Definition
A Shore hardness tester is an instrument used to measure the ability of soft to semi-rigid elastomers or plastics to resist indenter pressing. The measurement is called the Shore hardness value, which is dimensionless and is often used to characterize the softness and hardness of non-metallic materials such as rubber, thermoplastic elastomers, silicones, and similar polymers. The instrument takes its name from its inventor, Albert Ferdinand Sauer.
Principle
The measurement principle of the Shore hardness tester is based on the static press-in method. The instrument presses a needle of a specific shape vertically into the surface of the specimen under the action of the specified spring test force. When the presser plane is perfectly aligned with the specimen surface, the length of the needle extending out of the foot plane determines the indicated position of the needle on the dial. The deeper the needle pressing, the softer the material, and the lower the hardness value displayed; Conversely, the shallower the pressing depth, the harder the material, and the higher the hardness value displayed. The basic relationship can be expressed as follows: the hardness value is inversely proportional to the depth of pressing.
Measurement method
Measurements of Shore hardness testers follow standardized operating procedures. First, the specimen should have sufficient thickness and a flat surface. Position the durometer vertically on the specimen to ensure smooth contact between the foot and the surface of the specimen, and quickly apply enough force to make the foot fit perfectly with the specimen. Read the instantaneous maximum value or stable value within the specified time after the pressing foot comes into contact with the specimen. Common scales include type A, type D and type OO, among which type A is suitable for softer materials, type D is suitable for harder materials, and OO type is suitable for extremely soft materials. When measuring, choose the appropriate scale according to the expected hardness range of the material and indicate it in the report.
Influencing factors
Shore hardness measurements are influenced by a variety of factors. Insufficient specimen thickness can lead to insufficient support, resulting in low readings. Changes in ambient temperature affect the modulus of polymer materials, which affects hardness values. The calibration of the pin geometry and spring force is a key factor in the instrument itself, which needs to be checked regularly using standard hardness blocks. If the operator's force speed and reading timing do not meet the standard requirements, human error will be introduced. In addition, the surface curvature, texture, and internal residual stresses of the specimen may also affect the measurement results.
Application
Shore hardness testers have a wide range of applications in industrial quality control and research and development. In the rubber products industry, it is used to test the hardness of tires, seals, rubber rollers and shoe soles. In the plastics industry, it is suitable for evaluating the hardness of materials such as flexible PVC, TPE, etc. In the medical field, it is used to measure the softness and hardness of medical polymer materials such as silicone prostheses and catheters. In addition, Shore hardness is also a routine testing index in product acceptance and material formulation research in auto parts, sporting goods, daily consumer goods and other industries.
Selection
When choosing a Shore hardness meter, the first consideration is the hardness range of the material being tested. For soft elastomers, A-type rulers are usually used. For rigid plastics or harder rubber, consider the D-type ruler; For extremely soft materials such as sponges and gels, OO rulers are more suitable. Secondly, the accuracy and calibration convenience of the instrument should be considered, and compliance with relevant national or international standards (such as GB/T, ISO, ASTM) is the basic requirement. Whether the usage environment requires a portable or desktop model, and whether it needs data storage and output functions, are also considerations when selecting a model. Finally, ensure that the instrument supplier can provide reliable technical support and calibration services.