Research On The Impregnated Diamond Bit For Concrete Core Drilling

Currently,concrete structures serve as the foundation of construction projects.As a variety of construction projects grows rapidly,so does the use of impregnated diamond bits for core-pulling quality detection and reinforcement engineering drilling.Due to the strong abrasiveness and high strength of concrete and the reinforcement inside the pile foundation,therefore,the bit had low drilling efficiency,short bit life and easy-broken teeth.The traditional matrix formula series with tungsten carbide has adjustable matrix wear resistance,However,the toughness is low,and the cold-pressing formability is poor.It is difficult to process high-efficiency bits by cold-pressed,therefore the drills have low drilling efficiency and thereby making them unsuitable for concrete drilling.To replace the traditional matrix formula series,it is critical to investigate a matrix formula series with adjustable wear resistance,good toughness,and ease of cold-pressing.Thus,it is conducive to developing a cold-pressed impregnated diamond drill bit with high drilling efficiency,long bit life,good toughness,and continuous teeth,which is suitable for concrete for corepulling quality detection and reinforcement engineering drilling.This paper centres on the issues of the bit structure design,diamond concentration and particle size design,matrix formula design of diamond bit,sintering process parameter design,diamond concentration and particle size design,field drilling test,and bit finite element simulation.The following are the main findings:(1)To address the issue of low concrete drilling efficiency,a coldpressed impregnated diamond drill bit with varying concentrations and particle sizes has been studied and designed,i.e.,the inner,outer,and middle layers of the drill bit are designed with varying diamond concentrations and particle sizes.The layered structure of the drill bit alters the contact mode and stress state between the bit lip surface and the concrete,with the result of forming more broken free surfaces on the concrete surface,reducing contact area and it can drill at a nearly constant speed,thus increasing the drilling efficiency.(2)In light of the problems that exist in concrete drilling as well as the requirements of concrete lithology on bit matrix performance and bit layered structure design,this paper studied and designed the matrix formula of an impregnated diamond bit with pre-alloyed Fe powder as the main body.A small amount of pre-alloyed Cr-Fe was used as the skeleton material in the diamond bit matrix formula,and another pre-alloyed Fe was used as the intermediate regulating material.The mixing test of the pre-alloyed Fe-based powder matrix was then performed using the extreme vertex design method,and the regression equations of matrix composition,hardness,and bending strength were fitted.The effects of various mass fractions and matrix compositions on the matrix properties of a pre-alloyed Fe-based powder were investigated.The optimal ratio range of each matrix composition was determined based on concrete and conventional diamond parameters.(3)The physical and mechanical properties,and the microstructure,of Fe-based sintered bodies with varying mass fractions were studied at different sintering temperatures and holding times.The Fe-based sintered body had the best mechanical properties when the sintering temperature was 940 ℃ and the holding time was 5 minutes.Cu、660-Cu alloy had a significant effect on the relative density of the Fe-based sintered body at the same sintering temperature and holding time,so did pre-alloyed Fe on its bending strength,and Ni、Co on its bending strength and loss rate of bending strength.(4)The differences in physical and mechanical properties and microstructures of various pre-alloyed Fe-based powder matrix formulation systems were compared,and the optimal content of each component of the pre-alloyed Fe-based powder matrix formula was determined by designing the formulation system of diamond drill bits based on concrete drilling.The skeleton phase pre-alloyed Cr-Fe was approximately 5 wt%,pre-alloyed Fe was about 35 wt%,Cu was about 20 wt%,660-Cu was about 20 wt%,Ni was about 10 wt%,Co was about 10 wt%.(5)Considering the drilling characteristics of concrete,the diamond parameter experiment was carried out based on the determined formula.The reasonable concentration and particle size of the diamond were also accordingly determined.The pre-alloyed Fe-based matrix was coldpressed to form various concentrations and sizes of impregnated diamond bits.Micro-drilling and field drilling tests were performed on widely used C30 and C35 concrete.The results show that Fe-based matrix diamond bits’ drilling efficiency and service life have been increased by more than 20%,with promising experimental results.In terms of concrete field drilling,diamond bits with varying concentrations and particle sizes solve the problems of low drilling efficiency,short service life,and easybroken teeth.(6)The finite element analysis software ANSYS was used to compare and analyse the equivalent stress of the drill bit at the moment of cutting into concrete under static load and the drilling process of the drill bit under dynamic conditions based on the drilling characteristics of concrete.The concrete breaking mechanism of the layered impregnated diamond bit was discussed in conjunction with the results of the microdrilling bench test and the field test,providing a theoretical basis for the application design of other engineering diamond bits.