Wear of Tungsten Carbide Waterjet Nozzle
Wear of Tungsten Carbide Waterjet Nozzle
Drilling hard rock with waterjet cutting is considered to be an efficient way to improve the work life of the cemented carbide blades. This article will briefly talk about the experiment on the wear of the YG6 tungsten carbide waterjet nozzle when it is used in limestone drilling. The experiment result will show that the waterjet pressure and nozzle diameter play an important influence on the wear of the tungsten carbide waterjet cutting nozzle.
1. Introduction of waterjet
A waterjet is a liquid beam with high velocity and pressure and is used for cutting, shaping, or caving. Since the waterjet system is simple and the cost is not very expensive, it is widely used for 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 was damaged seriously in hard rock drilling. If a 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.
2. Materials and experimental procedures
The materials used in this experiment are the YG6 cemented carbide waterjet nozzle and the hard material limestone.
2.2 Experimental procedures
This experiment was performed at room temperature, and keep the drilling speed at 120 mm/min and rolling speed at 70 rounds/min for 30 min in the experiments, aimed to investigate the influence of different water jet parameters including jet pressure, nozzle diameter, on the wear characteristics of the cemented carbide waterjet cutting tube.
3. Results and discussion
3.1. Effect of water jet pressure on the wear rates of the cemented carbide blades
It is shown that the wear rate is quite high without the help of the water jet, but the wear rates decrease sharply when the water jet joins in. The wear rates decrease when the jet pressure increases. Nevertheless, the wear rate decreases slowly when the jet pressure is over 10 MPa.
The wear rates are affected by the mechanical stress and temperature of the blades, and the water jet is helpful to reduce the mechanical stress and temperature.
Higher jet pressure could also increase the thermal exchange efficiency to reduce the working temperature. Heat transfer takes place when the water jet flows through the surface of the blade, with a cooling effect. This cooling process can approximately be regarded as the process of convective heat transfer outside a flat plate.
3.2. Effect of the nozzle diameter on the wear rates of the cemented carbide blades
A bigger nozzle diameter means a larger impact area and more impact force to the limestone, which helps to reduce the mechanical force on the blade and lessen its wear of it. It is shown that wear rates decrease with the increase of the nozzle diameter of the drill bit.
3.3. Wear mechanism of cemented carbide blade drill rock with a water jet
The failure type of the cemented carbide blades in water jet drilling is not the same as that in dry drilling. No serious fractures are detected in the drilling experiments with the water jet under the same zoom scope and the surfaces mainly show wear morphology.
There are mainly three reasons to explain the different results. Firstly, a water jet can effectively decrease surface temperature and thermal stress. Secondly, the water jet provides impact force to crack the limestone, and it helps to decrease the mechanical force on the blade. Thus, the sum of thermal stress and mechanical stress which can induce serious brittle fractures could be lower than the material strength of the blade in drilling with water. In the third place, the water jet with higher pressure could form a comparatively cooler water layer to lubricate the blade and could rush away the hard abrasive particles in the rock like a polisher. Therefore, the surface of the blade in water jet drilling is much smoother than that in dry drilling, and the wear rate will decrease while the water jet pressure increases.
Although a wide range of brittle fractures is avoided, there will still be surface damage on the blades in rock drilling with a water jet.
The wearing process of cemented carbide blades in limestone drilling with a water jet could be divided into two stages. Initially, in underwater jet-assisted conditions, micro-cracks appear on the edge of the blade, probably caused by local mechanical abrasion and thermal stress which is induced by the flash temperature. The Co phase is much softer than the WC phase and it is easy to be worn. So when the blade mills the rock, the Co phase is worn first, and with particles washed away by the water jet, the porosity between grains is larger and the surface of the blade becomes more uneven.
Then, this kind of micro-surface damage expands from the edge to the center of the blade surface. And this polishing process continues from the edge to the center of the blade surface. When the drill bit drills into the rock continuously, the polished surface on the edges will form new micro-cracks which then extend to the center of the blade surface because of mechanical abrasion and thermal stress caused by flash temperature.
Therefore, this roughing-polishing process is repeated from the edge to the center of the blade surface constantly, and the blade will become thinner and thinner until it cannot work.
4.1 The pressure of the water jet plays an important role in the wear rates of cemented carbide drill bits in rock drilling with the water jet. The wear rates decrease with the increase of the jet pressure. But the decline speed of wear rates is not even. It declines more and more slowly when the jet pressure is over 10 MPa.
4.2 Reasonable nozzle structure can improve the wear resistance of the cemented carbide blades. Moreover, increasing the diameter of the jet nozzle could decrease the wear rates of the blades.
4.3 Surface analysis demonstrated that cemented carbide blades in limestone drilling with a water jet show circular action of brittle fracture, grain pullout, and polishing, which induces the material removal process.
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Waterjet machining is one of the fastest-developing machining processes. A lot of industries have adopted the process because of the high quality of cutting through diverse materials. Its environmental friendliness, and the fact that materials are not deformed by heat during cutting.
Because of the high pressure generated during the process, industrial water jet cutting must be handled carefully by experts at all stages of cutting. At ZZBETTER, you can get experienced experts to handle all of your waterjet machining needs. We are also a one-stop rapid prototyping manufacturer, specializing in CNC Machining, sheet metal fabrication, rapid injection molding, and various types of surface finishes. Don’t hesitate to reach out to us and get a free quote today.
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