Certification and Registration
ISO 48: Determination of IRHD Hardness of Vulcanized or Thermoplastic Rubber
Category:
Mechanical
ISO 48 Standard Description
ISO 48 Rubber, vulcanized or thermoplastic - Determination of hardness (hardness between 10IRHD and 100IRHD)
ISO 48 Standard Overview
Due to its excellent elasticity, wear resistance and sealing properties, rubber is widely used in tires, sealing rings, vibration damping pads, medical devices and other applications. In these applications, rubber products often require appropriate hardness according to their service conditions. Hardness is an important indicator for evaluating the ability of rubber to resist indentation and deformation under external forces.
ISO 48 specifies methods for determining the hardness of vulcanized or thermoplastic rubber. It covers standard hardness tests for flat surfaces and apparent hardness tests for curved surfaces. The test results are expressed in International Rubber Hardness Degrees (IRHD), with a measurement range from 10 IRHD to 100 IRHD.
ISO 48 Four Hardness Test Methods
ISO 48 distinguishes test methods based on differences in indenter ball diameter and applied force, allowing hardness measurement for different types of rubber products. ISO 48 specifies four methods for standard hardness determination:
Method N (Normal Test)
Applicable to rubber with a hardness range of 35 IRHD to 85 IRHD. The range may generally be extended to 30 IRHD to 95 IRHD.
Method H (High-Hardness Test)
Applicable to harder rubber materials with a hardness range of 85 IRHD to 100 IRHD.
Method L (Low-Hardness Test)
Applicable to softer rubber materials with a hardness range of 10 IRHD to 35 IRHD.
Method M (Microtest)
Method M is a reduced-scale version of Method N, used for smaller or thinner specimens. It applies to hardness ranges of 35 IRHD to 85 IRHD and may also be extended to 30 IRHD to 95 IRHD.
In addition, ISO 48 specifies four methods for determining apparent hardness on curved surfaces: CN, CH, CL and CM. These methods are modified versions of Methods N, H, L and M respectively and are specifically designed for hardness testing of curved rubber materials.
They apply to two conditions:
a) The specimen or product is large enough to directly support the hardness tester;
b) The specimen or product is small and needs to be placed together with the hardness tester on a reference platform.
For condition b), an alternative method is to place the specimen on a dedicated specimen holder of the hardness tester.
ISO 48 Scope of Application
ISO 48 applies to the measurement of rubber hardness.
ISO 48 Test Principle
The depth of indentation made by a spherical indenter is first measured under a smaller contact force, followed by measurement under a larger indentation force. The difference between the two indentation depths is used to calculate the hardness value.
(1) Specimen Preparation: Condition the specimens according to the specified requirements. Lightly dust the upper and lower surfaces of the specimen with talc powder and place it on a horizontal rigid platform.
(2) Initial Contact: Bring the measuring foot into contact with the specimen surface. Apply pressure to the loading rod and spherical indenter, applying the contact force to the rubber specimen for 5 seconds.
(3) Hardness Reading:
Two reading methods are available: direct scale reading and calibrated scale reading.
Direct Scale Reading: If the hardness tester is equipped with an IRHD scale, after 5 seconds of contact force, set the reading to 100, then apply the additional indentation force and maintain it for 30 seconds. The IRHD hardness value can then be read directly.
Calibrated Scale Reading: If the hardness tester uses a calibrated scale, record the indentation difference D after applying the additional indentation force for 30 seconds. When using a microtest device, multiply the D value by the scale factor 6, then convert it to the IRHD value using Table 3-5 or the corresponding calibration curve.
Note: During loading, unless the instrument is designed without friction resistance, the tester should be gently vibrated to ensure measurement accuracy.
ISO 48 Basis for determination
The International Rubber Hardness Degree (IRHD) value is determined using one of the following methods:
(1) Obtain the corresponding value from the reference tables;
(2) Use the curve charts generated from these tables;
(3) Use an IRHD scale designed according to calculated table data and matched with the indentation measuring device for direct IRHD reading.
More Building Material Hardness Testing Standards
ASTM D2240 Standard Test Method for Rubber Properties — Durometer Hardness
ASTM D785 Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials
ASTM D2583 Standard Test Method for Indentation Hardness of Rigid Plastics by Means of a Barcol Impressor
ASTM D1415 Standard Test Method for Rubber Property — International Hardness
ISO 868 Plastics and ebonite — Determination of indentation hardness by means of a durometer (Shore hardness)
ISO 2039-1 Plastics — Determination of hardness — Part 1: Ball indentation method
ISO 2039-2 Plastics — Determination of hardness by the ball indentation method — Part 2: Rockwell hardness
SATISFY has a professional technical team specializing in building material testing and provides testing services for building materials according to various international standards. Our services include technical consultation, standard interpretation, sample testing, report review and product improvement recommendations. For more information, please contact SATISFY.
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