A Brief Review on Test Systems Using a Ball Probe for Determination of Cooling Characteristics of Quenchants

A wide variety of test systems have been developed to determine the cooling characteristics of quenchants. Among them, rational systems with good reliability and cost performance have been adopted as domestic and international standards. This review mainly focuses on test systems using a small ball probe and discusses their development processes, features, and potential uses. Although a test system with a ball probe is not defined in current standards, it is known that specific ones used in the past contributed to enhancing the test. This literature survey found a classic test system with 7-mm-dia. silver or 4-mm-dia. chromium-nickel balls, which was created rationally for using the lumped heat capacity method, and was applied to a variety of quenchants at the Kaiser Wilhelm Institute from 1928 to 1931. The institute finally increased the diameter of the silver ball probe to 20 mm due to manufacturing problems and applied it to various quenchants, which was widely applied until the ISO 9950 standard using an Inconel cylindrical probe was established. In latter half of this report, prototypes of the test system using a small ball probe created by the author’s group since 2011 were briefly reviewed. This work solved the problem in the previous small ball probes with the current technology. The latest prototype uses a 4-mm-dia. platinum ball probe with a 0.25-mm-dia. sheathed thermocouple inserted into the center. The probe heated radiantly in a fixed state with halogen lumps is cooled in the quenchant in the container which is elevated by an electric linear actuator for robotics. This container movement creates a simple relative flow of quenchant around the probe, which has not been seen in the previous test systems. The use of the small ball probe has realized the compact and short-term test system.