Demolding Time Research Articles

Integrated simulation method and experimental validation for the vacuum induction melting process

In Vacuum Induction Melting (VIM), reduction of defects such as porosity and cracking is critical to improve electrode integrity. Traditional simulation method ignores the temperature drop of liquid metal as it passes through the tundish, leading to inaccuracies in predicting the solidification process in the mold. Additionally, the crack of ingot may occur during demolding process, which is always overlooked. This paper presents an integrated simulation method that includes the flow model of liquid metal in the tundish, as well as the solidification model and the stress model of ingot in the mold. Based on these models, the criterion for demolding time is established based on First and Fourth Strength Theories. The entire VIM process from pouring to demolding can be analyzed comprehensively through this simulation method. The method is validated by 500 kg Inconel 718 VIM trial including the temperature measurement of outer mold wall, the height measurement of liquid metal in the tundish and longitudinal sectioned experiment of ingot. The suitable criteria for porosity of 500 kg Inconel 718 ingot, including shrinkage porosity and shrinkage cavity, have been found to be the Niyama criterion threshold of 15 K0.5s0.5cm−1 and Classical porosity model. Finally, the impact of each process parameter on porosity and demolding time is studied through this method for 500 kg Inconel 718 ingot. This method is not only applied to 500 kg ingot but also to larger ingot, thereby providing a basis for the VIM process optimization.

Analysis of influence of concrete aggregate in evaluation of form removal time of concrete using ultrasonic pulse velocity methods

Recently, due to the increase in high-rise and large-scale buildings, the use of ordinary aggregates has increased, and research is continuously being conducted on the use of lightweight aggregates to reduce weight. However, because concrete exhibits different compressive strength due to material influences, it is believed that there will be a difference in the form demoulding time for ordinary aggregate and lightweight aggregate in the early age. In order to evaluate the characteristics of concrete in a quantitative manner, an experiment was conducted to predict the time of form demolding through correlation by measuring compressive strength and ultrasonic pulse velocity (UPV). In this study, the target strengths of normal aggregate concrete (NC) and lightweight aggregate concrete (LC) were set at 30 MPa, 45 MPa, and 60 MPa. To reach the target strength of each test specimen, the W/B ratio was set to 41.0%, 33.0%, and 28.0%. In addition, in order to meet the same mixing conditions, the mixing was carried out by setting the fine aggregate excluding aggregate, W/B ratio, and cement amount to the same level. In the case of compressive strength, NC30 was 13.4% higher than LC30 at 24 h, and NC45 and LC45 showed similar compressive strength. NC60 showed 29.9% higher compressive strength than LC60, and it can be seen that NC generally shows higher compressive strength than LC. It can be seen that as the target intensity increases, the difference between NC and LC at the same target intensity increases. At 24 h, UPV showed 21.9% and 11.9% lower rates for NC30 and NC45 compared to NC60. Additionally, compared to LC60, LC30 and LC45 showed 22.3% and 12.2% lower UPV, and it is believed that the timing of form demolding can be evaluated by utilizing the fact that UPV varies depending on aggregate and W/B ratio. The prediction models for NC and LC based on the correlation between compressive strength and UPV showed a coefficient of determination (R2) of 0.90 or higher. Although the cement content significantly impacts the UPV of concrete, UPV may vary depending on the porosity and density of the aggregate, thus making it necessary to consider these factors for strength estimation.

An orthogonal experimental study on the influence of steam-curing on mechanical properties of foam concrete with fly ash

Foam concrete can be widely utilized as precast walls for its low density, excellent heat resistance and sound insulation. The challenge of its application is its low strength due to the porous matrix, which prolongs the demolding time. Steam curing at an early time is a common strategy to improve its early-age strength. Here, an orthogonal experiment (OA16) was adopted to investigate the influence of curing parameters on the properties of foam concrete. Specific compressive strengths (SCS) given as the ratio of the strength and the density at 12 h (12 h) and 28 days (28d) were calculated to evaluate the early-age and long-age strength. The range analysis and the analysis of variance (ANOVA) showed that the optimum steam-curing system that can yield the highest 12 h SCS (1.9 MPa, which meets the demand for demolding) is that preheating temperature of 25 ℃, preheating duration of 4 h, curing temperature of 50 ℃, together with 1.5% early-strength agent Na2SO4. Compared to the normal cured concrete, the addition of mineral power (fly ash by 20%) will successfully increase the early-age strength under steam curing, while XRD, SEM and FTIR analysis all show there are more hydrated products formed after steam curing and the activity of fly ash is activated to form C-S-H gels. However, improving early-age strength too much will lead to a deficiency of later-age strength growth. MIP analysis also exhibited high pore probability in the sample cured under higher steam-curing temperatures. These results can provide experiences for the wide application of foam concrete in precast walls and help improve the efficiency of their template turnover.

Achieving energy savings and early-ages strength enhancement of prefabricated cement components: Combined application of direct electric curing and sodium sulphate

Accelerated curing regimes are widely used to produce prefabricated concrete elements to improve construction quality and reduce time costs. A new accelerated curing regime, direct electric curing (EC), is proposed, and its effect on the performance of cement paste and energy consumption is discussed and compared with the common accelerated curing regime (steam curing). The results show that EC can significantly accelerate the early-ages hydration process of cement paste and increase its 1-d content of hydration products. The compressive strength (1–28 d) of the electro-cured specimen is higher than of the standard-cured sample, but its sorptivity coefficient and drying shrinkage value increases slightly due to the coarsening of the pore structure. EC can greatly improve the energy utilization efficiency in the process of curing cement sample, and its 1-d energy consumption per cubic meter of sample per MPa is only 3.65% of that in steam curing. In order to further improve the energy efficiency of EC, sodium sulphate (SS) is incorporated to the cement paste as a hardening accelerator. Incorporation of SS can further improve the early-ages strength of cement sample, making its 8-h compressive strength (1.5–2% SS) surpass the 1-d strength of steam-cured and electric-cured plain pastes. This means that the combined application of EDS and SS can not only shorten the demoulding time (saving time cost), but also further improve the energy utilization efficiency. The 8-h energy consumption (kWh/m3⸳MPa) of electro-cured cement sample after incorporating 1% SS is only 1.18% of that of steam curing and 35.8% of that of single EC. Under the synergistic acceleration of SS and EC, the energy consumed by curing prefabricated components is significantly reduced, which could lead to an energy revolution and promote sustainable development in building engineering.

Numerical Design and Optimisation of Self-Compacting High Early-Strength Cement-Based Mortars

The use of SCC in Europe began in the 1990s and was mainly promoted by the precast industry. Precast companies generally prefer high early-strength concrete mixtures to accelerate their production rate, reducing the demoulding time. From a materials science point of view, self-compacting and high early-strength concrete mixes may be challenging because they present contradicting mixture design requirements. For example, a low water/binder ratio (w/b) is key to achieving high early strength. However, it may impact the self-compacting ability, which is very sensitive to Vw/Vp. As such, the mixture design can be complex. The design of the experimental approach is a powerful tool for designing, predicting, and optimising advanced cement-based materials when several constituent materials are employed and multi-performance requirements are targeted. The current work aimed at fitting models to mathematically describe the flow ability, viscosity, and mechanical strength properties of high-performance self-compacting cement-based mortars based on a central composite design. The statistical fitted models revealed that Vs/Vm exhibited the strongest (negative) effect on the slump-flow diameter and T-funnel time. Vw/Vp showed the most significant effect on mechanical strength. Models were then used for mortar optimisation. The proposed optimal mixture represents the best compromise between self-compacting ability—a flow diameter of 250 mm and funnel time equal to 10 s—and compressive strength higher than 50 MPa at 24 h without any special curing treatment.

Pilot Study on Shrinkage and Fracture of Materials Based on the Alkali-Activated Slag: Influence of Curing Regime

The paper presents the results of a pilot study focused on the shrinkage process and fracture parameters of two fine-grained materials prepared from ground granulated blast furnace slag and silica sand. Two different activators were used - liquid sodium silicate and sodium hydroxide. The components ratio and the activator dose were the same for both materials and were as follows: activator dose of 6% Na2O by the slag weight, 1% of lignosulfonate plasticizer, and the ratio of slag:water:sand of 1:0.45:3. All specimens matured at room temperature. For each material, four curing regimes were designed with respect to the potential application on-site (especially different upper surface treatment and demoulding time). The shrinkage measurement lasted more than 2.5 years, after which fracture tests were performed on the same sets of specimens. Although only a slight nuance was in designed curing conditions, the results showed different sensitivity of investigated materials and monitored parameters to the particular curing regimes.

FUNDAMENTAL STUDY ON THE INFLUENCE OF DEMOLDING TIME AND FORMWORK MATERIAL ON THE COLOR OF COLORED MORTAR

The effects of the demolding time and formwork material on the color of the colored mortar were investigated. As a result of the experiment, the influence of the demolding time on the color of the color mortar was small. In addition, when rubber and metal (stainless) were used as the material of the formwork, in some cases, the color unevenness of the mortar could be suppressed more than when the coated plywood board was used.

Effects of ambient temperature, formwork type, and demolding time on the thermal deformation of sidewall concrete in underground engineering: Experiment, simulation, and engineering practice

Formwork type (FT) and demolding time (DT) profoundly affect sidewall concrete's thermal deformation and stress. However, FT and DT are mostly based on subjective judgments, and lack of quantitative research data. Therefore, this paper proposes a method combining laboratory experiments, computer simulation, and engineering practice to study the effects of ambient temperature, different FTs, and DT on the sidewall's temperature change with time, temperature distribution in space, displacement change with time, thermal deformation, temperature stress for the first time. Results show that: the hydration heat release of cementitious material is the driving force for thermal deformation; in the height and depth directions, sidewall temperature is high in the middle and low on both sides; the use of steel formwork produces less thermal deformation and lower temperature stress than the use of wood formwork; when using steel formwork, it is recommended that the DT be 9 d in winter and 7 d in summer; for wood formwork, the DT be 12 d in winter and 10 d in summer. The recommended DT for the specific FT in different ambient temperature can be calculated by applying the research method in this paper. The research results can provide helpful thinking for decision-making on the engineering site.

Characterization of Epoxy-Based Rapid Mold with Profiled Conformal Cooling Channel.

Based on the experience of the foundry industry, reducing the demolding time is the key for mass production of wax patterns with sophisticated geometries. Integration of numerical simulation and rapid tooling technology for decreasing the time to market is essential in advanced manufacturing technology. However, characterization of epoxy-based rapid molds with a profiled conformal cooling channel (PCCC) using computer-aided engineering simulation of the epoxy-based rapid mold with PCCC was not found in the literature. In this study, epoxy-based rapid molds with PCCC were characterized numerically and experimentally. The cooling performance of wax injection molds with two different kinds of cross-sections of the cooling channel was investigated. Four pairs of injection molds with PCCC were implemented using four different kinds of material formulations. It was found that the cooling performance of the PCCC was better than a circular conformal cooling channel (CCCC) since the PCCC maintained a more uniform and steady cooling performance of injection-molded product than CCCC. Epoxy resin added with 41 vol.% Cu powder seems to be a cost-effective empirical material formulation in terms of cooling time and material costs. This empirical material formulation provided an injection mold with low material cost and good cooling performance simultaneously compared to an injection mold fabricated with commercial material. The cooling performance could reach 88% of that of the injection mold fabricated with commercial material. The material cost of making the injection mold was only about 60% of that of the injection mold fabricated with commercial material. The coolant flow rate had no significant effect on the cooling time, whereas the cooling time of the wax pattern was affected by coolant temperature significantly.

Effect of concrete under continuous load on demoulding time during construction

Based on the current construction progress of each floor of the building, under the action of continuous construction load, the concrete strength at this time is only about 80% of that at the same age without load. It is suggested that when the test block maintained under the same conditions reaches 85% of the design strength, the whole structure is not easy to crack, which is not safe.

Effects of Ambient Temperature, Formwork Type, and Demolding Time on the Thermal Deformation of Sidewall Concrete in Underground Engineering: Experiment, Simulation, and Engineering Practice

Effects of Ambient Temperature, Formwork Type, and Demolding Time on the Thermal Deformation of Sidewall Concrete in Underground Engineering: Experiment, Simulation, and Engineering Practice

Influence of the Composition and Curing Time on Mechanical Properties of Fluidized Bed Combustion Fly Ash-Based Geopolymer.

This paper presents novel research on a fluidized bed combustion (FBC) fly ash-based geopolymer as a contribution to the problem of FBC fly ash disposal, and a proposal for a new geopolymer composition—an environmentally friendly material that is possible to use in construction. Geopolymer samples of various composition (containing FBC fly ash as the main raw material, metakaolin and CRT glass as additional components, and sodium silicate and sodium hydroxide as activators) were subjected to flexural and compressive strength tests. An investigation on the effect of the demolding time was carried out on one selected mixture. The test showed that both the composition and the demolding time have a decisive influence on the basic mechanical properties. A mixture containing FBC fly ash to metakaolin in a mass ratio of 3:1, removed from the mold after 14 days, was found to be the best in terms of the mechanical parameters expected from a material that could be used in construction, e.g., for the production of precast elements. According to the results obtained, FBC fly ash is a promising and environmentally friendly raw material for the production of geopolymer, with good mechanical properties and low density. Moreover, a high compressive strength can be obtained by curing the geopolymer at ambient temperature.

Evaluation of Suitability of Carboxymethyl Cellulose in Performance Improvement of Sodium Lauryl Sulfate Foam and Compressive Strength of Foam Concrete

Abstract Currently, foam concrete is commonly used for various construction applications such as partitions, filling grades, road embankment infills, and sound and heat insulation. It is to be noted that the foam production parameters have significant influence on the cellular structure of foam concrete, which governs the material properties of concrete. Hence, in an attempt to improve the foam quality, the present work focuses on evaluation of the suitability of viscosity enhancing agent carboxymethyl cellulose (CMC) in performance improvement of foam produced with surfactant sodium lauryl sulfate (SLS) for use in foam concrete production. Firstly, the influence of the addition of CMC on behavior of foam produced with surfactant SLS was studied by evaluating essential characteristics such as foam density, foam stability, and viscosity of surfactant solution. As a next step, the microstructure of foam and its behavior in cement slurry and mortar at the optimized concentrations of SLS and CMC were studied. Experimental studies revealed that the addition of 0.2 % CMC to 2.5 % SLS surfactant solution resulted in a 134 % increase in viscosity of surfactant solution, which eventually resulted in tremendous improvement in foam quality in terms of 34 % reduction in foam drainage (at the 5th minute after foam generation) and 22 % reduction in larger size foam bubbles (D90). Furthermore, as the air void microstructure of foam concrete is dependent on the foam bubble sizes, the reduction in foam bubble sizes resulted in 20 % enhancement in compressive strength of foam concrete. The addition of CMC is also found to affect the workability of foam concrete mixes, which is evident from the reduction in flow spread and the increase in flow time. Also, as the foam has retarding properties, the increase in foam content is found to increase the demolding time requirement of foam concrete specimens.

Minimizing corner cracking during the de-moulding process of industrial-size GFRP components: a case study

This article, through an industrial-level case study, presents workflows employed for decision-making to mitigate cracking of glass fibre reinforced polymer (GFRP) parts in tight radii corner locations, often resulting from displacement-controlled de-moulding processes. Namely, using process simulation to evaluate the cure cycle of the GFRP composite parts, it was possible to optimize the time of de-moulding and reduce the potential for part damage. It was observed that the most significant factors influencing the corner defect were boundary conditions of the part during de-moulding, the workshop temperature and part thickness. The poorest process design case was identified as hot workshop temperature, a laminate with thickness on the upper end of tolerances and a boundary condition where most sides are free, allowing for the development of larger moment forces at the tight corners. Further to this, a de-moulding time chart was developed to account for the changes in material properties as a function of temperature and material thickness, allowing for the in situ decision-making of technicians to reduce the occurrence of corner cracks.

Research on synthesis and properties of amphoteric early strength polycarboxylate superplasticizer

The amphoteric early strength polycarboxylate superplasticizer (AE-PCE) was synthesized by free radical aqueous solution polymerization, and using acrylic acid (AA), isobutylene alcohol polyoxyethylene ether (HPEG, molecular weight 4000) and dimethyl diallyl ammonium chloride (DMDAAC) as monomers. In this work, the structure of AE-PCE were characterized by FTIR, the hydration behavior of concrete were investigated by using TAM AIR isothermal microcalorimetry and scanning electron microscope, and properties of AE-PCE were studied by cement paste and concrete experimental. The results show that the quaternary ammonium cationic functional group has been successfully introduced into the molecular structure of polycarboxylate superplasticizer. The synthesized amphoteric early strength polycarboxylate superplasticizer (AE-PCE) can accelerate the hydration rate, significantly shorten the setting time and improve the early strength of concrete, and the effect of promoting coagulation and early strength is better than similar foreign products. Applied to the production process of subway shield segments, AE-PCE can effectively shorten the demoulding time of shield segments and improve the production efficiency under low temperature conditions in winter.

Effect of Admixtures on the Thermo-Physical Properties of Non Autoclaved Light Weight Block Using Marble Dust

In the present study, use of marble dust an inert filler produced by the marble cutting industries in the development of light weight block (LWB) of density 800 kg/m3 by non-auto clave method has been studied. Various mechanical and thermo-physical properties have been evaluated. It has been possible to replace cement by up to 20% when no additive is used. With the use of activator and super plasticizer at 50% replacement of cement by marble dust, compressive strength and water absorption are well within the Indian standard code 2185. With the use of accelerator and super plasticizer it is possible to reduce the de moulding time from 48 hrs to 6 hrs. Thermal conductivity of blocks varies from 1.16 to 2.30 [W/mK]. The variation in thermal conductivity depends upon its density which varies from 800 kg/m3 to 2400 kg/m3.

Effect of propylene glycol, rapeseed glycerine, and corn starch modified polyol blends parameters on the properties of thermal insulating polyurethane foams

Water-blown polyurethane foams have some drawbacks such as intensive shrinkage, relatively high density, skin peeling phenomena post blowing, and longer demold time. These drawbacks can be partiall...

Effects of Different Backing Materials of Hybrid Rapid Tooling on the Demolding Time in the Hot Embossing Process

Fresnel lenses are becoming more and more important because they are widely used as optical elements for concentrating solar power. Micro-hot embossing is a promising approach to fabricate Fresnel lenses. Precision optical elements must be more quickly and cheaply introduced to the market due to the pressure of global competition. The thermal conductivity of Aluminum (Al)-filled epoxy resins is lower than that of conventional mold steel materials. This work demonstrates a technique for fabricating hybrid rapid tooling with different backing materials to investigate the demolding efficiency in the hot embossing process. It was found that the Al was strongly recommend as backing material for fabricating hybrid rapid tooling due to cost, demolding time efficiency and dimensional accuracy of the embossed parts. Demolding efficiencies for the hot embossing mold with backing materials of copper, aluminum and steel about 78 %, 68 % and 50 % can be enhanced compared to that of the conventional rapid tooling. The replication rate exceeding 96 % in the hot embossing mold manufacturing process can be reached. The transcription rate exceeding 93 % in the hot embossing process can be obtained.DOI: http://dx.doi.org/10.5755/j01.ms.24.3.13897

A Study of Rapeseed Oil-Based Polyol Substitution with Bio-based Products to Obtain Dimensionally and Structurally Stable Rigid Polyurethane Foam

Water-blown polyurethane foams from low functionality polyols are characterized by intensive shrinkage, high density, post blowing, and longer demold time. These drawbacks can be partially, or fully, eliminated by varying chemical parameters of the main components. Therefore, an aliphatic polyester rapeseed oil-based polyol was modified with bio-based glycerin (RGL) and propylene glycol (RPG). The impact of the molecular weight and hydroxyl value of the blends were evaluated by testing obtained bio-based polyurethane foams. Compared to RGL-based foams, RPG-modified foams had the strictest standard (EN 13165) requirements regarding dimensional stability. These foams demonstrated a reduced apparent density from 12.6 to 20.8%, a faster foam curing capability by 47%, and the shortest demold time due to the open cell structure. The RGL modified foams had better cross-linking capability, slower ageing of thermal conductivity, and an increased compressive strength of 82.7% compared to the non-modified foam.

Demoulding vertical elements: Recommendations for apply maturity functions

Many standards recommend different minimum demoulding times depending on site conditions. Different parameters are taken into account in determining the minimum demoulding time, but the only one that is always taken into account is concrete temperature. Therefore, a methodology for determining the minimum demoulding times for vertical elements of self-compacting concrete (SCC) based on maturity functions is studied.Maturity functions establish a relationship between maturity and in-situ resistance. While maturity may be measured by measuring the temperature over time, there are different option for determining resistance in-situ, and thus the objective of this work is focused on methods for measuring resistance at early ages.An experimental study was carried out to establish which method for determining resistance in-situ is best suited to the determination of the resistance-maturation curve. To that end, the suitability and consistency of each method were studied.In addition, an experimental validation of the methodology was carried out, in which the demoulding methodology was applied to 11 columns tested at a construction site. The validation was carried out with two different types of SCC and different types of formwork.