Rockwell Hardness Testing

Rockwell Hadness Testing

Rockwell Hardness Testing - Rockwell hardness testing differs from Brinell testing in that the indenters and the loads are smaller and therefore the resulting indentation on the specimen is smaller and shallower. Rockwell testing is suitable for materials having hardness beyond the scope of Brinell testing. Rockwell testing is faster as compared to Brinell testing because diameter of indentation need not be measured; the rockwell machine gives arbitrary direct reading. Unlike Brinell testing, rockwell testing needs no surface preparation (polishing, etc.) of the specimen whose hardness is to be measured.
Procedure for Measuring Hardness (a) Test piece is placed upon the machine. The machine dial is showing any reading. (b) Hand wheel is turned, thereby raising the test piece up against the steel ball indenter till the needle on the dial reads zero. This applies minor load. (c) Major load is applied by pressing the crank provided on the righthand side of the machine (not shown). (d) Crank is turned in the reverse direction thereby withdrawing major load but leaving minor load applied. (e) Hand wheel is rotated and the test piece is lowered.
	At this stage, the hardness of the test piece material can be directly read from the dial scale. There are two scales on a rockwell testing machine, i.e. 'B' scale and 'C' scale. B scale uses a steel ball indenter whereas a diamond cone penetrator is employed for measuring hardness on C scale. B scale is for testing materials of medium hardness such as low and medium carbon steels in the annealed condition. The working range of this scale is from 0 to 100. C scale is used for testing materials harder than B 100. C scale is commonly used for testing the hardness of alloy cast irons. In rockwell hardness testing, the minor load for all cases is 10 kg whereas major loads for scales C and Bare 150 and 100 kg respectively (including minor load).
Vickers Hardness Test In Vickers hardness test, a known load (P) (from 1 to 120 kg) is applied for a specified time to the surface of the material through a square base pyramid diamond having 136° between opposite faces. The two diagonals of the resulting square indentation on the test piece are measured with a micrometer microscope and averaged, (D, mm). The Vickers hardness number is calculated as follows VHN = 1.854 P / D2 Before conducting Vickers hardness test, the surface of the specimen should be flat and of sufficient polish so that any remaining scratches do not cause difficulty in locating the corners of the indentation when diagonals are measured. The impression of Vickers indenter on the specimen being very small, peak (and not average) values of hardness can be determined on the weld from root to face. In the same length of the specimen, more hardness readings can be taken with Vickers hardness test than with Brinell or Rockwell hardness tests.

Home | Site map | Submit Article | Directory | Search