Abstract
The cooling characteristics of a liquid quenchant are usually determined by a laboratory test using a small cylindrical probe with one thermocouple in its geometrical center. The reasons why the results of the laboratory tests do not represent the real quenching intensity of quenching workpieces in workshop conditions are described. Instead, a new Liščić/Petrofer probe with a larger mass, having three thermocouples, is used for measurement and recording real quenching intensity during industrial practice. The working principle of this probe is the measurement of dynamic of heat extraction, which is best represented by the change of temperature gradients. The temperature gradient method and the Liščić/Petrofer probe are described using an example of quenching in mineral oil at room temperature, without agitation. Calculation of the heat-transfer coefficient, as well as distinctive characteristics of the cooling curves recorded and heat-transfer data calculated when using the Liščić/Petrofer probe is explained. For impartial analysis and use of results obtained by using the new probe, six characteristic criteria from the relevant diagrams are used. Based on selected tests with the new probe, the influence of quenchant temperature and agitation rate on the quenching intensity is shown in numerical form for mineral oil and for water. A series of 26 tests has proved that: (1) the results obtained by the new probe and method have provided information that is not obtainable from small laboratory probes; (2) the new method is sufficiently sensitive to clearly differentiate the results when changes of some quenching parameters (bath temperature or agitation rate) occur; and (3) the Liščić/Petrofer probe can be used for different kinds of liquid quenchants at different quenching conditions typically encountered in industrial practice.
