Examination of wear damage to rock-mining hardmetal drill bits

WC/Co mining bits from a drill head used for drilling holes for roof support bolts in a mine were examined using a focused ion beam scanning electron microscope (FIB-SEM). This was combined with energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analyses to study the chemical interaction between the drill bit and the rock. It was found that at the surface of the buttons there was depletion of cobalt, change in chemistry of the remaining binder regions, and changes to the morphology of the WC grains. Tribochemistry calculations were done to understand the possible formation of silicides at the surface of the drill bits, and thus emphasise the importance of quartz content in rock on wear. The evidence of mechanical damage combined with chemical reactions is another step towards understanding the complete wear process in hardmetal mining tools.     

Near-surface phenomena occurring in cemented carbides with different binders during rotary-percussive drilling of reinforced concrete: FE simulation and microstructural investigations

Rotary-percussive drilling through steel rebar in reinforced concrete subjects drill bits to intensive thermomechanical loading and wear. Significant microstructural changes occur in near-surface regions. These include, but are not limited to, micro- and mesoscopic cracking; fracture at WC-binder interfaces; WC comminution; partial WC dissolution and rearrangement; surface decarburization; binder depletion and pore formation; and the creation of secondary phases within the binder [1–4].Cemented carbide drill bits with three different binders (Co, CoNi and Ni) were drilled in steel reinforced concrete. After sectioning the drill bits, numerous analysis methods were employed to identify the type and composition of phases present; to characterize microstructural changes and wear phenomena; and to locally measure the properties of the modified surface microstructure. Noticeable differences between the binder types are evident.A variety of finite element (FE) simulation methods were used to describe the thermo-mechanical loading spectrum acting on the drill bits. Transient (dynamic) impact loading and quasi-static indentation simulations calculated the stresses and temperatures generated in the application. The magnitude, orientation vectors and spatial distribution of the simulated stress and temperature fields were correlated with the experimental findings regarding crack initiation sites and regions experiencing thermo-mechanically induced surface microstructural and compositional modification. This paper presents some of these findings from extensive experimental and simulation studies.     

钎焊镀钛金刚石钻头的研制及其钻进性能分析

分别使用Ni-Cr和Cu-Sn-Ti等2种合金钎料真空钎焊制作镀钛和无镀层金刚石钻头,通过钻进玻化砖试验,研究了4类钻头的钻进性能。试验结果表明:Ni-Cr钎料钎焊制作的镀钛金刚石钻头与无镀层金刚石钻头比较,钻头平均寿命下降了41.7%;Cu-Sn-Ti钎料钎焊制作的镀钛与无镀层金刚石钻头比较,钻头平均寿命相当,但镀钛金刚石钻头的钻孔效率更高,并对其机理进行了分析。      

Comprehensive analysis of delamination in drilling of composite materials with various drill bits

Beside the twist drill, the effects of various drill geometries were rarely discussed in analytical fashion. This study presents a comprehensive analysis of delamination in use of various drill types, such as saw drill, candle stick drill, core drill and step drill. In this analysis, the critical thrust force at the onset of delamination is predicted and compared with the twist drill.     

辅磨料金刚石地质钻头试验研究

本文采用五种粒度金刚石作为辅磨料,共设计了13种不同配方的孕镶金刚石钻头进行钻进混凝土的试验,探讨了在相同胎体成份下钻头所加入辅磨料的参数设计对其性能的影响。本研究发现合适粒度和浓度的辅磨料添加,不但可以提高钻头的寿命,而且也能提高其锋利性。室内试验研究表明:加入粒度为120/140目、浓度为6%左右的辅磨料时,能使钻头在钻进混凝土时,效率和寿命分别提高40%和150%。     

Taguchi analysis of delamination associated with various drill bits in drilling of composite material

This paper presents a prediction and evaluation of delamination factor in use of twist drill, candle stick drill and saw drill. The approach is based on Taguchi’s method and the analysis of variance (ANOVA). An ultrasonic C-Scan to examine the delamination of carbon fiber-reinforced plastic (CFRP) laminate is used in this paper. The experiments were conducted to study the delamination factor under various cutting conditions. The experimental results indicate that the feed rate and the drill diameter are recognized to make the most significant contribution to the overall performance. The objective was to establish a correlation between feed rate, spindle speed and drill diameter with the induced delamination in a CFRP laminate. The correlation was obtained by multi-variable linear regression and compared with the experimental results.     

煤矿井下随钻测量定向钻进用PDC钻头的研制

煤矿井下随钻测量定向钻进需要设计高品质的PDC钻头。本论文从PDC钻头的结构参数到PDC切削齿的选型均进行了较深入的分析研究;同时研制了96 mm胎体式定向钻进用PDC钻头,并进行了现场试验,共钻进1个主孔和4个分支孔,平均钻进时效为4.12 m/h,累计进尺达1 001.6 m。试验结果表明,该钻头造斜效果好,使用寿命长,完全能满足使用要求。     

提高金刚石钻头耐磨性和降低烧结温度的试验研究

目前，大多数金刚石钻头采用粉末冶金热压疗法烧结，热压法普遍存在烧结温度较高，对金刚石的原始强度产生不利的影响，也直接影响钻头的质量。同时，胎体配方还比较单一．钻头的耐磨性能不理想，在强研磨性岩层或破碎岩层中钻进寿命较低：这两方面的问题有待进一步研究解决。本文针对这两个问题，采用正交设计方法，在胎体材料中通过加入磷与硼元素，进行了有益的试验研究。结果表明：烧结温度有所下降，钻头的性能有了提高。     

用于钻进钢筋混凝土构件的金刚石钻头的研制

钢筋混凝土结构因内部有钢筋,且自身强度等级较高,在钻孔过程中施工难度大,钻进效率低,经常出现钻头断齿现象。针对这些现象,从调整钻头胎体性能、改进钻头结构和增加磨料种类3个方面进行试验。为提高金刚石钻头钻进效率,采用中软性能的钻头胎体,并添加立方氮化硼（CBN）磨料,提高钻头工作唇面上磨料的切削性能;为使钻头钻进平稳,采用斜水口和奇数齿结构钻头,防止钻齿在孔底与钢筋产生全断面接触,避免钻齿瞬时冲击载荷过大而发生断齿。试验结果表明:使用?75mm钻头,钻进压力6.5 MPa、钻头线速度2.1 m/s、冷却液流量25 L/min时,钻头的平均钻进时效可达到1.12m/h,钻头寿命28m,无断齿现象;表明本试验的钻头设计工艺正确,结构合理,可满足施工现场的生产需求。      

Study on dry friction and wear resistance of a WC-Co particle reinforced iron matrix composite material

In order to select a suitable material for the rolling mill guide application, the dry sliding friction and wear resistance of a tungsten carbide combining cobalt (WC-Co) particle reinforced chromium cast iron composite material were studied. In particular, the wear resistance was discussed in detail. The results showed that the composite material demonstrates 25 times the wear resistance of high Cr cast iron, and 9 times the wear resistance of heat resistant steel. However, the average friction factor in the stable friction stage showed a relationship of μComposites/45#steel>μHigh chromium cast iron/45#steel>μHeat resistant steel/45 # steel. The wear resistance mechanism of the composite material was associated with the reinforcing particles, which protruded from the worn surface to bear the friction load when the matrix material surface was worn, thereby reducing the abrasive and adhesive wear. In addition, the matrix material possessed suitable hardness and toughness, providing a support to the reinforcements.     

铸造碳化钨颗粒增强PDC钻头胎体的三体磨损行为

采用无压浸渗工艺制备了铸造碳化钨颗粒增强PDC钻头胎体材料,胎体材料组织均匀,胎体中碳化钨颗粒完整,碳化钨颗粒与铜合金基体形成均匀扩散层。重点研究了PDC钻头胎体的三体磨料磨损行为和磨损机理。结果表明:铸造碳化钨颗粒形貌是影响PDC钻头胎体三体磨料磨损行为的主要因素。相对于破碎铸造碳化钨,球形碳化钨内部微裂纹少且无应力集中,具有耐磨增效作用,可显著提高PDC钻头胎体材料的三体磨损性能。球形碳化钨颗粒增强PDC钻头胎体的相对耐磨性是破碎碳化钨颗粒增强PDC钻头胎体的10倍。破碎碳化钨颗粒增强PDC钻头胎体的磨损表面呈现大量铜合金基体犁沟,多角状碳化钨颗粒被磨损变圆滑;而球形碳化钨颗粒增强PDC钻头胎体的磨损表面碳化钨颗粒突出林立,少量碳化钨颗粒被折断或发生破裂。     

电镀金刚石钻头钻削碳纤维复合材料研究

碳纤维复合材料钻孔加工时极易产生分层、毛刺、撕裂等缺陷,是典型的难加工材料。针对碳纤维复合材料特点,以电镀金刚石钻头为研究对象,从钻削轴向力、钻孔出口质量等方面分析电镀金刚石钻头钻孔特点,并与硬质合金麻花钻进行对比,得出结论：电镀金刚石钻头钻削碳纤维复合材料时钻削轴向力较小,钻削质量较好,更适合于碳纤维复合材料的加工;钻头转速提高有利于减小钻孔缺陷的产生,钻削轴向力随钻头转速的升高而降低,随钻头直径的增大而增大;最后,通过多元线形回归方法得出电镀金刚石钻头钻削力经验公式。     

扭转冲击对PDC钻头钻进效果影响的仿真模拟分析

PDC钻头组合扭力冲击器在均质岩层钻进时,克服了PDC钻头不能用于硬岩层钻进的难点。为了分析扭转冲击对PDC钻头钻进效果的影响,采用ansys/ls-dyna软件对PDC钻头有扭转冲击及无扭转冲击钻进两种情况进行了仿真分析,得出了PDC钻头钻进时,钻头的运动及岩层的破坏图形。通过比较两种不同条件下的图形,发现有扭转冲击作用使PDC钻头平稳钻进,对破岩具有额外的贡献,并能减少井斜度。     

Investigation of wear resistance of drill bits with WC,Diamond-DLC,and TiAlSi coatings with respect to mechanical properties of rock

Drilling is an important engineering operation with extensive application in many fields of industry including mining engineering, oil and gas exploration and exploitation, civil engineering, groundwater management, etc. Drill bits must be able to endure enormous stresses that gradually wear them down during the drilling operation. In rock drilling, wear resistance is a key determinant of the drill bit lifetime and hence the drilling cost, thus basically affecting the choice of drilling method for any given rock type. With the advent of new wear-resistant materials, they can be used to improve the resistance of drill bits against wear and erosion. This study investigated the wear resistance of drill bits with tungsten carbide (WC) coating, DLC-Diamond coating, and titanium-silica‑aluminum (TiAlSi) coating when drilling in three types of hard rock, namely Khoshtinat Granite (A₁), White Natanz Granite (A₂) and Nehbandan Granite (A₃). The drilling tests were performed on cuboid specimens using a drilling machine at rotation speeds of 850, 900 and 950 rpm and penetration rates of 12, 18 and 24 mm/min. The results showed that for any fixed drilling conditions, the wear rates of the TiAlSi drill bit in A₁, A₂, and A₃ were respectively 48%, 52%, and 60% lower than those of the WC drill bit. In the same rocks, the Diamond-DLC drill bit also showed 42%, 44.25%, and 55% lower wear rates than the WC drill bit. in addition to the observed changes in wear rate of the drill bits, the surface roughness created by these drills represents the optimum performance of the TiAlSi drill bit. It was observed that, as the mechanical properties of the rock (uniaxial compressive strength, Mohs hardness, Schimazek's abrasivity index and Young's Modulus) increased, the tested drill bits showed wider differences in terms of wear resistance. As the TiAlSi drill bit had the lowest wear rate (27%) and after that, the Diamond-DLC drill bit showed a better wear (30%) performance than the WC drill bit (60%).     

钎焊金刚石套料钻钻削CFRP的孔质量研究

采用钎焊金刚石套料钻进行了钻削碳纤维增强树脂基复合材料(CFRP)试验,使用测力仪与三维视频显微镜对钻削过程中的钻削力以及孔出、入口缺陷进行了测试与观察.实验结果表明:钎焊金刚石套料钻钻削CFRP时,相同转速下,钻削力随进给量的增大而增大;相同进给量下,钻削力随转速的增大而增大,且进给量对钻削力的影响大于转速的影响;已...     

Effects of special drill bits on drilling-induced delamination of composite materials

Drilling is the most frequently employed operation of secondary machining for fiber-reinforced materials owing to the need for joining structures. Delamination is among the serious concerns during drilling. Practical experience proves the advantage of using such special drills as saw drill, candle stick drill, core drill and step drill. The experimental investigation described in this paper examines the theoretical predictions of critical thrust force at the onset of delamination, and compares the effects of these different drill bits. The results confirm the analytical findings and are consistent with the industrial experience. Ultrasonic scanning is used to evaluate the extent of drilling-induced delamination. The advantage of these special drills is illustrated mathematically as well as experimentally, that their thrust force is distributed toward the drill periphery instead of being concentrated at the center. The allowable feed rate without causing delamination is also increased. The analysis can be extended to examine the effects of other future innovative drill bits.     

超细WC-Co硬质合金及其磨损性能研究

采用低温化学镀方法在超细WC颗粒表面进行金属钴包覆,烧结包覆后的复合粉体制备新型硬质合金NYG（WC-3%Co）.研究了超细WC-Co硬质合金的力学性能、断口形貌和显微结构,在销盘式磨损试验机上进行干滑动磨损实验.结果表明,在硬质合金烧结过程中,沿WC晶界均匀分布的金属钴不仅起粘结剂作用,也起抑制剂作用阻碍晶粒的长大;新型硬质合金的抗弯强度、断裂韧性、硬度和耐磨性能均得到较大提高;在干滑动摩擦条件下,新型WC-Co硬质合金的失效以塑性变形及细小碳化钨相颗粒脱落为特征.     

Nanocrystalline CVD diamond coatings for drilling of WC-Co parts

Drilling of pre-sintered cemented carbide parts is a challenging task due to the high hardness and abrasive nature of the WC grains. This operation is commonly done using uncoated cemented carbide drill bits but the tool life is very limited requiring tool re-sharpening after a few holes. A solution for the improvement of the tool performance is here exploited by the use of nanocrystalline diamond (NCD) films as high abrasion resistant coatings. These coatings were grown in a hot filament chemical vapor deposition (HFCVD) reactor. Filament temperatures in the range of 1940-1980 °C were crucial to obtain highly adherent and very uniform coatings at the cutting edge and on the surfaces of the flutes. The performance of the coated tools was evaluated in through-hole drilling of a pre-sintered cemented carbide showing outstanding cutting efficiency when compared to that of an uncoated tool: maximal 940 mm/min infeed rates (app. 1 s to drill 17 mm) instead of 20 mm/min for the latter; absence of tool wear in contrast to a flank wear of about 50 μm in the uncoated tool after only 4 holes; hole edge integrity even at the highest infeed rates while grain decohesion at the hole edge takes place when using bare drill bits.     

The study on the chip formation and wear behavior for drilling forged steel S48CS1V with TiAlN-coated gun drill

The solid carbide gun drill was coated with TiAlN, and a comprehensive evaluation on the wear behavior and chip formation had been performed on it for machining forged steel S48CS1V at a cutting speed of 12.66 mm/s (4400 rpm) with a continuous Minimum Quantity Lubrication (MQL). Cutting torque had been measured versus with the quantity of the machined crankshaft. The cutting torque curves revealed the three wear stages that were the initial stage, the semi-steady stage and the disastrous stage. Gun drill with TiAlN coating suffered from adhesive wear on the wear pad and chemical diffusion wear on flank face. Additionally, sliding wear and chipping were the wear forms. The high temperature and stress played the important roles in the adhesive and chemical diffusion wears. The high alternative stress produced the plastic deformation and cold welding for the atomic absorption and thus it made the grains of carbide substrate tearing-off from deforming cobalt bond, therefore adhesive wear took place.