Roller leveler driving apparatus

Abstract

 A roller leveler comprises a plurality of bottom straightening rolls that are disposed at intervals below the pass-line of the workpiece and top straightening rolls that are disposed, zigzagged with respect to the bottom straightening rolls, above the same pass line. The workpiece is caused to move forward by driving the top and bottom straightening rolls simultaneously while being flattened. A driving apparatus for this roller leveler has a torque-limiting coupling that is attached to all or all but one output shafts from a driving unit. Even if any excess friction torque develops in the roller leveler, no greater torque than the predetermined one is transmitted to the driving unit since the torque-limiting coupling absorbs the energy produced by the excess torque. Also, even when the output of the driving unit works concentratedly on only one of the intermediate or distribution shafts, the torque-limiting coupling reduces the excess torque to the predetermined level (Figure 4).

Description

BACKGROUND OF THE INVENTION

[0001] This invention relates to an apparatus for driving a roller leveler that levels such steel plates, especially heavier-gage ones than those which develop excess unbending reactive force and torque during leveling.

[0002] Until recently, lower-strength grades for ship- building and general industrial machinery accounted for the majority of steel plates. High-tensile steels used to be manufactured by applying an off-line reheating treatment after finish rolling. Accordingly, the hot roller leveler immediately after the finishing mill more often than not dealt with plates of lower tensile strength. As a result, the hot roller leveler was not subjected to any large reactive force and,. therefore, did not require any large driving force.

[0003] Recently, there has been a notable increase in the demand for plates for line pipe. To meet this growing demand, a newly developed process, known as the continuous in-line quality control cooling process, combining controlled rolling and forced cooling immediately after rolling has been put to increasing use. This process is designed to manufacture high-tensile steel plates in-line that used to be manufactured through the application of off-line heat treatment. Meanwhile, plate flatness requirements have been growing increasingly stringent. Because of these recent changes, the hot roller leveler must now

[0004] provide heavier flattening to steels of higher strength under greater pressure. Therefore, the hot roller leveler for use in the continuous in-line quality control cooling process must have:

(1) High enough rigidity to withstand the high pressure involved in the flattening operation; and

(2) High-power driving means.

[0005] Fig. 1 shows an example of a roller leveler driving apparatus of the conventional type which essentially comprises a drive motor 1,' speed reducer 2, distributor 3 and spindle (not shown).

[0006] The rotation produced by the drive motor 1 is reduced by the reduction gears 4 in the speed reducer 2 and then transmitted to five intermediate shafts 6 via large distribution gears 5. The rotation is further transmitted to thirteen driving shafts 8 via small distribution gears 7 in the distributor 3. Thus, the power from the motor 1 is transmitted to each pair of top and bottom leveling rolls (not shown) through a spindle (not shown) coupled to each of the driving shafts 8.

[0007] With the five intermediate shafts 6 mechanically coupled to the large distribution gears 6, the following problems have arisen from time to time;

1) Positive or negative torque works on each spindle for some reason.

2) The power of the motor 1 works on only one of the driving shafts 8 or intermediate shafts 6.

[0008] When either or both of these troubles occur(s) during operation, an enormous amount of torque developes on each spindle, causing the spindle and/ or the shear pin in a coupling 9 to fracture. As a consequence, the flattening ability of the level gets lessened to such a level that only plates of lower rigidity can then be leveled.

SUMMARY OF THE INVENTION

[0009] The object of this invention is to provide an apparatus for driving a roller leveler that permits steel plates to be leveled safely and smoothly, avoiding the development of excess torque that might lead to the fracture of the drive unit.

[0010] According to this invention, a torque-limiting coupling is attached to all, or all but one, output shafts to which the motion of a single driving unit is transmitted in an apparatus for driving a roller leveler which comprises a plurality of bottom straightening rolls that are disposed at intervals below the pass line of the piece and top straightening rolls that are disposed, zigzagged with respect to the bottom rolls, above the same pass line. The apparatus sends the piece forward while flattening by driving the bottom and top rolls simultaneously.

[0011] Even if any excess torque develops in the roller leveler, the torque control coupling absorbs the energy generated by it, so no torque greater than the predetermined level is transmitted to the driving unit. Also, conversely, even if the output of the driving unit works concentratedly on a single intermediate or distribution shaft, the torque transmitted is kept to the predetermined level.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] 

Fig. 1 is a plan view of a driving apparatus of the conventional type;

Figs. 2 and 3 illustrate the mechanism by which friction torque is produced, Fig..2 shows the relationship between the travel speed of the plate and the radius of curvature, while Fig. 3 shows the magnitude of friction torque;

Fig. 4 is a plan view of a driving apparatus according to this invention;

Fig. 5 is a cross section seen in the direction of the arrows A-A in Fig. 4; and

Fig. 6 is a system diagram of another embodiment of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Now this invention will be described in detail by referring to the accompanying drawings.

[0014] Taking interest in the cause that produces the positive and negative excess torque mentioned previously, the inventors made various studies. The studies have shown that the excess torque results from the friction torque that develops between the plate and rolls when there is any difference in the amount of reduction between the entry and exit ends of the roller leveler. They have further shown that the magnitude of the friction torque is proportional to the magnitude of the force produced in reaction to the leveling action.

[0015] Figs. 2 and 3 briefly show the mechanism by which the friction torque is produced. In Fig. 2, the plate 11 is bent by the i-th leveling roll 10 arid gets curved to a radius R_i at a point of contact with the roll. Since the center of curvature O can be an instantaneous one, the relationship between the velocity V_. of the neutral plane in the direction of plate thickness and the peripheral velocity V_o of the roll can be expressed as follows, if the peripheral velocity V is constant and, in addition, equal to the surface velocity of the plate or, in other words, if no slippage occurs between the surface of the plate and the roll:

[0016] Under the aforementioned conditions, it may ^gen- erally be said that the velocity V_i of the neutral plane increases with an increase in the amount of reduction or a decrease in the radius of curvature R_i. Ordinary roller levelers perform what is known as the skew or slant pressing in which heavier pressing is given at the entry side than at the exit side, so the amount of pressing achieved varies from roll to roll. In Fig. 2, for example, δ_i ^> δ_i+1 or ^R_i ^< R_i+1. In this type of skew pressing, however, the velocity of the neutral plane V_i of the plate tends to become different on different rolls, such as V_i ^> V_i+1 in Fig. 2. Then, equation (1) or the aforesaid condi-. tions do not hold. Then, slippage occurs between the plate and rolls in order to reduce the roll-to-roll speed difference as the neutral plane velocity V_i of the plate 11 should essentially be constant. The re- a sult is the creation of/frictional force, as shown in Fig. 3. P_a, P_b and P_c designate the reactive forces that are developed against the leveling action on the rolls 10a, 10b and 10c, µ the coefficient of kinetic friction, fa and f_c the frictional forces. If the roll radius is r, then the frictional torques T_a and T_c can be expressed as follows:

[0017] Equations (2) and (3) show that the friction torque is proportional to the reactive force against the leveling action. The reactive force varies from roll to roll as it increases with an increase in the amount of pressing. As may be evident from the relationship expressed by equation (1), therefore, a group of rolls that provide heavier pressing cause the plate to move forward at a higher speed, thus producing a greater friction torque. Consequently, such a group of rolls tend to rotate other group or groups of rolls that provide lighter pressing (and, therefore, impart lower travelling speed and develop smaller reactive force). Therefore, ^a/positive friction torque develops on the group of rolls providing heavier pressing whereby the plate is caused to move forward through the rolls while a being flattened, whereas/negative friction torque develops on the group of rolls providing lighter pressing whereby the rolls are rotated by the motion of the plate. Since the driving apparatus of the roller leveler is designed to drive groups of rolls through a mechanical coupling, positive and negative torques are exchanged among the individual groups. Being much greater than the flattening torque that is derived from an ordinary theoretical equation, the friction torque often causes the fracture of a spindle and other troubles. Even if the driving force for each roll is varied in advance depending on the roll-diameter, the development of the friction torque cannot be avoided since it arises if the amount of pressing and/or roll diameter varies, even slightly, from roll to roll. Providing a separate driving apparatus to each roll is also virtually meaningless because the friction torque develops in each unit. The foregoing may be summarized as follows:

1) A friction torque develops if the amount of reduction or roll diameter varies among a plurality of rolls that are driven by a driving apparatus through a mechanical coupling.

2) Friction torque is proportional to the amount of the reactive force against the flattening action. The sum of overall friction torque remains constant. Therefore the development of the positive and negative friction torques cannot be prevented by driving individual rolls by different driving apparatuses.

3) The slippage between the plate and rolls may produce scratches on the surface of the plate.

[0018] A friction torque can be caused also by other phenomena than those described above, such as:

(1) The expansion or contraction that occurs where the workpiece is particularly heavily pressed while it is being repeatedly bent in the course of flattening; and

(2) The shrinkage that results from the lowering of the temperature of the workpiece being flattened on a hot roller leveler.

[0019] This invention perfectly eliminates the likelihood of the roller leveler driving apparatus of getting damaged or broken by the excess friction torque deve- lopped between the plate and leveler rolls and permits the plate to be straightened safely and smoothly. A roller leveler driving apparatus embodying the principle of this invention will be described in the following by reference to Fig. 4.

[0020] The arrangement and structure of a motor 1, speed reducer 2 and distributor 3 are identical to those shown in Fig. 1. The driving method is of the mechanical coupling type whereby the rotation from the motor is transmitted to thirteen distribution shafts 8a through 8m by way of five intermediate shafts 6a through 6e. Couplings 12 and a torque-limiting coupling 13 are attached to the distribution shafts 8a through 8m on the output side of the distributor 3. Here the torque-limiting coupling is a generic name given to couplings such as hydraulic or friction clutch coupl- ingsthat keep substantially constant the torque that is transmitted from the driving side to the driven side, or in the opposite direction,

[0021] even if the torque developed exceeds the predetermined level, by absorbing the energy produced by such excess torque. The rotation of the intermediate shaft 8a is transmitted through a small distribution gear 7a to the distribution shafts 8a and 8b. Similarly, the rotation of the intermediate shaft 6b is transmitted to the distribution shafts 8c, 8d and 8e, that of the intermediate shaft 6c to the distribution shafts 8f, 8g and 8h, that of the intermediate shaft 6d to the distribution shafts 8i, 8j and 8k, and that of the intermediate shaft 6e to the distribution shafts 81 and 8m. Fig. 5 is a cross section

[0022] in the direction of the arrows A-A in Fig. 4.

[0023] The function of the torque-limiting coupling is to limit the amount of torque working on the individual distribution shafts 8a through 8m. Even if any excess friction torque is developed as a result of a slippage between the plate and roll, no torque greater than the predetermined one is transmitted to the driving unit. Even if, conversely, the power of the motor 1 works concentratedly on only one intermediate or distribution shaft, no torque greater than the predetermined one is allowed to develop. While the positive and negative friction torques are being eliminated, such an amount of torque as is necessary for flattening is transmitted through the torque-limiting coupling to ensure a smooth leveling operation.

[0024] With all excess torque reduced to the predetermined level, the roller leveler is now able to perform its leveling function stably freed from the excess- torque-induced breakage of its driving unit or other troubles.

[0025] In order to prevent the slippage between the plate and rolls, the torque-limiting coupling may be equipped with a mechanism to vary, either stepwise or continuously, the level of the torque transmitted therethrough.

[0026] In the preferred embodiment just described, one torque-limiting coupling 13 is attached to all distribution shafts 8a through 8m. Or otherwise, as shown in Fig. 6, an independent motor may be provided to each roll, with a torque-limiting coupling 13 attached to all or all but one distribution shafts in each driving unit.

[0027] By controlling the rotating speed of the motor, no speed difference arises between the shaft and the plate, if only one shaft is left uncoupled, whereby the development of the positive and negative friction torques can be prevented. However, two or more shafts should not be left uncoupled since, in that case, there arises a speed difference between either or any of the shafts and the plate.

[0028] The driving apparatus according to this invention is suited for use with roller levelers that flatten steel plates and other plate-formed products, especially those products which develop excess reactive force and torque during leveling. The driving apparatus of this invention can be used not only with hot roller levelers but also with all kinds of roller levelers.

Claims

Driving apparatus for a roller leveler which comprises a plurality of bottom straightening rolls that are disposed at intervals below the pass line of the workpiece and top straightening rolls that are disposed, zigzagged with respect to the bottom rolls, above the same pass line, and sends the workpiece forward while flattening by driving the bottom and top rolls simultaneously, characterized in that a torque-limiting coupling is attached to all or all but one output shafts from a single driving unit.

Drawing