The effects of chamfer and back rake angle on PDC cutters friction

Abstract

Single PDC cutter tests at a high pressure cell were conducted and analyzed to gain an understanding of the effect of cutter geometry on its frictional response. First, sets of tests conducted with sharp non-chamfered cutters are analyzed. A decreasing trend between the friction angle and back rake angle is consistently observed. The reason can be attributed to a change in flow direction of the rock in front and near the cutting face. A linear relationship between the friction angle and cutter back rake angle is proposed. The coefficient of this relationship can be calculated using the rock internal friction angle and at least one drilling data for the given drilling fluid and contacting surfaces.Four sets of tests with cutters of different diameters (13 and 16 mm) and chamfer lengths (0.010 and 0.016 inch) were conducted. The test results are presented and analyzed using the abovementioned semi empirical model. The method is to associate a chamfered cutter's action to an equivalent non-chamfered cutter back rake angle. It is observed that applying the test data to this analysis produces results that make physical sense with the geometric shape of a chamfered cutter.Finally, contact stress data, for the range of back rake angles tested, confirm a strong increasing trend with back rake angle. The observations indicate that, for the conditions of these tests, that the frictional response of a cutter with developed wear flat is dominated by the wear flat friction itself.