ASTM D785-08(2015)
Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials

Standard No.

ASTM D785-08(2015)

Release Date

2008

Published By

American Society for Testing and Materials (ASTM)

Status

Be replaced

Replace By

ASTM D785-23

Latest

ASTM D785-23

Scope

4.1 A Rockwell hardness number is a number derived from the net increase in depth impression as the load on an indenter is increased from a fixed minor load to a major load and then returned to a minor load (Procedure A). A Rockwell alpha (α) hardness number represents the maximum possible remaining travel of a short-stroke machine from the net depth of impression, as the load on the indenter is increased from a fixed minor load to a major load (Procedure B). Indenters are round steel balls of specific diameters. Rockwell hardness numbers are always quoted with a scale symbol representing the indenter size, load, and dial scale used. This test method is based on Test Methods E18. Procedure A (Section 11) yields the indentation of the specimen remaining 15 s after a given major load is released to a standard 10-kg minor load. Procedure B (Section 12) yields the indentation of the indenter into the specimen after a 15-s application of the major load while the load is still applied. Each Rockwell scale division represents 0.002-mm (0.00008-in.) vertical movement of the indenter. In practice, the Rockwell hardness number is derived from the following relationship:

where:
HR	=	the Rockwell hardness number, and
e	=	the depth of impression after removal of the major load, in units of 0.002 mm. This relation only holds for the E, M, L, R, and K scales.

4.2 A Rockwell hardness number is directly related to the indentation hardness of a plastic material, with the higher the reading the harder the material. An α hardness number is equal to 150 minus the instrument reading. Due to a short overlap of Rockwell hardness scales by Procedure A, two different dial readings on different scales may be obtained on the same material, both of which may be technically correct.

4.3 For certain types of materials having creep and recovery, the time factors involved in applications of major and minor loads have a considerable effect on the results of the measurements.

4.4 The results obtained by this test method are not generally considered a measure of the abrasion or wear resistance of the plastic materials in question.

4.5 Indentation hardness is used as an indication of cure of some thermosetting materials at room temperature. Generally, an uncured specimen has a hardness reading below normal.

4.6 Each Rockwell hardness scale in Table 1 is an extension of the proceeding less severe scale, and while there is some overlap between adjacent scales, a correlation table is not desirable. Readings on one material may be satisfactory for such a table, but there is no guarantee that other plastic materials will give corresponding readings because ......

ASTM D785-08(2015) Referenced Document

• ASTM D2240 Standard Test Method for Properties of Rubber &8212; Durometer Hardness*， 2024-04-20 Update
• ASTM D4000 Standard Classification System for Specifying Plastic Materials
• ASTM D618 Standard Practice for Conditioning Plastics for Testing
• ASTM D883 Standard Terminology Relating to Plastics
• ASTM E18 Standard Test Methods for Rockwell Hardness of Metallic Materials
• ASTM E691 Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• ISO 2039-2 Plastics; Determination of hardness; Part 2 : Rockwell hardness

ASTM D785-08(2015) history

• 2023 ASTM D785-23 Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials
• 2008 ASTM D785-08(2015) Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials
• 2008 ASTM D785-08 Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials
• 2003 ASTM D785-03 Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials
• 1998 ASTM D785-98e1 Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials