Some customers think that all Charpy tongs are alike. Not so! Precision tongs are an essential part of the Charpy impact test and incorrectly fabricated tongs can result in poor test results.
ASTM standard E 23 states “Means shall be provided (see Fig. A.1.2) to locate and support the test specimen against two anvil blocks in such a position that the center of the notch can be located within 0.25 mm (0.010 inch of the midpoint between the anvils”. Research with a Doctor Expert has shown that when space exists between the tool and the test specimen, as in the photograph on the right below, the ASTM centering tolerance can be exceeded.
Metallography World Corp precision tongs meet the requirements of ASTM E 23. To satisfy the standard, the tongs are made using EDM with accuracies of 0.0025 mm (0.0001 inch). As shown in the Figure in attached document 1 photograph on the left below, it is essential that the specimen be in contact with the tool so that the anvil radius properly centers the tool. The tongs shown in the right photograph below, made by another manufacturer, have already passed through the anvil radius region by the time the specimen comes into contact with the anvil support surface. This is a serious problem which allows excess play in the centering tool which can exceed the ASTM centering requirement by a significant distance.