| Cubic boron nitride （cBN） vitrified bond tools have many advantages: high efficiency ofgrinding, high machining accuracy, long service life，etc. They are used in grinding threadmachining because they can significantly improve the thread’s performance and prolong theservice life of the thread. However, domestic tools’ disadvantages, such as poor stiffness,sharp corners to keep poor, easy to clog and low efficiency, limited their application anddevelopment. Therefore, research and development of cBN grinding tools are hot spots in thefield of machining.The methods of DTA, X-diffraction analysis, scan-electrcscope and energy spectrumanalysis had been used to syudy the influence of molar ratio about ZnO/Na2O （Z） andMgO/Li2O （M） on the properties of Al2O3-B2O3-SiO2-RO-R2O vitrified bonds. The influenceof Z, the content of bonds, pressure and sintering temperature on cBN grinding wheels werealso researched. The main conclusions were drawn as following:In this vitrified bond system, the addition of ZnO reduced the quartz crystal andLi2OAl2O37.5SiO2phase. And by increasing the ratio of Z, the content of quartz crystalreduced, the Li2OAl2O37.5SiO2phase increased, the size of crystallites decreased, the vitrifiedbonds’ topographic crystal temperature, softening temperature, refractoriness, chemicalstability increased first and then decreased, while the expansivity was reduced. When the Zvalue was2.50, the chemical stability was the best, the expansivity was the lowest,4.2758×10-6K-1, and the bending strength was the largest,123.38MPa. In this system, with theincreasing of the ratio of M, the vitrified bonds’ refractoriness, chemical stability increased,while the expansivity increased first and then decreased. When the value of M was0.67,Mg（Zn）Al2O4and quartz crystal were founded in vitrified bonds. And when sinteringtemperature increased, the content of quartz crystal reduced, Mg（Zn）Al2O4phase increased,the size of crystallites decreased first and then increased, while the bending strength increasedfirst and then decreased.By increasing the content of bonds, the porosity and absorption of tools decreased firstand then increased, instead, bulk density, strength, hardness, G-ratio increased first and thendecreased. By increasing the pressure, the porosity and absorption of tools decreased first andthen kept nvariability, but, bulk density, strength, hardness, G-ratio and the grinding efficiency increased first and then kept nvariability. By increasing the sintering temperature, the porosityand absorption of tools developed into "V" shape, however, bulk density, strength, hardness,G-ratio and the grinding efficiency showed inverted "V"-type movements. When the optimalproperties of tools were obtained, the content of bonds was23-26wt%, pressure was25MPa,the sintering temperature was870℃. Walnut shell, amylum, calcium carbonate were all usedas pore-creating agents, their appropriate adding quantity were8-16wt%,4-16wt%,8-12wt%respectively. Moreover, walnut shell was more appropriate than others because of the linearrelation between the content of walnut shell and the porosity, hardness, strength of the cBNtools were better. The vitrified bond cBN wheels used bond （M=0.67） had the greateststrength, the highest G-ratio, which were better for coarse grinding thread. When vitrifiedbond cBN wheels contained bond （Z=2.50） and12wt%of walnut shell, their porosities wasthe highest and hardness was uniformity, which grinded cast iron with no walling up,complete edges and not broken cBN grits. Therefor, it was good for fine grinding thread.Compared with imported products, this tool could the G-ratio was highest to220increased by69.2%, the manufacture efficiency was2.3times and made the surface roughness of thethread about0.16-0.20μm. |
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