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A durometer is an instrument used to measure the hardness of materials, typically elastomers and polymers such as rubber, plastic, and foam. The term also refers to the scale of hardness itself. Hardness in this context is defined as a material's resistance to indentation. The durometer scale was defined by Albert F. Shore, who developed the measurement device in the 1920s. There are several scales on the durometer, with the most common being the Shore scales, which include Shore A, Shore D, and Shore OO, each designed for a different range of materials. Shore A is used for softer materials, Shore D for harder ones, and Shore OO for very soft or gel-like materials. The higher the number on the scale, the harder the material.
When using a durometer, a calibrated spring is used to press a standardized indenter against the material. The depth of the indentation reflects the material's hardness. For example, a reading of 20 on the Shore A scale indicates a very soft rubber, while a reading of 85 suggests a much harder rubber. Durometer readings are essential in various industries, from automotive to medical, as they help in material selection, quality control, and predicting how a material will perform in its intended application. According to the American Society for Testing and Materials (ASTM), the standard method for durometer hardness testing of rubber materials is ASTM D2240, ensuring consistency in measurements across different users and applications.
As a gauge that can be used to check the hardness of a given material, the durometer can be used in a number of different applications. It functions by analyzing a given substance, and then assigning it a number to denote the level of harness and durability. A lower number would indicate a softer nature for the substance, while a higher number would indicate the product is harder and less susceptible to bending or cracking.
Along with the number, there is also often a hardness rating, with softer materials being indicated by an “A” and harder being rated as “D.” As a result, a substance that had an overall rating of A30 would be considered not very hard, compared to a substance with a reading of D70. Readings are generally based on checking several spots along the surface of the material and then making a cumulative rating based on the data.
While a durometer can technically be used to test the hardness of just about any substance, the main uses of the device are associated with measuring the hardness of rubber or plastic products. Generally, manufactures will have a range that they consider ideal for the type of goods they produce.
For instance, the producer of various types of plastic mats would perhaps want all its products to have a hardness rating of somewhere in the middle range. This method would indicate durability but with a degree of flexibility as part of the final product. Being able to periodically test the production process will help to keep the hardness of the finished products within an acceptable range on the Mohs scale, resulting in products that are of equitable quality to one another.
Along with plastic mats, products like the rubber wheels on roller skates are required to be relatively hard, so that they will hold up to a lot of wear and tear. On the other hand, a welcome mat made from rubber or plastic would need to be softer. Using a durometer during the manufacturing process to ensure the mix of materials results in the level of hardness required can save a company a great deal of time and resources. Regular checks will quickly identify any deviation from the standards employed by the company.