Rock breakage and temperature variation of naturally worn PDC tooth during cutting of hard rock and soft rock

Although experiments and simulations of new polycrystalline diamond compact (PDC) tooth cutting have been conducted, the rock breakage and temperature variation of the worn PDC tooth cutting are still unclear. Thus, naturally worn PDC teeth removed from a worn PDC bit were used to determine the rock breakage and temperature variation of hard rock and soft rock using force sensors, high-speed photography, and thermal infrared instruments. The effects of wear on cutting force, temperature variation, and cutting chips were studied. The results indicate that the cutting force variation is different in granite and sandstone. The temporary increasing time of the sandstone cutting force is 0.04–0.063 s, which is less than for granite cutting (0.04–0.075 s). Greater wear of the cutter increases the time for the cutting force to increase from zero to an extreme value. The maximum cutting force of granite is 6.7 times greater than that of sandstone; the temperature increase of the PDC tooth in cutting granite is seven times greater than in cutting sandstone. As the wear increases, there is extreme fluctuation in the cutting force and temperature variation, which is attributed to the periodic removal of larger flake cutting chips. The relationship between the wear and the mechanical specific energy per unit mass (MSEP) and the coefficient of friction (COF) is discussed. It was found that as the wear increases, the cutting temperature and the MSEP quickly increase, and the COF decreases. This study is helpful in comprehensively understanding the rock breakage and heat generation of naturally worn PDC teeth in deep wells, which is beneficial for estimating the PDC cutter life and failure.