Advanced Energy

Precise Temperature Control assures High Quality Steel

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Courtesy of Advanced Energy

Process monitoring during continuous casting using special ratio-pyrometers and thermal imagers from LumaSense

Today’s increasing quality standards and higher energy costs demand more accurate and consistent temperature control in every step of the steel making process. Steel manufacturing consists of high temperature manufacturing steps that use significant amounts of energy. Processes such as coke oven heating, continuous casting, furnace reheating, hot rolling, forging, sintering, and annealing are becoming more and more expensive. With increasing energy prices at all-time highs, the cost of doing business has significantly increased. Steel facilities need the right tools to ensure they optimize energy usage across their facilities.

Continuous casting is the process where the molten steel is cooled and solidified into billets or slabs. The core is still usually molten with a hard outer shell.

Molten metal is transferred from the ladle into a tundish, where it is slowly tapped into the casting machine. The mold in which the steel slips into is water cooled. The operator’s challenge is to keep the steel within the channel and control the cooling rate. This can be difficult due to variations in the tundish temperature.

In the production process of semifinished steel products in continuous casting plants, the measurement of temperatures is an ongoing daily task, however the control of the secondary cooling phase is a key issue. Only exact temperature control in the cooling process enables the production of steel grades, that meet high-end market requirements. The manner in which the strands are cooled in each batch is crucial to the final quality of the steel.

There are different target temperatures for different types of steel, which require a control range of 600°C to 1200°C. Exceeding or undershooting the permissible temperature limits leads to a devaluation of the material and thus a lower product yield. For efficient process control, the recording of the temperature values at the outlet section of the strand is a significantly important function. Accurate cooling processes at perfectly controlled temperatures result in a high surface quality of the strands and ensure optimally formed inner structures of the strands. In this process IMPAC pyrometers and MIKRON thermography systems measure mold temperatures and coil temperatures in the backbend and cooling zones.

The surface of the material in the tundish is examined using a Thermal Imaging Camera to identify any irregularities such as crack formations. In turn, this ensures that the molten material can be poured easily from the tundish with a minimum amount of material adhering to the sides of the vessel.

Equipment for efficient temperature monitoring during Continuous casting Lumasense Ratio Type “SG”-pyrometers are specially designed for continuous casting processes. They are installed between the individual cooling zones, and continuously measure the respective strand temperatures. LumaSense pyrometers ISR 12-LO/SG and IGAR 12-LO/SG with protection class IP65 can withstand the harsh ambient conditions, caused by high temperatures, cooling water mist and soiling, over many years, by employing special continuous casting optics.

As an alternative solution to the pyrometers, just two LumaSense thermal imaging cameras monitor the complete backbend zone and thus enable multiple temperature measurements of the individual strands at different points in the backbend zone. This allows the individual strands to be recorded on three sides. Thus the continuous casting process is monitored and controlled using the most appropriate measurement points.

Using the combination of accurate hot-edge detection and temperature profile imaging, together with a very rugged stainless steel protective housing, LumaSense MCS640-HD thermal imaging cameras are able to control continuous casting processes better than any other imaging system.

Summary
LumaSense infrared thermometers accurately measure cooling requirements of slabs, billets, or blooms to ensure product uniformity and provide equipment operators with immediate temperature information that is critical to the cooling process.

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