JPS6140728B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing shape defects in a steel strip in a continuous annealing furnace, and in particular, to an analysis of the cause of shape defects and a method for preventing shape defects in a steel strip in a continuous annealing furnace. This invention relates to a method for preventing defects in the shape of a belt.

Conventionally, in continuous annealing furnaces, shape defects that occur in the quenching zone immediately after soaking are corrected in the overaging treatment zone installed next to the quenching zone, and those that cannot be corrected are processed using a skin pass or a skin pass after the continuous annealing furnace. Correction was performed using forced correction devices such as tension levelers.

However, in this method, it is necessary to provide an overaging treatment zone immediately after the quenching zone due to the line configuration, and to provide a skin pass mill or tension leveler after annealing, which requires extra equipment. In particular, in recent years, as an operating method for manufacturing composite structure high-strength cold-rolled steel sheets, methods have been considered in which the steel strip is taken out of the furnace immediately after the quench zone and is wound without passing through a skin pass or tension leveler. There is. In this case, an overaging zone, skin pass mill, tension leveler, etc. are not required. However, due to this, there is a risk that the steel strip may suffer from shape defects, and countermeasures are required in this case.

FIG. 1 is a side sectional view showing an example of a general rapid cooling zone.

A soaking zone is provided before the quenching zone, and an overaging zone is provided subsequent to the rapid cooling zone, and the steel strip 1 passes through each zone in sequence. In the rapid cooling zone, a plurality of cooling devices 2 are provided in each horizontal row so as to sandwich the steel strip 1 .

The meandering of the steel strip 1 is corrected by steering rolls provided in the soaking zone, and then sent to the quenching zone where it is rapidly cooled from the soaking temperature to a predetermined cooling temperature before being sent out of the furnace. For example, in the case of manufacturing a composite structure high-strength cold-rolled steel sheet, the temperature of the steel in the soaking zone is 700°C to 900°C, and the temperature of the steel strip at the exit of the quenching zone is around 100°C.

FIG. 2 shows an example of plate temperature characteristics in the quenching zone.

A to F in FIG. 2 correspond to path positions A to F in the rapid cooling zone in FIG. 1, and this is an example in which cooling is almost completed between A and B. In such a region where the temperature changes suddenly, the temperature difference in the width direction of the steel strip is large, so that the steel strip 1 is likely to have a poor shape due to the collapse of the internal stress balance.

Causes of shape defects include differences in temperature in the strip width direction, uneven tension in the steel strip in the strip width direction that appears as a result of strip meandering and uneven strip temperature, and tension between the steel strip and the machine in the quenching zone. Contact with equipment, etc.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for preventing shape defects of a steel strip in a continuous annealing furnace, which addresses each cause of shape defects and eliminates the above-described conventional drawbacks.

The present invention, in an operation method in which a steel strip is pulled out of the furnace and wound immediately after quenching, determines which of the three causes of shape defectiveness falls under immediately after the quench zone,
Based on this, the rapid cooling zone is controlled or an alarm is generated.

As shown in Figure 1, there are 3 tension gauges placed at various locations in the rapid cooling zone.
a and 3b are installed to detect the balance of tension in each part of the steel strip 1. Furthermore, a plate thermometer (scanning type thermometer) 4 is installed in the quenching zone to measure the temperature unevenness of the steel strip 1.
a and 4b are provided. In addition, a shape detector 5 for detecting shape abnormalities of the steel strip 1 is installed at the outlet of the quenching zone.
(for example, an overcurrent displacement meter).

First, when a signal indicating a defective shape is output from the shape detector 5, the tension balance is checked by the tension meter 3b. Next, the plate temperature unevenness in the plate width direction is checked using the plate thermometers 4a and 4b. If both the plate temperature unevenness and tension balance are within the allowable values, an alarm will be output. This alarm means that a shape defect has occurred such as contact between the steel strip 1 and the cooling device 2, and the operator must immediately inspect the quenching zone. Note that if the tension is balanced but uneven plate temperature occurs, an alarm is output. This alarm requests plate temperature control (feedback control to the cooling device using a plate thermometer).

If the tension gauges 3a and 3b detect an abnormality in the tension balance, check the plate temperature unevenness using the plate thermometers 4a and 4b, and if the plate temperature unevenness is within the allowable range, check for slippage of the steel strip in the quenching zone. Since it is possible that the steel strip is meandering due to an abnormality in the roll balance, an alarm is output in response to this, and the line speed is reduced and the tension in the furnace is controlled to increase.

Further, if the tension balance is disrupted and the plate temperature is uneven, and there is a positive correlation between the two, an alarm is output and the plate temperature is controlled. Note that if a positive correlation is not found between the two, appropriate measures are taken depending on the degree of the shape defect.

That is, if the shape defect is within a separately determined reference value, an alarm is output and plate temperature control is performed. If the tension does not fall within this reference value, immediate action is required, so an alarm is output, a tension balance correction process is performed, and the operator is requested to monitor the situation.

As mentioned above, the plate temperature control execution time at alarm~ is determined in relation to the response characteristics of the furnace.
In reality, it takes several tens of seconds to several minutes. Furthermore, if the defective shape is resolved by plate temperature control, the related alarms are reset. If the defective shape is not resolved, it can be assumed that the imbalance of tension is a major factor, and the process proceeds to alarm processing. Note that this process is performed with priority over plate temperature control using a normal plate thermometer, and after entering a stable region, normal plate temperature control is resumed.

FIG. 3 is a flowchart showing the above series of processes.

According to the present invention, shape control can be performed in a continuous annealing furnace, and there is no need to provide a skin pass or tension leveler in a subsequent process. In particular, in the production of composite structure high-strength cold-rolled steel sheets, it is desirable to direct the steel sheets to a refining line without passing through a skin pass mill, and the present invention is optimally applied.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of the quenching zone, FIG. 2 is a characteristic diagram of plate temperature characteristics in the quenching zone, and FIG. 3 is a processing flow chart of the present invention. 1... Steel strip, 2... Cooling device, 3a, 3b...
Tension meter, 4a, 4b... Plate thermometer, 5... Shape detector.

Claims (1)

[Claims] 1. Based on the tension balance detected by a tension meter installed on a roll in a quenching zone constituting a continuous annealing furnace and the plate temperature unevenness of the steel strip in the quenching zone, A method for preventing shape defects in a steel strip in a continuous annealing furnace, characterized by controlling each of plate temperature, tension, and speed. 2. In claim 1, a first alarm requests inspection of the rapid cooling zone according to the value of the plate temperature unevenness when the tension balance is abnormal;
A method for preventing shape defects of a steel strip in a continuous annealing furnace, characterized by outputting a second alarm and a plate temperature control signal. 3. In claim 1, when the tension balance is normal and the plate temperature unevenness is abnormal,
Alternatively, when the tension balance and the plate temperature unevenness are both normal and there is no correlation between the two, the output of the third alarm and the line speed of the quenching zone or the tension in the furnace are controlled. Method for preventing poor shape of belts. 4. According to claim 1, when the tension balance and the plate temperature unevenness are both normal and have a positive correlation, the plate temperature control and the fourth alarm are output. Method for preventing shape defects of steel strips in an annealing furnace. 5. In claim 1, when both the tension balance and the plate temperature unevenness are normal and there is no correlation between them, and the process is performed with priority given to plate temperature control, plate temperature control and 5. A method for preventing shape defects of a steel strip in a continuous annealing furnace, characterized by outputting an alarm.