DE69224490T2 - Rolling mill, hot rolling system, rolling process and rolling mill retrofitting process - Google Patents

Description

The invention relates to a four-high hot rolling mill which has an excellent suitability for controlling the profile of flat rolled stock, a hot rolling system, a hot rolling method and a method for retrofitting hot rolling mills.

This type of rolling mill, which has been known for some time (see, for example, JP-A-47-27159), differs from conventional four-high rolling mills in that the longitudinal axes of the two work rolls in the horizontal rolling plane are inclined relative to each other by predetermined small angles to the rolling direction, so that their longitudinal axes cross each other in the central section of the rolled stock. This roll arrangement is particularly intended to improve the control of the thickness of the rolled stock across its width, since the offset of the ends of the work rolls relative to the ends of the back-up rolls leads, in a known manner, to a certain compensation for the bending of the rolls caused by the rolling force. However, this oppositely directed inclination of the work rolls led to serious technical problems. In particular, the excessive axial thrust loads acting on the roller bearings of the work rolls and the excessive wear of the support roll barrels are the reasons why this type of rolling mill has never been used in practice.

EP-A-0 184 481 describes another four-high rolling mill with crossed work rolls with a pair of support rolls arranged perpendicular to the longitudinal axis of the flat rolling stock. and a pair of work rolls inclined in the horizontal planes relative to one another in a common housing such that the axes of the work rolls cross each other and also the axis of the rolled stock. The small angle of inclination of 0.2º to 2º between the work roll axis and the axis of the flat rolled stock can be controlled or adjusted by an adjusting device in the form of wedges or hydraulic cylinders arranged between the side surfaces of the work roll chocks and the windows in the housing.

In this type of four-high mill, since the work rolls cross the backup rolls, a huge axial thrust is exerted on both the work rolls and the backup rolls along the axis of the rolls, as described in "Research of Machines", Vol. 42, No. 10 (1990), pages 71, 72. This thrust, which varies depending on the crossing angle, is about 30% of the rolling loads. The large-diameter thrust bearing of the backup roll can withstand this thrust. However, it is very difficult for the work roll, whose roll chocks and bearings are much smaller than those of the backup rolls, to withstand such high axial thrust loads. Furthermore, the crossing of the work roll and its backup roll causes relative slippage between the contact areas of the rolls, thereby causing wear of both roll barrels. Since the work rolls must be replaced every two or three hours due to the wear caused by the rolling stock, which is much greater than the wear caused by the relative slip, the replacement of the work rolls does not cause any problems. However, replacement of the backup rolls is usually done every ten to twenty days and requires a long time. Therefore, frequent replacement of the backup rolls significantly reduces the productivity of the entire rolling mill system due to rapid wear.

In the publication "Technical Report" of Mitsubishi Heavy Industrial Co., Ltd., Vol. 21, No. 6 (1984), pages 61 to 67, another type of crossed roll mill is disclosed in which a pair of rolls consisting of an upper work roll and an upper backup roll and a pair of rolls consisting of a lower work roll and a lower backup roll are arranged in a casing in such a way that the axes of the two pairs of rolls cross each other. In this pair-crossed roll mill, the generation of an extreme axial thrust between the backup roll and the work roll is suppressed. Since the centers of the metal chocks of the backup rolls, which are directly subjected to the rolling load, are displaced with respect to the center of the reduction screw, a torque is applied to the metal chock, thereby generating a local load acting on the mill. This prevents a uniform rolling process and accelerates the wear of the metal chock and the bearing. To eliminate these disadvantages, a very rigid support can be provided to balance the drive side and the operating side of the rolling mill. However, the provision of such a rigid support increases the overall size of the rolling mill.

In this pair-crossed roll mill, adjustments of the crossing angle are required during rolling in response to changes in the rolling load or the profile of the rolled material or to correct the pre-set crossing angle. The metal chocks of the upper and lower support rolls must be moved sideways under the enormous rolling loads during rolling, which requires special bearings and a heavy adjustment system for this lateral adjustment. This makes the design of the pair-crossed roll mill more complicated. Also, due to the penetration of scale, Extensive maintenance is required in the special bearing of the lower metal chock.

In commercial four-high rolling mills, in which the work rolls are parallel to each other, the axial thrust on the work rolls during hot rolling is generally 1 to 2% of the rolling loads. In rolling mills with pairs of crossed rolls, the axial thrust acting on the crossed work rolls is approximately 5% of the rolling load.

A well-known way to reduce roll barrel wear is to reduce the friction between the respective pairs of roll surfaces by supplying a lubricant either directly to the rolled material and/or to the barrel surfaces of the working or back-up rolls.

In recent years, a so-called hot rolling oil (in a concentration of 1% or less) has been used in hot rolling for the purpose of reducing the wear of the work rolls, the rolling load and the rolling energy. The hot rolling oil is characterized in that its lubricating effect is maintained on a material present in the roll attack having a high temperature of 700ºC or more and in that it contains a large amount of fatty oil such as beef tallow. A lubricating oil consisting mainly of a mineral oil, which may be a soluble oil containing an emulsifier, has a significantly deteriorated or lost lubricating effect at high temperatures and therefore has no adverse effect on the attack.

For example, US-A-3 208 253 describes a system for the alternate supply of rolling lubricant and cooling water to the barrels of working and backup rolls during the rolling process. During the periods when there is no rolling stock in some of the rolling stands, the application of the lubricant is interrupted and a non-lubricating Coolant, preferably water, is supplied to the roll barrels. At the same time as new rolling stock enters a rolling stand, the supply of lubricant is resumed and the application of cooling water is stopped.

It is true that this system can avoid a slip effect at the moment of attack when the new rolling stock enters the roll gap. However, this publication does not address the slip problem encountered in a rolling mill with crossed rolls or the special requirements for the lubricant in hot rolling.

It is the object of the invention to provide a hot rolling process and a hot rolling mill for rolling flat rolled stock by crossing work rolls, in which excessive axial thrust loads of the work rolls and high wear of the barrels of the support rolls and other components are prevented.

According to the invention, this object is achieved by a hot rolling mill as defined in patent claim 1 and also by the methods defined in patent claims 10 and 13.

A crucial aspect of the invention is based on the discovery that by inclining only the two work rolls, the effect of compensating for the undesirable bending of the work rolls caused by the rolling force is achieved, so that even at small inclination angles in the range of 1º, effective control of the flatness of the rolled stock across its entire width is possible. The crossing of the work rolls only produces a first axial thrust force acting between the backup roll and the associated work roll and a second axial thrust force acting between the rolled stock and the work roll. The first and second axial thrust forces are directed in opposite directions, so that the thrust load actually acting on one of the bearings of the work roll is the difference between the first and second thrust forces and is therefore smaller than the first axial thrust force. The controlled application of the mineral-based lubricant into the contact portion between the respective work roll and the backup roll only reduces the coefficient of friction at that contact portion so that the first axial thrust force is also reduced and the roll chocks of the work rolls and the backup rolls can be designed smaller in accordance with the reduced amounts of thrust loads.

By using a mineral-based lubricating oil, which is normally of low viscosity, the lubricating effect is restricted to this contact section only, and lubrication is ineffective in the feed area of the roll gap, so that sufficient friction is maintained between the barrel surface of the work roll and the rolled stock. The above criterion has the effect of reducing excessive axial thrust forces on the rolls and their bearings to the limits of conventional four-high rolling mills, effectively reducing wear of the roll surfaces.

The lubricant supply device should be provided for the controlled injection of a suitable lubricant at the inlet side of the gap area between the work roll and the backup roll over the entire length of the gap area.

Further advantages of the invention are the relatively simple structure, the possibility of program-free rolling and the possibility of changing or adjusting the profile of the rolling stock during the rolling process by controlling the inclination of the axes of the work rolls.

The inventors have discovered that during hot rolling the drawing-in properties in the roll gap are not affected when lubricants according to the invention are used. Even if, after passing through the contact section between the work roll and the backup roll, some of the lubricant adheres to the surface of the hot work roll and burns off, a corresponding amount of lubricant adheres to the surface of the relatively cooler backup roll, even if a coolant is transferred from the work roll to the surface of the backup roll. Additionally or alternatively, means may be provided to prevent the coolant for the work rolls from reaching the respective roll surfaces of the backup rolls. In certain cases, the lubricant supply may only take place during the actual rolling process and be interrupted in the periods between the rolling of successive rolled stock.

Further advantages, particularly in relation to a program-free rolling process, result from an additional axial displacement of the inclined work rolls during the rolling process, which leads to an improved distribution of the wear of the barrel and, accordingly, to a longer operating time. This adjustment of the work rolls in the axial direction and the adjustment of their crossed inclined position is suitably carried out by a separate device consisting of hydraulic cylinders, which require only relatively little space and can generate high actuating forces.

The invention can be used in particular as at least one stand in the finishing rolling group. It is also possible and causes no difficulties to retrofit existing rolling stands at a later date with the means and components according to the invention.

The above and other objects, features and advantages of the present invention will be apparent from the following Description with reference to the accompanying drawings.

Fig. 1 is a schematic view of an embodiment of a four-high rolling mill with crossed work rolls according to the invention, viewed in the direction of the axis of a roll;

Fig. 2 shows a device for moving a work roll in its axial direction in the four-high rolling mill with crossed work rolls shown in Fig. 1;

Fig. 3 is a diagram showing the results of experiments carried out to investigate the change in profile due to changes in the crossing angle during rolling;

Fig. 4 shows a roll grinding device for the backup rolls contained in the four-high rolling mill with crossed work rolls shown in Fig. 1;

Fig. 5 shows how a roll lubricant and a coolant are supplied to the four-high rolling mill with crossed work rolls shown in Fig. 1;

Fig. 6 is a diagram showing the relationship between the crossing angle of the work roll in the four-high rolling mill with crossed work rolls, the thrust coefficient between the work roll and the backup roll, and the thrust coefficients between the work roll and the rolled product;

Fig. 7 is a diagram showing the relationship between the crossing angle of the work rolls in the four-high rolling mill with crossed work rolls according to the present invention, the thrust coefficient between the work roll and the backup roll, and the thrust coefficient between the work roll and the rolled product obtained under the condition that a roll lubricant is supplied between the rolls;

Fig. 8 is a view with the rolls shown from above and showing the direction of thrust generated by crossing the work rolls in the four-high rolling mill with crossed work rolls;

Fig. 9 is a view showing the rolls in their axial direction and illustrating the direction of thrust generated by crossing the work rolls in the four-high rolling mill with crossed work rolls;

Fig. 10 is a graph showing the relationship between the crossing angles of the work rolls, which differ depending on the type of roll lubricant supplied between the rolls of the four-high rolling mill with crossed work rolls, which is an embodiment of the present invention, and the wear of the backup rolls;

Fig. 11 is a graph showing the results of experiments conducted to investigate the change in lubricating property (friction coefficient) by the temperature of the lubricant;

Fig. 12 is a view in the axial direction of the roller, illustrating the experiments shown in Fig. 11;

Fig. 13 is a schematic view of the roll axis from above showing the influence of a displacement of the axis of a backup roll caused by crossing the work rolls of the four-high rolling mill with crossed work rolls;

Fig. 14 is a schematic view of the roll axes viewed in the axial direction of the rolls, showing the influence of a deviation of the axis of the backup roll caused by crossing the work rolls of the four-high rolling mill with crossed work rolls;

Fig. 15 is a schematic view explaining a difference in forces applied to the hydraulic actuators on the operating and driving sides of the rolling mill, which is calculated based on the the crossing of the work rolls in the four-high rolling mill with crossed work rolls generated thrust; and

Fig. 16 is a schematic view of a hot rolling mill in which the embodiment of the four-high rolling mill with crossed work rolls according to the invention is used as a finishing rolling mill.

Referring to Figures 1 and 2, a four-high crossed roll mill comprises upper and lower work rolls 7 and upper and lower support rolls 8 which support the work rolls. Work roll chocks 16 are provided at the roll ends of each of the work rolls 7 so as to rotatably support the work roll 7. Each of the work roll chocks 16 has two vertical side surfaces 16a and side projections 16 at the upper and lower ends of its side surfaces. A hydraulic cylinder device or adjusting device 11 acts in the horizontal direction on each of the side surfaces 16a. The adjusting devices 11 comprise a cylinder member 11a and a piston 10 having a piston head 10a and a spherical pressure portion 10b. On the inside of the cylinder element 11a, an enlarged end plate 11b is provided which is pressed against the vertical side surfaces 16a of the chocks 16 for the work rolls. Each of the cylinder devices 11 is slidably arranged in a separate housing chamber 11c. The cylinder device 11 of each work roll chock acts against another axis symmetrical to its horizontal axis in order to prevent lateral moments and displacements. Furthermore, the contact surfaces of the cylinder end plates 11a are large enough for a uniform transmission of a strong compressive force to the work roll chocks 16. The cylinder devices 11 are securely guided in the chambers 11c so that they can compensate for and withstand the transverse forces generated by vertical movements of the work rolls 8 and their roll chocks 16. The free end portions of the end plates 11b of the cylinder member 11a can act as a stop device for limiting the movement of the cylinder member 11a in the chamber 11c. As shown in Fig. 2, at the outer end of each of the chocks 16 for the work rolls, two parallel axial projections 16c with transversely directed outer end portions 16d are provided.

The two support rollers 8 of the rolling stand are held rotatably by chocks 17 for the support rollers. The rolling load is transferred to the support rollers 8 via the roller chocks 17. As shown in Fig. 1, elements 18 in the form of a pressure plate are provided on the lateral sides of the chocks 17 of the support rollers, which are arranged in cutouts 20a of the housing 20. Each pressure plate 18 acts on the hydraulic adjusting device 19 at least in the horizontal direction transverse to the longitudinal axis of the support roller 8. Guide elements 18a are fastened to the outer sides of the pressure plates 18, which are slidably engaged with slots 18b formed in the housing parallel to the adjusting device 19.

The chocks 16 of the work rolls and the chocks 17 of the backup rolls are arranged so as to face window surfaces 20a of a pair of stands 20 provided upright in the axial direction of the roll of the rolling stand. For rolling the rolling stock 9 to be rolled, rolling loads are applied to the individual rolls by actuators (not shown) provided in an upper or lower portion of the housing 20.

In order to incline the axes of the upper and lower working rolls 7 in relation to the axes of the support rolls 8 in a horizontal plane and to adjust the axes of the upper and lower working rolls 7 in a crossed manner with respect to each other, the hydraulic adjusting devices 11 are provided on extension blocks 30 of the housing 20, which Side surfaces of each of the work roll chocks 16 provided at the two ends of each of the upper and lower work rolls 7 face each other. The upper and lower work rolls can be adjusted in a crossed manner with respect to each other by operating the two hydraulic adjusting devices 10 and 11; namely, the hydraulic adjusting devices 10 and 11 comprise pistons and cylinders. The pistons of the adjusting devices have piston heads arranged in engagement with the extension blocks 30, whereas the cylinders of the adjusting devices engage with the chocks 16 of the upper and lower work rolls. Accordingly, the hydraulic adjusting devices 10 and 11 can be operated to move the cylinders of the adjusting devices such that the chocks 16 of the upper and lower work rolls are relatively moved so that the upper and lower work rolls are crossed. Hydraulic oil is supplied to the hydraulic adjusting device 10 via a changeover valve 14. To detect the movement of a ram of the hydraulic adjusting device 10, a sensor 13 detects a displacement of a rod 12 mounted on the ram. The hydraulic adjusting device 10 is driven by a work roll crossing angle control device 40 which adjusts the change-over valve 14 based on a signal corresponding to the rolling conditions. The work roll crossing angle control device 40 also performs feedback control of the hydraulic adjusting device 10 to obtain a desired crossing angle of the upper and lower work rolls 7 using the signal from the sensor 13.

The crossing angle can be changed during rolling, i.e. under enormous rolling loads.

Fig. 3 presents the results of the experiments carried out to investigate the changes in the profile of the rolled rolled stock by changing the crossing angle during rolling. It can be seen that by changing the crossing angle from 0.5º to 0.9º a flat material can be modified to have a concave profile.

Hydraulic oil is supplied to the hydraulic adjusting device 11 via a pressure reducing valve 15 so that the hydraulic adjusting device 11 can be pressed against the chock 16 of the work roll 16 with the required force.

To move the work roll 7 in its axial direction, two hydraulic cylinders 22 for driving the work roll along its axis are provided on the two sides of each of the work roll chocks 16 on the housing 20. Hydraulic oil is sealed in the hydraulic cylinders 22 via a pilot check valve 31 to enable the position of the hydraulic cylinders 22 to be maintained. The rods of the hydraulic cylinders 22 are coupled to a common movable block 21. Locking portions 21a detachably provided on the common movable block 21 engage with projecting portions 16d formed on the end portion of the work roll chock 16, thereby transmitting the driving force of the hydraulic cylinders 22 to the work roll chock 16, thereby enabling the work roll 7 to be moved in its axial direction.

Although not shown, the operation of moving the work roll 7 in the axial direction is controlled by a motion control device according to the rolling conditions.

As shown in Figures 1 and 2, lubricant supply nozzles 1 are arranged between the upper working roll 7 and the upper support roll 8 and between the lower working roll 7 and the lower support roll 8 along the rolling axes for supplying lubricant. The position of the The lubricant supply nozzle 1 is not limited to that shown in Figs. 1 and 2, but the nozzle 1 may be arranged at any position where it can supply the lubricant, which is a lubricating agent, between the rollers. As is apparent from Fig. 2, the nozzle 1 has a plurality of nozzle holes arranged in a row and extending in the axial direction of the rollers 7 and 8 so that the lubricant can be uniformly supplied to the rollers.

Since a large amount of coolant is supplied to the working roll 7 from a nozzle 2, it is expedient to arrange a scraper device 32 in order to prevent the lubricant from being washed away (see Fig. 5).

In order to prevent the occurrence of play of the upper and lower backup rolls 8 during rolling, a hydraulic adjusting device 19 is provided on the window surface 20a of the housing 20 opposite the side surface of the backup roll chock 17 provided at each of the roll ends of each of the upper and lower backup rolls 8. A pressure plate 18 for transmitting the driving force of the hydraulic adjusting device 19 is slidably mounted on the stand 20. The hydraulic pressure of the hydraulic adjusting device 19 is applied to the backup roll chock 17 via the pressure plate 18 in order to exclude play of the upper or lower backup roll 8.

For grinding the roll surface during rolling, a roll grinder 6 is provided near the roll surface of both the upper and lower backup rolls 8. The roll grinder 6 is moved in the axial direction of the backup roll 8 by a drive motor 24 as shown in Fig. 4. The amount to which the roll is ground is adjusted by a grinding quantity adjusting device 6a.

As shown in Fig. 5, in the four-high rolling mill with crossed work rolls, the rolled material is fed into a container 26 is supplied from the lubricant supply nozzle 1 by means of a pump 27 through a shuttle valve 28 as a spray between the work roll 7 and the backup roll 8. When a lubricant control unit 50 receives a signal representing the rolling conditions such as the end or start of the supply of the rolling stock to be rolled, it switches the shuttle valve 28 and thereby stops the spraying of the lubricant from the lubricant supply nozzle 1 onto the roll surface.

Roll cooling nozzles 2 and 3 are used to cool the working roll and the backup roll.

In the above-mentioned four-high cross-roll mill, the work rolls 7 are moved in opposite directions, causing them to cross each other, whereas the backup rolls 8 are not moved in the horizontal direction. This cross-roll mill is suitable for use in a strip hot rolling mill in which a large crown must be set in the rolled stock 9 to be rolled, and it is particularly suitable for use as the front stand of the finishing mill. During hot rolling, cooling water is sprayed from the cooling nozzles 2 and 3 mainly onto the upper and lower work rolls 7 due to the attacking properties of the rolled stock 9 to be rolled.

In crossed work roll rolling, the most important requirement concerns the management of the thrust exerted on the work rolls. Fig. 6 are diagrams showing the crossing angle θ of the work rolls in the four-high crossed work roll mill, the thrust coefficient uTR between the work roll and the backup roll, and the thrust coefficient uTM between the work roll and the rolled material, respectively. In Fig. 6, the abscissa represents the crossing angle θ of a single work roll with respect to a line perpendicular to the rolling direction. The ordinate represents the thrust coefficient uT. The coefficient utm is a percentage obtained by dividing an axial thrust force applied by the rolling stock 9 to a single work roll 7 by the rolling load. The coefficient uTM is a function of the crossing angle θ and other conditions such as tension. In general, the greater the tension, the lower the thrust coefficient uTm. When only the crossing of the upper and lower work rolls 7 is carried out, the thrust generated between the backup roll 8 and the work roll 7 differs depending on the rolling conditions. In Fig. 6, three examples of such thrusts are shown as curves uTR1, uTR2 and uTR3. The curve uTR1 of the thrust coefficients shows the results of the experiments in which only water was supplied between the backup roll 8 and the work roll 7. The curve uTR2 shows the results of the experiments in which the concentration of the lubricating oil present in the water supplied to the two rolls was low. The curve uTR3 shows the results of the experiments in which the concentration of the lubricating oil in the water was higher than that in the curve uTR2. As can be seen from Fig. 6, the thrust uTR can be significantly reduced by supplying the lubricating oil between the rollers. The thrust uTR can be selected by selecting the concentration of the lubricating oil. In the above experiments, the concentration was changed. However, the amount of the emulsion of lubricating oil and water can be changed to change the thrust.

Fig. 7 shows the thrust coefficient uWT applied to the work roll 7 when the axes of the work rolls cross the rolling stock 9 and the axes of the backup rolls, with the backup rolls 8 fixed in the horizontal direction, that is, the value obtained by dividing the actual thrust on a work roll by the rolling load. The thrust coefficient uWT is a percentage which is the sum of the thrust coefficient uTR applied by the backup roll to the associated work roll according to Fig. 6 and the thrust coefficient uTm applied by the rolling stock to this work roll.

It is pointed out that the direction of the thrust applied by the rolling stock 9 to be rolled to the work roll 7 and that of the thrust applied by the backup roll 8 are opposite to each other.

This is explained in detail with reference to Figures 8 and 9.

Fig. 8 shows the relationship shown in Fig. 9 between the speed between the work roll 7 and the rolled material 9 at a contact section A and that between the work roll 7 and the backup roll 8 at a contact section B. VM indicates the speed of the rolled material at the contact section, VW the peripheral speed of the work roll and VB the peripheral speed of the backup roll.

The work roll 7 is subjected to both the thrust in the direction of a relative speed ΔVA between the work roll 7 and the rolled material 9 and the thrust in the direction of a relative speed ΔVB between the work roll 7 and the backup roll 8. The directions of these relative speeds are opposite to each other.

At a contact portion A, the rolling stock 9 is rolled, and the thrust coefficient uTm shown in Fig. 6 is relatively small. Further, as shown in Fig. 6, in the water spray, the maximum magnitude of the thrust coefficient uTR1 is about 30%, the direction of uTR1 is opposite to that of uTm, the thrust applied from the backup roll 8 to the associated work roll is large, and the thrust coefficient uWT1 of the work roll is about 25%. In a rolling mill used, the thrust must be 5% or less due to the design of the thrust bearing. In this method Therefore, such a thrust cannot be achieved. The wear of the backup roll and the work roll are also large. When the lubricating oil is supplied at a low concentration, uWT2 is 2% or less, which is approximately the same as the value obtained in normal rolling. When the concentration of the lubricating oil is increased, by appropriately adjusting the concentration of the lubricating oil, it is possible to reduce the thrust to the values obtained in a normal rolling mill where the work rolls do not cross each other.

Although uTR = uTm is the most desirable value from the viewpoint of reducing the thrust applied to the work roll, uTR < uTm is desirable from the viewpoint of preventing wear of the roll.

Fig. 10 shows the results of experiments in which the wear of the backup roll 8 was significantly reduced by lubrication between the work roll 7 and the backup roll 8 through the lubricant supply nozzle 1. The material of the backup rolls 8 was a special steel with a hardness of HS60º, whereas that of the work rolls 7 was a high chromium steel of HS75º. The contact load P between the rolls was 180 kg/mm. The total number of revolutions was 250,000. The crossing angles between the rolls were 0º, 0.6º and 1.2º. In the strip hot rolling mill, the backup roll used in the front stand of the finishing mill is replaced with a new one after 200,000 revolutions. The backup roll in the rear stand of the finishing mill is rotated 200,000 times before being replaced with a new one. As can be seen from Fig. 10, when the lubricant is supplied, the wear of the backup roll can be reduced to 1/5 to 1/10 of the value obtained when water is supplied. In the normal four-high rolling mill where the rolls do not cross each other, the wear of the backup roll is reduced due to the scale that separates from the rolled products. dissolves, or the like, several tens of µm of wear occurs by the time the roll has been rotated 250,000 times. The wear that occurs when the work rolls cross each other can also be considered as the sum of the wear that occurs in the conventional case and that shown in Fig. 10. However, lubrication is also effective in reducing the conventional wear.

In the rolling mill in which only the work rolls 7 cross each other, it could be assumed that an equivalent profile occurs between the rolls, thereby increasing the pressure at the middle portion. However, this does not happen for the following reason. When the length of the roll surface is 2000 mm, the diameter of the work roll 7 is 700 mm, the diameter of the backup roll 8 is 1500 mm and the crossing angle θ of the work roll 7 is 1.2º, a gap CR of the end portions of the two rolls is expressed as follows:

where R₁ and R₂ are the radius of the working roll 7 and that of the backup roll 8, respectively.

This gap corresponds to that obtained by grinding off 0.40 mm of crown on the back-up roll 8. In a rolling mill in practical use, safe operation is ensured even if a crown of 1 mm or more is provided.

A crossing angle of 1.2º is sufficient to ensure adequate steering capability. In addition, it can ensure the advantage resulting from a variation in the profile of the backup roll 8 (it has been estimated that a crossing angle of 1.2º is 10 to 20% more advantageous). Therefore, the crossing angle θ can be smaller than in the rolling mill with pair-crossed rolls.

The second requirement for the rolling mill with crossed work rolls is lubrication between the rolls.

In recent years, a so-called hot rolling oil (in a concentration of 1% or less) has been used in hot rolling for the purpose of reducing the wear of the work rolls, the rolling load and the rolling energy. This hot rolling oil is characterized in that it can maintain its lubricating effect on a rolling stock present in the roll attack having a high temperature of 700ºC or more and contains a large amount of fatty oil such as beef tallow. A lubricating oil composed mainly of mineral oil, which may be a soluble oil containing an emulsifier, has a significantly deteriorated or lost lubricating effect at high temperatures and therefore has no adverse effect on the attack.

This will be explained in detail using the results of the experiments shown in Fig. 11. In Fig. 11, a (section A) and a (section B) correspond to a (section A) and a (section B) in Fig. 12, respectively. This means that a mineral oil type lubricating oil (containing soluble oils) has a very low lubricating performance that ensures a friction coefficient as high as the friction coefficient without lubrication at the (section B) where it is in contact with the hot-rolled stock, but has a good lubricating performance that ensures a low friction coefficient at the (section A) with a low temperature. An example of the lubricating oil is "Daphne Roll Oil SL-2" (trade name) manufactured by IDEMITSU KOSAN, Japan. The lubricant is based on mineral oil, contains a special emulsifier, a substance to improve lubricity and an anti-corrosion agent and has the following physical properties:

A fatty lubricating oil such as beef tallow has lubricating performance not only at (section A) but also at (section B) with high temperatures. Therefore, this type of lubricating oil can cause failure of the attack at the beginning of the rolling stock to be rolled.

If a lubricant of the type which can be washed off by the cooling water supplied from the roll cooling nozzles 2 and 3 is selected, the application of the lubricant can be carried out during the entire rolling process. This means that when acceleration or deceleration is carried out after the rolling stock leaves the roll, the lubricant supply is stopped, the work rolls are retracted to a position where the crossing angle is 0º and then the roll balancing force is increased. Due to the crossing of only the work rolls 7, the crossing resistance is lower and the crossing process can be carried out quickly with one rotation of the rolls. It is therefore advisable to reduce the crossing angle to zero after the rolled material 9 leaves the roll.

The wear of the rolls, which would be caused by slippage of the rolls to a great extent if only water were supplied between the rolls, can be reduced considerably by supplying the lubricant in the manner mentioned above. However, this increases the extent to which the central portion of the roll is worn. Therefore, the on-line roll grinder 6 shown in Fig. 5 is used for grinding the outer surface of the backup roll 8 to be straight or to have a predetermined profile.

On-line grinding equipment has been proposed for grinding the work roll 7, which is frequently replaced with a new one. However, maintenance of the work roll 7 is very difficult because the work roll 7 is very hard, high quality is required for surface finishing, and space is insufficient due to the arrangement of a guide or cooling water. For the backup roll 8, polishing is not so troublesome because space is sufficient, the roll is not as hard as the work roll, and high surface quality is not required as the work roll. Even when correction of the roll profile is not required, the backup roll 8 is replaced for polishing because a fatigue layer generated due to the Hertz stress by the contact of two rolls must be removed. Therefore, if the profile correction and the removal of the fatigue layer can be carried out simultaneously, the roll replacement interval of the backup roll 8 can be greatly increased. Replacement of the backup roll 8 is such a hard work that it is usually carried out at the time of periodic repair. In practical operation, the replacement of the support roller is carried out periodically. When using However, according to the above method, the polishing work of the backup roll 8 can be omitted by the rolling plate. In this case, the rolling mill carries out the polishing of the backup roll 8 without using a costly large backup roll grinding device by using the online grinding device. The backup roll grinding device can be used not only in the above-mentioned four-high rolling mill with crossed work rolls but also in all kinds of rolling mills for the backup roll, such as four-high, five-high or six-high rolling mills.

Regarding the displacement of the crossing point due to a clearance of the roll bearing, the largest clearance occurs at a gap between the metal chock of the roll and the stand 20 or the projecting block 30. The crossing mechanism for the work rolls 7 may be provided with a mechanism for reducing the clearance. In the case of the backup roll, since the gap thereof is normally fixed, in this invention it is set to a small value during rolling and to a large value during replacement of the roll. Alternatively, the chock of the backup roll 8 may be pressed against the stand in one direction under a fixed hydraulic pressure during rolling, the pressure being released during replacement of the roll.

The necessity of such a construction is discussed with reference to Figures 13 and 14.

An inclination of the backup roll 8 around the center of the intersection of the work roll 7 due to the clearance between the bearing of the backup roll 8 and the stand 20 may cause a slight shift in the intersection angle of the work roll 7, but does not cause a serious problem. However, the displacement of the axis of the backup roll 8 by e in the rolling direction shifts the intersection point of the two rolls in the axial direction by a = e/θ, causing a difference in the gap of the upper and lower work rolls 7, which results in a zigzag movement of the rolled stock 9. To eliminate this, the reduction level must be corrected by Sdf. If R₁ is the radius of the work roll 7, R₂ is the radius of the backup roll 8 and L is the distance between the reduction screws, a deviation of the center of the two rolls by c shown in Fig. 14 increases the roll passage g to c²/2 (R₁ + R₂), thereby reducing the difference G of the gaps at the right and left reduction positions as follows:

A reduction screw difference Sdf corresponding to G is determined by the following equation.

For a large strip hot rolling mill, when R₁ = 700/2 = 350 mm, R₂ = 1500/2 = 750 mm, L = 3000 mm and θ = 1.20, Sdf is determined by the following equation where the unit of e is mm.

Since it is practically impossible to correct Sdf, i.e. the reduction level corresponding to e, e must be reduced to a value that can be neglected in practical operation. According to experience, in the finishing strip hot rolling mill rolling thick strips, Sdf is 0.05 mm in the front mill and about 0.025 mm in the rear mill. At this time, the allowable deviation e of the center of the backup roll is ± 1 mm in the front mill and ± 0.5 mm in the rear mill. However, the smaller the better.

In the strip hot rolling mill currently in practice, program-free rolling is the essential element, and displacement of the work rolls in the axial direction is crucial for distributing wear. Therefore, the ability to control the profile and the function of distributing wear are requirements for the strip hot rolling mill. Since the axial thrust force acting on the work roll 7 is reduced in this embodiment, the mechanism for displacing the work roll can be kept simple.

A difference in the rolling force applied to the adjusting device is explained. According to Fig. 15, when a thrust F₁ is applied by the rolling stock while a thrust F₂ is generated between the rolls 7 and 8, a load difference ΔQ occurs between the right and left adjusting devices. ΔQ is determined as follows according to Fig. 15:

If L = 3000 mm, DW = 700 mm, DB = 1500 mm, F₁ = F₂ = 0.05 P, that is, if the thrust is 5%, then:

This means that 2.4% of the rolling load is generated. When the thrust is 10%, ΔQ reaches 4.8%.

Therefore, a reduction of the thrusts F₁ and F₂, especially the thrust F₂ between the rollers, is advantageous.

A difference in the reduction forces adversely affects the correction of the zigzag movement because a difference in the loads is detected during the correction and the reduction forces are adjusted so that a difference is reduced to zero. Although it is possible to carry out a correction of the zigzag movement by using the load difference ΔQ obtained from the thrust and stored in advance, Changes in thrust cause disruption of the zigzag correction, and therefore a reduction in thrust as great as possible is desired.

The operation of the above-described embodiment concerning the four-high rolling mill with crossed work rolls is described below.

According to Figures 1 to 2, the upper and lower work rolls 7, which roll the rolling stock 9, are pressured from two of their sides by means of the hydraulic adjusting devices 10 and 11 in such a way that their axes are each inclined in opposite directions by θ. During rolling, the work rolls 7 are held in this position. The crossing angle of the work roll 7 is adjusted in the manner described below. The sensor 13 provided on the hydraulic adjusting device 10 detects the stroke of the adjusting device, i.e. the position of the chock 16 of the work roll, via the rod 12. The other hydraulic adjusting device 11 exerts pressure on the chock 16 of the work roll with a pressure force that is adjusted by the pressure reducing valve 15. After setting the crossing angle of the work roll with the shuttle valve 14 open, the shuttle valve 14 is closed to maintain the set crossing angle.

The chocks 17 of the backup rolls 8, which hold the work rolls 7, are pressed during rolling by the hydraulic adjusting devices 19 via the pressure plates 18 against the window surfaces 20a of the stand 20, which are remote from the hydraulic adjusting devices 19, in such a way that the backup rolls 8 can be held in a fixed state. A device for moving the work roll 7 is described in detail below. The chock 16 of the work roll is held by the movable cross block 21. The chock 16 can be moved together with the movable block 21 in the axial direction of the work roll 7. being guided by a locking frame 23 by means of the hydraulic cylinders 22 built into the movable block 21. Since the chock 16 of the work roll 7 is displaced toward the rolling direction due to the crossing, the movable block 21 must be rotated according to the position of the chock 16. Therefore, the guide portion of the movable block 21 is made cylindrical so that it can follow the process of crossing the rolls.

To compensate for the wear of the backup roll 8 caused by the relative sliding speed ΔVB (Fig. 9) generated between the rolls by the crossing of the work rolls 7, the roll grinding device 6 shown in Fig. 3 is provided. The grinding device 6 is moved together with the drive motor 24 in the axial direction of the backup roll 8, whereby the roll surface is polished in a straight or curved shape.

The lubrication of the roll surface will be described below with reference to Fig. 5. A coolant is supplied to the work roll 7 from the cooling nozzles 2 and 3 to cool the work roll. A lubricant is supplied from the lubricant supply nozzle 1 in an appropriate concentration to the vicinity of the entrance of the passage between the work roll 7 and the backup roll 8 to reduce the thrust between the rolls. The lubricant is supplied to the lubricant supply nozzle 1 from the tank 26 by the pump 27 via the changeover valve 28. Therefore, the supply of the lubricant can be adjusted at appropriate times, for example, when the rolled stock leaves the roll or when the rolled stock to be rolled is supplied to the roll, by closing the changeover valve 28.

The most convenient position for supplying the lubricant through the lubricant supply nozzle 1 is shown in Fig. 5. However, a lubricant can also be supplied to other positions, for example to the circumference of the support roller 8, so that it can finally be fed from there between the rollers.

As is apparent from the above description, the four-high rolling mill with crossed work rolls according to the present embodiment is capable of overcoming the disadvantages caused by crossing only the work rolls and can therefore be put into practical use.

The mechanisms and constructions necessary to achieve the required functions have been described. However, it should be noted that the object of the invention can also be achieved by other similar mechanisms. Instead of the hydraulic adjusting devices 10, 11, a worm adjusting device or a wedge mechanism, for example, can be used to achieve an intersection of the work rolls 7.

The above-mentioned four-high rolling mill with crossed work rolls can be manufactured without a new mill by retrofitting an existing four-high rolling mill by reusing the housing 20 of the existing mill. The existing four-high rolling mill, in which the pair of work rolls 7 and the pair of backup rolls 8 for respectively supporting the work rolls 7 on the roll casing 20 are provided, is upgraded to the four-high rolling mill with crossed work rolls in the manner described below: The hydraulic adjusting devices 10 and 11, which are the hydraulic device that can be operated in the direction in which the rolling stock 9 to be rolled is fed, are arranged at the positions on the roll casing 20 that are opposite to the roll chocks 16 of the work rolls 7, so that the work rolls 7 can be inclined with respect to the backup rolls 8 in the horizontal plane such that the axes of the work rolls 7, the axes of the backup rolls 8 and the axes of the work rolls 7 cross each other. Likewise, the hydraulic cylinders 22 that control the hydraulic devices which can be actuated in the axial direction of the work roll 7, are arranged such that the engagement of the hydraulic cylinders 22 with the roll chock 16 of the work roll 7 enables the work roll 7 to move in its axial direction. The lubricant supply device 1 for supplying a lubricant is arranged between the work roll 7 and the backup roll 8.

As a result, a rolling mill in which only crossing of the work rolls 7 is provided can be manufactured using the housing 20 of the existing rolling mill. Since in this rolling mill the work rolls 7 can be moved in their axial direction during rolling, program-free rolling is permitted. Furthermore, since the thrust applied to the work roll 7 can be reduced to an extent that does not cause problems even when the work rolls 7 cross each other by the action of the lubricant supplied from the lubricant supply device 1 between the work roll 7 and the backup roll 8, the roll can have an excellent ability to control the profile of the rolled material 9.

An example of the application of the above-described four-high rolling mill with crossed work rolls to a hot rolling system is described below with reference to Fig. 16.

Fig. 16 shows a hot rolling system in which a connecting device 63 for sequentially connecting the rolled rolling stock 9 is provided between the rough rolling stands 61 and the finishing rolling stands 62, and in which the rolling stock is connected to one another by the connecting device 63 after rolling by the rough rolling stands 61, the connected rolling stock being continuously rolled by the finishing rolling stands 62. At least one of the finishing rolling stands 62 is formed by the rolling stand described above, which has the pair of work rolls 7 and the pair of backup rolls 8 for respectively holding the work rolls 7 and in which the axes of the support rolls are not inclined in the horizontal plane, whereas the work rolls 7 can be inclined with respect to the support rolls 8 in the horizontal plane such that the axes of the work rolls 7 cross the axes of the support rolls 8 and that the work rolls cross each other, the work rolls 7 being movable in their axial direction and the lubricant supply device 1 for supplying a lubricant is provided between the work roll 7 and the support roll 8.

It is therefore possible to create a rolling stand in which only a crossing of the working rolls 7 is provided.

Furthermore, since the work rolls 7 are movable in their axial direction, they can be moved in the axial direction during rolling, thus enabling program-free rolling.

Moreover, since the lubricant supply device 1 is provided for supplying a lubricant between the work roll 7 and the backup roll 8, the thrust applied to the work roll 7 can be reduced to an extent that does not cause a problem in practical operation even when the work rolls cross each other by the action of the lubricant supplied between the work roll 7 and the backup roll 8. It is therefore possible to provide a rolling mill with crossed work rolls which has an excellent ability to control the profile of the rolling stock 9 to be rolled.

Therefore, the crossed work roll mill can be used as the finishing mill of the hot rolling system, in which the rolled stock rolled by the roughing mills is continuously rolled by the finishing mills.

The above-described rolling mill according to the present embodiment has a simpler structure than the conventional four-high rolling mill with pairs of crossed rolls and is suitable for more effective control of the profile of the sheet. The rolling mill according to the invention described above has a further advantage in that it can significantly reduce the thrust applied to the work roll, which is the most essential requirement of the crossed roll rolling mill. Accordingly, the thrust bearing can be simply constructed, a reduction in the diameter of the work roll is made possible, and displacement of the work roll is facilitated. The latter is crucial in the continuous rolling process in which the work roll must be displaced during rolling. In the present embodiment, changes in the crossing angle can be carried out easily and quickly since they are changes in the crossing angle of the rotating rolls. Therefore, the present embodiment is suitable for continuous rolling. Also, wear of the rolls which would be caused by slippage of the rolls can be significantly reduced by using a suitable lubricant. By using the online grinding device, the problem involving wear is improved and removal of the fatigue layer is enabled, and therefore the interval of replacement operation of the backup rolls, which is a tedious task, is greatly increased.

Claims (13)

1. Four-high hot rolling mill with - a roller stand (20) - a pair of work rolls (7) which are adjustable in horizontal planes and are oriented obliquely, the actuators (10, 11) of which act between the chocks (16) of the work rolls and the support blocks (30) of the roll stand (20) so that the axes of the work rolls (7) intersect with each other and also with the axis of the rolled material (9), and - a pair of support rolls (8) aligned transversely to the rolling stock axis, - wherein a first axial thrust force F₂ is exerted by each support roll (8) on the associated work roll (7) and a second axial thrust force F₁ from the rolling stock (9) acts on the work roll (7) so that a thrust force actually acting on the work roll (7) is equal to a difference (F₂ - F₁) between the first and second thrust forces (F₂ and F₁), characterized in that a lubricant supply device (1, 26-28, 50) is provided for the controlled supply of an axial thrust force reducing lubricant over the entire length of the contact zone between each work roll (7) and its associated backup roll (8), which contains a lubricating oil consisting mainly of mineral oil, in order to reduce the first axial thrust force (F₂) to such an extent that the axial thrust force actually acting on the work roll (7) is reduced to 5% or less of the maximum rolling force. 2. Roll stand according to claim 1, characterized in that in order to obtain a desired crossing angle between the upper and lower work rolls (7) during the rolling operation, a work roll crossing angle control (40) is provided for carrying out a feedback control of the actuating elements (10, 11) acting on the work roll chocks (16) using the signals of a sensor (13). 3. Roll stand according to claim 1 or 2, characterized in that the working rolls (7) are axially displaceable in opposite directions. 4. Roll stand according to one of claims 1 to 3, characterized in that one of the chocks (16) of each work roll (7) is detachably connected to a cross block (21) which is connected to the stand (20) by two hydraulic cylinders (22) and is guided on a fixed frame (23). 5. Roll stand according to one of claims 1 to 4, characterized in that roll cooling nozzles (2, 3) are provided for spraying cooling water against the working rolls (7). 6. Roll stand according to claim 5, characterized in that a scraper (32) is provided on each work roll (7) in order to prevent mixing of the cooling water with the lubricant. 7. Roll stand according to one of claims 1 to 6, characterized in that a hydraulic device (19) is provided on a surface of a column window, which presses a chock (17) of the support roll (8) against the other side of this window. 8. Rolling stand according to one of claims 1 to 7, characterized in that grinding devices (6) movable in the axial direction of the support rollers (8) are provided for grinding the barrel surface of the support rollers (8). 9. rolling stand according to one of claims 1 to 8, characterized in that a control device (50) is provided for controlling the lubricant supply to the contact zone between the working roll (7) and the backup roll (8) in accordance with the rolling conditions. 10. Hot rolling mill with a group of rough rolling stands (61) and a group of finishing stands (62), characterized in that at least one rolling stand of the group of finishing stands (62) is designed according to one of claims 1 to 9. 11. Method for hot rolling flat stock in a four-high stand, in which, in order to control the crowning of the flat stock (9), the axes of the work rolls (7) are aligned obliquely in the horizontal relative to the axes of the backup rolls during rolling, so that the axes of the work rolls intersect with one another and with the axes of the backup rolls, a first thrust force (F₂) being exerted by each backup roll (8) on the associated work roll (7) in an axial direction which is opposite to an axial direction in which a second thrust force (F₁) from the flat stock (9) acts on this work roll, so that an actual thrust force acting on this work roll (7) is equal to the difference (F₂ - F₁) between the first and second thrust forces, characterized in that a lubricant which is a mainly mineral oil-based containing lubricating oil, is supplied in a controlled manner to the contact zone between each work roll (7) and each backup roll (8) over their entire length during rolling in order to reduce the first axial thrust force (F₂) to such an extent that the thrust force actually acting on this work roll (7) is reduced to 5% or less of the maximum rolling force. 12. Rolling method according to claim 11, characterized in that the working rolls (7) are displaced in opposite axial directions. 13. Procedure for converting a four-high stand with the stages - Providing a hydraulic device (10) in a position on the stand (20) opposite a roll chock of each work roll (7), so that by means of this device, which can be operated in the direction of passage of the flat material (9), the axes of the work rolls (7) can be inclined horizontally relative to the axes of the support rolls (8), so that the axes of the work rolls cross each other and the axes of the support rolls, - providing another hydraulic device (21, 22) on the housing (20) which is effective in an axial direction of each work roll and which can act on the chock (16) of the work roll (7) to move the work roll in its axial direction, and - Providing a supply device for a controlled supply of a lubricant which reduces the axial thrust forces and which contains a lubricating oil composed mainly of mineral oil, into the contact zone between the working rolls and the associated back-up roll over their entire length, - so that the axial thrust force actually exerted on the working roll by lubricating this zone is not greater than 5% of the maximum rolling force exerted on the flat stock to be rolled during rolling operation of the stand.