【作者】 吕宝伟；

【导师】 闫法强； 陈大明；

【作者基本信息】 山东理工大学 ， 材料学， 2008， 硕士

【摘要】 ZrO₂瓷球是一种应用前景广阔的高品质研磨介质,但现有的球坯成型技术生产效率低、制备成本高、产品质量差,已经成为制约ZrO₂瓷球规模化生产的瓶颈。研究探讨ZrO₂瓷球的高效成型生产技术是近年来国内外研究的热点。滚制成型法投资少,效率高,可实现自动化生产,是生产小颗粒瓷球最理想的制备工艺。但由于ZrO₂属瘠性原料,颗粒间结合性差,不易滚制成型,也是滚制成型没有被广泛应用于ZrO₂瓷球生产的主要原因。本文以含3mol%Y₂O₃的ZrO₂粉体为原料,采用滚制成型技术和常压烧结工艺制备了ZrO₂研磨介质球。研究了pH值、分散剂、固相含量等因素对浆料流变性能的影响,以及球磨时间对ZrO₂颗粒尺寸的影响,制备出了高固低粘适用于喷雾造粒用ZrO₂浆料;通过对ZrO₂球坯在滚制过程中的生长机理和受力分析,建立了相关的数学模型。研究了球核的制备方法,分析了粘结剂水溶液的含量、滚锅的直径、倾角、转速、球坯粒径、滚制时间及球坯的抛光时间对ZrO₂球坯性能的影响;利用力学性能测试和扫描电镜等分析方法,讨论了烧结制度对ZrO₂研磨介质球耐磨性的影响。实验研究表明:ZrO₂浆料在不同的pH值环境中,其浆料粘度差别较大,选择弱碱条件有利于ZrO₂颗粒的分散。随着固相含量的提高,浆料的粘度提高。为获得流动性好的浆料,需要加入适量分散剂,但分散剂加入量超过一定限度后,反而起到相反作用。球核粒度可影响球坯的滚制,本实验采用成型压力为150MPa的等静压成型后破碎过筛,选择30目至60目之间颗粒可用作滚制成型的球核。通过对粉体链接、滚制成长机理和球坯受力的分析和相关数学模型的建立,发现滚锅的转速、倾角、直径和球坯粒径是相互影响的。要使球坯具有最佳的长大环境,在成型过程中,随着球坯的长大,需要相应提高滚锅的转速和倾角;不同直径的滚锅应选择不同的转速和倾角。水溶液中加入聚乙烯醇可提高颗粒间的界面结合力,明显改善ZrO₂粉体的成型性能,当聚乙烯醇含量为1wt‰时,球坯具有最高的密度和必需的强度。水溶液和粉体要一定比例加入,实验结果表明:当含有1wt‰聚乙烯醇的水溶液与粉体质量比为1:9时,具有最佳的成型效果,其加入量与球坯粒径的平方成正比。随着球坯长大,球坯逐步致密,粒径越来越均匀,圆度越来越好。为使球坯更加致密和表面更加光滑,在停止加料后,需要对球坯继续滚制抛光,最佳抛光时间为2h。由于球坯在滚制过程中,球坯表面产生较高的温度和饱和的湿度,如果滚制后立即取出,会使球坯表面水分快速挥发导致收缩过大,产生表面裂纹。因此在滚制结束后需要将球坯在滚锅中静置20～40min保湿降温。静置时间与大气的温度和相对湿度有关,温度高、湿度大静置时间短,反之静置时间长。球坯在干燥过程中,干燥环境要由低温高湿（相对湿度大于60%,室温）逐步转为高温低湿（相对湿度小于10%,温度110℃）,干燥周期40h,使球坯水分小于0.5%。烧结温度和保温时间显著影响ZrO₂研磨介质球的性能,烧结温度低或保温时间短,ZrO₂研磨介质球不能完全烧结,压碎强度和体积密度低,自磨损率高;烧结温度过高或保温时间过长,ZrO₂研磨介质球晶粒长大且不均匀,起增韧作用的四方相含量降低,瓷球体积密度虽高,但压碎强度降低,自磨损率升高;当烧结温度为1550℃、保温时间为2h时,ZrO₂研磨介质球具有最好的耐磨性能,体积密度5.91g/cm³,压碎强度2416N,自磨损率2.6ppm/h。更多还原

【Abstract】 ZrO₂ ceramic ball is a kind of outstanding grinding media,which is used extensively and has a promising feature.Although the existing forming techniques have low efficiency, high cost and low product quality,which has become the bottleneck that limits its commercial scale production.Recently,much attention has been focused on the investigation of high efficient forming and production techniques all over the world. Rolling ball method,which has been recognized for its low cost,high efficiency and automatable fabrication,has become a kind of excellent technique for producing small size ceramic balls.But ZrO₂ is a kind of lean stuff and the particles bond imfirmly,that make it difficult to form balls,also it is the mainly reason why rolling method has not been used extensively to make ZrO₂ ceramic balls up to now.In this paper,ZrO₂ ceramic grinding media balls were made from ZrO₂ powder,which contains 3 mol%Y₂O₃ by rolling ball method and pressureless sintering technique.High solid loading and low viscosity slurry which is suitable to spray Granulating was made by the investigation on the effects of the factors such as pH value of the slurry,dispersant and solid loading to the flow properties of the slurry and the influences of milling time to the particles size;relative mathematical model was built through the analysis of the growth mechanism and stress of the zirconia green ball during the rolling process.Also the fabrication of ball core and the effects of various parameters such as the content of binder, the diameter,obliquity and roll velocity of ball-forming machine,the green balls’ diameter, rolling time and the polishing time to the behaviors of zirconia green ball were studied; The effects of sintering system on the wearable modulus of zirconia ceramic media balls were analyzed by mechanical test and SEM analytic methods.The results of the study showed that zirconia slurry possesses different properties with different pH value and have different viscosities.Slightly alkaline system is in favor of the dispersion of zirconia particles.The viscosity increases with the solid loading of the slurry. Therefore appropriate amount of dispersant was added to make slurry with good flow properties and the excess of dispersant gets the opposite effect.The size of ball core affects the manufacture of green ball,in this study,optimum size of ball cores were made by isostatic compaction under 150MPa pressure and thereafter crushing and grading the particles.The particles with the size between 30 mesh to 60 mesh can be used as ball core.The analysis on the link of powder,stress and growth mechanism of balls and the relative mathematical model show that the diameter,obliquity and rolling velocity of ball-forming machine and the size of green balls interact and support each other.The rolling velocity and obliquity of ball-forming machine should be enhanced as the green ball grows gradually.Different sizes of ball-forming machine need different rolling velocity and obliquity.The addition of polyvinylalcohol（PVA） in aqueous solution can improve the interfacial bonding force and contribute to the forming performance of zirconia powder obviously.The highest density and strength of the green ball can be obtained when the PVA content is 1wt‰and the addition of powder and aqueous solution should have a set ratio.The experiment results show that the optimal ratio of the aqueous solution which contains 1wt‰PVA to the weight of powder is 1:9 and the amount of addition is in direct ratio to the quadratic of the size of green ball.The green balls become compacter as they grow gradually and have more homogeneous size and circularity.The green balls should be polished after stop charging for get the compactest and lubricious surface.The optimal polishing time is 2 hours.The surface of the green balls have high temperature and saturated humidity during rolling,if the green balls were taken out immediately after finishing rolling,the water on the surface would volatilize quickly which would lead to surface shrinking and cracking. Hence it is necessary to leave the green balls in the ball-forming machine after finishing rolling for 20 to 40 minutes for keeping humidity and letting the temperature decrease gradually.The laying aside time is relative to the temperature and relative humidity of the atmosphere and it is shorter if there is high temperature and humidity.During the dry process,the temperature should keep from low to high at the beginning（the relative humidity is more than 60%,RT） and then keep from high to low（The relative humidity is less than 10%and temperature is 110℃）,the dry cycle is 40 hours and the content of water in green balls is less than 0.5%.Sintering temperature and tempering time effect the properties of zirconia ceramic media balls distinctly,the ceramic media balls can’t be sintered absolutely with low sintering temperature and short tempering time,which turn to possess low crushing strength and volume density but high wearable modulus;also overly high sintering temperature and long tempering time would make zirconia grains grow tremendously and have inhomogeneous size and the cubic zirconia which contribute to toughening effect decrease too,and that balls have low crushing strength and high wearable modulus, although the volume density is high.Zirconia ceramic media balls has the optimal wear performance when they were sintered in 1550℃for 2h and the volume density is 5.91g/cm³,crushing strength is 2416N,wearable modulus is 2.6ppm/h.更多还原