Ceramic Mold Research Articles

Determination of cooling of Al—Si melt flow front in thin vertical cavity of ceramic shell for upper supply

The thermophysical properties of ceramic mould are experimentally determined, which made it possible to refi ne the method for calculating of the temperature of the Al—Si melt flow front when filling thin vertical cavity.

METHODS OF UNCREASING OF THE WAX MODEL SURFACE PRIMARY WETTABILITY DURING LOST-WAX CASTING

Lost-wax casting is one of the most advanced ways to obtain geometrically complex castings of high quality. One of the main factors influenced on the casting properties is the quality of the ceramic mold face layer. A uniform deposition of the ceramic slurry can be achieved by condition of the wax surface is well wetted by the suspension dispersion medium. Since the surface of the wax model is hydrophobic and the dispersion medium of ceramic suspension is water, an increase of wettability may be achieved not only by SAS-wetting agent adding in suspension composition but also by activating of the model surface by chemical or physical methods. The paper presents the results of the different ways of chemical activation influence on the wettability of the wax model surface.

Investigations of Model Multilayer Ceramic Casting Molds in a Raw State by Nondestructive Methods.

This article presents the results of research on the use of modern nondestructive methods such as 3D scanning, thermography and computed tomography (CT) to assess the quality of multilayer ceramic molds. Tests were performed on spherical samples of multilayer ceramic molds in the raw state. Samples were made of molding sands composed of quartz and molochite powders, the alcoholic binder hydrolyzed ethyl silicate (ZKE) and an aqueous binder based on colloidal silica. Thickness measurements of spherical forms were made using a 3D scanner. Porosity measurements were made using CT. Additionally, thermography observations of the mold cooling process were made with controlled temperature and humidity. The results of temperature measurements of samples were compared with measurements of thickness and porosity. The practical goal was to determine the possibility of using thermography, 3D scanning and CT as a quick method for detecting mold defects by varying their thickness, porosity and cracks and for final verification of the ceramic molds’ condition before casting.

Characterisation Of FGD Sludge From One of Glass Industrial in Malaysia and Their Potential as Ceramic Mould

Flue Gas Desulfurization (FGD) is a waste incineration process used to eliminate sulfur dioxide (SO2) from flue gas power plants. Limestone/gypsum was injected into the plant to trap sulfur dioxide and change their chemical composition from calcium carbonate to calcium sulfate dehydrate, known as FGD sludge wet scrubber. Nowadays, it is necessary to overcome the environmental pollution caused by the massive production of FGD sludge waste through recycling. In this research, FGD sludge was characterised to reveal its chemical composition, crystalline phase, and FTIR spectra characteristics. FGD sludge recorded a moderate alkaline with a pH of 8.24. Based on the XRD result, FGD sludge was mainly composed of gypsum (CaSO4•2H2O) and anhydrite (CaSO4). XRF analysis also shows that FGD sludge was mainly composed of calcium oxide, sulfur trioxide, silica, and potassium oxide.

Проблеми вибору матеріалів керамічних форм для одержання фасонних виливків із титанових сплавів

Проблеми вибору матеріалів керамічних форм для одержання фасонних виливків із титанових сплавів

Toughening of Ceramic Shell Mould with Rice Husk Fiber (CSm-RH) to Improve Strength Property and Mould Performance

For ages, ceramic shell mould (CSm) have been extensively applied in investment casting industry. The formation of CSm requires multiple steps of dipping, layering drying and firing stages. The later steps are very crucial as the solidification thin layer CSm that consist of loose ceramic particles easily cracks when exposed to the higher thermal effect. The inclusion of fiber or any reinforces phases is able to enhance fired ceramic body and also strengthen the green ceramic structure. Thus, the feasibility of rougher NaOH treated rice husk fiber (RHT) prior embedded into composited structure has shown a significant CSm improvement by induced a better adhesion properties and larger bonding area with brittle ceramic matrix, resulted in increased green strength (1.34 MPa) and fired body strength (4.32 MPa). Owing to the decomposed of lignin layer in CSm with untreated rice husk fiber (CSm-RHU) exhibited a higher porosity that provide a better permeation paths of air flow during molten metal pouring as increased 30 % from the standard CSm permeability, giving an enormous benefit for investment casting cooling process. Overall, the incorporation of RHT fiber in a CSm matrix of both green and fired body governed in toughening of brittle ceramic body, hence avoid failure to the casting mould.

Improving the process of casting into ceramic molds using additive technologies for cluster manufacturing

The study covers the free linear shrinkage of samples from PLA, HIPS, and ABS filaments used for FDM 3D printing in the ranges of extrusion operating temperatures (t). It was found that the PLA filament features by shrinkage values in the range of 0.2–0.6 % at Δt =200÷220 °С. HIPS filaments (Δt = 220÷240 °С) and ABS filaments (Δt = 240÷270 °С) have a shrinkage of 0.3–0.8 %. Linear shrinkage values must be taken into account when designing mathematical models of the future cast product. The influence of the print density dр (degree of internal structure filling) on the ash residue A when burning out samples obtained from the studied filaments was investigated. It was shown that the A value also increases with an increase in dр (5–15–30 %). The PLA filament has minimum A values (0.19–0.48 %). It was concluded that the PLA filament features the highest processability in the FDM 3D printing of casting patterns for casting into refractory ceramic molds (RCM) in terms of the set of free linear shrinkage and ash residue indicators. Clusters were made by FDM 3D printing from the PLA filament to produce «Nozzle» castings by casting into RCMs. Clusters were used to form RCMs. When burning out the clusters from RCMs, it was found that some RCMs cracked under linear heating. This was due to excessive pressure exerted by the expanding filament when heated to its softening temperature, and pressure exerted by gas emitted during the subsequent filament burn-out. The proportion of cracked RCMs increased with an increase in the heating rate. A stepwise mode of RCM heating combined with RCM calcination was developed in order to prevent cracking. There was no RCM cracking when clusters were removed in the stepwise mode. Experimental «Nozzle» castings were obtained from BrA9ZH3L bronze. The casting quality met the design documentation requirements.

Microstructural and Physical Properties of Yttria Stabilized Zirconia (YSZ) Prepared by Ceramic Injection Moulding (CIM)

Ceramic injection moulding (CIM) is a near net shape process to produce smaller and intricate parts at a competitive cost. However, fine particle size (nano scale) used for such injection moulding process generally leads to agglomeration, higher binder content and critical dimensional shrinkage which results in defects on the sintered components. This study extensively investigates the characteristics of Yttria Stabilized Zirconia (YSZ) for CIM process. YSZ parts were moulded by CIM process that utilized a multi-component binder system using palm stearin (PS) and polyethylene (PE) in 60:40 (vol %) ratio. The powders were characterized using particle size analyzer, pycnometer density and scanning electron microscopic (SEM). The binders were characterized by the pycnometer density, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Powders loading were choosen by the critical powder volume percentage (CPVP) through oil absorption test. YSZ powder was mixed with the binders at different powder loadings ranging from 58 to 60 vol% based on CPVP. The parts were injected moulded, thermal debound, pre-sintered and sintered. The microstructure, green strength and hardness of the sintered part at different powder loadings were investigated. A large porous region was clearly observed at 58 vol% compared to 60 vol%. All samples were sintered at 1350°C, with the highest green strength and hardness were 13MPa and 357.42 HV respectively was given by the sintered part at powder loading of 60 vol.

Ancient Ceramic Casting Molds from the Southern Russian Far East: Identification of Alloy Traces via Application of Nondestructive SEM-EDS and pXRF Methods

The investigation presented in this paper is a unique assemblage of ceramic casting molds discovered at one of the sites from the Bohai period (698–926) in the territory of the southern Russian Far East. The main research aim is to recognize probable traces of metal alloys cast in ceramic molds. Nondestructive pXRF and SEM-EDS methods were used as the research instruments for detecting the expected alloys’ chemical components. As a result, the elements Pb, Sn, Cu, and As were indicated at the surfaces of the molds’ cavities with evidence of carbonization caused by the casting process. Preliminarily, two groups of alloys were distinguished: lead-bearing alloys and lead-free alloys. Our new insights are in good accordance with the results of previous investigations on chemical compositions of bronzes from the Bohai period archaeological sites of the southern Russian Far East. In particular, data on the examination of ceramic molds confirm the conclusion that various kinds of copper alloys were known and used in the bronze casting craft of the Bohai period.

Modern materials and technologies in the production of artificial casting

The publication highlights the production of artistic castings by investment casting using combined ceramic molds. The features of the application of a refractory coating, duplex curing of ceramic shells, cutting of molds, removal of the model composition, annealing of ceramic molds, pouring and separation of the gating‑feeding system under conditions of mass production are considered. Hydrolyzed ethyl silicate (ETS) and aqueous alkaline silica sol are used as a binder. The hydrolysis is carried out with an acidic catalyst. The strength of forms on an aqueous binder before calcination (bending strength σi) is from 1.5 to 2 MPa. The presented technology allows flexible coverage of the entire range of art products. Castings weighing from 5 to 10 kg can be produced in one batch, which significantly reduces the production cycle.

Влияние микролегирования иттрием и гафнием на прочностные характеристики и морфологию карбидной фазы сплава ЖС3ДК-ВИ при замедленной кристаллизации

There are analyzed the melts of the ZhS3DK-VI alloy with different levels of strength characteristics and the factors influencing their reduction, differences in the macro and microstructure of the alloy, the effect of the crystallization rate when pouring the melt into hot and cold ceramic molds are determined. Since when casting parts, the level of properties is determined on separately cast samples, in the technology of manufacturing samples, the casting parameters of the corresponding part must be observed, and when increasing the strength characteristics due to changing technological parameters, it is imperative to consider the possibility of changing the technology of casting parts. However, for parts of complex configuration, cast from heat-resistant nickel alloys, it is often impossible to change the technology, therefore the only way to influence the properties of the material is to use microalloying with rare earth elements, for example, yttrium and hafnium. The introduction of these alloying elements in small amounts has a positive effect on factors that reduce the properties of the ZhS3DK-VI alloy, such as the unfavorable shape and topography of the carbide phase, or even slightly change the chemical composition of carbides. The article analyzes the effect of microalloying with hafnium and yttrium on the morphology and topography of the carbide phase; positive changes in the microstructure and strength characteristics at room temperature of the heat-resistant nickel alloy ZhS3DK-VI are noted. The technology of microalloying the melt has been developed to obtain satisfactory valuesof strength characteristics in tensile tests and impact toughness at room temperature. Microalloying the ZhS3DK-VI alloy with hafnium in a concentration of 0.15...0.25 % made it possible to increase the strength characteristics on samples for mechanical tests by 10…15 %, provided that the melt was drained into hot ceramic molds and slowed down. Higher concentrations of hafnium during slow crystallization lead to the formation of eutectic phases uncharacteristic for the ZhS3DK-VI alloy, requiring a decrease in the heat treatment temperature, which, accordingly, leads to a decrease in the level of long-term strength at 850 °C.

Cast Iron Parts Obtained in Ceramic Molds Produced by Binder Jetting 3D Printing-Morphological and Mechanical Characterization.

Mechanical behavior and characteristics of two different types of materials: cast iron with lamellar graphite EN-GJL-250 and cast iron with spheroidal graphite EN-GJS-400-15 which were cast in ceramic molds using gravitational casting method has considered in this research. The ceramic molds were obtained by 3D printing method. First, a finite element analysis was developed to determine Tresca and von Mises stresses and the deformations of the ceramic molds under an applied pressure of 25 MPa. Samples were produced by gravitational casting using two types of cast iron materials. Mechanical tests were made using samples produced from these two types of materials and microstructure analysis evaluation of fractured zones was realized by scanning electron microscopy. Obtained results were finally used for designing, developing, and producing of one ‘hydraulic block’ of a railway installation by the Benninger Guss company of Switzerland.

Regional temperature control in ceramic injection moulding: An approach based on cooling rate optimisation

The injection moulding of ceramic components with uneven wall thickness presents challenges due to differential cooling rates developing in the injected parts, which cause premature solidification of the feedstock at thin features and lead to detrimental defects, worsening in components from green to sintered states. To cope with this, suitable mould thermal control approaches have to be selected and validated, as current control methods are based on the achievement of a uniform cavity surface temperature, which is not tailored to such complex geometries. In this work, a novel thermal control system is proposed, based on regional mould temperatures, implemented with the use of Peltier modules, which locally and independently heat and cool different cavity features according to their thickness. The regional temperature profiles are optimised over time with the use of a coupled Finite Element - Particle Swarm Optimisation (FE-PSO), to achieve uniform cooling rates throughout the moulded components. The performance of this approach is compared to both constant ambient mould temperature and Rapid Heat Cycle Moulding (RHCM) techniques, which instead aim at achieving uniform temperatures throughout the mould cavity surface. Results show that the novel proposed method, based on regional temperature control and uniform cooling rates, promotes the simultaneous solidification of features with a 10-times difference in surface-to-volume ratio. Due to this, in terms of components quality, the novel method brings the advantages of higher dimensional control and reduction of differential shrinkage compared to the other analysed approaches, thus increasing the capability to use injection moulding to manufacture ceramic components characterised by non-uniform wall thickness.

Effect of a Powder Mould in the Post-Process Thermal Treatment of ABS Parts Manufactured with FDM Technology.

The post-process thermal treatment of thermoplastics improves their mechanical properties, but causes deformations in parts, making them unusable. This work proposes a powder mould to prevent dimensional part deformation and studies the influence of line building direction in part deformations in a post-process thermal treatment of 3D printed polymers. Two sets of ABS (acrylonitrile butadiene styrene) test samples manufactured by fused deposition modelling (FDM) in six different raster directions have been treated and evaluated. One set has been packed with a ceramic powder mould during thermal treatment to evaluate deformations and mould effectiveness. Thermogravimetric tests have been carried out on ABS samples, concluding that the thermal treatment of the samples does not cause degradations in the polymeric material. An analysis of variance (ANOVA) was performed to study internal building geometry and mould influence on part deformation after the thermal treatment. It can be concluded that powder mould considerably reduces dimensional deformations during the thermal treatment process, with length being the most affected dimension for deformation. Attending to the length, mould effectiveness is greater than 80% in comparison to non-usage of moulding, reaching 90% when the building lines are in the same direction as the main part.

Influence of process parameters in gel casting of a pure yttria nanopowder to fabricate transparent ceramics

The goal of this research is to fabricate pure transparent yttria ceramics through gel casting and vacuum sintering. A specific processing method has been used and optimized for this purpose. A pure yttria nanopowder was synthesized as the starting material to produce pure transparent ceramics through a low-temperature sintering process. It was attempted to minimize the undesirable nanopowder hydration by using the as-synthesized yttria nanopowder and a rapid deagglomeration and slurry preparation process. The synthesized nanopowders were deagglomerated to enhance the efficiency of both powder shaping and sintering stages. Carrageenan was used as the gelling agent because it is a low-cost and abundant material, and because the temperature is the only catalyst needed for its gelation; therefore, it is possible to control its gelation to obtain high-density and pure optical ceramics. The effect of the deagglomeration method and the processing parameters, including the amounts of dispersant, gelling agent, solid loading, pH, and deagglomeration time, on the rheology of slurry, density, and microstructure of the obtained green yttria ceramics was examined and optimized in order to obtain high solid loading nanoyttria suspensions of 38 vol%, which is more than those obtained in many of the previous investigations. The precise gelling temperature and time were measured, and green gel cast ceramics with a density of 63 % of the theoretical density were produced. A rapid deagglomeration and slurry preparation method was used instead of using a conventional planetary ball-milling approach to minimize the risk of the hydrolysis of yttria nanopowder. No sintering aid was necessary, and transparent yttria ceramics with 99 % of the theoretical density were produced after vacuum-furnace sintering at 10-2 mbar and 1715 °C.

First Evidence of “Earth Wax” Inside the Casting Molds from the Roman Era

This research was focused on the analysis of material composition and organic residues present in three molds found in the Moravian region (Czech Republic) belonging to the Roman era. X-ray fluorescence spectroscopy pointed out the possible remelting of Roman objects in Barbarian territory. The analysis of organic residues retrieved from the internal part of mold #2 by pyrolysis-gas chromatography/mass spectrometry proved the presence of ozokerite wax (“earth wax”). Consequent analysis of this organic residue by Atmospheric Solids Analysis Probe–ion mobility spectrometry–high-resolution mass spectrometry (ASAP-IMS-HRMS) confirmed the presence of ceresin, the main component of ozokerite. Ceresin was also detected in a sample of the organic residue from mold #1. Note that this is the first application of ASAP-IMS-HRMS in archaeological research. The remains of earth wax in molds suggest the production of wax models as an intermediate stage for the production of lost-wax ceramic casting molds.

Development of Ceramic Items Injection Moulding Technology Using Computer Modeling

Development of Ceramic Items Injection Moulding Technology Using Computer Modeling

Debinding behaviour and sintering temperature-dependent features of coloured zirconia fabricated by ceramic injection moulding

Zirconia (ZrO2) is one of ceramic materials that has very good mechanical and chemical properties suitable for biomedical applications as well as other industrial applications. ZrO2 ceramics, in fact, has been used in orthodontic dentistry. Nowadays, ZrO2 has been played its role in decorative and jewelry purposes, such as watchcases and artificial stones. Ceramic injection moulding (CIM), a near-net shape manufacturing process that can produce small, complex-shaped components and is suitable for large volume production, is one of the best powder fabrication methods. In this work, CIM was carried out in order to form the coloured-ZrO2 specimens. Binders used in the feedstock preparation are composed mainly of polyethylene glycol (PEG) and polyvinyl butyral (PVB). A laboratory-scaled, plunger-typed injection moulding machine was used to fabricate the coloured-ZrO2 components with various sizes and shapes. Debinding was carried out by water immersion and thermal debinding. Various sintering conditions were also performed. The specimens after sintering were subjected to be characterised and tested. The results showed that the binder removal rates using water related to geometry of the specimens, surface area and volume were taken into account. Sintering temperatures played important roles on properties, microstructure as well as the appearance and shades of the coloured-ZrO2 fabricated by ceramic injection moulding.

The mechanisms of high-efficiency grinding for micro/meso-structural arrays on ceramic moulds through an innovative wheel truing technology

The precision fabrication of ceramic moulds for the mass-production of micro/meso-structural arrays places a tremendous challenge to the manufacturing industry. This work aims to reveal the physics behind the processes so as to address this technological challenge. A new method for texturing the diamond grinding wheel surface with a micro-abrasive waterjet is proposed for highly efficient form-grinding of ceramic moulds into the required micro/meso-structural surfaces. It shows that this technology provides some unique advantages in improving the sharpness and geometrical accuracy of the grinding wheels. The mechanisms about material removal and texture formation in grinding wheel truing are investigated to enable the precise control of micro/meso-structure generation on the grinding wheel. A theoretical model is established to study the effect of grinding wheel surface micro/meso-textures and grain trajectory on the quality of the ground mould surface and reveal the reflection mechanism of the ground marks on the mould surface. Furthermore, an integrated rough-fine grinding strategy is proposed which is shown to significantly increase the grinding efficiency by 15–24 times. It is found that ductile domain grinding of ceramic moulds to achieve the required contour profile of 6.7 μm PV accuracy and a surface roughness Ra of less than 40 nm can be achieved.

Interface Reaction between Directional Solidified Superalloy DZ40M and Ceramic Mould

The interfaces between DZ40M directional solidified superalloy and ceramic mould (SiO2-base core and Al2O3-base shell) was studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that there was a serious interface reaction between DZ40M and ceramic cores，which resulted in many reaction pits (~100μm deep), Si rich residue alloys and Zr rich subglobose oxides on the inner surface. And the interface reaction between DZ40M and ceramic shell induced a ~50μm of pink sand burning layer. The thermal analysis showed that the reactions between DZ40M and core or shell were similar: the active alloy constituents (Zr, Al, Ti and Cr) were oxidized and became oxides or solid solution with the core or shell components (SiO2, Al2O3 or Fe2O3), but the interface characterization of DZ40M/core and DZ40M/shell was different because the shell had the main content of Al2O3 and impurity of Fe2O3, while those of the core were SiO2 and CaO, respectively.