Influence of Gating System Parameters of Die-Cast Molds on Properties of Al-Si Castings

The resulting quality of castings indicates the correlation of the design of the mold inlet system and the setting of technological parameters of casting. In this study, the influence of design solutions of the inlet system in a pressure mold on the properties of Al-Si castings was analyzed by computer modelling and subsequently verified experimentally. In the process of computer simulation, the design solutions of the inlet system, the mode of filling the mold depending on the formation of the casting and the homogeneity of the casting represented by the formation of shrinkages were assessed. In the experimental part, homogeneity was monitored by X-ray analysis by evaluating the integrity of the casting and the presence of pores. Mechanical properties such as permanent deformation and surface hardness of castings were determined experimentally, depending on the height of the inlet notch. The height of the inlet notch has been shown to be a key factor, significantly influencing the properties of the die-cast parts and influencing the speed and filling mode of the mold cavity. At the same time, a significant correlation between porosity and mechanical properties of castings is demonstrated. With the increasing share of porosity, the values of permanent deformation of castings increased. It is shown that the surface hardness of castings does not depend on the integrity of the castings but on the degree of subcooling of the melt in contact with the mold and the formation of a fine-grained structure in the peripheral zones of the casting.     

三种铸造金属全冠戴用后IL-6在实验犬牙龈组织中的表达

目的 研究三种铸造金属全冠戴用后IL-6在牙龈组织中的表达.方法 选择纯钛、钴铬钼及铜合金,分别给狗行铸造全冠修复,建立12只实验动物模型,随机分成4组(每组3只):对照组,纯钛组,钴铬钼合金组及铜合金组.然后采用电感耦合等离子体质谱仪(ICP-MS)来定量测定戴冠前、戴冠2周、戴冠1月、戴冠2月及戴冠3月时牙龈组织中金属离子的种类和浓度,并且应用免疫组化EnVision二步法检测IL-6在牙龈组织中的表达.结果 戴冠2周、1月、2月及3月时铜合金组牙龈组织中IL-6的表达率显著高于钴铬钼合金组,钴铬钼合金组又明显高于纯钛组和空白对照组,而纯钛组与空白对照组之间无显著差异(P＞0.05).IL-6在牙龈组织中的表达率与牙龈组织中Co、Cr、Cu离子浓度的升高成正相关.结论 本研究动物模型证明牙科铸造合金修复体戴入后由于合金腐蚀而析出的金属离子会改变机体的免疫应答,使炎症因子IL-6的表达增加.     

铸造桩表面喷砂处理对牙根抗折性能影响的体外实验研究

目的：研究铸造桩表面喷砂处理对牙根抗折性能的影响。方法：20颗近期拔除的单根第一前磨牙,根管治疗后于釉牙骨质界冠方1.5mm截冠,随机分为2组,铸造桩核及金属全冠修复。实验组铸造桩粘固前表面喷砂处理,对照组不作处理。试件包埋于丙烯酸树脂块中,在电子万能实验机上进行测试。结果：对照组牙根折裂强度为2.773±0.357kN,实验组牙根折裂强度为3.113±0.357kN,2组间差异具有统计学意义（P〈0.05）。结论：对铸造金属桩表面进行喷砂处理,可以提高桩核冠修复后牙根的抗折强度。     

上颌全口义齿铸造腭托后堤区的网状设计与临床观察

目的：评价上颌全口义齿铸造金属腭侧基托后堤区网状设计的临床效果。方法：采用刮除石膏的方法形成后堤区,在上颌基托硬腭区采用金属板设计,牙槽嵴及基托后缘10mm（后堤区）范围采用金属网加强塑料基托设计。在戴牙后1个月对上颌义齿固位效果进行评价。对由于后堤区封闭不佳造成的固位不良者,进行后堤区重衬后再次评价。结果：158例患者中,139例固位佳,15例固位一般,4例固位差。单纯由后堤区边缘封闭不良造成的固位一般11例,固位差3例,经后堤区重衬后对此14例再次评价,固位佳9例,固位一般5例。结论：上颌全口义齿铸造金属腭侧基托后堤区的网状设计,既保持了常规设计的优点,又克服了其不能重衬的缺点,减少了全口义齿的失败率。     

The Use of Barley Malt as a Binder in Molding Sand Technology

The aim of this study was to attempt to use barley malt as a natural, organic binder in the technology of molding sand. TGA analysis of the binder was performed, during which temperatures of thermal decomposition of its components were determined. The results of TG/DTG analysis show that a loss of ~75% of mass of the MB binder is organic matter. Over 50% of this is starch. The results indicate the possibility of using a binder made of barley malt as a binding material for quartz sand grains. This fact was confirmed by tests carried out with use of SEM. During the observations, it was found that barley malt forms smooth bridges connecting individual grains of quartz sand. The typical properties of molding sands with barley malt were also determined, compared to sands containing commonly used binders. At the same time, the influence of the content of this binder on flowability, permeability, strength properties, and wear resistance was assessed. It has been found that increasing the binder content in molding mass results in an increase in strength and wear resistance, as opposed to flowability and permeability. Test castings were also made. It was found that the addition of a binder made of barley malt has a positive effect on the surface quality of castings. This was confirmed by roughness measurements of the test castings. At the same time, a tendency to excessive gas evolution during pouring was shown, with higher contents of this binder. Moreover, greater amounts of barley malt in the molding sand (MB 5%) as compared to the lower content (MB 2%) increased the thickness of the burnt layer of the sand by 25%. This is due to the exothermic reaction when more binder is burnt. It is extremely important from the point of view of the regeneration of molding sand.     

Removal of Stair-Step Effects in Binder Jetting Additive Manufacturing Using Grayscale and Dithering-Based Droplet Distribution

Binder jetting is a layer-based additive manufacturing process for three-dimensional parts in which a print head selectively deposits binder onto a thin layer of powder. After the deposition of the binder, a new layer of powder is applied. This process repeats to create three-dimensional parts. The binder jetting principle can be adapted to many different materials. Its advantages are the high productivity and the high degree of freedom of design without the need for support structures. In this work, the combination of binder jetting and casting is utilized to fabricate metal parts. However, the achieved properties of binder jetting parts limit the potential of this technology, specifically regarding surface quality. The most apparent surface phenomenon is the so-called stair-step effect. It is considered an inherent feature of the process and only treatable by post-processing. This paper presents a method to remove the stair-step effect entirely in a binder jetting process. The result is achieved by controlling the binder saturation of the individual voxel volumes by either over or underfilling them. The saturation is controlled by droplet size variation as well as dithering, creating a controlled migration of the binder between powder particles. This work applies the approach to silica sand particle material with an organic binder for casting molds and cores. The results prove the effectiveness of this approach and outline a field of research not identified previously.     

Dual-Scale Porosity Alumina Structures Using Ceramic/Camphene Suspensions Containing Polymer Microspheres

This study demonstrates the utility of thermo-regulated phase separable alumina/camphene suspensions containing poly(methyl methacrylate) (PMMA) microspheres as porogens for the production of multi-scale porosity structures. The homogeneous suspension prepared at 60 °C could undergo phase separation during freezing at room temperature. This process resulted in the 3D networks of camphene crystals and alumina walls containing PMMA microspheres. As a consequence, relatively large dendritic pores with several tens of microns size could be created as the replica of frozen camphene crystals. In addition, after the removal of PMMA microspheres via heat-treatment, micron-sized small spherical pores could be generated in alumina walls. As the PMMA content with respect to the alumina content increased from 0 vol% to 40 vol%, while the camphene content in the suspensions was kept constant (70 vol%), the overall porosity increased from 45.7 ± 0.5 vol% to 71.4 ± 0.5 vol%. This increase in porosity is attributed to an increase in the fraction of spherical pores in the alumina walls. Thus, compressive strength decreased from 153 ± 18.3 MPa to 33 ± 7.2 MPa. In addition, multi-scale porosity alumina objects with a honeycomb structure comprising periodic hexagonal macrochannels surrounded by dual-scale porosity walls were constructed using a 3D plotting technique.     

辐射对豚鼠鼻黏膜组织结构及微血管的影响

目的：探讨辐射对豚鼠鼻黏膜结构及微血管的损伤。方法：选择健康豚鼠84只，随机分为对照组（12只）及照射组（72只）。均在同样条件下喂养。将照射组豚鼠置于直线加速器射线内照射，每周1次，每次照射5Gy，计3周，总剂量15Gy，建立辐射损伤动物模型。分别于照射后0．5、1.0、2．0、3．0、5．0、6．0个月处死动物12只，随机取6只做鼻腔黏膜微血管铸型，另6只做病理检查。对照组在假照射后6个月处死动物，随机各选6只分别做鼻黏膜微血管铸型检查和病理检查。结果：照射组豚鼠的鼻黏膜辐射后早期表现为急性炎症反应，黏膜大量坏死、脱落，电镜下见仅少部分黏膜表面还被覆着正常的纤毛结构。以后黏膜开始修复，至6个月时基本结束，但大部分黏膜失去了正常的纤毛柱状上皮结构特点，部分区域甚至代为组织转化的鳞状上皮；微血管铸型可见，早期改变为毛细血管扩张充血及血管内皮细胞肿胀，以后逐渐出现毛细血管的扭曲变形、闭塞及中断，毛细血管数量大量减少，致血液回流障碍，微静脉萎瘪。后期部分区域出现新生的毛细血管，但结构紊乱，不具备微循环的功能。结论：鼻黏膜的损伤、晚期的鳞状上皮组织转化以及鼻黏膜微循环的破坏是放疗后鼻腔功能障碍的病理学基础。     

液态乳胶在面动脉铸型中的应用

目的 采用液态乳胶进行面动脉铸型，了解人体上、下唇血管构筑，以指导唇缺损修复时各种邻近皮瓣的评估和选择。方法 用液态白色乳胶（工业半成品橡胶）与中国画颜料混合后灌注面动脉，10％盐酸液腐蚀并清除软组织，观察上、下唇血管构筑；同时进行双侧面动脉不同灌注压力自身对照。结果 乳胶铸型血管丰满、色泽鲜艳，灌注压力大的一侧面动脉粗于对侧，面动脉及其一、二级分支显示清晰。结论 液态乳胶对反映大块组织中较粗的血管及其一、二级分支有其长处，故较适合面动脉及其分支的铸型。灌注时管腔内的压力越大，铸型的血管充盈越好。面动脉铸型在唇缺损修复时邻近皮瓣的选择中有一定参考价值。     

游离端缺失种植义齿上部结构整铸支架固位体的适合性

采用三维坐标测量方法考察游离端缺失种植义齿基桩位置改变的情况下，两种非贵金属合金上部结构整铸支架固位体的适合性。结果表明：固位体的变形在三种不同种植基桩位置之间和两种合金之间均无统计学差异，但各固位体在水平向和Ｈｅ龈向均有不同程度的变形，而且颈缘的收缩有较Ｈｅ方大的趋势，说明较长的非贵金属合金上部结构整铸支架固位体的适合性有待改善。