Rationale
A Shore hardness tester is an instrument that characterizes the hardness of a material by measuring the depth at which a pressure needle is pressed into the surface of a material under a specific spring force. Its measured value is dimensionless, and higher values indicate greater material hardness. This principle is based on the ability of materials to resist elastic deformation and is widely used in the rapid hardness detection of non-metallic elastoplastic materials such as rubber, plastics, and flexible synthetic materials.
Key differences between Type A, Type D and Type AX
The different models of Shore hardness testers are primarily designed for materials with different hardness ranges, with the core difference being the pin geometry and the spring force applied. Confusing models will cause the measurement data to deviate seriously from the true value, affecting the judgment of material properties and quality control.
The difference between needle shape and force can be conceptualized by the following formula, where the hardness value H is related to the pressing depth h:
H = k * (F / A)
Here, H is the Shore hardness value, k is the coefficient related to the instrument constant, F is the force exerted by the spring, and A is the effective contact area between the needle and the material. Different models of F and A are designed differently to adapt to different hardness ranges.
Parameter comparison
For the sake of clear distinction, the key technical parameters and typical application areas of the three models are summarized as follows. The table width is set to 100% for easy access on mobile devices.
| model | Type A |
| Needle shape | The tip is a flat-headed cylinder with a diameter of 0.79mm |
| Spring Force (N) | Approx. 0.55-8.06 |
| Applicable hardness range (Shaw) | 20-90 HA |
| Typical application materials | Soft rubber, elastomers, thermoplastic elastomers, printing rubber rollers |
| Examples of corresponding standards | ASTM D2240, ISO 868 |
| model | Type D |
| Needle shape | The tip is a 30° cone angle and a conical tip with a diameter of 0.1mm |
| Spring Force (N) | Approx. 0-44.5 |
| Applicable hardness range (Shaw) | 30-90 HD |
| Typical application materials | Hard rubber, plastic (e.g. PVC, nylon), hard thermoplastic elastomer |
| Examples of corresponding standards | ASTM D2240, ISO 868 |
| model | AX type |
| Needle shape | Same as type A, it is a flat-headed cylinder |
| Spring Force (N) | Approx. 0.55-8.06 (but the overall structure of the instrument is optimized for low hardness) |
| Applicable hardness range (Shaw) | 0-20 HA (designed for ultra-soft materials) |
| Typical application materials | Sponges, foams, gels, extremely soft silicone rubber |
| Examples of corresponding standards | ASTM D2240 (Specific to Low Hardness Range) |
Selection precautions
Correct selection is the prerequisite for obtaining valid data. For intermediate hardness materials, there may be overlapping intervals where both types A and D types can be used, which need to be determined according to specific product standards or customer requirements. When measuring, the specimen should be thick enough (usually greater than 6mm), with a flat and smooth surface, and should be placed on a hard, horizontal support table below. Each specimen should be measured at least three times at different locations, taking the median as the result. The ambient temperature should be stable, as temperature changes can affect the modulus and hardness of the rubber.
Summary
The design of Shore hardness tester A, D and AX has its own focus. Type A is suitable for conventional soft to medium hardness rubber; Type D is used for harder materials; The AX model is specifically designed to solve the measurement problems of ultra-soft materials. Understanding the design differences between the force and the needle, and strictly selecting and operating according to the hardness range of the material and relevant test standards, is the key to ensuring accurate and comparable hardness data.