Loewy Ltd
Current assignee: Davy Loewy Ltd
Priority date: 1980-04-03
Filing date: 1981-01-13
Publication date: 1981-10-14
Also published as: GB2073080B

Abstract

In the continuous hot rolling of strip, the strip passes from the end of a finishing train (11) to a cooling zone (21) and to a multi-coiler (16, 18). A flying shear (14) is positioned downstream of the cooling zone, in order to cut the continuous strip into coil lengths. Pinch rolls (13, 15) are located upstream of the shear (14) to ensure that a subsequent strip length is held under tension following each shearing operation, and before the leading end of the length is coiled. <IMAGE>

Description

SPECIFICATION Method of, and apparatus for, the hot rolling of metal strip This invention relates to the hot rolling of metal strip, and particularly, but not exclusively, of steel strip.

It has recently been proposed to operate the finishing train of a hot strip mill continuously, by pressure welding nose to tail successive slabs rolled in a roughing train and feeding the composite slab to the finishing train. Problems then arise in handling the hot strip leaving the finishing train; the strip must be cut up into coil lengths prior to coiling, but if it is sheared immediately downstream of the mill train, each sheared leading strip end is a potential cobble risk. For this reason, it may be necessary to run out the leading end of each strip to the coilers at a relatively low safe speed; to bring that about the mill must be decelerated to the safe speed until the leading end is gripped by a coiler and then accelerated again up to its top speed.The mill yield may then be reduced by two factors -- ioss of strip due to cobbles and loss of production time through having to feed each leading end to the coiler and having to thread the coiler at reduced mill speed.

In the present invention, shearing is performed in close proximity to the copier so as to maintain the strip in a continuous length over the danger area of the strip run out and cooling roller tables between the finishing train and the coiler. Thus, one aspect of the invention lies in a method for the hot rolling of strip in which a hot rolling mill train delivers a rolled strip in continuous form; the continuous strip is led under tension through a strip cooling zone to a shear, which is located downstream of the cooling zone and which cuts the strip into coil lengths, and thence to a multi-coiler coiling installation, and in which the tension of the strip during passage through the cooling zone is maintained by pinch rolls adjacent to, and upstream of the shear during each interval between shearing of the strip and the subsequent gripping of the newly sheared leading end of the strip downstream of the shear. Once the leading end of the continuous strip has been gripped by the pinch rolls adjacent the shear, the mill train can be maintained at a desired high rolling speed for the remainder of the production run, since the danger of cobbles is removed by the strip being held continuously under tension between the mill train and those pinch rolls.

Preferably there are two pairs of pinch rolls adjacent the shear, one upstream and the other downstream of the shear. Following a shearing operation, the upstream pinch rolls can control the newly sheared leading end, while the downstream pinch rolls control the trailing end of the newly sheared coil lengths. The downstream pinch rolls may also direct each coil length to the coiler selected for it.

A second aspect of the invention resides in continuous rolling equipment comprising a hot strip rolling mill train, a cooling zone downstream of the mill train, a flying shear downstream of the cooling zone, a multi-coiler coiling installation downstream of the shear, and a pair of pinch rolls adjacent to, and upstream of, the shear to maintain the strip in the cooling zone under controlled tension during the interval, subsequent to shearing when the continuous strip is not held downstream of the shear.

Preferably, there are two pairs of pinch rolls, one upstream of the shear and one between the shear and the coilers to control the tail end of each sheared strip during coiling. The pinch rolls downstream of the shear may be adjustable in order to direct the leading end of each sheared strip towards one or other of the coilers.

In the cooling zone the strip temperature is brought down by water cooling means from rolling temperature to one suitable for coil handling and storage, or to impart certain metallurgical properties.

At present the only practical means by which individual lengths of thin material may be conveyed at high speed to the coilers has been found to be a straight length of roller table incorporating a section of water sprays. Such a system offers the minimum possible resistance to the passage of the leading end of the strip.

However, because of the rate at which heat can be extracted from the strip by the spray system, the cooling zone forms a significant proportion (approximately one third) of the overall length of the mill.

Means are being continually sought, therefore, to improve the heat transfer rate of the cooling system to minimise this length so as to reduce the building length and thus the plant costs. The need for such an improvement is further heightened by the fact that, as the output of hot strip mills has increased, so has their finishing speeds and also the length of the section between the finishing stands and the hot strip coilers. The following table illustrates the trend. The stages of mill development are quoted as Generation I, Generation II and Generation Ill, and these are typically mills of the 1950's, 1 960's and 1970's respectively.

Mill Generation I II Ill Annual Output tonnes per year (ratio) 1-2 3 5 Finishing Speed m/sec. 11 17 25 Table Length (Stand 7 to Coiler) 100 1 50 190 The means by which the heat transfer of the cooling system has been improved have been in two stages. First, the water spray system has been replaced by laminar flow columnar cooling and this, in its turn, is now being replaced by curtain water cooling.

Since the output from the finishing mill train in this invention is a continuous strip and since, once the leading end of the strip has been passed down the run-out table and threaded into the pinch rolls, the likelihood of the strip forming a "cobble" is reduced, it is possible to employ more effective forms of cooling the strip. Thus, according to a preferred form of the invention, the cooling zone comprises or includes at least one liquid cooling tank in which the strip is totally immersed in a cooling liquid.

The liquid cooling tank may be a water bath, a salt bath, an oil bath, or a fluidised bed, for example, according to the heat exchange rate required and, for the same reasons, these media may be at any desired temperature. The cooling system may also be in various sections according to the degree of control required to cover the product range of the mill. Thus, the system may comprise a single cooling tank, or a series of tanks, any number of which would be in use at any one time. Furthermore, such arrangements may be supplemented by a section, or sections, of water spray, laminar jet, or water curtain cooling to provide a means of fine control on the overall cooling rate required.

The invention will be more readily understood by way of example from the following description of hot strip rolling mill equipment and its operation, reference being made to the accompanying drawings, in which Figures 1 to 7 show successive stages in the rolling and coiling process, and Figures 8 to 10 illustrate modifications in the cooling zone of Figure 1 to 7.

In the drawings, the final stand of the finishing train of a hot strip mill is indicated at 1 The slabs or break downs from the roughing train (not shown) are welded end to end and are rolled down in the finishing train in a continuous operation of the latter. The continuous strip 12 leaving the stand 11 passes over the run-out table 20 and through the water cooling zones, which are shown only in Figure 1 and 21, and passes through a first pair of pinch rolls 13 located downstream of the table and cooling zones.Immediately downstream of pinch rolls 13 is a flying shear 14 which is followed successively by a second pair of pinch rolls 1 5, and a first coiler 1 6 below the level of the passline between the mill and pinch rolls 13, a third pair of pinch rolls 1 7 and a second coiler 18; a further coiler or coilers may be provided if necessary. Pinch rolls 1 5 are adjustable between a first position shown in Figure 1, in which it directs the strip downwardly to coiler 1 6, and a second position shown in Figure 3, in which it directs the strip horizontally to pinch rolls 1 7 and thence to coiler 1 8.

The leading end of the continuous strip at the start of the production run is led at threading speed to and through pinch rolls 13, which can be open as shown in Figure 1, and past shear 14 to pinch rolls 15 which is in position to direct the strip to coiler 16. Once the leading end is properly gripped by rolls 1 5 and tension developed in the strip, the mill is accelerated to the required rolling speed.

As the coil on coiler 1 6 is nearing its maximum size, pinch rolls 1 3 are closed (Figure 2) and thereafter maintains tension in the strip downstream of stand 11. Pinch rolls 1 5 are then moved to their vertical position, and may be opened as shown. When the coil is almost completed, pinch rolls 1 5 are closed on the strip to control the tail end of the severed strip, and shear 14 is operated (Figure 3).

After shearing (Figure 4), the tail end of the first coil is drawn down the throat of coiler 1 6 by the wrapping action of the coiler mandrel. The leading end of the second strip 12', which is shown in chain line, is fed by pinch rolls 1 5 over coiler 1 6 to pinch rolls 1 7 and coiler 18. Figure 5 shows the second strip being coiled on coiler 18; the first coil has been removed from coiler 1 6 and, because tension is maintained by pinch rolls 1 7, pinch rolls 1 3 can be opened if required, pinch rolls 1 5 are in their open position, and in tilted position.

When the coil on coiler 1 8 is nearing completion pinch rolls 1 5 are closed, ready to direct the leading end of the next sheared strip to coiler 16, while pinch rolls 13, if previously opened, are closed on the strip to maintain tension after shearing. Shear 24 is operated to sever the strip (Figure 6).

After shearing, the tail end of the second strip is drawn on to coiler 1 8, and the leading end of the third coil is directed by pinch rolls 1 5 to coiler 1 6 (Figure 7). The sequence of shearing and coiling on to coilers 1 6 and 18 alternately is then repeated for the remainder of the run.

As will be appreciated, pinch rolls 1 5 have two functions:- 1. to deflect strip to coiler 16, when in in position shown in Figures 1, 6 and 7, and 2. to maintain tension on the tail end of a strip running out to coiler 16, while allowing the leading end of the next strip to be fed to coiler 18 (Figure 4).

Alternatively, pinch rolls 1 5 may be of the fixed type being always in the deflecting position of Figures 1, 6 and 7 and performing function (1) above, and a second pair of pinch rolls (not shown) installed in the throat of coiler 1 6. Function (2) above would then be performed by having pinch rolls 1 5 open and by having the throat pinch rolls control the tension in the strip running out to coiler 1 6.

The shear 14 may be operated automatically. For example, the length of the strip passing the shear may be measured and the shear operated to give a required coil weight, or those parts of the strip corresponding to the slab welds may be detected and the shear operated to cut at the slab joints. In the latter case, detection may be performed in a number of ways, as by introducing radio-active particles at the point of weld.

In the arrangement of Figure 8, a single cooling station is substituted for the curtains 21 between the last stand 11 and the pinch rolls 13. The cooling station comprises a large tank 30 containing a cooling liquid such as water. Rollers 31, 32 are positioned at the entrance and exit respectively of the tank and a further roller 33 is positioned approximately halfway along the length of the tank; roller 33 can be raised and lowered into and out of the tank 30.

The leading end of the strip 12 is fed slowly from the last stand 1 over the rollers 31, 32 and beneath the roller 33 which is positioned above the surface of the liquid in the tank. The leading end is then fed between the pinch rolls 13 as before and secured to the coiler 1 6. Roller 33 is next lowered to cause the strip 12 to pass into and out of the liquid in the tank so as to be totally immersed in the tank.

By varying the level of the liquid in the tank and adjusting the position of the roller 33 in the tank, the length of material which is immersed in the liquid is adjusted. Once threading has been completed, the finishing train and the coiler are brought up to speed and the strip material is fed continuously from the finishing train, through the tank and to the coiler. As before, when a coil of appropriate size has been formed, the strip is severed by the shear 5 and the leading end passed to a second coiler.

In the arrangement shown in Figure 9, two separate cooling tanks 35, 36 are arranged end-to-end and the strip 12 can be passed through one or both of the tanks. The tanks may contain different liquids and the liquids can be at different temperatures.

In the arrangement shown in Figure 10, two separate cooling tanks 35, 36 are again shown arranged in end-to-end relation. Between the downstream tank 36 and the pinch rolls 13, further cooling means, such a water jets or curtains 37, are employed.

The means by which the heat extraction rate of the system could be determined and controlled would be: (a) choice of cooling medium (b) temperature of cooling medium (c) transport time in cooling medium -- options available:- (i) vary length of strip in cooling medium by varying surface level of cooling medium with respect to strip loop in cooling medium (ii) vary length of strip in cooling medium by varying the number of cooling sections in use at any one time.

Claims

1. A method for the continuous hot rolling of strip in which a hot rolling mill train delivers a rolled strip in continuous form, and in which that strip is led under tension through a strip cooling zone to a shear, which is located downstream of the cooling zone and which cuts the strip into coil lengths, and thence to a multi-coiler coiling installation, and in which the tension of the strip during passage through the cooling zone is maintained by pinch rolls adjacent to, and upstream of the shear during each interval between shearing of the strip and the subsequent gripping of the newly sheared leading end of the strip downstream of the shear.

2. A method for the continuous hot rolling of strip in which a hot rolling mill train delivers a rolled strip in continuous form, and in which that strip is led through a strip cooling zone and is cut into coil lengths by a shear downstream of the cooling zone, and the coil lengths are coiled in a multi-coiler coiling installation, and in which the continuous strip is maintained under tension through the cooling zone, in each interval between shearing of the strip and the subsequently gripping of the newly sheared leading end downstream of the shear, by a first pair of pinch rolls adjacent to, and upstream of the shear, while the trailing end of the newly sheared coil length is controlled by a second pair of pinch rolls located downstream of the shear.

3. A method for the continuous hot rolling of strip according to claim 2, in which the second pinch rolls are adjustable to direct the sheared strip optionally to either of two coilers of the coiling installation.

4. A method for the continuous hot rolling of strip according to any one of the preceding claims, in which in the cooling zone the strip is passed through a tank of cooling liquid.

5. A method for the continuous hot rolling of strip according to claim 4, in which the residence time of the strip in the cooling tank is adjustable.

6. A method for the continuous hot rolling of strip according to claim 4 or claim 5, in which the strip is passed successively through a plurality of liquid cooling tanks.

7. A method for the continuous hot rolling of strip according to any one of claims 4 to 6, in which the strip is additionally passed through a water spray or curtain.

8. Continuous rolling equipment comprising a continuous hot strip mill train, a cooling zone downstream of the mill train, a flying shear downstream of the cooling zone, a multi-coiler coiling installation downstream of the shear, and a pair of pinch rolls adjacent to, and upstream of, the shear to maintain the strip in the cooling zone under controlled tension during the interval, subsequent to shearing when the continuous strip is not held downstream of the shear.

9. Continuous rolling equipment comprising a continuous hot strip mill train, a cooling zone downstream of the mill train, a flying shear downstream of the cooling zone, a multi-coiler coiling installation downstream of the shear, a pair of pinch rolls adjacent to, and upstream of, the shear to maintain the strip in the cooling zone under controlled tension during the interval, subsequent to shearing when the continuous strip is not held downstream of the shear, and a second pair of pinch rolls adjacent to but downstream of the shear for controlling the trailing end of the sheared strip.

10. Continuous rolling equipment according to claim 9, in which the pinch rolls downstream of the shear is adjustable to direct the leading end of each sheared strip optionally to either of the coilers.

11. Continuous rolling equipment according to any one of claims 8 to 10, in which the cooling zone includes a liquid cooling tank for the immersion of the strip.

12. Continuous rolling equipment according to claim 1 1, in which the cooling zone includes a second liquid cooling tank arranged in sequence after the first such tank.

13. Continuous rolling equipment according to claim 11 or claim 12, in which the cooling zone further includes a water spray or curtain.

14. A method for the continuous hot rolling of strip, substantially as herein described with reference to the accompanying drawing.

1 5. Continuous hot rolling equipment substantially as herein described with reference to the accompanying drawing.