Down-the-hole drill bit applied to open pit coal mining and manufacturing method of down-the-hole drill bit

Abstract

The invention discloses a down-the-hole drill bit applied to open pit coal mining and a manufacturing method of the down-the-hole drill bit, and relates to the technical field of mining mechanical drilling equipment, in particular to the down-the-hole drill bit applied to open pit coal mining and the manufacturing method of the down-the-hole drill bit applied to open pit coal mining. The front end of the base body guiding cylindrical section is provided with a base body large end, the end face of the base body large end is embedded with alloy column teeth, and the rear end is provided with a base body tail end. The manufacturing method comprises the following steps: heating round steel, forging, normalizing and tempering to obtain a drill billet; normalizing and annealing after rough machining to refine grains; machining to form a step shaft-shaped drill bit base body; carrying out vacuum quenching and tempering treatment; the tail end of the base body and the guide cylindrical section are subjected to finish machining to ensure high form and position precision; after the tooth holes are drilled, alloy column teeth are embedded through induction heating. By optimizing the structural design and the heat treatment process, the wear resistance and stability of the drill bit are improved, the service life of the drill bit is prolonged, and the drill bit is suitable for open-pit coal mine mining conditions.

Description

Technical Field

[0001] This invention relates to the field of drilling equipment technology in mining machinery, specifically to a down-the-hole drill bit for open-pit coal mining and its manufacturing method. Background Technology

[0002] Down-the-hole (DHH) drill bits are crucial tools in open-pit coal mining, and their performance directly impacts construction efficiency and cost. During the stripping of surface rock in open-pit coal mines, DHH rigs are typically used for drilling. Unlike hard mineral strata, coal-bearing rock formations generally have relatively low hardness but heterogeneous structure. This geological characteristic presents compatibility issues for DHH drill bits traditionally designed for high-hardness rock formations.

[0003] Conventional down-the-hole drill bits, designed to handle hard rock formations, typically require extremely high hardness and wear resistance. However, when used in softer coal mine formations, their excessive hardness can lead to insufficient toughness. Under sustained impact loads and complex stresses, the drill bit matrix is ​​prone to fracture due to its inability to effectively absorb and disperse energy. Simultaneously, the drill bit edges are highly susceptible to chipping failure due to the mismatch in toughness between the matrix material and the drill bit's surface under stress. Furthermore, traditional alloy tooth fixing processes (such as interference-fitting or conventional heat-insertion) are prone to slight movement or loosening of the alloy teeth under high-frequency impact conditions in soft rock formations due to insufficient consolidation strength. This not only exacerbates wear on the tooth holes but also contributes to edge chipping.

[0004] These frequent abnormal failures, such as matrix fractures and edge chipping, not only significantly shorten the service life of the drill bit and increase tool consumption costs, but also seriously affect the overall construction progress due to the need for frequent shutdowns to replace the drill bit. Summary of the Invention

[0005] The purpose of this invention is to provide a down-the-hole drill bit for open-pit coal mining and its manufacturing method. By optimizing the drill bit matrix structure design and key processes such as heat treatment, precision machining and induction heating inlay of alloy column teeth, the overall mechanical properties, wear resistance and service life of the drill bit are effectively improved, ensuring that it has higher drilling accuracy, stability and operation efficiency in complex and harsh open-pit coal mine rock formations.

[0006] To achieve the above objectives, this invention provides the following technical solution: a down-the-hole drill bit for open-pit coal mining and its manufacturing method. The guide cylindrical section of the base body is located at the front end of the drill bit, and its primary function is to guide and stabilize the borehole during drilling. When the drill bit drills into the rock, this cylindrical section fits tightly against the drilled hole wall, effectively preventing radial swaying or deviation caused by uneven force on the drill bit, thus ensuring the straightness and roundness of the borehole, which is particularly important for deep-hole drilling. The large end of the base body directly bears the impact and crushing functions. Its end face is designed with sufficient area and a reasonable geometry to scientifically arrange multiple alloy cylindrical teeth. This design allows impact energy to be evenly transmitted to each cylindrical tooth and act on the rock strata, avoiding excessive stress concentration. The tail end of the base body is the key interface connecting the drill bit and the drill rod of the down-the-hole impactor. Its structural strength and dimensional accuracy directly affect whether impact energy can be efficiently and without damage transmitted from the drill rod to the drill bit body. The organic combination of these three parts constitutes a stable structure that can efficiently crush rock and ensure borehole quality.

[0007] Furthermore, round steel bars of specific materials and specifications are selected and heated to the austenitizing temperature using a medium-frequency induction furnace or other heating equipment to impart good plasticity and fluidity. Subsequently, they are forged on an air hammer or hydraulic press. The purpose of this process is not merely shaping, but more importantly, to break down any potential defects such as porosity and voids within the cast steel billet through immense pressure, and to break down coarse dendrites and columnar crystals into fine equiaxed grains. Simultaneously, microcracks are closed, significantly improving the material's density and mechanical properties. Immediately after forging, normalizing is performed, using air cooling to transform the austenite into finer pearlite and ferrite structures, eliminating the non-equilibrium structure and internal stresses formed during forging. This is followed by stress-relief tempering, where the steel is held at a temperature below the critical temperature and then slowly cooled to further eliminate residual stress, stabilize the microstructure, and provide a high-quality steel billet with dimensional stability and extremely low internal stress for subsequent machining.

[0008] Further, the forged and preliminarily heat-treated steel billet undergoes rough machining to remove surface oxide scale, decarburized layer, and forging defects, obtaining a billet close to its final shape while leaving sufficient finishing allowance. However, the cutting forces during rough machining introduce new machining stresses. Therefore, normalizing is necessary again. The main function of normalizing here is to refine grains that may have grown due to the heat effect of rough machining, homogenizing the microstructure and preparing an ideal initial microstructure for the final heat treatment. The subsequent annealing process involves heating the workpiece to full austenitization and then cooling it in the furnace at a very slow rate. This process spheroidizes the lamellar cementite in the pearlite microstructure, transforming it into a spherical pearlite microstructure with lower hardness and better plasticity. This microstructure not only significantly reduces hardness, facilitating subsequent machining, but more importantly, its internal structure is stable, and internal stress is fully eliminated, ensuring the long-term dimensional stability of the rough-machined billet during storage and subsequent processing.

[0009] Furthermore, the machining process must strictly adhere to the dimensional tolerances in the drawings, forming the base guide cylindrical section, the base large end, and the base tail end. The outer circular surface of the base guide cylindrical section needs to ensure high dimensional accuracy and surface finish to fulfill its guiding function. The end face shape and angle of the base large end need to be precisely machined, as subsequent tooth holes will be located here, and its geometric accuracy directly affects the arrangement angle of the alloy column teeth and the rock-breaking efficiency. The machining of the threaded or splined connection structures at the base tail end is particularly critical, ensuring the connection accuracy and strength with the impactor drill rod; any deviation may lead to loosening of the connection, energy transfer loss, or even premature thread failure. This stage of machining is a key forming step in realizing the product design functions.

[0010] Furthermore, the machined drill bit substrate is placed in a vacuum heat treatment furnace and heated in a high-vacuum environment. This completely prevents oxidation and decarburization of the workpiece surface at high temperatures, maintaining a smooth surface and stable composition. After heating to the predetermined austenitizing temperature and holding it at that temperature for a sufficient period, vacuum quenching is performed. Inert gases such as high-purity nitrogen are introduced for rapid cooling, transforming austenite into high-hardness martensite. Immediately afterwards, vacuum tempering is performed. By adjusting the tempering temperature and time, the quenched martensite is transformed into tempered martensite or troostite, significantly improving toughness while maintaining high hardness, eliminating quenching stress, and stabilizing the microstructure and dimensions. This entire vacuum heat treatment process ensures that the drill bit substrate obtains a uniform and deep hardened layer, while the core maintains good toughness, thus possessing excellent resistance to impact fatigue.

[0011] Furthermore, after the drill bit body undergoes final heat treatment to achieve high hardness, its tail end and guide cylindrical section require precision machining to meet the final dimensions and geometric tolerances required by the drawings. The connecting threads or splines at the tail end of the body need to be ground to precise dimensions to ensure a tight and smooth fit with the drill pipe, avoiding stress concentration due to improper fit. The outer cylindrical surface of the guide cylindrical section needs precision grinding to ensure its cylindricity, straightness, and surface roughness. Crucially, precision machining must ensure extremely high coaxiality between the axis of the guide cylindrical section and the connecting reference axis at the tail end of the body. This geometric accuracy is one of the decisive factors in ensuring that the drill bit does not wobble or vibrate during operation, thereby extending drill bit life and improving drilling quality. Precision machining is the final perfection of key mating surfaces and functional surfaces.

[0012] Furthermore, after the critical structural dimensions of the drill bit base are machined, high-precision CNC drilling machines or machining centers are used to drill holes for embedding alloy post teeth on the end face of the large end of the base, which bears the impact load, according to the pre-designed tooth layout. The machining accuracy requirements for these holes are extremely high, including hole position, depth, diameter, and most critically, the shape and inclination angle of the hole bottom. The hole diameter must form a precise interference fit with the shank diameter of the alloy post tooth. The inclination angle of the hole directly determines the working rake angle of the post tooth, affecting rock-breaking efficiency and shear resistance. The shape of the hole bottom must match the shape of the post tooth bottom to ensure uniform stress distribution during embedding. The machining quality of each hole directly affects the firmness of the embedded alloy post tooth and its stress state during operation, and is a prerequisite for preventing tooth loss or breakage.

[0013] Furthermore, before inserting the alloy cylindrical teeth, the large end of the drill bit base needs to be locally heated. Induction heating is the preferred method. Its principle is to use high-frequency alternating current to generate an alternating magnetic field through an induction coil, inducing eddy currents inside the metal workpiece to achieve heating. The advantages of this method are rapid heating, high thermal efficiency, and highly concentrated heat in the area where the teeth need to be inserted, minimizing the thermal impact on other parts of the drill bit and avoiding potential degradation and deformation of heat treatment performance caused by overall heating. By precisely controlling the power, frequency, and heating time of the induction heating equipment, the tooth hole area at the large end of the base can be uniformly heated to the preset insertion temperature, causing the diameter of the tooth hole to slightly increase due to thermal expansion, preparing for the smooth insertion of the alloy cylindrical teeth and the formation of an interference fit.

[0014] Furthermore, once the large end of the drill bit reaches the predetermined temperature through induction heating, the operator uses specialized tools to quickly and accurately press the pre-prepared carbide shanks, according to specifications and quality requirements, into the expanded tooth holes one by one. The carbide shanks are typically made of tungsten-cobalt-based carbide, possessing extremely high hardness and wear resistance. During the insertion process, it is crucial to ensure accurate positioning of the shanks, with their top working contours conforming to the designed tooth layout curve. As the drill bit base cools naturally or in a controlled manner in the air, the base steel contracts, generating a significant clamping force on the cylindrical shank of the carbide shanks, forming a robust interference fit. This hot-setting process ensures that the carbide shanks will not loosen or fall off when subjected to strong impacts and abrasive wear. After insertion, a complete down-the-hole drill bit with highly efficient rock-breaking capabilities is assembled.

[0015] Furthermore, the superior performance of the drill bit relies on two aspects of precision manufacturing: first, structural precision, which ensures extremely high dimensional and positional accuracy of the guide cylindrical section and the tail end of the base body through precision machining. This is the structural foundation for ensuring smooth operation, straight boreholes, and efficient energy transfer. Second, connection reliability, where the alloy spur teeth on the large end of the base body must be inlaid and fixed using advanced induction heating. Induction heating ensures process controllability and localization, avoiding the effects of overall heat treatment, while the resulting interference fit provides the necessary connection strength to resist impact under extreme working conditions. The combination of these two aspects constitutes the fundamental guarantee for the long service life and high efficiency of this down-the-hole drill bit in the harsh drilling operations of open-pit coal mines.

[0016] This invention provides a down-the-hole drill bit for open-pit coal mining and its manufacturing method, which has the following beneficial effects: 1. Steel billets are obtained through heated round steel forging, normalizing, and stress-relief tempering. The rough-machined parts then undergo secondary normalizing and annealing. The core purpose of this series of heat treatment processes is to fully refine the metal grains within the drill bit's matrix. Grain refinement is a key means of improving the toughness and strength of metallic materials, effectively preventing the initiation and propagation of microcracks. Subsequent vacuum quenching and vacuum tempering further optimize the metallographic structure of the matrix, achieving a more balanced strength and toughness profile that matches the lower hardness of open-pit coal mine strata. This internal-to-external performance optimization fundamentally reduces the risk of matrix fracture in the drill bit under impact loads, thereby significantly extending its overall service life.

[0017] This technical solution places particular emphasis on precision machining of the tail end and the cylindrical guide section in the middle of the heat-treated drill bit body to ensure high dimensional and positional accuracy between them. This measure directly addresses the potential for drill bit misalignment during use. The high-precision guide section acts like a guide rail, providing stable guidance for the drill bit during drilling, effectively suppressing abnormal oscillation and deviation, thereby ensuring the perpendicularity of the borehole and the smoothness of the hole wall. This not only reduces scrap or repair work caused by drilling deviations but also makes the drilling process smoother, directly improving the efficiency and quality stability of drilling operations.

[0018] In the tooth-fixing process, an innovative induction heating method is used to locally heat the large end of the drill bit base, after which the alloy column teeth are inserted into the pre-made tooth holes. Induction heating has the advantages of rapid heating speed and controllable heat-affected zone, enabling the area around the tooth hole in the base metal to quickly reach the optimal heat-fitting temperature and generate appropriate thermal expansion. During the cooling process, the contraction of the base metal creates a strong and uniform clamping force on the alloy teeth. This interference fit method makes the alloy teeth extremely secure, greatly suppressing any slight loosening or displacement that may occur under repeated and severe impacts, fundamentally reducing the risk of alloy teeth falling off or chipping at the edge of the large end due to weak tooth fixing.

[0019] This manufacturing method is not simply machining; rather, it employs a complete and rigorous process combining heat treatment and machining. From the pre-heat treatment of the forging billet to the secondary heat treatment after rough machining to stabilize the microstructure, and finally to the vacuum heat treatment for shaping, each step aims to eliminate internal stresses generated in the previous process and optimize the microstructure. This multi-stage, multi-process approach ensures that every drill bit body leaving the factory has uniform and stable internal properties, avoiding early failures of individual products due to fluctuations in material properties. This guarantees the reliability and consistency of product quality in mass production, providing reliable tool support for large-scale construction.

[0020] This invention addresses the specific contradiction in open-pit coal mining: the rock strata have relatively low hardness, yet drill bits are prone to brittle fracture and fragmentation. Conventional drill bits, designed to handle hard rock strata, often sacrifice toughness for excessive hardness, resulting in failure in soft coal rock due to insufficient toughness. This solution, through targeted design of materials and processes, successfully produces a drill bit with "balanced toughness," whose strength-to-toughness ratio is highly compatible with the physical properties of coal rock strata. This tailored design effectively solves the pain points in this specific application scenario, reducing not only the frequency and cost of drill bit replacements but also ensuring continuous and efficient operation, bringing significant time and economic benefits to the entire open-pit coal mine stripping and blasting project. Attached Figure Description

[0021] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the structure of the large end of the substrate and the large end of the substrate of the present invention. Detailed Implementation

[0023] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses consistent with some aspects of this disclosure as detailed in the appended claims.

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] Example 1: An Example Based on Drill Bit Matrix Structure Design This embodiment focuses on the specific details of the down-the-hole drill bit base structure described in claim 1. The drill bit base 1, as the core skeleton of the entire drill bit, directly affects the stability, guidance, and service life of the drilling process. In this embodiment, the drill bit base 1 is integrally forged from high-strength alloy steel to ensure its ability to withstand impact loads and torsional moments.

[0026] The guide cylindrical section 2 is a crucial part of the front end of the drill bit body 1. Its diameter is precisely calculated and slightly smaller than the borehole diameter. Its core function is to immediately contact the borehole wall after the drill bit cuts into the rock strata, stabilizing the drill bit and preventing deviation. The length of the guide cylindrical section 2 is optimized; if it is too short, the guiding effect will be poor, and if it is too long, the frictional resistance with the borehole wall will increase. Its outer cylindrical surface needs to be finely ground to have a low surface roughness, in order to reduce friction and wear during drilling.

[0027] The large end 3 of the base body is the part with the largest diameter at the front end of the drill bit base 1, and it is connected to the guide cylindrical section 2 of the base body through a smooth conical transition. The end face of the large end 3 is the main rock-breaking working face, and it is designed with a reasonable curved surface shape to facilitate the discharge of rock powder. Multiple alloy cylindrical teeth 4 are embedded and fixed on the end face of the large end 3 of the base body in an optimal tooth arrangement (such as equiangular spiral arrangement, concentric circle arrangement, or a combination thereof). These alloy cylindrical teeth 4 are made of hard alloy material and are the actuators for directly impacting and breaking coal and rock. Their exposed height and tilt angle (pitch angle or back tilt angle) have been optimized through dynamic simulation to achieve high rock-breaking efficiency and good impact toughness.

[0028] The base tail end 5 is located at the rear end of the drill bit base 1, and its structure is designed for reliable connection with the chuck or extension rod of the down-the-hole impactor. Typically, the base tail end 5 is designed with external threads or internal splines to ensure that impact energy and torque are efficiently transmitted to the drill bit. The coaxiality between the base tail end 5 and the base guide cylindrical section 2 is crucial; any deviation can cause severe vibration of the drill bit during drilling, accelerating drill wear and even breakage.

[0029] In summary, this embodiment, through the coordinated design of the base guide cylindrical section 2, the base large end 3, and the base tail end 5, constitutes a stepped shaft-shaped drill bit base 1 with good rigidity, stable guidance, and reliable connection, providing a solid foundation for the efficient rock breaking of the alloy column teeth 4.

[0030] Example 2: An Example Based on Forging Billet Preparation and Initial Heat Treatment This embodiment describes in detail the preparation method of the drill bit substrate 1 blank according to claims 2 and 3. The initial properties of the drill bit substrate 1 largely depend on the forging quality of its steel billet and the initial heat treatment process.

[0031] First, high-quality round steel with a specific chemical composition is selected as the raw material. Its carbon content and alloying elements (such as chromium, molybdenum, and vanadium) must meet the requirements for high strength and high toughness. The round steel is placed in a heating furnace and uniformly heated to the austenitizing temperature (e.g., 1100℃ - 1200℃) to completely transform its microstructure into austenite and fully dissolve the alloying elements. Subsequently, the round steel heated to the predetermined temperature is placed on a forging press for forging. The purpose of this forging process is not only to obtain a preliminary shape close to the contour of the drill bit matrix 1, but more importantly, to break up the coarse dendrites and carbides in the as-cast microstructure through intense plastic deformation, weld internal defects such as porosity and shrinkage, and form dense fibrous flow lines, significantly improving the material's density, strength, and toughness.

[0032] After forging, to eliminate internal stress caused by uneven cooling and microstructure transformation during forging, and to refine the coarse austenite grains resulting from high-temperature forging, the forging must be normalized immediately. The normalizing process involves reheating the forging to 30-50°C above Ac3, holding it at that temperature for a period, and then cooling it in still air. Through recrystallization, a finer and more uniform pearlite and ferrite microstructure is obtained. However, the relatively rapid cooling rate after normalizing leaves some residual stress; therefore, stress-relief tempering must be performed immediately after normalizing. Stress-relief tempering is typically carried out below Ac1 (e.g., 550°C - 650°C). Holding at this temperature enhances atomic diffusion, effectively reducing and homogenizing residual stress within the forging and stabilizing the microstructure.

[0033] After the forging, normalizing, and stress-relief tempering processes described above, a drill bit billet with a preliminary refined internal structure and relieved stress is obtained. However, the microstructure is still not stable enough, and the mechanical properties are not optimal. Therefore, after the subsequent rough machining (turning the outer diameter, end faces, etc., to remove oxide scale and most of the machining allowance), the rough-machined part is subjected to another normalizing and annealing heat treatment. The purpose of this normalizing is to further refine the local microstructure changes that may be caused by rough machining and to make the microstructure more uniform. The subsequent annealing (usually full annealing) involves slowly heating the workpiece to above Ac3, holding it at that temperature for a long time, and then cooling it in the furnace to obtain a near-equilibrium state with finer pearlite and ferrite grains, minimizing hardness and improving plasticity, preparing for subsequent machining, and ultimately obtaining a rough-turned billet with stable microstructure and good machinability.

[0034] Example 3: An Example Based on Matrix Forming and Final Heat Treatment This embodiment describes in detail the precision forming of the drill bit substrate 1 and its final heat treatment strengthening process based on claims 4 and 5.

[0035] After obtaining a rough blank with stable microstructure and properties, the process proceeds to the precision machining stage. Using CNC lathes and other equipment, the rough blank is machined to precisely form the stepped shaft structure described in claim 1. Specifically, the front guide cylindrical section 2, the connected and larger diameter large end section 3, and the rear end section 5 are machined. The transition fillets between each step must be smooth and free of sharp corners to avoid stress concentration. This stage of machining must ensure the dimensional tolerances and preliminary shape and position tolerances of each cylindrical surface, laying the foundation for final heat treatment deformation control and subsequent finishing.

[0036] The mechanical properties (hardness, strength, and toughness) of the machined drill bit substrate 1 do not yet meet the requirements of high-intensity rock drilling in open-pit coal mines. Therefore, final quenching and tempering treatment (tempering) is necessary to obtain excellent comprehensive mechanical properties. This embodiment employs an advanced vacuum heat treatment process. The drill bit substrate 1 is placed in a vacuum furnace and heated to the quenching temperature (e.g., 850℃-950℃, the specific temperature depending on the steel grade) under a high vacuum environment. The vacuum environment effectively prevents oxidation and decarburization of the workpiece at high temperatures, maintaining surface finish and dimensional accuracy. After sufficient holding time, high-purity nitrogen or argon gas is introduced into the furnace for rapid cooling (gas quenching). Vacuum quenching yields a high-hardness, high-strength martensitic structure.

[0037] However, the martensite structure after quenching is brittle, has high internal stress, and is dimensionally unstable, making it unsuitable for direct use. Therefore, vacuum tempering must be performed immediately after quenching. The workpiece is reheated to a temperature below Ac1 (e.g., 500℃-600℃), held for a sufficient time, and then cooled in the furnace or by gas purging. During tempering, the unstable martensite decomposes into tempered sorbite or tempered troostite, greatly eliminating internal stress. While maintaining high strength and hardness, toughness and plasticity are significantly improved, resulting in comprehensive mechanical properties with a good balance of strength and toughness. Thus, the heat treatment strengthening process of the drill bit matrix 1 is complete, its internal structure is stable, and it possesses the high wear resistance, high fatigue strength, and sufficient impact toughness required to withstand the harsh working conditions of down-the-hole drilling in open-pit coal mines.

[0038] Example 4: An Example Based on Geometric Accuracy Assurance and Tooth Hole Machining This embodiment, based on claims 6 and 7, focuses on how to ensure the critical dimensional accuracy of the drill bit body 1 and the preparation of the tooth holes for the inlay of the alloy column teeth 4.

[0039] After final heat treatment (quenching and tempering), the drill bit base 1 has achieved the required hardness and strength. However, minor heat treatment deformation is unavoidable, and the surface exhibits oxidation (very slight oxidation during vacuum heat treatment) and dimensional allowances. Therefore, precision machining of critical areas is necessary. The focus of precision machining is on the tail end 5 of the base and the guide cylindrical section 2 of the base. The connecting threads or splines at the tail end 5 of the base need to be ground using a precision thread grinder or spline grinder to ensure the accuracy of the connection dimensions and the integrity of the thread profile. This is crucial for ensuring a reliable connection with the impactor and for energy transmission.

[0040] Simultaneously, the outer cylindrical surface of the base guide cylindrical section 2 needs to be precision ground on an external cylindrical grinding machine. The objectives of this process are: first, to achieve precise diameter tolerances to ensure a reasonable clearance with the hole wall; second, to obtain extremely low surface roughness and reduce friction; and third, and most importantly, to ensure extremely high coaxiality between the outer cylindrical surface of the base guide cylindrical section 2 and the connection datum (such as the mean diameter of the thread or the axis of the spline) of the base tail end 5. Typically, the coaxiality error is required to be controlled within a very small range (e.g., 0.02mm - 0.05mm). High dimensional and positional accuracy is the core guarantee for ensuring the straightness of the drill bit's drilling, reducing uneven wear and vibration, and extending the life of the drill bit.

[0041] After completing the aforementioned finishing processes, the machining of tooth holes for inlaying the alloy column teeth 4 begins on the end face of the large end 3 of the base body. Machining these tooth holes is another crucial step in drill bit manufacturing. First, based on a pre-designed tooth layout diagram, the position of each tooth hole needs to be precisely located on the end face of the large end 3 of the base body using a CNC machining center or a dedicated drill jig. Then, using a carbide drill bit or reamer at a specific angle, with high rotational speed and feed control, each tooth hole is drilled (or reamed). The diameter, depth, and bottom shape of the tooth holes (usually flat or slightly tapered) have strict requirements and must precisely match the dimensions of the alloy column teeth 4. The axial direction of the tooth holes (i.e., the installation angle of the alloy column teeth 4) also needs to be precisely ensured, as this directly affects the rock-breaking angle and stress state. The inner walls of the machined tooth holes should be smooth and clean, free of burrs and cracks, preparing for subsequent interference fit inlay.

[0042] Example 5: Example of fixed connection based on alloy column teeth This embodiment, based on claims 8 and 9, describes in detail the key process of reliably fixing the alloy column teeth 4 to the drill bit base 1.

[0043] The bonding strength between the alloy protruding teeth 4 and the drill bit body 1 directly determines the service life of the drill bit. This embodiment adopts an interference fit process with induction heating. First, the pre-prepared alloy protruding teeth 4 need to be prepared. These alloy protruding teeth 4 are hard alloys made of tungsten carbide particles and cobalt-based binder phase through powder metallurgy. They have extremely high hardness and wear resistance, but their impact toughness is relatively poor compared to steel substrates.

[0044] Before embedding, the large end 3 of the drill bit base 1 is locally heated. Induction heating is used, with a high-frequency or medium-frequency induction coil aligned with the area of ​​the large end 3. When alternating current passes through the coil, an alternating magnetic field is generated, causing eddy currents to form inside the metal of the large end 3, resulting in rapid heating. Induction heating has advantages such as fast heating speed, high thermal efficiency, and heat concentration on the surface. By precisely controlling the heating power and time, the large end 3 is heated to a predetermined temperature range. This temperature must be strictly controlled; if the temperature is too low, the base expansion will be insufficient, making it difficult to press in the alloy protruding teeth 4; if the temperature is too high, it may lead to degradation of the mechanical properties of the base metal or generate excessive thermal stress.

[0045] After the large end 3 of the base body is heated to the predetermined temperature, the diameter of the tooth hole on it slightly increases due to thermal expansion. At this time, the alloy cylindrical tooth 4, which is at room temperature, is immediately aligned with the tooth hole using a special fixture, and is pressed smoothly and quickly into the bottom of the tooth hole under the action of a press. Due to the temperature difference, "hot fitting" is achieved. After the drill bit base 1 cools naturally to room temperature, the large end 3 of the base body contracts, thereby generating a huge clamping force on the alloy cylindrical tooth 4, forming a strong interference fit. This fixing method can effectively transfer the impact load from the steel base body to the alloy cylindrical tooth, while avoiding the weld fatigue that may exist in brazing and the influence of high temperature on the alloy properties.

[0046] After all the alloy protruding teeth 4 are inlaid, the final assembly of the down-the-hole drill bit is completed. If necessary, the exposed tips of the alloy protruding teeth 4 can be ground to ensure their height is consistent. The down-the-hole drill bit produced in this way has high dimensional and positional accuracy in its base guide cylindrical section 2 and base tail end 5. The alloy protruding teeth 4 on the base big end 3 are firmly fixed by induction heating, making it particularly suitable for efficient and long-life rock drilling operations in open-pit coal mines.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A down-the-hole drill bit for open-pit coal mining and its manufacturing method, comprising a drill bit substrate (1), characterized in that: The drill bit base (1) has a base guide cylindrical section (2) at its front end, a base big end (3) at its front end, an alloy column tooth (4) on the end face of the base big end (3), and a base tail end (5) at its rear end.

2. The down-the-hole drill bit for open-pit coal mining and its manufacturing method according to claim 1, characterized in that: The method for manufacturing the drill bit substrate (1) includes heating round steel for forging, and then normalizing and stress-relieving tempering the forged round steel to obtain a drill bit billet.

3. The down-the-hole drill bit for open-pit coal mining and its manufacturing method according to claim 2, characterized in that: The drill bit steel billet is rough machined, and then the rough machined part is subjected to normalizing and annealing heat treatment to refine the internal grains, thereby obtaining a rough blank with stable microstructure and properties.

4. The down-the-hole drill bit for open-pit coal mining and its manufacturing method according to claim 3, characterized in that: The rough blank is machined to form the drill bit base (1) in the shape of a stepped shaft. The drill bit base (1) includes a base guide cylindrical section (2), a base big end (3) and a base tail end (5).

5. A down-the-hole drill bit for open-pit coal mining and its manufacturing method according to claim 4, characterized in that: The drill bit substrate (1) is heated, and then vacuum quenched and vacuum tempered to complete the heat treatment process of the drill bit substrate (1).

6. The down-the-hole drill bit for open-pit coal mining and its manufacturing method according to claim 5, characterized in that: The tail end (5) and guide cylindrical section (2) of the heat-treated drill bit base (1) are precision machined to achieve high form and position accuracy between the guide cylindrical section (2) and the tail end (5).

7. A down-the-hole drill bit for open-pit coal mining and its manufacturing method according to claim 6, characterized in that: Drill tooth holes on the large end (3) of the finished drill bit body (1) for mounting alloy column teeth (4).

8. A down-the-hole drill bit for open-pit coal mining and its manufacturing method according to claim 7, characterized in that: The large end (3) of the substrate is heated by induction heating in preparation for the inlay of the alloy column teeth (4).

9. A down-the-hole drill bit for open-pit coal mining and its manufacturing method according to claim 8, characterized in that: After heating the large end (3) of the base, the pre-prepared alloy column teeth (4) are inserted into the tooth holes to complete the assembly of the drill bit.

10. A down-the-hole drill bit for open-pit coal mining and its manufacturing method according to claim 1, characterized in that: The guide cylindrical section (2) and tail end (5) of the drill bit base (1) are precision machined to ensure dimensional accuracy, and the alloy column teeth (4) on the large end (3) of the base are fixed by induction heating.

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