ADVANCED MATERIALS & PROCESSES | MAY/JUNE 2025 34 larger weight loads of up to 50 kg. This type of test bridges the gap between the superficial Rockwell and micro Vickers machines. These systems have a manual turret. SHORE TESTERS (DUROMETERS) Shore A portable hardness testers are used on rubber and leather materials, and Shore D testers are targeted to hard plastics such as bowling balls and hard hats. Electronic durometers for measuring Shore A and Shore D values are designed to fit comfortably and firmly in a user’s hand. A large LED display and simple three-button control make this device easy to use. PORTABLE HARDNESS TESTERS There are two popular digital methods of portable hardness testing. The first is dynamic impact, based on the Leeb principle of hardness, developed by Dietmar Leeb in the 1970s. A spring loaded impact body is thrust to the test surface, affecting rebound. Initial thrust and rebound speed is measured in a noncontact mode, calculated as a Leeb hardness value, and then automatically converted to Rockwell C, B, Brinell, Vickers, and Shore values. Also, because it is portable the tester can be brought to the workpiece, which is especially useful when testing large and/or cumbersome parts (Fig. 4). This method has resulted in efficient, fast, and accurate portable hardness testing results. However, when a mark or indentation on the workpiece must be avoided, ultrasonic testing is a great solution. Advanced nondestructive portable hardness testers utilize ultrasonics with ultrasonic contact impedance (UCI) technology, enabling a portable hardness tester to test special surfaces on small and thin workpieces without marking the surface. These units can test metals as thin as 2 mm throughout all scales, hard or soft. UCI technology is available on both manual and motorized systems. The motorized probe systems are used to test very thin coatings and platings, or surfaces with a very high polish finish. UCI is based on a 136° diamond at the end of a vibrating rod being depressed into the test surface at a fixed load. The difference in ultrasonic vibration frequency is then calculated into a hardness value. The UCI test procedure is slower than the dynamic impact style, however the UCI method has the advantages of being nondestructive and is able to test thin and small work parts. Previously, destructive indentations made on such sample pieces meant the garbage heap for those tested. Using ultrasonics, this is no longer the outcome. These systems have an open architecture and can be calibrated to read any metal, in any hardness scale, with reference samples to perform initial calibration. Ultrasonic portable hardness testing is ideal for applications such as bearings, pistons, and valves, among many others. Key industries for this type of testing include aerospace, automotive, and medical parts as well as knife blade manufacturing, to name just a few. ~AM&P For more information: John Richardson, product coordinator, The L.S. Starrett Company, 121 Crescent St., Athol, MA 01331, 888.674.7443, jrichardson@ starrett.com, www.starrett.com. Fig. 4 — All of the portable hardness testers shown in this photograph are transportable while ultrasonic hardness testers (shown at top and right) produce nondestructive hardness testing results and are built for use on the shop floor.
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