We do 14 RTF test for our copper 8mm copper rod. This test includes holding 250mm sample in chuck jaw. Rotating 14 revolution in forward direction and later in reverse direction till it breaks. Getting more than 22 reverse revolutions considered as best rod. Sometimes we getting less than 20 revolutions for same casting and rolling parameters. Anyone knows what factors affecting this test?
This is a torsion test and as such quickly gives the tester an indication of the metallurgical properties of the copper rod sample including copper purity, hardness and shear strength. The test also tells the tester about the uniformity of the copper rod sample (Internal voids, foreign inclusions and so on.) Like all testing, there will be variances in the results and thus there will be a normal distribution. I imagine you have a handle on this with some sort of SPC program.
It is assumed of course that the outside surface of the rod is smooth, undamaged and that the jaws do not contribute to the failure.