Temperature Applications

- Welder

- Strip in the Heating Zones

- Strip in the Soaking/ Cooling Zones
          

Steel consumers and competitive market conditions are driving steel mills to produce higher quality products more cost effectively.  In order to meet these demands, steel mills must implement better controls to manage the temperature and surface character of the steel strip during the annealing process. For example, high strength steels for the automotive industry require tight temperature control in order to maintain material properties and keep scrap rates and coil reheats to a minimum.

Traditionally, single-wavelength and dual-wavelength infrared thermometers (i.e. ratio or two-color) have been used for strip temperature control within an annealing line. As the graph below illustrates, the fundamental challenge with using these technologies is that sensor accuracy can vary greatly with the emissivity of the steel strip. Unfortunately in an annealing process, the emissivity of the steel strip can vary significantly and unpredictably as the result of:

• Changes in alloy, surface texture, surface oxidation, grain growth, and elemental migration
• Abnormal operating conditions, such as a furnace leak, a bad roll, or a reheated coil

The existence of these temperature errors is best illustrated when product properties do not correlate with the measured strip temperature, or when a phantom temperature change occurs
at the welded seam of the strip. With single- and dual-wavelength sensors, the traditional approach to minimizing these errors has been to adjust the sensors or process setpoint for each product, but, as the table above illustrates, the effectiveness of this strategy is limited.

Application Requirement	Single Wavelength	Dual Wavelength	Multi Wavelength
Accurate Measurement of Common Steel Alloys	YES (1)	YES	YES
Compensate for Abnormal Operating Conditions	NO	YES	YES
Accurate Measurement of Advanced Steel Alloys	NO	NO	YES

With advances in technology, Williamson has developed a new multi-wavelength sensor that is specifically designed to meet the challenging requirements at the annealing line. Without the need to make any adjustments, this new sensor provides more accurate and reliable temperature measurement across a wide range of steel alloys under a variety of operating conditions. With these high performance sensors, it is now possible to obtain tighter control of physical properties, as well as reduce scrap rates, coil reheats, and costly coil downgrades.

Features of Multi-Wavelength Sensors

• Accurate strip temperature measurement with no sensor adjustment for Carbon Steels, Tool Steels, High Strength Steels, Electrical Steels, Stainless Steels, and High Temperature Steels 
• Automatic compensation for strip emissivity and e-slope variation 
• Real-time measurement of strip temperature and surface emissivity for process verification and optimization 
• Dramatic reduction in sensitivity to warm furnace wall reflections

STEEL MILL APPLICATION BROCHURE