November 2022 Volume 4

EQUIPMENT & TECHNOLOGY

Industrial Heating Technology Tips: Five Best Practices for Non-Contact Temperature Measurement By Josh Carney

Heating metal stock prior to forging is a main tenet of hot forging operations. The temperature to which the stock is heated depends on the base element plus any alloying elements. Controlling the temperature is critical to producing a quality forging, that is, one without surface defects, grain growth, or decarburization. In forging, several different methods of heating are employed. These include gas furnace, electric furnace, or induction heating. The choice usually depends on the material, process, and producer preferences. This variation in heating methods naturally leads to different means of measuring and controlling the temperature of forging stock. Two of the most popular instruments for temperature measurement are the contact thermocouple and the non-contact infrared (IR) thermometer. An IR thermometer, also known as a pyrometer, enables fast response measurement of high temperature objects. It also can make measurements at a distance in conditions that would be unsuitable or even unsafe for human operators. This article discusses the use of IR pyrometers in forging and presents several ‘best practices’ for using andmaintaining pyrometer accuracy. I. Heating and Process Control When viewed as a process, material heating for forging has two key components. The first is material heating- the act of adding thermal energy to the forge stock. There are several modes of heating for forging including: • Direct heating by electromagnetic induction • Direct heating by combustion of fossil fuels • Indirect heating by combustion of fossil fuels • Indirect heating by resistive heating elements i.e., glow bars

Figure 1: The four typical modes of heating in forging The second component of material heating is temperature control. Heating forging stock to the required temperature is critical to producing high quality forgings. The action of measuring temperature and adjusting heating controls is termed process control. For every heating mode, there exists at least one kind of process control.

Figure 2: Typical process control loop diagram In the process control loop diagram shown in figure two, the set point (SP) represents the desired temperature of the forge stock. The process variable (PV) is the feedback from the temperature measurement apparatus. If the SP is incorrect, this results in an incorrect output (temperature). If the PV is incorrect or inaccurate,

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FIA MAGAZINE | NOVEMBER 2022