Cemented Carbide Blades Wear Characteristics In Drilling LimestoneⅡ

Water jet is a liquid beam with high velocity and pressure, and is used singly or jointly with tools for operations such as cutting, shaping and carving. Since water jet system is simple and the cost is not very expensive, it is widely used in metal machining and medical operation. Cemented carbide is the dominant material in machining and mining tools for its unique combination of hardness, toughness and inexpensive price. However, the cemented carbide tool damaged seriously in hard rock drilling. If water jet is used to assist the drill bit, it could impact the rock to reduce the blade force and exchange the heat to cool the blade temperature therefore, it would be an effective way to improve the work life of the cemented carbide blade when water jet is used in rocking drilling .

Various failure mechanisms of ordinary cemented carbide drill bits in rock drilling are studied. Beste charts the wear phenomena of cemented carbide rock-drill bits, such as crack formation, occurrence of reptile skin and various wear mechanisms. Stjernberg reports that the drilling process produces temperature fluctuations in the surface region, which leads to high tensile stresses and accelerates the forms of cracks. In Montgomery's survey, the minimum wear rate of cemented carbide in granite drilling occurs at a specific hardness point, which corresponds to the point of maximum compressive strength, and there are also other reports on investigating the wear process of drill bit in rock drilling. Lots of literatures have shown that cemented carbide exhibits strong life time-limiting fatigue sensitivity at room temperature. But Kindermann reported the fatigue mechanisms in cemented carbides are strongly temperature-dependent. At higher temperatures, the oxidation of the binder ligaments near crack tips and brittle –ductile transitions of mixed carbides seem to play an important role in the fatigue behaviors. In addition, the service temperatures of the tools rise much higher than the room temperature and influence their working lives. The service temperatures of rock drilling bits are estimated to lie between 300 and 500°C. In tests with WC/Co sliding against sandstone, a glassy phase is produced which indicates flash-temperatures of 1250°C or more. Oxidation behavior of the cemented carbide bits will occur in rock drilling , and the mechanical properties will be influenced.

Although water jet seems to be a good way to solve the above problems, but the wear of the cemented car bide blades in hard rock drilling under water jet is a dynamic process, whose wear mechanisms and patterns are not well characterized or understood. Moreover, little work has been published on the wear characteristics of t he cemented carbide blades in drilling hard rock with water jet.

The goal of this work was to investigate wear characteristics of the cemented carbide blades in drilling hard rock with water jet. Limestone is a typical hard rock in the practical engineering applications. In this paper, the wear rates of cemented carbide blades under different water jet parameters in limestone drilling were measured, and the wear mechanisms of these cemented carbide blade in limestone drilling with water jet were examined with microstructure analysis of the wear surface.

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