Shrinkage Formation Research Articles

Drying of Durum Wheat Pasta and Enriched Pasta: A Review of Modeling Approaches

Models on drying of durum wheat pasta and enriched pasta were reviewed to identify avenues for improvement according to consumer needs, product formulation and processing conditions. This review first summarized the fundamental phenomena of pasta drying, mass transfer, heat transfer, momentum, chemical changes, shrinkage and crack formation. The basic equations of the current models were then presented, along with methods for the estimation of pasta transport and thermodynamic properties. The experimental validation of these models was also presented and highlighted the need for further model validation for drying at high temperatures (>−100°C) and for more accurate estimation of the pasta diffusion and mass transfer coefficients. This review indicates the need for the development of mechanistic models to improve our understanding of the mass and heat transfer mechanisms involved in pasta drying, and to consider the local changes in pasta transport properties and relaxation time for more accurate description of the moisture transport near glass transition conditions. The ability of current models to describe dried pasta quality according to the consumers expectations or to predict the impact of incorporating ingredients high in nutritional value on the drying of these enriched pasta was also discussed.

Intraperitoneal mesh devices for small midline hernias: mesh behavior in a porcine model.

Although clinical data on long-term efficacy are lacking, the use of self-expanding devices for intraperitoneal placement in the management of small midline hernias has been popularized. In the present experimental study, two different devices were investigated regarding tissue ingrowth, adhesion formation and solid mesh placement. Two devices of 4.3 cm diameter, one ePTFE-containing small pore polypropylene mesh (PP/ePTFE) and a multi-layered large-pore polypropylene patch with an oxidized cellulose anti-adhesive barrier (PP/ORC), both containing a self-deployment system, were placed intraperitoneally at the linea alba of 24 female pigs. A first laparoscopy was performed to evaluate mesh positioning against the abdominal wall. 1 (n = 6), 2 (n = 6), 4 (n = 6) and 12 weeks (n = 6) later, mesh appearance was inspected and adhesion formation was assessed. All meshes were excised for histological evaluation. Folding of the patch was more frequently observed at PP/ePTFE, yet no excessive cupping was noticed. Adhesions predominantly presented at short-term evaluation. Overall adhesion formation at all samples was significantly more extensive for PP/ORC (p = 0.048). Massive shrinkage was observed for PP/ORC: after a 12-week period 22% residual surface was preserved, compared to 83% for PP/ePTFE (p < 0.001). While at short-term inflammatory reaction was comparable, at long-term PP/ORC induced a significant more pronounced inflammatory and foreign body reaction. Although a strong deployment system provides adequate initial placement, shrinkage and excessive adhesion formation are much more prominent in the large-pore multi-layered restorbable devices compared to the ePTFE patch. This might influence long-term clinical outcome and caution seems warranted.

Theoretical study on influence of steel composition on solidification behaviour in ingot casting of low alloy steels at similar casting conditions

The effect of chemical composition of four different steel grades on solidification of 4 MT ingot at similar casting conditions has been examined using finite element model. As a consequence of change in grade dependent thermophysical properties, variations were obtained in velocity of the solidifying metal, which varied with carbon content, temperature distribution, mushy zone formation, porosity and piping. Microsegregation, which is measured by local solidification time, increased with increasing carbon content due to variation in solidus and liquidus. Alloy steels were found more prone to formation of shrinkage and central porosity compared to carbon steels. It is observed that solidification behaviour could not be related to specific thermophysical property, and combination of thermophysical properties and the alloy solidification characteristics affect the same. Improvement in alloy steel ingot quality was achieved through variation in hot top design. This study shows that steel ingot quality and yield is affected by subtle changes in composition.

Integrated Simulation of Flow and Solidification Shrinkage Formation Behavior of Pure Aluminum Casting Using Particle Method

Integrated Simulation of Flow and Solidification Shrinkage Formation Behavior of Pure Aluminum Casting Using Particle Method

Toxicological effects and recovery of the corneal epithelium in Cyprinus carpio communis Linn. exposed to monocrotophos: an scanning electron microscope study

This study was conducted based on the evidence of fish habitats in North India being affected by organophosphate pesticides draining from agricultural fields into bodies of water, especially during the rainy season. Various tissues of fish such as scales, gills ovaries, kidney, and liver have been studied from the toxicological point of view, but the toxicological effects of aquatic pollutants on fish cornea have not been investigated to date. We conducted comparative toxicological studies on the cornea of Cyprinus carpio communis using two sublethal (0.038 and 0.126 ppm) concentrations of monocrotophos pesticide for 30 days. Corneas from all the groups were evaluated by a scanning electron microscope. The fish exposed to the monocrotophos pesticide developed corneal necrosis due to the formation of crystalloid-like structures, thinning and shrinkage of microridges on the corneal epithelium. After 30 days, fish from the monocrotophos-treated tank were transferred to normal environmental conditions. After 60 days under natural condition, epithelial cells did not fully recover. In conclusion, exposure to monocrotophos induces irreversible changes in the cornea of C. carpio communis. As fish and mammalian visual systems share many similarities, the reported finding may offer useful insights for further toxicological and ophthalmological studies in humans.

Metallurgical failure analysis of acetabular metal-backed screws

Screws are often used in total hip arthroplasty to increase the cementless acetabular metal-backed fixation stability. This study aimed at identifying metallurgical factors related to metal-backed screw fractures in two cases of premature total hip arthroplasty revision. A preliminary analysis of radiographs and retrieved parts was performed. Fractured screws were subjected to fracture analysis, energy dispersive X-ray spectroscopy (EDS) and metallographic analysis. A finite element analysis was performed to predict the stresses experienced by the screws. Two factors were identified: titanium alloy microstructure, consisting of alpha phase plates with oxygen-rich alpha case and as cast Cr–Co alloy with dendritic microstructure and unfavorably aligned shrinkage formation. Finite element analysis has showed enough level of stress to predict screw fracture in the case of unbounded metal-backed and bone interface.

Numerical simulation of macrosegregation in steel ingots using a two-phase model

A two-phase model for the prediction of macrosegregation formed during solidification is presented. This model incorporates the descriptions of heat transfer, melt convection, solute transport, and solid movement on the system scale with microscopic relations for grain nucleation and growth. Then the model is used to simulate the solidification of a benchmark industrial 3.3-t steel ingot. Simulations are performed to investigate the effects of grain motion and pipe shrinkage formation on the final macrosegregation pattern. The model predictions are compared with experimental data and numerical results from literatures. It is demonstrated that the model is able to express the overall macrosegregation patterns in the ingot. Furthermore, the results show that it is essential to consider the motion of equiaxed grains and the formation of pipe shrinkage in modelling. Several issues for future model improvements are identified.

Formation of Underpressure in an Apple Cylinder during Convective Drying

The aim of the study was to experimentally determine drying-related shrinkage and internal pressure formation during convective drying of a cylindrical sample of apple tissue. Simultaneous measurements of mean moisture content, internal material temperature at four points, axial pressure inside the sample, and sample shrinkage were performed on an axially rotating apple cylinder, continuously weighed using telemetry. The sample was dried at three temperatures, 40, 50, and 60°C, and one air velocity. Development of negative pressure inside the sample reaching −90 kPa was observed. Radial shrinkage of the sample reached 50% on drying completion. In order to simulate the process, a model incorporating differential balance of stresses with heat and mass transfer balances was constructed and solved. The dependence of Young's modulus on moisture content was measured. The simulated results satisfactorily described the drying curve, temperature curve, and pressure magnitude but underestimated shrinkage.

Modelling of macrosegregation in steel ingots: benchmark validation and industrial application

The paper presents the recent progress made by the authors on modelling of macrosegregation in steel ingots. A two-phase macrosegregation model was developed that incorporates descriptions of heat transfer, melt convection, solute transport, and solid movement on the process scale with microscopic relations for grain nucleation and growth. The formation of pipe shrinkage at the ingot top is also taken into account in the model. Firstly, a recently proposed numerical benchmark test of macrosegregation was used to verify the model. Then, the model was applied to predict the macrosegregation in a benchmark industrial-scale steel ingot. The predictions were validated against experimental data from the literature. Furthermore, macrosegregation experiment of an industrial 53-t steel ingot was performed. The simulation results were compared with the measurements. It is indicated that the typical macrosegregation patterns encountered in steel ingots, including a positively segregated zone in the hot top and a negative segregation in the bottom part of the ingot, are well reproduced with the model.

Application of particle method to the casting process simulation

Casting processes involve many significant phenomena such as fluid flow, solidification, and deformation, and it is known that casting defects are strongly influenced by the phenomena. However the phenomena complexly interacts each other and it is difficult to observe them directly because the temperature of the melt and other apparatus components are quite high, and they are generally opaque; therefore, a computer simulation is expected to serve a lot of benefits to consider what happens in the processes. Recently, a particle method, which is one of fully Lagrangian methods, has attracted considerable attention. The particle methods based on Lagrangian methods involving no calculation lattice have been developed rapidly because of their applicability to multi-physics problems. In this study, we combined the fluid flow, heat transfer and solidification simulation programs, and tried to simulate various casting processes such as continuous casting, centrifugal casting and ingot making. As a result of continuous casting simulation, the powder flow could be calculated as well as the melt flow, and the subsequent shape of interface between the melt and the powder was calculated. In the centrifugal casting simulation, the mold was smoothly modeled along the shape of the real mold, and the fluid flow and the rotating mold are simulated directly. As a result, the flow of the melt dragged by the rotating mold was calculated well. The eccentric rotation and the influence of Coriolis force were also reproduced directly and naturally. For ingot making simulation, a shrinkage formation behavior was calculated and the shape of the shrinkage agreed well with the experimental result.

A model for regular desiccation cracks formation

A desiccation theory is developed providing a rational framework for a three-dimensional analysis of shrinkage and crack formation in a stiff clay surface layer. With the present model, we are estimating the shrinkage stress and the chemical potential variation in a morpheme produced after cracking, in a stiff clay surface layer, in terms of measurable quantities. In regular shrinkage morphemes, the shrinkage stresses are calculated from the shrinkage displacement and moisture content change. Other parameters such as the water mobility are introduced in order to express the chemical potential and the entropy changes in terms of the moisture content change and temperature at various instants of time.

Numerical Simulation Analysis on Shrinkage and Porosity of ZL101A Alloy Mechanism Box

The Shrinkage and porosity of ZL101A alloy mechanism box prepared by sand gravity casting process was investigated. The solidification process was simulation analysis by using InteCAST software and the original casting process was optimized based on the above simulated results. The results showed that the shrinkage and porosity defects’ position of ZL101A alloy mechanism box were accurately predicted by the analysis procedure which was from liquid distribution to shrinkage formation and then to Niyama shrinkage porosity. The shrinkage and porosity of the ZL101A alloy mechanism box prepared by optimized process were clearly reduced and the distribution of them was reasonable. Keywords: InteCAST software;ZL101A; Mechanism box; Shrinkage and porosity; Numerical simulation

Shrinkage evaluation in ductile iron as influenced by mould media and inoculant type

The present work was undertaken in hypereutectic ductile irons, to simultaneously study cooling curves, specimen contraction curves, microstructures and shrinkage tendencies as a function of inoculant selection and mould rigidity. Specific equipment was developed for simultaneous recording of cooling and contraction curves. The highest level of both concentrated and total shrinkage was recorded on the green sand mould system, where a much higher level of the initial eutectic expansion was observed, as compared to furan resin moulds. It was found that the Ca,Ce,S,O–FeSi inoculation gives the highest nodule count and a unique wide distribution of nodules sizes (large and small size nodules, in a peculiar ratio), as well as lower tendency to shrinkage formation. Also, the strongest graphitising effect before the start of eutectic solidification and more prolonged graphitising throughout the end of eutectic freezing characterise were observed with this complex inoculant system in addition to its peculiar action on minimising the shrinkage tendency of ductile irons.

Numerical Simulation of Shrinkage Formation of Pure Sn Casting Using Particle Method

Shrinkage formation often causes fatal defects in castings. Recently, the development of computer technology has provided us with a useful and effective method to predict shrinkage formation. A particle method is a Lagrangian method that uses discrete objects as calculation elements which is referred to as particles, and they can move freely in the space. Therefore, this method can calculate shrinkage formation directly. In this study, solidification simulation and flow simulation programs based on the particle method were combined considering the temperature-dependency of density. The program was applied to the solidification problem of a cylindrical pure Sn casting, and the predicted shrinkage was compared with experimental results. First, the calculation stability for a still fluid was discussed and an improved method was proposed. The flow of a fluid during solidification is quite slow; however, the particle method has a fundamental difficulty in calculating slow flow phenomena. Therefore, creep flow was assumed.When the inertia force was not considered, the calculation stability improved significantly, and introduction of a gravity adjustment coefficient reduced calculation time significantly. Next, the proposed method was applied to shrinkage formation analysis with an influence of air-cooling. As a result, predicted shrinkage shape agreed well with experimental result. [doi:10.2320/matertrans.M2011186]

Development in Glass Shells Production from Silicon-Doped GDP for Noncryogenic LMJ Target

Glass shells made from the pyrolysis of silicon-doped glow discharge polymers (Si-GDP) are particularly interesting for many noncryogenic target applications. We investigated the possibility of developing millimeter glass shells with >10-μm-thick walls to achieve a half-life of several months. Although previous studies have already demonstrated their feasibility, important developments are still needed to finely understand the role each step plays on the final glass shell’s properties. The adjustment of plasma deposition parameters and pyrolysis conditions allowed us to control shell shrinkage and defect formation. In the case of 7.4 at. % Si-GDP slowly pyrolyzed, we obtained spherical and smooth glass shells with near 100% yield. We also demonstrated that adjusting sintering temperature can produce fully dense glass shells from 2.2 to 2.4 g/cm3. Finally, deuterium pressurized capsules >3 MPa with a half-life of 8 months are obtained.

A Study on Ductile Iron Production without the Use of Feeders

This paper investigates the effects of graphite added as a conditioner, of Lantanum containing nodulariser and of pouring temperature on the formation of shrinkage porosity in ductile iron casting with an eutectic composition. In this experiment for each heat the cooling curves were recorded by the use of Quick-Cups (thermal analysis cups) and different solidification parameters such as TElow, GRF1, GRF2 and TS were calculated and compared with the porosity which was found from the microstructure examination. The results show that there is a good correlation between the amount of the shrinkage formation and the thermal analysis values. Also this experiment confirm that by using certain treating elements and pouring temperature which was between 1340-1350°C it is possible to eliminate the shrinkage defects in ductile iron castings without using feeders.

Caesalpinia sappan aqueous extract's growth inhibiting and apoptosis-inducing effects on human ovarian cancer cell

Objective To observe caesalpinia sappan aqueous extract's growth inhibiting and apoptosis inducing effects on human ovarian cancer cell line SKOV3. Methods Cell growth inhibiting effect was detected by cytometry; Examined were by trypan blue staining under a light microscope; Electronic microscopy was used to observe ultrastructure of SKOV3 cell affected by caesalpinia sappan aqueous extract's;With different concentration of caesalpinia sappan aqueous extract's acting on cells, cells cycle and apoptosis rate were analyzed by flow cytometry (FCM). Results The growth of SKOV3 was inhibited effectively by caesalpinia sappan aqueous extract's; typical morphology of apoptosis (cell shrinkage, chromatin condensation and apoptotic body formation) were observed and in a concentration-dependent manner. Flow cytometry detection showed: the experiment in vitro revealed growth of SKOV3 after treatment by caesalpinia sappan aqueous extract's at the different concentration. Apoptosis rate was increased with the increasing of the concentration of caesalpinia sappan aqueous extract's. Conclusion Caesalpinia sappan aqueous extract's can obviously inhibit growth of human ovarian cancer cell line SKOV3 and induce its apoptosis. Key words: Neoplasms, experimental; Ovarian neoplasms; Caesalpinia sappan aqueous extract's; Apoptosis

Grain refinement of AA333 aluminium cast alloy by Al–Ti granulated flux

Addition of grain refiner is an option to obtain higher mechanical properties of aluminium cast alloy. Grain refiner will react with molten aluminium and will form nucleant particles that initiate solidification. Therefore, the grain refiner will also be useful to control the solidification processes to reduce shrinkage formation. This study evaluated grain refinement in AA333 aluminium alloys by using Al–Ti granulated flux. Experiments were conducted by adding 0.056 and 0.078 wt.% Ti granulated flux to the molten aluminium during rotary gas bubble floatation and it was subsequently transferred into the Low Pressure Die Casting (LPDC) holding furnace. The pressure in the LPDC holding furnace was initially 256 kPa and no stirring was applied. The melt was injected to cylinder head moulds with cycle time of 180 s. Samples were cut at the thin and thick sections of the cylinder head to analyze the effects of cooling rate on grain refinement. Fading of grain refiner was studied for the period of 4 h. Hardness testing and microstructural observation were conducted. The results showed that addition of Al–Ti granulated flux for 0.056 and 0.078 wt.% Ti, increased the hardness and lowered the dendrite arm spacing (DAS). The refinement is more significant in thin samples, because of the assistance by higher cooling rate. The mechanism of grain refinement of Al–Ti granulated flux in AA333 alloy is a combination of high growth restriction factor by the large amount of solute and nucleation by Al 3Ti particles. Fading of grain refiner was detected by the increase in DAS, the lowering of Ti concentration in the melt and the reduction in hardness and strength. The pressure utilized in LPDC was not adequate to give stirring effect to prevent fading.

The control of porosity at nano scale in resorcinol formaldehyde carbon aerogels

Organic aerogels were synthesized by sol–gel polymerization of resorcinol (R) with formaldehyde (F) catalyzed by sodium carbonate (C) followed by vacuum drying. The influence of the resorcinol/sodium carbonate ratio (R/C) on the porous structure of the resultant aerogels was investigated. The nitrogen adsorption–desorption measurements show that the aerogels possess a well developed porous structure and mesoporosity was found to increase with increasing the R/C ratio. Carbon aerogels were obtained by carbonization of RF aerogels. The carbonization temperature impacts the microstructure of the aerogels by pore transformations during carbonization probably due to the formation of micropores and shrinkage of the gel structure. The results showed that a temperature of 1073 K is more effective in the development of the pore structure of the gel. Activated carbon aerogels were obtained from the CO2 activation of carbon aerogels. Activation results in an increase in the number of both micropores and mesopores, indicative of pore creation in the structure of the carbon. Activation at higher temperatures results in a higher degree of burn off and increases the pore volume and the surface area remarkably without change of the basic porous structure, pore size, and pore size distribution.

Investigation of microporosity formation mechanisms in A356 aluminium alloy castings

The problem of microporosity formation during solidification of aluminum alloy castings has great commercial importance and engineering interest due to its detrimental effects on mechanical properties. The present study concentrates on the mechanisms of microporosity formation in aluminium alloy castings. The microstructural characterisation of the produced samples was carried out with image analysis and SEM. It was observed that formation of shrinkage induced interdendritic porosity depends on solidification mode of the sample. The precipitation of intermetallic s-Al5FeSi platelets in the interdendritic liquid were also found to promote the interdendritic porosity formation by blocking interdendritic feeding. The results reveal that the oxide inclusions have a significant effect on formation of hydrogen precipitation induced regular micropores.