Definition
A spring hardness tester is a portable hardness testing tool that evaluates the surface hardness of a material by measuring the height of displacement or rebound created by the spring under specific pressures. It is not in the medical or pharmaceutical field, but is mainly used in industrial materials, coatings, plastics, rubber and metal processing industries for quality control and on-site rapid testing.
Principle
The instrument is based on Hooke's law of springs and the principle of energy conversion. When the indenter of the test pen acts perpendicular to the surface of the material, the internal spring is compressed, and its deformation is proportional to the force applied. By measuring the compression displacement of the spring or the rebound height after release, the ability of the material to resist local plastic deformation, i.e., the hardness value, can be indirectly deduced. Some models use the principle of dynamic testing, which calculates the ratio of the impact body's rebound velocity to the impact velocity to obtain a hardness reading.
Its basic relationship can be expressed as: F = kx, where F is the spring force, k is the spring stiffness coefficient, and x is the compression displacement. Hardness values are usually converted to standard hardness units (such as Shore hardness) through calibration curves or built-in algorithms.
Measurement method
Make sure the surface to be measured is flat and clean before measuring. The test pen is placed vertically on the sample and pressure is applied at a uniform speed until the trigger point is reached, at which point the instrument automatically records the data. Static tests require the pressure to be stable for a short time, while dynamic tests require rapid pressure and release. It is recommended to average each sample multiple times at different locations to reduce the effect of local non-uniformity. Operation should follow relevant industry standards, such as ISO 868 (plastics and hard rubbers) or ASTM D2240 (rubber hardness), to ensure consistent measurement conditions.
Influencing factors
Measurement results are influenced by a variety of factors. Insufficient material thickness may result in insufficient support and low readings. Excessive surface curvature or too high roughness will affect the contact state of the indenter head. Changes in ambient temperature can alter spring properties or material properties. The speed and verticality of the operator's force can also introduce deviations. In addition, the calibration status, indenter shape and spring aging of the instrument itself need to be checked and maintained regularly.
Applications
Spring hardness test pens are suitable for applications where fast, non-destructive testing is required. In the rubber manufacturing industry, it is used to monitor the degree of vulcanization and product consistency. The plastic molding industry can use it to assess material curing status or aging changes. It is commonly used in the coating industry to test the curing hardness of paint films or coatings. In addition, it is widely used in the quality inspection of printing and packaging materials and the processing of small metal parts. It makes up for the limitations of benchtop hardness testers that are not portable, making them suitable for production lines or outdoor use.
Selection considerations
When selecting a type, it is necessary to comprehensively consider the characteristics of the material being tested and the testing requirements. First, select the appropriate range and resolution model according to the range of material softness and hardness, such as Shore A type for softer materials (such as elastomers), and Shore D type for harder materials (such as hard plastics). Secondly, considering the test environment, it is advisable to choose a shockproof and dustproof design for outdoor or vibration occasions. You also need to pay attention to the data output method, such as whether you need a digital display or Bluetooth data transmission. The availability of calibration services and compliance with relevant industry standards are also important. Finally, the ergonomics of the operation and the cost of maintenance should be within the scope of the assessment.