Fundamental Research On Precision Grinding Technology In Machining High-Rigidity Rotary Sphere

High-performance sphere valve, which can resists high temperature of over 500 centigrade, high pressure of over 30MPa, wearing, thermal impact and heat erosion, is one of key components used in delivery and control of high temperature and high pressure coal oil liquid in coal liquification engineering, and also used in steel smelting, petroleum chemical engineering and nuclear power. In order to satisfy the bad working conditions stated above, the surface of close part of sphere valve must be harden processed, which rigidity of HRC can up to 62. So it is a large difficult problem in machining high rigidity and high precision sphere. At the same time, it is a core-technology of sphere valve manufacturing in coal liquification. In order to solve the difficulty in high-rigidity rotary sphere precision manufacturing, the grinding method and equipment which is suitable to machining high-rigidity rotary sphere was designed, the precision grinding mechanism of high-rigidity coating material was researched, and the geometric error compensation technique in machining high-rigidity rotary sphere was discussed in this paper. At last, the results and achievements obtained above were used in high-rigidity rotary sphere grinding precisely, a large number of grinding experiments were performed, and high-quality and high-accuracy sphere machining were realized successfully. The whole research possesses better systematicness, promotes the localization of this technology, and has large profits for economic and society.The grinding method which is suitable to machining high-rigidity rotary sphere precisely was designed. The machining theory is discussed in the following. Work piece and cup wheel perform rotation movement and their axial line are intersect in a point, then the machining position and feed direction can be adjusted by coordinate movement of wheel. Uniqueness of the mechanical design is that the four points, which are the rotation center of spindle, tail stock, rotary work table and grinding head, intersect in a point so as to ensure the machining accuracy.The grinding force in machining high-rigidity coating precisely was researched in theory and experiment. The reason which is using flat grinding instead of sphere grinding was explained and its feasibility was discussed too. The flat grinding course of cup wheel was analyzed, the concept of effective grinding width was put forward and cutting model of grit was analyzed too. Due to a research blank in high-rigidity grinding force theoretical model, the theoretical formula of grinding force was deduced. By performing experimental research on grinding force in machining WC-Co coating, the characteristic of it was analyzed, the relationships between grinding parameters and grinding force, grinding force ratio, grinding energy and character frequency were explored.The grinding temperature in machining high-rigidity coating precisely has been researched in theory, numerical simulation and experiment. According to working condition in grinding high-rigidity coating by cup wheel, theoretical models of grinding temperature field were built by means of trapezium moving heat source and triangle moving heat source. Heat analysis method of FEM was applied to grinding temperature field simulation of WC-Co coating grinded by cup wheel, the analysis procedure and results were discussed too. Experiments of grinding temperature were performed by using thermocouple, and the relationships between grinding parameters and grinding temperature were discussed. Experimental results of grinding temperature controlling showed that grinding temperature may be decreased rapidly by injecting coolant to grinding area. Experimental results of XRD phase analysis of work piece surface indicated that grinding temperatures have not obvious effect on property of work piece under maximum grinding parameters.The wear of grinding wheel in machining high-rigidity coating precisely was researched. The wear mechanism of wheel was analyzed. Experimental results showed that there were many wear formats including abrasion wear, grit falling off, bond wear and adhesion wear. The theory of on-line evaluation on wheel's wear was introduced and feature extraction method based on wavelet packet decomposition was applied to inspection and evaluation of wheel's wear. Experimental results may provide references for time selection of wheel's dressing and exact definition of wheel's life.In order to improve the machining precision of sphere, geometric error compensation for NC precision sphere grinding machine was researched. Firstly, motion errors of movement couple, rotation couple and orthogonal couple were analyzed. Secondly, method, theory and procedures of model building of geometric errors were given and the model was deduced. Lastly, experiments on geometric error compensation showed the effectiveness of the error model.On the basis of researches on grinding method for machining high-rigidity rotary sphere precisely, grinding mechanism of high-rigidity coating, and geometric error compensation for sphere grinding, experimental researches on high-rigidity rotary sphere precision grinding were performed. The rigidity of grinding head may change, but it can satisfy the precision grinding after eliminating clearance of feed system. The constant pressure grinding was put forward in order to avoiding damage to grinding course. And evaluation standards for grinding parameters, which are material remove rate, surface quality and shape precision, were given. A large number of experiments were performed to research the relationships between grinding parameters and evaluation standards. By adjusting grinding parameters and balancing three evaluation standards, high-precision and high-quality machining of high-rigidity rotary sphere were realized.