| The corrosion resistance of Ni-Cr alloy casing and its processing technology is an important strategic factor involving national energy security.However,due to its high alloy content,the cutting tool force process encounters certain complex conditions.These conditions include lubricating the surface,reduced grinding and poor heat transfer.In addition,the work hardening phenomenon is serious being particularly vulnerable to “stick to the tool” and built-up edges to cause short tool life and unstable process quality.This cutting technology has become a bottleneck constraining the development,production and application of Ni-Cr tool tubing and casing.A thorough study of Ni-Cr alloy corrosion during oil casing machining revealed four key factors in the preparation of related technologies involved with dedicated thread cutting of the alloy casings.These factors are: matrix material,surface coating,cutting edge microstructure and macroscopic geometric structure.A special tool was prepared,promoted and put into into practice.First,because of the difficult processing characteristics and cemented carbide matrix design principle of Ni-Cr alloy corrosion oil casing,apart from grain refinement,the addition of different forms of solid solution can improve red hardness,strength and grain refinement etc of cemented carbide.The research results show that the four element solid solution powder(W,Ti,Ta,Nb)was added to improve the physical and mechanical properties of WC-7%Co cemented carbide.The cemented carbide produced a solid solution strengthening effect with the average WC grain size of about 0.9 ? m;the flexural strength,hardness and fracture toughness reached2289.9MPa,92.3HRA,9.67MPa·m1/2 respectively;and high temperature hardness reached HV1482.1MPa(600 ?).This series of performances showed that four element duplex alloy has high hot hardness,with the ability to maintain high hardness when cutting Ni-Cr super alloy difficult materials.Second,combined with the difficult processing characteristics of Ni-Cr alloy corrosion oil casing there are problems including sticky debris and wear when cutting better design compactness was obtained with high power or high ionization ratecontaining Cr,Si three(Al,Ti)N nanostructures PVD coating.Analysis showed coating hardness and a modulus of elasticity,TiAlSiXN coating has higher wear resistance with its high hardness and elastic modulus.This conclusion has also been demonstrated when experimenting with a coating of Ni-Cr alloy blade cutting.At the same time through sliding friction and high temperature tribiology of the coating analysis,it shows that the optimal frictional performance of TiAlSiXN when coating the Ni-Cr alloy at temperature at 25?,300?,600?.The latter was by far the worst in friction due to the surface roughness and high temperature heavy debris.These results further validate the H/E conclusions of the sliding friction and wear tests.Third,because the “hard and soft” machinability of Ni-Cr alloy,modeling and finite element analysis on forming turning of difficult processing characteristics of Ni-Cr alloy corrosion oil casing.It was necessary to design a precision molding thread cutter with high reliability and high stability giving particular focus to finite element analysis and optimization of cutting tool edge.Optimal design is the reinforced edge with variable scale within the cross section of cutting edge method which has quadratic control parameters.The result is a variable cutting edge reinforced belt with waterfull type PZ1=0.06 mm,PZ2=0.03 mm.According to the principle of comb-shaped complex tool cutting edge which has the best cutting performance,the design for comb-shaped complex cutting edge tool has at least one fine cutting tooth and one coarse cutting tooth with each section of the cutting line having a different reinforcing band “Variable scale edge reinforced with a new structure”.According to the tool path and pattern forming method of thread cutting,considering the cutting load and production efficiency,a tridentate external thread cutter was designed with double holes clamp structure,and a internal thread cutter with single Li loaded and single tooth clamp structure.Fourth,the special comb-shape complex cutting tool for Ni-Cr alloy corrosion oil casing requires high–precision in accuracy of tooth and edge performance.Through optimization of grinding technology,combined with actual practice,the developed molding tool grinding parameters are as follows: coarse grinding tooth two cutters,with grinding depth 0.5mm,cutting speed 10mm/min.Grinding wheels used metal-ceramic bond diamond wheel,size 240#,concentration 100%.Fine grinding toothed,its grinding depth 0.12 mm,cutting speed 15mm/min.metal bond diamond wheel,size180#,concentration 100%.In the meantime,according to the design requirements for Ni-Cr alloy threadcutting edge,we developed a composite edge enhanced treatment processes with sandblasting,polishing and special grinding processes.Finally,based on the requirements of Ni-Cr alloy pipe thread for processing precision and surface smoothness,the cutting parameters of Ni-Cr alloy pipe threading were optimized.If the machine rigidity allows,it should be smaller depth of cut and larger cutting speed.Preferably the cutting speed vc=90~120m/min,cutting depth ap=0.03~0.06 mm.At the same time,we field tested the prepared production of inner and outer thread blades which showed an average life expectancy of 25~30head/piece,and were relatively stable with anti-wear properties significantly improved.The main failures were crater wear of the rake face,and flank face wear. |
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