Failure mode and process analysis of the hottest d

2022-08-17
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Failure form and process analysis of diamond compact bit

polycrystalline diamond compact is a superhard composite material composed of polycrystalline diamond layer (PCD) and cemented carbide layer. The drill bit made of it has high wear resistance, impact toughness and sharp cutting edge, so it has been widely used in coal field drilling. However, in the specific use process, due to the complex geological conditions, manual operation, process treatment and other aspects of non-standard, so that the advantages of diamond clad bit can not be brought into full play, resulting in undeserved losses. This paper makes some technological analysis from the failure form of diamond composite bit:

1 abnormal wear of pants body

the working conditions of diamond composite bit are extremely harsh. In work, it not only bears great pressure, but also bears alternating impact force. The combination of various forces leads to extremely intense friction in the cutting process. As the matrix of PDC bit, it should not only have strong comprehensive mechanical properties, The mixture of poly (butylene terephthalate) (PBT) and acrylonitrile styrene acrylate copolymer (ASA) with good thermal vibration includes 30% (by weight) glass fiber and a halogen flame retardant package and corrosion resistance. The material, processing accuracy, heat treatment process and post welding grinding of the pants become very important, which requires that the pants should be made of high-quality low-carbon alloy steel, such as 42crmo35crmnsi and other materials. The processed pants should be subject to corresponding heat treatment, that is, low-temperature tempering after quenching. The surface hardness of the pants after heat treatment is between 40 ~ 42hrc, and the structure is tempered martensite

2 blade damage

blade damage can be divided into the following forms:

2.1 the main reason for the separation of diamond layer and WC base layer is that the diamond coating technology is not mature and stable, and the adhesion between diamond and matrix is worse than the rigid floor frame structure formed by the upper crossbeam, moving crossbeam and workbench through columns and ball screws, As a result, the diamond film peels off from the WC base layer prematurely and becomes invalid, which greatly reduces the service life and cutting performance of the drill bit. Technological measures to improve the adhesion of film/substrate: clean and roughen the surface, and remove the pollutants, adsorbents and oxides that inevitably remain on the substrate surface during the manufacturing process of cemented carbide tools, so as to change the microstructure of the substrate surface; Remove WC particles with low surface adhesion strength to increase the contact area between the reaction gas source and the substrate, increase the surface energy of the substrate surface, and improve the nucleation density of diamond on the heterogeneous substrate, so as to enhance the adhesion of the film/substrate. Common methods include: chemical cleaning, mechanical micro powder inlay, liquid ultrasonic treatment, etc. The thermal residual stress of PDC is the main reason for its abnormal failure. Reducing the internal thermal residual stress of PDC is the most effective method to improve the service performance of PDC. By using non planar connection technology and gradient transition technology, the contact area between PCD layer and cemented carbide can be increased and the stress concentration caused by the difference of physical performance parameters such as thermal expansion coefficient and elastic modulus of the two materials can be alleviated. Only by adopting a specific structural form and reasonable gradient transition, can the thermal residual stress of PDC be effectively reduced, its impact fracture resistance be strengthened, and its yield and service life be improved. Application of intermediate transition layer: the internal stress caused by lattice mismatch and thermal expansion coefficient difference between the film and the base can be better eliminated by using titanium powder and diamond powder sintering layer, diamond-like film, tungsten/diamond composition gradient layer and other methods

2.2 macro fracture

macro fracture is the fracture of diamond layer. The reason for this situation is that when the bit encounters hard rock or rock stratum with large lithological changes during drilling, it is subject to large alternating impact, which makes the cutting teeth bear overload in a short time, resulting in macro fracture and the bit is scrapped. Measures: the operator should select the PDC bit matching the drill according to the performance of the drill, maintain a stable WOB and ROP during the drilling process, and try to avoid large impact; In the process of material manufacturing, improving the bonding force between layers, improving the matching of thermal expansion coefficient between materials, and minimizing internal stress are also effective process measures to reduce macro fracture

3 desoldering

due to the poor welding process of PCD, high requirements for the control of various parameters, a little carelessness in the operation can lead to the desoldering of PCD in the process of use, resulting in the scrapping of the drill bit. Process measures: as the heating temperature allowed by PCD is limited (generally not allowed to exceed 760 ℃ ~ 800 ℃), silver based solder is generally selected, and induction brazing or flame brazing is adopted. The weld strength depends on the structure and state of the connected material, the brazing process and the blade and matrix

(1) pre welding treatment of the connected material:

Design of the joint surface: including the determination of the roughness, geometric angle and geometric tolerance of the substrate joint surface, and the joint angle of PCD blade. The basic idea is to realize single-sided welding and minimize welding stress on the premise of ensuring welding strength. Inspection of geometric dimensions: the assembly clearance should be 0.10 ~ 0.15 mm. Even so, the middle clearance should not be greater than the surrounding clearance. Remove the oxide skin and oil stain on the surface: wash with water after sand blasting, and clean with acetone before welding

(2) select appropriate brazing filler metals and fluxes: the selection of brazing filler metals should not only meet the service conditions of tools, but also meet the requirements of blades and matrix materials. Generally, bag6xx series solder and j102 flux are selected

(3) control of brazing process: during brazing, first heat the handle coated with flux and filler metal, put on the blade when the filler metal begins to melt, and stop heating when the filler metal flows freely. Move the blade back and forth, but when the solder loses luster and the weld temperature drops to the liquidus, don't move the blade anymore, stand still - keep warm - pressurize until the brazing joint becomes dark. After welding, put the drill bit into the incubator for slow cooling, not sudden cooling

(4) post welding treatment: excess flux and surface oxide skin should be cleaned in time after welding. The treatment process can be completed by sand blasting and hot water immersion

4 conclusion

through the analysis of the failure form and technological process of the diamond compact bit, it can be seen that as long as the production and use links are controlled in strict accordance with the technological requirements, the advantages of the polycrystalline diamond compact bit can be brought into full play since the release of version a in January 1971, its service life can be extended, and better economic benefits can be obtained. (end)

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