Recent Industrial Application and Perspectives of Rheo-Diecast Process in China

The Rheo-diecast process has been rapidly developed and increasingly used in China in the recent 5 years. The high solid fraction (solid content close to 50%) rheo-diecast components were commercially used in the transportation markets mainly because of lightweight. The mechanical properties of the high solid fraction rheo-diecast components are obviously superior than that of the conventional liquid diecast parts. The defects such as oxide, gas entrapment, shrinkage porosities are well prevented in the high solid fraction rheo-diecast parts. The high solid fraction rheo-diecast parts can be fully T6 heat treated. A comparison between high solid fraction rheo-diecast part and conventional liquid diecast part will be described in detail. The low solid fraction (solid content 5-20%) rheo-diecast components were widely used in the 5G communication markets. The future perspectives of Rheo-diecast process will be described at last. 1. Cost reduction. 2. Production consistency. 3. New Rheo-diecast alloys development. 4. Numerical simulation of Rheological filling.

A New Model for Predicting the Maximum Gas Entrapment Concentration in a Yield Stress Fluid

Summary Gas entrapment is a typical phenomenon in gas-yield stress fluid two-phase flow, and most of the related research focuses on the entrapped condition of the single bubble. However, the amount of entrapped gas, which is more meaningful for engineering, is rarely involved. In this paper, a theoretical model for calculating the maximum gas entrapment concentration (MGEC) is established for the first time. The critical distance between horizontal and vertical entrapped bubbles was determined by the yielded region caused by the buoyancy and the coupled stress field around the multiple bubbles. The MGEC is the ratio of a single bubble volume to its domain volume, which is calculated from the distance between the vertical and the horizontal bubbles. By comparing with the experimental results, the average error of MGEC calculated by this model is 4.42%, and the maximum error is 7.32%. According to the prediction results of the model, an empirical equation that can be conveniently used for predicting MGEC is proposed.

Suprachoroidal Gas: A Rare Complication of Intravitreal Injection of Perfluoropropane

This is a case report of a 75-year-old pseudophakic male, who presented with a massive submacular hemorrhage on a background of neovascular age-related macular degeneration. Intravitreal perfluoropropane was used to attempt pneumatic displacement of the submacular hemorrhage. The next day, subconjunctival gas was observed, with no gas seen in the vitreous cavity. Fundal examination showed suprachoroidal detachment. CT images confirmed gas entrapment, with no choroidal hemorrhage identified. The following case report describes suprachoroidal gas as a complication of intravitreal injection of perfluoropropane for pneumatic displacement of submacular hemorrhage. To our knowledge, this is the first such case in the literature. We describe the approach in differentiating suprachoroidal gas from hemorrhage and comment on a plausible mechanism for this complication. This report also serves as a review of the current state of knowledge in the area of suprachoroidal gas as a complication of pneumatic retinopexy and sutureless vitrectomy.

Assessment of the suitability of a gate design modification compared to the change in pressing velocity considering the distribution of gases in the casting volume

The qualitative properties of high pressure die castings are closely correlated with their internal structure, which is directly conditioned by the gas entrapment in the melt volume during the casting cycle. It is known that the gas entrapment in the volume of the melt and their subsequent distribution into the cast can be reduced by changing the technological parameters of the casting cycle or by the modification of the gating system design. The contribution addresses the issue of which variant of the gas content reduction is more efficient regarding the gas entrapment and the nature of the melt flow in the runners. The experiments are based on a real casting process. The established design solution of the gating system and the technological parameters setting are considered as a referential. Different gating system modifications were designed where the design modification is connected with the cross-section of a gate, in which the final acceleration of the melt flow occurs. The observed melt velocity in the gate is considered as a correlation factor, based on which the modification in the piston velocity is determined. The assessed parameter is the gas entrapment in the cast volume at the end of the filling phase. Assessment of the casting cycle and evaluation of experiments is performed using simulation program Magmasoft. Based on the performed analyses, it can be stated that the gate design modification will affect the filling regime of the die cavity by changing the melt velocity in gate, but the nature of the melt flow in runners remains unchanged. Modification of the piston velocity affects the filling regime of the die cavity, and also the nature of the melt flow as it passes through the runners, thereby promoting the gas entrapment in the melt volume. Therefore, it is necessary to pay an increased attention to the design of the gating system and only after debugging the design to proceed to the optimization of technological parameters.

Selection of Biopolymers and Lubricants to Mitigate Stabilization of Gas/Air Entrapment in ERD Wells: Offshore Abu Dhabi

The paper will present lessons learnt to mitigate the stabilization of the air/gas entering into lubricious biopolymer water-based system which decreased density of mud while drilling. The system selected for its highly lubricious properties and formation damage free properties to accommodate the usage of resistivity equipment provided excellent results in the field. Performance was almost equivalent to non-aqueous drilling fluid. However, the stabilization of gas/air entering the mud was encountered generating drilling troubles and risk of well control problems. An extensive study performed, consisted of assessing interactions between components and containments of the mud system with gas/air, crude-oil and drill solids introduced from the reservoir. The testing involved the adding of air from air-compressor for 60-second while mud sample is sheared at 6000 rpm. The mud weights of samples were measured before addition of air, right after and 60-second after the aeration. The percentage of density drop was calculated. Target value was maximum drop of 5% within 60 second after stopping the addition of air. Several combinations of polymers, lubricants, contaminants and other additives were evaluated. The study demonstrated that the interactions between crude-oil, polymers and lubricants can highly stabilize air/gas entrapment in the biopolymer water base mud system. The phenomena led to significant density decrease, drilling troubles, well control and safety issue in the field. They can also increase the viscosity of the biopolymer mud system. However, highly stabilized air/gas entrapment can be removed by the addition of emulsion breaker at concentration less than 1.5%vol of mud. In addition, the type and nature of the lubricant plays a major role in the stabilization of air/gas entrapment. The selection of the polymers should be combined with the choice of lubricant during the design phase to minimize the gas entrapment. Knowledge gained from the study establish a new testing protocol to assess in the laboratory the air/gas entrapment close to field shear conditions. The testing protocol showed good correlation with the field. The testing protocol can be used during the design phase or for investigations. It will improve the overall design of mud system where highly lubricious fluid is needed. Combination of polymers and lubricants did also provide low air/gas entrapment tendency.

Application of Vacuum Techniques in Shell Moulds Produced by Additive Manufacturing

This research shows the feasibility of the additive manufacturing technique (AM), Binder Jetting (BJ), for the production of shell moulds, which are filled by vacuum suction in the field of aluminium parts production. In addition, this study compares the gravity pouring technique and highlights the advantages of using vacuum techniques in AM moulds. A numerical simulation was carried out to study the behaviour of the liquid metal inside the moulds and the cooling rate of parts was analysed. The results show that in the gravity-pouring mould, the velocity in the gate causes moderate turbulence with small waves. However, vacuum suction keeps the velocity constant by eliminating waves and the filling process is homogeneous. Regarding dimensional accuracy, the staircase effect on the surface of the 3D moulds was the most critical aspect. The vacuum provides very homogeneous values of roughness across the entire surface of the part. Similarly, 3D scanning of castings revealed more accurate dimensions thanks to the help of vacuum forces. Finally, the microstructure of the cross section of the moulded parts shows that the porosity decreases with the vacuum filled. In both cases, the origin of the pores corresponds to gas entrapment and shrinkage during the filling process, the binder vaporization and nucleation points creation, leading to pores by shrinkage, gas entrapment or a mixture of both. This is the first study that uses vacuum filling techniques in moulds created by BJ, demonstrating the feasibility and advantages of AM using vacuum techniques, as an alternative to traditional casting.

Weakly charged droplets fundamentally change impact dynamics on flat surfaces

Weakly charged droplets eliminate gas entrapment and bubbles during an impact on flat surfaces.