Full definition
Durometer is a crucial tool in evaluating the hardness of elastomers and plastics, measuring indentation hardness by pressing a calibrated spring-loaded indenter into the material. The durometer is primarily available in two types based on the hardness range: Type A and Type D, as defined by ASTM D2240. Type A durometers are designed for soft to medium-hard elastomers, typically falling within the 20-90 Shore A range, which encompasses most industrial rubber materials used in seals and gaskets. This type features a truncated cone indenter, which allows for accurate hardness measurement in softer materials. In contrast, Type D durometers are used for harder materials such as rigid plastics and hard polyurethane, where the hardness exceeds 90 Shore A. These instruments utilize a sharp cone indenter suitable for penetrating denser surfaces.
The measurement procedure involves placing the durometer firmly against a flat specimen surface, which must be at least 6 mm thick to ensure accurate readings. For reliable results, the hardness value should be taken after a specified duration—1 second per ASTM guidelines or 3 seconds as per DIN 53505 standards—with a minimum of five readings taken and averaged for accuracy. The testing should be conducted at a controlled temperature of 23 ± 2°C to avoid external influences on the material's hardness. Calibration of the durometer plays a vital role in maintaining measurement precision. It is essential to verify the instrument against standard test blocks periodically. Digital durometers have enhanced the measurement process by offering improved repeatability and ease of use.
Hardness measurement is critical in the elastomer industry, as it is one of the most frequently specified properties in rubber product datasheets and purchase specifications. The durometer reading not only informs material selection but also influences the performance characteristics of rubber products in various applications. Materials with inappropriate hardness levels may lead to premature failure in service, thus impacting the overall reliability of equipment and machinery. Therefore, understanding durometer readings is essential for engineers and procurement managers when specifying materials for industrial applications.