Search Results (146)

The re-valorisation of oyster-shell waste offers a sustainable pathway for producing eco-efficient construction materials. This study investigates the physical, mechanical, and durability performance of natural hydraulic lime (NHL) mortars incorporating oyster shells (OSs), applied to solid bricks representative of historical masonry. Two formulations were developed: one with 24% replacement of NHL by oyster-shell powder (OSP, <150 µm) and another with 30% substitution of sand by oyster-shell aggregate (OSA, 0–4 mm), both compared with a control mortar. Mortars were tested in standard molds and directly applied to bricks, including under accelerated aging conditions (temperature and humidity cycles). Results revealed that shell-incorporated mortars applied to bricks exhibited higher bulk density and compressive strength, and lower porosity, capillary water absorption, and water vapor permeability, compared with mold-cast samples. The performance for the shell-based mortars highlights the substrate–mortar interaction, consistent with the behavior of traditional lime-based systems, and the microscope characterization (poro-Hg and X-ray tomography). Shell-incorporated mortars retained stable properties after aging, with variations below 10% compared to unaged mortars. These findings demonstrate the feasibility of oyster shells as partial replacements for lime and sand, confirming its potential as an eco-efficient strategy for sustainable mortars in conserving and rehabilitating historic masonry buildings. Full article

This study addresses the fabrication challenges associated with producing diverse geometries for concrete dry connections, particularly regarding cost, time, and geometric limitations. The research investigates methods for fabricating precise, rebar-free dry connections in concrete, focusing on stamping and green-state computer numerical control (CNC) milling. These methods are evaluated using metrics such as dimensional accuracy, tool abrasion, and energy consumption. In the stamping process, a design of experiments (DOE) approach varied water content, concrete age, stamping load, and operational factors (vibration and formwork) across cone, truncated cone, truncated pyramid, and pyramid geometries. An optimal age range of 90 to 105 min, within a broader operational window of 90 to 120 min, was identified. Geometry-specific exceptions, such as approximately 68 min for the truncated cone and 130 min for the pyramid, were attributed to interactions between shape and age rather than deviations from general guidance. Within the tested parameters, water fraction primarily influenced lateral geometric error (diameter or width), while age most significantly affected vertical error. For green-state milling, both extrusion- and shotcrete-printed stock were machined at 90 min, 1 day, and 1 week. From 90 min to 1 week, the total milling energy increased on average by about 35%, and at one week end-face (head) passes caused substantially higher tool wear, with mean circumference losses of about 3.2 mm for head engagement and about 1.0 mm for side passes. Tool abrasion and energy demand increased with curing time, and extrusion required marginally more energy at equivalent ages. Milling was conducted in two engagement modes: side (flank) and end-face (head), which were evaluated separately. End-face engagement resulted in substantially greater tool abrasion than side passes, providing a clear explanation for tolerance drift in final joint geometries. Additionally, soil-based forming, which involves imprinting the stamp into soft, oil-treated fine sand to create a reversible mold, produced high-fidelity replicas with clean release for intricate patterns. This approach offers a practical alternative where friction and demolding constraints limit the effectiveness of direct stamping. Full article

The simulation of solidification microstructures of cast alloys is crucial to the integrated “process–microstructure–property” numerical simulation. In order to verify the accuracy of the solidification microstructure simulation results, the solidification microstructures of WE54 alloy under both metal mold casting (MMC) and sand mold casting (SMC) conditions were simulated using the CAFE (Cellular Automaton–Finite Element) method, and the simulation results were validated experimentally. First, the effects of microstructure simulation parameters on the results were investigated, including nucleation density (n), nucleation undercooling (ΔT), and dendrite tip growth kinetics parameters (a₂, a₃). The results showed that, with the maximum surface nucleation undercooling (ΔT_s,max) kept constant, increasing the maximum volume nucleation undercooling (ΔT_v,max) significantly increases the proportion of columnar grains in the ingot structure. Moreover, when nucleation parameters remain constant, increasing a₂ and a₃ leads to expansion of the columnar grain zone. Secondly, numerical simulations of the solidification microstructure of WE54 alloy under different solidification conditions were carried out. The results indicated that as the cooling rate increases, the grain structure of the ingot becomes significantly refined, and the proportion of columnar grains decreases notably. Based on these findings, the simulation parameters suitable for simulating the solidification process and microstructure of MMC and SMC WE54 alloy were determined. Simulations of the temperature field and solidification microstructure were performed and compared with experimental results. Full article

Resin-based binders are one of the main materials used in foundry molding and core sands. Self-curing sand with furfuryl resin is one of the most popular technologies in the production of molds and cores for complex, critical castings made of iron and non-ferrous alloys. It has dominated small-batch production and the production of large-sized castings. This work is part of the research on new molding sands for mold additive manufacturing (3D printing). Three-dimensional printing technology in the production of sand-casting molds and cores is finding increasing industrial application in the production of castings from non-ferrous metal alloys. The aim of the research presented in this paper was to determine the influence of furfuryl resin type (classical and designed for 3D printing of sand molds) on cast iron casting properties. The pouring parameters were elaborated on the basis of the MAGMA software. Microscopic observations of castings, produced in classical and 3D-printed molds, were conducted, as well as an assessment of the roughness of the samples. The gas emissions from molding sands with both types of furfuryl resin were tested and analyzed in the context of the roughness of the castings obtained. It was proven that molding sand with furfuryl resin designed for 3D printing was characterized by lower gas emissions, which, in the case of molding sands with organic binders, is beneficial from an environmental point of view. Full article

As an innovative approach to advancing sustainable construction, this study explores the integration of molybdenum tailings as fine aggregate in 3D-printed mortar. The rheological and mechanical properties of the developed mixtures are systematically investigated. Environmental and economic assessments demonstrate that molybdenum tailings sand exhibits negligible global warming potential (GWP), acidification potential (AP), and cumulative energy demand (CED), completely avoiding the environmental impacts associated with natural sand extraction. Economically, full replacement with molybdenum tailings reduces material costs, as the tailings are typically provided without charge by mining enterprises. Furthermore, the template-free 3D printing technology eliminates formwork-related environmental impacts and simplifies construction processes. Experimental results indicate that mortars with cement-to-sand ratios between 1:1 and 1:2 possess favorable printability, with nozzle movement parameters significantly influencing printed dimensions. While increased molybdenum tailings content reduces mechanical strength, the cement-to-sand ratio exerts a more pronounced effect. The compressive strength of mold-printed and free-printed mortar reaches 55–75% and 35–55% of conventional mortar, respectively. Anisotropy analysis reveals minimal directional dependence in flexural strength, whereas compressive strength shows clear anisotropy, with X-direction strength measuring approximately 70% of that in the Y direction. This research provides valuable insights into the sustainable design and performance optimization of 3D-printed mortar using industrial byproducts. Full article

This paper presents three simple and efficient advanced optimization algorithms, namely the best–worst–random (BWR), best–mean–random (BMR), and best–mean–worst–random (BMWR) algorithms designed to address unconstrained and constrained single- and multi-objective optimization tasks of the metal casting processes. The effectiveness of the algorithms is demonstrated through real case studies, including (i) optimization of a lost foam casting process for producing a fifth wheel coupling shell from EN-GJS-400-18 ductile iron, (ii) optimization of process parameters of die casting of A360 Al-alloy, (iii) optimization of wear rate in AA7178 alloy reinforced with nano-SiC particles fabricated via the stir-casting process, (iv) two-objectives optimization of a low-pressure casting process using a sand mold for producing A356 engine block, and (v) four-objectives optimization of a squeeze casting process for LM20 material. Results demonstrate that the proposed algorithms consistently achieve faster convergence, superior solution quality, and reduced function evaluations compared to simulation software (ProCAST, CAE, and FEA) and established metaheuristics (ABC, Rao-1, PSO, NSGA-II, and GA). For single-objective problems, BWR, BMR, and BMWR yield nearly identical solutions, whereas in multi-objective tasks, their behaviors diverge, offering well-distributed Pareto fronts and improved convergence. These findings establish BWR, BMR, and BMWR as efficient and robust optimizers, positioning them as promising decision support tools for industrial metal casting. Full article

In this work, a core mold which combines excellent high-temperature compressive properties and rapid water solubility was successfully fabricated by using polyvinyl alcohol (PVA) as the adhesive and quartz sands as reinforcing particles. The influence of the molecular weight and alcoholysis degree of PVA, the concentration of PVA and the size of the quartz sands on the compressive performance and water penetration rate of core molds was studied in detail. The results revealed that core molds which were prepared using PVA-4 (i.e., a degree of polymerization of 2400 and an alcoholysis degree of PVA of 88%) and 160–200 mesh quartz sands with a mass ratio of 1.2:10 possessed a 160 °C compressive strength of 7.4 MPa, a 160 °C compressive modulus of 179.3 MPa and 50 °C water penetration rate of 0.94 mm/s. Furthermore, a validation experiment was conducted to verify the efficacy of using the as-prepared core mold to fabricate a hollow composite part, which shows a promising application in industrial sectors. Full article

This study presents an effective route for producing functionally graded metal matrix composites with enhanced abrasion wear resistance by incorporating ex situ Fe–WC preforms into austenitic stainless-steel castings. The preforms, produced by cold-pressing mixed WC and Fe powders, were positioned in the desired locations in sand molds and reacted in situ with the molten steel during casting. This process generated a metallurgically bonded reinforcement zone with a continuous microstructural and compositional gradient, characteristic of a Functionally Graded Material (FGM). Near the surface, the microstructure consisted of a martensitic matrix with WC particles and (W,Fe,Cr)₆C carbides, while towards the base metal, it transitioned to austenitic dendrites with an interdendritic network of Cr- and W-rich carbides, including (W,Fe,Cr)₆C, (Fe,Cr,W)₇C₃, and (Fe,Cr,W)₂₃C₆. Vickers hardness measurements revealed surface-adjacent values (969 ± 72 HV 30) approximately six times higher than those of the base alloy, and micro-abrasion tests demonstrated a 70% reduction in micro-abrasion wear rate in the reinforced zones. These findings show that WC dissolution during casting enables tailored hardness and abrasion wear performance, offering an accessible manufacturing solution for high-demand mechanical environments. Full article

This study presents the results of research on the use of Portland cement as a binder for producing semi-permanent molds intended for large-scale castings made from complex alloyed steels. Based on the conducted experiments, the optimal composition of a molding mixture based on Portland cement was determined to manufacture large molds with high operational performance. The technological properties of the mixtures were investigated, focusing on the flowability, sedimentation stability, and strength after curing. The recommended mixture composition is as follows: Portland cement—18.75%; sand—56.5%; quartz powder—25%; water—25%. To accelerate the hardening process, the use of curing accelerators is advised. The most effective additives are a 9% aluminum nitrate solution at 0.6–1.5% by weight or sodium aluminate at 3–4%. This composition ensures the required strength within a short curing time. A specific thermal treatment regime is also recommended to further stabilize the mold structure: heating to 450 °C at a rate of 75 °C per hour, holding for 2 h, followed by controlled cooling together with the furnace. Full article

Additive manufacturing (AM) has brought significant breakthroughs to the construction sector, such as the ability to fabricate complex geometries, enhance efficiency, and reduce both material usage and construction waste. However, several challenges must still be addressed to fully transition from conventional construction practices to innovative and sustainable green alternatives. This study investigates the use of non-cementitious traditional mixtures for green construction applications through 3D printing using Liquid Deposition Modeling (LDM) technology. To explore the development of mixtures with enhanced physical and mechanical properties, natural pine and cypress wood shavings were added in varying proportions (1%, 3%, and 5%) as sustainable additives. The aim of this study is twofold: first, to demonstrate the printability of these eco-friendly mortars that can be used for conservation purposes and overcome the challenges of incorporating bio-products in 3D printing; and second, to develop sustainable composites that align with the objectives of the European Green Deal, offering low-emission construction solutions. The proposed mortars use hydrated lime and natural pozzolan as binders, river sand as an aggregate, and a polycarboxylate superplasticizer. While most studies with bio-products focus on traditional methods, this research provides proof of concept for their use in 3D printing. The study results indicate that, at low percentages, both additives had minimal effect on the physical and mechanical properties of the tested mortars, whereas higher percentages led to progressively more significant deterioration. Additionally, compared to molded specimens, the 3D-printed mortars exhibited slightly reduced mechanical strength and increased porosity, attributable to insufficient compaction during the printing process. Full article

This study investigates hazardous emissions from foundry binder systems, comparing organic resins (phenolic urethane, furan, and alkaline-phenolic) and clay-bonded green sand with inorganic alternatives (sodium silicate and geopolymer). The research was conducted at the Fundaciόn Azterlan pilot plant (Spain), involving controlled chamber tests for the production of 60 kg iron alloy castings in 110 kg sand molds. The molds were evaluated under two configurations: homogeneous systems, where both mold and cores were manufactured using the same binder (five trials), and heterogeneous systems, where different binders were used for mold and cores (four trials). Each mold was placed in a metallic box fitted with a lid and an integrated gas extraction duct. The lid remained open during pouring and was closed immediately afterward to enable efficient evacuation of casting gases through the extraction system. Although the box was not completely airtight, it was designed to direct most exhaust gases through the duct. Along the extraction system line, different sampling instruments were strategically located for the precise measurement of contaminants: volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), phenol, multiple forms of particulate matter (including crystalline silica content), and gases produced during pyrolysis. Across the nine trials, inorganic binders demonstrated significant reductions in gas emissions and priority pollutants, achieving decreases of over 90% in BTEX compounds (benzene, toluene, ethylbenzene, and xylene) and over 94% in PAHs compared to organic systems. Gas emissions were also substantially reduced, with CO emissions lowered by over 30%, NO_x by more than 98%, and SO₂ by over 75%. Conducted under the Greencasting LIFE project (LIFE 21 ENV/FI/101074439), this work provides empirical evidence supporting sodium silicate and geopolymer binders as viable, sustainable solutions for minimizing occupational and ecological risks in metal casting processes. Full article

This study presents a simulation modeling of the gravity filling of a sand casting mold with gray cast iron EN-GJL-250. An analysis of the fluid flow, the nature of the filling of the casting mold, and the possibility of forming defects, such as voids and porosity due to metal shrinkage during the crystallization process, was performed. The simulation was performed using specialized software for simulating metal casting processes. The software allows the modeling of fluid dynamics and thermal conditions during the filling of the casting mold. The results obtained show the influence of the design of the sprue system, pouring temperature, and casting geometry on the movement of the fluid flow and the crystallization of the metal. The simulation also allows the visualization of turbulence and temperature gradients, helping to localize areas prone to defects. The results of this study could improve the quality of the specific casting and aid in selecting appropriate technology for the casting of a small series of high-quality castings. Full article

Traditional sand casting is limited by mold fabrication, cost control, and data collection, which restrict its further advancement. However, 3D sand printing technology represents a sophisticated rapid prototyping approach that directly utilizes three-dimensional models to fabricate complex sand molds and cores, thereby bypassing the traditional mold-making steps. This technology significantly enhances production efficiency and design flexibility, thereby advancing the modernization of casting processes. In the context of wind tunnel testing, the application of 3D-printed sand shell additive manufacturing has successfully produced sand molds and cores for the non-axisymmetric intake duct structures. This demonstrates the feasibility of this technology for complex casting applications and its capability to meet experimental requirements. Full article

To address the challenge of imprecise micro-droplet formation control in piezoelectric jetting devices used in sand mold 3D printing and apply on-demand inkjet printing technology to sand mold manufacturing, this study first explains the working principle of a piezoelectric shear-mode printhead. A mathematical model of the droplet ejection process is then established based on Computational Fluid Dynamics (CFD). Building upon this model, numerical simulations of droplet generation, breakup, and flight are conducted by using the Volume of Fluid (VOF) model within the Fluent module of the Workbench 2020 R2 platform. Finally, under consistent driving conditions, the effects of key parameters—viscosity, surface tension, and inlet velocity—on the ejection process are investigated through simulation. Based on the results, appropriate ranges and recommended values for ink properties are determined. This study provides significant engineering value for improving the stability and precision of droplet formation in industrial sand mold 3D printing. Full article

Sand mold milling plays a critical role in digital mold-free casting, but it is prone to damage such as corner collapse, collapse, and cracks during the machining process. To address this issue, ultrasonic vibration was used for sand mold milling in this study. By incorporating the solid–liquid transition model for sand mold cutting and considering the deformation characteristics of the shear zone, a prediction model for ultrasonic milling forces in sand mold was developed and experimentally validated. The results demonstrate that increasing the spindle speed and decreasing the feed rate lead to a decrease in cutting force. At high speeds, there is a 15% error between the dynamic milling force model and experimental values. Compared with conventional processing methods, ultrasonic processing reduces cutting force by 19.5% at a frequency of 25.8 kHz and amplitude of 2.97 μm, minimizes defects like sand particle detachment pits on the surface of sand mold, significantly improves surface quality, and enables precise, stable, high-precision, and efficient sand mold processing. Full article