巷道下向小孔径锚固孔钻进产渣特征及高效钻头设计

Fragments generation characteristics and design of a kind of efficient rockbreaking bit during borehole drilling with small diameter at a downward angleof coal mine roadway

煤矿巷道下向锚固孔钻进是巷道围岩锚固控制的重要环节,成孔质量与锚固效果成正比。长期以来,小孔径下向锚固孔排渣困难是高质量快速成孔的瓶颈问题。因此,为了降低钻渣生成尺寸,提高排渣效率,利用理论分析、数值模拟、实验室实验及现场测试相结合的方法,研究了现有PDC两翼式钻头产渣尺寸及其周边钻渣运移特征,研发了一种小孔径下向锚固孔高效破岩钻头,优化了钻头进出液通道尺寸,并对设计钻头工作性能进行了分析验证。结果表明:现有PDC两翼式钻头在钻孔底部均会形成中心岩柱结构,其尺寸随钻头刀片间距的增加而增加。中心岩柱是大尺寸钻渣的主要来源,中心岩柱尺寸越大,产生的粒径>2.5 mm的钻渣平均尺寸也越大。改变刀片结构,消除孔底中心岩柱,可降低钻渣生成尺寸;现有钻头结构会造成钻渣局部聚集,导致钻渣上返能量损失;设计的高效破岩钻头因其结构优势较普通钻头更能够减少液渣混合流的能量损失,使钻渣具有更高的上返速度,更有利于钻渣顺利排出;高效破岩钻头的主副刀片会使钻孔底部形成平台结构,保证了孔底岩石均为切削破坏,消除了孔底中心岩柱,使钻渣平均尺寸明显低于其他类型钻头,也具有更高的破岩效率;现场试验结果表明,高效破岩钻头有效降低了钻渣生成尺寸,具有更高的成孔速度及排渣效率,工作性能良好。

Borehole drilled at a downward angle is an important part for roadway bolting support.How well the bolt is anchored depends,in part,on borehole quality.A major factor that can reduce borehole quality is the difficulty of discharging rock fragments from a small diameter borehole drilled at a downward angle.Therefore,to reduce the fragment size to improve the discharging efficiency,theoretical analysis,numerical simulation,laboratory experiment,and filed test was adopted to explore the correlations between the fragment size and blade spacing.A kind of efficient rock breaking bit of the small diameter borehole drilled at a downward angle was developed.The sizes of bit channels were optimized,and the performance of the bit were also analyzed and verified.The results indicate that the central rock pillar will appear in the bottom of the borehole during the drilling process of the normal PDC two-wing drill bits.The sizes of the central rock pillar increase with blade spacing,which is the main source of the fragments with large size and leads to the increase of the mean size of the fragments with the particle sizes greater than 2.5 mm.The fragment size can be reduced by changing the blade structure to eliminate the central rock pillar.The structure of the normal bit could cause local gathering and energy loss of the fragments.Benefiting from the structure advantages the designed bit can reduce the energy loss of mixed flow to make the fragments get higher velocity and is more conducive to the smooth discharging compared with the normal bit.The main and auxiliary blades of the designed bit will make the rock at the bottom of the borehole form a platform.They can ensure that the rock at the bottom of the hole failed due to cutting to and eliminate the central rock pillar.So that the mean fragment size is significantly lower than other types of bits,and it also has higher rock breaking efficiency.The field test results demonstrate that the designed bit can effectively reduce the fragment size,and has higher drilling speed and fragment discharging efficiency.The research results of this paper have a certain guiding role and reference value for the theory and equipment research of the rapid and high-quality formation of a small diameter borehole drilled at a downward angle.