Properties of alumina-based ceramic cores

Fused corundum is a rather promising raw material for preparing an alumina-based ceramic core due to its excellent high temperature resistance and chemical inertness.In this study,alumina-based ceramic cores were prepared using fused corundum as the matrix material,and the effect of varying silica powder contents on the properties of the alumina-based ceramic cores,including the sintering shrinkage,the flexural strength,and the high temperature deformation was investigated.The mineralization mechanisms of the silica on the alumina-based ceramic core were also analyzed.The optimum addition amount of silica in this experiment is 8% in weight.At that moment,the aluminum-based core has both a low sintering shrinkage coefficient of 0.66% and better properties:the room temperature flexural strength is 22.19 MPa,the high temperature flexural strength is 21.54 MPa,the high temperature deformation is 0.93 mm,and the residual flexural strength is 47.41 MPa.     

石英含量对刚玉基陶瓷型芯材料性能的影响

研究了石英含量对刚玉墓陶瓷型芯强度、收缩率、气孔率和体积密度的影响.试验结果表明:在相同的烧结温度下,随着石英含量的增加,型芯的抗弯强度、收缩率不断增大;相同SiO2含量,型芯的抗弯强度、收缩率随烧结温度的升高而增大;在相同的烧结温度下,随着SiO2含量的增多,样品的显气孔率先增加后减小,存在极值;同一成分含量,当SiO2含量≦15%,随烧结温度的升高,样品的显性气孔率增加,而当SiO2为20%,1450℃烧结时型芯的显性气孔率最大.SEM、XRD、EDS分析结果表明,玻璃相的生成和消耗关系是影响型芯显气孔率的重要因素.     

3D printing of tantalum parts based on low molecular mass organic gel system

In this study, 3D gel printing based on a low molecular mass organic gel system was employed to fabricate complex-shaped Ta parts. As opposed to a polymeric gel system, this system was initiated by heat transition. To obtain suitable printing slurry with 62 vol% solid content, 2.5 wt% resin was introduced to improve green body strength and 0.55 wt% oleic acid was added to modify the viscosity. As a result, the printed samples had relatively good surface quality without defects or pores observed on the surface. Ta particles were closely bound by dibenzylidene sorbitol (DBS) gelators. After sintering, a uniform shrinkage was obtained with a shrinkage of 11%, but the surface quality of the as sintered samples was improved. Sintering decreased the surface roughness from 4.0 μm to 2.8 μm. Besides, the as-sintered Ta samples had a relatively dense and homogenous microstructure. The relative density of the as-sintered sample was about 98%. Therefore, 3D gel printing is a promising method to prepare complex-shaped Ta parts with minimal material waste.     

气压烧结——一种大有前途的氮化硅陶瓷制备方法

介绍了气压烧结氮化硅陶瓷的研究开发成果 ,论述了气压烧结的生产工艺及其显微结构与力学性能 ,并与传统的生产方法进行了对比。气压烧结制备的氮化硅陶瓷可形成原位增韧结构 ,具有高韧性、高强度和好的耐磨性。并可直接制取接近最终形状的各种复杂形状制品 ,从而可大幅度降低生产成本和加工费用 ,适用于大规模生产     

Determination of non-uniform sintering shrinkage in MIM powder compacts by digital image processing

An in-situ monitoring system for sintering shrinkage was devised to study the nonuniform deformation of injection moulded powder compacts. The monitoring system is based on the digital image correlation method and has a modified image processing software compared to the conventional method. The system consists of a bell-type sintering furnace and an optical image processing set-up, enabling one to measure two- and three-dimensional changes in the compacts during sintering on a non-contact and real time basis. Nonuniform and anisotropic sintering shrinkage was precisely determined for two types of complex-shaped powder compacts of stainless steel (SUS304) prepared by metal injection moulding at room temperatures up to 1543 K.     

一种解决陶瓷型芯开裂的方法

介绍一种解决复杂陶瓷型芯开裂的工艺方法,对于结构复杂、厚薄悬殊、存在细长形状的陶瓷型芯,在压制成型和烧结过程中极易出现开裂,运用常规的裂纹解决方法效果不明显.通过在陶瓷型芯预埋芯骨的方法,能显著提高陶瓷型芯的压制和烧结合格率,进而提高熔模精密铸件的合格率.     

V型船用发动机气缸体铸件排气技术的应用

针对V型船用发动机气缸体铸件尺寸相对较大,砂型和砂芯一般都使用树脂做粘结剂,且大多数采用立式全包裹砂芯浇注方式,砂型和砂芯遇高温铁液,树脂会分解产生大量气体,若不能及时排出气体,从而导致铸件产生气孔、气隔、及气缩等缺陷的问题,因此对砂芯生产工艺和排气系统进行了一系列改进,批量生产出合格铸件.     

硅树脂添加量对氧化铝基陶瓷型芯性能的影响

以氧化铝粉末为基体,添加具有粘结性和一定陶瓷产率的硅树脂粉末,通过干压成型和无压烧结制备出氧化铝基陶瓷型芯,重点研究了硅树脂添加量对氧化铝基陶瓷型芯性能的影响。结果表明:硅树脂在裂解过程中会形成二氧化硅,二氧化硅与氧化铝基体发生反应形成新相莫来石。由于硅树脂在交联和裂解过程中会释放大量气体,导致烧结体失重,且气体的逸出会抑制由烧结引起的收缩,因此,随着硅树脂添加量增加,产生的气体量增加,烧结体的失重率增加,收缩率降低。硅树脂含量的增加使得烧结体的气孔率变大和体积密度减小,烧结体的室温抗弯强度逐渐减小。硅树脂的添加虽然降低了其室温强度,但是保证了陶瓷型芯的尺寸精度。     

过桥箱盖铸件的工艺改进

QT450-10过桥箱盖铸件在生产过程中产生缩孔、缩松、挤砂、芯子大、生产效率低等问题,通过将原工艺中的#1芯改为上型吊砂、设计了φ60 mm×35 mm定位芯头定位、一型布置3件、增加出气片和出气针等措施,该铸件出品率由原先的65%提高到70.2%、砂芯质量减少19 kg、生产效率提高50%、废品率控制在2.5%以内。     

消失模铸造球墨铸铁件收缩缺陷计算机模拟的处理方法

本文主要讨论了初始温度场和铸型硬度对消失模铸造球墨铸铁件收缩缺陷的影响,用计算机数据采集系统测试了消失模和空腔铸造的初始温度场分布。结果表明,两者初始温度场分布仅有微小差别,不同真空度下消失模铸型硬度的测试结果表明,消失模铸型的硬度高于普通湿型砂铸型,并且硬度分布更均匀 ,这一特点可以减少球铁石墨化膨胀引起的型壁移动,根据上述测试,确立了球铁件消失模铸造收缩缺陷的计算机模拟及预测方法,模拟结果与实际生产铸件的解剖结果吻合较好。     

湿砂型铸铁件的胀砂、缩孔、缩松缺陷--湿砂型铸铁件缺陷讲座(五)

叙述胀砂与缩孔、缩松的关系，说明提高砂型刚度对防止胀砂、缩孔、缩松的重要性。指出型砂强度和砂型的紧实程度是常温下影响湿砂型刚度的主要因素。对影响湿砂型浇注时的刚度的各种因素进行了分析。     

具有梯度特性的齿科修复复合材料制备及表征

本工作的目的是研究原生牙齿的梯度力学性能,制备聚合物渗透陶瓷网络(PICN)复合材料,模拟天然牙的力学行为。采用纳米压痕法测定了牙釉质和牙本质的弹性模量和维氏硬度。结果表明,原生牙齿的力学性能具有梯度特性。树脂填充部分烧结硅铝酸钠、氧化铝和氧化锆的力学性能有很大差异。通过逐步改变陶瓷组分,实现了力学性能的梯度变化。一种是纳米玻璃相硅铝酸钠/微米α氧化铝层合复合材料。陶瓷坯体的烧结温度为700℃,保温时间分别为2、4和6 h。对复合材料的抗弯强度、断裂韧性、弹性模量和硬度进行了测试,结果表明:硅铝酸钠/微米α氧化铝复合材料的弹性模量和硬度呈现梯度特性。另一种是3Y-TZP/微米α氧化铝层合复合材料。坯体烧结温度分别为1150和1200℃,保温时间为2h。其弹性模量和硬度均呈现梯度特性。SEM观察表明,过渡区形成了相互咬合的网络结构。与普通均质材料不同,本研究制备的复合材料具有各向异性。因此,复合材料的力学性能更接近于原生牙齿。     

Study on roasting process of zircon-silica sol ceramic mould

Dry stock of silica sol ceramic mould was prepared by using of colloidal moulding technique with an optimized vacuum drying process.Effect of roasting process on the shrinkage rate and compressive strength of zircon-silica sol ceramic mould,and the relationship between the roasting temperature and microstructure of zircon-silica sol ceramic mould were studied.The optimum roasting temperature of zircon-silica sol ceramic mould gained by the experiments is 900℃ and the holding time is 2 h.The scanning electro...     

Influence of Sintering Temperature on Microstructure and Mechanical Properties of Al_2O_3 Ceramic via 3D Stereolithography

In this work,aluminum oxide(Al_2O_3) ceramic samples were fabricated by 3D stereolithography printing.Printing process was followed by debinding and sintering.In addition,the effect of sintering temperature on micro structure and properties was investigated.Flexure strength was observed to increase with increasing sintering temperature due to fewer pores,fewer defects and stronger grain boundary bonding of samples at higher sintering temperatures.Maximum flexure strength of 138.5 MPa was obtained when sintering temperature was 150℃.Furthermore,the shrinkage along length direction decreased with the decreasing sintering temperature until reaching minimum value of 1.02% after sintering at 1200℃.After sintering at 1280℃,flexure strength was 24.0 MPa and the shrinkage along length direction was 2.1%,which meets demands of ceramic core.     

结晶型塑料注射制品收缩率影响因素分析

分析了注射制品的收缩机理及收缩过程,并讨论了结晶型塑料注射成型过程中模腔平均压力、熔体温度、模温、充模速率、成型时间等工艺条件和模具设计、制品结构对其收缩率的影响及制品后收缩率的因素,给出了减小制品收缩率,提高制品尺寸稳定性的方法。     

盒形锁具外壳模锻缺陷分析及模具优化

针对智能锁具外壳模锻过程中出现的开裂问题,通过数值模拟分析了模锻过程中金属的流动规律,发现凸台处的开裂原因在于金属流入凸台型腔时,凸台心部金属流动速度快,凸台四周金属则因模具摩擦流动速度慢,从而在该处形成了挤压缩孔,并进一步发展成为向板厚方向深入的折叠,该折叠经模具压平后出现在锻件表面,其形状类似裂纹。在此基础上,提出了在凸台处冲孔和增大凸台斜度两种改进方法,来增大凸台处的充填阻力和减小凸台心部金属的流动速度。数值模拟结果表明,这两种方法都能有效避免缩孔、折叠和裂纹的产生,出于简化模具考虑,采用增大凸台斜度的改进方法。实际盒形锻件完好、无折叠缺陷。     

垂直分型灰铸铁轴流泵体大孔出流等压等流量工艺

采用湿型、对开垂直分型工艺、挤压造型生产轴流泵体,浇注系统按等压等流量进行设计.型芯用覆膜砂壳芯,为解决变形,砂芯内腔放灰铁压块.按此工艺生产,成品率达90%以上.     

Comparative study of the fabrication of ultrafine Ti（C,N）-based cermets by spark plasma sintering and conventional vacuum sintering

Spark plasma sintering (SPS) and conventional vacuum sintering (VS) were employed to fabricate ultrafine Ti(C,N)-based cermets. The shrinkage behavior, microstructure, and porosity and mechanical properties of the samples fabricated by SPS were compared with those of the samples sintered by VS using optical microscopy, scanning electron microscopy, universal testing machine, and rockwell tester. The results are as follows: (1) The shrinkage process occurred mainly in the range of 1000-1300℃ during the VS process, and only a 0.2% linear shrinkage ratio appeared below 800℃；during the SPS process, a 60% dimensional change occurred below 800℃ as a result of pressure action. (2) By utilizing the SPS technique, it is difficult for obtaining fully dense Ti(C,N)-based cermets. Due to the much existence of pores and uncombined carbon, the mechanical properties of the sintered samples by SPS are inferior to sintered ones by VS. (3) grain size of the samples sintered by SPS is still below 0.5μm, but not by VS; because of low sintering temperature, there are no typical core/rim structures formed in the sintered samples by SPS1; the main microstrures of the sintered samples by SPS2 are a white core/grey shell sstructure, whereas by VS show a typical black core.grey shell structure.     

玻璃纤维对陶瓷浆料的流动性及铸型强度的影响

研究了在陶瓷浆料中加入玻璃纤维对浆料粘度及陶瓷坯体抗拉强度的影响。选择的陶瓷坯体以石英砂、硅溶胶为主要原料,玻璃纤维的直径为16μm,长度为1～3mm。结果表明,在陶瓷型中加入一定量的玻璃纤维后,陶瓷型的抗拉强度会升高;在焙烧温度为400℃时,在一定范围内,随着玻璃纤维增加,陶瓷型抗拉强度呈线性增加,从0.175MPa增加至0.221MPa,陶瓷浆料的粘度也会呈指数形式增大。     

Micro machining of pre-sintered ceramic green body

Ceramic materials are widely used in industrial products because of their excellent properties such as resistance to erosion, high temperature and wear. Those properties pose difficulty in processing ceramic materials to desired shapes and dimensions, especially in micro machining of ceramics using micro tools because of the low mechanical strength of tiny tools and the extreme hardness of ceramics. The machining of ceramic green body may be a solution to the problem. However, the low strength of ceramic green body results in low machining accuracy such as damage at the edges of micro features. In this paper, the pre-sintering of ceramic materials was used to enhance the material strength, and hence to improve the machining accuracy. Microstructures of pre-sintered ceramic green bodies at different temperatures were observed and analyzed. The mechanical strength of pre-sintered ceramics was measured. It was confirmed that the mechanical strength of ceramics increased with an increase of pre-sintering temperature. There was no obvious shrinkage after pre-sintering at below 850 °C. The edge damage of machined micro features was reduced significantly. The tool wear increased with the increase of pre-sintering temperature. Finally, a 3D micro feature was machined and the fully sintering shrinkage was compensated accurately.