Continuous casting mold temperature field online monitoring technology

Abstract: Taking the thin slab continuous casting funnel-shaped mold of Zhujiang Steel Plant as the research object, a dynamic monitoring software for the temperature field of the mold was developed. The temperature of the copper plate is actually measured with a pre-embedded thermocouple on site, and the temperature and heat flow changes of the copper plate of the copper mould tube are dynamically monitored online. It provides important theoretical basis and practical reference data for further analyzing the influence of each process parameter on the copper mould tube temperature, optimizing production process parameters and copper mould tube shape design.

Introduction

The thin slab continuous casting and rolling production line represents the direction of the development of flat steel product production technology with its short process, low infrastructure investment, low energy consumption, high metal yield rate, and high technology integration. In 1998, my country’s first production line was put into operation at Zhugang Iron and Steel Co., Ltd. Currently, including projects under construction, there are a total of 7 thin slab continuous casting and rolling production lines in my country, and their total production capacity will exceed 10 million t/a. Research on thin slab production processes has also received attention.

The core part of CSP thin slab continuous casting that is different from conventional continuous casting production lines lies in its copper mould tube. The characteristics of small thickness, high casting speed and high superheat make the thin slab continuous casting mold bear greater challenges in terms of wear, thermal corrosion, hot cracking, deformation and other aspects. The design, processing, maintenance and theoretical research of its funnel-shaped copper mould tube are very difficult, which has become the magic weapon for the comprehensive development of CSP around the world. In the past, the thin slab continuous casting mold of Zhujiang Steel Plant was used as the research object, and the three-dimensional temperature field of the copper plate of the mold was calculated using the finite element method. This article introduces the development of online monitoring technology for the temperature field of the copper mould tube, as well as the actual measurement of the temperature of the copper plate using embedded thermocouples on site, and the online dynamic monitoring of the temperature and thermal changes of the copper plate of the copper mould tube.

The necessity of copper mould tube wall temperature and heat flow monitoring

The smooth progress of the continuous casting process and the quality of the cast slabs depend on the degree of automation of the continuous casting process. The key to the specific realization of continuous casting process automation often depends on whether the detection methods of process parameters are accurate, timely, stable and automated.

The short thin slab process means less flexibility in production. Abnormalities in any link will directly affect the smoothness of the entire process. Therefore, online monitoring and control technology has very important practical significance in the thin slab continuous casting and rolling production line.

The copper mould tube is the “heart” of the continuous casting machine. The temperature field and heat flow of the mold reflect the heat transfer between the slab and the copper mould tube. They are the main parameters for understanding the solidification status of the slab and the uniformity of the shell. They are also important parameters that need to be detected for the automation of the continuous casting process.

The role of copper mould tube temperature and heat flow monitoring

(1) Used for steel breakout accident prediction. Through data collection, display and statistical analysis, we can provide early warning of steel breakouts and accidents to reduce production accidents.

(2) Understand the heat transfer status and heat flow distribution uniformity in the copper mould tube. Targeted measures are taken to make the solidified shell thickness uniform, and at the same time, quantitative data support can be provided for mold taper and size design.

(3) Provide process control to optimize the process and dynamic online information on the status of the slab to ensure stable and efficient production.

(4) Provide diagnostic data regarding casting machine maintenance and design. Provide quantitative data to realize the transformation of equipment from periodic maintenance to condition maintenance.

(5) Provide reliable measured data for computer numerical simulation of slab solidification, heat transfer, lubrication and other phenomena in the continuous casting mold. Perform results verification and correct boundary conditions.

(6) Further develop the core part of the copper mould tube visualization technology. Provide core monitoring technology and important analytical data for intelligent monitoring and control of copper mould tubes.

Core technology of copper mould tube online monitoring

Technical principles

Real-time temperature data are obtained through a signal acquisition system using a thermocouple installed in the copper plate of the copper mould tube. Then the temperature of the temperature measurement point is converted into the temperature field inside the copper mould tube through the developed calculation module, and the results are displayed on the computer screen in the form of isothermal cloud diagrams and curves. Facilitates direct observation or offline analysis by operators and researchers.

Hardware composition

1 Computer 2 Communication card 3 A /D card 4 Thermocouple

(1, 2, and 3 are located in the main control room, and 4 is located on the continuous casting platform)

Figure 1 Schematic diagram of the hardware composition of the monitoring system

The main components are shown in Figure 1.

(1) Intelligent I/O – S-TC (A/D conversion) – Based on LonWorks fieldbus technology, 8 differential inputs, 16-bit conversion accuracy, accepts 0~2.5V voltage input, and can directly measure thermocouple signals. Multiple blocks are connected in series according to the number of measurement channels.

(2) LonWorks network PCI interface card – used for communication between intelligent I/O modules and computers.

(3) J-type thermocouple-temperature sensor, measurable temperature range 0 ~1000%.

(4) Thermocouple compensation wire.

Software composition

(1) V isuallon – used for LonWorks network management, network testing, program downloading, and network variable bundling.

(2) LN SDDE SERVER-DDE driver provides a general DDE interface for other programs, which can collect, transform and process data.

(3) Human-machine interface software – uses the DDE interface to record the measured temperature and display the visual part of the dynamic picture.

Dynamic visual interface

The visual interface of the monitoring software mainly includes 4 parts (see Figures 2~4).

Figure 2 Main interface of monitoring software – thermocouple temperature column chart and curve display

Figure 3 Monitoring software main interface – thermocouple temperature numerical display and background color alarm

Figure 4 Main interface of monitoring software – wide area temperature field cloud diagram display

(1) Thermocouple temperature bar graph and curve display;

(2) Thermocouple temperature numerical display and background color alarm;

(3) copper mould tube temperature field cloud diagram display;

(4) copper mould tube thermal flow field cloud diagram display.

Based on the copper mould tube temperature field detection and the copper mould tube cooling water temperature measurement data, the dynamic measurement level display of the copper mould tube heat flow field is completed. The results and distribution are similar to the temperature field distribution (see Figure 4).

Main functions of the system

(1) Thermocouple data can be collected online and saved into an Excel worksheet.

(2) The thermocouple temperature, copper mould tube temperature field, and heat flow field can be displayed online in different forms such as bar graphs, curves, numbers, and cloud graphs.

(3) Save the normal pouring and accident status data of continuous casting and perform offline analysis to further develop breakout prediction software.

Measurement results

Thermocouples are distributed across the wide surface, with a total of 3 rows & 8 columns = 24 thermocouples on each hot surface. There are 8 thermocouples per row along the width and 3 thermocouples per row along the height (see Figure 3).

Temperature distribution rules

The temperature distribution pattern is shown in Figure 5.

Number of thermocouples on the wide surface of the copper mould tube (3 rows of thermocouples, 8 in each row)

Figure 5 Thermocouple temperature curve in the width direction of the copper mould tube

Cause Analysis

The possible reason for the occurrence of such a temperature distribution pattern is that the high-temperature steel flow at the two side exits of the nozzle creates two high-temperature zones near the meniscus. Under the dual effects of the static pressure of the molten steel and the shrinkage force of the shell, the mold shell may separate from the surface of the mold. This situation may be the reason for the low temperature at the second row of thermocouples.

Consequences

When such a temperature distribution pattern occurs, the consequences are:

(1) The two high-temperature zones near the meniscus will increase the thermal wear of the copper mould tube and may cause recrystallization on the surface of the copper plate of the copper mould tube.

(2) If the two second highest temperature points are caused by the close contact between the billet shell and the copper mould tube, this area may also be an area prone to wear.

Solutions

In order to avoid uneven temperature distribution in the copper mould tube and reduce its uneven wear, we can start by reducing and stabilizing the temperature of the intermediate tank, optimizing the design of the immersed nozzle, and optimizing the shape of the copper mould tube funnel. These methods await further research and development.

Conclusion

Online dynamic monitoring of the hot surface temperature and heat flow of the thin slab continuous casting mold is not only the basis for predicting steel breakouts, but can also monitor the usage status of the mold, improve and optimize the mold, and improve production efficiency and product surface quality.

This paper adopts the method of pre-embedding thermocouples on the copper mould tube to collect the actual temperature changes of the copper plate during the continuous casting process in real time. On this basis, an online dynamic monitoring technology for the temperature field of the copper mould tube is developed. This will lay a good foundation for further improving the technical level and research level in the field of thin slab continuous casting in my country.

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