JPH057084B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for rapidly stopping a continuous hot rolling mill, and more particularly to a method for rapidly stopping a continuous hot rolling mill when the operation of a continuous hot rolling mill is stopped due to trouble occurring during rolling operations.

In continuous hot rolling mills, it is often necessary to rapidly stop the operation of the rolling mill due to troubles such as abnormal tension occurring in the rolled material during rolling operations.
In this case, if the rotation of the rolling roll is suddenly stopped, the rolling roll will stop with the hot rolled material still bitten, and a large amount of heat will be transferred from the surface of the rolled material to the surface of the rolling roll. Cracks called "kame cracks" occur on the surface of the roll. When this type of crack occurs, the roll must be removed from the mill and reground. Therefore, it is desired to develop an improvement measure since it causes inconveniences such as a decrease in rolling efficiency and a deterioration in the roll unit consumption. Conventionally, as a countermeasure against this problem, a command to raise the upper roll or lower the lower roll (hereinafter referred to as release of rolling) is issued at the same time as the rapid stop command to widen the gap between the upper and lower rolls. However, releasing the reduction of the rolling roll during rolling also involves releasing the elongation generated in the housing of the rolling stand due to the rolling load, which results in a considerable stroke and requires a considerable amount of time. In particular, as shown in Table 1, in the case of the rolling stand F1 which has a large rolling reduction, a considerable amount of time is consumed to release the rolling. On the other hand, the drive motor for the rolling rolls is stopped very quickly. Therefore, in the conventional method of rapidly stopping the drive motor of each rolling roll and releasing the reduction at the same time, when the rotation of the rolling roll, especially the rolling roll with a large reduction amount, is stopped, the rolling load still remains, and the rolling The above-mentioned "cracking" occurs because a part of the roll surface is pressed against the surface of the rolled material.
occurs. In addition, when the rolling speed is slow, the time required to stop rolling is shortened, but the time required to release the roll is not shortened. Therefore, when the rolling speed stops, the surface of the rolling roll is in pressure contact with the rolled material. This increases the number of opportunities for cracks to occur, leading to more occurrences of "kame cracking". Furthermore, as shown in Table 1, the time required for each rolling stand to stop varies, and as a result, the rolled material may be cut or cobbled between the rolling stands, making troubleshooting work even more difficult. The present invention seeks to solve these problems with previous methods of rapidly stopping continuous hot rolling mills.

The object of the present invention is a method for rapidly stopping the operation of a continuous hot rolling mill without causing cracks in the rolls of the continuous hot rolling mill, and without causing cuts or cobbles in the rolled material. It's about getting.

According to the present invention, when suddenly stopping a continuous hot rolling mill during operation, first all rolling stands start releasing the reduction of the rolling rolls, and at the same time all rolling stands decelerate to almost the same deceleration end time. After that, the rolling rolls of each rolling stand start low-speed operation at a pre-selected speed,
A method for rapidly stopping a continuous hot rolling mill is provided, which comprises continuing low-speed operation of each rolling stand for a predetermined period of time, and stopping each rolling stand after the rolling rolls of a desired rolling stand are released. .

An embodiment of the method of the present invention will now be described with reference to the accompanying drawings.

The present invention enables the rolling mill to take some time to complete even when it is necessary to quickly stop the rolling mill due to problems such as abnormal tension occurring in the rolled material during rolling operations using a continuous hot rolling mill. In order to prevent cracking of the rolling rolls and the occurrence of cuts and cobbles in the rolled material even when consumed, to ensure the safety of the equipment in operation, and to stop the rolling mill without hindering the resumption of rolling work. The gist of this method is to reliably release the desired rolling of the rolls before completely stopping the drive motor of each roll. In addition, when an emergency stop is performed due to a failure of the rolling mill itself, it is necessary to stop the rolling mill as quickly as possible, and therefore it is outside the scope of the present invention.

Table 1 shows an example of the residual load and stopping time at sudden stop in a 7-high continuous hot finishing rolling mill for each rolling stand F1 to F7. In Table 1, the rolling stands F1 to F5 are stopped with the rolling load applied to them, and in this state, the rolled material is pressed against the rolling rolls, so cracks occur as described above. In rolling stands F6 and F7, the rolling load is zero and the rolled material is separated from the rolling rolls, so cracks do not occur. In the case of Table 1, the reduction amount of the rolling stand F1, which has the largest amount of reduction, is 14 mm, and it takes about 20 seconds for the rolling roll to be released from pressure contact with the rolled material. Therefore, rolling stand 6
In F1, cracks will no longer occur if the car is stopped for 20 seconds or more. The same thing can be applied to other rolling stands, but in order to prevent cuts and cobbles from occurring in the rolled material, the rolling stand that requires the largest amount of reduction in all rolling stands and requires a long time to separate the rolling rolls from the rolled material. F1
must be stopped at the same time as the roll release time. Table 1 also shows that the time required to stop rolling stand F7 is 7.5 seconds and that the rolling reduction amount of rolling stand F3 is 5.1 mm.

Figure 1 shows the number of revolutions of each rolling roll from when a sudden stop command is issued until the stop when all rolling stands are stopped in 20 seconds in line with rolling stand F1, which requires the longest time to release rolling. In the diagram showing the transition, the solid lines are for each rolling roll F1, F2, F3, F.
4, F5, F6, and F7, the dotted line shows the sudden stop time and rotation speed due to the deceleration characteristics unique to each roll when stopping each roll without considering cracks. The one-dot chain line shows the time course of release of rolling of the first rolling stand F1. As shown by the solid line in FIG. 1, when all the rolling stands are aligned with the first rolling stand F1 and stopped at the same time, the length of the rolled material that is rolled during deceleration tends to become too large. Furthermore, when rolling is released, rolling stands tend to be released in order starting from the rolling stand at the later stage, which causes cobbles. This is because even though the rolls in the front rolling stand are still rolling and the rolled material is starting to stretch towards the rear rolling stand, if the rolls in the latter rolling stand do not roll, the rolled material that was stretched in the front rolling stand will not roll. When pushed, a "cobble" occurs in the area adjacent to the rear stand.

In view of the above facts, the present invention intends to decelerate all rolling stands as quickly as possible. Specifically, all rolling stands are decelerated in approximately the same time as No. 7 rolling stand F7, which has the longest stop time shown in Table 1, and the mechanically permissible low speed is such that it does not cause any trouble to oil film bearings, etc. Rotation is started at , and this low-speed rotation is continued for a predetermined period of time until all rolling rolls are released from the rolled material, and then all rolling stands are completely stopped. The speed of this low-speed rotation, which is maintained for a predetermined period of time, is set so that it becomes slightly faster as it approaches the later rolling stands, and is stopped in a state where the rolled material is under some tension to prevent cutting of the rolled material and occurrence of cobbles. To prevent. Since all the rolling stands are kept rotating at low speed and then stopped, the length of the rolled steel material is shorter than in the case of FIG. 1, and the occurrence of cuts and cobbles in the rolled material can be reduced. Note that it is preferable to allow a certain amount of time for the duration of low-speed operation of each rolling stand in consideration of cases where the rolling reduction amount is large or low-speed rolling operations where the deceleration time is short.

In the embodiment of the present invention shown in FIG. 2, even if some cracks occur in the front rolling stand, rolling can continue as is, so it can be used when it is necessary to shorten the time spent on stopping. For example, if the rolls of the first and second rolling stands F1 and F2 are sacrificed to some extent, the rolls of the third rolling stand are
A method for stopping all the rolling rolls is established based on the point in time when rolling stands F3 and subsequent rolling rolls are released from the rolled material.

In this case, it can be seen from Table 1 that the rolling reduction amount of the third rolling stand F3 is 5.1 mm, but it takes about 8 seconds to actually raise the rolling roll by this rolling amount and release the rolling roll from the rolled material. . Therefore, in consideration of the case where the rolling reduction amount is large, a 3 second margin is added, and the time required for all rolling stands to stop after a rapid stop command is set to approximately 11 seconds. On the other hand, all rolling stands have a stop time of the seventh rolling stand F7.
The main motor is controlled to decelerate in almost the same amount of time corresponding to 7.5 seconds. Furthermore, the rotation speed of the low-speed rotation that is continued before all the rolling stands stop is set, for example, F1: 4 rpm, F2: 5 rpm, F3: 6 rpm,
F4, F5, F6: 7 rpm, F7: 8 rpm, and each rolling stand shifts to low speed rotation at the time a1 when it reaches the above-mentioned low speed rotation speed, that is, in this example, about 7.5 seconds after the rapid stop command, The main rolling mill is controlled so that all rolling stands stop at time a2, which is approximately 11 seconds after the rapid stop command and 3.5 seconds after the shift to low speed rotation. The shaded area in FIG. 2 indicates the period during which low speed rotation is maintained.
The rotation of the rolls in each rolling stand is controlled as described above, and the rolling release of each rolling roll is started by a command issued at the same time as the rapid stop command. When the rotational speed of each rolling roll reaches time point a1 of the low rotational speed in FIG. 2, a low speed rotation holding timer is activated. After that, all the rolling stands are sequentially stopped at a time point a2 when the set time of the timer has elapsed, but during this time, the rolls of the third rolling stand F3 are released from the rolled material as shown by the dashed line.
Of course, the rolls after the fourth rolling stand F4 have already been released, so they will not be affected by heat from the rolled material. In this case, the first rolling stand F1 and the second rolling stand F2 have not yet been released from the rolling material, but the second rolling stand F1
2 is released immediately after 1.1 seconds, and the first rolling stand F1 is released after 3 seconds, and the contact with the rolled material is for a short time, and the occurrence of cracks is extremely small. There will be no impact. Note that even if the stop command (a2) for all rolling stands is represented by the timer of the final rolling stand, the difference in stopping time does not matter because the rotational speed of each rolling roll at that time is low.

Figure 3 shows a flow chart of the process in Figure 2. First, when a trouble occurs, it is determined whether the rolling mill itself is malfunctioning or not, requiring an emergency stop. When it is determined that there is no rolling force, a command is issued for a rapid stop, but at the same time a command is issued for releasing the rolling of each rolling stand. The rapid stop command starts to reduce the rotation speed of each rolling roll, but after detecting whether the rotation speed has reached the set rotation speed, a timer is used to maintain low speed rotation for a predetermined time and the timer turns off. At this point, a command to stop all rolling stands is issued.

When rolling work is carried out according to the present invention, approximately 50 sets of rolling rolls are used and approximately 60% of the conventional method (for 3 months)
The number of cracks that previously occurred has been reduced to approximately 15%, and the occurrence of cuts and cobbles in the rolled material during rapid stops has been significantly reduced, greatly contributing to improvements in rolling efficiency and roll consumption. The place was hot.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the change in the number of rotations of each rolling roll during the period from the rapid stop command of the hot continuous rolling mill to the stop, and Fig. 2 is a diagram showing the transition of the rotation speed of each rolling roll during the period from the rapid stop command to the stop of the hot continuous rolling mill according to the present invention. FIG. 3 is a flow chart showing the sequence of commands and rotation speed settings in the process from rapid stop to stop in FIG. 2.

【table】

Claims (1)

[Scope of Claims] 1. When suddenly stopping a hot continuous rolling mill during operation, first all rolling stands start releasing the reduction of the rolling rolls, and at the same time all rolling stands have almost the same deceleration end time. After slowing down to
The rolling rolls of each rolling stand are started to operate at low speed at a preselected mechanically permissible speed, and the low speed operation of each rolling stand is continued for a predetermined period of time to achieve the rolling reduction of the rolling rolls of the desired rolling stand. A method for rapidly stopping a continuous hot rolling mill, comprising stopping each rolling stand after the rolling stand is released. 2. The scope of claims characterized in that, although the speed is approximately similar to the low-speed operation speed of each of the rolling stands, the rolling rolls in the later stage are selected to be slightly faster than the rolling rolls in the preceding stage. A method for rapidly stopping a continuous hot rolling mill as described in item 1.