| Conical pick is a kind of cutter which can directly break coal and rock in the fully mechanized mining equipment of coal mine,such as shearer and roadheader.In the coal mining and tunneling operation,the working conditions of conical pick are harsh and complex,which leads to its frequent failure,causing huge consumption,seriously affecting the production cost and efficiency of enterprises,and greatly restricting the competitiveness of conical pick in China.In order to meet the needs of development of the production of coal enterprises and enhance the competitiveness of conical pick in China,it is urgent to improve the quality of pick and extend the service life of pick,which has become an important research topic in the research field of conical pick.At present,the research on multiple quality characteristics of conical pick by manufacturing process is not thorough enough,the means are not comprehensive enough,and the effect needs to be further improved.Cryogenic treatment technology is an extension of conventional heat treatment process,which is a green,environmentally friendly,modern and advanced manufacturing technology that can significantly improve the mechanical properties of materials,and has a wide application prospect.Therefore,this dissertation takes the pick as the research object,takes the improvement of the manufacturing process of conical pick as the main line,takes the multiple quality characteristics regulation of conical pick as the goal,takes cryogenic treatment technology as the regulation means,explores the regulation mechanism to comprehensively guarantee the multiple quality characteristics of conical pick,and explores the influence mechanism of cryogenic treatment,so as to provide theoretical and technical support for improving the quality level of conical pick in China.The main research contents and conclusions are as follows:(1)By analyzing the user requirements of conical pick and transforming them into quality characteristics,the critical quality characteristics of conical pick are identified as wear resistance of pick head,wear resistance of carbide tip,hardness of pick head,and then the key processes affecting the key quality characteristics of conical pick in the manufacturing process are quenching,tempering and brazing.Based on the analysis of the failure mode,failure mechanism and coping strategies of conical pick,a new regulation method is proposed to improve the multiple quality characteristics of conical pick by introducing cryogenic treatment technology in the key process of manufacturing process of conical pick.(2)The regulation mechanism of thermo-mechanical treatment on the multiple quality characteristics of pick body material(42Cr Mo)was studied.It was found that the thermo-mechanical treatment could effectively improve the hardness and wear resistance of pick body material,but the impact toughness decreased.The hardness increased by 2.5 HRC,the wear resistance increased by19.9%,and the impact toughness decreased by 1.7 J.The micro influencing mechanism of thermo-mechanical treatment on pick body material is explored.The carbides in the hardened pick body material are refined,dispersed and evenly distributed,and the fine troostite structure is obtained,so that the wear resistance of the pick body material is improved.(3)The regulation mechanism of cryogenic treatment on the multiple quality characteristics of pick body material(42Cr Mo)was studied.It is found that the cryogenic treatment can effectively improve the wear resistance,impact toughness and bending strength of pick body material.The optimal process parameters of cryogenic treatment are-196°C of cryogenic temperature,12 h of cryogenic time and one cycle,and correspondingly,hardness is basically unchanged,and wear resistance,impact toughness and bending strength are increased by 23.8%,16.2%and 6.1%respectively.The comprehensive regulation of multiple quality characteristics of pick body material is realized.At the same time,wear mechanism,impact fracture mechanism and micro influencing mechanism of cryogenic treatment on pick body material are studied.It is found that the wear mechanism is mainly abrasive wear with slight adhesive wear and oxidation wear.The impact fracture mechanism is quasi cleavage fracture,showing brittle fracture.The micro influencing mechanism is that cryogenic treatment can promote carbides segregation and carbides precipitation in microstructure of pick body material.Meanwhile,the relative softening of the matrix and the dispersion of fine carbides make the impact toughness and bending strength increase.(4)The regulation mechanism of cryogenic treatment and its process parameters on the multiple quality characteristics of cemented carbide materials(YG11C,YG13C,YG15C)of pick tip was systematically studied.It is found that cryogenic treatment can significantly improve microhardness and wear resistance of cemented carbides.After cryogenic treatment,the microhardness and wear resistance of YG11C cemented carbide are increased the most by 71.4 HV and70.3%respectively,that of YG13C cemented carbide are increased the least by33.5 HV and 35.1%respectively,and that of YG15C cemented carbide are increased medially by 65.7 HV and 45.1%respectively.In addition,wear mechanism and micro influencing mechanism of cryogenic treatment on cemented carbide material of pick tip are explored.It is found that the wear mechanism is abrasive wear of tungsten carbide and adhesive wear of cobalt phase.The micro influencing mechanism is that cryogenic treatment can promote the transformation of?-Co to?-Co in cemented carbides,so as to improve hardness and wear resistance of cemented carbides.The greater the degree of cobalt transformation,the higher the hardness and wear resistance improved.(5)On the basis of the above research on the regulation mechanism of cryogenic treatment on pick body material and cemented carbide material of pick tip,the regulation mechanism of cryogenic treatment and its process parameters on the multiple quality characteristics of conical pick is studied.It is found that cryogenic treatment can greatly improve wear resistance of conical pick without significantly affecting hardness and slightly reducing impact toughness.When the process parameters were-196°C of cryogenic temperature and 12 h of cryogenic time,hardness of conical pick remained basically unchanged,impact toughness decreased by 1.5 J·cm-2,and wear resistance increased by 41.6%,realizing the regulation of multiple quality characteristics of conical pick.In a word,this dissertation verifies the effectiveness of cryogenic treatment process to regulate the comprehensive quality characteristics of conical pick,and establishes a new optimized manufacturing process to improve the comprehensive quality characteristics of conical pick,which is of great significance to improve the quality level of conical pick in China. |
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