Experimental study of the effect of the threading process on the mechanical and tribological behaviors of the triangular thread

The aim of this work is to develop an experimental device useful to evaluate the friction coefficient in triangular thread joints (M12) manufactured with rolling and machining processes, and therefore, to relate precisely the clamping force to the tightening torque. Experimental static tests of clamp force during 10 tightening–loosening cycles were applied to specific threaded specimens obtained with the rolling and machining process. To analyze the mechanical and tribological behaviors of the manufactured threads, the torque coefficient ( K ) (nut factor), the average friction coefficient ( μ m ), and the clamped force ( F ) have been evaluated during 10 cycles of tightening–loosening. The results of this study showed that the range of the variability of the torque coefficient and friction coefficient is between 0.151 and 0.54 and from 0.19 to 0.69 for the rolled thread, respectively. However, these coefficients are between 0.187 and 0.55 and from 0.25 to 0.72 for the machined thread, respectively. The clamping force preserves a linear relationship with the tightening torque and decreases as the number of tightening increases. The use of the rolling process to manufacture the thread joint can preserve a higher mechanical resistance and ameliorate the tribological behavior of the thread compared to the machining process.