Rockwell & Superficial Hardness
Rockwell and Superficial hardness testing shall be performed in accordance with the latest revision of ASTM E18.
There are two general classifications of the Rockwell test: the Rockwell hardness and the Rockwell superficial hardness test. In the Rockwell hardness test the preliminary test force is 10 kgf. Total test forces are 60 kgf, 100 kgf and 150 kgf. In the Rockwell superficial hardness test, the preliminary test force is 3 kgf and total test forces are 15 kgf, 30 kgf, 45 kgf. The indenter of either test shall be of spheroconical or spherical configuration The standard indenters are the diamond spheroconical and tungsten carbide ball indenters' 1/16, 1/8, 1/4, 1/2 inch in diameter. Annex 3 or A3. STANDARDIZATION OF ROCKWELL INDENTERS, covers the requirements of indenters to be used. The dust, dirt, grease and scale shall not be allowed to accumulate on the indenter as this will affect the test. Anvils used for indention’s must be suitable for specimen. Cylindrical pieces shall be tested with a V-grooved anvil Flat pieces shall be tested on a flat anvil, whose plane is perpendicular to the axis of the indenter. The anvils shall be clean and smooth and free from pits, scratches, dust, dirt and grease. The anvil and indenter shall be set properly by running two tests not used in calculations.
The test specimens shall be clean and prepared in a way that alteration of the surface hardness is minimized. Flat specimens' surfaces should be flat and parallel to indenter and anvil. The thickness of the test piece or of the layer under test should be as dictated in Table 7, 8, 9, and 10 of ASTM E18. The general rule, is the thickness should be 10 times the depth of the indenter. For tests on convex cylindrical surfaces the corrections given in Tables 11, 12, 13, and 14 of ASTM E18 shall be applied.
Place the specimen on the proper anvil and bring the indenter in contact with specimen until the machine engages the minor load. This indicates machine is ready for reading and will give automatic readout. There should be a minimum 3 readings per sample and 4 readings for bolt testing. Each reading should be a distance of three times the diameter of the indenter apart. Take an average of the readings for the final result. If technician believes that a reading is not representative of material an additional 3 readings can be used to replace the one.
Before each test using a different scale, start of a day, or change of indenter the machine will be calibrated using NIST traceable hardness blocks. This calibration will be logged and recorded using hardness block limits with an average of three readings for each test block. After testing the final report will include Rockwell hardness number, scale used, and readings to nearest the whole number by rounding in accordance with ASTM E29.