In the steelmaking process, temperature measurement is central to every important decision. Essentially, from when raw materials are delivered to a coke oven until they receive their final coating (galvanizing) – temperature control determines quality of product, operational efficiency, and safety at the plant. As a result, non-contact infrared pyrometers are gaining popularity as the go-to method for obtaining accurate and instantaneous temperature data for processes that cause damage to other methods of temperature sensing.
Conditions during steel fabrication create challenges for traditional measurement instruments, due to extremely high temperatures (greater than 2,500°C), extremely fast-moving material, fast oxidising surface of steel, as well as the production process being extremely dusty, smoky and affected by electrical noise. Pyrometers allow continuous monitoring without interfering with normal production.
How Does Pyrometer Technology Work?
The role of a pyrometer is to measure radiation in infrared light that is given off by hot materials, and by converting this radiation energy into a temperature value, a pyrometer provides temperature data. A single-colour pyrometer measures radiation at one specific wavelength. Therefore, a single-colour pyrometer is most effective when used against stable emissivity targets that also have clear optical pathways.
Ratio or two-color pyrometers detect radiation emitted from an object at two wavelengths. They also correct for any changes in emissivity, any blockage of the view of the object due to obstructions, and any changes in the optical path (due to air) between the object and the pyrometer. Because emissivity is constantly changing based on temperature and surface conditions, this type of pyrometer is especially useful for monitoring molten metal processes.
A fiber optic pyrometer works differently than a two-color or ratio pyrometer. In fiber optic pyrometers, the measurement head is located away from the processing electronics via optical fibers. This protects delicate electronic components from extreme heat and electromagnetic interference. The response time of fiber optic pyrometers varies; some have a fast response of around 2 milliseconds used in high-speed applications, while other pyrometers have slower response times of several hundred milliseconds when used to gather data for stable process monitoring.
Steel Manufacturing Process
Steel production follows a complicated path in which iron ore mined from the earth is processed through three distinct processes – refining, melting, and processing – all of which result in the manufacture of finished steel products. First, ironmaking produces molten iron from ore; second, during the steelmaking process, impurities are removed and the chemical composition is controlled. Finally, casting and rolling produce the finished form of steel that meets the requirements for size, strength, and mechanical properties, among others.
Primary Ironmaking Applications
Coke Oven Carbonization Control
Coke ovens convert metallurgical coal into coke at 900-1,100°C over 14-18 hour cycles. Temperature uniformity affects coke quality and energy consumption—too low produces weak coke with high volatiles, too high wastes fuel and damages refractories. Tempsens P450 series provide rugged monitoring with cooling jacket compatibility, covering 600-3,000°C ranges for complete cycle control.
Sintering Process Temperature Profiling
Sinter plants aggregate iron ore fines at peak temperatures of 1,300-1,400°C. Temperature distribution determines product strength and energy consumption. Tempsen A450c/A450C+ FOPL and A450C FOPL two-color fiber optic models handle extreme dust with wide-angle heads that scan large bed areas while electronics remain protected remotely.
Monitoring of Hot Blast Stove Dome
During operation of regenerative stoves, the hot blast air Temperature reaches 1,300-1,400 Degrees Celsius in a dusty combustion environment. The operation of wide area dome monitoring will prevent the deterioration of refractories through excessive heat while maintaining sufficient hot blast air Temperature. Tempsens A450C+ pyrometers allow for remote temperature measurement without water cooling; they will capture the spatial Temperature Distribution over large surface areas.
Blast Furnace Taphole Temperature
Molten iron at 1,450-1,550°C flows through tapholes with low emissivity amid dust, smoke, and flame. Accurate measurement optimizes tapping schedules and slag separation. The Tempsens A450C+ two-color pyrometer penetrates interference with small spot optics and through-the-lens sighting, focusing precisely on the metal stream.
Secondary Steelmaking and Refining
Basic Oxygen Furnace Ladle Temperature
BOF ladle tapping requires rapid measurement at 1,600-1,680°C with ±3°C accuracy for oxygen blowing and alloy addition decisions. Heavy dust and flame create measurement challenges. Tempsens A450C+/A450C FOPL with software and peak picker automatically captures each ladle’s temperature, filtering interference while providing cooling jackets and OLED display for on-site configuration.
Continuous Casting Operations
Tundish and Strand Temperature Control: Continuous casting monitors a tundish (1,450 – 1,550 °C), mold exit and secondary cooling zone (800 – 1,000 °C) temperature to effectively control shell growth and to mitigate breakout incidences. The Tempsens A450C utilizes two-color fiber optic technology that allows for stability under both steam and scale conditions and has ceramic-tipped sight tubes combined with air-cooled optics to protect the optics from damage caused by any electromagnetic interference to the electronics.
Hot Rolling Operations
Reheating Furnace and Rolling Temperature: Reheating furnaces bring billets to 1,100-1,250°C for uniform rolling. During rolling at speeds up to 20 m/s, scale layers complicate measurement. Tempsens A250/A250+ series uses peak picker and small spot optics to penetrate scale, with millisecond-stamped data logging and OLED displays enabling real-time mill parameter correlation.
Thermo-Mechanical Treatment (TMT) Process
TMT bars need precise surface-to-core gradients—900°C surface, 1,000-1,050°C core—before quenching to develop martensitic rims. Tempsens A250/ A250+ and A450/ A450+ series deliver ±0.3% accuracy with 2 millisecond response, featuring laser targeting and analog/digital outputs (4-20 mA, RS-485) for closed-loop quench control.
Wire and Rod Mill Temperature
Wire and rod move at 10-100 m/s with rapid heat loss from high surface-area-to-volume ratios. High ambient temperatures near mill stands challenge sensor survival. Tempsens A250 FOPL fiber optic pyrometer offers 2 millisecond response with spot sizes down to 1 mm, positioning electronics remotely while eliminating electromagnetic interference.
Heat Treatment and Finishing
Annealing Furnace Temperature Control: Annealing processes at 650-850°C require ±5°C uniformity across coils or strip width to ensure consistent grain size and mechanical properties in batch, continuous, normalizing, and stress-relieving operations. Tempsens A250 /A250+ delivers accurate measurement in oxidizing atmospheres with cooling jackets and quartz windows, enabling multiple-unit installation for width-wise temperature profiling.
Galvanizing Lines
Low-temperature measurement on unoxidized metal surfaces needs specialized instruments. Tempsens A150 works for low emissivity surfaces, ensuring final appearance, coating quality, and enhanced line speed.
Why Steel Plants Trust Tempsens Pyrometers
Tempsens pyrometers provide industry-leading advantages:
- High accuracy across 600°C–3000°C.
- Fiber optic technology for EMI-heavy zones.
- Fast response time for moving steel.
- Narrowband spectral design for metals.-
- High-temperature survivability.
- Stable performance in dusty, smoky, and high-radiation environments.
- Seamless integration with plant control systems (4–20 mA, RS485, Modbus, Ethernet).
Strategic Benefits for Steel Producers
- Reduced scrap and reprocessing
- Improved mechanical properties and metallurgical consistency
- Optimized energy consumption in furnaces
- Extended refractory and equipment life
- Safer high-temperature handling
- Increased throughput through non-stop monitoring
- In steelmaking, temperature control is quality control—and Tempsens is built for both.
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People Also Ask
What is the purpose of a pyrometer?
To measure high temperatures without physical contact using infrared radiation detection.
What is a 3-color pyrometer?
A multiple wavelength infrared pyrometer that adjusts for emissivity variation providing extremely stable measurements for molten steel.
