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Advanced non-contact temperature measurement in foundries for process control and quality assurance

The temperature of liquid metal at the point of casting can significantly affect the quality of a cast part, determining its mechanical properties and the presence of defects such as cavities. Temperature monitoring of the liquid metal of each part as it is poured into moulds is, therefore, essential in any foundry production process. Making an accurate and reliable temperature measurement of liquid metal is always challenging. Measurements are affected by shiny or changing surface conditions, the sometimes hot, dirty, and smoky environment, and by layers of slag or dross forming on the surface of the liquid metal. Thermocouples are often used to make these measurements by dipping them into the liquid metal within a ladle, typically just before the liquid metal is poured into moulds. Dip thermocouples deliver an average temperature for the liquid metal at a particular depth within the ladle, and they take a few seconds to equilibrate. As this measurement is usually a manual process, it requires the operator to be very close to the hot molten metal and unpleasant atmosphere. Thermocouple readings tend to be inconsistent, with two or three different thermocouple measurements likely to produce two or three different results. The dipping tips for each thermocouple need to be replaced after at least one or two measurements, resulting in an ongoing cost.

Although the costs for a disposable thermocouple may seem low, at around €1.00 each, if 20 thermocouples are used each day, continuous costs are approximately €600.00 per month or €7,200.00 per year. Furthermore, it is impossible to use thermocouples in the liquid pouring stream itself, so the most accurate temperature reading for the part to be poured is not being measured.   Non-contact pyrometers and thermal imagers are hugely advantageous for accurate temperature reading of the metal at the moment of pouring. Infrared technology provides fast, accurate, continuous measurement. A portable handheld pyrometer, fixed installed pyrometer or thermal imager can be used to measure from a safe distance, reducing operator risk. 

In a ladle or furnace vessel, oxides, silicates and other impurities appear on the surface of the liquid metal forming a thin and variable slag or dross layer. This affects the emissivity and the temperature of the metal, making it more difficult to achieve an accurate infrared temperature reading. However, measurement of the stream during pouring or tapping enables a direct line of sight to the liquid metal itself.  The tapping process, where the liquid metal is poured into moulds, is also the latest and most exact point to measure the temperature of the liquid metal before it is poured into forms and solidifies. Measurement at this point provides the best assessment of the quality and metallurgical properties of the metal product. 

Accurate temperature measurements of the metal surface are provided by infrared pyrometers or imagers optimised for liquid metal temperature measurement. Also, live analysis of infrared signal strength can be used to control the end of a tap. When the proportion of slag or dross increases, the emissivity increases, which is detected as an increase in infrared signal strength.  AMETEK Land produces a range of expert solutions to ensure precise, continuous liquid metal measurements, using non-contact systems based around pyrometer and thermal imaging technology for the best fit to each application.

Portable pyrometers

The Cyclops C055L Meltmaster portable, handheld pyrometer is specially designed for liquid temperature measurements between 1000 to 2000°C. Lightweight, rugged, and easy to use, it can process data within milliseconds to deliver the real-time metal temperature. Providing an accuracy of 0. 5 per cent of reading and a meltmaster application mode, up to 10,000 readings can be logged in the Cyclops C055L for further processing. The industrial rubber casing and heat-protective case are specifically designed for use in foundry environments. Unlike thermocouples, no consumables are required, so the average return on investment is between three and six months for all types of metal foundries.

Stationary pyrometers and systems

A standard infrared pyrometer is not sufficient by itself to obtain a precise reading of the liquid metal stream temperature. Expert signal and application-orientated processing is also required to ensure a stable, accurate and reliable measurement delivered to the operator and the process control system. With the SPOT R100 and the Auto Pour System, AMETEK Land provides two stationary pyrometer-based systems for liquid metal and pouring streams. They are specially designed to continuously provide temperature readings of each tapping stream and process, 24/7. The accurate and fast temperature reading is based on special algorithms providing accurate and reliable temperature readings – either as a stand-alone solution (SPOT R100) or with an external display processor (Auto Pour).

Stationary thermal imagers and systems

High-resolution thermal imagers also provide a highly effective solution for measuring liquid metal, especially with variable conditions and/or changing positions of the tapping stream. Unlike pyrometers, which rely on special data processing of the measurements to determine the tapping temperature, a thermal imager measures the pouring stream across a large number of pixels, and processes the data with additional data processing functions and algorithms. Even a moving pouring stream or several tapping streams in one field of view can be monitored and measured consistently, while a wide number of camera pixels are taking the temperature reading and processing the tapping temperature continuously, so a thermal imager is more effective. AMETEK Land supplies the NIR-656 and NIR-2K full radiometric infrared imaging cameras, which produce continuous live, high-definition thermal images for effective continuous monitoring of liquid metal at the tapping point up to 30Hz measuring rate. The IMAGEPro thermal imaging, monitoring and processing software processes all data online, connected to the process control system via multiple ways, using I/O-modules, Ethernet-Modbus, TCP or UPC-UA digital interfacing. These systems are a possible solution for continuous 24/7 and reliable temperature measurement of foundry tapping processes and part-orientated documentation and process control.

Contact: AMETEK Land, Land Instruments International Ltd, Dronfield, UK. Tel: +44 1246 417691, email: [email protected]  web: www.ametek-land.com

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