Gas-assisted Injection Research Articles

Numerical investigation on the spray characteristics of biodiesel with gas-assisted atomization injection

Atomization is crucial for the application of biodiesel in APEs. GAAI is effective in solving the fuel atomization difficulty. The GAAI spray characteristics of biodiesel by numerical simulation are investigated. The influences of ambient pressure, fuel injection duration, and ambient temperature on spray characteristics are emphasized. The results show that a relatively large ambient pressure leads to a relatively small spray penetration depth and SMD. Smaller droplets are more susceptible to gas flow than larger droplets, and larger fuel droplets tend to move independently. A relatively long injection duration suggests that the fuel stays in the gas-assisted injector for too much time, resulting in excessive accumulation of droplets at the outlet of the nozzle. The larger the droplet size is, the less affected it is by ambient temperature. When the ambient temperature increases, the density of the ambient gas decreases, reducing momentum exchange between the gas and droplets. The temperature of large fuel droplets remains approximately the same as the initial fuel temperature.

Effects of Processing Method and Parameters on the Wall Thickness of Gas-Projectile-Assisted Injection Molding Pipes.

Gas-Projectile-Assisted Injection Molding (G-PAIM) is a new injection molding process derived from the Gas-Assisted Injection Molding (GAIM) process by introducing a projectile to it. In this study, the short-shot method and the overflow method of both the G-PAIM and GAIM processes were experimentally compared and investigated in terms of the wall thickness of the pipes and its uniformity. The results showed that the wall thickness of the G-PAIM molded pipe was thinner and more uniform than that of the GAIM molded pipe, and the wall thickness of the pipe molded by the Gas-Projectile-Assisted Injection Molding Overflow (G-PAIM-O) process was the most uniform. For the G-PAIM-O process, the influence of processing parameters, including melt temperature, gas injection delay time, gas injection pressure, melt injection pressure and mold temperature, on the wall thickness and uniformity of the G-PAIM-O pipes were studied via the single-factor experimental method. It was found that the effects of gas injection delay time and gas injection pressure on the wall thickness of the G-PAIM-O pipes were relatively significant. The wall thickness of the pipes increased with the increase in gas injection delay time and decreased with the increase in gas injection pressure. The melt temperature, melt injection pressure and mold temperature had little effect on the wall thickness of the G-PAIM-O pipes. In general, the wall thickness uniformity of the G-PAIM-O pipes was slightly affected by these processing parameters.

Metal Injection Molding Using Gas-Assisted Technology for Optimizing Density Uniformity and Part Weight Reduction

To control the product density uniformity and weight reduction for metal injection molding (MIM), this study investigated the influence of using gas-assisted technology to assess if uniform part density can be achieved. The findings show that gas-assisted molding has great potential for improving density uniformity, particularly for the part density at the position far away from the gate. The green parts and final parts also significantly improve density uniformity and shrinkage. Interestingly, the gas-assisted technology applied to MIM shows similar molding characteristics and advantages over gas-assisted injection molding of polymers. This also enables the design of MIM parts with a non-uniform thickness with a hollowed core in the thick portion.

A novel strategy to reduce carbon emissions of heavy oil thermal recovery: Condensation heat transfer performance of flue gas-assisted steam flooding

• Flue gas-assisted steam flooding was investigated to reduce carbon emissions. • Flue gas-assisted steam flooding improved the oil recovery factor by 20.02%. • Flue gas treatment and injection processes for steam injection wells were designed. • Site application showed that the underground CO 2 storage rate was 74.5%. • The novel strategy is suitable for a small-scale steam generator used in oilfields. In this paper, the flue gas-assisted steam flooding process from a novel perspective of condensation heat transfer performance was investigated to reduce carbon emissions of heavy oil thermal recovery. More specifically, steam condensation heat transfer coefficients with and without flue gas were tested, and heat transfer and oil recovery for steam flooding assisted by flue gas in a sandpack were studied. The experimental results indicate that the existence of the gas film on the condensation block increased the heat transfer resistance and decreased the condensation heat transfer coefficient. The gas channeling of flue gas provided a flow path for the steam and promoted heat transfer deep into the sandpack. Flue gas-assisted steam flooding improved the oil recovery factor by 20.02% compared with steam flooding, and 46.4% of the injected flue gas could be stored in the sandpack. The storage of flue gas could be divided into two parts: the flue gas dissolved in the residual heavy oil and the flue gas trapped in the porous media. Flue gas treatment and injection processes for steam injection wells were designed. Site application of flue gas-assisted steam injection showed that the oil production increased by 28.3%, and the underground CO 2 storage rate was 74.5%. The novel strategy of flue gas treatment and injection with steam greatly reduces the carbon emissions of heavy oil thermal recovery, which is very applicable for small-scale steam generator used in oilfields.

Gas Assisted Injection Molding of an Industrial Part: 3D Simulation Provides Virtual Molding Trials

Abstract Techniques developed for three-dimensional simulation of gas assisted injection molding of thermoplastics are here extended to a complex industrial application, a car door handle, providing uniquely detailed insights into the molding process. Handling of the three stages of the process – plastic filling, and primary and secondary gas penetration – is described in terms of the boundary and initial conditions applied. Predictions for plastic filling patterns are compared successfully with molding results, and provide detailed forewarning of potential problems due to weld surfaces and air-traps. Particular emphasis is placed on accurate modeling of secondary gas penetration, which is also validated against practical results. A further novel feature is the export of an STL model of the gas core, providing a CAD model of the finished molding for subsequent in-service analysis.

Reducing the Burn Marks on Injection-Molded Parts by External Gas-Assisted Injection Molding.

A burn mark is a sort of serious surface defect on injection-molded parts. In some cases, it can be difficult to reduce the burn marks by traditional methods. In this study, external gas-assisted injection molding (EGAIM) was introduced to reduce the burn marks, as EGAIM has been reported to reduce the holding pressure. The parts with different severities of burn marks were produced by EGAIM and conventional injection molding (CIM) with the same molding parameters but different gas parameters. The burn marks were quantified by an image processing method and the quantitative method was introduced to discuss the influence of the gas parameters on burn marks. The results show that the burn marks can be eliminated by EGAIM without changing the structure of the part or the mold, and the severity of the burn marks changed from 4.98% with CIM to 0% with EGAIM. Additionally, the gas delay time is the most important gas parameter affecting the burn marks.

Computer modeling of the gas assisted injection molding process - computer simulations vs. practice

Modern computer programs for simulation of polymer processing allow to conduct numerical calculations on the movement of the injected material, not only in the classical injection molding process. It is possible to simulate non-standard injection methods, e.g. gas assisted injection process. The paper presents the results of computer simulations and real gas-assisted injection. These results were compared and the compliance of numerical calculations with the results of practical tests was assessed. It has been shown that advanced algorithms of computer simulation programs enable modeling of phenomena specific to the injection method under consideration. The ability to conduct simulations of polymer processing processes (including gas-assisted injection) allows to shorten the time of implementation of molds for production, eliminate construction errors and expanding knowledge about the course of the actual process. The work focuses on the gas-assisted injection process by filling the forming cavity entirely in the melt filling phase. Particular attention was paid to the gas channel formation process and the parameters that determine its shape and dimensions.

THE EFFECTS OF HIGH DENSITY POLYETHYLENE ADDITION TO LOW DENSITY POLYETHYLENE POLYMER ON MECHANICAL, IMPACT AND PHYSICAL PROPERTIES

Polyethylene materials are the most widely used polymers which we encountered everywhere in our daily life. Some of the advantages of the polyethylenes are the diversity of production types, corrosion resistance, electrical insulation and recyclability. The main production methods are compression molding, transfer molding, rotational molding, injection molding, gas-assisted injection molding, extrusion and blown film extrusion techniques. It is possible to increase the mechanical properties of low density polyethylene materials by addition of high density polyethylene materials. Both polymer has same monomers but their chemical structure and bonding properties are different. Their physical properties can change with their chemical structure and bonding properties. In this study, 25%, 50% and 75% by weight of high density polyethylene were added to low density polyethylene. Granules were pre-mixed with a mechanical mixer before production of the samples. Plastic injection molding machine was used for specimen preparation. Density, hardness, tensile test, three-point bend test, compression test, tear test and Izod impact tests were performed. Densities and hardness values of the polymer blends decrease by the increasing amount of low density polyethylene. In general, it was observed that the mechanical properties of the polymer blends increase as the high density polyethylene content increase.

FEM of Gas-Assisted Injection Molding Based on 3D Model

The gas-assisted injection molding (GAIM) process is so complicated that increasing reliance has been placed on CAE (Computer Aided Engineering) as a tool for both mold designers and process engineers. In this paper, a 3D theoretical model and numerical scheme is presented to simulate the GAIM process, in which an equal-order velocity-pressure formulation method is employed to eliminate the pressure oscillation. In addition, the whole flow field including the gas and melt regions is calculated using a uniform momentum equation with the viscosity of gas raised to a certain order of magnitude, and a 3D control volume scheme is employed to track the flow front of the melt and gas. Finally, the validity of the model has been tested through case studies and experimental verification.

Reducing the Sink Marks of a Crystalline Polymer Using External Gas-Assisted Injection Molding

External gas-assisted injection molding (EGAIM) has been used to reduce the sink marks of amorphous polymer products, but that of crystalline polymer products has not yet been reported. EGAIM of a crystalline polymer product was investigated in this study, and the influences of process parameters on the sink marks were discussed based on experiments. An isotactic polypropylene (iPP) product was fabricated by EGAIM under different process conditions. A uniform design was applied as an experimental design to investigate the influences of the process parameters on the sink marks. A regression equation was established to describe the quantitative relationship between the important parameters and sink marks in which a data-processing method was applied to determine the optimal value of Fα at significant level α to reduce the possibility of omission of some important parameters. The results show that EGAIM was effective in reducing the sink marks in these iPP products, and the most important parameters were the cooling time, gas pressure, and gas time. This study also provides the quantitative relationship between the important parameters and sink marks as reference for the research of EGAIM on crystalline polymer.

An approximation to the PTT viscoelastic model for gas assisted injection moulding simulation

An approximation to the Phan-Thien Tanner (PTT) constitutive model is developed with the aim of giving low-cost simulation of Gas Assisted Injection Moulding (GAIM) while incorporating important viscoelastic characteristics. It is shown that the developed model gives a response typical of full viscoelastic models in transient and steady-state uniaxial and constant shear rate deformations. The model is incorporated into a 3D finite element GAIM simulation which uses the ‘pseudo-concentration’ method to predict residual polymer, and applied to published experimental results for a Boger fluid and a shear-thinning polystyrene melt.It is shown that the simulation gives a very good match to published results for the Boger fluid which show increasing Residual Wall Thickness (RWT) with increasing Deborah number. Against the shear-thinning polymer, the quality of match depends upon which of two ‘plausible’ relaxation times is chosen; qualitatively different results arise from two different means of estimating a single relaxation time. A ‘multi-mode’ approach is developed to avoid this uncertainty. It is shown that the multi-mode approach gives decreasing RWT with increasing Deborah number in agreement with the published experimental results, and avoids the issues that arise from estimating a single relaxation time for a molten polymer.

Effect of gas on the polymer temperature in external gas-assisted injection molding

Abstract The introduction of gas is the principal difference between external gas-assisted injection molding (EGAIM) and conventional injection molding. In this study, the effects of gas thickness and gas delay time on polymer temperature were discussed. A modified one-dimensional transient heat conduction model of polymer was established to reveal the relationships between polymer temperature and gas thickness and gas delay time in EGAIM. The temperature histories of polymer were obtained by the simulation methods, including Moldflow and ANSYS, and were verified by comparing the experimental data to numerical simulation results. The effects of gas thickness and gas delay time on the temperature histories of polymer will be discussed in detail. The results showed that the polymer temperature is strongly affected by the heat preservation of gas, which in turn, increases with the increase of gas thickness and delay time. This paper provides quantitative methods and theoretical guidance for the study of the effects of gas on the polymer temperature in EGAIM.

Symulacje wtryskiwania grubościennej wypraski z zastosowaniem programu Moldex3D

Simulation of thick-walled part produced by standard injection molding (IM), gas-assisted injection molding (GAIM) and microcellular injection molding (MuCell) for two plastic types: ABS and POM using Moldex3D R15 software. It was found high reducing mass and reducing cooling times and decreasing sink mark, volumetric shrinkage and warpage deformations of parts analyzed by GAIM and MuCell compared to IM.

Macroscopic and mesoscopic simulation of viscoelastic free surface flow in gas‐assisted injection moulding process

AbstractIn this work, an improved simple coupled level‐set and volume of fluid (S‐CLSVOF) method is proposed to trace the moving interfaces in gas assisted injection moulding (GAIM) process based on the viscoelastic FENE‐P model. Firstly, the Kreisselmeier‐Steinhauser (KS) function constructed by means of Boolean operations is adopted as the shape level set (LS) function to precisely represent the complex mould cavities. Then, the benchmark problem of two‐dimensional deformation is used to verify the ability of the S‐CLSVOF method for capturing the moving interfaces. The stress birefringence is calculated and compared with the experiment result. Finally, the proposed method is further applied to the mould filling and gas penetration processes in GAIM. The macroscopic bubble appearance, temperature distribution, and the behaviour of the mesoscopic molecular orientation are shown and analyzed in detail. Due to the complexity of the gas‐liquid interaction, the phenomenon of asymmetrical gas flow is clearly observed in the gas penetration process. The influences of the macroscopic parameters on the macroscopic gas flows and mesoscopic molecular orientation are also discussed, such as insert positions, melt temperatures, and gas delay time. The numerical results illustrate that the coupled method can be applied to the multiscale numerical simulation of viscoelastic flows with complex free surfaces and provide significant guidance for the GAIM process.

Influence of Diameter on the Templated Crystallization of Polyethylene/Carbon Material Fiber Composites under Intense Shear Flow.

In this study, carbon fibers (CFs) and carbon nanofibers (CNFs) were introduced into polyethylene (PE) and intensive shear flow was imposed on the melt during the melt second flow caused by gas penetrating the melt during the gas-assisted injection molding (GAIM). The effect of fiber diameter on crystalline morphologies of obtained composites was deeply studied. The results revealed the fact that no matter whether CFs or CNFs were introduced into the PE matrix or not, the orientation degree of PE lamellae would increase during the melt second flow. Hybrid shish-kebab structures were difficult to be formed in GAIM CF/PE composites and only a few oriented PE lamellae overgrew on the local surface of CFs. However for GAIM CNF/PE composites, the formation of hybrid shish-kebab structures was clearly observed in the entire thickness. The structural diversity was mainly ascribed to the difference of CF diameter, showing obvious size-dependent effect.

Foaming Mechanism of Polypropylene in Gas-Assisted Microcellular Injection Molding

In our recent study, it is reported that gas-assisted microcellular injection molding (GAMIM) is a promising method to fabricate plastic foams with good surface quality, high weight reduction, and improved mechanical performance. To clarify the foaming mechanism, the crystallization behaviors of polypropylene in both conventional injection molding (CIM) and gas-assisted injection molding (GAIM) were studied. It is found that GAIM can significantly promote melt crystallization and refine crystals. To explore the improvement mechanism of crystallization, a numerical model was developed to simulate the filling and cooling processes of CIM and GAIM. The simulation results show that the much stronger shear field and the faster cooling rate lead to the refinement of crystals in GAIM. Finally, a crystallization-driven cell nucleation model was proposed to explain the improved foaming behavior of polypropylene in GAMIM. This paper provides a deep understanding of the foaming behavior and hence benefits the foaming process design.

Three‐dimensional simulations of non‐isothermal flow for gas penetration in complex cavity during gas assisted injection moulding process

AbstractIn this paper an R‐function is employed to construct the shape level set (LS) function for representing the complex mould cavity in a gas‐assisted injection moulding (GAIM) process. With the shape LS function, the continuity, momentum, and energy equations can be extended for solving the gas‐liquid two‐phase flows using the finite volume and immersed boundary methods. Firstly, an improved simple coupled level set and volume of fluid (S‐CLSVOF) method is proposed to track the moving interfaces of gas‐liquid interface and polymer melt front. Then the benchmark problems of the two‐ and three‐dimensional deformation tests are carried out to verify the ability of the improved S‐CLSVOF method. At last, the gas penetration processes are simulated in two different complex mould cavities. The numerical results show that the improved S‐CLSVOF method has higher accuracy than the S‐CLSVOF method, and the coupled numerical framework can successfully depict the asymmetry phenomenon of gas flow, racetracking, and fountain phenomena, which has great significance in determining processing conditions and designing mould cavities.

Visualization of counter pressure mechanism in gas-assisted injection molding process

Gas-assisted injection molding (GAIM) refers to injecting gas into the short shot melt during the filling stage. Compressed gas is used as the medium to push the melt and to provide the packing pressure. In GAIM, the hollow area and penetration length are the main factors that will affect the quality of molded parts. This study has applied a Gas Counter Pressure (GCP) mechanism and has discussed the effect of GCP in the GAIM process with in-mold visualization of this complex molding flow. This study introduces a counter pressure mechanism in a thick paper-clip-shaped cavity design. The flow field under different counter pressure conditions is observed by high-speed photography, the fiber orientations are analyzed with SEM, and the affected penetration length and hollow area are measured relatively. The experimental results show that when the GCP is applied to GAIM, although the hollow area is reduced, the penetration length will be increased, so as to make the quality of molded part more uniform and reduce the shrinkage. And a quantitative measuring method of two-stage penetration time span is proposed to get more in-depth discussion about the interactions between GCP and GAIM.

Discretization of three-dimensional free surface flows and moving boundary problems via elliptic grid methods based on variational principles

A new boundary-fitted technique to describe free surface and moving boundary problems is presented. We have extended the 2D elliptic grid generator developed by Dimakopoulos and Tsamopoulos (2003) [19] and further advanced by Chatzidai et al. (2009) [18] to 3D geometries. The set of equations arises from the fulfillment of the variational principles established by Brackbill and Saltzman (1982) [21], and refined by Christodoulou and Scriven (1992) [22]. These account for both smoothness and orthogonality of the grid lines of tessellated physical domains. The elliptic-grid equations are accompanied by new boundary constraints and conditions which are based either on the equidistribution of the nodes on boundary surfaces or on the existing 2D quasi-elliptic grid methodologies. The capabilities of the proposed algorithm are first demonstrated in tests with analytically described complex surfaces. The sequence in which these tests are presented is chosen to help the reader build up experience on the best choice of the elliptic grid parameters. Subsequently, the mesh equations are coupled with the Navier–Stokes equations, in order to reveal the full potential of the proposed methodology in free surface flows. More specifically, the problem of gas assisted injection in ducts of circular and square cross-sections is examined, where the fluid domain experiences extreme deformations. Finally, the flow-mesh solver is used to calculate the equilibrium shapes of static menisci in capillary tubes.

A novel gas-assisted microcellular injection molding method for preparing lightweight foams with superior surface appearance and enhanced mechanical performance

This paper proposed a novel gas-assisted microcellular injection molding (GAMIM) method by combining the gas-assisted injection molding (GAIM) with the microcellular injection molding (MIM). Firstly, under the assistance of the high-pressure gas from the GAIM, the amount of the polymer melt required for fully filling the mold cavity is reduced in the GAMIM compared with that in the MIM, thus leading to a high weight reduction of the foamed part. Secondly, the high-pressure assisted gas from the GAIM can dissolve all the cells generated in the melt filling stage back into the polymer melt, thus improving the molded part's surface appearance by eliminating the surface sliver marks. Thirdly, the secondary foaming process in a steady state triggered by releasing the high-pressure assisted gas makes the foamed part have a fine cellular structure and a compact solid skin layer, which can help to enhance the part's mechanical properties. In order to verify the effectiveness of the GAMIM, comparison experiments of the MIM and the GAMIM were conducted. The results demonstrate that the GAMIM can not only significantly increase the weight reduction, but also greatly improve the surface appearance and mechanical properties of the foamed part.