BS EN ISO 6506-3:2005 pdf – Metallic materials — Brinell hardness test — Part 3: Calibration of reference blocks.
1 Scope This part of ISO 6506 specifies a method for the calibration of reference blocks to be used in the indirect verification of Brinell hardness testing machines as described in ISO 6506-2. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 376:2004, Metallic materials — Calibration of force-proving instruments used for verification of uniaxial testing machines ISO 4287, Geometrical Product Specifications (GPS) — Surface texture: Profile method — Terms, definitions and surface texture parameters ISO 6506-1:2005, Metallic materials — Brinell hardness test — Part 1: Test method ISO 6506-2:2005, Metallic materials — Brinell hardness test — Part 2: Verification and calibration of testing machines 3 Manufacture of reference blocks 3.1 The block shall be specially manufactured for use as a hardness-reference block. NOTE Attention is drawn to the need to use a manufacturing process which will give the necessary homogeneity, stability of structure and uniformity of surface hardness. 3.2 Each metal block to be calibrated shall be of a thickness not less than: ⎯ 16 mm for 10 mm balls; ⎯ 12 mm for 5 mm balls; ⎯ 6 mm for smaller balls. NOTE 12 mm for 10 mm balls may be used only if the hardness of the reference block is greater than 150 HBW. 3.3 The reference blocks shall be free of magnetism. It is recommended that the manufacturer shall ensure that the blocks, if of steel, have been demagnetized at the end of the manufacturing process.
3.5 The test surface shall be free from scratches which interfere with the measurement of the indentations (see Table 1). 3.6 To verify that no material is subsequently removed from the reference block, the thickness at the time of calibration shall be marked on it to the nearest 0,1 mm, or an identifying mark shall be made on the test surface [see 8.1.e)]. 4 Calibration machine 4.1 In addition to fulfilling the general requirements specified in Clause 3 of ISO 6506-2:2005, the calibration machine shall also meet the requirements given in 4.2 to 4.8. 4.2 The machine shall be verified directly in intervals not exceeding twelve months. Direct verification involves: a) calibration of the test force; b) verification of the indenter; c) calibration of the measuring device; d) verification of the testing cycle, if this is not possible, at least the force versus time behaviour. 4.3 The instruments used for verification and calibration shall be traceable to national standards. 4.4 Each test force shall be measured using an elastic proving device (of ISO 376:2004, Class 0,5 or better) and the measurement shall agree with the nominal value to within ± 0,1 %. 4.5 The indenters shall be verified and shall meet the requirements given in 4.3 of ISO 6506-2:2005, with the exception that the tolerances on the diameter of the balls shall meet requirements given in Table 2.
4.7 The testing cycle shall conform to the testing cycle described in ISO 6506-1 and shall be timed with an uncertainty less than ± 0,5 s. 4.8 The characteristics of the hardmetal balls are specified in 220.127.116.11 of ISO 6506-2:2005. 5 Calibration procedure The reference blocks shall be calibrated in a calibration machine as described in Clause 4, at a temperature of (23 ± 5) °C, using the general procedure described in ISO 6506-1. During calibration, the thermal drift should not exceed 1 °C. The time from the initial application of force to the time the full test force is reached shall not be less than 6 s nor greater than 8 s. The duration of the test force shall be 10 s to 15 s. The mechanism which controls the application of the force shall ensure that the speed of approach of the ball immediately before it touches the block is not more than 1 mm/s. 6 Number of indentations On each reference block, five indentations shall be made uniformly distributed over the entire test surface. To reduce the measurement uncertainty, more than five indentations should be made.