Structure Design And Experimental Research On A Reverse Circulation Drill Bit With A Spiral Slot

The continuous coring drilling technology with reverse circulation by hollow-through air down-hole hammer is to use the compressed gas as a circulating medium,drive the DTH hammer to break the rock bottom,and carry the core from the center channel to the surface,so as to realize the drilling technology of continuous coring.When the DTH hammer is working normally,compressed air enters into the DTH hammer through the top joint and core barrel from the annular space of the double-wall drill pipes and drive it to high-frequency vibration in order to broke the hole bottom rock.Due to the high pressure gas driving DTH hammer are all through the annular space between the double-wall drill pipes to the bottom of the hole and return by the center passage,there is no air leakage phenomenon between the outer wall of drill pipes and borehole.So the Air-DTH hammer drilling has a great advantage when broking the stratum.The reverse circulation drill bit is a critical component as the tool of rock broking and determines the good and bad effect of reverse circulation.So the performance of the reverse circulation drill bit can directly affect the efficiency of drilling.In order to further improve the drilling efficiency,a large number of scholars at home and abroad have been working on the research on the structure of the reverse circulation bit.While this paper proposes that the spiral flow can be introduced in the reverse circulation drill bit and it can combine with the structure characteristics of the reverse circulation drill bit.And then a new type of spiral suction reverse circulation drill bit(auger drill bit)is designed.It can use its strong suction force to improve the drill bit reverse circulation effect.By means of CFD numerical simulation and experiment this paper has contrast the auger drill with annular jet reverse circulation bit(annular bit)and verified that inside of the new spiral suction reverse circulation drill bit can effectively form spiral flow and improve the effect of reverse circulation drill bit.And through a series of experimental tests of auger drill bit parameters such as helix Angle of spiral vane,spiral blade length,number of spiral vane and the gap size of spiral nozzles,and optimize them.(1)Inside the new type of spiral suction reverse circulation drill bit it can effectively form spiral flow and improve the reverse circulation effect.(2)With the same intake air volume,the swirling drill bit has a higher suction volume than the annular drill bit,when the bottom nozzles opened,the maximum suction of the swirling drill bit can be 1.44 times the annular drill bit;when the bottom nozzles sealed,the maximum suction of the swirling drill bit can be 1.26 times the annular drill bit.(3)The numerical simulation results are in good agreement with experimental test results.Especially for swirling drill bit,when the bottom nozzles opened,the maximum error of the experimental and simulation results does not exceed 9.05%.When the bottom nozzles sealed,the maximum error is only 2.1%,in the follow-up research on swirling drill bit,numerical simulation methods can be used for further study;(4)When the bottom nozzles opened,the reverse circulation effect of the drill bit is mainly affected by the intensity of the nozzles to form a swirling flow,the energy loss caused by the nozzles resistance,and the bottom nozzles diversion.When the bottom nozzles sealed,the reverse circulation effect of the drill bit is mainly affected by the intensity of the nozzles to form a swirling flow and the energy loss caused by the nozzles resistance.Different swirled structure parameters will affect the intensity of the spiral nozzles to form a spiral and the nozzles resistance,thus affecting the reverse circulation effect of the drill bit.(5)The helical angle of the spiral blades which measured from horizontal have a significant effect on the reverse circulation effect of the drill bit.The smaller the helical angle is,the stronger the swirling intensity is.But at the same time,the nozzles resistance will be greater,resulting in more energy loss and bottom nozzles split.The length of the spiral blades have little effect on the ability of the nozzles to form a swirling flow,but increasing the length of the spiral blades will greatly increase the nozzles resistance.As a result,the energy loss and the split of the bottom nozzles increase,which reduces the reverse circulation effect of the drill bit.The numbers of spiral blades have little effect on the reverse circulation effect of the drill bit.With the increase of the numbers of blades,the swirling intensity of spiral nozzles first increases slightly and then decreases,but the nozzles resistance increase with the increase of spiral blades.The gap size between the spiral nozzles has a significant effect on the reverse circulation effect of the drill bit.The smaller the gap between nozzles,the stronger the intensity of the nozzles to form a swirling flow.But at the same time,the nozzles resistance will be greater,resulting in more energy loss and bottom nozzles split.In this experiment,when helical angle of the spiral blades is 60°,the length of spiral blades is 10 mm,the number of spiral blades is 3,the gap between the nozzles is 1.5mm,the reverse circulation effect of the drill bit is the best.