JPH0350614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling vibration of a mold for continuous metal casting.

In general, in a continuous casting machine that uses only machine oscillation, the oscillation stroke during casting remains constant and does not change, and the oscillation frequency is variable within a certain range. Therefore, even if the powder flow conditions were poor during casting, it was not possible to control the increase or decrease in the amount of powder flow. This is because it is known that when the oscillation frequency is increased, the amount of powder flowing in decreases, and when the oscillation frequency is decreased, the negative strip time cannot be secured, leading to a locking breakout.

Generally, uneven inflow of powder increases surface defects such as vertical cracks. Furthermore, it is known that when the amount of powder flowing in is insufficient, the occurrence of restraint breakouts increases.

If there is uneven inflow of powder, the temperature of the mold wall in areas where the powder is thicker will be lower, and the mold wall temperature will be higher in areas where the powder is thinner. Therefore, the amount of temperature fluctuation per unit time at the temperature measurement point provided in the mold wall below the surface of the hot water becomes large when there is uneven inflow of powder. Furthermore, if the powder does not flow sufficiently, this will appear as an abnormal rise in the mold wall temperature, resulting in a large amount of temperature fluctuation.

On the other hand, a method has recently been proposed for applying ultrasonic vibration to a continuous casting mold to prevent seizure between the slab and the mold. It was confirmed that by measuring the amount of temperature fluctuation over time, the lubrication situation between the mold and the slab can be evaluated, and by adjusting the amount of vibration of the mold based on that, a good lubrication condition can always be obtained. .

That is, the present invention provides a vibration control method for a continuous casting mold in which ultrasonic vibration is applied to the mold.
Temperature differences within a unit time are determined continuously or intermittently using temperature measurement points provided within the mold wall in a height range of ~300 mm, and the ultrasonic output is adjusted to reduce the temperature difference. The present invention is a vibration control method for a continuous casting mold, and is also a mold vibration control method for simultaneously adjusting ultrasonic output and machine oscillation vibration.

According to the present invention, by using ultrasonic excitation in combination with machine oscillation, it is possible to increase the amount of powder flowing in, and the oscillation mark on the slab surface becomes shallower, resulting in cracks and other problems on the slab surface. Defects are reduced.

Further, in the case of only ultrasonic excitation, the amount of powder flowing in is proportional to the ultrasonic excitation power, that is, the amplitude, and as a result of the disappearance of oscillation marks, surface defects are also reduced.

The present inventors analyzed these phenomena and used the amount of variation in mold wall temperature per unit time as a means to evaluate the degree of uniformity of powder inflow.
As a method of controlling the amount of powder flowing in, by adjusting the ultrasonic excitation power and machine oscillation frequency, it is possible to easily maintain the best powder flowing condition, that is, the best mold lubrication condition, and as a result, the slab In addition to improving the surface quality of the mold, it was found that the occurrence of restrictive breakouts caused by poor mold lubrication could be greatly reduced.

The measurement point for the mold wall temperature needs to be close to the hot water surface in the mold height direction, but if it is too close to the hot water surface, it will be greatly affected by changes in the hot water surface level, so Desirably 10mm or more downward. Also, if it is too low, it will not reflect the powder flow situation, so it is preferable to set it up to 300mm below the hot water surface.

The temperature measurement method of the present invention may be a thermometer embedded in the mold wall through the cooling water passage, such as a thermocouple, or a thermometer installed through the inside of a bolt for fixing the mold copper plate. Furthermore, a thermometer installed on the combined surface of the combined mold may be used, but it is advantageous to use a thermometer close to the inner surface of the mold wall in terms of response speed and the ability to clearly see temperature changes.

Examples according to the present invention will be described below.

Example 1 Slab size 1000mm x 210mm, casting speed 1.0m/
Since machine oscillation was not performed under the casting conditions of min and ultrasonic frequency of 14 KHz, the ultrasonic excitation output was varied.

Figure 1 shows the temperature output from a thermocouple installed at a depth of 3 mm from the surface of the copper plate on the short side of the mold assembly section located 60 mm below the hot water level.

The vertical axis is the measured temperature, and the horizontal axis is time.

The idea of temperature difference within unit time is shown in the same figure.

FIG. 2 shows the amount of temperature fluctuation within one minute for the same thermocouple. Under these conditions, by adjusting the ultrasonic output to 4 to 5 Kw, the amount of temperature fluctuation was reduced, and the powder flow conditions and lubrication between the mold and slab were optimized.

Example 2 Slab size 1800mm x 210mm, casting speed 1.3m/
min, machine oscillation frequency 115Hz, machine oscillation stroke 7mm, ultrasonic frequency
Ultrasonic excitation output under 14KHz casting conditions.
Changed from 0Kw to 5.5Kw.

Figure 3 shows, on the vertical axis, the difference between the maximum and minimum temperatures within 1 minute of a thermocouple installed at a depth of 3 mm from the short side copper plate surface of the mold assembly part located 60 mm below the hot water level. It is.

A region where the amount of temperature fluctuation is minimum is observed at a position where the ultrasonic output is 2Kw to 3Kw.

FIG. 4 shows the relationship between the surface quality of the slab and the amount of mold wall temperature fluctuation. It can be seen that the surface quality of the slab improves as the amount of temperature fluctuation decreases, that is, as the powder flow becomes more uniform. Under these conditions, by adjusting the ultrasonic output within the range of 2 to 3 Kw, it was possible to reduce the cast iron handling rate to zero.

Although the above example is for continuous slab casting, it is clear that the invention can be similarly applied to continuous bloom and billet casting.

As explained above, according to the present invention, by adjusting the amount of mold vibration such as ultrasonic vibration and machine oscillation frequency, so as to reduce the amount of temperature fluctuation on the mold wall, the distance between the mold and the slab is reduced. As a result of being able to maintain the best possible lubrication conditions, the surface quality of the slab can be greatly improved, and useful effects such as reducing locking breakout accidents due to poor lubrication are brought about.

[Brief explanation of drawings]

Fig. 1 is a chart showing the concept of temperature difference within unit time, Fig. 2 is a chart of mold temperature fluctuation amount and ultrasonic excitation output of the present invention, and Fig. 3 is a chart of another example of the present invention. Chart of mold temperature variation and ultrasonic excitation output, 4th
The figure is a chart of the cast iron handling rate and mold temperature fluctuation amount according to the present invention.

Claims (1)

[Claims] 1. In a vibration control method for a continuous casting mold in which ultrasonic vibration is applied to the mold, temperature measurement points provided in the mold wall at a height range of 10 to 300 mm below the molten metal surface are used to measure the temperature per unit time. 1. A method for controlling vibration of a continuous casting mold, characterized by continuously or intermittently determining a temperature difference within the mold, and adjusting ultrasonic output so as to reduce the temperature difference. 2. In a continuous casting mold vibration control method in which ultrasonic vibrations are applied to the mold, temperature differences within a unit time are continuously measured using temperature measurement points installed in the mold wall at a height range of 10 to 300 mm below the molten metal surface. 1. A method for controlling vibration of a mold for continuous casting, characterized in that the ultrasonic output and machine oscillation vibration are adjusted such that the temperature difference is determined periodically or intermittently, and the ultrasonic output and machine oscillation vibration are reduced.