ASTM D 2240 – 05 Standard Test Method for Rubber Property—Durometer Hardness

Scope
1.1 This test method covers twelve types of rubber hardness measurement devices known as durometers: Types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. The procedure for
determining indentation hardness of substances classified as thermoplastic elastomers, vulcanized (thermoset) rubber, elas-tomeric materials, cellular materials, gel-like materials, and
some plastics is also described.
1.2 This test method is not equivalent to other indentation hardness methods and instrument types, specifically those described in Test Method D 1415 .
1.3 This test method is not applicable to the testing of coated fabrics.
1.4 All materials, instruments, or equipment used for the determination of mass, force, or dimension shall have traceability to the National Institute for Standards and Technology,
or other internationally recognized organizations parallel in nature.
1.5 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only. Many of the stated dimensions in SI are direct conver-
sions from the U. S. Customary System to accommodate the instrumentation, practices, and procedures that existed prior to the Metric Conversion Act of 1975.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applicability of regulatory limitations prior to use

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1. Overview
The **ASTM D2240-05** standard outlines the procedure for measuring the hardness of rubber, elastomers, and other polymers using a durometer. This method provides a numerical value that represents the material's resistance to indentation under specified conditions.

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2. Test Purpose
The durometer hardness test evaluates:

• Elasticity: Measures how well a material resists deformation under load.
• Durability: Indicates the material's suitability for various applications, such as seals, tires, and elastomeric parts.
• Consistency: Ensures uniformity in material production and quality control.

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3. Types of Durometers
ASTM D2240 defines several types of durometers, each designed for specific materials:

• Type A: Used for softer materials such as rubber and elastomers.
• Type D: Designed for harder materials like hard rubber and plastics.
• Type OO: Suitable for very soft materials like foam and gels.
• Other Types (C, E, M, O, etc.): Specialized for specific material properties or applications.

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4. Test Procedure
The test involves applying a specified force to an indenter and measuring the material's resistance.

• a. Sample Preparation:
  - Test samples must be flat, smooth, and at least 6 mm thick.
  - For thinner samples, layers of the same material can be stacked.
• b. Test Environment:
  - Conduct the test at a standard temperature of 23°C (73.4°F).
  - Allow the sample to condition at the test temperature for a minimum of 1 hour.
• c. Durometer Application:
  - Place the durometer perpendicular to the sample surface.
  - Apply the force steadily without shock and hold for 1–3 seconds (depending on the material type).
• d. Reading and Recording:
  - Read the durometer scale directly.
  - Take at least 5 measurements at different points on the sample and calculate the average hardness value.

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5. Test Results
Durometer Hardness Scale:
- The hardness is reported as a number on a scale of **0 to 100**, where:
  - 0: Indicates no resistance to indentation.
  - 100: Indicates maximum resistance.

Interpretation of Results:
- Softer materials (lower values): Flexible and elastic.
- Harder materials (higher values): Rigid and durable.

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6. Applications
The ASTM D2240-05 standard is widely used in industries such as:

• Automotive: Tires, seals, and gaskets.
• Construction: Rubber mats, flooring, and insulation.
• Medical: Elastomeric components in medical devices.
• Consumer Goods: Foam products, rubber handles, and footwear.

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7. Limitations
While durometer hardness testing is simple and effective, it has some limitations:

• Only measures surface properties; internal material consistency is not evaluated.
• Results can vary with sample thickness or surface irregularities.
• Not suitable for very small or highly curved samples.

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8. Conclusion
The **ASTM D2240-05 Durometer Hardness Test** is a reliable and widely used method for assessing the hardness of rubber, elastomers, and polymers. By following the standard procedure, manufacturers and quality control teams can ensure material consistency, performance, and suitability for various applications.

Key Highlights:

• Hardness measured on a scale of 0 to 100.
• Multiple durometer types for different material properties.
• Requires precise sample preparation and controlled testing conditions.

References: ASTM D2240-05, material testing handbooks, and industry best practices.