The diamond bit generates a lot of heat and cuttings when drilling at high speed. In order to ensure the proper circulation of the wash/slurry, water outlets and internal and external flume must be designed in the end part of the drill body. The shape and number of water orifice have a certain influence on the drill footage efficiency.
Influence of nozzle shape on footage efficiency
At present, there are four kinds of water spout shapes commonly used in geological coring bit, which are straight water spout, positive spiral water spout, reverse spiral water spout and bottom water spout. The spiral nozzle is designed to solve the problem of poor circulation in the case of high concentration of washing liquid or mud slurry. Positive and reverse circulation nozzle respectively correspond to the drilling of positive and reverse circulation drilling tool. The huge whirlpool generated during high-speed rotation can speed up the flow rate of liquid and achieve the purpose of efficient penetration. The bottom jet nozzle is commonly used in the coring bit with rope, in order to prevent the plug of the nozzle from burning the drill. However, the actual effect is not very obvious, and it has a negative effect on the footage efficiency of the bit, so it is not widely used. The most used is the straight water nozzle, not only this design helps the processing of the bit, in the actual drilling process is easier to make debris discharge, speed up the liquid circulation, protect the head of the drill body at the same time speed up the footage efficiency, the drill is using this water nozzle design.
Influence of nozzle width on footage efficiency
Bit spout widths are 4mm, 6mm, 8mm, 10mm, 12mm, and 14mm. The wider the nozzle, the larger the pump capacity and pressure, or the mud pump, the more efficient the drilling will be. Similarly, the more water outlets there are, the greater the water flow per unit time, and the greater the footage efficiency should be. However, too much water mouth will occupy too much of the tire body area, so that the matrix surface of diamond cutting rock is reduced, which is unfavorable to efficient drilling. At the same time, the bearing area of the first tire body teeth is small, which is easy to cause the problem of drill bit tire loss. As a result, the 110mm diamond bit used 12 water outlets, which not only satisfied the normal circulation of the flushing fluid, but also ensured that the appropriate cutting area of the diamond body ensured that each single crystal had sufficient axial pressure to drill.
At present, many manufacturers produce ultra-small teeth drill bits, aiming to reduce the contact area between the drill head and the rock layer to achieve the purpose of speeding up the footage. In fact, the footage efficiency of the drill is not only determined by the simple water orifice factor, but too much water orifice will make it difficult for the diamond to get enough pressure into the rock. It is impossible to drill hard rock layer by increasing the number of water orifice alone. A gold drill with a 6-8 degree carcass should be used. This kind of drill has a reasonable nozzle shape and quantity, and most importantly, it is the enemy of extremely hard rock formations.
