Research On The Preparation Of Vitrified Bond CBN Grinding Wheel

With a small grinding force, high grinding efficiency, low grinding temperature, long service life, easy dressing, good grinding quality and a series of superior performance, vitrified CBN grinding wheel is widely used in the field of automotive, aerospace, tools, cutting tools, molds, bearings, engineering ceramics etc. However, the domestic research work of vitrified CBN grinding wheel is in the early stage. And the performance of this kind of product is far from the imported one.According to the shortage of manufacturing technology of vitrified bond and vitrified CBN grinding wheel in our country, firstly the vitrified bond with flexural strength more than 100MPa was obtained by optimizing the composition of vitrified bond and analyzing and comparing the flexural strength, hardness, refractoriness, liquidity and thermal expansion coefficient of the bond; Secondly, the effects of sintering temperature, heating rate, holding time, pressure, the relative content of bond and CBN, the particle size and content of auxiliary abrasive, the particle size and content of pore-forming agent on the properties of vitrified bond CBN grinding wheel were investigated. Finally, the vitrified bond CBN grinding wheel was prepared and the grinding performance was tested. The following conclusions were obtained:A group of raw materials including SiO2, B2O3, Al2O3, Na2O, Li2O, MgO, CaO and ZnO was used as the major composition of the vitrified bond. Under the condition of the total moles of alkali-metal oxides keeping constant, the strength and hardness of the vitrified bond with more than one types of alkali-metal oxide (Na2O and Li2O existing together) are superior to which with one type of alkali-metal oxide (existing only Na2O or Li2O). In the double-alkali bonds, vitrified bond's flexural strength, hardness and fluidity gradually increase while the refractoriness and thermal expansion coefficient decrease with the relative content of Li2O increasing. After sintering at 800?, three crystal phases Ca3B2O6, Al2ZnO and LiAlO2 were found in the double-alkali bonds. The content of LiAlO2 increases with the increasing of Li2O.In the preparing of the grinding wheel, the flexural strength of the grinding wheel was significantly affected by the sintering temperature and holding time. With the increasing of heating rate, the flexural strength decreases gradually. Lower degree of flexural strength was induced by the faster heating rate. The flexural strength of the grinding wheel is relatively ideal when the molding pressure is between 30MPa to 60MPa and improves as the pressure goes up. When the content of bonds is from 22wt% to 28wt%, the flexural strength of the grinding wheel reaches 55-63MPa. The particle size and content of green silicon carbide have an important influence on structure of vitrified bond CBN grinding wheel. When the particle of green silicon carbide is smaller than CBN's, it can improve the microstructure and increase the intensity of vitrified bond CBN grinding wheel. Sugar plays a pore-forming role and is suitable for the pore-forming agent of vitrified CBN grinding wheel under a certain size and content.When the 45# hardened steels were grinded by the prepared vitrified CBN grinding wheel, the grinding efficiency of vitrified bond CBN grinding wheel and the surface quality of work-piece increased with the increasing of linear velocity of grinding wheel, and the wear amount of the grinding wheel with high wear resistance was very small after grinding for a long time.