Friction characteristics and grinding model of cemented carbide for drilling bit affected by WC grain size and rotational speed

Abstract

Rotary drilling remains a common geological drilling technique, and drilling costs have increased significantly due to the wear of cemented carbide (WC/Co) drill bits. Material selection and optimization of drilling parameters are effective ways to reduce bit wear. To investigate the wear pattern of cemented carbide materials for drill bits applicable to different soft and hard formations under different rotational speeds, and to provide references for reducing the wear of drill bits from the perspectives of material selection and drilling rotational speed selection. In this study, the effect on WC/Co drill bit wear rate (W_r) of WC grain size and rotational speed is investigated. The findings indicate a positive correlation between W_r and rotational speed, whereas the coefficient of friction (f_c) displays a negative correlation with rotational speed. The G0.5, G1, and G1.5 have the highest wear rates at rotational speeds of up to 500 r/min, which are 0.38 %, 0.55 % and 0.63 %, respectively. The results demonstrated a positive correlation between the grain size of WC in WC/Co and W_r. The W_r of G1.5 reaches the maximum at rotational speeds (i.e.,100, 200, 300, 400, and 500 r/min), with 0.19 %, 0.21 %, 0.29 %, 0.52 %, and 0.63 %, respectively. The WC/Co material, which exhibits a fine WC grain size, displays a low f_c. It is observed that as the rotational speed and WC grain size increased, the width and depth of the wear marks also increased. The oxide layer produced by frictional heat generation has a friction-reducing effect at low speeds, but at high speeds, the oxide layer will peel off. Compared to WC/Co with coarse WC grains, fine WC grains retain their particle integrity during wear, this results in a reduction in the temperature rise caused by the friction of WC fragments. A grinding model of WC/Co is constructed, which better predicts the change rule of W_r with rotational speed and WC grain size. The results offer a theoretical foundation for the selection of drill bit materials and drilling process parameters.