What is it about?
In most cases in practice quenching of heated metallic workpieces is performed in liquid media (different kinds of oils, polymer-solutions in water and water). Every of this quenchants has different quenchihg intensity, which depends also on the quenchant's temperature and its agitation rate. In order to measure the quenching intensity a small laboratory probe (cylinder of 12,5 mm dia. x 60 mm) having one thermocouple can be used or a multithermocouple probe (cylinder of 50 mm dia x 200 mm ) for workshop conditions.
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Why is it important?
Every quenching operation is a complicated thermo-and fluid dynamic process having different phases (film boiling, nucleate boiling, and convection), on which resulting hardness distribution as well as distortion of the hardened workpiece depends. Therefore it is extremely important to measure the heat extraction during quenching i.e. to record the cooling curve, and to calculate the heat transfer coefficient between the workpiece's surface and the quenching medium, as function of time and as function of surface temperature. For real engineering components, this is possible only by the bigger multithermocouple probe.
Perspectives
Writing this article my objective was to introduce the Liscic/Petrofer multithermocouple probe which is nowadays unique in the world, and to show cooling diagrams obtained simultaneously for 3 thermocouples at every quenching experiment, in real time. From this recorded data heat flux, heat transfer coefficient, and amount of heat extracted in every moment can be calculated. The advantage of this probe is the fact that it is applicable for all kinds of liquid quenchants, and can compare the quenching intensity among them. It is also applicable for different quenching techniques (immersion quenching, intensive quenching, delayed quenching, martempering, austempering).
Professor BOZIDAR LISCIC
Faculty for Mech. Engineering
Read the Original
This page is a summary of: Measurement and Recording of Quenching Intensity in Workshop Conditions Based on Temperature Gradients, Materials Performance and Characterization, July 2016, ASTM International,
DOI: 10.1520/mpc20160007.
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