Visualization and control of the ladle furnace used for steel production at POLDI Hütte

POLDI Hütte is a strong and stable company with a longstanding reputation for the production of high-grade, alloy, tool, high-speed, stainless, and fire-resistant steels. In 2004, the company decided to reconstruct the ladle furnace. The general contractor of the entire investment was Prvni zelezarska spolecnost Kladno. Electrical switchboards and equipment in the field of measurement and control, including the automated control of the furnace, were implemented by the subcontractor, the AMIKRO company.

Ladle furnace

The company has a 3-phase electric arc furnace, AC, which is used to process 25–30 tons of steel. The most common treatment method is alloying, i.e., adding ingredients to achieve the required properties according to a prespecified chemical composition, which is determined by the standard. This includes heating the steel to a casting temperature ranging from 1,500 to 1,680 °C.

The current flowing through the electrodes is usually between 10 and 20 kA. The structural design of the furnace allows for changing the selected level of power on the transformer without interrupting the melting process. Alloying steel is automated by a weighing line that brings the required ingredients from 12 reservoirs. The ingredients are fed directly into the arc furnace from the line without interrupting the melting process.

Forming line automated control system

Control is carried out from the operator's control desk and from the station via the PROFIBUS SOFTNET OPC server, which enables direct access to the Siemens S7 functions.

The visualization is created with the Reliance 3 SCADA/HMI system using hardware keys (1,000 data points). Among other things, it provides data reading (chemical analysis, temperature measurement) by using scripts as well as data logging and the accessibility of the data over the network.

The basic display consists of 2 horizontal windows. The upper window displays the required visualization screen and the lower window is dedicated to displaying the most important information about the melting process status, malfunctions, and visualization screen preset buttons. The application consists of several visualization screens, the basic screen being "Ladle Furnace". Dialog windows for control devices are written with the help of scripts and are initialized by placing the cursor on the device and left-clicking.

Simple graphics were chosen to support quick overviews of the system status (pump operation, valve status, limit switch positions, flow status). This solution supports a low learning curve for all operators using the program and, consequently, the safe and error-free operation of the whole system.

Examples of visualization windows

Visualization of the ladle furnace

Devices on the PROFIBUS concentrator