Casting Surface Research Articles

Freckle Defect Formation near the Casting Interfaces of Directionally Solidified Superalloys.

Freckle defects usually appear on the surface of castings and industrial ingots during the directional solidification process and most of them are located near the interface between the shell mold and superalloys. Ceramic cores create more interfaces in the directionally solidified (DS) and single crystal (SX) hollow turbine blades. In order to investigate the location of freckle occurrence in superalloys, superalloy CM247 LC was directionally solidified in an industrial-sized Bridgman furnace. Instead of ceramic cores, Alumina tubes were used inside of the casting specimens. It was found that freckles occur not only on the casting external surfaces, but also appear near the internal interfaces between the ceramic core and superalloys. Meanwhile, the size, initial position, and area of freckle were investigated in various diameters of the specimens. The initial position of the freckle chain reduces when the diameter of the rods increase. Freckle area follows a linear relationship in various diameters and the average freckle fraction is 1.1% of cross sectional area of casting specimens. The flow of liquid metal near the interfaces was stronger than that in the interdendritic region in the mushy zone, and explained why freckle tends to occur on the outer or inner surfaces of castings. This new phenomenon suggests that freckles are more likely to occur on the outer or inner surfaces of the hollow turbine blades.

Determination of Metal/Die Interfacial Heat Transfer Coefficients in Squeeze Casting of Wrought Aluminum Alloy 7075 With Variations in Section Thicknesses and Applied Pressures

Squeeze casting of wrought aluminum 7075 was carried out on a 75-ton hydraulic press. Metal/die interface heat transfer phenomena in squeeze casting of the alloy were investigated. To facilitate experimental measurements, a five-step casting mold was designed for the experiments. The five-step casting consisted of five different section thicknesses of 2, 4, 8, 12, and 20 mm. Squeeze casing experiments were performed under the applied hydraulic pressures of 30, 60, and 90 MPa. Temperatures were measured at the casting surface and at various specific locations inside the die. At each step, thermocouples were placed at 2, 4, and 6 mm away from the inside die face. Based on the measured temperature results, the interfacial heat transfer coefficients (IHTCs) and heat fluxes were determined by solving the one-dimensional transient heat conduction equation with the inverse method. With increasing the casting section thicknesses from 2 to 20 mm, the peak IHTC values varied from 1683.46 W/m2 K to 9473.23 W/m2 K, 2174.78 W/m2 K to 13,494.05 W/m2 K, and 3873.45 W/m2 K to 15,483.01 W/m2 K for the applied hydraulic pressures of 30, 60, and 90 MPa, respectively.

Simultaneous Effect of Plunger Motion Profile, Pressure, and Temperature on the Quality of High-Pressure Die-Cast Aluminum Alloys

High-pressure die casting has been used widely to manufacture a large variety of products with high dimensional accuracy and productivity. Although this process has a considerably lower cycle time than the other metal forming processes, it is not yet optimized, due to the complexity of the process and the number of parameters to be controlled. Hence, the identification of the parameters affecting quality of castings is the current challenge toward efficient and effective production. In their previous work, the authors proposed and validated some novel kinematic parameters of the plunger, which explain and forecast both the static mechanical properties and the internal quality of castings. The present work extends such an approach by including two other meaningful parameters, which describe the effect of upset pressure and temperature on the final outcome. These parameters are here formulated and have been validated by means of a statistically significant sample manufactured with different plunger motion profiles, upset pressures, and temperatures of the melt and die. The quality of the castings was assessed through static mechanical properties and density measurements. As further proof, internal defects were analyzed on the fracture surfaces of some meaningful castings.

Evaluation of bond strength between fire-damaged normal concrete substance and ultra-high-performance fiber-reinforced concrete as a repair material

Purpose This study aims to investigate and compare the interfacial bond characteristics between fire-damaged normal concrete substrate and ultra-high-performance fiber-reinforced concrete (UHPFRC) as a repair material. Design/methodology/approach First, fire-damaged normal concrete was prepared. Then, with a cast surface, the substrate was subjected to different surface moisture conditions. Three types of moisture conditions were set, namely, air dry, saturated surface dry (SSD) and wet. Slant shear and splitting cylinder tests were conducted to determine the interfacial bond strength of the composite. Findings In general, results indicate that surface moisture conditions significantly influence bond strength. The substrate under SSD condition exhibited the highest bond strength. The findings suggest that UHPFRC is a promising material for the repair and reuse of fire-damaged concrete structures. Originality/value This study compares the bond strength between fire-damaged normal concrete and UHPRC.

Evaluation of the α-Case with TiO2 in Mold for Titanium Investment Casting

Molten titanium easily reacts with not only oxygen, carbon, and nitrogen but also the ceramic mold to form an α-case on the casting surface. However, the brittle α-case must be removed by chemical milling because it weakens the mechanical properties of the casting. The aim of this study is to evaluate and suppress the formation of the α-case by including TiO2 in the mold. Titanium powder was added into the alumina mold in order to facilitate the formation of TiO2 by the oxidation of titanium during mold firing. Another way to include TiO2 in the mold was to simply add TiO2 into the alumina mold. Optical microscopy and the micro-Vickers hardness test were used to characterize the α-case. The composition and morphology of the molds were confirmed using X-ray diffraction and field emission scanning electron microscopy. The mold with added titanium (Al2O3 + Ti) was effective in controlling the α-case. However, the interfacial reactions of the mold with the added TiO2 (Al2O3 + TiO2) exhibited distinct differences in α-case formation compared to the Ti-added mold (Al2O3 + Ti), while having almost identical compositions.

Utilization of Fabric Formwork for Improving the Durability of Concrete from Supersulfated Cement

In this paper, the durability of fabric formwork-based concrete made from supersulfated cement was studied. The study involved comparison of chloride and carbonation resistance, pH values, and water absorption between of surfaces of SSC, the one being cast and the other cast in fabric formwork. It was shown that the use of fabric formwork minimized the pore volume near the surface, maintained the pH values at higher profile depths and showed improved durability when compared to the mould-cast surface. Carbonation depths were reduced by approximately 35% and calculated ab sorption rates were found to be approximately 40% lower at the fabric cast surface, indicating that fabric formwork is a promising aspect towards promoting the comeback of SSC in construction.

On Degradation of Cast Iron Surface-Protective Paint Coat Joint

Abstract The paper is a presentation of a study on issues concerning degradation of protective paint coat having an adverse impact on aesthetic qualities of thin-walled cast-iron castings fabricated in furan resin sand. Microscopic examination and microanalyses of chemistry indicated that under the coat of paint covering the surface of a thin-walled casting, layers of oxides could be found presence of which can be most probably attributed to careless cleaning of the casting surface before the paint application process, as well as corrosion pits evidencing existence of damp residues under the paint layers contributing to creation of corrosion micro-cells

Analiza wpływu głębokości szlifowania na chropowatość powierzchni odlewu mineralnego

Analiza wpływu głębokości szlifowania na chropowatość powierzchni odlewu mineralnego

Pre-hardened tool steels failure analysis in die-casting

Heat checking is one of the principal causes of termination die-casting molds life. Thermal fatigue cracking of dies because of thermal and mechanical loads may condense the lifetime of the die. The surface quality of dies and as a result the surface of castings is degraded due to cracks. New pre-hardened tool steel known as TOOLOX44, addresses the issue by improving the elimination of heat treatment and optimization of impact toughness. This research investigates thermal fatigue cracking of dies by applying TOOLOX44 in the die casting mold specimen. The surface defect during experimental test was identified by visual analysis of the surface and potential causes of the undesirable effect were analyzed and shown by Cause effect diagram. In addition, microstructures of Toolox44 were analyzed by Light optical microscope and Scanning electron microscope. Finally, chemical compositions of typical TOOLOX44 compared TOOLOX44 sample in 20000 cycles test.

The Formation Mechanism of Sweat Phosphide in a New Form and Comparison with Expansion Scab in the Gray Cast Iron Castings

The present study compares the formation mechanism of two common defects in gray iron castings, sweat phosphide in a new form and expansion scab. Normally, when a solid crust occurs on the surface of gray iron castings, it is called “a scab.” In this study, we compared these two defects by means of standard metallography procedure and scanning electron microscopy. The result indicates that a scab caused by sand expansion is accompanied by sand particles beneath the solid crust and its microstructure is identical with the casting, while there are no sand particles beneath the sweat phosphide and its microstructure differs from casting.

Scaling Up and Characterization of Single‐Layer Fuel Cells

AbstractSingle‐layer fuel cells (SLFCs) are the product of recent advances in low‐temperature solid‐oxide fuel cell (SOFC) research and development. Conventional three‐layer materials comprising an anode, an electrolyte, and a cathode have been replaced by one‐layer materials that can integrate all of the functions of fuel cell anodes, electrolytes, and cathodes into one function. Excellent performance, simple technology, and ultra‐low cost have increased the potential of SLFCs for commercialization. Therefore, methods should be developed to scale up this innovative and advanced SOFC technology for engineering use and further commercial applications. This work reports the scaling up of an SLFC through powder material preparation, pulp preparation and tape casting, cold‐press shaping, hot pressing, and final surface reduction to fabricate 6 cm×6 cm engineering cells with an active area of 25 cm2. Each SLFC delivers approximately 10 W of power at 525–550 °C. The performance of the device is comparable with or even better than that of conventional SOFCs. A maximum output power of 12.0 W (0.48 W cm−2) is obtained from the 6 cm×6 cm SLFC at 550 °C. This study develops a scaling‐up technology that uses tape casting and hot pressing to enhance the commercial uses of SLFC.

Research of opportunities for adaptation of computer-integrated mixture preparation systems to conditions of foundries in Ukrainian enterprises producing wear-resistant cast iron

The problems associated with the possibility of adaptation of modern computer-integrated control systems for control of imported mixture preparation equipment to the conditions of the foundries in Ukrainian enterprises are considered. It is emphasized that ensuring the given quality of a mixture is an important factor in determining the performance characteristics of wear-resistant cast iron castings. It is shown that the use of modern imported mixture preparation systems suggests the possibility of supplementing by models and algorithms of Ukrainian developments in the synthesis of molding compounds, and optimal control of mixture preparation processes. Proposed options that can complement the QualiMaster AT1/ SandReport/ SandExpert system are a variant of its adaptation to the conditions of foundries of the Ukrainian enterprises. These options are based on mathematical models «mixture composition – mixture properties» in the form of regression equations and algorithms for optimal control of mixture preparation sections. The use of these solutions provides the ability to improve performance, particularly durability of wear-resistant cast iron castings, working in conditions of intensive abrasive friction. This is due to the fact that factor in improving the durability is high quality of working surfaces formed at the «casting surface – molding sand» interface.

Study on Type C Coal Fly ash as an Additive to Molding Sand for Steel Casting

Study of physio-chemical properties studies such as granulometric analysis, moisture, X ray fluorescence etc. were performed with Type C coal—combustion fly ash to investigate their potential as a distinct option for molding sand in foundry, thereby reducing the dependency on latter. Technological properties study such as compressive strength, tensile strength, permeability and compaction of various compositions of fly ash molding sand (10, 20 and 30 % fly ash substitute to chemically bonded sand) were performed and compared with silica molding sand. Steel casting production using this fly ash molding sand was done and the casting surface finish and typical casting parameters were assessed. It was noted that a good quality steel casting could be produced using type C fly ash molding sand, which effectively replaced 20 % of traditional molding sand and binders thereby providing greater financial profits to the foundry and an effective way of fly ash utilization (waste management).

Effect of cerium addition on casting/chill interfacial heat flux and casting surface profile during solidification of Al-14%Si alloy

In the present investigation, Al-14 wt. % Si alloy was solidified against copper, brass and cast iron chills, to study the effect of Ce melt treatment on casting/chill interfacial heat flux transients and casting surface profile. The heat flux across the casting/chill interface was estimated using inverse modelling technique. On addition of 1.5% Ce, the peak heat flux increased by about 38%, 42% and 43% for copper, brass and cast iron chills respectively. The effect of Ce addition on casting surface texture was analyzed using a surface profilometer. The surface profile of the casting and the chill surfaces clearly indicated the formation of an air gap at the periphery of the casting. The arithmetic average value of the profile departure from the mean line (Ra) and arithmetical mean of the absolute departures of the waviness profile from the centre line (Wa) were found to decrease on Ce addition. The interfacial gap width formed for the unmodified and Ce treated casting surfaces at the periphery were found to be about 35µm and 13µm respectively. The enhancement in heat transfer on addition of Ce addition was attributed to the lowering of the surface tension of the liquid melt. The gap width at the interface was used to determine the variation of heat transfer coefficient (HTC) across the chill surface after the formation of stable solid shell. It was found that the HTC decreased along the radial direction for copper and brass chills and increased along radial direction for cast iron chills.

Numerical simulation of casting process to assist in defects reduction in complex steel tidal power component

In order to reduce defects and improve casting quality, ProCAST software is performed to study the solidification process of discharge bowl. Simulated results of original casting process show that the hot tearing is serious at the intersection of blades and outer or inner rings. The shrinkage porosity appears at the bottom of discharge bowl and the transition area of wall thickness. Based on the formation mechanisms of the defects, the structure of chills attached on the outer surface of discharge bowl casting is optimized. The thickness of chills ranges from 25mm to 35mm. The positions of chills corresponded to the outer surface of the T-shaped parts. Compared to the original casting design (without chills), the hot tearing and shrinkage porosity of the discharge bowl are greatly improved with addition of chills.

Effect of the Surface Layer of Iron Casting on the Growth of Protective Coating During Hot-Dip Galvanizing

Abstract The paper presents the results of investigations of the growth of protective coating on the surface of ductile iron casting during the hot-dip galvanizing treatment. Ductile iron of the EN-GJS-600-3 grade was melted and two moulds made by different technologies were poured to obtain castings with different surface roughness parameters. After the determination of surface roughness, the hot-dip galvanizing treatment was carried out. Based on the results of investigations, the effect of casting surface roughness on the kinetics of the zinc coating growth was evaluated. It was found that surface roughness exerts an important effect on the thickness of produced zinc coating.

Influence of furfuryl moulding sand on flake graphite formation in surface layer of ductile iron castings

The influence of the use of moulding sand with furan resin, prepared both with fresh sand and reclaimed matrix, on the formation of a flake graphite formation at the surface layer of ductile iron castings has been investigated. A series of experimental heats of ductile iron cast in moulds made of moulding sand characterised by different levels of surface active elements (sulphur, oxygen) were performed. The effect of the wall thickness and the initial temperature of the metal in the mould cavity on the formation of flake graphite in the surface layer of the casting is shown in the paper. Investigations carried out by means of scanning electron microscopy (energy dispersive X-ray spectroscopy and wavelength dispersive X-ray spectroscopy) showed concentration of gradient profiles of surface active elements in the castings surface layer, which are responsible for their quality. Finally, it has been shown that there exists a significant effect of the quality of the sand on the formation of the flake graphite layer and the surface characteristics of ductile iron castings.

Occurrence and effect of casting skin in compacted graphite iron

Most iron castings retain their as cast surfaces because of their geometric complexity and to minimise the machining costs. However, the mechanical properties that are documented in standards (i.e. ASTM) are tested on fully machined test bars. Therefore, the effect of the as cast surface and subsurface features (commonly referred as ‘casting skin’) on mechanical properties should be evaluated. Preliminary works have shown the negative effect of the casting skin on mechanical properties of grey and ductile irons. This paper reviews the recent works on the casting skin effect on tensile and fatigue properties in compacted graphite and ductile irons. It was found that the tensile and fatigue strength were reduced by 9 and 40% respectively because of the presence of the casting skin. In addition, the correlations between processing parameters (e.g. nodularity and section thickness) and the casting skin features were presented. The experimental results suggest that the Mg depletion because of metal–mould and metal–air interactions was the main reason for the formation of the casting skin.

Effects of immersion disinfection of agar-alginate combined impressions on the surface properties of stone casts.

This study investigated the effects of disinfection of agar-alginate combined impressions on the surface properties of the resulting stone casts. Two brands of cartridge-form agar impression material and one alginate impression material were used. Agar-alginate combined impressions of smooth glass plates were prepared. The impressions were immersed in 0.55% ortho-phthalaldehyde solution or 0.5% sodium hypochlorite solution for 1, 3, 5 and 10 min. A stone cast made with an impression that had not been immersed was prepared as a control. The surface roughness (Ra) of the stone casts was measured, and the cast surfaces were observed by SEM. Immersion of agar-alginate combined impressions in 0.5% sodium hypochlorite solution for up to 10 min had no serious adverse effects on the surface properties of the stone casts. In contrast, even 1 min of immersion in 0.55% ortho-phthalaldehyde solution caused deterioration of the cast surface properties.

模拟古代灰口铸铁的三种表面状态在碱液中的电化学行为

采用极化曲线法，研究模拟古代灰口铸铁的裸表面、无氯有锈表面和除氯后表面三种表面在碱液中的电化学行为，结果表明，模拟古代灰口铸铁在亚硝酸钠溶液环境中，存在特定的[ ]/[ ]比值，可以使得亚硝酸钠对钝化膜的修复作用与氯离子对钝化膜的破坏作用达到动态平衡，这个动态平衡点为估算除氯后锈层中含氯量(即除氯程度)提供可能性。 By using polarization curve methods, this paper studied the electrochemical behaviors of three surfaces in lye including the bare surface of simulated ancient grey cast iron, rust surface and sur-face after chloride removal. The result showed that simulated ancient grey cast iron under NaNO2 environments had certain [ ]/[ ] quality ratio. A dynamic balance was achieved between repairing effect to passive film by NaNO2 and damage effect to passive film by chloride ion. This dynamic point may help to estimate the chloride chlorinity in the rust layer which also called the dechlorination level.