Hardness is a fundamental mechanical property of materials, defined as the resistance to local penetration by an indenter. Measuring it makes it possible to check the quality of heat treatments (hardening, annealing, case hardening, nitriding), to select the correct material for friction and wear applications, to verify compliance with supply specifications and to estimate other properties indirectly, such as tensile strength. Measurement technologies cover metals, rubbers, plastics, coatings, textile yarns and special materials, with increasingly sophisticated portable and bench instruments.
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Hardness measurement methods
For metals, the main standardised methods are: Rockwell (HRA, HRB, HRC, HRN, HRT), based on the residual penetration depth of a diamond or steel-ball indenter under preliminary and main loads; Brinell (HBW), which measures the diameter of the indentation left by a tungsten carbide ball; Vickers (HV), with a square-based diamond pyramid and optical measurement of the indentation diagonal; Knoop (HK) for microhardness on thin layers. The portable Leeb (dynamic rebound, HL/HLD scale) and UCI (Ultrasonic Contact Impedance) methods allow on-site measurements on large parts and complex geometries. For rubbers and plastics, the Shore scale (A, D, B, C, O, OO) is used, along with the IRHD method for small, thin parts.
Categories of instrument covered
The section includes Shore hardness testers for rubber and plastic, IRHD and micro-IRHD hardness testers to ISO 48, portable hardness testers for metals with Leeb and UCI technologies, Rockwell, Brinell and Vickers bench hardness testers for the metallographic laboratory, specialised hardness testers for yarns and fabrics (yarn package hardness), instruments for coating hardness (pencil, Buchholz indentation, Persoz, König), and bases and test stands for repeatable measurements.
Industrial applications
Hardness testers are used in the quality control of heat-treated steels, foundry castings, forged components and welds (checking the HAZ – heat affected zone), in mapping hardness gradients through the depth (case depth) for case-hardened gears and nitrided shafts, and in checking technical rubbers (gaskets, oil seals, anti-vibration parts), tyres, plastic and PVC profiles, stoppers and caps, textile yarns and bobbins, and paint coatings. The portable Leeb/UCI methods are particularly valued in shipbuilding, railways, energy and oil & gas for on-site inspections.
Standards and regulations
The reference standards for metals are ISO 6506 (Brinell), ISO 6507 (Vickers), ISO 6508 (Rockwell), ISO 16859 (Leeb), DIN 50159 (UCI), ASTM E10, E18, E92, E384. For rubbers and plastics, ISO 48 (IRHD), ISO 7619 (Shore) and ASTM D2240 apply. For coatings, ISO 15184 (pencil hardness), ISO 3231 (Buchholz) and ISO 1522 (Persoz and König) are used. Hardness testers are calibrated with ISO 17025 certified reference blocks, compliant with the accuracy classes defined by the respective standards.
Selection criteria
Selecting the most suitable hardness tester must take into account the material (hard or soft metal, rubber, plastic, coating), the size and accessibility of the part (bench or portable), the depth of the treatment to be measured, the minimum material thickness (the rule of 10× the indentation depth), the environmental conditions, the acceptance tolerances and integration with the company quality system. The child pages describe each type of instrument in detail, with technical parameters, scale ranges and typical applications.
The correlation between different hardness scales (for example HV ↔ HRC ↔ HB) is governed by standardised conversion tables (ASTM E140) but is valid only for specific materials and groups; for critical applications it is always preferable to carry out the measurement in the scale originally prescribed by the specification or the technical drawing.
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